Instruction Manual
Sound Intensity Probe Type 50AI
G.R.A.S.
Sound & Vibration
Skovlytoften 33, 2840 Holte, Denmark
www.gras.dk
Sound-intensity Probe Type 50AI
Revision 6 June.2014
G.R.A.S. Sound & Vibration
CONTENTS
1.
Introduction and Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Main Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Microphones. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Preamplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Available Versions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.
Input Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.
Output Socket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.
Handling and Assembling the Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.
Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.1 Preamplifier Inputs A and B. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Sound-intensity Axis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1 Use with Power Module Type 12AB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1
4.2
4.3
4.4
4.5
5.1
5.2
5.3
5.4
5.5
5.6
The Microphones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Probe Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Physical Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Assembling the Probe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using the Windscreen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
All versions:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Version B. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Version C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Version D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Version HP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Version LD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
12
12
12
14
16
16
16
17
17
17
G.R.A.S. Sound & Vibration
1.
Introduction and Description
The Sound-intensity Probe Type 50AI (Fig. 1.1) is a two-microphone sound intensity probe. It
has a pair of G.R.A.S. phase-matched ½″ microphones Type 40AI (Fig. 1.2), two G.R.A.S. ¼″
microphone preamplifiers Type 26AA, solid spacers, remote control handle and connection
cable. The probe is adjustable, durable and fully complies with the following requirements:
• IEC 61043, Electroacoustics - Instruments for the Measurement of Sound Intensity - Measurements with Pairs of Pressure Sensing Microphones, 1993 for Class 1 Sound-intensity
probes.
Fig. 1.1 The Sound-intensity Probe Type 50AI
Sound-intensity Probe Type 50AI - Page 4
G.R.A.S. Sound & Vibration
1.1
Main Components
The main components of the Sound-intensity Probe Type 50AI are:
• Sound Intensity Microphone Pair Type 40AK
• Two Microphone Preamplifiers Type 26AA
• Four solid spacers of various lengths and a spacer cup (see Fig. 1.5)
• Remote-control handle with (where applicable) up to two push buttons for controlling measurements
See also Fig. 1.8.
The Type 50AI is delivered in a carrying case similar to the one shown in Fig. 1.2, complete with
microphones, preamplifiers, standard accessories and a remote-control handle.
Fig. 1.2 The type of carrying case delivered with the Type 50AI
1.1.1Microphones
The microphones (Fig. 1.3) are high sensitivity, free-field ½″ condenser microphones with a
uniquely-designed pressure equalization system that ensures extremely well defined phase
characteristics. The microphones and preamplifiers are mounted on the end of the telescopic
arm of the Remote-control handle. To cover the full frequency range from 50 Hz to 10 kHz, the
Type 50AI is delivered with four solid interchangeable spacers for spacing the microphones at
12 mm, 25 mm, 50 mm and 100 mm.
Sound-intensity Probe Type 50AI - Page 5
G.R.A.S. Sound & Vibration
Fig. 1.3
1.1.2
Showing similar pairs of phase-matched ½″ microphone cartridges
Above: Type 40AK, which includes spacers and three adapters for ¼″ preamplifiers as supplied with the Type 50AI.
Below: Type 40AI, which includes cartridges only
Preamplifiers
The small ¼″ diameter and 40 mm long microphone preamplifiers (Fig. 1.4) are housed in
robust, stainless steel casings which enable novel probe designs that reduce disturbances to
the sound field otherwise brought about by the effects of shadows and diffraction. Symmetry of
design enables reliable calibrations as described in the proposed standard (ISO/DIS 9614-2) for
sound power measurements using sound-intensity measurements.
Fig. 1.4 Pair of ¼″ Preamplifiers Type 26AA supplied with the Type 50AI
GR0040
RA0266
Spacer cup
12 mm spacer 25 mm spacer
RA0265
RA0264
RA0263
50 mm spacer
100 mm spacer
Fig. 1.5 Showing the various spacers and the spacer cup supplied with the Type 50AI
Sound-intensity Probe Type 50AI - Page 6
G.R.A.S. Sound & Vibration
1.2
Available Versions
Various versions of the Type 50AI are available for direct use with a wide range of general-purpose frequency analysers as well as specialised sound intensity analysers. Fig. 1.6 shows the
main external features of the various versions.
