in-situ production test car audio systems - aes.org production test of car audio systems , 5 causes...

In-situ Production Test of Car Audio Systems , 1

In-situ Production Test

of

Car Audio Systems

Tutorial

AES 2017 International Conference

on Automotive Audio

Stefan Irrgang

KLIPPEL GmbH, Dresden, Germany


Scope

• „In-Situ“:

in situ may describe the way a measurement is

taken, that is, in the same place the phenomenon

is occurring without isolating it from other systems

or altering the original conditions of the test. (Wikipedia)

• Production Test: 100% testing

• Car Audio System:

Complete chain: Source, Processing, Amp,

Speaker, Enclosures, Radiation


Car Production EOL test

Headunit

Balance / Fader

LF RF

RRLR

Control

Commands

window buzz

grill

buzz

Needs from market:

• More bass

• More channels

• Higher level

Problem:

Parasitic vibrations:

Very annoying

Easy detectable

Related to product

quality / reputation

Complains are

expensive


Why End-Of-Line Testing?

Basic Goal Separate defect units from delivered goods

simple PASS/FAIL decision using limits

Ultimate Goal Avoid manufacturing of defect units

use diagnostics to get meaningful characteristics used as feedback in controlling the production process and life cylce


Causes of Critical Defects

Headunit

Balance / Fader

LF RF

RRLR

Control

Commands

window buzz

grill

buzz

Survey: 1. Mounting

• Speaker • Panels • Plastic Clips

2. Parts

• Speaker • Enclosure • Sub-Assemblies

Supplier test is not sufficient!


Input

Signal

Output

Signal

Desired

SystemNoise

Defects

StimulusMeasured

Signal

Undesired Defects • Buzzing panels

• Cable beat

• Loose particles

• Air leak noise

Designed Performance • Frequency Response

• Directivity

• Non-linear Distortion

Reproduced Sound Quality Generation of Signal Distortion in an Audio System

Non-correlated signals • Production noise

• Sensor noise

• Car noise (engine, AC)


Left Audio

Channel

Engine

RightAudio

Channel

Excitation of Parasitic Vibration by the Mechanical Transfer Path

loudspeaker

car engine

tire-road

Excitation by

mechanical

Vibration

Sources depend on

• distance between

source and

resonators

• audio channel (left,

right)

independent of

• size of the resonator grill buzz


Excitation of Parasitic Vibration via Acoustical Transfer Path

Left

Audio

Channel

Engine

Right

Audio

Channel

car engine

Excitation by Sound Pressure

Sources

all

loudspeakers

tire-road

interial panel

door buzz

depend on

• size of the resonator

• total sound pressure

independent of

• distance of source

and resonator

• audio channel (left,

right)


Loose Panel: Buzz problem

Most defects behave as a nonlinear oscillator

• active above a critical amplitude

• powered and synchronized by stimulus Loose joint

(Nonlinearity)

parasitic resonator

Externally excited

spring

mass

Loose joint

(Nonlinearity)

parasitic resonator

Externally excited

spring

mass

time one period

vibration

distortion signal


Re-Design

Production

Testing

Problem?

Subjective or Objective Testing?

PASS

FAIL

OR


Human Testing at the Assembling Line? Consequences

• Protect and avoid fatigue of the human ears

• regular breaks • low SPL

• Need for trained operators

• should be more sensitive than the end user

• Need for sufficient time for human inspection • flexible and long cycle times

• Good for double check at sample basis • Use off-line diagnostics station

Human testing is expensive, not critical, not reliable since highly subjective !


Objective Measurement

Techniques


Evaluation in Target Application Condition (in-situ)

Head-

unit

~

audio

signal

amplifier

u, i

microfone

wooferparasitic vibration

u, i

amplifier

internal

sound

sourcesambient

noise

Instrument

(R&D)

artificial test

signal

Instrument

(QC)

Field Measurements • applicable to all units

• ordinary audio signals (music)

• external sound sources

• using hardware in car

• operated by end-user

Lab R&D Measurements • prototypes + Samples

• not time critical

• optimal lab conditions

• using separate equipment

(artificial head, analyzer, ...)

• operated by engineer

EOL Measurements • applicable to all units

• as fast as possible

• external sound sources

• using hardware in car

(+ test microphone)

• automated


State of the Art 100% EOL

Extremely heterogenous:

• Nothing

• rely on manufacturing process stability

• Subjective

• each car driven by test driver, also testing sound

• Objective

• Electrical:

• Field Diagnostics: Connection only

• Acoustic:

• Single Tone Tests: Connection only

• Multitone Tests: Response, Level, Distortion, Phase

• „burned fingers“ with rattling detection


How to check Audio Systems?

Electrical Measurement • Simple current and voltage sensor

• Can be implemented as a diagnostic system in the audio amplifier

• Fast diagnostics of each transducer possible

• Full ambient noise immunity

• Poor detection of defects (no feedback from mechanics)

Acoustical Measurement • Test microphone in car interior required

• Ambient noise may corrupt measurement

• Detection of defects (Rub&Buzz, door buzzing)

advantage

disadvantage


What can be measured with

electrical tests? Linear Distortion • Impedance • Thiele / Small Parameter (Re, fs)

Regular Distortion (caused by Nonlinearities) • Coil offset • Stiffness asymmetry • Polarity from inductance (ANC!)

Defects (Irregular Distortion) • Loose connections

EOL relevant


What can be Measured with

Acoustical Tests?

