User Manual/Handbook: Microphone Handbook - For

Technical
Documentation
Microphone Handbook
For the Falcon™ Range of Microphone Products
Brüel&Kjær
B
K
WORLD HEADQUARTERS: DK-2850 Nærum • Denmark •
Telephone: +4542800500 •Telex: 37316 bruka dk • Fax: +4542801405 •
e-mail: [email protected] • Internet: http://www.bk.dk
BA 5105 –12
Microphone Handbook
Revision February 1995
Brüel & Kjær
Falcon™ Range of Microphone Products
Microphone Handbook
BA 5105 –12
Trademarks
Microsoft is a registered trademark and Windows is a trademark of Microsoft Corporation.
Copyright © 1994, 1995, Brüel & Kjær A/S
All rights reserved. No part of this publication may be reproduced or distributed in
any form or by any means without prior consent in writing from Brüel & Kjær A/S,
Nærum, Denmark.
0−2
Falcon™ Range of Microphone Products
Microphone Handbook
Brüel & Kjær
Contents
1. Introduction....................................................................................................................... 1 – 1
1.1
1.2
1.3
1.4
About the Microphone Handbook ...............................................................................
About the Falcon™ Range of Microphone Products ..................................................
The Microphones .........................................................................................................
The Preamplifiers........................................................................................................
1–2
1–2
1–2
1–8
2. Prepolarized Free-field 1/2" Microphone Type 4188 ....................... 2 – 1
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
2.11
2.12
2.13
2.14
2.15
2.16
2.17
2.18
Introduction ................................................................................................................. 2 – 2
Sensitivity .................................................................................................................... 2 – 4
Frequency Response.................................................................................................... 2 – 5
Directional Characteristics ....................................................................................... 2 – 13
Dynamic Range ......................................................................................................... 2 – 16
Equivalent Volume and Calibrator Load Volume ................................................... 2 – 19
Capacitance ............................................................................................................... 2 – 20
Polarization Voltage .................................................................................................. 2 – 20
Leakage Resistance ................................................................................................... 2 – 21
Stability ..................................................................................................................... 2 – 21
Effect of Temperature ............................................................................................... 2 – 22
Effect of Ambient Pressure ....................................................................................... 2 – 25
Effect of Humidity ..................................................................................................... 2 – 26
Effect of Vibration ..................................................................................................... 2 – 27
Effect of Magnetic Field ............................................................................................ 2 – 27
Electromagnetic Compatibility................................................................................. 2 – 27
Specifications Overview ............................................................................................ 2 – 28
Ordering Information................................................................................................ 2 – 28
3. Prepolarized Free-field 1/2" Microphone Type 4189 ....................... 3 – 1
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
BE 1373 – 12
Introduction ................................................................................................................. 3 – 2
Sensitivity .................................................................................................................... 3 – 5
Frequency Response.................................................................................................... 3 – 6
Directional Characteristics ....................................................................................... 3 – 14
Dynamic Range ......................................................................................................... 3 – 15
Equivalent Volume and Calibrator Load Volume ................................................... 3 – 18
Capacitance ............................................................................................................... 3 – 20
Polarization Voltage .................................................................................................. 3 – 20
Leakage Resistance ................................................................................................... 3 – 21
Stability ..................................................................................................................... 3 – 21
Falcon™ Range of Microphone Products
Microphone Handbook
0−3
Contents
3.11
3.12
3.13
3.14
3.15
3.16
3.17
3.18
Effect of Temperature ...............................................................................................
Effect of Ambient Pressure .......................................................................................
Effect of Humidity .....................................................................................................
Effect of Vibration .....................................................................................................
Effect of Magnetic Field ............................................................................................
Electromagnetic Compatibility.................................................................................
Specifications Overview ............................................................................................
Ordering Information................................................................................................
3 – 22
3 – 25
3 – 26
3 – 27
3 – 27
3 – 27
3 – 28
3 – 28
4. Free-field 1/2" Microphone Type 4190......................................................... 4 – 1
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
4.10
4.11
4.12
4.13
4.14
4.15
4.16
4.17
4.18
Introduction ................................................................................................................. 4 – 2
Sensitivity.................................................................................................................... 4 – 5
Frequency Response.................................................................................................... 4 – 6
Directional Characteristics....................................................................................... 4 – 13
Dynamic Range ......................................................................................................... 4 – 14
Equivalent Volume and Calibrator Load Volume ................................................... 4 – 17
Capacitance ............................................................................................................... 4 – 19
Polarization Voltage.................................................................................................. 4 – 19
Leakage Resistance ................................................................................................... 4 – 21
Stability ..................................................................................................................... 4 – 21
Effect of Temperature ............................................................................................... 4 – 22
Effect of Ambient Pressure ....................................................................................... 4 – 25
Effect of Humidity ..................................................................................................... 4 – 27
Effect of Vibration ..................................................................................................... 4 – 27
Effect of a Magnetic Field ......................................................................................... 4 – 27
Electromagnetic Compatibility................................................................................. 4 – 28
Specifications Overview ............................................................................................ 4 – 28
Ordering Information................................................................................................ 4 – 28
5. Free-field 1/2" Microphone Type 4191......................................................... 5 – 1
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
5.10
5.11
5.12
5.13
5.14
5.15
0−4
Introduction ................................................................................................................. 5 – 2
Sensitivity.................................................................................................................... 5 – 5
Frequency Response.................................................................................................... 5 – 6
Directional Characteristics....................................................................................... 5 – 13
Dynamic Range ......................................................................................................... 5 – 14
Equivalent Volume and Calibrator Load Volume ................................................... 5 – 17
Capacitance ............................................................................................................... 5 – 19
Polarization Voltage.................................................................................................. 5 – 19
Leakage Resistance ................................................................................................... 5 – 21
Stability ..................................................................................................................... 5 – 21
Effect of Temperature ............................................................................................... 5 – 22
Effect of Ambient Pressure ....................................................................................... 5 – 25
Effect of Humidity ..................................................................................................... 5 – 27
Effect of Vibration ..................................................................................................... 5 – 27
Effect of Magnetic Field ............................................................................................ 5 – 27
Falcon™ Range of Microphone Products
Microphone Handbook
Brüel & Kjær
Contents
5.16
5.17
5.18
Electromagnetic Compatibility................................................................................. 5 – 28
Specifications Overview ............................................................................................ 5 – 28
Ordering Information................................................................................................ 5 – 28
6. Pressure-field 1/2" Microphone Type 4192 .............................................. 6 – 1
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
6.10
6.11
6.12
6.13
6.14
6.15
6.16
6.17
6.18
Introduction ................................................................................................................. 6 – 2
Sensitivity .................................................................................................................... 6 – 5
Frequency Response.................................................................................................... 6 – 6
Directional Characteristics ....................................................................................... 6 – 13
Dynamic Range ......................................................................................................... 6 – 14
Equivalent Volume and Calibrator Load Volume ................................................... 6 – 17
Capacitance ............................................................................................................... 6 – 19
Polarization Voltage .................................................................................................. 6 – 19
Leakage Resistance ................................................................................................... 6 – 21
Stability ..................................................................................................................... 6 – 21
Effect of Temperature ............................................................................................... 6 – 22
Effect of Ambient Pressure ....................................................................................... 6 – 25
Effect of Humidity ..................................................................................................... 6 – 27
Effect of Vibration ..................................................................................................... 6 – 27
Effect of Magnetic Field ............................................................................................ 6 – 27
Electromagnetic Compatibility................................................................................. 6 – 28
Specifications Overview ............................................................................................ 6 – 28
Ordering Information................................................................................................ 6 – 28
7. Low-frequency Pressure-field 1/2" Microphone Type 4193 ....... 7 – 1
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9
7.10
7.11
7.12
7.13
7.14
7.15
7.16
7.17
7.18
BE 1373 – 12
Introduction ................................................................................................................. 7 – 2
Sensitivity .................................................................................................................... 7 – 5
Frequency Response.................................................................................................... 7 – 7
Directional Characteristics ....................................................................................... 7 – 15
Dynamic Range ......................................................................................................... 7 – 16
Equivalent Volume and Calibrator Load Volume ................................................... 7 – 20
Capacitance ............................................................................................................... 7 – 22
Polarization Voltage .................................................................................................. 7 – 22
Leakage Resistance ................................................................................................... 7 – 24
Stability ..................................................................................................................... 7 – 24
Effect of Temperature ............................................................................................... 7 – 26
Effect of Ambient Pressure ....................................................................................... 7 – 28
Effect of Humidity ..................................................................................................... 7 – 30
Effect of Vibration ..................................................................................................... 7 – 30
Effect of Magnetic Field ............................................................................................ 7 – 30
Electromagnetic Compatibility................................................................................. 7 – 31
Specifications Overview ............................................................................................ 7 – 31
Ordering Information................................................................................................ 7 – 32
Falcon™ Range of Microphone Products
Microphone Handbook
0−5
Contents
8. 1/2" Microphone Preamplifier Type 2669 ................................................. 8 – 1
8.1
8.2
8.3
8.4
8.5
8.6
8.7
8.8
8.9
8.10
Introduction ................................................................................................................. 8 – 2
Frequency Response.................................................................................................... 8 – 4
Dynamic Range ........................................................................................................... 8 – 5
Phase Response ........................................................................................................... 8 – 8
Effect of Temperature ................................................................................................. 8 – 8
Effect of Magnetic Fields ............................................................................................ 8 – 9
Electromagnetic Compatibility (EMC)....................................................................... 8 – 9
Brüel & Kjær’s Patented Charge-injection Calibration Technique......................... 8 – 10
Specifications Overview ............................................................................................ 8 – 11
Ordering Information................................................................................................ 8 – 11
9. Accessories ......................................................................................................................... 9 – 1
9.1
Accessories Available .................................................................................................. 9 – 2
Index
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Falcon™ Range of Microphone Products
Microphone Handbook
Brüel & Kjær
Chapter 1
Introduction
BE 1372 – 12
Falcon™ Range of Microphone Products
Microphone Handbook
1− 1
Chapter 1 — Introduction
About the Microphone Handbook
1.1
About the Microphone Handbook
This handbook contains specific information about Brüel & Kjær’s Falcon™ Range of
1/2" microphone products. It contains a chapter on each of the microphones, a chapter on 1/2" Microphone Preamplifier Type 2669 which can be used with these microphones, and a list of the available accessories which can also be used with these
microphones.
1.2
About the Falcon™ Range of Microphone Products
Brüel & Kjær’s Falcon Range of microphone products includes six 1/2" condenser
microphones and a microphone preamplifier covering, between them, a very wide
range of needs and applications.
They are the culmination of over 40 years of leadership in top quality condenser
microphones and preamplifiers for precision acoustic measurements. The Falcon
Range of microphone products will meet your demands whether they be in complying with ANSI or IEC standards or in acoustic research.
1.3
The Microphones
1.3.1
Robust and Stable
The microphones in the Falcon Range are robust and can even withstand an IEC
68-2-32 1 m drop test onto a hard wooden block without suffering more than
±0.1 dB change in sensitivity. They are made of carefully selected materials and
alloys to ensure excellent stability and are virtually unaffected by industrial and
similarly hostile environments. During manufacture, each microphone is artificially
aged at a high temperature to ensure good long-term stability. As a result of all
this, Brüel & Kjær has extended their warranty period to three years.
No ecologically damaging materials are used in the manufacture and packaging of
these microphones.
1.3.2
Selecting a Microphone for Your Needs
To make sure you select the right microphone to match your needs, you will probably have to consider one or more of the following:
1− 2
●
Standards (IEC or ANSI)
●
Frequency range
●
Polarization
●
Sound field.
Falcon™ Range of Microphone Products
Microphone Handbook
Brüel & Kjær
Chapter 1 — Introduction
The Microphones
The following, together with the flow chart shown in Fig.1.1 and the comparitive
list of specifications shown in Table 1.2, will help you to make your decision.
Start
Yes
ANSI
or
IEC 651
ANSI
S 1.4 1983
Type 1
or S 1.12
Type M
S 1.12
Type 0
and
Type 1
S 1.4
Standards
No
Pressurefield
IEC
Type 0
Type 1
Infrasound
Type 1
Free-field
or
Pressure-field
No
Yes
Freefield
Audio freq. or
Extended freq.
Audio
freq.
Extended
freq.
External
Polarization
Yes
4192
4193
4188 + DZ 9566
4191
4192
4193
4190
4191
4188
4189
4193
4192
4191
4190
No
Frequency
Analysis
No
Yes
4189
4188
940369e
Fig.1.1 Flow chart to help you choose the right microphone in the Falcon™ Range for your needs
Measurement Standards
You can use these microphones in noise measurement systems satisfying either
ANSI or IEC standards (or their local equivalents). The microphones use only 50%
to 70% of the tolerances allowed by these standards.
Frequency Ranges
All six microphones cover the audio frequency range. If, however, you want to measure at frequencies down to 0.07 Hz (for infrasound measurements), choose Lowfrequency Pressure-field 1/2" Microphone Type 4193, or at frequencies up to 40 kHz
(for harmonic distortion measurements on loudspeakers) choose Free-field 1/2" Microphone Type 4191.
Polarization/Preamplifier
Prepolarized microphones are required on certain portable sound level meters
(which do not provide external polarization) and are a good choice in tough and
BE 1372 – 12
Falcon™ Range of Microphone Products
Microphone Handbook
1− 3
Chapter 1 — Introduction
The Microphones
humid environments. Externally polarized microphones are more stable, also at
high temperatures. All can be used with Brüel & Kjær’s 1/2 " Microphone Preamplifier Type 2669. The two prepolarized microphones (Types 4188 and 4189) can also be
used with Brüel & Kjær’s Preamplifier Type 2671.
Free-field Response or Pressure-field Response
The four free-field response microphones (Types 4188 to 4191) cover specific IEC
requirements and should be used in sound fields where reflections are negligible.
The two pressure-field response microphones (Types 4192 and 4193) should be used
for measurements in acoustic couplers. They also cover specific ANSI requirements
and can be used in diffuse sound fields.
As Replacements for Traditional Brüel & Kjær Microphones
Table 1.1 shows what traditional Brüel & Kjær microphones (type approval permitting) can be replaced by microphones from the Falcon Range.
Traditional Microphone
Falcon Range
4155
4189
4165
4190
4133/4149
4191
4134
4192
4147
4193
4166
4188*/4190*/4192*
4176
4188*/4189*
Table 1.1
Replacement of traditional Brüel & Kjær microphones
with ones from the Falcon™ Range
Microphone Specifications
The design and construction of each microphone results in a reliable transducer of
high sensitivity and low temperature dependence. Most of the data given for the
microphones in this handbook are for open-circuit conditions, which means that the
microphone looks into an infinitely high impedance. Table 1.2 summarises the most
important specifications for the microphones in the Falcon Range. In practice,
however, a microphone is used with a preamplifier which slightly influences the
given responses. When you use a Brüel&Kjær preamplifier (for example, 1/2 " Microphone Preamplifier Type 2669), the input impedance is very high (high resistance,
low capacitance), and the loading on the microphone cartridge is insignificant.
1− 4
Falcon™ Range of Microphone Products
Microphone Handbook
Brüel & Kjær
Chapter 1 — Introduction
The Microphones
Specification
Description
Type 4188
Type 4189
Prepolarized Free- Prepolarized Freefield
field
Type 4190
Type 4191
Type 4192
Type 4193
Low Noise
Free-field
Free-field
Pressure-field
Infrasound,
Pressure-field
Nominal
Open-circuit
Sensitivity
31.6 mV/Pa
50 mV/Pa
50 mV/Pa
12.5 mV/Pa
12.5 mV/Pa
12.5 mV/Pa
Polarization
Voltage
0
0
200
200
200
200
Optimized
Frequency
Response
±1 dB:
12.5 Hz to 8 kHz
±2 dB:
8 Hz to 12.5 kHz
± 1 dB:
10 Hz to 8 kHz
± 2 dB:
6.3 Hz to 20 kHz
±1 dB:
5 Hz to 10 kHz
±2 dB:
3.15 Hz to 20 kHz
±1 dB:
5 Hz to 16 kHz
±2 dB:
3.15 Hz to 40 kHz
± 1 dB:
±1 dB:
5 Hz to 12.5 kHz 0.12Hz to12.5 kHz
± 2 dB:
±2 dB:
3.15 Hz to 20 kHz 0.07 Hz to 20 kHz
Main
Standards
IEC 651 Type 1,
ANSI S1.4 1983
IEC 651 Type 1
IEC 651 Type 0
and Type 1
IEC 651 Type 0
and Type 1, ANSI
S1.12 Type M
ANSI S1.4 Type 1, ANSI S1.4 Type 1,
ANSI S1.12 Type ANSI S1.12 Type
M
M
Lower Limiting
Freq. (–3 dB)
1 to 5 Hz
2 to 4 Hz
1 to 2 Hz
1 to 2 Hz
1 to 2 Hz
10 to 50 mHz
Diaphragm
Resonance
Frequency
9 kHz
14 kHz
14 kHz
34 kHz
23 kHz
23 kHz
Inherent Noise
14.2 dB (A)
14.5 dB (Lin)
14.6 dB (A)
15.3 dB (Lin)
14.5 dB (A)
15.5 dB (Lin)
20.0 dB (A)
21.4 dB (Lin)
19.0 dB (A)
21.3 dB (Lin)
19.0 dB (A)
21.3 dB (Lin)
3% Distortion
Limit
146 dB
146 dB
148 dB
162 dB
162 dB
162 dB
Maximum SPL
(Peak)
157 dB
158 dB
159 dB
171 dB
171 dB
171 dB
Nominal
Capacitance
12 pF
14 pF
16 pF
18 pF
18 pF
18 pF
Equivalent
Volume
65 mm3
46 mm3
46 mm3
11.6 mm3
8.8 mm3
8.8 mm3
Calibrator Load
Volume
208 mm3
260 mm3
250 mm3
190 mm3
190 mm3
190 mm3
Pistonphone
4228 Correction
(with DP 0776)
+0.02 dB
0.00 dB
0.00 dB
+0.02 dB
+0.02 dB
+0.02 dB
Operating
Temperature
Range
–30 to 125 °C
(–22 to 257°F)
(up to 70°C with
corrector)
–30 to 150 °C
(–22 to 302°F)
Temperature
Coefficient
+0.005 dB/ °C
–0.001 dB/ °C
–0.007 dB/ °C
–0.002 dB/ °C
–0.002 dB/ °C
–0.002 dB/ °C
Pressure
Coefficient
–0.021 dB/kPa
–0.010 dB/kPa
–0.010 dB/kPa
–0.007 dB/kPa
–0.005 dB/kPa
–0.005 dB/kPa
–30 to 150 °C (–22 to 302°F)
(can be used up to +300°×C (572 °F) but with a permanent sensitivity change
of typically + 0.4 dB which stabilises after one hour)
Operating
Humidity Range
0 to 100%RH (without condensation)
Effect of
Humidity
< 0.1 dB/100%RH
Effect of
Vibration (SPL
63.5 dB
62.5 dB
62.5 dB
65.5 dB
65.5 dB
65.5 dB
7 dB
6 dB
4 dB
16 dB
16 dB
16 dB
with axial 1 m/s2)
Effect of
Magnetic Field
(SPL with 80 A /m,
50 Hz field)
Table 1.2 Comparision of main specifications for the different microphones in the Falcon™ Range
BE 1372 – 12
Falcon™ Range of Microphone Products
Microphone Handbook
1− 5
Chapter 1 — Introduction
The Microphones
1.3.3
Physical Dimensions
Dimensions
(mm)
Type 4188
Type 4189
Type 4190
Type 4191
Type 4192
Type 4193
Microphone
Length (with
grid)
14.9
17.6
17.6
13.5
13.5
13.5
Housing
Length (without grid)
14.0
16.3
16.3
12.6
12.6
12.6
Housing
Diameter
(± 0.03 mm)
12.7
12.7
12.7
12.7
12.7
12.7
Housing
Front-end
Length
6.4
6.2
6.2
6.1
6.1
6.1
Diaphragm
Ring Diameter
12.0
12.0
12.0
12.0
12.0
12.0
Depth to Centre Terminal
4.6
4.6
4.6
4.6
4.6
4.6
Preamplifer
Thread
(60 UNS–2)
11.7
11.7
11.7
11.7
11.7
11.7
Preamplifer
Thread Length
3.0
3.5
3.5
3.5
3.5
3.5
Protection
Grid Thread
(60 UNS–2)
12.7
12.7
12.7
12.7
12.7
12.7
Protection
Grid Diameter
(± 0.02 mm)
13.2
13.2
13.2
13.2
13.2
13.2
Table 1.3 Dimensions of the different microphones in the Falcon™ Range
1.3.4
Calibration
For general routine calibration you can check the sensitivity at 1 kHz with Sound
Level Calibrator Type 4231, or at 250 Hz with Pistonphone Type 4228. For a thorough calibration, Multifunction Acoustic Calibrator Type 4226 allows you to measure both sensitivity and frequency response.
An in-situ check, which also takes the state of the microphone into account, is
Brüel & Kjær’s Charge-Injection Calibration technique which is a patented feature
of 1/2 " Microphone Preamplifier Type 2669 (see Chapter 8).
1− 6
Falcon™ Range of Microphone Products
Microphone Handbook
Brüel & Kjær
Chapter 1 — Introduction
The Microphones
1.3.5
Microphone-data Disk
Introduction
A 31/2" data disk which supplements the calibration chart is supplied with all microphones in the Falcon Range except Prepolarized Free-field 1/2 " Microphone
Type 4188.
It contains calibration data in the \DATA directory and a presentation program,
Brüel & Kjær Microphone Viewer, in the root directory. The calibration data on each
disk is described in the relevant chapters of the handbook. The Brüel & Kjær Microphone Viewer program must be installed on your computer’s hard disk before use
using the installation program SETUP.EXE supplied on the data disk (see below).
Computer Requirements
Brüel & Kjær Microphone Viewer requires:
●
Windows™ version 3.1 installed on your computer
●
31/2" 1.4 Mbyte disk drive
●
1.5 Mbytes free disk space
●
VGA or SVGA display (minimum 640× 480 pixels)
Installing Brüel & Kjær Microphone Viewer
1. Insert the data disk in drive A.
2. Start Windows.
3. Click on the File menu in the Program Manager.
4. Select Run and type A:\SETUP.EXE.
5. Click on OK.
6. When SETUP.EXE asks you where you want to install the program, click on
OK.
Unless you have selected another directory, SETUP.EXE installs the program in
C:\BK–MIC. Two files (VBRUN300.DLL and VER.DLL) are installed in the
\WINDOWS\SYSTEM directory. These files are common for Visual Basic programs and can also be used by other programs.
About Brüel & Kjær Microphone Viewer
Brüel & Kjær Microphone Viewer shows the individual microphone’s data supplied
on the data disk in either graphical or tabular form.
BE 1372 – 12
Falcon™ Range of Microphone Products
Microphone Handbook
1− 7
Chapter 1 — Introduction
The Preamplifiers
When the program is started from Windows™, the calibration data in the \DATA
directory of the disk in the A drive is shown. If no data is found, the Open box
automatically appears. Select the Sensitivity file to access all data associated with
the microphone. Selecting a Result or Work file will only give you access to that
particular response.
The data can be copied to the hard disk using the Copy Microphone Data function
in the File menu. Individual data files are named with the microphone’s serial
number to prevent file name conflicts with data files from other microphones.
The data shown can also be printed out or copied to the clipboard for further
processing in spreadsheets and text editors.
When a Sensitivity file is selected, all frequency responses are obtained by adding
the relevant corrections and the low-frequency response to the actuator response.
Any additional information about Brüel & Kjær Microphone Viewer can be seen in
the README.TXT file. In addition, help in the form of hypertext is included
throughout to guide you.
1.4
The Preamplifiers
The 1/2 " Microphone Preamplifier Type 2669 has been developed for making precision acoustic measurements with Brüel & Kjær’s wide range of condenser microphones. You can connect 1/2 " microphones directly and 1", 1/4 " and 1/8 " types using
adaptors.
The preamplifier, cable and its connectors all fulfil EMC requirements.
You can verify the condition of the microphone, preamplifier and cable in-situ using
Brüel & Kjær’s patented Charge-injection Calibration technique. This means that
you can detect defects in the entire measurement set-up, including the microphone.
The preamplifier’s low output impedance allows long extension cables to be used
without problems.
The robust, compact design means that you can use the 1/2 "Microphone Preamplifier Type 2669 over a wide range of environmental conditions. The cable, which you
can detach from the preamplifier, is very thin but strong and remains flexible down
to –20 °C.
The 1/2 " Microphone CCLD Preamplifier Type 2671 has been developed for use with
prepolarised microphones in mind.
Full details of the 1/2 " Microphone CCLD Preamplifier Type 2671 are available in
the 2671 Product Data Sheet.
1− 8
Falcon™ Range of Microphone Products
Microphone Handbook
Brüel & Kjær
Chapter 2
Prepolarized Free-field 1/2 " Microphone
Type 4188
BE 1374 – 12
Falcon™ Range of Microphone Products
Microphone Handbook
2− 1
Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Introduction
2.1
Introduction
2.1.1
Description
Fig.2.1 Prepolarized Free-field 1/2" Microphone Type 4188 with Protection Grid DD 0525 (included)
Prepolarized Free-field 1/2" Microphone Type 4188 is a prepolarized 1/2" free-field
microphone and offers some significant advantages when used with portable instruments. For example, smaller associated instruments with low power consumption
can be used. A general advantage is the improved reliability of the associated
preamplifier in humid and polluted atmospheres. These factors make this prepolarized condenser microphone particularly suitable for field measurements, both outdoors and in industrial environments. It is suited to IEC 651 Type 1 measurements
and, when fitted with the supplied Random Incidence Corrector DZ 9566, is also
suited to ANSI S 1.4 – 1983 Type 1 measurements.
The microphone is polarized by a fixed charge-carrying layer deposited on the backplate. This layer is negatively charged which, at low frequencies, results in a positively increasing output voltage for a positively increasing incident sound pressure.
As a prepolarized microphone, it is externally marked by a pair of grooves.
This rugged microphone is built to ensure high stability under a variety of conditions. For example, the stainless steel alloy diaphragm withstands polluted industrial environments. The diaphragm clamping ring is firmly secured to ensure the
microphone’s reliability, even when the microphone is used without its protection
grid. When the microphone is used without its protection grid, it can be easily
flush-mounted or inserted into closed volumes as it can be supported by the diaphragm clamping ring, provided that a force of less than 5 Newtons is applied.
It is supplied with a calibration chart.
2− 2
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Introduction
2.1.2
The Calibration Chart
Each microphone is supplied with an individual calibration chart (see Fig.2.2)
which gives the microphone’s open-circuit pressure sensitivity together with the
typical capacitance and free-field and random-incidence frequency responses* . When
these are combined with the microphone’s typical data supplied in this chapter, the
individual microphone’s response under various conditions can be determined.
Prepolarized Condenser Microphone Cartridge Type 4188
Serial No.:
1740259
30.9
dB re 1 V/Pa or
mV/Pa
N.G.
Signature: .......................................
1. July 1993
Caution: Static electricity discharge directly on the centre terminal may damage the prepolarization of the
cartridge. Therefore, ensure that the housing of the cartridge makes contact before the centre terminal.
Sensitivity: The loaded sensitivity is typically 0.05 dB lower than the sensitivity stated. The random-field
sensitivity is the same as the pressure sensitivity. The free-field sensitivity at 1000 Hz is 0.15 dB higher
than the pressure sensitivity.
Free-field calibration with Sound Level Calibrators at 1000 Hz: Adjust the Sound Level Meter, or other
measurement equipment, to indicate 0.15 dB lower SPL than the actual SPL produced by the calibrator.
Capacitance: 12pF (typical)
Polarization Voltage (external): 0 V
Date:
K
The two grooves means “prepolarized”, i.e. 0V external polarization voltage.
Refer to the 4188 Product Data for further information.
3
3
Typical free-field response for 0˚ incidence
without random incidence corrector
2
See also rear side.
Typical random-field response with random incidence corrector
2
Tol.
BC0211-11
–30.2
7/6-'89
Brüel & Kjær
Open-circuit Pressure Sensitivity at 1013 hPa 23˚C and 50% RH:
Frequency: 1000 Hz
B
1
1
Tol.
0
0
-1
-1
Tol.
-2
Tol.
-2
Frequency response satisfies IEC 651 Type 1
-3
1
2
5
10
20
50
100 200
500
1k
2k
Frequency response satisfies ANSI S 1.4–1984 Type 1
-3
5k
10k
20k
1
2
5
10
20
50
100 200
500
1k
2k
5k
10k
20k
930776e
Fig.2.2 Microphone calibration chart (front and back)
Open-circuit Sensitivity
The stated open-circuit pressure sensitivity is valid at the reference frequency
(1000 Hz) for random-incidence and pressure-field conditions. The free-field sensitivity at the reference frequency (1000 Hz) is 0.11 dB higher than the pressure sensitivity.
Ambient Conditions
The ambient conditions are measured continuously during calibration at the factory.
The calibration results obtained at the measured environmental calibration conditions are corrected to the stated reference ambient conditions (23°C, 101.325 kPa
and 50% RH).
Frequency Responses
Two typical frequency responses are shown on the calibration chart. Both are normalized to 0 dB at the reference frequency (1000 Hz).
The left-hand curve on the rear side of the calibration chart is the open-circuit 0°incidence free-field response for the microphone without the supplied Random Incidence Corrector DZ 9566.
*Random-incidence response with supplied Random Incidence Corrector DZ 9566.
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Sensitivity
The right-hand curve on the rear side of the calibration chart is the open-circuit
random-incidence response for the microphone with the supplied Random Incidence
Corrector DZ 9566.
Each microphone’s individual lower limiting frequency is measured to ensure that it
is within the specified tolerances (see Fig.2.3).
2.1.3
Recommended Recalibration Interval
With normal handling of the microphone and any associated instrument,
Brüel & Kjær recommends that the microphone be recalibrated every 2 years.
Prepolarized Free-field 1/2" Microphone Type 4188 is very stable over this period
(see section 2.10 to section 2.12). Improper handling is by far the most likely cause
of change in the microphone’s properties. Any damage which causes improper operation can probably be detected using a sound level calibrator. In many cases, the
damage can be seen by carefully inspecting the protection grid and diaphragm.
2.2
Sensitivity
2.2.1
Open-circuit Sensitivity
The open-circuit sensitivity is defined as the sensitivity of the microphone when not
loaded by the input impedance of the connected preamplifier (the termination is
described in IEC 1094–2). The sensitivity is measured for the individual microphone
at 1000 Hz and stated on the microphone’s calibration chart (see section 2.1.2). The
nominal sensitivity is shown in Table 2.1.
Nominal open-circuit sensitivity
mV/Pa
dB re 1 V/Pa
31.6
–30
Accepted Deviation
(dB)
±2
Table 2.1 Nominal open-circuit sensitivity
2.2.2
Loaded Sensitivity
When loaded by a preamplifier, the sensitivity of the microphone is given by:
SC = SO + G
where
2− 4
SC
SO
G
(2.1)
= overall sensitivity of microphone and preamplifier combination
= open-circuit sensitivity of microphone
= voltage gain of microphone and preamplifier combination (in dB)
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Frequency Response
With Microphone Preamplifier Type 2639: G = –0.15 dB
With 1/2" Microphone Preamplifier Type 2669: G = –0.30 dB
Example
Loaded sensitivity of typical microphone with 1/2" Microphone Preamplifier Type
2669:
SC = –29.8 + (–0.30) = –30.1 dB
2.2.3
K-factor
Some types of Brüel & Kjær instruments use the K-factor (correction factor) or the
KO-factor (open-circuit correction factor) for calibration.
K = – 26 – S C
(2.2)
K O = – 26 – S O
(2.3)
Example
Correction factor for typical microphone with 1/2" Microphone Preamplifier Type
2669:
K = –26 – (–30.1) = +4.1 dB
Open-circuit correction factor for typical microphone with 1/2" Microphone Preamplifier Type 2669:
KO = –26 – (–29.8) = +3.8 dB
2.3
Frequency Response
2.3.1
General
In acoustic measurements, there are three types of sound field:
●
Free field
●
Pressure field
●
Diffuse field
The microphone is optimized to have a flat frequency response in one of these
sound fields. This response is called the optimized response. A microphone’s response in a diffuse field is equivalent to its random-incidence response.
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Frequency Response
This section shows the microphone’s typical free-field and random-incidence responses together with the microphone’s typical actuator response obtained using
Electrostatic Actuator UA 0033. The low-frequency response described in section
2.3.4 is common for all types of response.
All frequency responses and correction curves are shown with a frequency resolution of 1/12-octave.
2.3.2
Optimized Response (0°-incidence Free-field Response)
Response (dB)
5
dB
Tol.
Tol.
Tol.
Tol.
0
–5
– 10
1
Fig.2.3
10
100
1k
10 k
Frequency (Hz)
100 k
940894e
Typical free-field response of the microphone with Protection Grid DD 0525 and the microphone’s specified tolerances. The low-frequency response is valid when the vent is exposed to
the sound field
Prepolarized Free-field 1/2" Microphone Type 4188 meets the requirements of IEC
651, Type 1 and ANSI S1.4 – 1983 Type 1.
2.3.3
Actuator Response
The microphone’s frequency response is determined by adding corrections for the
type of sound field to its actuator response obtained using Electrostatic Actuator
2− 6
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Frequency Response
UA 0033. This is a reproducible and practical method for calibrating a microphone’s
frequency response.