Type 50AI version B
Has built-in remote-control functions for direct connection to, and control of, sound-intensity
measuring systems from a wide range of suppliers such as 01dB, Müller-BBM and NeutrixCortex.
Can be used directly with the G.R.A.S. Intensity Module Type 12AB (see also section 3.1),
which provides all necessary voltages for the remote-control functions and powering the preamplifiers.
The Intensity Module Type 12AB (which is battery-operated) has two standard BNC output
sockets for connecting to analysers that don’t have special microphone-preamplifier inputs and
a 9-pin D-sub socket wired up for connecting directly to the RS232 port of a computer (Fig. 3.2);
thus enabling software to be controlled by the remote control facilities of this version of the
Sound-intensity Probe.
Use with the Type 12AB enables direct use with 01dB Sound Intensity systems.
Type 50AI
version B
version D
version LD
Type 50AI
version HP
Type 50AI
version C
Fig. 1.6 Showing the markings and external features on the remote-control handles of the various
versions of the Type 50AI
Sound-intensity Probe Type 50AI - Page 7
G.R.A.S. Sound & Vibration
Type 50AI version C
Can be connected directly to any analyser with two standard 7-pin LEMO microphone-preamplifier inputs.
Can be used with the following G.R.A.S. Power Modules, which provide all necessary voltages
for powering the preamplifiers:
• Intensity Module Type 12AB (see description above under version B)
• Power Module Type 12AA
(via the included adapter cable AC0003, which splits the output from a 12-pin LEMO socket
into two 7-pin LEMO plugs)
The Power Module Type 12AA (which is battery-operated) has two standard BNC output sockets for connecting to analysers that don’t have special microphone-preamplifier inputs.
Type 50AI version D
Similar to version B but uses an internal 9-V battery (already fitted on delivery) for enabling its
remote-control functions. Fig 1.7 shows how to gain access to the battery.
Type 50AI version HP
Has built-in remote-control functions for direct connection to, and control of, Hewlett-Packard
analysers such as the types HP 3569A and HP 35670A Opt UK4.
Both of these analysers will support the LEDs marked OVERLOAD and MEASURING as well as
the control button marked START/GATE.
Type 50AI version LD
Has built-in remote control functions for direct use and control of Larson Davis analysers such
as the types LD2900 and LD3000.
Unscrew and
remove
Slide cover
back
Fig. 1.7 Access to the 9 -V battery located inside the remote-control handle of the
Type 50AI version D. The battery should be disconnected / reconnected while inside the remote-control handle
Sound-intensity Probe Type 50AI - Page 8
Pair of RA0001
Right-angled adapters
RA0003
Straight adapter
Preamplifier inputs
GR0040
Spacer cup
RA0266
12 mm spacer
RA0265
25 mm spacer
Type 40AI
Pair of phase-matched ½″ microphones
Telescopic arm
Fig. 1.8 Showing the main components of the Sound-intensity Probe Type 50AI prior to assembly
Pair of Type 26AA
¼″ preamplifiers
Swivel head
RA0264
50 mm spacer
Remote-control buttons
RA0263
100 mm spacer
Output socket
G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 9
G.R.A.S. Sound & Vibration
2.
Input Channels
The Type 50AI has two input channels, one
for each microphone preamplifier. The channels are marked A and B on the remote-control
handle, see Fig. 2.1.
2.1
Input for channel A
Input for channel B
Preamplifier Inputs A and B
A and B refer to the two channels of the probe.
Channel A is reserved for the leading microphone, i.e. the microphone first struck by an
acoustic wave front (see Fig. 2.2). When this
happens, this should be interpreted as a positive component of the sound intensity in the
direction from microphone A to microphone B.
2.2
Sound-intensity Axis
Fig. 2.2 illustrates the origin and direction of
positive sound-intensity vectors. This positive
direction is always from microphones A to B.
