QC – Air Leak Stethoscope (ALS)
S30
Module of the KLIPPEL QC SYSTEM (QC Version 5, Document Revision 1.2)
FEATURES
•
Detection and localization of
air leaks and other defects
•
Auralization of defect symptoms
•
Processing kernel from Air
Leak Detection (ALS)
•
Interactive operation
•
No reference DUT required
Air Noise
Hole
Leak
Coil
Rubbing
BENEFITS
•
Diagnostics of defective units
•
Ear protection
•
Subjective and objective
evaluation of defects
•
Root cause analysis
•
Operator training
Subjective
Evaluation
Port Noise
Objective
Testing
MODulation
DETerministic
Random
QC System
DESCRIPTION
The Air Leak Stethoscope is a powerful off-line diagnostics tool dedicated to detecting and localizing air leaks and other audible defects in audio systems of any kind and size. A hand-held “stethoscope” microphone is used to trace the place of origin of defect noise and distortion. Special signal processing is applied to assess and classify air noise and defect distortion. Additionally, the
isolated distortion signal is played back via headphones for subjective evaluation and ear protection.
The ALS is the interactive counterpart to the Air Leak Detection (ALD) on-line testing module
sharing the same signal processing kernel and distortion measures.
Article number
4000-243
CONTENT
1
Overview ........................................................................................................................................................ 2
2
Requirements ................................................................................................................................................. 3
3
Parameters and Results .................................................................................................................................. 4
4
Examples ........................................................................................................................................................ 4
5
References ...................................................................................................................................................... 6
6
Patents ........................................................................................................................................................... 6
QC – Air Leak Stethoscope (ALS)
1
1.1
1 Overview
S30
Overview
Principle
The ALS is designed for interactive defect detection and localization in loudspeakers and
audio systems. In order to stimulate air leakage noise and mechanical defects, the device
under test (DUT) is excited with low frequency tone ensuring high excursion and high
pressure in the enclosed air volumes (e.g. cabinet, dust cap).
The acoustical response is recorded with a hand-held microphone which is moved around
the DUT by the operator. Signal processing is applied to extract distortion components
which are used to calculate dedicated single value measures (MODulation, DETerminstic,
Random). A colour bar display indicates the distortion level in an intuitive way relative to
the acoustical background noise floor which is measured separately. No actual testing
limits based on reference units are required.
Additionally, the isolated distortion signal may be played back via the host PC’s audio
interface for subjective evaluation. Using insulated headphones, the operator’s ears are
protected while providing a listening sensitivity which is beyond the human hearing.
Please find more background information on the signal processing and definition of
measures in the specification S18 – Air Leak Detection (ALD).
1.2
Results
Measures
The ALS provides the same result
data as the Air Leak Detection
module:
•
•
•
MODulation (modulated
noise)
o MODabs (absolute)
o MODrel (relative)
DETerministic (deterministic
distortion)
o DETabs (absolute)
o DETrel (relative)
o DET(L)abs (absolute)
o DET(L)rel (relative)
Random (sporadic distortion)
The distortion levels of these measures are provided in the result table. However, the
main display is a colour bar diagram which displays the distortion levels qualitatively for
easy interpretation.
Auralization &
Wave Export
In order to evaluate defect distortion, the ALS
suppress the actual test tone and low order
harmonics in the sound pressure response. The
residual signal can be exported to a WAVE file
or immediately played back to the standard
audio device of the host PC. This makes it
possible to auralize defect symptoms with
enhanced sensitivity while protecting the ears
of harmful sound pressure levels.
QC System
Using this feature, the ALS can be operated in
order to localize defects without using the PC
monitor.
KLIPPEL QC System
Page 2 of 6
QC – Air Leak Stethoscope (ALS)
2
2.1
S30
2 Requirements
Requirements
Hardware
Scheme (Passive
DUT)
Leak
Test
Microphone
DUT
Ambient Noise
Microphone
(optional)
Auralization
PUSH
PUSH
Production Analyzer
I
0
FireWire
Power
USB
Digital I/0
Amplifier
Speaker 1
Speaker 2
OUT1
OUT2
MIC1
LINE1
LINE2
MIC2
USB
Amplifier
PUSH
Power
Components
•
•
•
•
•
•
Output
Input
KLIPPEL Production Analyzer
PC with audio interface (sound card)
Test microphone (“stethoscope”)
Optional: ambient noise microphone
Power amplifier (for passive systems only)
Optional: headphones (for auralization)
For more information about hardware requirements please refer to C3 QC Set.