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940666e
Fig.2.4 Typical actuator response measured with Electrostatic Actuator UA 0033
Response (Degrees)
0
– 45
– 90
– 135
– 180
100
1k
10 k
Frequency (Hz)
100 k
940667e
Fig.2.5 Typical actuator phase response measured with Electrostatic Actuator UA 0033
The microphone is polarized by a fixed charge-carrying layer deposited on the backplate. This layer is negatively charged which, at low frequencies, results in a positively increasing output voltage for a positively increasing incident sound pressure.
2.3.4
Low-frequency Response
The low-frequency response (see Fig.2.3) is the typical response with the vent exposed to the sound field. If the vent is not exposed to the sound field, the sensitivity
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Frequency Response
increases from 0 dB at the reference frequency (1000 Hz) to approximately 0.6 dB at
1Hz.
For applications where the vent is not exposed to the sound field, take care to
ensure proper static pressure equalization to prevent static displacement of the
diaphragm.
The microphone’s low-frequency response is common for all types of sound field.
The microphone’s lower limiting frequency (–3 dB) is between 1 and 5 Hz with the
vent exposed to the sound field. This is measured during production to ensure that
specifications are fulfilled.
2.3.5
Free-field Response
The microphone’s free-field correction curves are shown in Fig.2.6, Fig.2.8 and
Fig.2.10. These corrections are added to the microphone’s actuator response obtained using Electrostatic Actuator UA 0033 in order to determine the free-field
response at any angle of incidence. The typical free-field response at 0° incidence
with and without the protection grid, and with Random Incidence Corrector
DZ 9566 are shown in Fig.2.7, Fig.2.9 and Fig.2.11, respectively.
2− 8
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Frequency Response
Correction (dB)
15
12.5
0°
10
30°
7.5
5
60°
Random
2.5
0
180°
90°
– 2.5
150°
120°
θ°
–5
– 7.5
– 10
500
1k
10k
Frequency (Hz)
50k
940795/1e
Fig.2.6
Free-field correction curves for the microphone with Protection Grid DD 0525
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940884e
Fig.2.7 Typical free-field response (0°-incidence) for the microphone with Protection Grid DD 0525
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Frequency Response
Correction (dB)
15
12.5
10
0°
30°
7.5
5
60°
Random
2.5
90°
180°
0
150°
120°
– 2.5
θ°
–5
– 7.5
– 10
500
1k
10k
Frequency (Hz)
50k
940805/1e
Fig.2.8
Free-field correction curves for the microphone without
protection grid
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940935e
Fig.2.9 Typical free-field response (0°-incidence) for the microphone without protection grid
2 − 10
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Frequency Response
Correction (dB)
15
12.5
0°
10
30°
7.5
180°
90°
5
60°
Random
2.5
0
– 2.5
150°
θ°
120°
–5
– 7.5
– 10
500
1k
10k
Frequency (Hz)
50k
940796/1e
Fig.2.10 Free-field correction curves for the microphone with Random Incidence Corrector DZ 9566
Response (dB)
5
dB
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940933e
Fig.2.11 Typical free-field response (0°-incidence) for the microphone with Random Incidence Corrector DZ 9566
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Frequency Response
2.3.6
Random-incidence Response
A microphone’s response in a diffuse sound field is equivalent to its random-incidence response. The microphone’s random-incidence correction curves are shown in
Fig.2.6, Fig.2.8 and Fig.2.10. These corrections are added to the microphone’s actuator response obtained using Electrostatic Actuator UA 0033 in order to determine
the random-incidence response. The typical random-incidence with and without the
protection grid, and with Random Incidence Corrector DZ 9566 are shown in
Fig.2.12, Fig.2.13 and Fig.2.14, respectively.
The random-incidence corrections are calculated from the free-field corrections
measured in 5° steps according to Draft IEC 1183–1993.
Response (dB)
5
dB
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940934/1e
Fig.2.12 Typical random-incidence response for the microphone with Protection Grid DD 0525
Response (dB)
5
dB
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940885/1e
Fig.2.13 Typical random-incidence response for the microphone without protection grid
2 − 12
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Directional Characteristics
Response (dB)
5
dB
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940883/1e
Fig.2.14 Typical random-incidence response for the microphone with Random Incidence Corrector
DZ 9566
2.4
Directional Characteristics
Typical directional characteristics are given in Fig.2.15 to Fig.2.17. The characteristics are normalised relative to the 0° response.
BE 1374 – 12
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Directional Characteristics
Note: The non-symmetrical responses are at frequencies outside the microphone’s
nominal operating range (16 and 20 kHz).
0°
0°
0
–5
– 10
– 15
– 20
– 25
– 20
90°
5
0
5
270°
–15
–5
– 10
–15
– 20
– 25
– 10
– 20
–5
– 15
0
– 10
5
°
–5
90°
60
0°
°
0
30
60
5
°
0°
270°
30
0°
0°
°
33
30
33
30
6.3 kHz
20 kHz
8 kHz
θ°
10 kHz
0°
0°
0°
24
12
12.5 kHz
12
0°
24
180°
21
15
0°
0°
15
180°
21
0°
5 kHz
0°
16 kHz
940778e
Fig.2.15 Typical directional characteristics of the microphone with Protection Grid DD 0525
0°
0°
0
–5
– 10
– 15
– 20
– 25
– 20
90°
5
0
5
270°
–15
–5
– 10
–15
– 20
– 25
– 10
– 20
–5
– 15
0
– 10
5
°
–5
90°
60
0°
°
0
30
60
5
°
0°
270°
30
0°
0°
°
33
30
33
30
6.3 kHz
θ°
20 kHz
0°
0°
24
12
8 kHz
10 kHz
0°
12
0°
24
12.5 kHz
°
0
15
0°
180°
21
°
0
15
5 kHz
180°
21
0°
16 kHz
940779e
Fig.2.16 Typical directional characteristics of the microphone without protection grid
2 − 14
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Directional Characteristics
0°
0°
0
–5
– 10
– 15
– 20
– 25
– 20
90°
5
0
5
270°
–15
–5
– 10
–15
– 20
– 25
– 10
– 20
–5
– 15
0
– 10
5
°
–5
90°
60
0°
°
0
30
60
5
°
0°
270°
30
0°
0°
°
33
30
33
30
8 kHz
6.3 kHz
20 kHz
θ°
0°
12
12.5 kHz
0°
0°
0°
24
24
12
10 kHz
0°
15
0°
180°
21
0°
180°
15
5 kHz
21
0°
16 kHz
940781e
Fig.2.17 Typical directional characteristics of the microphone with Random Incidence Corrector
DZ 9566
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Dynamic Range
2.5
Dynamic Range
Definition
The dynamic range is the range between the upper limit (determined by distortion)
and the inherent noise floor. Both limits are influenced by the preamplifier. This
section gives values for the microphone with and without a preamplifier.
Inherent Noise
The microphone’s inherent noise is due to thermal movements of the diaphragm.
These vary proportionally with the square root of the absolute temperature (in °K).
The inherent noise increases with increasing temperature. With reference to 20 °C,
the inherent noise changes by + 0.5 dB at 55 °C and by − 0.5 dB at − 12 °C. The
maximum variation of this noise for different samples of Prepolarized Free-field 1/2"
Microphone Type 4188 is ± 1 dB.
The preamplifier’s effect on the inherent noise of the combined microphone and
preamplifier depends on the sensitivity and capacitance of the microphone (for 1/2"
Microphone Preamplifier Type 2669, see Fig. 2.18 and Chapter 8).
2 − 16
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Dynamic Range
Sound Pressure Level
re 20 µPa (dB)
25
20
L
L
A
15
L
A
A
10
Microphone
and
Preamplifier
Combination
5
0
Microphone
Preamplifier
– 5.
10
100
1k
10 k
Frequency (Hz)
20 k
M
P
C
940716e
Fig.2.18 1/3 -octave-band inherent noise spectrum. The shaded bar graphs are the broad-band
(20 Hz to 20 kHz) noise levels and the white bar graphs the A-weighted noise levels of the
microphone (M), 1/2" Microphone Preamplifier Type 2669 (P) and microphone and preamplifier combination (C)
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Dynamic Range
Distortion
The distortion is determined mainly by the microphone but, at the highest operation levels, the preamplifier also contributes to the distortion (see Fig. 2.19).
Distortion (%)
10
2nd
Harmonic
1
3rd
Harmonic
0.1
0.01
125
135
145
SPL (dB)
155
940400e
Fig.2.19 Typical distortion characteristics of the microphone, both
open-circuit and with 1/2 " Microphone Preamplifier Type
2669
The distortion is dependent on the capacitance parallel to the microphone. It increases with increasing capacitance. The distortions given in Table 2.2 and Table
2.3 are valid for a parallel capacitance of 0.5 pF. The distortion is measured at
100 Hz but can be assumed to be valid up to approximately 5 kHz (that is, where
the diaphragm displacement is predominantly stiffness-controlled). Distortion measurement methods for higher frequencies are not available.
Maximum Sound Pressure Level
In general, the microphone should not be exposed to sound pressure levels which
produce voltages higher than the maximum input voltage specified for the connected preamplifier. After an overload, the preamplifier needs time to recover and, during this recovery period, you cannot measure validly. The maximum input voltage
for most Brüel & Kjær preamplifiers is ± 50 V (with a 130 V supply). This voltage is
2 − 18
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Equivalent Volume and Calibrator Load Volume
Lower Limit
1 Hz bandwidth
at 1 kHz (dB)
1
Upper Limit
/3-octave band
at 1 kHz (dB)
A-weighted (dB)
Linear 20 Hz to
20 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
–0.9
14.2
14.5
146
157
– 24.5
Table 2.2 Dynamic range of the microphone
Lower Limit
1 Hz bandwidth
at 1 kHz (dB)
– 21.7
1
Upper Limit
/3-octave band
at 1 kHz (dB)
A-weighted (dB)
Linear 20 Hz to
20 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
1.9
15.8
20.1
146
157
Table 2.3 Dynamic range of the microphone with 1/2" Microphone Preamplifier Type 2669
produced by a nominal Prepolarized Free-field 1/2" Microphone Type 4188 at a Peak
level of 158 dB (re 20 µPa).
The microphone’s distortion increases smoothly as a function of sound pressure
level until the diaphragm’s displacement becomes so large that it hits the back
plate. When this occurs (at a Peak level of 157 dB), the output voltage is clipped.
We recommend not to expose Prepolarized Free-field 1/2" Microphone Type 4188 to
levels higher than 157 dB (Peak).
2.6
Equivalent Volume and Calibrator Load Volume
Equivalent Volume
For some applications it is practical to express the acoustic impedance of the microphone diaphragm in terms of an equivalent volume. This makes it easier to evaluate the effect of microphone loading on closed cavities or acoustic calibration
couplers.
The typical equivalent volume of Prepolarized Free-field 1/2" Microphone Type 4188
is 65 mm3.
Calibrator Load Volume
When the microphone with its protection grid is inserted into the coupler of a
calibrator, it will load the calibrator by a volume of 208 mm2 at 250 Hz.
Load volume correction to Pistonphone Type 4228 Calibration Level (with
Adaptor DP 0776): +0.02 dB
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Capacitance
2.7
Capacitance
The microphone’s impedance is determined by its capacitance. In addition, the
preamplifier’s input resistance and capacitance load the microphone. This loading
determines the electrical lower limiting frequency and the capacitive input attenuation. However, with modern preamplifiers, this loading is very small and is included
in the preamplifier gain, G (see section 2.2.2). Only in special cases with high
capacitive loading does the fall in capacitance with frequency have to be taken into
account.
Typical capacitance (at 1000 Hz): 12 pF.
Capacitance (pF)
20
18
16
14
12
10
100
1k
Hz
10k
Frequency (Hz)
100k
940597e
Fig.2.20 Variation of capacitance with frequency
2.8
Polarization Voltage
The polarization charge of Prepolarized Free-field 1/2" Microphone Type 4188 is
negative. Therefore, the output voltage is positive for a positive pressure applied to
the diaphragm.
At the factory, the microphone is polarized with a permanent charge. Therefore, do
not apply an external voltage to the microphone. In order to ensure the correct
polarization during use, the centre terminal of the microphone must be kept at the
same DC potential as the housing. Therefore, connect the preamplifier pin normally
used for the polarization voltage supply to ground potential (0 V). It is not sufficient
to leave it open circuit.
2 − 20
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Leakage Resistance
Accidentally connecting the microphone to a 200 V external polarization will not
damage the microphone. However, the sensitivity will fall by at least 8 dB and the
frequency response will change by 1 or 2 dB. We do not recommend use in this way.
Warning! Static electricity can destroy the microphone’s built-in charge.Therefore,
when mounting the microphone on a preamplifier, the housings of the microphone
and preamplifier must be connected before the centre pins make contact. The designs of Brüel & Kjær preamplifiers and sound level meters ensure this.
2.9
Leakage Resistance
The microphone’s leakage resistance is greater than 5×108 Ω at 90%RH and 23°C.
2.10 Stability
2.10.1 Mechanical Stability
The microphone’s design with respect to mechanical stability is improved compared
with traditional Brüel & Kjær microphones. The diaphragm clamping ring is less
sensitive to accidental force and the protection grid is significantly reinforced.
Therefore, the microphone can withstand mechanical shocks better than traditional
Brüel & Kjær microphones.
The sensitivity change of the microphone is less than 0.1 dB after a free fall of 1 m
onto a solid hardwood block (re IEC 68–2–32).
This improved mechanical stability makes Prepolarized Free-field 1/2" Microphone
Type 4188 well-suited for surface mounting and for mounting in small couplers as
no mechanical adaptor is required to protect the diaphragm clamping ring. The
microphone can be supported by the diaphragm clamping ring directly on the coupler’s surface. Any force of less than 5 Newtons will cause a change in sensitivity of
less than 0.005 dB. This makes the microphone well-suited for fitting in small,
plane wave couplers used for reciprocity calibration and any other small coupler
with a well-defined volume.
2.10.2 High-temperature Stability
The diaphragm is made of a stainless steel alloy. The alloy has been carefully
selected and is very resistant to heat. This means that the diaphragm tension (and
therefore the sensitivity) remain the same, even after several hours’ operation at
high temperature.
The microphone has been tested at temperatures up to 125°C. Below 125°C, no
changes occur. At 125°C, the sensitivity can be permanently changed within the
first hour by less than 0.1 dB. After this, the sensitivity can be permanently
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Effect of Temperature
changed within the next 10 hours by a similar value. These changes are due to
decreasing charge of the electret.
Note: Special adaptors (inserted between the microphone and preamplifier) must be
made for high-temperature applications in order to protect the preampifier from
heat conduction and radiation.
2.10.3 Long-term Stability
The microphone’s long-term stability is determined by the stability of the electret
charge. The charge decays very slowly even in humid conditions. See Brüel & Kjær
Technical Review no. 4, 1979 and the specifications given below:
> 1000 years/dB (dry air at 20°C)
> 10 hours/dB (dry air at 125°C)
> 40 years/dB (air at 20°C, 90%RH)
> 6 months/dB (air at 50°C, 90%RH)
2.11 Effect of Temperature
By careful selection of materials, optimization of the design and artificial ageing,
the effect of temperature has been made to be very low.
The microphone has been designed to operate at temperatures from − 30 to 125°C
(70°C with Random Incidence Corrector DZ 9566). See section 2.10.2 for permanent
changes in sensitivity at temperatures at 125°C.
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Effect of Temperature
The reversible changes are shown in Fig.2.21 as a change in sensitivity and in
Fig.2.22 and Fig.2.23 as changes in the frequency response normalized at 250 Hz.
Response (dB)
0.5
0.0
– 0.5
– 1.0
– 1.5
– 2.0
– 2.5
– 50
0
50
100
150
200
250
Temperature (°C)
300
940873e
Fig.2.21 Typical variation in sensitivity (at 250 Hz) as a function
of temperature, relative to the sensitivity at 20° C
Temperature Coefficient (1000 Hz):
+0.005 dB/°C, typical (for the range –10 to +50°C)
The effect of temperature on the free-field response (see Fig.2.23) of the microphone
is the sum of the following effects:
BE 1374 – 12
●
the calculated effect of the change in the speed of sound due to temperature on
the 0°-incidence free-field correction
●
the measured change in the actuator response due to temperature (see Fig.2.22).
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Effect of Temperature
Response (dB)
1.5
1.0
0.5
– 10 °C
0.0
+ 50 °C
– 0.5
– 1.0
– 1.5
500 Hz
1k
Frequency (Hz) 50 k
10 k
940772e
Fig.2.22 Typical variation in actuator response (normalized at
250 Hz) as a function of temperature, relative to the response at 20° C (see Fig.2.4)
Response (dB)
1.5
1.0
– 10°C
0.5
0.0
– 0.5
50°C
– 1.0
– 1.5
500 Hz
1k
10 k
Frequency (Hz) 50 k
940806/1e
Fig.2.23 Typical variation in 0°-incidence free-field response with
Protection Grid DD 0525 (normalized at 250 Hz) as a
function of temperature, relative to the response at 20° C
(see Fig.2.7)
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Effect of Ambient Pressure
2.12 Effect of Ambient Pressure
The microphone’s sensitivity and frequency response are affected by variations in
the ambient pressure. This is due to changes in air stiffness in the cavity behind
the diaphragm, and changes in air mass in the small gap between the diaphragm
and the back plate. The effects are shown in Fig.2.24 to Fig.2.26.
The typical pressure coefficient at 250 Hz for Prepolarized Free-field 1/2" Microphone Type 4188 is –0.021 dB/kPa, well within the ± 0.03 dB/kPa limits required for
Type 1 sound level meters by IEC 651.
Correction (dB)
3
– 40kPa
change
2
– 20kPa
change
1
– 10kPa
change
0
–1
500
1k
10k
Frequency (Hz)
50k
940762e
Fig.2.24 Typical variation in frequency response (normalized at
250 Hz) from that at 101.3 kPa as a function of change in
ambient pressure
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Effect of Humidity
Response (dB)
30
20
(d)
10
0
(c)
(b)
– 10
– 20
500
(a)
1k
10k
Frequency (Hz)
50k
940753e
Fig.2.25 Typical effect of ambient pressure on actuator response (a) at 101.3 kPa (b) − 40 kPa change
(c) − 80 kPa change (d) at 2 kPa
Response (dB)
4
2
0
–2
–4
–6
1
10
100
Ambient Pressure (kPa)
1000
940758e
Fig.2.26 Typical variation in sensitivity at 250 Hz from that at 101.3 kPa as a function of ambient
pressure
2.13 Effect of Humidity
Due to the microphone’s high leakage resistance, humidity has, in general, no effect
on the microphone’s sensitivity or frequency response. The microphone has been
tested according to IEC 68–2–3 and the effects of humidty on the sensitivity at
250 Hz and the frequency response have been found to be less than 0.1 dB at up to
95% RH (non-condensing) and 40°C.
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Effect of Vibration
2.14 Effect of Vibration
The effect of vibration is determined mainly by the mass of the diaphragm and is at
its maximum for vibrations applied normal to the diaphragm. A vibration signal of
1 m/s2 RMS normal to the diaphragm typically produces an equivalent Sound Pressure Level of 63.5 dB for a microphone fitted with Protection Grid DD 0525.
2.15 Effect of Magnetic Field
The effect of a magnetic field is determined by the vector field strength and is
normally at its maximum when the field direction is normal to the diaphragm. A
magnetic field strength of 80 A/m at 50 Hz (the test level recommended by IEC and
ANSI) normal to the diaphragm produces a typical equivalent Sound Pressure Level of 7 dB. Higher frequency components in the microphone output become dominant at field strengths greater than 500 to 1000 A/m.
2.16 Electromagnetic Compatibility
See Chapter 8.
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Chapter 2 — Prepolarized Free-field 1/2" Microphone Type 4188
Specifications Overview
2.17 Specifications Overview
OPEN-CIRCUIT SENSITIVITY (1000 Hz)*:
–30 dB ±2 dB re 1 V/Pa, 31.6 mV/Pa*
CALIBRATOR LOAD VOLUME (250 Hz):
208 mm3
PRESSURE COEFFICIENT (250 Hz):
–0.021 dB/kPa, typical
POLARIZATION VOLTAGE:
External: 0 V
PISTONPHONE TYPE 4228 CORRECTION:
with DP 0776:
+0.02 dB
INFLUENCE OF HUMIDITY:
<0.1 dB/100 %RH
FREQUENCY RESPONSE:
0° incidence free-field response:
12.5 Hz to 8 kHz: ±1 dB
8 Hz to 12.5 kHz: ±2 dB
In accordance with IEC 651, Type 1 and ANSI
S1.4 – 1983
LOWER LIMITING FREQUENCY (–3 dB):
1 Hz to 5 Hz (vent exposed to sound)
PRESSURE EQUALIZATION VENT:
Rear vented
TYPICAL CARTRIDGE THERMAL NOISE:
14.2 dB (A) 14.5 dB (Lin.)
UPPER LIMIT OF DYNAMIC RANGE:
3% distortion:
>146 dB SPL
MAXIMUM SOUND PRESSURE LEVEL:
157 dB (peak)
DIAPHRAGM RESONANCE FREQUENCY:
9 kHz, typical (90° phase shift)
OPERATING TEMPERATURE RANGE:
–30 to +125°C (–22 to 257°F)
Max. 70°C (158°F) when fitted with Randomincidence Corrector DZ 9566
CAPACITANCE (POLARIZED):
12 pF, typical (at 1000 Hz)
OPERATING HUMIDITY RANGE:
0 to 100 % RH (without condensation)
EQUIVALENT AIR VOLUME (101.3 kPa):
65 mm3
STORAGE TEMPERATURE:
–30 to + 70°C (–22 to 158°F)
TEMPERATURE COEFFICIENT (250 Hz):
+0.005 dB/°C, typical (for the range –10 to
+50°C)
* Individually calibrated
VIBRATION SENSITIVITY (<1000 Hz):
Typically 63.5 dB equivalent SPL for 1 m/s2 axial
acceleration
MAGNETIC FIELD SENSITIVITY:
Typically 7 dB SPL for 80 A/m, 50 Hz field
ESTIMATED LONG-TERM STABILITY:
> 1000 years/dB (dry air at 20°C)
> 10 hours/dB (dry air at 125°C)
> 40 years/dB (air at 20°C, 90% RH)
> 6 months/dB (air at 50°C, 90% RH)
DIMENSIONS:
Diameter: 13.2 mm (0.52 in) (with grid)
12.7 mm (0.50 in) (cartridge housing)
14.35 mm (0.56 in) (with DZ 9566)
Height:
14.9 mm (0.59 in) (with grid)
14.0 mm (0.55 in) (without grid)
16.7 mm (0.66 in) (with DZ 9566)
Thread for preamplifier mounting: 11.7 mm –
60 UNS
The data above are valid at 23°C, 101.3 kPa and
50%RH, unless otherwise specified.
2.18 Ordering Information
Preamplifier
Type 2669: 1/2" Microphone Preamplifier
Type 2671: 1/2" Microphone Preamplifier
Calibration Equipment
Type 4231: Sound Level Calibrator
Type 4226: Multifunction Acoustic Calibrator
Type 4228: Pistonphone
UA 0033: Electrostatic Actuator
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Ordering Information
Other Accessories
UA 0308: Dehumidifier
UA 0254: Set of 6 Windscreens (UA 0237) 90 mm (3.5 in)
UA 0469: Set of 6 Windscreens (UA 0459) 65 mm (2.6 in)
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Ordering Information
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Chapter 3
Prepolarized Free-field 1/2 " Microphone
Type 4189
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Introduction
3.1
Introduction
3.1.1
Description
Fig.3.1 Prepolarized Free-field 1/2" Microphone Type 4189 with Protection Grid DB 3420 (included)
Prepolarized Free-field 1/2" Microphone Type 4189 is a prepolarized 1/2" free-field
microphone and offers some significant advantages when used with portable instruments. For example, smaller associated instruments with low power consumption
can be used. A general advantage is the improved reliability of the associated
preamplifier in humid and polluted atmospheres. These factors make this prepolarized condenser microphone particularly suitable for field measurements, both outdoors and in industrial environments. In addition, it is suited to IEC 651 Type 1
measurements and frequency analysis measurements.
This microphone is polarized by a fixed charge-carrying layer deposited on the backplate. This layer is negatively charged which, at low frequencies, results in a positively increasing output voltage for a positively increasing incident sound pressure.
As a prepolarized microphone, it is externally marked by a pair of grooves.
The rugged microphone is built to ensure high stability under a variety of conditions. For example, the stainless steel alloy diaphragm withstands polluted industrial environments. The diaphragm clamping ring is firmly secured to ensure the
microphone’s reliability, even when the microphone is used without its protection
grid. When the microphone is used without its protection grid, it can be easily
flush-mounted or inserted into closed volumes as it can be supported by the diaphragm clamping ring, provided that a force of less than 5 Newtons is applied.
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Introduction
The microphone is supplied with individual calibration data on a calibration chart
and on a 31/2" data disk in a case. This case can also contain a 1/2" Microphone
Preamplifier Type 2669.
3.1.2
The Calibration Chart
Each microphone is supplied with an individual calibration chart (see Fig.3.2)
which gives the microphone’s open-circuit sensitivity, polarized capacitance and
free-field and actuator frequency responses.
B
K
7/6-'89
Prepolarized Free-field
1/2" Microphone Type 4189
+5
Bruel & Kjær
Calibration Chart
dB
Serial No:
418911A
+1
0
–1
-26.6
46.8
Open-circuit Sensitivity*, S0:
Equivalent to:
Uncertainty, 95 % confidence level
dB re 1V/Pa
Valid At:
Temperature:
Ambient Static Pressure:
Relative Humidity:
Frequency:
Polarization Voltage, external:
Free-field Response 0° Sound Incidence
mV/Pa
0.2 dB
14.1 pF
Capacitance:
Dotted Curve Shows Typical Response
23
101.3
50
250
0
–5
°C
kPa
%
Hz
V
Actuator Response
– 10
Sensitivity Traceable To:
DPLA: Danish Primary Laboratory of Acoustics
NIST: National Institute of Standards and Technology, USA
– 15
0° Sound Incidence
IEC 1094-4: Type WS 2 F
Environment Calibration Conditions:
101.5 kPa
20 °C
55 % RH
Procedure: 704215
Date: 21. Apr. 1994
Signature:
*K0 = – 26 – S0 Example: K0 = – 26 – (– 26.2) = + 0.2 dB
– 20
BC 0224 – 12
1
2
5
10
20
See the microphone handbook for further information
50
100
200
500
1k
2k
5k
20 k
10 k
Frequency Hz
40 k
940950e
Fig.3.2 Microphone calibration chart
Open-circuit Sensitivity
The stated open-circuit sensitivity is valid at the reference frequency (251.2 Hz* ) for
free-field, random-incidence and pressure-field conditions. The stated uncertainty is
the U95 value (the value valid for 95% confidence level).
Ambient Conditions
The ambient conditions are measured continuously during calibration at the factory.
The calibration results obtained at the measured Environmental Calibration Conditions are corrected to the reference ambient conditions stated under Valid At (23°C,
101.325 kPa and 50% RH).
Frequency Responses
Two individual frequency responses are shown on the calibration chart. Both are
normalized to 0 dB at the reference frequency (251.2 Hz*).
*The exact reference frequency is 102.4 Hz (re ISO 266).
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Introduction
The upper curve on the calibration chart is the individual microphone’s open-circuit
0°-incidence free-field response. This response is the optimized response for Prepolarized Free-field 1/2" Microphone Type 4189.
The lower curve on the calibration chart is the individual microphone’s electrostatic
actuator response measured with Electrostatic Actuator UA 0033. This response is
used to determine free-field responses at angles of incidence other than 0° and
responses in other types of sound field. The individual microphone’s electrostatic
actuator response is also available on the data disk.
The dotted part of the curve is the typical low-frequency response. Each microphone’s individual lower limiting frequency is measured to ensure that it is within
the specified tolerances (see Fig.3.3).
3.1.3
Data Disk
The 31/2" data disk supplied with each microphone supplements the calibration
chart. It contains individual calibration data and correction curves (see Table 3.1)
with a frequency resolution of 1/12-octave as comma-separated ASCII text files under the \DATA directory.
File Name
Content
Frequency Range
S#######.BKMa
Sensitivity calibration
251.2 Hz
A#######.BKMa
Actuator response
200 Hz – 22 kHz
F#######.BKRb
Free-field response
1 Hz – 22 kHz
4189L.BKTc
Low-frequency response
1 Hz – 190 Hz
4189F.BKCd
Free-field corrections without protection grid
200 Hz – 22 kHz
4189FG.BKCd
Free-field corrections with protection grid
200 Hz – 22 kHz
4189R.BKCd
Random-incidence corrections without protection grid
200 Hz – 22 kHz
4189RG.BKCd
Random-incidence corrections with protection grid
200 Hz – 22 kHz
4189P.BKCd
Pressure-field corrections
200 Hz – 22 kHz
Table 3.1
a.
b.
c.
d.
Calibration data and corrections contained on the data disk. Note: ####### is the microphone’s serial number
Individual calibration data (measured).
Low-frequency response combined with actuator response and free-field corrections.
Typical response for Prepolarized Free-field 1/2" Microphone Type 4189.
Corrections for Prepolarized Free-field 1/2" Microphone Type 4189.
These text files can be viewed on Microsoft® Windows™ using the Brüel & Kjær
Microphone Viewer program (BK–MIC.EXE) supplied on the disk. They can also be
accessed by a suitable spreadsheet for further processing or printing.
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Sensitivity
Brüel & Kjær Microphone Viewer must be installed before use (see section 1.3.5).
3.1.4
Recommended Recalibration Interval
With normal handling of the microphone and any associated instrument,
Brüel & Kjær recommends that the microphone be recalibrated every 2 years.
Prepolarized Free-field 1/2" Microphone Type 4189 is very stable over this period
(see section 3.10 to section 3.12). Improper handling is by far the most likely cause
of change in the microphone’s properties. Any damage which causes improper operation can probably be detected using a sound level calibrator. In many cases, the
damage can be seen by carefully inspecting the protection grid and diaphragm.
3.2
Sensitivity
3.2.1
Open-circuit Sensitivity
The open-circuit sensitivity is defined as the sensitivity of the microphone when not
loaded by the input impedance of the connected preamplifier (the termination is
described in IEC 1094–2). The sensitivity is measured for the individual microphone
at 251.2 Hz and stated on the microphone’s calibration chart (see section 3.1.2) and
data disk (see section 3.1.3). The nominal sensitivity is shown in Table 3.2.
Nominal open-circuit sensitivity
mV/Pa
dB re 1 V/Pa
50
–26
Accepted Deviation
(dB)
± 1.5
Table 3.2 Nominal open-circuit sensitivity
3.2.2
Loaded Sensitivity
When loaded by a preamplifier, the sensitivity of the microphone is given by:
SC = SO + G
where
SC
SO
G
(3.1)
= overall sensitivity of microphone and preamplifier combination
= open-circuit sensitivity of microphone
= voltage gain of microphone and preamplifier combination (in dB)
With Microphone Preamplifier Type 2639: G = –0.1 dB
With 1/2" Microphone Preamplifier Type 2669: G = –0.25 dB
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Frequency Response
Example
Loaded sensitivity of typical microphone with 1/2" Microphone Preamplifier Type
2669:
SC = –26.3 + (–0.25) = –26.55 dB
3.2.3
K-factor
Some types of Brüel & Kjær instruments use the K-factor (correction factor) or the
KO-factor (open-circuit correction factor) for calibration.
K = – 26 – S C
(3.2)
K O = – 26 – S O
(3.3)
Example
Correction factor for typical microphone with 1/2" Microphone Preamplifier Type
2669:
K = –26 – (–26.55) = +0.55 dB
Open-circuit correction factor for typical microphone with 1/2" Microphone Preamplifier Type 2669:
KO = –26 – (–26.3) = +0.3 dB
3.3
Frequency Response
3.3.1
General
In acoustic measurements, there are three types of sound field:
●
Free field
●
Pressure field
●
Diffuse field
The microphone is optimized to have a flat frequency response in one of these
sound fields. This response is called the optimized response. A microphone’s response in a diffuse field is equivalent to its random-incidence response.
This section shows the microphone’s typical free-field, pressure-field and randomincidence responses together with the microphone’s typical actuator response obtained using Electrostatic Actuator UA 0033. The low-frequency response described
in section 3.3.4 is common for all types of response.
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Frequency Response
All frequency responses and correction curves are shown with a frequency resolution of 1/12-octave.
3.3.2
Optimized Response (0°-incidence Free-field Response)
Response (dB)
5
Tol.
Tol.
0
Tol.
Tol.
–5
– 10
1
10
Fig.3.3
100
1k
10 k
Frequency (Hz)
100 k
940896e
Typical free-field response of the microphone with Protection Grid DB 3420 and the microphone’s specified tolerances. The low-frequency response is valid when the vent is exposed to
the sound field
The frequency response of Prepolarized Free-field 1/2" Microphone Type 4189 meets
the requirements of IEC 651 Type 1.
3.3.3
Actuator Response
The microphone’s frequency response is determined by adding corrections for the
type of sound field to its actuator response obtained using Electrostatic Actuator
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Frequency Response
UA 0033. This is a reproducible and practical method for calibrating a microphone’s
frequency response.
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940668e
Fig.3.4 Typical actuator response (magnitude) measured with Electrostatic Actuator UA 0033
Response (Degrees)
0
– 45
– 90
– 135
– 180
100
1k
10 k
Frequency (Hz)
100 k
940669e
Fig.3.5 Typical actuator response (phase) measured with Electrostatic Actuator UA 0033
This microphone is polarized by a fixed charge-carrying layer deposited on the backplate. This layer is negatively charged which, at low frequencies, results in a positively increasing output voltage for a positively increasing incident sound pressure.