The origin of the sound-intensity axis lies on the
geometric centre of the pair of probe microphones.
Markings for channels A and B
Fig. 2.1 Showing the inputs and markings for the two preamplifier inputs
Sound-intensity Probe Type 50AI - Page 10
G.R.A.S. Sound & Vibration
A
leading mic.
B
trailing mic.
Type 40AK pair
A
B
+
Direction
of positive
intensity
Origin of intensity axis
Fig. 2.2 Showing the microphones ‘A’ and ‘B’ which correspond with channels A and B respectively. ‘A’ is the leading microphone and is struck first by a
sound wave
Sound-intensity Probe Type 50AI - Page 11
G.R.A.S. Sound & Vibration
3.
Output Socket
The pin connections of the LEMO output socket at the base of the Type 50AI are shown in
Fig. 3.1. The four inner pins, i.e. 9, 10, 11 and 12 are for enabling a dialogue between a user
and an analyser/computer via an RS232 port. They are used to:
a)Transmit the state (pressed/not pressed) of the two push buttons on the handle of the Type
50AI
When pressed:
the blue button transmits Data Set Ready
the grey button transmits Clear To Send
b)Signal the responses via the two LEDs also on the handle of the Type 50AI
When lit:
the red LED is signalling Request To Send
the white LED is signalling Data Terminal Ready
By suitably programming the analyser’s/computer’s software, measurements and data acquisition can be controlled interactively via the push buttons and LEDs.
Fig. 3.1 12-pin LEMO female socket 1B (external view). The four inner pins are for connecting directly to an RS232 computer port
3.1
Use with Power Module Type 12AB
If the Type 50AI is used with a G.R.A.S. Power Module Type 12AB, pins 9, 10, 11 and 12
(Fig. 3.1) automatically have an outlet via the RS232 port of the Type 12AB (see Fig. 3.2) for
further connection to an analyser/computer.
Fig. 3.2 9-pin female D-sub connector socket of the Power Module Type 12AB for connecting directly to an RS232 computer port (external view)
Sound-intensity Probe Type 50AI - Page 12
G.R.A.S. Sound & Vibration
4.
Handling and Assembling the Probe
4.1
The Microphones
The Microphones Type 40AI (Fig. 1.3) are a pair of special free-field microphones with
extremely well-controlled phase characteristics. They are delivered as a matched pair each with
individual calibration data as well as data on differences between their phase responses.
These microphones have a unique pressure equalisation system which ensures a well defined
lower-limiting frequency and an extremely low sensitivity to sound pressures at the pressure
equalisation channels. Therefore, they can be calibrated in single-port phase calibrators such as
the G.R.A.S. Intensity Calibrator Type 51AB.
4.2
Probe Design
The design of the Sound-intensity Probe minimises acoustic reflections and the influence of
diffraction. This has been achieved by removing any physical, reflective components from the
sound path at 0° incidence. Since sound waves at 0° incidence are the main contributors to the
total sound intensity level, it is important that disturbances in this direction be minimised.
The thin, 2 mm diameter preamplifier cables will have no influence on the sound field since they
constitute a highly irregular surface with negligible reflections. The effects of acoustic diffraction
and reflection from the physical parts of the Sound-intensity Probe are below 0.15 dB.
Microphones are supplied as pairs (Type 40AI) or as sets (Type 40AK) which include spacers
and three preamplifier adapters (two right-angled and one straight).
The distances between microphones and preamplifiers have been kept to a minimum in order
to avoid problems with any stray capacitance and sensitivity to vibration. While amplitude
characteristics are little influenced, the phase characteristics of a Sound-intensity Probe can
be critically affected by even very small vibrations in the conductors carrying the raw signals
from the microphones. Therefore, the ¼″ preamplifiers are mounted in rigid contact with the ½″
microphones via short adapters (right-angled and/or straight). This also eliminates problems
with non-matching capacitances between microphones and preamplifiers, which could give rise
to phase problems.