2.2
Software
•
•
2.3
KLIPPEL QC Standard System
Air Leak Stethoscope license
Acoustics
Environment
The ALS does not have any specific acoustical requirements. Anechoic or insulated rooms
may improve performance due to lower background noise.
Ambient Noise
Sporadic disturbances are usually not critical for the ALS off-line application because the
measurement is performed repeatedly. However, the steady noise floor should be as slow
as possible.
However, using an additional ambient noise microphone, corrupted measurements can be
identified and the results invalidated. Please refer to S18 – Air Leak Detection (ALD) for
more information.
KLIPPEL QC System
Page 3 of 6
QC – Air Leak Stethoscope (ALS)
3
3.1
Setup Parameters (Selection)
STIMULUS
Time – Measurement time (incl.
preloop)
Frequency – Test tone frequency
Voltage (rms) – stimulus voltage
Measurement Results
Symbol
Min
Typ
Max
Unit

0.45
0.45
0.97
s
4
0
50
1
1000
200
Hz
V
test
�stim

Measured Name
Symbol
Unit
Modulated distortion (absolute)
MODabs
dB
Modulated distortion (relative)
MODrel
dB
Deterministic leak distortion (absolute)
DET(L)abs
dB
Deterministic leak distortion (deterministic)
DET(L)rel
dB
Deterministic distortion (absolute)
DETabs
dB
Deterministic distortion (relative)
DETrel
dB
Random
dB
Random Distortion
4
4.1
S30
Parameters and Results
Parameter
3.2
3 Parameters and Results
Examples
Production Offline Diagnostics of Multimedia Speakers
During the end-of-line test of multimedia
speakers, all DUTs are tested for Rub &
Buzz defects and air leakage using the KLIPPEL QC System (e.g. ALD).
Failed units are transferred to an off-line
diagnostics station which is equipped with
the ALS in order to localize the defect root
cause. The test signal may be played back
directly via Bluetooth or USB connection.
Leaky
Terminal
The example shown here shows a speaker
with leaky input terminal due to faulty
mounting.
MODulation
DETerministic
Random
Production Analyzer
OUT1
KLIPPEL QC System
OUT2
MIC1 LINE1 LINE2 MIC2
Page 4 of 6
QC – Air Leak Stethoscope (ALS)
4.2
S30
4 Examples
Inspection of Professional Speaker
The incoming goods inspection in a rental
company for professional audio products
(PA speakers, stage monitors…) is crucial to
identify damage due to ageing or misuse.
Defecitve
Surround
The ALS is a powerful tool to identify and
localize such defects easily. Using noise
insulated headphones the operator can test
the equipment at critical playback levels
with maximal sensitivity while protecting
the ears.
PUSH
PUSH
Production Analyzer
I
0
OUT1
MIC1
OUT2
LINE1
LINE2
MIC2
PUSH
Amplifier
Output
Input
4.3
Localization of Parasitic Vibration in Car Interior
After assembling the audio system in car
manufacturing, a short acoustical end-ofline test is performed focussing on mounting defects and parasitic vibration (speaker
induced buzzing).
In case the test failed, the ALS is used to
quickly localize the problem in the car interior for immediate repair.
OBD
AUX in
Headunit
grill
buzz
Ambient Noise
Mic Signal
(outside)
LF
RF
Audio
Interface
Stethoscope
Mic in Car
Test
PC
LR
RR
window buzz
KLIPPEL QC System
Production
Master
Control
Page 5 of 6
QC – Air Leak Stethoscope (ALS)
5
5 References
S30
References
5.1
Related Modules
•
•
•
C3 QC Set
S18 Air Leak Detection (ALD)
S22 DIF-AUR Difference Auralization
5.2
Manuals
•
•
Manual Air Leak Stethoscope
Manual Air Leak Detection
5.3
Publications
6
W.Klippel, R.Werner; “Measurement of Turbulent Air Noise Distortion in
Loudspeaker Systems”, J. Audio Eng. Soc., Vol. 59, No. 7/8, 2011 July/August
Patents
Germany
102009033614
USA
12/819,455
China
201010228820.8
Find explanations for symbols at:
http://www.klippel.de/know-how/literature.html
Last updated: March 29, 2017
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