3.3.4
Low-frequency Response
The low-frequency response (see Fig.3.3) is the typical response with the vent exposed to the sound field. If the vent is not exposed to the sound field, the sensitivity
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Frequency Response
increases from 0 dB at the reference frequency (251.2 Hz) to approximately 0.3 dB at
1Hz.
For applications where the vent is not exposed to the sound field, take care to
ensure proper static pressure equalization to prevent static displacement of the
diaphragm.
The microphone’s low-frequency response is common for all types of sound field.
The microphone’s lower limiting frequency (–3 dB) is between 2 and 4 Hz with the
vent exposed to the sound field. This is measured during production to ensure that
specifications are fulfilled.
3.3.5
Free-field Response
The microphone’s free-field correction curves are shown in Fig.3.6 and Fig.3.8.
These corrections are added to the microphone’s actuator response obtained using
Electrostatic Actuator UA 0033 in order to determine the free-field response at any
angle of incidence. The typical free-field response at 0° incidence with and without
the protection grid are shown in Fig.3.7 and Fig.3.9.
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Frequency Response
Correctionn (dB)
15
12.5
0°
10
30°
7.5
5
60°
2.5
Random
180°
0
90°
120°
150°
– 2.5
θ°
–5
– 7.5
– 10
500
1k
10k
Frequency (Hz)
50k
940804/1e
Fig.3.6
Free-field correction curves for the microphone with Protection Grid DB 3420
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940886e
Fig.3.7 Typical free-field response (0° incidence) for the microphone with Protection Grid DB 3420
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Frequency Response
Correction (dB)
15
12.5
10
0°
7.5
30°
5
2.5
60°
90°
Random
180°
0
150°
120°
– 2.5
θ°
–5
– 7.5
– 10
500
1k
10k
Frequency (Hz)
50k
940803/1e
Fig.3.8
Free-field correction curves for the microphone without
protection grid
Response (dB)
5
dB
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940887e
Fig.3.9 Typical free-field response (0° incidence) for the microphone without protection grid
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Frequency Response
3.3.6
Random-incidence Response
A microphone’s response in a diffuse sound field is equivalent to its random-incidence response. The microphone’s random-incidence correction curves are shown in
Fig.3.6 and Fig.3.8. These corrections are added to the microphone’s actuator response obtained using Electrostatic Actuator UA 0033 in order to determine the
random-incidence response. The typical random-incidence response with and without the protection grid are shown in Fig.3.10 and Fig.3.11.
The random-incidence corrections are calculated from the free-field corrections
measured in 5° steps according to Draft IEC 1183–1993.
Response (dB)
5
dB
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940936/1e
Fig.3.10 Typical random-incidence response for the microphone with Protection Grid DB 3420
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940937/1e
Fig.3.11 Typical random-incidence response for the microphone without protection grid
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Frequency Response
3.3.7
Pressure-field Response
The microphone’s pressure-field correction curve is shown in Fig.3.12. This correction is added to the microphone’s actuator response obtained using Electrostatic
Actuator UA 0033 in order to determine the pressure-field response. The typical
pressure-field response is shown in Fig.3.13.
In practice, the pressure-field response is often regarded as being equal to the
actuator response as the difference between them is small compared to the uncertainty related to many types of measurement.
Correction (dB)
4
3
2
1
0
–1
100
1k
10 k
Frequency (Hz)
100 k
940865e
Fig.3.12 Pressure-field correction for the microphone
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940869e
Fig.3.13 Typical pressure-field response for the microphone
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Directional Characteristics
3.4
Directional Characteristics
Typical directional characteristics are given in Fig.3.14 and Fig.3.15. The characteristics are normalised relative to the 0° response.
0°
0°
0
–5
– 10
– 15
– 20
– 25
– 20
90°
5
0
5
270°
–15
–5
– 10
–15
– 20
– 25
– 10
– 20
–5
– 15
0
– 10
5
°
–5
90°
60
0°
°
0
30
60
5
°
0°
270°
30
0°
0°
°
33
30
33
30
31.5 kHz
25 kHz
6.3 kHz
20 kHz
θ°
0°
12
12.5 kHz
0°
0°
2
24
12
8 kHz
10 kHz
°
40
0°
15
0°
180°
21
0°
15
5 kHz
180°
21
0°
16 kHz
940786e
Fig.3.14 Typical directional characteristics of the microphone with Protection Grid DB 3420
3 − 14
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Dynamic Range
0°
0°
0
–5
– 10
– 15
– 20
– 25
– 20
90°
5
0
5
270°
–15
–5
– 10
–15
– 20
– 25
– 10
– 20
–5
– 15
0
– 10
5
°
–5
90°
60
0°
°
0
30
60
5
°
0°
270°
30
0°
0°
°
33
30
33
30
31.5 kHz
25 kHz
6.3 kHz
20 kHz
8 kHz
10 kHz
0°
0°
24
12
0°
12
0°
24
θ°
12.5 kHz
0°
15
0°
180°
21
15
180°
21
0°
5 kHz
0°
16 kHz
940783e
Fig.3.15 Typical directional characteristics of the microphone without protection grid
3.5
Dynamic Range
Definition
The dynamic range is the range between the upper limit (determined by distortion)
and the inherent noise floor. Both limits are influenced by the preamplifier. This
section gives values for the microphone with and without a preamplifier.
Inherent Noise
The microphone’s inherent noise is due to thermal movements of the diaphragm.
These vary proportionally with the square root of the absolute temperature (in °K).
The inherent noise increases with increasing temperature. With reference to 20 °C,
the inherent noise changes by + 0.5 dB at 55 °C and by – 0.5 dB at – 12 °C. The
maximum variation of this noise for different samples of Prepolarized Free-field 1/2"
Microphone Type 4189 is ± 1 dB.
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Dynamic Range
The preamplifier’s effect on the inherent noise of the combined microphone and
preamplifier depends on the sensitivity and capacitance of the microphone (for 1/2"
Microphone Preamplifier Type 2669, see Fig. 3.16 and Chapter 8).
Sound Pressure Level
re 20 µPa (dB)
20
L
L
15
A
A
L
10
A
5
Microphone
and
Preamplifier
Combination
0
–5
Preamplifier
Microphone
– 10
10
100
1k
10 k
20 k M
P
C
Frequency (Hz)
940717e
Fig.3.16 1/3 -octave-band inherent noise spectrum. The shaded bar graphs are the broad-band
(20 Hz to 20 kHz) noise levels and the white bar graphs the A-weighted noise levels of the
microphone (M), 1/2" Microphone Preamplifier Type 2669 (P) and microphone and preamplifier combination (C)
3 − 16
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Dynamic Range
Distortion
The distortion is determined mainly by the microphone but, at the highest operation levels, the preamplifier also contributes to the distortion (see Fig. 3.17).
Distortion (%)
10
2nd
Harmonic
1
3rd
Harmonic
0.1
0.01
125
135
145
SPL (dB)
155
940501e
Fig.3.17 Typical distortion characteristics of Prepolarized Freefield 1/2" Microphone Type 4189
The distortion is dependent on the capacitance parallel to the microphone. It increases with increasing capacitance. The distortions given in Table 3.3 and Table
3.4 are valid for a parallel capacitance of 0.5 pF. The distortion is measured at
100 Hz but can be assumed to be valid up to approximately 5 kHz (that is, where
the diaphragm displacement is predominantly stiffness-controlled). Distortion measurement methods for higher frequencies are not available.
Maximum Sound Pressure Level
In general, the microphone should not be exposed to sound pressure levels which
produce voltages higher than the maximum input voltage specified for the connected preamplifier. After an overload, the preamplifier needs time to recover and, during this recovery period, you cannot measure validly. The maximum input voltage
for most Brüel & Kjær preamplifiers is ± 50 V (with a 130 V supply). This voltage is
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Equivalent Volume and Calibrator Load Volume
Lower Limit
1 Hz bandwidth
at 1 kHz (dB)
1
Upper Limit
/3-octave at
1 kHz (dB)
A-weighted (dB)
Linear 20 Hz to
20 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
–0.7
14.6
15.3
146
158
– 24.3
Table 3.3 Dynamic range of the microphone
Lower Limit
1 Hz bandwidth
at 1 kHz (dB)
– 23.2
1
Upper Limit
/3-octave at
1 kHz (dB)
A-weighted (dB)
Linear 20 Hz to
20 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
0.4
15.2
17.4
146
158
Table 3.4 Dynamic range of the microphone with 1/2" Microphone Preamplifier Type 2669
produced by a nominal Prepolarized Free-field 1/2" Microphone Type 4189 at a Peak
level of 154 dB (re 20 µPa).
The microphone’s distortion increases smoothly as a function of sound pressure
level until the diaphragm’s displacement becomes so large that it hits the back
plate. When this occurs (at a Peak level of 158 dB), the output voltage is clipped.
We recommend not to expose Prepolarized Free-field 1/2" Microphone Type 4189 to
levels higher than 158 dB (Peak).
3.6
Equivalent Volume and Calibrator Load Volume
Equivalent Volume
For some applications it is practical to express the acoustic impedance of the microphone diaphragm in terms of a complex equivalent volume. This makes it easier to
evaluate the effect of microphone loading on closed cavities or acoustic calibration
couplers.
The real and imaginary parts of the equivalent volume shown in Fig.3.18 are in
parallel. They are calculated from a simple R–L–C series model of the microphone
which gives the best overall approximation of the microphone’s diaphragm impedance.
The Models
The following equivalent models are valid at 101.325 kPa, 23 °C and 50%RH:
3 − 18
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Equivalent Volume and Calibrator Load Volume
Volume (mm3)
60
50
40
30
20
– V (Im)
10
V (Re)
0
– 10
100
1k
10k
Frequency (Hz)
100k
940949e
Fig.3.18 Typical equivalent volume (real and imaginary parts) based on mathematical model of
microphone
Model 1
C = 0.324 x 10 -12m5/N
L = 305kg/m4
R = 77 x 106 Ns/m5
where
C = acoustic diaphragm compliance
L = acoustic diaphragm mass
R = acoustic diaphragm damping resistance
Model 2
Vlf = 46 mm3
f0 = 16kHz
Q = 0.4
where
Vlf = low-frequency volume
f0 = diaphragm resonance frequency
Q = quality factor
Calibrator Load Volume
When the microphone with its protection grid is inserted into the coupler of a
calibrator, it will load the calibrator by a volume of 260 mm3 at 250 Hz.
Load volume correction to Pistonphone Type 4228 Calibration Level (with
Adaptor DP 0776): 0.00 dB
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Capacitance
3.7
Capacitance
The microphone’s impedance is determined by its capacitance. In addition, the
preamplifier’s input resistance and capacitance load the microphone. This loading
determines the electrical lower limiting frequency and the capacitive input attenuation. However, with modern preamplifiers, this loading is very small and is included
in the preamplifier gain, G (see section 3.2.2). Only in special cases with high
capacitive loading does the fall in capacitance with frequency have to be taken into
account.
Capacitance (pF)
20
18
16
14
12
10
100
1k
Hz
10k
Frequency (Hz)
100k
940599e
Fig.3.19 Variation of capacitance with frequency
Typical capacitance (at 250 Hz): 14 pF.
The capacitance is individually calibrated and stated on the calibration chart.
3.8
Polarization Voltage
The polarization charge of Prepolarized Free-field 1/2" Microphone Type 4189 is
negative. Therefore, the output voltage is positive for a positive pressure applied to
the diaphragm.
At the factory, the microphone is polarized with a permanent charge. Therefore, do
not apply an external voltage to the microphone. In order to ensure the correct
polarization during use, the centre terminal of the microphone must be kept at the
same DC potential as the housing. Therefore, connect the preamplifier pin normally
used for the polarization voltage supply to ground potential (0 V). It is not sufficient
to leave it open circuit.
3 − 20
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Leakage Resistance
Accidentally connecting the microphone to a 200 V external polarization will not
damage the microphone. However, the sensitivity will fall by at least 8 dB and the
frequency response will change by 1 or 2 dB. We do not recommend use in this way.
Warning! Static electricity can destroy the microphone’s built-in charge. Therefore,
when mounting the microphone on a preamplifier, the housings of the microphone
and preamplifier must be connected before the centre pins make contact. The designs of Brüel & Kjær preamplifiers and sound level meters ensure this.
3.9
Leakage Resistance
The microphone’s leakage resistance is greater than 5 × 1013 Ω at 90%RH and 23°C.
3.10 Stability
3.10.1 Mechanical Stability
The microphone’s design with respect to mechanical stability is improved compared
with traditional Brüel & Kjær microphones. The diaphragm clamping ring is less
sensitive to accidental force and the protection grid is significantly reinforced.
Therefore, the microphone can withstand mechanical shocks better than traditional
Brüel & Kjær microphones.
The sensitivity change of the microphone is less than 0.1 dB after a free fall of 1 m
onto a solid hardwood block (re IEC 68–2–32).
This improved mechanical stability makes Prepolarized Free-field 1/2" Microphone
Type 4189 well-suited for surface mounting and for mounting in small couplers as
no mechanical adaptor is required to protect the diaphragm clamping ring. The
microphone can be supported by the diaphragm clamping ring directly on the coupler’s surface. Any force of less than 5 Newtons will cause a change in sensitivity of
less than 0.005 dB. This makes the microphone well-suited for fitting in small,
plane wave couplers used for reciprocity calibration and any other small coupler
with a well-defined volume.
3.10.2 High-temperature Stability
The diaphragm is made of a stainless steel alloy. The alloy has been carefully
selected and is very resistant to heat. This means that the diaphragm tension (and
therefore the sensitivity) remain the same, even after several hours’ operation at
high temperature.
The microphone has been tested at temperatures up to 150°C. Below 150°C, no
changes occur. At 150°C, the sensitivity can be permanently changed within the
first hour by less than 0.05 dB. After this, the sensitivity can be permanently
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Effect of Temperature
changed within the next 10 hours by a similar value. These changes are due to
decreasing charge of the electret.
Note: special adaptors (inserted between the microphone and preamplifier) must be
made for high-temperature applications in order to protect the preampifier from
heat conduction and radiation.
3.10.3 Long-term Stability
The microphone’s long-term stability is determined by the stability of the electret
charge. The charge decays very slowly even in humid conditions. See Brüel & Kjær
Technical Review no. 4, 1979 and the specifications given below:
> 1000 years/dB (dry air at 20°C)
> 2 hours/dB (dry air at 150°C)
> 40 years/dB (air at 20°C, 90%RH)
> 1 year/dB (air at 50°C, 90%RH)
3.11 Effect of Temperature
By careful selection of materials, optimization of the design and artificial ageing,
the effect of temperature has been made to be very low.
The microphone has been designed to operate at temperatures from – 30 to 150°C.
See section 3.10.2 for permanent changes in sensitivity at temperatures at 150°C.
3 − 22
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Effect of Temperature
The reversible changes are shown in Fig.3.20 as a change in sensitivity and in
Fig.3.21 and Fig.3.22 as changes in the frequency response normalized at 250 Hz.
Response (dB)
0.5
0.0
– 0.5
– 1.0
– 1.5
– 2.0
– 2.5
– 50
0
50
100
150
200
250
Temperature (°C)
300
940874e
Fig.3.20 Typical variation in sensitivity (at 250 Hz) as a function
of temperature, relative to the sensitivity at 20° C
Temperature Coefficient (250 Hz):
–0.001 dB/°C, typical (for the range –10 to +50°C)
The effect of temperature on the free-field response (see Fig.3.22) of the microphone
is the sum of the following effects:
BE 1375 – 12
●
the calculated effect of the change in the speed of sound due to temperature on
the 0°-incidence free-field correction
●
the measured change in the actuator response due to temperature (see Fig.3.21).
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Effect of Temperature
Response (dB)
1.5
1.0
0.5
– 10 °C
0.0
+ 50 °C
– 0.5
– 1.0
– 1.5
500 Hz
1k
Frequency (Hz) 50 k
10 k
940773e
Fig.3.21 Typical variation in actuator response (normalized at
250 Hz) as a function of temperature, relative to the response at 20° C (see Fig.3.4)
Response (dB)
1.5
1.0
0.5
– 10°C
0.0
– 0.5
– 1.0
– 1.5
500 Hz
50°C
1k
10 k
Frequency (Hz) 50 k
940807/1e
Fig.3.22 Typical variation in 0°-incidence free-field response with
Protection Grid DB 3420 (normalized at 250 Hz) as a
function of temperature, relative to the response at 20° C
(see Fig.3.7)
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Effect of Ambient Pressure
3.12 Effect of Ambient Pressure
The microphone’s sensitivity and frequency response are affected by variations in
the ambient pressure. This is due to changes in air stiffness in the cavity behind
the diaphragm, and changes in air mass in the small gap between the diaphragm
and the back plate. The effects are shown in Fig.3.23 to Fig.3.25.
The typical pressure coefficient at 250 Hz for Prepolarized Free-field 1/2" Microphone Type 4189 is –0.010 dB/kPa, well within the ±0.03 dB/kPa limits required for
Type 1 sound level meters by IEC 651.
Correction (dB)
3
2
– 40kPa
change
1
– 20kPa
change
– 10kPa
change
0
–1
500
1k
10k
Frequency (Hz)
50k
940763e
Fig.3.23 Typical variation in frequency response (normalized at
250 Hz) from that at 101.3 kPa as a function of change in
ambient pressure
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Effect of Humidity
Response (dB)
30
20
(d)
10
0
(c)
(b)
(a)
– 10
– 20
500
1k
10k
Frequency (Hz)
50k
940754e
Fig.3.24 Typical effect of ambient pressure on actuator response
(a) at 101.3 kPa (b) – 40 kPa change (c) – 80 kPa change
(d) at 2 kPa
Response (dB)
4
2
0
–2
–4
–6
1
10
100
Ambient Pressure (kPa)
1000
940759e
Fig.3.25 Typical variation in sensitivity at 250 Hz from that at 101.3 kPa as a function of ambient
pressure
3.13 Effect of Humidity
Due to the microphone’s high leakage resistance, humidity has, in general, no effect
on the microphone’s sensitivity or frequency response. The microphone has been
tested according to IEC 68–2–3 and the effects of humidty on the sensitivity at
250 Hz and the frequency response have been found to be less than 0.1 dB at up to
95% RH (non-condensing) and 40°C.
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Effect of Vibration
3.14 Effect of Vibration
The effect of vibration is determined mainly by the mass of the diaphragm and is at
its maximum for vibrations applied normal to the diaphragm. A vibration signal of
1 m/s2 RMS normal to the diaphragm typically produces an equivalent Sound Pressure Level of 62.5 dB for a microphone fitted with Protection Grid DB 3420.
3.15 Effect of Magnetic Field
The effect of a magnetic field is determined by the vector field strength and is
normally at its maximum when the field direction is normal to the diaphragm. A
magnetic field strength of 80 A/m at 50 Hz (the test level recommended by IEC and
ANSI) normal to the diaphragm produces a typical equivalent Sound Pressure Level of 6 dB. Higher frequency components in the microphone output become dominant at field strengths greater than 500 to 1000 A/m.
3.16 Electromagnetic Compatibility
See Chapter 8.
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Specifications Overview
3.17 Specifications Overview
OPEN-CIRCUIT SENSITIVITY (250 Hz)*:
–26 dB ±1.5 dB re 1 V/Pa, 50 mV/Pa*
CALIBRATOR LOAD VOLUME (250 Hz):
260 mm3
INFLUENCE OF HUMIDITY:
<0.1 dB/100 %RH
POLARIZATION VOLTAGE:
External: 0 V
PISTONPHONE TYPE 4228 CORRECTION:
with DP 0776:
0.00 dB
VIBRATION SENSITIVITY (<1000 Hz):
Typically 62.5 dB equivalent SPL for 1 m/s2 axial
acceleration
TYPICAL CARTRIDGE THERMAL NOISE:
14.6 dB (A) 15.3 dB (Lin.)
MAGNETIC FIELD SENSITIVITY:
Typically 6 dB SPL for 80 A/m, 50 Hz field
UPPER LIMIT OF DYNAMIC RANGE:
3% distortion:
>146 dB SPL
ESTIMATED LONG-TERM STABILITY:
> 1000 years/dB (dry air at 20°C)
> 2 hours/dB (dry air at 150°C)
> 40 years/dB (air at 20°C, 90% RH)
> 1 year/dB (air at 50°C, 90% RH)
FREQUENCY RESPONSE*:
0° incidence free-field response:
10 Hz to 8 kHz: ± 1 dB
6.3 Hz to 20 kHz: ±2 dB
In accordance with IEC 651, Type 1
LOWER LIMITING FREQUENCY (–3 dB):
2 Hz to 4 Hz (vent exposed to sound)
PRESSURE EQUALIZATION VENT:
Rear vented
DIAPHRAGM RESONANCE FREQUENCY:
14 kHz, typical (90° phase shift)
CAPACITANCE (POLARIZED:
14 pF, typical (at 250 Hz)
EQUIVALENT AIR VOLUME (101.3 kPa):
46 mm3
MAXIMUM SOUND PRESSURE LEVEL:
158 dB (peak)
OPERATING TEMPERATURE RANGE:
–30 to +150°C (–22 to 302°F)
OPERATING HUMIDITY RANGE:
0 to 100 % RH (without condensation)
DIMENSIONS:
Diameter: 13.2 mm (0.52 in) (with grid)
12.7 mm (0.50 in) (without grid)
Height:
17.6 mm (0.68 in) (with grid)
16.3 mm (0.64 in) (without grid)
Thread for preamplifier mounting: 11.7 mm –
60 UNS
STORAGE TEMPERATURE:
–30 to + 70°C (–22 to 158°F)
TEMPERATURE COEFFICIENT (250 Hz):
–0.001 dB/°C, typical (for the range –10 to
+50°C)
* Individually calibrated
PRESSURE COEFFICIENT (250 Hz):
–0.010 dB/kPa, typical
The data above are valid at 23°C, 101.3 kPa and
50%RH, unless otherwise specified.
3.18 Ordering Information
Preamplifier
Type 2669: 1/2" Microphone Preamplifier
Type 2671: 1/2" Microphone Preamplifier
Calibration Equipment
Type 4231: Sound Level Calibrator
Type 4226: Multifunction Acoustic Calibrator
Type 4228: Pistonphone
UA 0033: Electrostatic Actuator
3 − 28
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Ordering Information
Other Accessories
UA 0308: Dehumidifier
UA 0254: Set of 6 Windscreens (UA 0237) 90 mm (3.5 in)
UA 0469: Set of 6 Windscreens (UA 0459) 65 mm (2.6 in)
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Chapter 3 — Prepolarized Free-field 1/2" Microphone Type 4189
Ordering Information
3 − 30
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Chapter 4
Free-field 1/2 " Microphone Type 4190
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4− 1
Chapter 4 — Free-field 1/2" Microphone Type 4190
Introduction
4.1
Introduction
4.1.1
Description
Fig.4.1 Free-field 1/2" Microphone Type 4190 with Protection Grid DB 3420 (included)
Free-field 1/2" Microphone Type 4190 is an externally-polarized microphone for general sound measurements and for standardized noise measurements in accordance
with the requirements of IEC 651 Type 0 and Type 1. With its low inherent noise
and frequency range from 3.15 Hz to 20 kHz, it is very well suited for a wide range
of precision audio-frequency sound measurements.
The microphone requires a polarization voltage of 200 V, provided by the instrument
or analyzer powering the associated preamplifier.
This rugged microphone is built to ensure high stability under a variety of conditions. For example, the stainless steel alloy diaphragm withstands polluted industrial environments. The diaphragm clamping ring is firmly secured to ensure the
microphone’s reliability, even when the microphone is used without its protection
grid. When the microphone is used without its protection grid, it can be easily
flush-mounted or inserted into closed volumes as it can be supported by the diaphragm clamping ring, provided that a force of less than 5 Newtons is applied.
The microphone is supplied with individual calibration data on a calibration chart
and on a 31/2" data disk in a case. This case can also contain a 1/2" Microphone
Preamplifier Type 2669.
4− 2
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Introduction
4.1.2
The Calibration Chart
Each microphone is supplied with an individual calibration chart (see Fig.4.2)
which gives the microphone’s open-circuit sensitivity, polarized capacitance and
free-field and actuator frequency responses.
B
K
7/6-'89
Free-field 1/2" Microphone
Type 4190
+5
Bruel & Kjær
Calibration Chart
dB
Serial No:
419011A
+1
0
–1
-26.4
47.7
Open-circuit Sensitivity*, S0:
Equivalent to:
Uncertainty, 95 % confidence level
dB re 1V/Pa
Valid At:
Temperature:
Ambient Static Pressure:
Relative Humidity:
Frequency:
Polarization Voltage, external:
Free-field Response 0° Sound Incidence
mV/Pa
0.2 dB
16.4 pF
Capacitance:
Dotted Curve Shows Typical Response
23
101.3
50
250
200
–5
°C
kPa
%
Hz
V
Actuator Response
– 10
Sensitivity Traceable To:
DPLA: Danish Primary Laboratory of Acoustics
NIST: National Institute of Standards and Technology, USA
– 15
0° Sound Incidence
IEC 1094-4: Type WS 2 F
Environmental Calibration Conditions:
100.1 kPa
25 °C
35 % RH
Procedure: 704216
Date: 21. Apr. 1994
Signature:
– 20
*K0 = – 26 – S0 Example: K0 = – 26 – (– 26.2) = + 0.2 dB
BC 0225 – 12
1
2
5
10
20
See the microphone handbook for further information
50
100
200
500
1k
2k
5k
20 k
10 k
Frequency Hz
40 k
940951e
Fig.4.2 Microphone calibration chart
Open-circuit Sensitivity
The stated open-circuit sensitivity is valid at the reference frequency (251.2 Hz* ) for
free-field, random-incidence and pressure-field conditions. The stated uncertainty is
the U95 value (the value valid for 95% confidence level).
Ambient Conditions
The ambient conditions are measured continuously during calibration at the factory.
The calibration results obtained at the measured Environmental Calibration Conditions are corrected to the reference ambient conditions stated under Valid At (23°C,
101.325 kPa and 50% RH).
Frequency Responses
Two individual frequency responses are shown on the calibration chart. Both are
normalized to 0 dB at the reference frequency (251.2 Hz*).
The upper curve on the calibration chart is the individual microphone’s open-circuit
0°-incidence free-field response. This response is the optimized response for Freefield 1/2" Microphone Type 4190.
*The exact reference frequency is 102.4 Hz (re ISO 266).
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Introduction
The lower curve on the calibration chart is the individual microphone’s electrostatic
actuator response measured with Electrostatic Actuator UA 0033. This response is
used to determine free-field responses at angles of incidence other than 0° and
responses in other types of sound field. The individual microphone’s electrostatic
actuator response is also available on the data disk.
The dotted part of the curve is the typical low-frequency response. Each microphone’s individual lower limiting frequency is measured to ensure that it is within
the specified tolerances (see Fig.4.3).
4.1.3
Data Disk
The 31/2" data disk supplied with each microphone supplements the calibration
chart. It contains individual calibration data and correction curves (see Table 4.1)
with a frequency resolution of 1/12-octave as comma-separated ASCII text files under the \DATA directory.
File Name
Content
Frequency Range
Sensitivity calibration
251.2 Hz
A#######.BKMa
Actuator response
200 Hz – 22 kHz
F#######.BKRb
Free-field response
1 Hz – 22 kHz
4190L.BKTc
Low-frequency response
1 Hz – 190 Hz
4190F.BKCd
Free-field corrections without protection grid
200 Hz – 22 kHz
4190FG.BKCd
Free-field corrections with protection grid
200 Hz – 22 kHz
4190R.BKCd
Random-incidence corrections without protection grid
200 Hz – 22 kHz
4190RG.BKCd
Random-incidence corrections with protection grid
200 Hz – 22 kHz
4190P.BKCd
Pressure-field corrections
200 Hz – 22 kHz
S#######.BKM
Table 4.1
a.
b.
c.
d.
a
Calibration data and corrections contained on the data disk. Note: ####### is the microphone’s serial number
Individual calibration data (measured).
Low-frequency response combined with actuator response and free-field corrections.
Typical response for Free-field 1/2" Microphone Type 4190.
Corrections for Free-field 1/2" Microphone Type 4190.
These text files can be viewed on Microsoft® Windows™ using the Brüel & Kjær
Microphone Viewer program (BK–MIC.EXE) supplied on the disk. They can also be
accessed by a suitable spreadsheet for further processing or printing.
Brüel & Kjær Microphone Viewer must be installed before use (see section 1.3.5).
4− 4
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Sensitivity
4.1.4
Recommended Recalibration Interval
With normal handling of the microphone and any associated instrument,
Brüel & Kjær recommends that the microphone be recalibrated every 2 years.
Free-field 1/2" Microphone Type 4190 is very stable over this period (see section
4.10 to section 4.12). Improper handling is by far the most likely cause of change in
the microphone’s properties. Any damage which causes improper operation can
probably be detected using a sound level calibrator. In many cases, the damage can
be seen by carefully inspecting the protection grid and diaphragm.
4.2
Sensitivity
4.2.1
Open-circuit Sensitivity
The open-circuit sensitivity is defined as the sensitivity of the microphone when not
loaded by the input impedance of the connected preamplifier (the termination is
described in IEC 1094–2). The sensitivity is measured for the individual microphone
at 251.2 Hz and stated on the microphone’s calibration chart (see section 4.1.2) and
data disk (see section 4.1.3). The nominal sensitivity is shown in Table 4.1.
Nominal open-circuit sensitivity
mV/Pa
dB re 1 V/Pa
50
–26.0
Accepted Deviation
(dB)
± 1.5
Table 4.2 Nominal open-circuit sensitivity
4.2.2
Loaded Sensitivity
When loaded by a preamplifier, the sensitivity of the microphone is given by:
SC = SO + G
where
SC
SO
G
(4.1)
= overall sensitivity of microphone and preamplifier combination
= open-circuit sensitivity of microphone
= voltage gain of microphone and preamplifier combination (in dB)
With Microphone Preamplifier Type 2639: G = –0.1 dB
With 1/2" Microphone Preamplifier Type 2669: G = –0.2 dB
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Frequency Response
Example
Loaded sensitivity of typical microphone with 1/2" Microphone Preamplifier Type
2669:
SC = –26.3 + (–0.2) = –26.5 dB
4.2.3
K-factor
Some types of Brüel & Kjær instruments use the K-factor (correction factor) or the
KO-factor (open-circuit correction factor) for calibration.
K = – 26 – S C
(4.2)
K O = – 26 – S O
(4.3)
Example
Correction factor for typical microphone with 1/2" Microphone Preamplifier Type
2669:
K = –26 – (–26.5) = +0.5 dB
Open-circuit correction factor for typical microphone with 1/2" Microphone Preamplifier Type 2669:
KO = –26 – (–26.3) = +0.3 dB
4.3
Frequency Response
4.3.1
General
In acoustic measurements, there are three types of sound field:
●
Free field
●
Pressure field
●
Diffuse field
The microphone is optimized to have a flat frequency response in one of these
sound fields. This response is called the optimized response. A microphone’s response in a diffuse field is equivalent to its random-incidence response.
This section shows the microphone’s typical free-field, pressure-field and randomincidence responses together with the microphone’s typical actuator response obtained using Electrostatic Actuator UA 0033. The low-frequency response described
in section 4.3.4 is common for all types of response.
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Frequency Response
All frequency responses and correction curves are shown with a frequency resolution of 1/12-octave.
4.3.2
Optimized Response (0°-incidence Free-field Response)
Response (dB)
5
Tol.
Tol.
Tol.
Tol.
0
–5
– 10
1
10
Fig.4.3
100
1k
10 k
Frequency (Hz)
100 k
940895e
Typical free-field response of the microphone with Protection Grid DB 3420 and the microphone’s specified tolerances. The low-frequency response is valid when the vent is exposed to
the sound field
The frequency response of Free-field 1/2" Microphone Type 4190 meets the requirements of IEC 651 Type 0 and Type 1.
4.3.3
Actuator Response
The microphone’s frequency response is determined by adding corrections for the
type of sound field to its actuator response obtained using Electrostatic Actuator
UA 0033. This is a reproducible and practical method for calibrating a microphone’s
frequency response.
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Frequency Response
Response (dB)
5
0
–5
– 10
– 15
– 20
100
Fig.4.4
1k
10 k
Frequency (Hz)
100 k
940670e
Typical actuator response (magnitude) measured with Electrostatic Actuator UA 0033
Response (Degrees)
0
– 45
– 90
– 135
– 180
100
Fig.4.5
1k
10 k
Frequency (Hz)
100 k
940671e
Typical actuator response (phase) measured with Electrostatic Actuator UA 0033
If the polarization voltage is positive (as it is with Brüel & Kjær instruments), the
output voltage is negative for a positive pressure applied to the diaphragm.
4.3.4
Low-frequency Response
The low-frequency response (see Fig.4.3) is the typical response with the vent exposed to the sound field. If the vent is not exposed to the sound field, the sensitivity
increases from 0 dB at the reference frequency (251.2 Hz) to approximately 0.3 dB at
1Hz.
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Frequency Response
For applications where the vent is not exposed to the sound field, take care to
ensure proper static pressure equalization to prevent static displacement of the
diaphragm.
The microphone’s low-frequency response is common for all types of sound field.
The microphone’s lower limiting frequency (–3 dB) is between 1 and 2 Hz with the
vent exposed to the sound field. This is measured during production to ensure that
specifications are fulfilled.