4.3
Physical Strength
From a physical point of view, a Sound-intensity Probe should be robust and easy to assemble
and dismantle. Typically, there are two points in a Sound-intensity Probe which can be identified as critical for physical strength and are the most likely to suffer damage and are the most
difficult to repair. These points are the threads on microphones and preamplifiers as well as on
the microphones’ protection grids. The connections between microphones and preamplifiers are
very delicate and carry both microphone signals and microphone polarisation voltages. Therefore, the preamplifier threads of the Type 50AI are supported by stainless steel ½″ to ¼″ adapters. There is also a protective guard within the ¼″ housing of each preamplifier. In addition, the
microphones’ protection grids are made of stainless steel to withstand rough physical treatment
since a buckled or damaged protection grid will almost invariably damage a microphone’s diaphragm beyond repair.
4.4
Assembling the Probe
The Sound-intensity Probe can be assembled in either a straight configuration or a symmetrical configuration The straight configuration (Fig. 4.1), is for intensity measurements close to
surfaces and general source location measurements. The symmetrical configuration (Fig. 4.2),
is ideal for sound power measurements, for example according to international standard ISO
9614-2 “Acoustics - Determination of sound power levels of noise sources using sound intensity” where a rotation test is required.
The probe on the Type 50AI consists of the parts shown in Fig. 4.4. Assemble as follows.
Sound-intensity Probe Type 50AI - Page 13
G.R.A.S. Sound & Vibration
1.Mount one of the microphones on the Right-angled adapter RA0001 and the other microphone on either the other Right-angle adapter for a symmetrical probe or on the Straight
adapter RA0003 for a straight-probe configuration.
Remove the yellow protection caps from the two Preamplifiers Type 26AA and mount the
microphone-adapter assemblies on the preamplifiers. Screw the Spacer cup GR0040
onto the protection grid of one of the microphones. Select an appropriate spacer (see
Fig. 5.1 for working frequency ranges) from the four supplied and screw this onto the
protection grid of the other microphone. In many cases, the 12 mm spacer RA0266 will
be appropriate and will cover the frequency range from 100 Hz to 6.3 kHz *.
Fig. 4.1 Straight setup using the 25-mm spacer
Fig. 4.2 Symmetrical setup using the 12-mm spacer
* According to the investigations of Jacobsen, Keith, and Krishnappa, diffraction effects at the intensity probe compensate for the insufficiencies of the finite difference approximation. The frequency range of intensity measurements may therefore be extended to frequencies up to 10kHz using ½″ probes with a 12 mm spacer.
Sound-intensity Probe Type 50AI - Page 14
G.R.A.S. Sound & Vibration
Pull apart
Push together
Fig. 4.3 Changing the spacer: Pull the two halves of the probe
apart, unscrew the spacer from the microphone grid, screw another spacer on and push the two halves of the probe together again.
2.Now assemble the probe head by pressing the free end of the spacer (mounted on the one
microphone) into the spacer cup mounted on the other microphone. To change the spacer,
in order to cover a different frequency range, dismantle the probe head by pulling the spacer
out of the spacer cup, unscrew the spacer and replace it with another one (see Fig. 4.3).
3.Mount the probe head by sliding one of the preamplifiers into the clamp (which can be locked
at angles of 0 °, 45 °, 90 °, 135 ° and 180 °) at the top of the telescopic arm and tighten the
finger screw (see the examples in Figs. 4.1 and 4.2). Connect the two preamplifiers to the
input connectors at the top of the tubes shown in Fig. 2.1. The left input connector is labelled
as channel A on the probe handle and the other input is labelled channel B. For the correct
sign of the intensity vector, the front, or leading microphone should be connected to input
channel A (see section 2.1).
4.Connect the probe to the analyser via the appropriate adapter cable (depending on the
specific type of analyser). The functions of the operating buttons and indicating LEDs on the
control handle are determined by the analyser in use and information about these should be
found in the instruction manual of the given analyser (see also sections 1.2 and 3.1).
4.5
Using the Windscreen
The Sound-intensity Probe Type 50AI includes an elliptical windscreen (AI0001) which can be
used whenever making outdoor measurements or when making indoor measurements in the
presence of bulk air movements. Use it only when measurements are influenced by wind. It
gives good protection at wind speeds greater than 0.5 m/s and can reduce pressure fluctuations
caused by turbulence by as much as 20 dB with this technique of intensity measurements.