4.3.5
Free-field Response
The microphone’s free-field correction curves are shown in Fig.4.6 and Fig.4.8.
These corrections are added to the microphone’s actuator response obtained using
Electrostatic Actuator UA 0033 in order to determine the free-field response at any
angle of incidence. The typical free-field response at 0° incidence with and without
the protection grid are shown in Fig.4.7 and Fig.4.9.
Correction (dB)
15
12.5
0°
10
30°
7.5
5
60°
2.5
Random
150°
0
90°
120°
180°
– 2.5
θ°
–5
– 7.5
– 10
500
1k
10k
Frequency (Hz)
50k
940802/1e
Fig.4.6
BE 1376 – 12
Free-field correction curves for the microphone with Protection Grid DB 3420
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Frequency Response
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940888e
Fig.4.7 Typical free-field response (0° incidence) for the microphone with Protection Grid DB 3420
Correction (dB)
15
12.5
10
0°
7.5
30°
5
2.5
60°
Random
150°
0
120°
90°
– 2.5
180°
θ°
–5
– 7.5
– 10
500
1k
10k
Frequency (Hz)
50k
940801/1e
Fig.4.8
4 − 10
Free-field correction curves for the microphone without
protection grid
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Frequency Response
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940889e
Fig.4.9 Typical free-field response (0° incidence) for the microphone without protection grid
4.3.6
Random-incidence Response
A microphone’s response in a diffuse sound field is equivalent to its random-incidence response. The microphone’s random-incidence correction curves are shown in
Fig.4.6 and Fig.4.8. These corrections are added to the microphone’s actuator response obtained using Electrostatic Actuator UA 0033 in order to determine the
random-incidence response. The typical random-incidence response with and without the protection grid are shown in Fig.4.10 and Fig.4.11.
The random-incidence corrections are calculated from the free-field corrections
measured in 5° steps according to Draft IEC 1183–1993.
Response (dB)
5
dB
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940938/1e
Fig.4.10 Typical random-incidence response for the microphone with Protection Grid DB 3420
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Frequency Response
Response (dB)
5
dB
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940939/1e
Fig.4.11 Typical random-incidence response for the microphone without protection grid
4.3.7
Pressure-field Response
The microphone’s pressure-field correction curve is shown in Fig.4.12. This correction is added to the microphone’s actuator response obtained using Electrostatic
Actuator UA 0033 in order to determine the pressure-field response. The typical
pressure-field response is shown in Fig.4.13.
In practice, the pressure-field response is often regarded as being equal to the
actuator response as the difference between them is small compared to the uncertainty related to many types of measurement.
Correction (dB)
4
3
2
1
0
–1
100
1k
10 k
Frequency (Hz)
100 k
940866e
Fig.4.12 Pressure-field correction for the microphone
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Directional Characteristics
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
100 k
Frequency (Hz)
940870e
Fig.4.13 Typical pressure-field response for the microphone
4.4
Directional Characteristics
Typical directional characteristics are given in Fig.4.14 and Fig.4.15. The characteristics are normalised relative to the 0° response.
Note: The non-symmetrical responses are at frequencies outside the microphone’s
nominal operating range (25 and 31.5 kHz).
0°
0°
0
–5
– 10
– 15
– 20
– 25
– 20
90°
5
0
5
270°
–15
–5
– 10
–15
– 20
– 25
– 10
– 20
–5
– 15
0
– 10
5
°
–5
90°
60
0°
°
0
30
60
5
°
0°
270°
30
0°
0°
°
33
30
33
30
31.5 kHz
25 kHz
6.3 kHz
20 kHz
8 kHz
θ°
0°
12
12.5 kHz
0°
0°
0°
24
24
12
10 kHz
°
0
15
0°
180°
21
°
0
15
5 kHz
180°
21
0°
16 kHz
940788e
Fig.4.14 Typical directional characteristics of the microphone with Protection Grid DB 3420
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Dynamic Range
0°
0°
0
–5
– 10
– 15
– 20
– 25
– 20
90°
5
0
5
270°
–15
–5
– 10
–15
– 20
– 25
– 10
– 20
–5
– 15
0
– 10
5
°
–5
90°
60
0°
°
0
30
60
5
°
0°
270°
30
0°
0°
°
33
30
33
30
31.5 kHz
25 kHz
6.3 kHz
8 kHz
θ°
0°
0°
24
12
10 kHz
0°
12
0°
24
20 kHz
12.5 kHz
0°
15
0°
180°
21
15
180°
21
0°
5 kHz
0°
16 kHz
940790e
Fig.4.15 Typical directional characteristics of the microphone without protection grid
4.5
Dynamic Range
Definition
The dynamic range is the range between the upper limit (determined by distortion)
and the inherent noise floor. Both limits are influenced by the preamplifier. This
section gives values for the microphone with and without a preamplifier.
Inherent Noise
The microphone’s inherent noise is due to thermal movements of the diaphragm.
These vary proportionally with the square root of the absolute temperature (in °K).
The inherent noise increases with increasing temperature. With reference to 20 °C,
the inherent noise changes by + 0.5 dB at 55 °C and by – 0.5 dB at – 12 °C. The
maximum variation of this noise for different samples of Free-field 1/2" Microphone
Type 4190 is ± 1 dB.
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Dynamic Range
The preamplifier’s effect on the inherent noise of the combined microphone and
preamplifier depends on the sensitivity and capacitance of the microphone (for 1/2"
Microphone Preamplifier Type 2669, see Fig. 4.16 and Chapter 8).
Sound Pressure Level
re 20 µPa (dB)
20
L
L
15
A
A
L
10
5
A
Microphone
and
Preamplifier
Combination
0
–5
Preamplifier
Microphone
– 10
10
100
1k
10 k
Frequency (Hz)
20 k M
P
C
940718e
Fig.4.16 1/3-octave-band inherent noise spectra. The shaded bar graphs are the broad-band (20 Hz
to 20 kHz) noise levels and the white bar graphs the A-weighted noise levels of the microphone (M), 1/2" Microphone Preamplifier Type 2669 (P) and microphone and preamplifier
combination (C)
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Dynamic Range
Distortion
The distortion is determined mainly by the microphone but, at the highest operation levels, the preamplifier also contributes to the distortion (see Fig. 4.17).
Distortion (%)
10
C
M
2nd
Harmonic
1
C
M
3rd
Harmonic
0.1
0.01
125
135
145
SPL (dB)
155
940498e
Fig.4.17 Typical distortion characteristics of the microphone with
1/2" Microphone Preamplifier Type 2669 (C) and unloaded (M)
The distortion is dependent on the capacitance parallel to the microphone. It increases with increasing capacitance. The distortions given in Table 4.3 and Table
4.4 are valid for a parallel capacitance of 0.5 pF. The distortion is measured at
100 Hz but can be assumed to be valid up to approximately 5 kHz (that is, where
the diaphragm displacement is predominantly stiffness-controlled). Distortion measurement methods for higher frequencies are not available.
Maximum Sound Pressure Level
In general, the microphone should not be exposed to sound pressure levels which
produce voltages higher than the maximum input voltage specified for the connected preamplifier. After an overload, the preamplifier needs time to recover and, during this recovery period, you cannot measure validly. The maximum input voltage
for most Brüel & Kjær preamplifiers is ± 50 V (with a 130 V supply). This voltage is
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Equivalent Volume and Calibrator Load Volume
Lower Limit
1 Hz bandwidth
at 1 kHz (dB)
1
Upper Limit
/3-octave band
at 1 kHz (dB)
A-weighted (dB)
Linear 20 Hz to
20 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
–0.7
14.6
15.3
148
159
–24.3
Table 4.3 Dynamic range of the microphone
Lower Limit
1 Hz bandwidth
at 1 kHz (dB)
–23.6
1
Upper Limit
/3-octave band
at 1 kHz (dB)
A-weighted (dB)
Linear 20 Hz to
20 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
0.0
15.0
17.0
147
154
Table 4.4 Dynamic range of the microphone with 1/2" Microphone Preamplifier Type 2669
produced by a nominal Free-field 1/2" Microphone Type 4190 at a Peak level of
154 dB (re 20 µPa).
The microphone will maintain its charge up to a Peak level of 159 dB (re 20 µPa).
Above this level, the diaphragm and back plate short-circuit. If this occurs, the
microphone needs one or two minutes to recharge before it is ready to measure
validly. We recommend not to expose Free-field 1/2" Microphone Type 4190 to levels
higher than 159 dB (Peak).
4.6
Equivalent Volume and Calibrator Load Volume
Equivalent Volume
For some applications it is practical to express the acoustic impedance of the microphone diaphragm in terms of a complex equivalent volume. This makes it easier to
evaluate the effect of microphone loading on closed cavities or acoustic calibration
couplers.
The real and imaginary parts of the equivalent volume shown in Fig.4.18 are in
parallel. They are calculated from a simple R–L–C series model of the microphone
which gives the best overall approximation of the microphone’s diaphragm impedance.
The Models
The following equivalent models are valid at 101.325 kPa, 23 °C and 50%RH:
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Equivalent Volume and Calibrator Load Volume
Volume (mm3)
60
50
40
30
20
– V (Im)
10
V (Re)
0
– 10
100
1k
10k
Frequency (Hz)
100k
940949e
Fig.4.18 Typical equivalent volume (real and imaginary parts) based on mathematical model of
microphone
Model 1
C = 0.324 x 10-12 m5/N
L = 305kg/m4
R = 77 x 106 Ns/m5
where
C = acoustic diaphragm compliance
L = acoustic diaphragm mass
R = acoustic diaphragm damping resistance
Model 2
Vlf = 46 mm3
f0 = 16kHz
Q = 0.4
where
Vlf = low-frequency volume
f0 = diaphragm resonance frequency
Q = quality factor
Calibrator Load Volume
When the microphone with its protection grid is inserted into the coupler of a
calibrator, it will load the calibrator by a volume of 250 mm3 at 250 Hz.
Load volume correction to Pistonphone Type 4228 Calibration Level (with
Adaptor DP 0776): 0.00 dB
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Capacitance
4.7
Capacitance
The microphone’s impedance is determined by its polarized capacitance. In addition,
the preamplifier’s input resistance and capacitance load the microphone. This loading determines the electrical lower limiting frequency and the capacitive input attenuation. However, with modern preamplifiers, this loading is very small and is
included in the preamplifier gain, G (see section 4.2.2). Only in special cases with
high capacitive loading does the fall in capacitance with frequency have to be taken
into account.
Capacitance (pF)
20
250 V
18
16
200 V
150 V
14
28 V
12
10
100
1k
Hz
10k
Frequency (Hz)
100k
940601e
Fig.4.19 Variation of capacitance with polarization voltage and frequency
Typical capacitance (at 250 Hz): 16 pF.
The capacitance is individually calibrated and stated on the calibration chart.
4.8
Polarization Voltage
Generally, a microphone is operated at its nominal polarization voltage. For Freefield 1/2" Microphone Type 4190, this is 200 V. As this polarization voltage is positive, the output voltage is negative for a positive pressure applied to the diaphragm.
In special cases where there is a risk of preamplifer overload or there are long
cables to be driven, choose a lower voltage. This will cause a lower sensitivity (see
Fig.4.20) and a change in the frequency response (see Fig.4.21).
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Polarization Voltage
Response (dB)
5
0
–5
–10
–15
–20
–25
5
10
20
50
100
200
500
Po. Voltage (V)
940681e
Fig.4.20 Variation in sensitivity (at 250 Hz) as a function of polarization voltage, relative to the sensitivity with a polarization voltage of 200 V
Response (dB)
2.5
2
28 V
1
150 V
0
250 V
-1
-2
-2.5
100
1k
Hz
10k
100k
Frequency (Hz)
940606e
Fig.4.21 Effect of polarization voltage on frequency response. The curves show the difference from
the response with a polarization voltage of 200 V (normalised at 250 Hz)
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Leakage Resistance
4.9
Leakage Resistance
To maintain the correct polarization voltage on the microphone, the microphone’s
leakage resistance must be at least 1000 times greater than the supply resistance
of the polarization charge, even under the most severe environmental conditions.
This resistance which is generally placed in the preamplifier, is typically 109 to
1010 Ω. Brüel & Kjær microphones have a very high leakage resistance which is
greater than 5×1015 Ω at 90%RH and 23°C.
4.10 Stability
4.10.1 Mechanical Stability
The microphone’s design with respect to mechanical stability is improved compared
with traditional Brüel & Kjær microphones. The diaphragm clamping ring is less
sensitive to accidental force and the protection grid is significantly reinforced.
Therefore, the microphone can withstand mechanical shocks better than traditional
Brüel & Kjær microphones.
The sensitivity change of the microphone is less than 0.1 dB after a free fall of 1 m
onto a solid hardwood block (re IEC 68–2–32).
This improved mechanical stability makes Free-field 1/2" Microphone Type 4190
well-suited for surface mounting and for mounting in small couplers as no mechanical adaptor is required to protect the diaphragm clamping ring. The microphone can
be supported by the diaphragm clamping ring directly on the coupler’s surface. Any
force of less than 5 Newtons will cause a change in sensitivity of less than 0.005 dB.
This makes the microphone well-suited for fitting in small, plane wave couplers
used for reciprocity calibration and any other small coupler with a well-defined
volume.
4.10.2 High-temperature Stability
The diaphragm is made of a stainless steel alloy. The alloy has been carefully
selected and is very resistant to heat. This means that the diaphragm tension (and
therefore the sensitivity) remain the same, even after several hours’ operation at
high temperature.
The microphone has been tested at temperatures up to 300°C. Below 170°C, no
changes occur. At 170°C, the sensitivity can be permanently changed within the
first 10 hours by less than 0.025 dB. After this, the sensitivity can be permanently
changed within the next 100 hours by a similar value. At 300°C, the sensitivity can
be permanently changed within the first hour by + 0.4 dB. After this, the sensitivity
can be permanently changed within the next 10 hours by less than + 0.4 dB.
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Effect of Temperature
Note: Special adaptors (inserted between the microphone and preamplifier) must be
made for high-temperature applications in order to protect the preampifier from
heat conduction and radiation.
4.10.3 Long-term Stability
Over a period of time, the mechanical tension in the diaphragm will decrease due to
stretching within the foil. This mechanism, which, in principle, causes an increased
sensitivity, is, however, very weak for the microphone. Measurement of this mechanism is not possible at room temperature.
At present, no exact value can be given for the microphone’s long-term stability but
measured changes at high temperatures indicate that Free-field 1/2" Microphone
Type 4190 is more than 10 times more stable than traditional Brüel & Kjær microphones. This indicates typical changes of less than 1 dB in 5000 years.
4.11 Effect of Temperature
By careful selection of materials, optimization of the design and artificial ageing,
the effect of temperature has been made to be very low.
The microphone has been designed to operate at temperatures from –30 to 300°C.
When the microphone is subjected to temperatures above 200°C, it may be discoloured but its functionality will remain unaffected. See section 4.10.2 for permanent
changes in sensitivity at temperatures above 170°C.
4 − 22
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Effect of Temperature
The reversible changes are shown in Fig.4.22 as a change in sensitivity and in
Fig.4.23 to Fig.4.25 as changes in the frequency response normalized at 250 Hz.
Response (dB)
0.5
0.0
– 0.5
– 1.0
– 1.5
– 2.0
– 2.5
– 50
0
50
100
150
200
250
Temperature (°C)
300
940875e
Fig.4.22 Typical variation in sensitivity (at 250 Hz) as a function
of temperature, relative to the sensitivity at 20° C
Temperature Coefficient (250 Hz):
–0.007 dB/°C, typical (for the range –10 to +50°C)
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Effect of Temperature
Response (dB)
1.5
1.0
0.5
+ 50 °C
0.0
– 10 °C
– 0.5
– 1.0
– 1.5
500 Hz
1k
10 k
Frequency (Hz) 50 k
940774e
Fig.4.23 Typical variation in actuator response (normalized at
250 Hz) as a function of temperature, relative to the response at 20° C (see Fig.4.4) over the temperature range
defined by IEC 651
Response (dB)
4
300° C
3
200° C
2
100° C
1
0
–1
–2
500
1k
10 k
Frequency (Hz)
50 k
940596e
Fig.4.24 Typical variation in actuator response (normalized at
250 Hz) as a function of temperature, relative to the response at 20° C (see Fig.4.4)
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Effect of Ambient Pressure
The effect of temperature on the free-field response (see Fig.4.25) of the microphone
is the sum of the following effects:
●
the calculated effect of the change in the speed of sound due to temperature on
the 0°-incidence free-field correction
●
the measured change in the actuator response due to temperature (see Fig.4.23).
Response (dB)
1.5
1.0
0.5
– 10°C
0.0
50°C
– 0.5
– 1.0
– 1.5
500 Hz
1k
10 k
Frequency (Hz) 50 k
940808/1e
Fig.4.25 Typical variation in 0°-incidence free-field response (normalized at 250 Hz) as a function of temperature, relative
to the response at 20° C (see Fig.4.7) over the temperature
range defined by IEC 651
4.12 Effect of Ambient Pressure
The microphone’s sensitivity and frequency response are affected by variations in
the ambient pressure. This is due to changes in air stiffness in the cavity behind
the diaphragm, and changes in air mass in the small gap between the diaphragm
and the back plate. The effects are shown in Fig.4.26 to Fig.4.28.
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Effect of Ambient Pressure
The typical pressure coefficient at 250 Hz for Free-field 1/2" Microphone Type 4190
is –0.010 dB/kPa, well within the ± 0.03 dB/kPa limits required for Type 0 and Type
1 sound level meters by IEC 651.
Correction (dB)
3
2
– 40kPa
change
1
– 20kPa
change
– 10kPa
change
0
–1
500
1k
10k
Frequency (Hz)
50k
940763e
Fig.4.26 Typical variation in frequency response (normalized at
250 Hz) from that at 101.3 kPa as a function of change in
ambient pressure
Response (dB)
30
20
(d)
10
0
(c)
– 20
500
(b)
(a)
– 10
1k
10k
Frequency (Hz)
50k
940755e
Fig.4.27 Typical effect of ambient pressure on actuator response
(normalized at 250 Hz) (a) at 101.3 kPa (b) – 40 kPa
change (c) – 80 kPa change (d) at 2 kPa
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Effect of Humidity
Response (dB)
4
2
0
–2
–4
–6
1
10
100
Ambient Pressure (kPa)
1000
940759e
Fig.4.28 Typical variation in sensitivity at 250 Hz from that at 101.3 kPa as a function of ambient
pressure
4.13 Effect of Humidity
Due to the microphone’s high leakage resistance, humidity has, in general, no effect
on the microphone’s sensitivity or frequency response. The microphone has been
tested according to IEC 68–2–3 and the effects of humidty on the sensitivity at
250 Hz and the frequency response have been found to be less than 0.1 dB at up to
95% RH (non-condensing) and 40°C.
4.14 Effect of Vibration
The effect of vibration is determined mainly by the mass of the diaphragm and is at
its maximum for vibrations applied normal to the diaphragm. A vibration signal of
1 m/s2 RMS normal to the diaphragm typically produces an equivalent Sound Pressure Level of 62.5 dB for a microphone fitted with Protection Grid DB 3420.
4.15 Effect of a Magnetic Field
The effect of a magnetic field is determined by the vector field strength and is
normally at its maximum when the field direction is normal to the diaphragm. A
magnetic field strength of 80 A/m at 50 Hz (the test level recommended by IEC and
ANSI) normal to the diaphragm produces a typical equivalent Sound Pressure Level of 4 dB. Higher frequency components in the microphone output become dominant at field strengths greater than 500 to 1000 A/m.
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Electromagnetic Compatibility
4.16 Electromagnetic Compatibility
See Chapter 8.
4.17 Specifications Overview
OPEN-CIRCUIT SENSITIVITY (250 Hz)*:
–26 dB ±1.5 dB re 1 V/Pa, 50 mV/Pa*
CALIBRATOR LOAD VOLUME (250 Hz):
250 mm3
PRESSURE COEFFICIENT (250 Hz):
–0.010 dB/kPa, typical
POLARIZATION VOLTAGE:
External: 200 V
PISTONPHONE TYPE 4228 CORRECTION:
with DP 0776:
0.00 dB
INFLUENCE OF HUMIDITY:
<0.1 dB/ 100 %RH
FREQUENCY RESPONSE*:
0° incidence free-field response:
5 Hz to 10 kHz: ± 1 dB
3.15 Hz to 20 kHz: ±2 dB
In accordance with IEC 651, Type 0 and Type 1
LOWER LIMITING FREQUENCY (–3 dB):
1 Hz to 2 Hz (vent exposed to sound)
PRESSURE EQUALIZATION VENT:
Rear vented
DIAPHRAGM RESONANCE FREQUENCY:
14 kHz, typical (90° phase shift)
CAPACITANCE (POLARIZED)*:
16 pF, typical (at 250 Hz)
EQUIVALENT AIR VOLUME (101.3 kPa):
46 mm3
TYPICAL CARTRIDGE THERMAL NOISE:
14.6 dB (A) 15.3 dB (Lin.)
UPPER LIMIT OF DYNAMIC RANGE:
3% distortion:
>148 dB SPL
MAXIMUM SOUND PRESSURE LEVEL:
159 dB (peak)
OPERATING TEMPERATURE RANGE:
–30 to +150°C (–22 to 302°F)
can be used up to +300°C (572°F) but with a
permanent sensitivity change of typically + 0.4 dB
which stabilises after one hour
OPERATING HUMIDITY RANGE:
0 to 100 % RH (without condensation)
VIBRATION SENSITIVITY (<1000 Hz):
Typically 62.5 dB equivalent SPL for 1 m/s2 axial
acceleration
MAGNETIC FIELD SENSITIVITY:
Typically 4 dB SPL for 80 A/m, 50 Hz field
ESTIMATED LONG-TERM STABILITY:
>1 000 years/dB at 20°C
>1 00 hours/dB at 150°C
DIMENSIONS:
Diameter: 13.2 mm (0.52 in) (with grid)
12.7 mm (0.50 in) (without grid)
Height:
17.6 mm (0.68 in) (with grid)
16.3 mm (0.64 in) (without grid)
Thread for preamplifier mounting: 11.7 mm –
60 UNS
STORAGE TEMPERATURE:
–30 to + 70°C (–22 to 158°F)
* Individually calibrated
TEMPERATURE COEFFICIENT (250 Hz):
–0.007 dB/°C, typical (for the range –10 to
+50°C)
The data above are valid at 23°C, 101.3 kPa and
50%RH, unless otherwise specified.
4.18 Ordering Information
Preamplifier
Type 2669: 1/2" Microphone Preamplifier
Calibration Equipment
Type 4231: Sound Level Calibrator
Type 4226: Multifunction Acoustic Calibrator
Type 4228: Pistonphone
UA 0033: Electrostatic Actuator
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Ordering Information
Other Accessories
UA 0308: Dehumidifier
UA 0254: Set of 6 Windscreens (UA 0237) 90 mm (3.5 in)
UA 0469: Set of 6 Windscreens (UA 0459) 65 mm (2.6 in)
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Chapter 4 — Free-field 1/2" Microphone Type 4190
Ordering Information
4 − 30
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Chapter 5
Free-field 1/2 " Microphone Type 4191
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5− 1
Chapter 5 — Free-field 1/2" Microphone Type 4191
Introduction
5.1
Introduction
5.1.1
Description
Fig.5.1 Free-field 1/2" Microphone Type 4191 with Protection Grid DB 3421 (included)
Free-field 1/2" Microphone Type 4191 is an externally-polarized microphone for general sound measurements and for standardized noise measurements in accordance
with the requirements of IEC 651 Type 0 and Type 1. With its low inherent noise
and frequency range from 3.15 Hz to 40 kHz, it is very well suited for a wide range
of precision audio-frequency sound measurements and electro-acoustic measurements on loudspeakers and microphones.
The microphone requires a polarization voltage of 200 V, provided by the instrument
or analyzer powering the associated preamplifier.
This rugged microphone is built to ensure high stability under a variety of conditions. For example, the stainless steel alloy diaphragm withstands polluted industrial environments. The diaphragm clamping ring is firmly secured to ensure the
microphone’s reliability, even when the microphone is used without its protection
grid. When the microphone is used without its protection grid, it can be easily
flush-mounted or inserted into closed volumes as it can be supported by the diaphragm clamping ring, provided that a force of less than 5 Newtons is applied.
The microphone is supplied with individual calibration data on a calibration chart
and on a 31/2" data disk in a case. This case can also contain a 1/2" Microphone
Preamplifier Type 2669.
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Introduction
5.1.2
The Calibration Chart
Each microphone is supplied with an individual calibration chart (see Fig.5.2)
which gives the microphone’s open-circuit sensitivity, polarized capacitance and
free-field and actuator frequency responses.
B
K
7/6-'89
Free-field 1/2" Microphone
Type 4191
+5
Bruel & Kjær
Calibration Chart
dB
Serial No:
419111A
+1
0
–1
-37.9
12.7
Open-circuit Sensitivity*, S0:
Equivalent to:
Uncertainty, 95 % confidence level
Capacitance:
Valid At:
Temperature:
Ambient Static Pressure:
Relative Humidity:
Frequency:
Polarization Voltage, external:
dB re 1V/Pa
Dotted Curve Shows Typical Response
Free-field Response 0° Sound Incidence
mV/Pa
0.2
dB
18.2
pF
–5
23 °C
101.3 kPa
50 %
250 Hz
200 V
Actuator Response
– 10
Sensitivity Traceable To:
DPLA: Danish Primary Laboratory of Acoustics
NIST: National Institute of Standards and Technology, USA
– 15
0° Sound Incidence
IEC 1094-4: Type WS 2 F
Environmental Calibration Conditions:
100.1 kPa
25 °C
35 % RH
Procedure: 704217
Date: 21. Apr. 1994
Signature:
– 20
*K0 = – 26 – S0 Example: K0 = – 26 – (– 38) = + 12 dB
BC 0226 – 12
1
2
5
10
20
See the microphone handbook for further information
50
100
200
500
1k
2k
5k
20 k
10 k
Frequency Hz
40 k
940952e
Fig.5.2 Microphone calibration chart
Open-circuit Sensitivity
The stated open-circuit sensitivity is valid at the reference frequency (251.2 Hz* ) for
free-field, random-incidence and pressure-field conditions. The stated uncertainty is
the U95 value (the value valid for 95% confidence level).
Ambient Conditions
The ambient conditions are measured continuously during calibration at the factory.
The calibration results obtained at the measured Environmental Calibration Conditions are corrected to the reference ambient conditions stated under Valid At (23°C,
101.325 kPa and 50% RH).
Frequency Responses
Two frequency responses are shown on the calibration chart. Both are normalized
to 0 dB at the reference frequency (251.2 Hz*).
The upper curve on the calibration chart is the individual microphone’s open-circuit
0°-incidence free-field response. This response is the optimized response for Freefield 1/2" Microphone Type 4191.
*The exact reference frequency is 102.4 Hz (re ISO 266).
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Introduction
The lower curve on the calibration chart is the individual microphone’s electrostatic
actuator response measured with Electrostatic Actuator UA 0033. This response is
used to determine free-field responses at angles of incidence other than 0° and
responses in other types of sound field. The individual microphone’s electrostatic
actuator response is also available on the data disk.
The dotted part of the curve is the typical low-frequency response. Each microphone’s individual lower limiting frequency is measured to ensure that it is within
the specified tolerances (see Fig.5.3).
5.1.3
Data Disk
The 31/2" data disk supplied with each microphone supplements the calibration
chart. It contains individual calibration data and correction curves (see Table 5.1)
with a frequency resolution of 1/12-octave as comma-separated ASCII text files under the \DATA directory.
File Name
Content
Frequency Range
Sensitivity calibration
251.2 Hz
A#######.BKMa
Actuator response
200 Hz – 40 kHz
F#######.BKRb
Free-field response
1 Hz – 40 kHz
4191L.BKTc
Low-frequency response
1 Hz – 190 Hz
4191F.BKCd
Free-field corrections without protection grid
200 Hz – 40 kHz
4191FG.BKCd
Free-field corrections with protection grid
200 Hz – 40 kHz
4191R.BKCd
Random-incidence corrections without protection grid
200 Hz – 40 kHz
4191RG.BKCd
Random-incidence corrections with protection grid
200 Hz – 40 kHz
4191P.BKCd
Pressure-field corrections
200 Hz – 22 kHz
S#######.BKM
Table 5.1
a.
b.
c.
d.
a
Calibration data and corrections contained on the data disk. Note: ####### is the microphone’s serial number
Individual calibration data (measured).
Low-frequency response combined with actuator response and free-field corrections.
Typical response for Free-field 1/2" Microphone Type 4191.
Corrections for Free-field 1/2" Microphone Type 4191.
These text files can be viewed on Microsoft® Windows™ using the Brüel & Kjær
Microphone Viewer program (BK–MIC.EXE) supplied on the disk. They can also be
accessed by a suitable spreadsheet for further processing or printing.
Brüel & Kjær Microphone Viewer must be installed before use (see section 1.3.5).
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Sensitivity
5.1.4
Recommended Recalibration Interval
With normal handling of the microphone and any associated instrument,
Brüel & Kjær recommends that the microphone be recalibrated every 2 years.
Free-field 1/2" Microphone Type 4191 is very stable over this period (see section
5.10 to section 5.12). Improper handling is by far the most likely cause of change in
the microphone’s properties. Any damage which causes improper operation can
probably be detected using a sound level calibrator. In many cases, the damage can
be seen by carefully inspecting the protection grid and diaphragm.
5.2
Sensitivity
5.2.1
Open-circuit Sensitivity
The open-circuit sensitivity is defined as the sensitivity of the microphone when not
loaded by the input impedance of the connected preamplifier (the termination is
described in IEC 1094–2). The sensitivity is measured for the individual microphone
at 251.2 Hz and stated on the microphone’s calibration chart (see section 5.1.2) and
data disk (see section 5.1.3). The nominal sensitivity is shown in Table 5.2.
Nominal open-circuit sensitivity
mV/Pa
dB re 1 V/Pa
12.5
–38
Accepted Deviation
(dB)
± 1.5
Table 5.2 Nominal open-circuit sensitivity
5.2.2
Loaded Sensitivity
When loaded by a preamplifier, the sensitivity of the microphone is given by:
SC = SO + G
where
SC
SO
G
(5.1)
= overall sensitivity of microphone and preamplifier combination
= open-circuit sensitivity of microphone
= voltage gain of microphone and preamplifier combination (in dB)
With Microphone Preamplifier Type 2639: G = –0.1 dB
With 1/2" Microphone Preamplifier Type 2669: G = –0.2 dB
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Frequency Response
Example
Loaded sensitivity of typical microphone with 1/2" Microphone Preamplifier Type
2669:
SC = –38.3 + (–0.2) = –38.5 dB
5.2.3
K-factor
Some types of Brüel & Kjær instruments use the K-factor (correction factor) or the
KO-factor (open-circuit correction factor) for calibration.
K = – 26 – S C
(5.2)
K O = – 26 – S O
(5.3)
Example
Correction factor for typical microphone with 1/2" Microphone Preamplifier Type
2669:
K = –26 – (–38.5) = +12.5 dB
Open-circuit correction factor for typical microphone with 1/2" Microphone Preamplifier Type 2669:
KO = –26 – (–38.3) = +12.3 dB
5.3
Frequency Response
5.3.1
General
In acoustic measurements, there are three types of sound field:
●
Free field
●
Pressure field
●
Diffuse field
The microphone is optimized to have a flat frequency response in one of these
sound fields. This response is called the optimized response. A microphone’s response in a diffuse field is equivalent to its random-incidence response.
This section shows the microphone’s typical free-field, pressure-field and randomincidence responses together with the microphone’s typical actuator response obtained using Electrostatic Actuator UA 0033. The low-frequency response described
in section 5.3.4 is common for all types of response.
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Frequency Response
All frequency responses and correction curves are shown with a frequency resolution of 1/12-octave.
5.3.2
Optimized Response (0°-incidence Free-field Response)
Response (dB)
5
Tol.
Tol.
Tol.
Tol.
0
–5
– 10
1
10
Fig.5.3
100
1k
10 k
Frequency (Hz)
100 k
940897e
Typical free-field response of the microphone with Protection Grid DB 3421 and the microphone’s specified tolerances. The low-frequency response is valid when the vent is exposed to
the sound field
The frequency response of Free-field 1/2" Microphone Type 4191 meets the requirements of IEC 651 Type 0 and Type 1, and ANSI S1.12 Type M.
5.3.3
Actuator Response
The microphone’s frequency response is determined by adding corrections for the
type of sound field to its actuator response obtained using Electrostatic Actuator
UA 0033. This is a reproducible and practical method for calibrating a microphone’s
frequency response.
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Frequency Response
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940672e
Fig.5.4 Typical actuator response (magnitude) measured with Electrostatic Actuator UA 0033
Response (Degrees)
0
– 45
– 90
– 135
– 180
100
1k
10 k
Frequency (Hz)
100 k
940673e
Fig.5.5 Typical actuator response (phase) measured with Electrostatic Actuator UA 0033
If the polarization voltage is positive (as it is with Brüel & Kjær instruments), the
output voltage is negative for a positive pressure applied to the diaphragm.
5.3.4
Low-frequency Response
The low-frequency response (see Fig.5.3) is the typical response with the vent exposed to the sound field. If the vent is not exposed to the sound field, the sensitivity
increases from 0 dB at the reference frequency (251.2 Hz) to approximately 0.2 dB at
1Hz.
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Frequency Response
For applications where the vent is not exposed to the sound field, take care to
ensure proper static pressure equalization to prevent static displacement of the
diaphragm.
The microphone’s low-frequency response is common for all types of sound field.
The microphone’s lower limiting frequency (–3 dB) is between 1 and 2 Hz with the
vent exposed to the sound field. This is measured during production to ensure that
specifications are fulfilled.
5.3.5
Free-field Response
The microphone’s free-field correction curves are shown in Fig.5.6 and Fig.5.8.
These corrections are added to the microphone’s actuator response obtained using
Electrostatic Actuator UA 0033 in order to determine the free-field response at any
angle of incidence. The typical free-field response at 0° incidence with and without
the protection grid are shown in Fig.5.7 and Fig.5.9.
Correction (dB)
15
0°
12.5
10
30°
7.5
5
2.5
Random
0
150°
120°
– 2.5
90°
θ°
180°
60°
–5
– 7.5
– 10
500
1k
10k
Frequency (Hz)
50k
940800/1e
Fig.5.6
BE 1377 – 12
Free-field correction curves for the microphone with Protection Grid DB 3421
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Frequency Response
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940890e
Fig.5.7 Typical free-field response (0° incidence) for the microphone with Protection Grid DB 3421
Correction (dB)
15
12.5
10
7.5
0°
5
30°
2.5
0
150°
120°
– 2.5
90°
θ°
–5
60°
– 7.5
– 10
500
Random
180°
1k
10k
Frequency (Hz)
50k
940799/1e
Fig.5.8
5 − 10
Free-field correction curves for the microphone without
protection grid
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Frequency Response
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940891e
Fig.5.9 Typical free-field response (0° incidence) for the microphone without protection grid
5.3.6
Random-incidence Response
A microphone’s response in a diffuse sound field is equivalent to its random-incidence response. The microphone’s random-incidence correction curves are shown in
Fig.5.6 and Fig.5.8. These corrections are added to the microphone’s actuator response obtained using Electrostatic Actuator UA 0033 in order to determine the
random-incidence response. The typical random-incidence response with and without the protection grid are shown in Fig.5.10 and Fig.5.11.
The random-incidence corrections are calculated from the free-field corrections
measured in 5° steps according to Draft IEC 1183–1993.
Response (dB)
5
dB
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940940/1e
Fig.5.10 Typical random-incidence response for the microphone with Protection Grid DB 3421
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Frequency Response
Response (dB)
5
dB
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940941/1e
Fig.5.11 Typical random-incidence response for the microphone without protection grid
5.3.7
Pressure-field Response
The microphone’s pressure-field correction curve is shown in Fig.5.12. This correction is added to the microphone’s actuator response obtained using Electrostatic
Actuator UA 0033 in order to determine the pressure-field response. The typical
pressure-field response is shown in Fig.5.13.
In practice, the pressure-field response is often regarded as being equal to the
actuator response as the difference between them is small compared to the uncertainty related to many types of measurement.
Correction (dB)
4
3
2
1
0
–1
100
1k
10 k
Frequency (Hz)
100 k
940867e
Fig.5.12 Pressure-field correction for the microphone
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Directional Characteristics
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
100 k
Frequency (Hz)
940871e
Fig.5.13 Typical pressure-field response for the microphone
5.4
Directional Characteristics
Typical directional characteristics are given in Fig.5.14 and Fig.5.15. The characteristics are normalised relative to the 0° response.
0°
0°
30
°
0°
30
60
0°
°
0°
60
0°
°
33
30
33
30
°
40 kHz
90°
5
0
0
5
270°
–5
– 10
– 15
– 20
– 25
– 20
–5
– 10
–15
– 20
– 25
–15
– 20
– 10
– 15
–5
– 10
0
–5
5
0
90°
5
270°
31.5 kHz
6.3 kHz
25 kHz
8 kHz
20 kHz
θ°
0°
12
12.5 kHz
0°
24
0°
24
12
10 kHz
0°
0°
15
0°
180°
21
0°
180°
15
5 kHz
21
0°
16 kHz
940793e
Fig.5.14 Typical directional characteristics of the microphone with Protection Grid DB 3421
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Dynamic Range
0°
0°
0
–5
– 10
– 15
– 20
– 25
– 20
90°
5
0
5
270°
–15
–5
– 10
–15
– 20
– 25
– 10
– 20
–5
– 15
0
– 10
5
°
–5
90°
60
0°
°
0
30
60
5
°
0°
270°
30
0°
0°
°
33
30
33
30
40 kHz
31.5 kHz
6.3 kHz
25 kHz
0°
24
0°
θ°
10 kHz
12
8 kHz
0°
12
0°
24
20 kHz
12.5 kHz
0°
15
0°
180°
21
15
180°
21
0°
5 kHz
0°
16 kHz
940792e
Fig.5.15 Typical directional characteristics of the microphone without protection grid
5.5
Dynamic Range
Definition
The dynamic range is the range between the upper limit (determined by distortion)
and the inherent noise floor. Both limits are influenced by the preamplifier. This
section gives values for the microphone with and without a preamplifier.
Inherent Noise
The microphone’s inherent noise is due to thermal movements of the diaphragm.
These vary proportionally with the square root of the absolute temperature (in °K).
The inherent noise increases with increasing temperature. With reference to 20 °C,
the inherent noise changes by + 0.5 dB at 55 °C and by – 0.5 dB at – 12 °C. The
maximum variation of this noise for different samples of Free-field 1/2" Microphone
Type 4191 is ± 1 dB.
5 − 14
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Dynamic Range
The preamplifier’s effect on the inherent noise of the combined microphone and
preamplifier depends on the sensitivity and capacitance of the microphone (for 1/2"
Microphone Preamplifier Type 2669, see Fig. 5.16 and Chapter 8).
Sound Pressure Level
re 20 µPa (dB)
30
L
25
L
L
A
20
A
A
15
Microphone
and
Preamplifier
Combination
10
5
Microphone
0
10
100
Preamplifier
1k
10 k
Frequency (Hz)
40 k
M
P
C
940719e
Fig.5.16 1/3 -octave-band inherent noise spectrum. The shaded bar graphs are the broad-band
(20 Hz to 40 kHz) noise levels and the white bar graphs the A-weighted noise levels of the
microphone (M), 1/2" Microphone Preamplifier Type 2669 (P) and microphone and preamplifier combination (C)
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Dynamic Range
Distortion
The distortion is determined mainly by the microphone but, at the highest operation levels, the preamplifier also contributes to the distortion (see Fig. 5.17).
Distortion (%)
10
C
M
2nd
Harmonic
1
C
M
3rd
Harmonic
0.1
0.01
135
145
SPL (dB) 155
165
940499e
Fig.5.17 Typical distorion characteristics of the microphone with
1/2" Microphone Preamplifier Type 2669 (C) and unloaded (M)
The distortion is dependent on the capacitance parallel to the microphone. It increases with increasing capacitance. The distortions given in Table 5.3 and Table
5.4 are valid for a parallel capacitance of 0.5 pF. The distortion is measured at
100 Hz but can be assumed to be valid up to approximately 5 kHz (that is, where
the diaphragm displacement is predominantly stiffness-controlled). Distortion measurement methods for higher frequencies are not available.
Maximum Sound Pressure Level
In general, the microphone should not be exposed to sound pressure levels which
produce voltages higher than the maximum input voltage specified for the connected preamplifier. After an overload, the preamplifier needs time to recover and, during this recovery period, you cannot measure validly. The maximum input voltage
for most Brüel & Kjær preamplifiers is ± 50 V (with a 130 V supply). This voltage is
5 − 16
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Equivalent Volume and Calibrator Load Volume
Lower Limit
1 Hz bandwidth
at 1 kHz (dB)
1
Upper Limit
/3-octave at
1 kHz (dB)
A-weighted (dB)
Linear 20 Hz to
40 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
4.6
20.0
21.4
162
171
–19.0
Table 5.3 Dynamic range of the microphone
Lower Limit
1 Hz bandwidth
at 1 kHz (dB)
–16.5
1
Upper Limit
/3-octave at
1 kHz (dB)
A-weighted (dB)
Linear 20 Hz to
40 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
7.1
21.4
25.8
161
166
Table 5.4 Dynamic range of the microphone with 1/2" Microphone Preamplifier Type 2669
produced by a nominal Free-field 1/2" Microphone Type 4191 at a Peak level of
166 dB (re 20 µPa).
The microphone will maintain its charge up to a Peak level of 171 dB (re 20 µPa).
Above this level, the diaphragm and back plate short-circuit. If this occurs, the
microphone needs one or two minutes to recharge before it is ready to measure
validly. We recommend not to expose Free-field 1/2" Microphone Type 4191 to levels
higher than 171 dB (Peak).
5.6
Equivalent Volume and Calibrator Load Volume
Equivalent Volume
For some applications it is practical to express the acoustic impedance of the microphone diaphragm in terms of a complex equivalent volume. This makes it easier to
evaluate the effect of microphone loading on closed cavities or acoustic calibration
couplers.
The real and imaginary parts of the equivalent volume shown in Fig.5.18 are in
parallel. They are calculated from a simple R–L–C series model of the microphone
which gives the best overall approximation of the microphone’s diaphragm impedance.
The Models
The following equivalent models are valid at 101.325 kPa, 23 °C and 50%RH:
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Equivalent Volume and Calibrator Load Volume
Volume (mm3)
12
10
8
6
4
– V (Im)
2
V (Re)
0
–2
100
1k
10k
Frequency (Hz)
100k
940947e
Fig.5.18 Typical equivalent volume (real and imaginary parts) based on mathematical model of
microphone
Model 1
C = 0.082 x 10-12 m5/N
L = 253kg/m4
R = 278 x 106 Ns/m5
where
C = acoustic diaphragm compliance
L = acoustic diaphragm mass
R = acoustic diaphragm damping resistance
Model 2
Vlf = 11.6 mm3
f0 = 35kHz
Q = 0.2
where
Vlf = low-frequency volume
f0 = diaphragm resonance frequency
Q = quality factor
Calibrator Load Volume
When the microphone with its protection grid is inserted into the coupler of a
calibrator, it will load the calibrator by a volume of 190 mm3 at 250 Hz.
Load volume correction to Pistonphone Type 4228 Calibration Level (with
Adaptor DP 0776): +0.02 dB
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Capacitance
5.7
Capacitance
The microphone’s impedance is determined by its polarized capacitance. In addition,
the preamplifier’s input resistance and capacitance load the microphone. This loading determines the electrical lower limiting frequency and the capacitive input attenuation. However, with modern preamplifiers, this loading is very small and is
included in the preamplifier gain, G (see section 5.2.2). Only in special cases with
high capacitive loading does the fall in capacitance with frequency have to be taken
into account.
Capacitance (pF)
20
250 V
18
200 V
150 V
28 V
16
14
12
10
100
1k
Hz
10k
Frequency (Hz)
100k
940604e
Fig.5.19 Variation of capacitance with polarization voltage and frequency
Typical capacitance (at 250 Hz): 18 pF.
The capacitance is individually calibrated and stated on the calibration chart.
5.8
Polarization Voltage
Generally, a microphone is operated at its nominal polarization voltage. For Freefield 1/2" Microphone Type 4191, this is 200 V. As this polarization voltage is positive, the output voltage is negative for a positive pressure applied to the diaphragm.
In special cases where there is a risk of preamplifer overload or there are long
cables to be driven, choose a lower voltage. This will cause a lower sensitivity (see
Fig.5.20) and a change in the frequency response (see Fig.5.21).
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Polarization Voltage
Response (dB)
5
0
–5
–10
–15
–20
–25
5
10
20
50
100
200
500
Po. Voltage (V)
940682e
Fig.5.20 Variation in sensitivity (at 250 Hz) as a function of polarization voltage, relative to the sensitivity with a polarization voltage of 200 V
Response (dB)
2.5
2
1
28 V
150 V
0
250 V
-1
-2
-2.5
100
1k
Hz
10k
100k
Frequency (Hz)
940607e
Fig.5.21 Effect of polarization voltage on frequency response. The curves show the difference from
the response with a polarization voltage of 200 V (normalised at 250 Hz)
5 − 20
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Leakage Resistance
5.9
Leakage Resistance
To maintain the correct polarization voltage on the microphone, the microphone’s
leakage resistance must be at least 1000 times greater than the supply resistance
of the polarization charge, even under the most severe environmental conditions.
This resistance which is generally placed in the preamplifier, is typically 109 to
1010 Ω. Brüel & Kjær microphones have a very high leakage resistance which is
greater than 5×1015 Ω at 90%RH and 23°C.
5.10 Stability
5.10.1 Mechanical Stability
The microphone’s design with respect to mechanical stability is improved compared
with traditional Brüel & Kjær microphones. The diaphragm clamping ring is less
sensitive to accidental force and the protection grid is significantly reinforced.
Therefore, the microphone can withstand mechanical shocks better than traditional
Brüel & Kjær microphones.
The sensitivity change of the microphone is less than 0.1 dB after a free fall of 1 m
onto a solid hardwood block (re IEC 68–2–32).
This improved mechanical stability makes Free-field 1/2" Microphone Type 4191
well-suited for surface mounting and for mounting in small couplers as no mechanical adaptor is required to protect the diaphragm clamping ring. The microphone can
be supported by the diaphragm clamping ring directly on the coupler’s surface. Any
force of less than 5 Newtons will cause a change in sensitivity of less than 0.005 dB.
This makes the microphone well-suited for fitting in small, plane wave couplers
used for reciprocity calibration and any other small coupler with a well-defined
volume.
5.10.2 High-temperature Stability
The diaphragm is made of a stainless steel alloy. The alloy has been carefully
selected and is very resistant to heat. This means that the diaphragm tension (and
therefore the sensitivity) remain the same, even after several hours’ operation at
high temperature.
The microphone has been tested at temperatures up to 300°C. Below 170°C, no
changes occur. At 170°C, the sensitivity can be permanently changed within the
first 10 hours by less than 0.025 dB. After this, the sensitivity can be permanently
changed within the next 100 hours by a similar value. At 300°C, the sensitivity can
be permanently changed within the first hour by + 0.4 dB. After this, the sensitivity
can be permanently changed within the next 10 hours by less than + 0.4 dB.
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Effect of Temperature
Note: Special adaptors (inserted between the microphone and preamplifier) must be
made for high-temperature applications in order to protect the preampifier from
heat conduction and radiation.
5.10.3 Long-term Stability
Over a period of time, the mechanical tension in the diaphragm will decrease due to
stretching within the foil. This mechanism, which, in principle, causes an increased
sensitivity, is, however, very weak for the microphone. Measurement of this mechanism is not possible at room temperature.
At present, no exact value can be given for the microphone’s long-term stability but
measured changes at high temperatures indicate that Free-field 1/2" Microphone
Type 4191 is more than 10 times more stable than traditional Brüel & Kjær microphones. This indicates typical changes of less than 1 dB in 5000 years.
5.11 Effect of Temperature
By careful selection of materials, optimization of the design and artificial ageing,
the effect of temperature has been made to be very low.
The microphone has been designed to operate at temperatures from – 30 to 300°C.
When the microphone is subjected to temperatures above 200°C, it may be discoloured but its functionality will remain unaffected. See section 5.10.2 for permanent
changes in sensitivity at temperatures above 170°C.
5 − 22
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Effect of Temperature
The reversible changes are shown in Fig.5.22 as a change in sensitivity and in
Fig.5.23 to Fig.5.25 as changes in the frequency response normalized at 250 Hz.
Response (dB)
0.5
0.0
– 0.5
– 1.0
– 1.5
– 2.0
– 2.5
– 50
0
50
100
150
200
250
Temperature (°C)
300
940876e
Fig.5.22 Typical variation in sensitivity (at 250 Hz) as a function
of temperature, relative to the sensitivity at 20° C
Temperature Coefficient (250 Hz):
–0.002 dB/°C, typical (for the range –10 to +50°C)
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Effect of Temperature
Response (dB)
1.5
1.0
0.5
– 10 °C
0.0
+ 50 °C
– 0.5
– 1.0
– 1.5
500 Hz
1k
10 k
Frequency (Hz) 50 k
940775e
Fig.5.23 Typical variation in actuator response (normalized at
250 Hz) as a function of temperature, relative to the response at 20° C (see Fig.5.4) over the temperature range
defined by IEC 651
Response (dB)
4
300° C
3
200° C
2
1
100° C
0
–1
–2
500
1k
10 k
Frequency (Hz)
50 k
940598e
Fig.5.24 Typical variation in actuator response (normalized at
250 Hz) as a function of temperature, relative to the response at 20° C (see Fig.5.4)
5 − 24
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Effect of Ambient Pressure
The effect of temperature on the free-field response (see Fig.5.25) of the microphone
is the sum of the following effects:
●
the calculated effect of the change in the speed of sound due to temperature on
the 0°-incidence free-field correction
●
the measured change in the actuator response due to temperature (see Fig.5.23).
Response (dB)
1.5
1.0
0.5
– 10°C
0.0
50°C
– 0.5
– 1.0
– 1.5
500 Hz
1k
10 k
Frequency (Hz) 50 k
940809/1e
Fig.5.25 Typical variation in 0°-incidence free-field response with
Protection Grid DB 3421 (normalized at 250 Hz) as a
function of temperature, relative to the response at 20° C
(see Fig.5.7) over the temperature range defined by
IEC 651
5.12 Effect of Ambient Pressure
The microphone’s sensitivity and frequency response are affected by variations in
the ambient pressure. This is due to changes in air stiffness in the cavity behind
the diaphragm, and changes in air mass in the small gap between the diaphragm
and the back plate. The effects are shown in Fig.5.26 to Fig.5.28.
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Effect of Ambient Pressure
The typical pressure coefficient at 250 Hz for Free-field 1/2" Microphone Type 4191
is –0.007 dB/kPa, well within the ±0.03 dB/kPa limits required for Type 0 and Type
1 sound level meters by IEC 651.
Correction (dB)
3
– 40kPa
change
2
– 20kPa
change
1
– 10kPa
change
0
–1
500
1k
10k
Frequency (Hz)
50k
940764e
Fig.5.26 Typical variation in frequency response (normalized at
250 Hz) from that at 101.3 kPa as a function of change in
ambient pressure
Response (dB)
30
(d)
20
10
(c)
0
(b)
– 10
– 20
500
(a)
1k
10k
Frequency (Hz)
50k
940756e
Fig.5.27 Typical effect of ambient pressure on actuator response
(a) at 101.3 kPa (b) – 40 kPa change (c) – 80 kPa change
(d) at 2 kPa
5 − 26
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Effect of Humidity
Response (dB)
4
2
0
–2
–4
–6
1
10
100
Ambient Pressure (kPa)
1000
940760e
Fig.5.28 Typical variation in sensitivity at 250 Hz from that at 101.3 kPa as a function of ambient
pressure
5.13 Effect of Humidity
Due to the microphone’s high leakage resistance, humidity has, in general, no effect
on the microphone’s sensitivity or frequency response. The microphone has been
tested according to IEC 68–2–3 and the effects of humidty on the sensitivity at
250 Hz and the frequency response have been found to be less than 0.1 dB at up to
95% RH (non-condensing) and 40°C.
5.14 Effect of Vibration
The effect of vibration is determined mainly by the mass of the diaphragm and is at
its maximum for vibrations applied normal to the diaphragm. A vibration signal of
1 m/s2 RMS normal to the diaphragm typically produces an equivalent Sound Pressure Level of 65.5 dB for a microphone fitted with Protection Grid DB 3421.
5.15 Effect of Magnetic Field
The effect of a magnetic field is determined by the vector field strength and is
normally at its maximum when the field direction is normal to the diaphragm. A
magnetic field strength of 80 A/m at 50 Hz (the test level recommended by IEC and
ANSI) normal to the diaphragm produces a typical equivalent Sound Pressure Level of 16 dB. Higher frequency components in the microphone output become dominant at field strengths greater than 500 to 1000 A/m.
BE 1377 – 12
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Electromagnetic Compatibility
5.16 Electromagnetic Compatibility
See Chapter 8.
5.17 Specifications Overview
OPEN-CIRCUIT SENSITIVITY (250 Hz)*:
–38 dB ±1.5 dB re 1 V/Pa, 12.5 mV/Pa*
CALIBRATOR LOAD VOLUME (250 Hz):
190 mm3
PRESSURE COEFFICIENT (250 Hz):
–0.007 dB/kPa, typical
POLARIZATION VOLTAGE:
External: 200 V
PISTONPHONE TYPE 4228 CORRECTION:
with DP 0776:
+0.02 dB
INFLUENCE OF HUMIDITY:
<0.1 dB/100 %RH
FREQUENCY RESPONSE*:
0° incidence free-field response:
5 Hz to 16 kHz ± 1 dB
3.15 Hz to 40 kHz ±2 dB
In accordance with IEC 651, Type 0, Type 1 and
ANSI S1.12, Type M
LOWER LIMITING FREQUENCY (–3 dB):
1 Hz to 2 Hz (vent exposed to sound)
PRESSURE EQUALIZATION VENT:
Side vented
DIAPHRAGM RESONANCE FREQUENCY:
34 kHz, typical (90° phase shift)
CAPACITANCE (POLARIZED)*:
18 pF, typical (at 250 Hz)
EQUIVALENT AIR VOLUME (101.3 kPa):
11.6 mm3
* Individually calibrated
TYPICAL CARTRIDGE THERMAL NOISE:
20.0 dB (A) 21.4 dB (Lin.)
UPPER LIMIT OF DYNAMIC RANGE:
3% distortion:
>162 dB SPL
MAXIMUM SOUND PRESSURE LEVEL:
171 dB (peak)
OPERATING TEMPERATURE RANGE:
–30 to +150°C (–22 to 302°F)
can be used up to +300°C (572°F) but with a
permanent sensitivity change of typically + 0.4 dB
which stabilises after one hour
OPERATING HUMIDITY RANGE:
0 to 100 % RH (without condensation)
VIBRATION SENSITIVITY (<1000 Hz):
Typically 65.5 dB equivalent SPL for 1 m/s2 axial
acceleration
MAGNETIC FIELD SENSITIVITY:
Typically 16 dB SPL for 80 A/m, 50 Hz field
ESTIMATED LONG-TERM STABILITY:
>1 000 years/dB at 20°C
>1 00 hours/dB at 150°C
DIMENSIONS:
Diameter: 13.2 mm (0.52 in) (with grid)
12.7 mm (0.50 in) (without grid)
Height:
13.5 mm (0.54 in) (with grid)
12.6 mm (0.50 in) (without grid)
Thread for preamplifier mounting: 11.7 mm –
60 UNS
STORAGE TEMPERATURE:
–30 to + 70°C (–22 to 158°F)
TEMPERATURE COEFFICIENT (250 Hz):
–0.002 dB/°C, typical (for the range –10 to
+50°C)
The data above are valid at 23°C, 101.3 kPa and
50%RH, unless otherwise specified.
5.18 Ordering Information
Preamplifier
Type 2669: 1/2" Microphone Preamplifier
Calibration Equipment
Type 4231: Sound Level Calibrator
Type 4226: Multifunction Acoustic Calibrator
Type 4228: Pistonphone
UA 0033: Electrostatic Actuator
5 − 28
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Ordering Information
Other Accessories
UA 0254: Set of 6 Windscreens (UA 0237) 90 mm (3.5 in)
UA 0469: Set of 6 Windscreens (UA 0459) 65 mm (2.6 in)
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Chapter 5 — Free-field 1/2" Microphone Type 4191
Ordering Information
5 − 30
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Chapter 6
Pressure-field 1/2 " Microphone
Type 4192
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6− 1
Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Introduction
6.1
Introduction
6.1.1
Description
Fig.6.1 Pressure-field 1/2" Microphone Type 4192 with Protection Grid DB 3421 (included)
Pressure-field 1/2" Microphone Type 4192 is an externally-polarized 1/2" pressurefield microphone for sound measurements requiring random-incidence response in
accordance with the requirements of ANSI S 1.4 Type 1 or for coupler measurements, for example, in connection with telephone and hearing aid testing. Furthermore, it also satisfies the requirements of ANSI S 1.12 Type M. With its low
inherent noise and frequency range from 3.15 Hz to 20 kHz, it is very well suited for
a wide range of precision audio-frequency sound measurements.
The microphone requires a polarization voltage of 200 V, provided by the instrument
or analyzer powering the associated preamplifier.
This rugged microphone is built to ensure high stability under a variety of conditions. For example, the stainless steel alloy diaphragm withstands polluted industrial environments. The diaphragm clamping ring is firmly secured to ensure the
microphone’s reliability, even when the microphone is used without its protection
grid. When the microphone is used without its protection grid, it can be easily
flush-mounted or inserted into closed volumes as it can be supported by the diaphragm clamping ring, provided that a force of less than 5 Newtons is applied.
The microphone is supplied with individual calibration data on a calibration chart
and on a 31/2" data disk in a case. This case can also contain a 1/2" Microphone
Preamplifier Type 2669.
6− 2
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Introduction
6.1.2
The Calibration Chart
Each microphone is supplied with an individual calibration chart (see Fig.6.2)
which gives the microphone’s open-circuit sensitivity, polarized capacitance and
pressure-field and random-incidence frequency responses.
kurve skal slutte her
Pressure-field
1/2" Microphone Type 4192
+5
Bruel & Kjær
Calibration Chart
dB
Serial No:
419205A
B
K
7/6-'89
-38.6
11.8
Open-circuit Sensitivity*, S0:
Equivalent to:
Uncertainty, 95 % confidence level
Random-incidence Response
+1
0
–1
dB re 1V/Pa
mV/Pa
Pressure-field Response
0.2 dB
18.4 pF
Capacitance:
Valid At:
Temperature:
Ambient Static Pressure:
Relative Humidity:
Frequency:
Polarization Voltage, external:
Dotted Curve Shows Typical Response
23
101.3
50
250
200
–5
°C
kPa
%
Hz
V
– 10
Sensitivity Traceable To:
DPLA: Danish Primary Laboratory of Acoustics
NIST: National Institute of Standards and Technology, USA
– 15
IEC 1094-4: Type WS 2 P
Environmental Calibration Conditions:
100.1 kPa
25 °C
35 % RH
Procedure: 704218
Date: 21. Apr. 1994
Signature:
– 20
*K0 = – 26 – S0 Example: K0 = – 26 – (– 38) = + 12 dB
BC 0227 – 12
1
2
5
10
20
See the microphone handbook for further information
50
100
200
500
1k
2k
5k
20 k
10 k
Frequency Hz
40 k
940158/1e
940953/1e
Fig.6.2 Microphone calibration chart
Open-circuit Sensitivity
The stated open-circuit sensitivity is valid at the reference frequency (251.2 Hz* ) for
free-field, random-incidence and pressure-field conditions. The stated uncertainty is
the U95 value (the value valid for 95% confidence level).
Ambient Conditions
The ambient conditions are measured continuously during calibration at the factory.
The calibration results obtained at the measured Environmental Calibration Conditions are corrected to the reference ambient conditions stated under Valid At (23°C,
101.325 kPa and 50% RH).
Frequency Responses
Two frequency responses are shown on the calibration chart. Both are normalized
to 0 dB at the reference frequency (251.2 Hz*).
*The exact reference frequency is 102.4 Hz (re ISO 266).
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Introduction
The lower curve on the calibration chart is the individual microphone’s open-circuit
pressure-field response. This response is the optimized response for the Pressurefield 1/2" Microphone Type 4192.
The upper curve on the calibration chart is the random-incidence response.
Both curves are determined by adding the relevant correction curve to the individual actuator response measured with Electrostatic Actuator UA 0033. The individual
microphone’s electrostatic actuator response is also available on the data disk.
The dotted part of the curve is the typical low-frequency response. Each microphone’s individual lower limiting frequency is measured to ensure that it is within
the specified tolerances (see Fig.6.3).
6.1.3
Data Disk
The 31/2" data disk supplied with each microphone supplements the calibration
chart. It contains individual calibration data and correction curves (see Table 6.1)
with a frequency resolution of 1/12-octave as comma-separated ASCII text files under the \DATA directory.
File Name
Content
Frequency Range
S#######.BKMa
Sensitivity calibration
251.2 Hz
A#######.BKMa
Actuator response
200 Hz – 22 kHz
P#######.BKRb
Pressure-field response
1 Hz – 22 kHz
4192L.BKTc
Low-frequency response
1 Hz – 190 Hz
4192F.BKCd
Free-field corrections without protection grid
200 Hz – 22 kHz
4192FG.BKCd
Free-field corrections with protection grid
200 Hz – 22 kHz
4192R.BKCd
Random-incidence corrections without protection grid
200 Hz – 22 kHz
4192RG.BKCd
Random-incidence corrections with protection grid
200 Hz – 22 kHz
4192P.BKCd
Pressure-field corrections
200 Hz – 22 kHz
Table 6.1
a.
b.
c.
d.
Calibration data and corrections contained on the data disk. Note: ####### is the microphone’s serial number
Individual calibration data (measured).
Low-frequency response combined with actuator response and free-field corrections.
Typical response for Pressure-field 1/2" Microphone Type 4192.
Corrections for Pressure-field 1/2" Microphone Type 4192.
These text files can be viewed on Microsoft® Windows™ using the Brüel & Kjær
Microphone Viewer program (BK–MIC.EXE) supplied on the disk. They can also be
accessed by a suitable spreadsheet for further processing or printing.
6− 4
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Sensitivity
Brüel & Kjær Microphone Viewer must be installed before use (see section 1.3.5).
6.1.4
Recommended Recalibration Interval
With normal handling of the microphone and any associated instrument,
Brüel & Kjær recommends that the microphone be recalibrated every 2 years.
Pressure-field 1/2" Microphone Type 4192 is very stable over this period (see section
6.10 to section 6.12). Improper handling is by far the most likely cause of change in
the microphone’s properties. Any damage which causes improper operation can
probably be detected using a sound level calibrator. In many cases, the damage can
be seen by carefully inspecting the protection grid and diaphragm.
6.2
Sensitivity
6.2.1
Open-circuit Sensitivity
The open-circuit sensitivity is defined as the sensitivity of the microphone when not
loaded by the input impedance of the connected preamplifier (the termination is
described in IEC 1094–2). The sensitivity is measured for the individual microphone
at 251.2 Hz and stated on the microphone’s calibration chart (see section 6.1.2) and
data disk (see section 6.1.3). The nominal sensitivity is shown in Table 6.2.
Nominal open-circuit sensitivity
mV/Pa
dB re 1 V/Pa
12.5
– 38
Accepted Deviation
(dB)
± 1.5
Table 6.2 Nominal open-circuit sensitivity
6.2.2
Loaded Sensitivity
When loaded by a preamplifier, the sensitivity of the microphone is given by:
SC = SO + G
where
SC
SO
G
(6.1)
= overall sensitivity of microphone and preamplifier combination
= open-circuit sensitivity of microphone
= voltage gain of microphone and preamplifier combination (in dB)
With Microphone Preamplifier Type 2639: G = – 0.1 dB
With 1/2" Microphone Preamplifier Type 2669: G = – 0.2 dB
BE 1378 – 12
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Frequency Response
Example
Loaded sensitivity of typical microphone with 1/2" Microphone Preamplifier Type
2669:
SC = –38.3 + (–0.2) = –38.5 dB
6.2.3
K-factor
Some types of Brüel & Kjær instruments use the K-factor (correction factor) or the
KO-factor (open-circuit correction factor) for calibration.
K = – 26 – S C
(6.2)
K O = – 26 – S O
(6.3)
Example
Correction factor for typical microphone with 1/2" Microphone Preamplifier Type
2669:
K = –26 – (–38.5) = +12.5 dB
Open-circuit correction factor for typical microphone with 1/2" Microphone Preamplifier Type 2669:
KO = –26 – (–38.3) = +12.3 dB
6.3
Frequency Response
6.3.1
General
In acoustic measurements, there are three types of sound field:
●
Free field
●
Pressure field
●
Diffuse field
The microphone is optimized to have a flat frequency response in one of these
sound fields. This response is called the optimized response. A microphone’s response in a diffuse field is equivalent to its random-incidence response.
This section shows the microphone’s typical free-field, pressure-field and randomincidence responses together with the microphone’s typical actuator response obtained using Electrostatic Actuator UA 0033. The low-frequency response described
in section 6.3.4 is common for all types of response.
6− 6
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Frequency Response
All frequency responses and correction curves are shown with a frequency resolution of 1/12-octave.
6.3.2
Optimized Response (Pressure-field Response)
Response (dB)
5
Tol.
Tol.
0
Tol.
Tol.
–5
– 10
1
10
Fig.6.3
100
1k
10 k
Frequency (Hz)
100 k
940863/1e
Typical pressure-field response of the microphone with Protection Grid DB 3421 and the
microphone’s specified tolerances. The low-frequency response is valid when the vent is exposed to the sound field
The frequency response of Pressure-field 1/2" Microphone Type 4192 meets the requirements of ANSI S1.4 -1983, Type 1 and ANSI S1.12, Type M.
6.3.3
Actuator Response
The microphone’s frequency response is determined by adding corrections for the
type of sound field to its actuator response obtained using Electrostatic Actuator
UA 0033. This is a reproducible and practical method for calibrating a microphone’s
frequency response.
BE 1378 – 12
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6− 7
Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Frequency Response
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940674/1e
Fig.6.4 Typical actuator response measured with Electrostatic Actuator UA 0033
Response (Degrees)
0
– 45
– 90
– 135
– 180
100
1k
10 k
Frequency (Hz)
100 k
940675/1e
Fig.6.5 Typical actuator phase response measured with Electrostatic Actuator UA 0033
If the polarization voltage is positive (as it is with Brüel & Kjær instruments), the
output voltage is negative for a positive pressure applied to the diaphragm.