Sound-intensity Probe Type 50AI - Page 15
G.R.A.S. Sound & Vibration
Straight
Symmetrical
Type 26AA
¼″ Preamplifier
RA0001
Right-angled adapter
RA0003
Straight adapter
Type 26AA
¼″ Preamplifier
RA0266
Spacer
GR0040
Spacer cup
Type 40AI
Matched pair of
microphones
RA0001
Right-angled adapter
Type 26AA
¼″ Preamplifier
Fig. 4.4 Exploded view of probe assembly. On the left: straight setup. On the right the branch for a
symmetrical setup
Sound-intensity Probe Type 50AI - Page 16
G.R.A.S. Sound & Vibration
5.
Specifications
5.1
All versions:
Sound-intensity microphone set Type 40AK comprising:
Matched pair ½″ mics.
Type 40AI
12 mm spacerRA0266
25 mm spacerRA0265
50 mm spacerRA0264
100 mm spacer
RA0263
See Fig. 5.1 for working frequency ranges
Preamplifiers:
Pair ¼″
Type 26AA
with 4-pin LEMO connector type FGG OB
Frequency response and phase matching:
IEC 1043 Class 1
Operating Temperature Range:
+5 °C to +40 °C
Weight:
0.4 kg (0.9lbs) Version B
Accessories included:
Windscreen 5.2
AI0001
Version B
Remote-control handle:
Built-in remote control functions for 01dB analysers. Two buttons for averaging control and two
LEDs for status indication and overload indication.
Accessories included:
5 m cableAA0021
Adapter cable
AC0002 (12-pin LEMO to 2 x 7-pin LEMO, plus remote- control male 6-pin mini DIN plug)
5.3
Version C
Remote-control handle:
General-purpose intensity handle with two 7-pin LEMO 1B output connectors.
Accessories included:
5 m cableAA0021
Adapter cable
AC0003 (12-pin LEMO to 2 x 7-pin LEMO)
Sound-intensity Probe Type 50AI - Page 17
G.R.A.S. Sound & Vibration
5.4
Version D
Remote-control handle:
Similar to version B but uses an internal 9-V battery for enabling its remote-control functions.
Accessories included:
5 m cableAA0021
Adapter cable
AC0005 (12-pin LEMO to 2 x 7-pin LEMO, plus remote- control female 9-pin D-sub plug)
5.5
Version HP
Remote-control handle:
Built-in remote control functions for Hewlett-Pakard analysers. One button for measurement
control. LEDs for status indication and overload indication.
Accessories included:
3 m cableAA0040
Adapter cable
AC0006 (12-pin LEMO to 2 x 7-pin LEMO, plus remote- control male 15-pin D-sub plug)
5.6
Version LD
Remote-control handle:
Built-in remote control functions for Larson Davies analysers (LD3000 or LD2900). One button
for measurement control. LEDs for status indication and overload indication.
Accessories included:
5 m cableAA0021
Adapter box AC0007 (for LD3000)
or
AC0004 (for LD2900)
Sound-intensity Probe Type 50AI - Page 18
G.R.A.S. Sound & Vibration
With ¼" Mics. Type 40BI and 6 mm spacer (RA0267)
12 mm (RA0266)
25 mm (RA0265)
d
50 mm (RA0264)
100 mm (RA0263)
10
100
1k
10k
100k
Frequency Hz
Fig. 5.1 Working frequency ranges covered by the various spacer lengths. The top bar is for the case when a Type
50AI is equipped with a pair of ¼″ intensity microphones (Type 40BI) and a 6 mm spacer (note the extend-
ed high-frequency range).
Manufactured to conform with:
CE marking directive:
93/68/EEC
WEEE directive:
2002/96/EC
RoHS directive:
2002/95/EC
G.R.A.S. Sound & Vibration continually strives to improve the quality of our products for our customers; therefore, the
specifications and accessories are subject to change.
Sound-intensity Probe Type 50AI - Page 19
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