6.3.4
Low-frequency Response
The low-frequency response (see Fig.6.3) is the typical response with the vent exposed to the sound field. If the vent is not exposed to the sound field, the sensitivity
increases from 0 dB at the reference frequency (251.2 Hz) to approximately 0.2 dB at
1Hz.
6− 8
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Frequency Response
For applications where the vent is not exposed to the sound field, take care to
ensure proper static pressure equalization to prevent static displacement of the
diaphragm.
The microphone’s low-frequency response is common for all types of sound field.
The microphone’s lower limiting frequency (–3 dB) is between 1 and 2 Hz with the
vent exposed to the sound field. This is measured during production to ensure that
specifications are fulfilled.
6.3.5
Free-field Response
The microphone’s free-field correction curves are shown in Fig.6.6 and Fig.6.8.
These corrections are added to the microphone’s actuator response obtained using
Electrostatic Actuator UA 0033 in order to determine the free-field response at any
angle of incidence. The typical free-field response at 0° incidence with and without
the protection grid are shown in Fig.6.7 and Fig.6.9.
Correction (dB)
15
12.5
0°
10
30°
7.5
5
60°
Random
2.5
90°
180°
150°
0
120°
– 2.5
θ°
–5
– 7.5
– 10
500
1k
10k
Frequency (Hz)
50k
940798/1e
Fig.6.6
BE 1378 – 12
Free-field correction curves for the microphone with Protection Grid DB 3421
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Frequency Response
Response (dB)
15
10
5
0
–5
– 10
100
1k
10 k
Frequency (Hz)
100 k
940892/1e
Fig.6.7 Typical free-field response (0° incidence) for the microphone with Protection Grid DB 3421
15
dB
12.5
10
0°
7.5
30°
5
60°
Random
2.5
0
150°
120°
90°
180°
– 2.5
θ°
–5
– 7.5
– 10
500
1k
10k
Frequency (Hz)
50k
940797/1e
Fig.6.8
6 − 10
Free-field correction curves for the microphone without
protection grid
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Frequency Response
Response (dB)
15
10
5
0
–5
– 10
100
1k
10 k
Frequency (Hz)
100 k
940893/1e
Fig.6.9 Typical free-field response (0° incidence) for the microphone without protection grid
6.3.6
Random-incidence Response
A microphone’s response in a diffuse sound field is equivalent to its random-incidence response. The microphone’s random-incidence correction curves are shown in
Fig.6.6 and Fig.6.8. These corrections are added to the microphone’s actuator response obtained using Electrostatic Actuator UA 0033 in order to determine the
random-incidence response. The typical random-incidence response with and without the protection grid are shown in Fig.6.10 and Fig.6.11.
The random-incidence corrections are calculated from the free-field corrections
measured in 5° steps according to Draft IEC 1183–1993.
Response (dB)
5
dB
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940942/1e
Fig.6.10 Typical random-incidence response for the microphone with Protection Grid DB 3421
BE 1378 – 12
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Frequency Response
Response (dB)
5
dB
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940943/1e
Fig.6.11 Typical random-incidence response for the microphone without protection grid
6.3.7
Pressure-field Response
The microphone’s pressure-field correction curve is shown in Fig.6.12. This correction is added to the microphone’s actuator response obtained using Electrostatic
Actuator UA 0033 in order to determine the pressure-field response. The typical
pressure-field response is shown in Fig.6.13.
In practice, the pressure-field response is often regarded as being equal to the
actuator response as the difference between them is small compared to the uncertainty related to many types of measurement.
Correction (dB)
4
3
2
1
0
–1
100
1k
10 k
Frequency (Hz)
100 k
940868e
Fig.6.12 Pressure-field correction for the microphone
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Directional Characteristics
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
100 k
Frequency (Hz)
940872/1e
Fig.6.13 Typical pressure-field response for the microphone
6.4
Directional Characteristics
Typical directional characteristics are given in Fig.6.14 and Fig.6.15. The characteristics are normalised relative to the 0° response.
0°
0°
0
–5
– 10
90°
0
5
–5
– 10
–15
– 20
6.3 kHz
– 15
– 20
– 25
– 20
5
270°
–15
– 25
– 10
– 20
–5
– 15
0
– 10
5
–5
90°
°
60
0
0°
°
5
30
60
0°
270°
30
°
0°
33
30
°
0°
33
30
25 kHz
8 kHz
0°
0°
0°
12
12.5 kHz
20 kHz
θ°
24
12
10 kHz
0°
24
0°
15
0°
180°
21
0°
15
5 kHz
180°
21
0°
16 kHz
940852/1e
Fig.6.14 Typical directional characteristics of the microphone with Protection Grid DB 3421
BE 1378 – 12
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Dynamic Range
0°
0°
–5
– 10
– 15
– 20
– 25
– 20
0
–15
90°
5
0
5
270°
– 10
–5
– 10
–15
– 20
– 25
–5
– 20
0
– 15
5
– 10
90°
°
60
–5
0°
°
0
30
60
5
°
0°
270°
30
0°
0°
°
33
30
33
30
25 kHz
6.3 kHz
20 kHz
8 kHz
θ°
0°
0°
0°
0°
24
24
12
10 kHz
12
12.5 kHz
0°
15
0°
180°
21
15
180°
21
0°
5 kHz
0°
16 kHz
940853/1e
Fig.6.15 Typical directional characteristics of the microphone without protection grid
6.5
Dynamic Range
Definition
The dynamic range is the range between the upper limit (determined by distortion)
and the inherent noise floor. Both limits are influenced by the preamplifier. This
section gives values for the microphone with and without a preamplifier.
Inherent Noise
The microphone’s inherent noise is due to thermal movements of the diaphragm.
These vary proportionally with the square root of the absolute temperature (in °K).
The inherent noise increases with increasing temperature. With reference to 20 °C,
the inherent noise changes by + 0.5 dB at 55 °C and by – 0.5 dB at – 12 °C. The
maximum variation of this noise for different samples of Pressure-field 1/2" Microphone Type 4192 is ± 1 dB.
6 − 14
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Dynamic Range
The preamplifier’s effect on the inherent noise of the combined microphone and
preamplifier depends on the sensitivity and capacitance of the microphone (for 1/2"
Microphone Preamplifier Type 2669, see Fig. 6.16 and Chapter 8).
Sound Pressure Level
re 20 µPa (dB)
30
L
25
L
L
20
A
A
A
15
Microphone
and
Preamplifier
Combination
10
5
Preamplifier
Microphone
0
10
100
1k
10 k
Frequency (Hz)
20 k
M
P
C
940720e
Fig.6.16 1/3-octave-band inherent noise spectrum. The shaded bar graphs are the broad-band
(20 Hz to 20 kHz) noise levels and the white bar graphs the A-weighted noise levels of the
microphone (M), 1/2" Microphone Preamplifier Type 2669 (P) and microphone and preamplifier combination (C)
BE 1378 – 12
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Dynamic Range
Distortion
The distortion is determined mainly by the microphone but, at the highest operation levels, the preamplifier also contributes to the distortion (see Fig. 6.17).
Distortion (%)
10
C
M
2nd
Harmonic
1
C
M
3rd
Harmonic
0.1
0.01
135
145
SPL (dB) 155
165
940499e
Fig.6.17 Typical distortion characteristics of the microphone with
1/2 " Microphone Preamplifier Type 2669 (C) and unloaded (M)
The distortion is dependent on the capacitance parallel to the microphone. It increases with increasing capacitance. The distortions given in Table 6.3 and Table
6.4 are valid for a parallel capacitance of 0.5 pF. The distortion is measured at
100 Hz but can be assumed to be valid up to approximately 5 kHz (that is, where
the diaphragm displacement is predominantly stiffness-controlled). Distortion measurement methods for higher frequencies are not available.
Maximum Sound Pressure Level
In general, the microphone should not be exposed to sound pressure levels which
produce voltages higher than the maximum input voltage specified for the connected preamplifier. After an overload, the preamplifier needs time to recover and, during this recovery period, you cannot measure validly. The maximum input voltage
for most Brüel & Kjær preamplifiers is ± 50 V (with a 130 V supply). This voltage is
6 − 16
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Equivalent Volume and Calibrator Load Volume
Lower Limit
1 Hz bandwidth
at 1 kHz (dB)
1
Upper Limit
/3-octave band
at 1 kHz (dB)
A-weighted (dB)
Linear 20 Hz to
20 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
1.2
19.0
21.3
162
171
–22.4
Table 6.3 Dynamic range of the microphone
Lower Limit
1 Hz bandwidth
at 1 kHz (dB)
–18.2
1
Upper Limit
/3-octave band
at 1 kHz (dB)
A-weighted (dB)
Linear 20 Hz to
20 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
5.4
20.7
25.4
161
166
Table 6.4 Dynamic range of the microphone with 1/2 " Microphone Preamplifier Type 2669
produced by a nominal Pressure-field 1/2" Microphone Type 4192 at a Peak level of
166 dB (re 20 µPa).
The microphone will maintain its charge up to a Peak level of 171 dB (re 20 µPa).
Above this level, the diaphragm and back plate short-circuit. If this occurs, the
microphone needs one or two minutes to recharge before it is ready to measure
validly. We recommend not to expose Pressure-field 1/2" Microphone Type 4192 to
levels higher than 171 dB (Peak).
6.6
Equivalent Volume and Calibrator Load Volume
Equivalent Volume
For some applications it is practical to express the acoustic impedance of the microphone diaphragm in terms of a complex equivalent volume. This makes it easier to
evaluate the effect of microphone loading on closed cavities or acoustic calibration
couplers.
The real and imaginary parts of the equivalent volume shown in Fig.6.18 are in
parallel. They are calculated from a simple R–L–C series model of the microphone
which gives the best overall approximation of the microphone’s diaphragm impedance.
The Models
The following equivalent models are valid at 101.325 kPa, 23 °C and 50%RH:
BE 1378 – 12
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Equivalent Volume and Calibrator Load Volume
Volume (mm3)
12
10
– V (Im)
8
6
4
2
V (Re)
0
–2
100
1k
10k
Frequency (Hz)
100k
940948e
Fig.6.18 Typical equivalent volume (real and imaginary parts) based on mathematical model of
microphone
Model 1
C = 0.062 x 10-12 m5/N
L = 710kg/m4
R = 119 x 106 Ns/m5
where
C = acoustic diaphragm compliance
L = acoustic diaphragm mass
R = acoustic diaphragm damping resistance
Model 2
Vlf = 8.8 mm3
f0 = 24kHz
Q = 0.9
where
Vlf = low-frequency volume
f0 = diaphragm resonance frequency
Q = quality factor
Calibrator Load Volume
When the microphone with its protection grid is inserted into the coupler of a
calibrator, it will load the calibrator by a volume of 190 mm3 at 250 Hz.
Load volume correction to Pistonphone Type 4228 Calibration Level (with
Adaptor DP 0776): +0.02 dB
6 − 18
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Capacitance
6.7
Capacitance
The microphone’s impedance is determined by its polarized capacitance. In addition,
the preamplifier’s input resistance and capacitance load the microphone. This loading determines the electrical lower limiting frequency and the capacitive input attenuation. However, with modern preamplifiers, this loading is very small and is
included in the preamplifier gain, G (see section 6.2.2). Only in special cases with
high capacitive loading does the fall in capacitance with frequency have to be taken
into account.
Capacitance (pF)
20
250 V
18
200 V
150 V
28 V
16
14
12
10
100
1k
Hz
10k
Frequency (Hz)
100k
940605e
Fig.6.19 Variation of capacitance with polarization voltage and frequency
Typical capacitance (at 250 Hz): 18 pF.
The capacitance is individually calibrated and stated on the calibration chart.
6.8
Polarization Voltage
Generally, a microphone is operated at its nominal polarization voltage. For Pressure-field 1/2" Microphone Type 4192, this is 200 V. As this polarization voltage is
positive, the output voltage is negative for a positive pressure applied to the diaphragm.
In special cases where there is a risk of preamplifer overload or there are long
cables to be driven, choose a lower voltage. This will cause a lower sensitivity (see
Fig.6.20) and a change in the frequency response (see Fig.6.21).
BE 1378 – 12
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Polarization Voltage
Response (dB)
5
0
–5
–10
–15
–20
–25
5
10
20
50
100
200
500
Po. Voltage (V)
940683e
Fig.6.20 Variation in sensitivity (at 250 Hz) as a function of polarization voltage, relative to the sensitivity with a polarization voltage of 200 V
Response (dB)
2.5
2
1
28 V
150 V
0
250 V
-1
-2
-2.5
100
1k
Hz
10k
100k
Frequency (Hz)
940608e
Fig.6.21 Effect of polarization voltage on frequency response. The curves show the difference from
the response with a polarization voltage of 200 V (normalised at 250 Hz)
6 − 20
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Leakage Resistance
6.9
Leakage Resistance
To maintain the correct polarization voltage on the microphone, the microphone’s
leakage resistance must be at least 1000 times greater than the supply resistance
of the polarization charge, even under the most severe environmental conditions.
This resistance which is generally placed in the preamplifier, is typically 109 to
1010 Ω. Brüel & Kjær microphones have a very high leakage resistance which is
greater than 5 × 1015 Ω at 90%RH and 23°C.
6.10 Stability
6.10.1 Mechanical Stability
The microphone’s design with respect to mechanical stability is improved compared
with traditional Brüel & Kjær microphones. The diaphragm clamping ring is less
sensitive to accidental force and the protection grid is significantly reinforced.
Therefore, the microphone can withstand mechanical shocks better than traditional
Brüel & Kjær microphones.
The sensitivity change of the microphone is less than 0.1 dB after a free fall of 1 m
onto a solid hardwood block (re IEC 68–2–32).
This improved mechanical stability makes Pressure-field 1/2" Microphone Type 4192
well-suited for surface mounting and for mounting in small couplers as no mechanical adaptor is required to protect the diaphragm clamping ring. The microphone can
be supported by the diaphragm clamping ring directly on the coupler’s surface. Any
force of less than 5 Newtons will cause a change in sensitivity of less than 0.005 dB.
This makes the microphone well-suited for fitting in small, plane wave couplers
used for reciprocity calibration and any other small coupler with a well-defined
volume.
6.10.2 High-temperature Stability
The diaphragm is made of a stainless steel alloy. The alloy has been carefully
selected and is very resistant to heat. This means that the diaphragm tension (and
therefore the sensitivity) remain the same, even after several hours’ operation at
high temperature.
The microphone has been tested at temperatures up to 300°C. Below 170°C, no
changes occur. At 170°C, the sensitivity can be permanently changed within the
first 10 hours by less than 0.025 dB. After this, the sensitivity can be permanently
changed within the next 100 hours by a similar value. At 300°C, the sensitivity can
be permanently changed within the first hour by + 0.4 dB. After this, the sensitivity
can be permanently changed within the next 10 hours by less than + 0.4 dB.
BE 1378 – 12
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6 − 21
Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Effect of Temperature
Note: Special adaptors (inserted between the microphone and preamplifier) must be
made for high-temperature applications in order to protect the preampifier from
heat conduction and radiation.
6.10.3 Long-term Stability
Over a period of time, the mechanical tension in the diaphragm will decrease due to
stretching within the foil. This mechanism, which, in principle, causes an increased
sensitivity, is, however, very weak for the microphone. Measurement of this mechanism is not possible at room temperature.
At present, no exact value can be given for the microphone’s long-term stability but
measured changes at high temperatures indicate that Pressure-field 1/2" Microphone Type 4192 is more than 10 times more stable than traditional Brüel & Kjær
microphones. This indicates typical changes of less than 1 dB in 5000 years.
6.11 Effect of Temperature
By careful selection of materials, optimization of the design and artificial ageing,
the effect of temperature has been made to be very low.
The microphone has been designed to operate at temperatures from – 30 to 300°C.
When the microphone is subjected to temperatures above 200°C, it may be discoloured but its functionality will remain unaffected. See section 6.10.2 for permanent
changes in sensitivity at temperatures above 170°C.
6 − 22
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Effect of Temperature
The reversible changes are shown in Fig.6.22 as a change in sensitivity and in
Fig.6.23 to Fig.6.25 as changes in the frequency response normalized at 250 Hz.
Response (dB)
0.5
0.0
– 0.5
– 1.0
– 1.5
– 2.0
– 2.5
– 50
0
50
100
150
200
250
Temperature (°C)
300
940876e
Fig.6.22 Typical variation in sensitivity (at 250 Hz) as a function
of temperature, relative to the sensitivity at 20° C
Temperature Coefficient (250 Hz):
–0.002 dB/°C, typical (for the range –10 to +50°C)
BE 1378 – 12
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Effect of Temperature
Response (dB)
1.5
1.0
0.5
– 10 °C
0.0
+ 50 °C
– 0.5
– 1.0
– 1.5
500 Hz
1k
10 k
Frequency (Hz) 50 k
940776e
Fig.6.23 Typical variation in actuator response (normalized at
250 Hz) as a function of temperature, relative to the response at 20° C (see Fig.6.4) over the temperature range
defined by IEC 651
Response (dB)
4
3
2
1
300° C
200° C
100° C
0
–1
–2
500
1k
10 k
Frequency (Hz)
50 k
940600e
Fig.6.24 Typical variation in actuator response (normalized at
250 Hz) as a function of temperature, relative to the response at 20° C (see Fig.6.4)
6 − 24
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Effect of Ambient Pressure
The effect of temperature on the free-field response (see Fig.6.25) of the microphone
is the sum of the following effects:
●
the calculated effect of the change in the speed of sound due to temperature on
the 0°-incidence free-field correction
●
the measured change in the actuator response due to temperature (see Fig.6.23).
Response (dB)
1.5
1.0
– 10°C
0.5
0.0
– 0.5
50°C
– 1.0
– 1.5
500 Hz
1k
10 k
Frequency (Hz) 50 k
940810/1e
Fig.6.25 Typical variation in 0°-incidence free-field response with
Protection Grid DB 3421 (normalized at 250 Hz) as a
function of temperature, relative to the response at 20° C
(see Fig.6.7) over the temperature range defined by
IEC 651
6.12 Effect of Ambient Pressure
The microphone’s sensitivity and frequency response are affected by variations in
the ambient pressure. This is due to changes in air stiffness in the cavity behind
the diaphragm, and changes in air mass in the small gap between the diaphragm
and the back plate. The effects are shown in Fig.6.26 to Fig.6.28.
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Effect of Ambient Pressure
The typical pressure coefficient at 250 Hz for Pressure-field 1/2" Microphone Type
4192 is –0.005 dB/kPa.
Correction (dB)
3
–40kPa
change
2
–20kPa
change
1
–10kPa
change
0
–1
500
1k
10k
Frequency (Hz)
50k
940765e
Fig.6.26 Typical variation in frequency response (normalized at
250 Hz) from that at 101.3 kPa as a function of change in
ambient pressure
Response (dB)
30
(d)
20
10
(c)
0
(a)
(b)
– 10
– 20
500
1k
10k
Frequency (Hz)
50k
940757e
Fig.6.27 Typical effect of ambient pressure on actuator response
(a) at 101.3 kPa (b) – 40 kPa change (c) – 80 kPa change
(d) at 2 kPa
6 − 26
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Effect of Humidity
Response (dB)
4
2
0
–2
–4
–6
1
10
100
Ambient Pressure (kPa)
1000
940761e
Fig.6.28 Typical variation in sensitivity at 250 Hz from that at 101.3 kPa as a function of ambient
pressure
6.13 Effect of Humidity
Due to the microphone’s high leakage resistance, humidity has, in general, no effect
on the microphone’s sensitivity or frequency response. The microphone has been
tested according to IEC 68–2–3 and the effects of humidty on the sensitivity at
250 Hz and the frequency response have been found to be less than 0.1 dB at up to
95% RH (non-condensing) and 40°C.
6.14 Effect of Vibration
The effect of vibration is determined mainly by the mass of the diaphragm and is at
its maximum for vibrations applied normal to the diaphragm. A vibration signal of
1 m/s2 RMS normal to the diaphragm typically produces an equivalent Sound Pressure Level of 65.5 dB for a microphone fitted with Protection Grid DB 3421.
6.15 Effect of Magnetic Field
The effect of a magnetic field is determined by the vector field strength and is
normally at its maximum when the field direction is normal to the diaphragm. A
magnetic field strength of 80 A/m at 50 Hz (the test level recommended by IEC and
ANSI) normal to the diaphragm produces a typical equivalent Sound Pressure Level of 16 dB. Higher frequency components in the microphone output become dominant at field strengths greater than 500 to 1000 A/m.
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Electromagnetic Compatibility
6.16 Electromagnetic Compatibility
See Chapter 8.
6.17 Specifications Overview
OPEN-CIRCUIT SENSITIVITY (250 Hz)*:
–38 dB ±1.5 dB re 1 V/Pa, 12.5 mV/Pa*
CALIBRATOR LOAD VOLUME (250 Hz):
190 mm3
PRESSURE COEFFICIENT (250 Hz):
–0.005 dB/kPa, typical
POLARIZATION VOLTAGE:
External: 200 V
PISTONPHONE TYPE 4228 CORRECTION:
with DP 0776:
+0.02 dB
INFLUENCE OF HUMIDITY:
<0.1 dB/100%RH
FREQUENCY RESPONSE*:
Pressure-field response:
5 Hz to 12.5 kHz: ±1 dB
3.15 Hz to 20 kHz: ±2 dB
In accordance with ANSI S1.4 -1983, Type 1
and ANSI S1.12, Type M
LOWER LIMITING FREQUENCY (–3 dB):
1 Hz to 2 Hz (vent exposed to sound)
PRESSURE EQUALIZATION VENT:
Side vented
DIAPHRAGM RESONANCE FREQUENCY:
23 kHz, typical (90° phase shift)
CAPACITANCE (POLARIZED)*:
18 pF, typical (at 250 Hz)
EQUIVALENT AIR VOLUME (101.3 kPa):
8.8 mm3
* Individually calibrated
TYPICAL CARTRIDGE THERMAL NOISE:
19.0 dB (A) 21.3 dB (Lin.)
UPPER LIMIT OF DYNAMIC RANGE:
3% distortion:
>162 dB SPL
MAXIMUM SOUND PRESSURE LEVEL:
171 dB (peak)
OPERATING TEMPERATURE RANGE:
–30 to +150°C (–22 to 302°F)
can be used up to +300°C (572°F) but with a
permanent sensitivity change of typically + 0.4 dB
which stabilises after one hour
OPERATING HUMIDITY RANGE:
0 to 100 % RH (without condensation)
VIBRATION SENSITIVITY (<1000 Hz):
Typically 65.5 dB equivalent SPL for 1 m/s2 axial
acceleration
MAGNETIC FIELD SENSITIVITY:
Typically 16 dB SPL for 80 A/m, 50 Hz field
ESTIMATED LONG-TERM STABILITY:
>1 000 years/dB at 20°C
>1 00 hours/dB at 150°C
DIMENSIONS:
Diameter: 13.2 mm (0.52 in) (with grid)
12.7 mm (0.50 in) (without grid)
Height:
13.5 mm (0.54 in) (with grid)
12.6 mm (0.50 in) (without grid)
Thread for preamplifier mounting: 11.7 mm –
60 UNS
STORAGE TEMPERATURE:
–30 to + 70°C (–22 to 158°F)
TEMPERATURE COEFFICIENT (250 Hz):
–0.002 dB/°C, typical (for the range –10 to
+50°C)
The data above are valid at 23°C, 101.3 kPa and
50%RH, unless otherwise specified.
6.18 Ordering Information
Preamplifier
Type 2669: 1/2" Microphone Preamplifier
Calibration Equipment
Type 4231: Sound Level Calibrator
Type 4226: Multifunction Acoustic Calibrator
Type 4228: Pistonphone
UA 0033: Electrostatic Actuator
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Ordering Information
Other Accessories
UA 0254: Set of 6 Windscreens (UA 0237) 90 mm (3.5 in)
UA 0469: Set of 6 Windscreens (UA 0459) 65 mm (2.6 in)
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Chapter 6 — Pressure-field 1/2" Microphone Type 4192
Ordering Information
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Chapter 7
Low-frequency Pressure-field
1/2 " Microphone Type 4193
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Introduction
7.1
Introduction
7.1.1
Description
Fig.7.1
Low-frequency Pressure-field 1/2" Microphone Type 4193 with Protection Grid DB 3421
and Adaptor UC 0211 (included)
Low-frequency Pressure-field 1/2" Microphone Type 4193 is an externally-polarized
1/2" pressure-field microphone. With its low inherent noise and frequency range
extending all the way from 70 mHz to 20 kHz, it is very well suited for measuring
infrasound, for example in ships engine rooms, in helicopters and in wind-buffeted
buildings. Furthermore, it satisfies the requirements of ANSI S 1.4 Type 1 and
ANSI S 1.12 Type M.
This microphone is supplied with a special Low-frequency Adaptor UC 0211 which,
because of the extra capacitance it introduces, has the effect of reducing the lower
cut-off frequency of the preamplifier — in the case of 1/2" Microphone Preamplifier
Type 2669, down to 0.1 Hz.
The microphone requires a polarization voltage of 200 V, provided by the instrument
or analyzer powering the associated preamplifier.
This rugged microphone is built to ensure high stability under a variety of conditions. For example, the stainless steel alloy diaphragm withstands polluted industrial environments. The diaphragm clamping ring is firmly secured to ensure the
microphone’s reliability, even when the microphone is used without its protection
grid. When the microphone is used without its protection grid, it can be easily
7− 2
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Introduction
flush-mounted or inserted into closed volumes as it can be supported by the diaphragm clamping ring, provided that a force of less than 5 Newtons is applied.
The microphone is supplied with individual calibration data on a calibration chart
and on a 31/2" data disk in a case. This case can also contain a 1/2" Microphone
Preamplifier Type 2669.
7.1.2
The Calibration Chart
Each microphone is supplied with an individual calibration chart (see Fig.7.2)
which gives the microphone’s open-circuit sensitivity, polarized capacitance, cut-off
frequency and pressure-field and random-incidence frequency responses. The data is
valid for a microphone without Adaptor UC 0211 fitted.
Low-frequency Pressure-field
1/2" Microphone Type 4193
+5
Bruel & Kjær
Calibration Chart
dB
Serial No:
4193000
B
K
7/6-'89
-38.0
12.6
Open-circuit Sensitivity*, S0:
Equivalent to:
Uncertainty, 95 % confidence level
Random-incidence Response
+1
0
–1
dB re 1V/Pa
mV/Pa
Cut-off Frequency (– 3 dB)
Pressure-field Response
0.2 dB
22 mHz
18.4 pF
Capacitance:
Valid At:
Temperature:
Ambient Static Pressure:
Relative Humidity:
Frequency:
Polarization Voltage, external:
Dotted Curve Shows Typical Response
23
101.3
50
250
200
–5
°C
kPa
%
Hz
V
– 10
Sensitivity Traceable To:
DPLA: Danish Primary Laboratory of Acoustics
NIST: National Institute of Standards and Technology, USA
– 15
IEC 1094-4: Type WS 2 P
Environmental Calibration Conditions:
100.1 kPa
25 °C
35 % RH
Procedure: 704219
Date: 21. Apr. 1994
Signature:
– 20
*K0 = – 26 – S0 Example: K0 = – 26 – (– 38) = + 12 dB
BC 0228 – 12
1
2
5
10
20
See the microphone handbook for further information
50
100
200
500
1k
2k
5k
20 k
10 k
Frequency Hz
40 k
940954/1e
Fig.7.2 Microphone calibration chart
Open-circuit Sensitivity
The stated open-circuit sensitivity is valid at the reference frequency (251.2 Hz* ) for
free-field, random-incidence and pressure-field conditions. The stated uncertainty is
the U95 value (the value valid for 95% confidence level).
Ambient Conditions
The ambient conditions are measured continuously during calibration at the factory.
The calibration results obtained at the measured Environmental Calibration Conditions are corrected to the reference ambient conditions stated under Valid At (23°C,
101.325 kPa and 50% RH).
*The exact reference frequency is 102.4 Hz (re ISO 266).
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Introduction
Frequency Responses
Two frequency responses are shown on the calibration chart. Both are normalized
to 0 dB at the reference frequency (251.2 Hz*).
The lower curve on the calibration chart is the individual microphone’s open-circuit
pressure-field response. This response is the optimized response for Low-frequency
Pressure-field 1/2" Microphone Type 4193.
The upper curve on the calibration chart is the random-incidence response.
Both curves are determined by adding the relevant correction curve to the individual actuator response measured with Electrostatic Actuator UA 0033. The individual
microphone’s electrostatic actuator response is also available on the data disk.
The dotted part of the curve is the typical low-frequency response. Each microphone’s individual lower limiting frequency is measured to ensure that it is within
the specified tolerances (see Fig.7.3).
7.1.3
Data Disk
File Name
Content
Frequency Range
S#######.BKMa
Sensitivity calibration
251.2 Hz
A#######.BKMa
Actuator response
200 Hz – 22 kHz
P#######.BKRb
Pressure-field response
1 Hz – 22 kHz
4193L.BKTc
Low-frequency response
1 Hz – 190 Hz
4193F.BKCd
Free-field corrections without protection grid
200 Hz – 22 kHz
4193FG.BKCd
Free-field corrections with protection grid
200 Hz – 22 kHz
4193R.BKCd
Random-incidence corrections without protection grid
200 Hz – 22 kHz
4193RG.BKCd
Random-incidence corrections with protection grid
200 Hz – 22 kHz
4193P.BKCd
Pressure-field corrections
200 Hz – 22 kHz
Table 7.1
a.
b.
c.
d.
Calibration data and corrections contained on the data disk. Note: ####### is the microphone’s serial number
Individual calibration data (measured).
Low-frequency response combined with actuator response and free-field corrections.
Typical response for Low-frequency Pressure-field 1/2" Microphone Type 4193.
Corrections for Low-frequency Pressure-field 1/2" Microphone Type 4193.
The 31/2" data disk supplied with each microphone supplements the calibration
chart. It contains individual calibration data and correction curves (see Table 7.1)
with a frequency resolution of 1/12-octave as comma-separated ASCII text files under the \DATA directory.
7− 4
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Sensitivity
These text files can be viewed on Microsoft® Windows™ using the Brüel & Kjær
Microphone Viewer program (BK–MIC.EXE) supplied on the disk. They can also be
accessed by a suitable spreadsheet for further processing or printing.
Brüel & Kjær Microphone Viewer must be installed before use (see section 1.3.5).
7.1.4
Adaptor UC 0211
Adaptor UC 0211 is for use of Low-frequency Pressure-field 1/2" Microphone Type
4193 with microphone preamplifers Types 2669 and 2639. The adaptor lowers the
electrical lower-limiting frequency (the –3 dB point) of the microphone/preamplifer
combination to 0.1 Hz (see section 7.3.2 and section 7.3.4).
The adaptor’s capacitance is 100 pF and it increases the preamplifer’s input capacitance.
In addition to extending the microphone/preamplifer combination’s frequency range,
the adaptor also:
7.1.5
●
Lowers the sensitivity (see section 7.2)
●
Increases the inherent noise (see Table 7.4)
●
Reduces the 3% distrotion limit (see Table 7.4)
●
Slightly changes the frequency response due to varying input capacitance with
frequency (see Fig.7.20 and section 7.3.1)
Recommended Recalibration Interval
With normal handling of the microphone and any associated instrument,
Brüel & Kjær recommends that the microphone be recalibrated every 2 years.
Low-frequency Pressure-field 1/2" Microphone Type 4193 is very stable over this
period (see section 7.10 to section 7.12). Improper handling is by far the most likely
cause of change in the microphone’s properties. Any damage which causes improper
operation can probably be detected using a sound level calibrator. In many cases,
the damage can be seen by carefully inspecting the protection grid and diaphragm.
7.2
Sensitivity
7.2.1
Open-circuit Sensitivity
The open-circuit sensitivity is defined as the sensitivity of the microphone when not
loaded by the input impedance of the connected preamplifier (the termination is
described in IEC 1094–2). The sensitivity is measured for the individual microphone
at 251.2 Hz and stated on the microphone’s calibration chart (see section 7.1.2) and
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Sensitivity
data disk (see section 7.1.3). The nominal sensitivity for a microphone without
Adaptor UC 0211 fitted is shown in Table 7.2.
Nominal open-circuit sensitivity
mV/Pa
dB re 1 V/Pa
12.5
– 38
Accepted Deviation
(dB)
± 1.5
Table 7.2 Nominal open-circuit sensitivity
7.2.2
Loaded Sensitivity
When loaded by a preamplifier, the sensitivity of the microphone is given by:
SC = SO + G
where
SC
SO
G
(7.1)
= overall sensitivity of microphone and preamplifier combination
= open-circuit sensitivity of microphone
= voltage gain of microphone and preamplifier combination (in dB)
With Microphone Preamplifier Type 2639: G = – 0.1 dB
With 1/2" Microphone Preamplifier Type 2669: G = – 0.2 dB
With 1/2" Microphone Preamplifier Type 2669 and Adaptor UC 0211: G = – 16.5 dB
(± 1 dB)
Example
Loaded sensitivity of typical microphone with 1/2" Microphone Preamplifier Type
2669:
SC = – 38.3 + (– 0.2) = – 38.5 dB
Loaded sensitivity of typical microphone with 1/2" Microphone Preamplifier Type
2669 and Adaptor UC 0211:
SC = – 38.3 + (– 16.5) = – 54.8 dB
7.2.3
K-factor
Some types of Brüel & Kjær instruments use the K-factor (correction factor) or the
KO-factor (open-circuit correction factor) for calibration.
7− 6
K = – 26 – S C
(7.2)
K O = – 26 – S O
(7.3)
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Frequency Response
Example
Correction factor for typical microphone with 1/2" Microphone Preamplifier Type
2669:
K = –26 – (–38.5) = +12.5 dB
Open-circuit correction factor for typical microphone with 1/2" Microphone Preamplifier Type 2669:
KO = –26 – (–38.3) = +12.3 dB
7.3
Frequency Response
7.3.1
General
In acoustic measurements, there are three types of sound field:
●
Free field
●
Pressure field
●
Diffuse field
The microphone is optimized to have a flat frequency response in one of these
sound fields. This response is called the optimized response. A microphone’s response in a diffuse field is equivalent to its random-incidence response.
This section shows the microphone’s typical free-field, pressure-field and randomincidence responses together with the microphone’s typical actuator response obtained using Electrostatic Actuator UA 0033. The low-frequency response described
in section 7.3.4 is common for all types of response.
All frequency responses and correction curves shown are valid for a microphone
without Adaptor UC 0211 fitted. If the adaptor is used with 1/2" Microphone Preamplifier Type 2669 to obtain an extended low-frequency response, the frequency response from 100 Hz to 10 kHz will roll off by less than 0.1 dB, and up to 20 kHz by
less than 0.5 dB.
All frequency responses and correction curves are shown with a frequency resolution of 1/12-octave.
7.3.2
Optimized Response (Pressure-field Response)
The frequency response of Low-frequency Pressure-field 1/2" Microphone Type 4193
meets the requirements of ANSI S1.4 -1983, Type 1 and ANSI S1.12, Type M.
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940864/1e
Fig.7.3
– 10
–5
0
5
0.1
1
Tol.
Tol.
10
100
Tol.
Tol.
1k
10 k
Frequency (Hz)
100 k
Typical pressure-field response of the microphone with Protection Grid DB 3421 and the microphone’s specified
tolerances. The low-frequency response is valid when the vent is exposed to the sound field
0.01
Response (dB)
Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Frequency Response
Brüel & Kjær
Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Frequency Response
7.3.3
Actuator Response
The microphone’s frequency response is determined by adding corrections for the
type of sound field to its actuator response obtained using Electrostatic Actuator
UA 0033. This is a reproducible and practical method for calibrating a microphone’s
frequency response.
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940674/1e
Fig.7.4 Typical actuator response measured with Electrostatic Actuator UA 0033
Response (Degrees)
0
– 45
– 90
– 135
– 180
100
1k
10 k
Frequency (Hz)
100 k
940675/1e
Fig.7.5 Typical actuator phase response measured with Electrostatic Actuator UA 0033
If the polarization voltage is positive (as it is with Brüel & Kjær instruments), the
output voltage is negative for a positive pressure applied to the diaphragm.
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Frequency Response
7.3.4
Low-frequency Response
The low-frequency response (see Fig.7.3) is the typical response with the vent exposed to the sound field. If the vent is not exposed to the sound field, the sensitivity
increases from 0 dB at the reference frequency (251.2 Hz) to approximately 0.2 dB at
1Hz.
For applications where the vent is not exposed to the sound field, take care to
ensure proper static pressure equalization to prevent static displacement of the
diaphragm.
The microphone’s low-frequency response is common for all types of sound field.
The microphone’s lower limiting frequency (–3 dB) is between 10 and 50 mHz with
the vent exposed to the sound field. If used with Adaptor UC 0211 and 1/2" Microphone Preamplifier Type 2669, the microphone’s lower limiting frequency (–3 dB) is
below 0.1 Hz with the vent exposed to the sound field. The ibdividual microphone’s
lower limiting frequency (–3 dB) is stated on its calibration chart.
7.3.5
Free-field Response
The microphone’s free-field correction curves are shown in Fig.7.6 and Fig.7.8.
These corrections are added to the microphone’s actuator response obtained using
Electrostatic Actuator UA 0033 in order to determine the free-field response at any
angle of incidence. The typical free-field response at 0° incidence with and without
the protection grid are shown in Fig.7.7 and Fig.7.9.
7 − 10
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Frequency Response
Correction (dB)
15
12.5
0°
10
30°
7.5
5
60°
Random
2.5
90°
180°
150°
0
120°
– 2.5
θ°
–5
– 7.5
– 10
500
1k
10k
Frequency (Hz)
50k
940798/1e
Fig.7.6
Free-field correction curves for the microphone with Protection Grid DB 3421
Response (dB)
15
10
5
0
–5
– 10
100
1k
10 k
Frequency (Hz)
100 k
940892/1e
Fig.7.7 Typical free-field response (0° incidence) for the microphone with Protection Grid DB 3421
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Frequency Response
15
dB
12.5
10
0°
7.5
30°
5
60°
Random
2.5
0
150°
120°
90°
180°
– 2.5
θ°
–5
– 7.5
– 10
500
1k
10k
Frequency (Hz)
50k
940797/1e
Fig.7.8
Free-field correction curves for the microphone without
protection grid
Response (dB)
15
10
5
0
–5
– 10
100
1k
10 k
Frequency (Hz)
100 k
940893/1e
Fig.7.9 Typical free-field response (0° incidence) for the microphone without protection grid
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Frequency Response
7.3.6
Random-incidence Response
A microphone’s response in a diffuse sound field is equivalent to its random-incidence response. The microphone’s random-incidence correction curves are shown in
Fig.7.6 and Fig.7.8. These corrections are added to the microphone’s actuator response obtained using Electrostatic Actuator UA 0033 in order to determine the
random-incidence response. The typical random-incidence response with and without the protection grid are shown in Fig.7.10 and Fig.7.11.
The random-incidence corrections are calculated from the free-field corrections
measured in 5° steps according to Draft IEC 1183–1993.
Response (dB)
5
dB
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940942/1e
Fig.7.10 Typical random-incidence response for the microphone with Protection Grid DB 3421
Response (dB)
5
dB
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940943/1e
Fig.7.11 Typical random-incidence response for the microphone without protection grid
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Frequency Response
7.3.7
Pressure-field Response
The microphone’s pressure-field correction curve is shown in Fig.7.12. This correction is added to the microphone’s actuator response obtained using Electrostatic
Actuator UA 0033 in order to determine the pressure-field response. The typical
pressure-field response is shown in Fig.7.13.
In practice, the pressure-field response is often regarded as being equal to the
actuator response as the difference between them is small compared to the uncertainty related to many types of measurement.
Correction (dB)
4
3
2
1
0
–1
100
1k
10 k
Frequency (Hz)
100 k
940868e
Fig.7.12 Pressure-field correction for the microphone
Response (dB)
5
0
–5
– 10
– 15
– 20
100
1k
10 k
Frequency (Hz)
100 k
940872e
Fig.7.13 Typical pressure-field response for the microphone
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Directional Characteristics
7.4
Directional Characteristics
Typical directional characteristics are given in Fig.7.14 and Fig.7.15. The characteristics are normalised relative to the 0° response.
0°
0°
–5
– 10
– 15
– 20
90°
0
5
–5
– 10
–15
– 20
6.3 kHz
– 25
– 20
0
–15
5
270°
– 10
– 25
–5
– 20
0
– 15
5
– 10
90°
°
60
–5
0°
°
0
30
60
5
°
0°
270°
30
0°
0°
°
33
30
33
30
25 kHz
8 kHz
20 kHz
θ°
0°
0°
24
12
12
12.5 kHz
0°
10 kHz
0°
24
180°
21
15
0°
0°
15
180°
21
0°
5 kHz
0°
16 kHz
940852/1e
Fig.7.14 Typical directional characteristics of the microphone with Protection Grid DB 3421
0°
0°
0
–5
– 10
– 15
– 20
– 25
– 20
90°
5
0
5
270°
–15
–5
– 10
–15
– 20
– 25
– 10
– 20
–5
– 15
0
– 10
5
–5
90°
°
60
0
0°
°
5
30
60
0°
270°
30
°
0°
33
30
°
0°
33
30
25 kHz
6.3 kHz
20 kHz
8 kHz
θ°
0°
0°
24
12
10 kHz
0°
0°
24
12
12.5 kHz
0°
15
180°
21
0°
0°
15
5 kHz
180°
21
0°
16 kHz
940853/1e
Fig.7.15 Typical directional characteristics of the microphone without protection grid
BE 1379 – 12
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7 − 15
Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Dynamic Range
7.5
Dynamic Range
Definition
The dynamic range is the range between the upper limit (determined by distortion)
and the inherent noise floor. Both limits are influenced by the preamplifier. This
section gives values for the microphone with and without a preamplifier.
Inherent Noise
The microphone’s inherent noise is due to thermal movements of the diaphragm.
These vary proportionally with the square root of the absolute temperature (in °K).
The inherent noise increases with increasing temperature. With reference to 20 °C,
the inherent noise changes by + 0.5 dB at 55 °C and by – 0.5 dB at – 12 °C. The
maximum variation of inherent noise for different samples of Low-frequency Pressure-field 1/2" Microphone Type 4193 is ± 1 dB.
The preamplifier’s effect on the inherent noise of the combined microphone and
preamplifier depends on the sensitivity and capacitance of the microphone (for 1/2"
Microphone Preamplifier Type 2669, see Fig. 7.16 and Chapter 8). When used with
1/2" Microphone Preamplifier Type 2669 and Adaptor UC 0211, the preamplifier’s
inherent noise dominates (see Table 7.4).
7 − 16
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Dynamic Range
Sound Pressure Level
re 20 µPa (dB)
30
L
25
L
L
20
A
A
A
15
Microphone
and
Preamplifier
Combination
10
5
Preamplifier
Microphone
0
10
100
1k
10 k
Frequency (Hz)
20 k
M
P
C
940720e
Fig.7.16 1/3-octave-band inherent noise spectrum. The shaded bar graphs are the broad-band
(20 Hz to 20 kHz) noise levels and the white bar graphs the A-weighted noise levels of the
microphone (M), 1/2" Microphone Preamplifier Type 2669 (P) and microphone and preamplifier combination (C). Valid for microphone without Adaptor UC 0211
BE 1379 – 12
Falcon™ Range of Microphone Products
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7 − 17
Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Dynamic Range
Distortion
The distortion is determined mainly by the microphone but, at the highest operation levels, the preamplifier also contributes to the distortion (see Fig. 7.18 and
Fig. 7.18).
Distortion (%)
10
C
M
2nd
Harmonic
1
C
M
3rd
Harmonic
0.1
0.01
135
145
SPL (dB) 155
165
940499e
Fig.7.17 Typical distortion characteristics of the microphone with
1/2 " Microphone Preamplifier Type 2669 (C) and unloaded (M)
7 − 18
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Dynamic Range
Distortion (%)
100
10
2nd
Harmonic
3rd
Harmonic
1
0.1
135
145
155
SPL (dB)
165
940500e
Fig.7.18 Typical distortion characteristics of the microphone fitted
with Adaptor UC 0211 and 1/2" Microphone Preamplifier Type 2669
The distortion is dependent on the capacitance parallel to the microphone. It increases with increasing capacitance. The distortions given in Table 7.3 to Table 7.4
are valid for a parallel capacitance of 0.5 pF. The distortion is measured at 100 Hz
but can be assumed to be valid up to approximately 5 kHz (that is, where the
diaphragm displacement is predominantly stiffness-controlled). Distortion measurement methods for higher frequencies are not available.
Lower Limit
1 Hz bandwidth
at 1 kHz (dB)
–22.4
1
Upper Limit
/3-octave band
at 1 kHz (dB)
A-weighted (dB)
Linear 20 Hz to
20 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
1.2
19.0
21.3
162
171
Table 7.3 Dynamic range of the microphone
BE 1379 – 12
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7 − 19
Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Equivalent Volume and Calibrator Load Volume
Lower Limit
1 Hz bandwidth
at 1 kHz (dB)
1
–18.2
Upper Limit
/3-octave band
at 1 kHz (dB)
A-weighted (dB)
Linear 20 Hz to
20 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
5.4
20.7
25.4
161
166
Table 7.4 Dynamic range of the microphone with 1/2" Microphone Preamplifier Type 2669
Lower Limit
1 Hz bandwidth
at 1 kHz (dB)
– 9.9
Table 7.5
1
Upper Limit
/3-octave band
at 1 kHz (dB)
A-weighted (dB)
Linear 1 Hz to
20 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
13.7
29.0
38.2
148
168
Dynamic range of the microphone with 1/2" Microphone Preamplifier Type 2669 and
Adaptor UC 0211
Maximum Sound Pressure Level
In general, the microphone should not be exposed to sound pressure levels which
produce voltages higher than the maximum input voltage specified for the connected preamplifier. After an overload, the preamplifier needs time to recover and, during this recovery period, you cannot measure validly. The maximum input voltage
for most Brüel & Kjær preamplifiers is ± 50 V (with a 130 V supply). This voltage is
produced by a nominal Low-frequency Pressure-field 1/2" Microphone Type 4193 at
a Peak level of 166 dB (re 20 µPa).
The microphone will maintain its charge up to a Peak level of 171 dB
Above this level, the diaphragm and back plate short-circuit. If this
microphone needs one or two minutes to recharge before it is ready
validly. We recommend not to expose Low-frequency Pressure-field 1/2"
Type 4193 to levels higher than 171 dB (Peak).
7.6
(re 20 µPa).
occurs, the
to measure
Microphone
Equivalent Volume and Calibrator Load Volume
Equivalent Volume
For some applications it is practical to express the acoustic impedance of the microphone diaphragm in terms of a complex equivalent volume. This makes it easier to
evaluate the effect of microphone loading on closed cavities or acoustic calibration
couplers.
7 − 20
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Equivalent Volume and Calibrator Load Volume
The real and imaginary parts of the equivalent volume shown in Fig.7.19 are in
parallel. They are calculated from a simple R–L–C series model of the microphone
which gives the best overall approximation of the microphone’s diaphragm impedance.
Volume (mm3)
12
10
– V (Im)
8
6
4
2
V (Re)
0
–2
100
1k
10k
Frequency (Hz)
100k
940948e
Fig.7.19 Typical equivalent volume (real and imaginary parts) based on mathematical model of
microphone
The Models
The following equivalent models are valid at 101.325 kPa, 23 °C and 50%RH:
Model 1
C = 0.062 x 10-12 m5/N
L = 710kg/m4
R = 119 x 106 Ns/m5
where
C = acoustic diaphragm compliance
L = acoustic diaphragm mass
R = acoustic diaphragm damping resistance
Model 2
Vlf = 8.8 mm3
f0 = 24kHz
Q = 0.9
where
BE 1379 – 12
Vlf = low-frequency volume
f0 = diaphragm resonance frequency
Q = quality factor
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7 − 21
Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Capacitance
Calibrator Load Volume
When the microphone with its protection grid is inserted into the coupler of a
calibrator, it will load the calibrator by a volume of 190 mm3 at 250 Hz.
Load volume correction to Pistonphone Type 4228 Calibration Level (with
Adaptor DP 0776): +0.02 dB
7.7
Capacitance
The microphone’s impedance is determined by its polarized capacitance. In addition,
the preamplifier’s input resistance and capacitance load the microphone. This loading determines the electrical lower limiting frequency and the capacitive input attenuation. However, with modern preamplifiers, this loading is very small and is
included in the preamplifier gain, G (see section 7.2.2). Only in special cases with
high capacitive loading does the fall in capacitance with frequency have to be taken
into account.
Capacitance (pF)
20
250 V
18
200 V
150 V
28 V
16
14
12
10
100
1k
Hz
10k
Frequency (Hz)
100k
940605e
Fig.7.20 Variation of capacitance with polarization voltage and frequency
Typical capacitance (at 250 Hz): 18 pF
The capacitance is individually calibrated and stated on the calibration chart.
7.8
Polarization Voltage
Generally, a microphone is operated at its nominal polarization voltage. For Lowfrequency Pressure-field 1/2" Microphone Type 4193, this is 200 V. As this polariza-
7 − 22
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Polarization Voltage
tion voltage is positive, the output voltage is negative for a positive pressure applied to the diaphragm.
In special cases where there is a risk of preamplifer overload or there are long
cables to be driven, choose a lower voltage. This will cause a lower sensitivity (see
Fig.7.21) and a change in the frequency response (see Fig.7.22).
Response (dB)
5
0
–5
–10
–15
–20
–25
5
10
20
50
100
200
500
Po. Voltage (V)
940683e
Fig.7.21 Variation in sensitivity (at 250 Hz) as a function of polarization voltage, relative to the sensitivity with a polarization voltage of 200 V
BE 1379 – 12
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7 − 23
Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Leakage Resistance
Response (dB)
2.5
2
1
28 V
150 V
0
250 V
-1
-2
-2.5
100
1k
Hz
10k
100k
Frequency (Hz)
940608e
Fig.7.22 Effect of polarization voltage on frequency response. The curves show the difference from
the response with a polarization voltage of 200 V (normalised at 250 Hz)
7.9
Leakage Resistance
To maintain the correct polarization voltage on the microphone, the microphone’s
leakage resistance must be at least 1000 times greater than the supply resistance
of the polarization charge, even under the most severe environmental conditions.
This resistance which is generally placed in the preamplifier, is typically 10 9 to
1010 Ω. Brüel & Kjær microphones have a very high leakage resistance which is
greater than 5×1015 Ω at 90%RH and 23°C.
7.10 Stability
7.10.1 Mechanical Stability
The microphone’s design with respect to mechanical stability is improved compared
with traditional Brüel & Kjær microphones. The diaphragm clamping ring is less
sensitive to accidental force and the protection grid is significantly reinforced.
Therefore, the microphone can withstand mechanical shocks better than traditional
Brüel & Kjær microphones.
7 − 24
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Stability
The sensitivity change of the microphone is less than 0.1 dB after a free fall of 1 m
onto a solid hardwood block (re IEC 68–2–32).
This improved mechanical stability makes Low-frequency Pressure-field 1/2" Microphone Type 4193 well-suited for surface mounting and for mounting in small couplers as no mechanical adaptor is required to protect the diaphragm clamping ring.
The microphone can be supported by the diaphragm clamping ring directly on the
coupler’s surface. Any force of less than 5 Newtons will cause a change in sensitivity
of less than 0.005 dB. This makes the microphone well-suited for fitting in small,
plane wave couplers used for reciprocity calibration and any other small coupler
with a well-defined volume.
7.10.2 High-temperature Stability
The diaphragm is made of a stainless steel alloy. The alloy has been carefully
selected and is very resistant to heat. This means that the diaphragm tension (and
therefore the sensitivity) remain the same, even after several hours’ operation at
high temperature.
The microphone has been tested at temperatures up to 300°C. Below 170°C, no
changes occur. At 170°C, the sensitivity can be permanently changed within the
first 10 hours by less than 0.025 dB. After this, the sensitivity can be permanently
changed within the next 100 hours by a similar value. At 300°C, the sensitivity can
be permanently changed within the first hour by + 0.4 dB. After this, the sensitivity
can be permanently changed within the next 10 hours by less than + 0.4 dB.
Note: Special adaptors (inserted between the microphone and preamplifier) must be
made for high-temperature applications in order to protect the preampifier from
heat conduction and radiation.
7.10.3 Long-term Stability
Over a period of time, the mechanical tension in the diaphragm will decrease due to
stretching within the foil. This mechanism, which, in principle, causes an increased
sensitivity, is, however, very weak for the microphone. Measurement of this mechanism is not possible at room temperature.
At present, no exact value can be given for the microphone’s long-term stability but
measured changes at high temperatures indicate that Low-frequency Pressure-field
1/2" Microphone Type 4193 is more than 10 times more stable than traditional
Brüel & Kjær microphones. This indicates typical changes of less than 1 dB in 5000
years.
BE 1379 – 12
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7 − 25
Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Effect of Temperature
7.11 Effect of Temperature
By careful selection of materials, optimization of the design and artificial ageing,
the effect of temperature has been made to be very low.
The microphone has been designed to operate at temperatures from –30 to 300°C.
When the microphone is subjected to temperatures above 200°C, it may be discoloured but its functionality will remain unaffected. See section 7.10.2 for permanent
changes in sensitivity at temperatures above 170°C.
The reversible changes are shown in Fig.7.23 as a change in sensitivity and in
Fig.7.26 to Fig.7.26 as changes in the frequency response normalized at 250 Hz.
Response (dB)
0.5
0.0
– 0.5
– 1.0
– 1.5
– 2.0
– 2.5
– 50
0
50
100
150
200
250
Temperature (°C)
300
940876e
Fig.7.23 Typical variation in sensitivity (at 250 Hz) as a function
of temperature, relative to the sensitivity at 20° C
Temperature Coefficient (250 Hz):
–0.002 dB/°C, typical (for the range –10 to +50°C)
7 − 26
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Effect of Temperature
Response (dB)
1.5
1.0
0.5
– 10 °C
0.0
+ 50 °C
– 0.5
– 1.0
– 1.5
500 Hz
1k
10 k
Frequency (Hz) 50 k
940776e
Fig.7.24 Typical variation in actuator response (normalized at
250 Hz) as a function of temperature, relative to the response at 20° C (see Fig.7.4) over the temperature range
defined by IEC 651
Response (dB)
4
3
2
1
300° C
200° C
100° C
0
–1
–2
500
1k
10 k
Frequency (Hz)
50 k
940600e
Fig.7.25 Typical variation in actuator response (normalized at
250 Hz) as a function of temperature, relative to the response at 20° C (see Fig.7.4)
BE 1379 – 12
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7 − 27
Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Effect of Ambient Pressure
The effect of temperature on the free-field response (see Fig.7.26) of the microphone
is the sum of the following effects:
●
the calculated effect of the change in the speed of sound due to temperature on
the 0°-incidence free-field correction
●
the measured change in the actuator response due to temperature (see Fig.7.24).
Response (dB)
1.5
1.0
– 10°C
0.5
0.0
– 0.5
50°C
– 1.0
– 1.5
500 Hz
1k
10 k
Frequency (Hz) 50 k
940810/1e
Fig.7.26 Typical variation in 0°-incidence free-field response with
Protection Grid DB 3421 (normalized at 250 Hz) as a
function of temperature, relative to the response at 20° C
(see Fig.7.7) over the temperature range defined by
IEC 651
7.12 Effect of Ambient Pressure
The microphone’s sensitivity and frequency response are affected by variations in
the ambient pressure. This is due to changes in air stiffness in the cavity behind
the diaphragm, and changes in air mass in the small gap between the diaphragm
and the back plate. The effects are shown in Fig.7.27 to Fig.7.29.
7 − 28
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Effect of Ambient Pressure
The typical pressure coefficient at 250 Hz for Low-frequency Pressure-field 1/2" Microphone Type 4193 is –0.005 dB/kPa.
Correction (dB)
3
–40kPa
change
2
–20kPa
change
1
–10kPa
change
0
–1
500
1k
10k
Frequency (Hz)
50k
940765e
Fig.7.27 Typical variation in frequency response (normalized at
250 Hz) from that at 101.3 kPa as a function of change in
ambient pressure
Response (dB)
30
(d)
20
10
(c)
0
(a)
(b)
– 10
– 20
500
1k
10k
Frequency (Hz)
50k
940757e
Fig.7.28 Typical effect of ambient pressure on actuator response
(a) at 101.3 kPa (b) – 40 kPa change (c) – 80 kPa change
(d) at 2 kPa
BE 1379 – 12
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7 − 29
Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Effect of Humidity
Response (dB)
4
2
0
–2
–4
–6
1
10
100
Ambient Pressure (kPa)
1000
940761e
Fig.7.29 Typical variation in sensitivity at 250 Hz from that at 101.3 kPa as a function of ambient
pressure
7.13 Effect of Humidity
Due to the microphone’s high leakage resistance, humidity has, in general, no effect
on the microphone’s sensitivity or frequency response. The microphone has been
tested according to IEC 68–2–3 and the effects of humidty on the sensitivity at
250 Hz and the frequency response have been found to be less than 0.1 dB at up to
95% RH (non-condensing) and 40°C.
7.14 Effect of Vibration
The effect of vibration is determined mainly by the mass of the diaphragm and is at
its maximum for vibrations applied normal to the diaphragm. A vibration signal of
1 m/s2 RMS normal to the diaphragm typically produces an equivalent Sound Pressure Level of 65.5 dB for a microphone fitted with Protection Grid DB 3421.
7.15 Effect of Magnetic Field
The effect of a magnetic field is determined by the vector field strength and is
normally at its maximum when the field direction is normal to the diaphragm. A
magnetic field strength of 80 A/m at 50 Hz (the test level recommended by IEC and
ANSI) normal to the diaphragm produces a typical equivalent Sound Pressure Level of 16 dB. Higher frequency components in the microphone output become dominant at field strengths greater than 500 to 1000 A/m.
7 − 30
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Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Electromagnetic Compatibility
7.16 Electromagnetic Compatibility
See Chapter 8.
7.17 Specifications Overview
7.17.1 Low-frequency Pressure Response 1/2" Microphone Type 4193
OPEN-CIRCUIT SENSITIVITY (250 Hz)*:
–38 dB ±1.5 dB re 1 V/Pa, 12.5 mV/Pa*
CALIBRATOR LOAD VOLUME (250 Hz):
190 mm3
PRESSURE COEFFICIENT (250 Hz):
–0.005 dB/kPa, typical
POLARIZATION VOLTAGE:
External: 200 V
PISTONPHONE TYPE 4228 CORRECTION:
with DP 0776:
+0.02 dB
INFLUENCE OF HUMIDITY:
>1 000 years/dB at 20°C
<0.001 dB/100%RH
TYPICAL CARTRIDGE THERMAL NOISE:
19.0 dB (A) 21.3 dB (Lin.)
VIBRATION SENSITIVITY (<1000 Hz):
Typically 65.5 dB equivalent SPL for 1 m/s2 axial
acceleration
FREQUENCY RESPONSE*:
Pressure-field response:
0.12 Hz to 12.5 kHz ± 1 dB
0.07 Hz to 20 kHz ±2 dB
In accordance with ANSI S1.4 – 1983, Type 1
and ANSI S1.12, Type M
LOWER LIMITING FREQUENCY (–3 dB):
0.01 Hz to 0.05 Hz (vent exposed to sound)
PRESSURE EQUALIZATION VENT:
Side vented
DIAPHRAGM RESONANCE FREQUENCY:
23 kHz, typical (90° phase shift)
CAPACITANCE (POLARIZED)*:
18 pF, typical (at 250 Hz)
EQUIVALENT AIR VOLUME (101.3 kPa):
8.8 mm3
* Individually calibrated
UPPER LIMIT OF DYNAMIC RANGE:
3% distortion:
>162 dB SPL
MAGNETIC FIELD SENSITIVITY:
Typically 16 dB SPL for 80 A/m, 50 Hz field
MAXIMUM SOUND PRESSURE LEVEL:
171 dB (peak)
ESTIMATED LONG-TERM STABILITY:
>1 00 hours/dB at 150°C
OPERATING TEMPERATURE RANGE:
–30 to +150°C (–22 to 302°F)
(can be used up to + 300°C (572°F) but with a
permanent sensitivity change of typically + 0.4 dB
which stabilises after one hour)
DIMENSIONS:
Diameter: 13.2 mm (0.52 in) (with grid)
12.7 mm (0.50 in) (without grid)
Height:
13.5 mm (0.54 in) (with grid)
12.6 mm (0.50 in) (without grid)
Thread for preamplifier mounting: 11.7 mm –
60 UNS
OPERATING HUMIDITY RANGE:
0 to 100 % RH (without condensation)
STORAGE TEMPERATURE:
–30 to + 70°C (–22 to 158°F)
TEMPERATURE COEFFICIENT (250 Hz):
–0.002 dB/°C, typical (for the range –10 to
+50°C)
The data above are valid at 23°C, 101.3 kPa and
50%RH, unless otherwise specified.
7.17.2 Adaptor UC 0211
LOWER CUT-OFF FREQUENCY:
0.1 Hz (with 1/2" Microphone Preamplifier Type
2669)
EFFECT ON HIGH FREQUENCY RESPONSE:
100 Hz to 10 kHz ± 0.1 dB
100 Hz to 20 kHz ± 0.5 dB
BE 1379 – 12
ATTENUATION:
16 dB
CAPACITANCE:
100 pF, typical
Falcon™ Range of Microphone Products
Microphone Handbook
DIMENSIONS:
Diameter: 12.7 mm (0.50 in)
Height:
14.1 mm (0.56 in)
Thread for preamplifier and microphone mounting: 11.7 mm – 60 UNS
7 − 31
Chapter 7 — Low-frequency Pressure-field 1/2" Microphone Type 4193
Ordering Information
7.18 Ordering Information
Preamplifier
Type 2669: 1/2" Microphone Preamplifier
Calibration Equipment
Type 4231: Sound Level Calibrator
Type 4226: Multifunction Acoustic Calibrator
Type 4228: Pistonphone
UA 0033: Electrostatic Actuator
Other Accessories
UA 0254: Set of 6 Windscreens (UA 0237) 90 mm (3.5 in)
UA 0469: Set of 6 Windscreens (UA 0459) 65 mm (2.6 in)
7 − 32
Falcon™ Range of Microphone Products
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Chapter 8
1/2"
BE 1380 – 12
Microphone Preamplifier
Type 2669
Falcon™ Range of Microphone Products
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8− 1
Chapter 8 — 1/2" Microphone Preamplifier Type 2669
Introduction
8.1
Introduction
8.1.1
Description
ZG 0350
(not included)
2669 B
Fig.8.1
2669 L
1/2 "
Microphone Preamplifier Type 2669 B and 2669 L
shown with LEMO to 7-pin Brüel & Kjær Adaptor
ZG 0350 (not included)
1/2"
Microphone Preamplifier Type 2669 is a general-purpose microphone preamplifier which includes the following features:
●
Built-in calibration facility for testing the complete measurement set-up
●
Thin and flexible cable with wide, working temperature range
●
High output current capability
●
Works with both dual and single power supplies
●
Fulfils electromagnetic compatibility (EMC) requirements EN 50081–1 and
pr EN 50081–2
The preamplifier is available in two versions, the 2669 L and the 2669 B. The only
difference is the connector at the instrument end for the preamplifier socket. The
2669 L is supplied with a detachable cable with a LEMO connector. The 2669 B is
supplied with a detachable cable with a Brüel & Kjær connector. The preamplifier
can be stored in the supplied case with a microphone mounted when not in use.
8− 2
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Chapter 8 — 1/2" Microphone Preamplifier Type 2669
Introduction
Alternativley, the preamplifier can be stored in the microphone’s case with the microphone when not in use.
8.1.2
Connections
Connection
Pin No.
LEMO (2669 L)
Brüel & Kjær (2669 B)
1
Calibration Input
Ground
2
Signal Ground
Polarization Voltage
3
Polarization Voltage
Calibration Input
4
Signal Output
Signal Output
6
5
Not connected
Power Supply Positive
6
Power Supply Positive
Not connected
7
Power Supply Negative/Ground
Casing
2669 B
2669 L
5
4
1
3
2
7
4
3
6
1
Cable's output plug
seen from outside
Not connected
5
2
7
940478/1e
Connected to instrument chassis
Table 8.1 Pin designations
8.1.3
Physical Dimensions
ø 12.7 mm
5 mm
70 mm
50 mm
940993e
Fig.8.2 Physical dimensions of the preamplifier and connector
BE 1380 – 12
Falcon™ Range of Microphone Products
Microphone Handbook
8− 3
Chapter 8 — 1/2" Microphone Preamplifier Type 2669
Frequency Response
8.2
Frequency Response
The frequency response of the preamplifier depends on the capacitance of the microphone connected to its input, and the capacitive load (for example, extension cables)
connected to the output.
2
10 nF
3 nF
3 m Standard Cable
30 nF
0
dB
47 pF
15 pF
–5
6.2 pF
– 10
– 12
0.1
1
10
20
20 k
100 k
Frequency (Hz)
941021e
Fig.8.3
Typical frequency response as a function of input (transducer) capacitance at low frequencies and as a function of capacitive loading at high frequencies
The low frequency curves in Fig.8.3 show the low-frequency response of the preamplifier for various capacitances typical of 1", 1/2 " and 1/4 " microphones. Note, they do
not show the lower cut-off frequencies of the microphones.
The effects of various capacitive output loads (cables etc.) on the high frequencies
are also shown. All curves shown in Fig.8.3 apply only for low signal levels where
the limitations shown in Fig.8.5 and Fig.8.6 have no influence.
8− 4
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Chapter 8 — 1/2" Microphone Preamplifier Type 2669
Dynamic Range
8.3
Dynamic Range
Overview:
Lower limit with 15 pF
microphone (µV)
Upper limit (±60 V
supply, f <10 kHz)a
Dynamic Range (dB)
147
A-weighted: 2.2
Lin. (20 Hz to 300 kHz):
10.0
50 VP
134
Table 8.2 Nominal open-circuit sensitivity
a. See Fig. 8.6 for upper limit at higher frequencies
Inherent Noise:
Noise re 1 µV
(dB)
15
L
10
5
A
0
–5
– 10
10
100
1k
10 k
Frequency (Hz)
Fig.8.4
BE 1380 – 12
20 k
940882e
Typical 1/3 -octave-band inherent noise spectrum measured with a 15 pF dummy microphone. The shaded bar graph is the broad-band (20 Hz to 20 kHz) noise level and the white
bar graph the A-weighted noise level. The circles represent levels at 1/3-octave-band centre
frequencies
Falcon™ Range of Microphone Products
Microphone Handbook
8− 5
Chapter 8 — 1/2" Microphone Preamplifier Type 2669
Dynamic Range
Distortion:
Distortion (THD): <–80 dB (1000 Hz, 25 V output, 3 m cable)
Maximum Output:
The maximum output of the preamplifier depends on the capacitive load (for example, extension cables) connected to the output. If the specified maximum output
current of the preamplifier is exceeded, the signal will be distorted.
Fig.8.5 and Fig.8.6 show the distortion-limited output when the preamplifier is
used with different power supplies.
100
VRMS
30
3
+
10
+
+
10
0
30
3
m
Ca
bl
e
nF
nF
nF
1
200
1k
10 k
Frequency (Hz)
100 k
200 k
940768e
Fig.8.5
8− 6
Upper limit of dynamic range (3% distortion) of preamplifier (powered by traditional Brüel & Kjær power supplies) due to capacitive loading as a function of
frequency. Note: These power supplies limit the maximum output current
Falcon™ Range of Microphone Products
Microphone Handbook
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Chapter 8 — 1/2" Microphone Preamplifier Type 2669
Dynamic Range
100
VRMS
Power ± 50 V (+ 100 V)
30
3
+
10
+
+
10
0
30
3
nF
m
Ca
bl
e
nF
nF
1
200
1k
10 k
Frequency (Hz)
100 k
200 k
940767e
Fig.8.6
Upper limit of dynamic range (3% distortion) of preamplifier (with a ± 50V DC supply voltage) due to capacitive loading as a function of frequency
Fig.8.7 shows the distortion limited output for three different voltage supplies, in
each case when the preamplifier is loaded by the 3 m cable normally supplied with
the preamplifier.
100
VRMS
± 60 V (120 V)
± 30 V (60 V)
10
± 14 V (28 V)
1
200
1k
10 k
Frequency (Hz)
100 k
200 k
940769e
Fig.8.7
BE 1380 – 12
Maximum output voltage as a function of supply voltage and frequency
Falcon™ Range of Microphone Products
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8− 7
Chapter 8 — 1/2" Microphone Preamplifier Type 2669
Phase Response
8.4
Phase Response
6.0
Degrees
4.0
6 pF
20 pF
2.0
0
50 pF
– 2.0
– 4.0
– 6.0
10
Fig.8.8
8.5
100
1k
10 k
100 k 200 k
Frequency (Hz)
940771e
Phase response as a function of input (transducer) capacitance (measured with the 3 m cable normally supplied with the preamplifier)
Effect of Temperature
As the temperature increases, the bias current in the the input amplifier increases.
This causes the inherent noise to increase and the input impedance to decrease
resulting in the effect shown in Fig.8.9.
300
100°C
nV/√Hz
150°C
100
30
50°C
25°C
10
3
200
1k
10k
Frequency (Hz)
100k
200k
940957e
Fig.8.9 Effect of temperature on inherent noise
Note: The preamplifier can withstand temperatures up to 150°C. However, we do
not recommend that it is exposed to this temperature over a longer period of time
as the product’s life expectancy is drastically reduced. In addition, we recommend
that you don’t use high supply voltages with long cables at this temperature for the
same reason.
8− 8
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Chapter 8 — 1/2" Microphone Preamplifier Type 2669
Effect of Magnetic Fields
8.6
Effect of Magnetic Fields
Typically <3 µV for 80 A/m at 50 Hz
8.7
Electromagnetic Compatibility (EMC)
1/2"
Microphone Preamplifier Type 2669 is constructed such that it is extremely
resistant to external electromagnetic radiation. This is important when measuring
near such things as radar and radio transmitters (for example, mobile telephones).
An important prerequisite for acheiving this immunity is that connected instrumentation also fulfil these requirements and that the preamplifier’s termination in the
measuring instrument is correctly constructed (see Fig.8.10). Brüel & Kjær equipment which are designed for connection with 1/2" Microphone Preamplifier Type
2669 L and the supplied extension cable fulfil the requirements for immunity to
external electromagnetic radiation.
~
+V
Generator for
charge injection
Preamplifier
input:
internal view
6
Chassis
1
4
+
2
7
5
3
–
Polarization
Voltage
100 k
– V (0 V)
940904e
Fig.8.10 Simplifed electronic construction of input circuit of 1/2"
Microphone Preamplifier Type 2669 for ensuring compliance with EMC requirements
Note: Brüel & Kjær equipment, typically those having the traditional Brüel & Kjær
microphone socket, do not fulfil these strict immunity reqirements.
1/2"
Microphone Preamplifier Type 2669 conforms to EMC requirements EN 50081–1
and pr EN 50081–2 when connected to an instrument that also conforms to these
regulations.
BE 1380 – 12
Falcon™ Range of Microphone Products
Microphone Handbook
8− 9
Chapter 8 — 1/2" Microphone Preamplifier Type 2669
Brüel & Kjær’s Patented Charge-injection Calibration Technique
8.8
Brüel & Kjær’s Patented Charge-injection Calibration
Technique
This is a new patented technique for verifying the entire measurement set-up including the microphone, the preamplifier and the connecting cable (see Fig.8.11).
The Charge-injection Calibration (CIC) technique is a method for remotely verifying
the condition of the entire measurement set-up including the microphone. This
is a great improvement over the earlier insert-voltage calibration method which
virtually ignores the state of the microphone. The CIC technique is very sensitive to
any change in the microphone’s capacitance which is a reliable indicator of the
microphone’s condition.
Housing
+
Cc
Cm
A
CIC
Ci
V0
Ri
Vi
V0
=
Vi
Microphone
Insertvoltage
cable
A
(C
m+
Cc
Ci + Cc
)
Calibration
Signal Source
Cm
A
Ci
V0
Ri
Vi
V0
=
Vi
Typical Values : Cm = 15 – 20 pF
Ci = 0.3 pF
A
Cc = 0.2 pF
( C C+ C )
m
m
i
A≈1
940528e
Fig.8.11 Charge-injection calibration (CIC) technique compared to insert-voltage calibration technique
The technique works by introducing a small but accurately defined capacitance C c
(typically 0.2 pF) with a very high leakage resistance (greater than 50000 GΩ) into
the circuit of the preamplifier, see Fig.8.11 (upper diagram). C i and R i represent
the preamplifier’s high input impedance and A its gain (≈ 1).
For a given calibration signal, V i, the output, V o of this arrangement will change
measurably, even for small changes in the microphone’s capacitance, C m. The CIC
technique is about 100 times more sensitive than the insert-voltage calibration arrangement shown in Fig.8.11 (lower diagram).
In the extreme case where there is significant leakage between the microphone’s
diaphragm and its backplate (C m becomes very large), the signal output will change
by tens of decibels compared with only tenths of a decibel using the insert-voltage
method.
Another important CIC feature is that, unlike the insert-voltage technique, it is far
less sensitive to external electrical fields.
8 − 10
Falcon™ Range of Microphone Products
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Chapter 8 — 1/2" Microphone Preamplifier Type 2669
Specifications Overview
8.9
Specifications Overview
FREQUENCY RESPONSE (re. 1 kHz):
3 Hz to 200 kHz, ± 0.5 dB
ATTENUATION:
0.25 dB (typical)
PHASE LINEARITY:
≤± 3° at 20 Hz to 100 kHz
PHASE MATCHING:
0.3 ° at 50 Hz
INPUT IMPEDANCE:
15 GΩ || 0.45 pF
OUTPUT IMPEDANCE:
25 Ω
MAX. OUTPUT CURRENT:
20 mA (peak)
Note: The max. output current can be limited by
the power supply.
MAX. OUTPUT VOLTAGE:
Total supply voltage –10 V (Vpeak peak)
OUTPUT SLEW RATE:
2 V/µs
DISTORTION (THD):
Less than –80 dB at 25 V out, 1 kHz
NOISE (15 pF DUMMY):
≤10.0 µV Lin. 20 Hz – 300 kHz
≤2.2 µV A weighted
POWER SUPPLY, DUAL:
±14 V to ± 60 V
POWER SUPPLY, SINGLE:
28 V to 120 V
OUTPUT DC OFFSET:
≈1 V for a dual supply, or
≈ 1/2 the voltage of a single supply
CURRENT CONSUMPTION:
3 mA plus output current
CALIBRATION INPUT:
Charge insert capacity, typically 0.2 pF
Max. 10 VRMS, input impedance: 1 nF
ENVIRONMENTAL:
Conforms to EMC requirements EN 50081–1
and pr EN 50081–2 when connected to an instrument that also conforms to these regulations
Note: the above are valid for a 15 pF mic. (1/2")
and a 3 metre cable
CONNECTOR TYPE:
LEMO type FGJ.OB.307 at preamplifier
LEMO type FGG.1B.307 (2669 L), or Brüel &
Kjær JP 0715 (2669 B) to measuring device
PIN CONNECTIONS:
5
2669 B
4
1
2
7
4
3
LEMO (L)
Brüel & Kjær (B)
1
Calibration input
Ground
2
Signal ground
Pol. voltage
3
Pol. voltage
Calibration input
4
Signal output
Signal output
5
Not connected
Power supply
positive
6
Power supply
positive
Not connected
7
Power supply
negative/ground
Not connected
Casing Connected to instrument chassis
2669 L
6
Pin
3
5
1
7
2
6
Cable's output plug
seen from outside
TEMPERATURE RANGE:
–20 to 60 °C
150 °C with increase in noise
HUMIDITY:
Up to 90% RH, non condensing
940478/1e
DIMENSIONS:
∅12.7 mm × 110 mm (including connector)
8.10 Ordering Information
Extension Cables
LEMO — LEMO:
AO 0414
Extension Cable 3 m (9.8 ft.)
AO 0415
Extension Cable 10 m (32.8 ft.)
AO 0416
Extension Cable 30 m (98.4 ft.)
EL 4004/xxExtension Cable length xx m (specified by customer)
Brüel & Kjær — Brüel & Kjær:
BE 1380 – 12
AO 0027
Extension Cable 3 m (9.8 ft.)
AO 0028
Extension Cable 10 m (32.8 ft.)
AO 0029
Extension Cable 30 m (98.4 ft.)
Falcon™ Range of Microphone Products
Microphone Handbook
8 − 11
Chapter 8 — 1/2" Microphone Preamplifier Type 2669
Ordering Information
Microphone Adaptors
DB 0375
Adaptor for 1" microphone
UA 0035
Adaptor for 1/4 " microphone
UA 0036
Adaptor for 1/8 " microphone
Other Accessories
8 − 12
ZG 0350
LEMO to 7-pin Brüel & Kjær adaptor
JJ 2617
Coaxial Input Adaptor for direct connection to input cables
UA 0196
Flexible Extension Rod
UA 1284
Stand
UA 1317
Microphone Holder
Falcon™ Range of Microphone Products
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Brüel & Kjær
Chapter 9
Accessories
BE 1381 – 12
Falcon™ Range of Microphone Products
Microphone Handbook
9− 1
Chapter 9 — Accessories
Accessories Available
9.1
Accessories Available
9.1.1
Microphone Accessories
Accessory
Prepolarized
Free-field
Microphone
Type 4188
Prepolarized
Free-field
Microphone
Type 4189
Free-field
Precision
Microphone
Type 4190
Free-field
Microphone
Type 4191
Pressure
Microphone
Type 4192
Low-frequency
Pressure
Microphone
Type 4193
Windscreen
UA 0237, UA 0459
•
•
•
•
•
•
Rain Cover
UA 0393
•
•
•
•
•
•
Nose Cone
UA 0386
•
•
•
•
•
•
Dehumidifier
UA 0308
•
•
•
Turbulence
Screen
UA 036
•
•
•
•
Table 9.1 Accessories available for the various microphones
9.1.2
Cables and Adaptors
Cable/Adaptor
Description
Notes
AO 0149
LEMO–LEMO cable (3 m)
Included with Preamplifier Type 2669 L
AO 0428
LEMO–Brüel & Kjær cable (3 m)
Included with Preamplifier Type 2669 B
ZG 0350
LEMO–Brüel & Kjær adaptor
AO 0414
LEMO–LEMO extension cable (3 m)
AO 0415
LEMO–LEMO extension cable (10 m)
AO 0416
LEMO–LEMO extension cable (30 m)
AR 0014
LEMO-LEMO flat cable (0.5 m)
Table 9.2 Cables and adaptors available from Brüel & Kjær
9− 2
Falcon™ Range of Microphone Products
Microphone Handbook
Brüel & Kjær
Index
1/2” Microphone Preamplifier Type 2669 8 – 1
2669, 1/2" Microphone Preamplifier 8 – 1
4188
Prepolarized Free-field 1/2" Microphone 2 – 1
4189
Prepolarized Free-field 1/2" Microphone 3 – 1
4190
Free-field 1/2" Microphone 4 – 1
4191
Free-field 1/2" Microphone 5 – 1
4192
Pressure-field 1/2" Microphone 6 – 1
4193
Low-frequency Pressure-field 1/2"
Microphone 7 – 1
4190, free-field microphone 4 – 7
4191, free-field microphone 5 – 7
4192, pressure-field microphone 6 – 7
4193, pressure-field microphone 7 – 9
Adaptor 9 – 2
LEMO–Brüel & Kjær 9 – 2
microphone 8 – 12
UC 0211 7 – 5
Ambient pressure
4188, prepolarized microphone 2 – 25
4189, prepolarized microphone 3 – 25
4190, free-field microphone 4 – 25
4191, free-field microphone 5 – 25
4192, pressure-field microphone 6 – 25
4193, pressure-field microphone 7 – 28
A
C
About the Microphone Handbook 1 – 2
9–1
Accessories 8 – 12,
4188, prepolarized microphone 2 – 29
4189, prepolarized microphone 3 – 29
4190, free-field microphone 4 – 29
4191, free-field microphone 5 – 29
4192, pressure-field microphone 6 – 29
4193, pressure-field microphone 7 – 32
microphone 9 – 2
Actuator frequency response
4188, prepolarized microphone 2 – 6
4189, prepolarized microphone 3 – 7
Cable 9 – 2
9–2
extension 8 – 11,
LEMO–Brüel & Kjær 9 – 2
LEMO–LEMO 9 – 2
Calibration
charge-injection 8 – 10
CIC 8 – 10
interval
4188, prepolarized microphone 2 – 4
4189, prepolarized microphone 3 – 5
4190, free-field microphone 4 – 5
4191, free-field microphone 5 – 5
BE 1382 – 12
Falcon™ Range of Microphone Products
Microphone Handbook
Index – 1
Index
4192, pressure-field microphone 6 – 5
4193, pressure-field microphone 7 – 5
Calibration chart
4188, prepolarized microphone 2 – 3
4189, prepolarized microphone 3 – 3
4190, free-field microphone 4 – 3
4191, free-field microphone 5 – 3
4192, pressure-field microphone 6 – 3
4193, pressure-field microphone 7 – 3
Calibration equipment
4188, prepolarized microphone 2 – 28
4189, prepolarized microphone 3 – 28
4190, free-field microphone 4 – 28
4191, free-field microphone 5 – 28
4192, pressure-field microphone 6 – 28
4193, pressure-field microphone 7 – 32
Calibrator load volume
4188, prepolarized microphone 2 – 19
4189, prepolarized microphone 3 – 19
4190, free-field microphone 4 – 18
4191, free-field microphone 5 – 18
4192, pressure-field microphone 6 – 18
4193, pressure-field microphone 7 – 22
Capacitance
4188, prepolarized microphone 2 – 20
4189, prepolarized microphone 3 – 20
4190, free-field microphone 4 – 19
4191, free-field microphone 5 – 19
4192, pressure-field microphone 6 – 19
4193, pressure-field microphone 7 – 22
Charge-injection calibration 8 – 10
CIC 8 – 10
Connections, Preamplifier Type 2669 8 – 3
D
Data disk
4189, prepolarized microphone 3 – 4
4190, free-field microphone 4 – 4
4191, free-field microphone 5 – 4
4192, pressure-field microphone 6 – 4
4193, pressure-field microphone 7 – 4
Dehumidifier 9 – 2
Description
4188, prepolarized microphone 2 – 2
4189, prepolarized microphone 3 – 2
4190, free-field microphone 4 – 2
4191, free-field microphone 5 – 2
4192, pressure-field microphone 6 – 2
4193, pressure-field microphone 7 – 2
Index – 2
Dimensions, Preamplifier Type 2669 8 – 3
Directional characteristics
4188, prepolarized microphone 2 – 13
4189, prepolarized microphone 3 – 14
4190, free-field microphone 4 – 13
4191, free-field microphone 5 – 13
4192, pressure-field microphone 6 – 13
4193, pressure-field microphone 7 – 15
Discolouration
4190, free-field microphone 4 – 22
4191, free-field microphone 5 – 22
4192, pressure-field microphone 6 – 22
4193, pressure-field microphone 7 – 26
Disk
data
4189, prepolarized microphone 3 – 4
4190, free-field microphone 4 – 4
4191, free-field microphone 5 – 4
4192, pressure-field microphone 6 – 4
4193, pressure-field microphone 7 – 4
Distortion
2669, preamplifier 8 – 6
4188, prepolarized microphone 2 – 18
4189, prepolarized microphone 3 – 17
4190, free-field microphone 4 – 16
4191, free-field microphone 5 – 16
4192, pressure-field microphone 6 – 16
4193, pressure-field microphone 7 – 18
Dynamic range
2669, preamplifier 8 – 5
4188, prepolarized microphone 2 – 16
4189, prepolarized microphone 3 – 15
4190, free-field microphone 4 – 14
4191, free-field microphone 5 – 14
4192, pressure-field microphone 6 – 14
4193, pressure-field microphone 7 – 16
E
Electromagnetic compatibility 8 – 9
EMC 8 – 9
Equivalent volume
4188, prepolarized microphone 2 – 19
4189, prepolarized microphone 3 – 18
4190, free-field microphone 4 – 17
4191, free-field microphone 5 – 17
4192, pressure-field microphone 6 – 17
4193, pressure-field microphone 7 – 20
9–2
Extension cable 8 – 11,
Falcon™ Range of Microphone Products
Microphone Handbook
Brüel & Kjær
Index
F
Free-field 1/2" Microphone Type 4190 4 – 1
Free-field 1/2" Microphone Type 4191 5 – 1
Free-field frequency response
4188, prepolarized microphone 2 – 8
4189, prepolarized microphone 3 – 9
4190, free-field microphone 4 – 9
4191, free-field microphone 5 – 9
4192, pressure-field microphone 6 – 9
4193, pressure-field microphone 7 – 10
Frequency response
2669, preamplifier 8 – 4
actuator
4188, prepolarized microphone 2 – 6
4189, prepolarized microphone 3 – 7
4190, free-field microphone 4 – 7
4191, free-field microphone 5 – 7
4192, pressure-field microphone 6 – 7
4193, pressure-field microphone 7 – 9
free-field
4188, prepolarized microphone 2 – 8
4189, prepolarized microphone 3 – 9
4190, free-field microphone 4 – 9
4191, free-field microphone 5 – 9
4192, pressure-field microphone 6 – 9
4193, pressure-field microphone 7 – 10
low-frequency
4188, prepolarized microphone 2 – 7
4189, prepolarized microphone 3 – 8
4190, free-field microphone 4 – 8
4191, free-field microphone 5 – 8
4192, pressure-field microphone 6 – 8
4193, pressure-field microphone 7 – 10
optimized
4188, prepolarized microphone 2 – 6
4189, prepolarized microphone 3 – 7
4190, free-field microphone 4 – 7
4191, free-field microphone 5 – 7
4192, pressure-field microphone 6 – 7
4193, pressure-field microphone 7 – 7
pressure-field
4189, prepolarized microphone 3 – 13
4190, free-field microphone 4 – 12
4191, free-field microphone 5 – 12
4192, pressure-field microphone 6 – 12
4193, pressure-field microphone 7 – 14
random-incidence
4188, prepolarized microphone 2 – 12
4189, prepolarized microphone 3 – 12
BE 1382 – 12
4190, free-field microphone 4 – 11
4191, free-field microphone 5 – 11
4192, pressure-field microphone 6 – 11
4193, pressure-field microphone 7 – 13
resolution
4188, prepolarized microphone 2 – 6
3–7
4189, prepolarized microphone 3 – 4,
4–7
4190, free-field microphone 4 – 4,
5–7
4191, free-field microphone 5 – 4,
6–
4192, pressure-field microphone 6 – 4,
7
4193, pressure-field microphone
7 – 4,
7–
7
H
Humidity
4188, prepolarized microphone 2 – 26
4189, prepolarized microphone 3 – 26
4190, free-field microphone 4 – 27
4191, free-field microphone 5 – 27
4192, pressure-field microphone 6 – 27
4193, pressure-field microphone 7 – 30
I
8–5
Inherent noise 5 – 15,
4188, prepolarized microphone 2 – 16
4189, prepolarized microphone 3 – 15
4190, free-field microphone 4 – 14
4191, free-field microphone 5 – 14
4192, pressure-field microphone 6 – 14
4193, pressure-field microphone 7 – 16
K
K-factor
4188, prepolarized microphone 2 – 5
4189, prepolarized microphone 3 – 6
4190, free-field microphone 4 – 6
4191, free-field microphone 5 – 6
4192, pressure-field microphone 6 – 6
4193, pressure-field microphone 7 – 6
L
Leakage resistance
4188, prepolarized microphone 2 – 21
4189, prepolarized microphone 3 – 21
4190, free-field microphone 4 – 21
4191, free-field microphone 5 – 21
Falcon™ Range of Microphone Products
Microphone Handbook
Index – 3
Index
4192, pressure-field microphone 6 – 21
4193, pressure-field microphone 7 – 24
LEMO–Brüel & Kjær adaptor 9 – 2
LEMO–Brüel & Kjær cable 9 – 2
LEMO–LEMO cable 9 – 2
LEMO–LEMO extension cable 9 – 2
Load volume, calibrator
4188, prepolarized microphone 2 – 19
4189, prepolarized microphone 3 – 19
4190, free-field microphone 4 – 18
4191, free-field microphone 5 – 18
4192, pressure-field microphone 6 – 18
4193, pressure-field microphone 7 – 22
Loaded sensitivity
4188, prepolarized microphone 2 – 4
4189, prepolarized microphone 3 – 5
4190, free-field microphone 4 – 5
4191, free-field microphone 5 – 5
4192, pressure-field microphone 6 – 5
4193, pressure-field microphone 7 – 6
Long-term stability
4188, prepolarized microphone 2 – 22
4189, prepolarized microphone 3 – 22
4190, free-field microphone 4 – 22
4191, free-field microphone 5 – 22
4192, pressure-field microphone 6 – 22
4193, pressure-field microphone 7 – 25
Low-frequency Pressure-field 1/2" Microphone
Type 4193 7 – 1
Low-frequency response
4188, prepolarized microphone 2 – 7
4189, prepolarized microphone 3 – 8
4190, free-field microphone 4 – 8
4191, free-field microphone 5 – 8
4192, pressure-field microphone 6 – 8
4193, pressure-field microphone 7 – 10
M
Magnetic field
2669, preamplifier 8 – 9
4188, prepolarized microphone 2 – 27
4189, prepolarized microphone 3 – 27
4190, free-field microphone 4 – 27
4191, free-field microphone 5 – 27
4192, pressure-field microphone 6 – 27
4193, pressure-field microphone 7 – 30
Maximum output
2669, preamplifier 8 – 6
Maximum Sound Pressure Level
Index – 4
4188, prepolarized microphone 2 – 18
4189, prepolarized microphone 3 – 17
4190, free-field microphone 4 – 16
4191, free-field microphone 5 – 16
4192, pressure-field microphone 6 – 16
4193, pressure-field microphone 7 – 20
Mechanical shock, stability
4188, prepolarized microphone 2 – 21
4189, prepolarized microphone 3 – 21
4190, free-field microphone 4 – 21
4191, free-field microphone 5 – 21
4192, pressure-field microphone 6 – 21
4193, pressure-field microphone 7 – 24
Microphone
accessories 9 – 2
adaptor 8 – 12
Microphone Preamplifier (1/2") Type 2669
8–1
N
Nose cone
9–2
O
Open-circuit sensitivity
4188, prepolarized microphone 2 – 4
4189, prepolarized microphone 3 – 5
4190, free-field microphone 4 – 5
4191, free-field microphone 5 – 5
4192, pressure-field microphone 6 – 5
4193, pressure-field microphone 7 – 5
Optimized frequency response
4188, prepolarized micrphone 2 – 6
4189, prepolarized micrphone 3 – 7
4190, free-field micrphone 4 – 7
4191, free-field microphone 5 – 7
4192, pressure-field micrphone 6 – 7
4193, pressure-field micrphone 7 – 7
Ordering information
2669, preamplifier 8 – 11
4188, prepolarized microphone 2 – 28
4189, prepolarized microphone 3 – 28
4190, free-field microphone 4 – 28
4191, free-field microphone 5 – 28
4192, pressure-field microphone 6 – 28
4193, pressure-field microphone 7 – 32
Output
maximum
2669, preamplifier 8 – 6
Output voltage
Falcon™ Range of Microphone Products
Microphone Handbook
Brüel & Kjær
Index
4188, prepolarized microphone
2 – 2,
2 – 7,
3 – 2,
3 – 8,
2 – 20
4189, prepolarized microphone
3 – 20
4190,
4191,
4192,
4193,
4 – 19
free-field microphone 4 – 8,
5 – 19
free-field microphone 5 – 8,
6 – 19
pressure-field microphone 6 – 8,
7 – 23
pressure-field microphone 7 – 9,
P
Phase response, Preamplifier Type 2669 8 – 8
Physical dimensions
microphones 1 – 6
Preamplifier Type 2669 8 – 3
Pin designations, Preamplifier Type 2669 8 – 3
Polarization voltage
4188, prepolarized microphone 2 – 20
4189, prepolarized microphone 3 – 20
4190, free-field microphone 4 – 19
4191, free-field microphone 5 – 19
4192, pressure-field microphone 6 – 19
4193, pressure-field microphone 7 – 22
Preamplifier
4188, prepolarized microphone 2 – 28
4189, prepolarized microphone 3 – 28
4190, free-field microphone 4 – 28
4191, free-field microphone 5 – 28
4192, pressure-field microphone 6 – 28
4193, pressure-field microphone 7 – 32
Preamplifier (1/2" Microphone) Type 2669 8 – 1
connections 8 – 3
dimensions 8 – 3
distortion 8 – 6
dynamic range 8 – 5
electromagnetic compatibility 8 – 9
frequency response 8 – 4
magnetic field 8 – 9
maximum output 8 – 6
ordering information 8 – 11
phase response 8 – 8
physical dimensions 8 – 3
pin designations 8 – 3
specifications 8 – 11
temperature 8 – 8
Prepolarized Free-field 1/2" Microphone Type
4188 2 – 1
Prepolarized Free-field 1/2" Microphone Type
4189 3 – 1
Pressure
BE 1382 – 12
ambient
4188, prepolarized microphone 2 – 25
4189, prepolarized microphone 3 – 25
4190, free-field microphone 4 – 25
4191, free-field microphone 5 – 25
4192, pressure-field microphone 6 – 25
4193, pressure-field microphone 7 – 28
Pressure-field 1/2" Microphone Type 4192 6 – 1
Pressure-field frequency response
4189, prepolarized microphone 3 – 13
4190, free-field microphone 4 – 12
4191, free-field microphone 5 – 12
4192, pressure-field microphone 6 – 12
4193, pressure-field microphone 7 – 14
R
Rain cover 9 – 2
Random-incidence frequency response
4188, prepolarized microphone 2 – 12
4189, prepolarized microphone 3 – 12
4190, free-field microphone 4 – 11
4191, free-field microphone 5 – 11
4192, pressure-field microphone 6 – 11
4193, pressure-field microphone 7 – 13
Range, dynamic
4188, prepolarized microphone 2 – 16
4189, prepolarized microphone 3 – 15
4190, free-field microphone 4 – 14
4191, free-field microphone 5 – 14
4192, pressure-field microphone 6 – 14
4193, pressure-field microphone 7 – 16
Recalibration
4188, prepolarized microphone 2 – 4
4189, prepolarized microphone 3 – 5
4190, free-field microphone 4 – 5
4191, free-field microphone 5 – 5
4192, pressure-field microphone 6 – 5
4193, pressure-field microphone 7 – 5
Resistance
leakage
4188, prepolarized microphone 2 – 21
4189, prepolarized microphone 3 – 21
4190, free-field microphone 4 – 21
4191, free-field microphone 5 – 21
4192, pressure-field microphone 6 – 21
4193, pressure-field microphone 7 – 24
Response, frequency
actuator
4188, prepolarized microphone 2 – 6
Falcon™ Range of Microphone Products
Microphone Handbook
Index – 5
Index
4189, prepolarized microphone 3 – 7
4190, free-field microphone 4 – 7
4191, free-field microphone 5 – 7
4192, pressure-field microphone 6 – 7
4193, pressure-field microphone 7 – 9
free-field
4188, prepolarized microphone 2 – 8
4189, prepolarized microphone 3 – 9
4190, free-field microphone 4 – 9
4191, free-field microphone 5 – 9
4192, pressure-field microphone 6 – 9
4193, pressure-field microphone 7 – 10
low-frequency
4188, prepolarized microphone 2 – 7
4189, prepolarized microphone 3 – 8
4190, free-field microphone 4 – 8
4191, free-field microphone 5 – 8
4192, pressure-field microphone 6 – 8
4193, pressure-field microphone 7 – 10
optimized
4188, prepolarized microphone 2 – 6
4189, prepolarized microphone 3 – 7
4190, free-field microphone 4 – 7
4191, free-field microphone 5 – 7
4192, pressure-field microphone 6 – 7
4193, pressure-field microphone 7 – 7
pressure-field
4189, prepolarized microphone 3 – 13
4190, free-field microphone 4 – 12
4191, free-field microphone 5 – 12
4192, pressure-field microphone 6 – 12
4193, pressure-field microphone 7 – 14
random-incidence
4188, prepolarized microphone 2 – 12
4189, prepolarized microphone 3 – 12
4190, free-field microphone 4 – 11
4191, free-field microphone 5 – 11
4192, pressure-field microphone 6 – 11
4193, pressure-field microphone 7 – 13
resolution
4188 prepolarized microphone 2 – 6
3–7
4189 prepolarized microphone 3 – 4,
4–7
4190 free-field microphone 4 – 4,
5–7
4191 free-field microphone 5 – 4,
6–
4192 pressure-field microphone 6 – 4,
7
4193 pressure-field microphone
7 – 4,
7–
S
Sensitivity
loaded
4188, prepolarized microphone 2 – 4
4189, prepolarized microphone 3 – 5
4190, free-field microphone 4 – 5
4191, free-field microphone 5 – 5
4192, pressure-field microphone 6 – 5
4193, pressure-field microphone 7 – 6
open-circuit
4188, prepolarized microphone 2 – 4
4189, prepolarized microphone 3 – 5
4190, free-field microphone 4 – 5
4191, free-field microphone 5 – 5
4192, pressure-field microphone 6 – 5
4193, pressure-field microphone 7 – 5
Sound Pressure Level
maximum
4188, prepolarized microphone 2 – 18
4189, prepolarized microphone 3 – 17
4190, free-field microphone 4 – 16
4191, free-field microphone 5 – 16
4192, pressure-field microphone 6 – 16
4193, pressure-field microphone 7 – 20
Specifications overview
2669, preamplifier 8 – 11
4188, prepolarized microphone 2 – 28
4189, prepolarized microphone 3 – 28
4190, free-field microphone 4 – 28
4191, free-field microphone 5 – 28
4192, pressure-field microphone 6 – 28
4193, pressure-field microphone 7 – 31
Stability
long-term
4188, prepolarized microphone 2 – 22
4189, prepolarized microphone 3 – 22
4190, free-field microphone 4 – 22
4191, free-field microphone 5 – 22
4192, pressure-field microphone 6 – 22
4193, pressure-field microphone 7 – 25
mechanical shock
4188, prepolarized microphone 2 – 21
4189, prepolarized microphone 3 – 21
4190, free-field microphone 4 – 21
4191, free-field microphone 5 – 21
4192, pressure-field microphone 6 – 21
4193, pressure-field microphone 7 – 24
7
Index – 6
Falcon™ Range of Microphone Products
Microphone Handbook
Brüel & Kjær
Index
T
Temperature
2669, preamplifier 8 – 8
4188, prepolarized microphone 2 – 22
4189, prepolarized microphone 3 – 22
4190, free-field microphone 4 – 22
4191, free-field microphone 5 – 22
4192, pressure-field microphone 6 – 22
4193, pressure-field microphone 7 – 26
Turbulence screen 9 – 2
V
Vibration
4188, prepolarized microphone 2 – 27
4189, prepolarized microphone 3 – 27
4190, free-field microphone 4 – 27
4191, free-field microphone 5 – 27
4192, pressure-field microphone 6 – 27
4193, pressure-field microphone 7 – 30
Volume
calibrator load
4188, prepolarized microphone 2 – 19
4189, prepolarized microphone 3 – 19
4190, free-field microphone 4 – 18
4191, free-field microphone 5 – 18
4192, pressure-field microphone 6 – 18
4193, pressure-field microphone 7 – 22
equivalent
4188, prepolarized microphone 2 – 19
4189, prepolarized microphone 3 – 18
4190, free-field microphone 4 – 17
4191, free-field microphone 5 – 17
4192, pressure-field microphone 6 – 17
4193, pressure-field microphone 7 – 20
W
Windscreens
BE 1382 – 12
9–2
Falcon™ Range of Microphone Products
Microphone Handbook
Index – 7
Index
Index – 8
Falcon™ Range of Microphone Products
Microphone Handbook
Brüel & Kjær