Linear Distortion • Frequency Response • Sensitivity / Level • Phase / Delay / Polarity

Non-linear Distortion • Harmonic Distortion • Intermodulation Distortion (R&D)

Irregular Distortion (Defects) • Parasitic vibration (Buzz) • Loose Particles / Parts • Air Leakage

EOL relevant


Frequency Response Test Tweeter disconnected

KLIPPEL

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90

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110

102 103 104

Soun

d P

ress

ure

[dB]

Frequency [Hz]

Frequency Response QC-Frequency Response

Acoustically significant, distinct symptom


Frequency Response Test Mat in front of speaker

KLIPPEL

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60

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85

90

95

102 103 104

Sou

nd P

ress

ure

[dB

]

Frequency [Hz]

Frequency Response with Mat

Acoustically not significant, no Rub&Buzz

EQU Tuning test?


• Ensure consistent excitation

• Adjust level in car to target value (94dB SPL)

• Define allowed deviation (+/- 0.5dB)

• Cope with different interiors

• Use existing EQU tuning (Level only)

• Repeated tests required

Volume

Control

Test

microphone

Level Alignment Automatic Adjustment of Average Level


Optimal Stimulus For Testing

Signal Stimulus Output

1V

Output

2V

Output

3V

Music

Multi-Tone

20 Hz – 20 kHz

Multi-Tone

20 Hz – 1 kHz

Sinussoidal Sweep

1 s

Most critical Stimulus

Open question: Which stimulus excites most defects?


Optimal Signal Analysis

Symptoms of Impulsive distortion • generate new spectral components at harmonics and between

• cover wide frequency range (up to 40 kHz)

• are masked by fundamental and low-order harmonics

• have low spectral energy (close to the noise level)

cannot be detected by conventional Analysis (e.g. THD)

fundamental SPL

frequency

Sound Pressure Spectrum

Regular distortion

2nd

3rd

4th Symptoms of defects

-80 dB

noise level noise


Time Domain Analysis

SPL

frequency

fundamental

Regular distortion

SPL fundamental

SPL fundamental fundamental

Regular distortion Regular distortion

FFT-1

rms-value

time

peak-value

phase spectrum

higher order

harmonics

360 deg

180 deg

0 deg

amplitude spectrum

Solution back to the time domain

• regular distortion generates low

crest factor

• most defects generate symptoms

with high crest factor

exploiting amplitude and phase of

higher-harmonics

peak value reveals small transients

(clicks)

High sensitivity for loudspeaker defects

and parasitic vibration


Speed

Problems: – Available measurement time limited – Positioning of external microphone in the car – Parasitic vibration of high-Q resonators need sufficient excitation – Measurements corrupted by ambient noise require a repetition of the test – Diagnostics of Multichannel systems

Solution: – Use internal (ANC, free speech) microphone – Mobile (wire-less) microphone – As short as possible - excitation with optimal sweep peed profile – Parallel signal processing and failure detection – Automatic repetition of invalid measurements – Minimize number of test clusters (masking effects)

Typical Single Sweep Test including processing: 1s


Measurement Without Defect

Left

Right

L+R


Measurement With Defect


Left

Audio

Channel

Engine

Right

Audio

Channel

OUT1 OUT2 MIC1 LINE1 LINE2 MIC2

Production Analyzer

Ambient Noise

Source

Test

Microphone

Defect

Source

Problem:

• Defect symptom can be 60-80dB below fundamental

• Noise is always present in plant

• More sensitive test more false rejects

Robustness in Production Environment?


Noise Attenuation by Car Body

0

5

10

15

20

25

30

35

40

45

10 2 10 3 10 4

Upper Class

Medium-Sized

Compact Class

Frequency [Hz]

Att

enuatio

n [dB

]

• Not sufficient for

sensitive Buzz

detection

• No compensation

technique

applicable

Noise Detection

required!


Reliable Detection of Invalid

Measurements

Solution:

1. Using a 2nd microphone (outside)

2. Predicting the effect at the test microphone (inside)

3. Applying the same analysis to test and to noise signal

4. Comparing the symptoms and detecting a corruption of the test signal

Left

Audio

Channel

Engine

Right

Audio

Channel

OUT1 OUT2 MIC1 LINE1 LINE2 MIC2

Production Analyzer

Ambient

Noise

Source

Noise

Microphone

Test

Microphone

Results: PASS, FAIL, NOISE (corrupted)


Merging Technique repeating measurement automatically and accumulating valid parts

Ambient noise disturbances

28 % valid

85% accumulated

62% accumulated

100% valid

Full immunity against random noise

A simple repeat in case of FAIL is NOT optimal!


Door Buzzing and Simulated Noise

ambient

noise

source

test microphone inside the car

Progress in Data Acquisition

fundamental

rub and buzz


EOL Test Implementation

Stimulus connections:

1. None: Stored in Headunit / Amp

2. Cables (diagnostics station only)

3. Digital Audio Stream (automotive bus)

4. Asynchronous stimulus (CD, USB, Bluetooth with Synchronization)

5. FM-Transmission

6. Wireless Audio Transmission

Processing:

1. External Test-PC

2. Internal Portable Test-PC

3. Headunit (low MIPS demand)

4. Cloud (wave file based)

Microphone connections:

1. None: Internal mic

2. Cables (diagnostics station only)

3. Wireless Audio Transmission

Headunit

USB

Ambient Noise

Microphone

CD Player

Audio

Interface

OBD

AUX in

Test

PC

Production

Master

Control

Test Mic

In Car

Wireless

In / Out

FMFile

../../../../audiofiles/videos for demo/QC car/ni pass.wmv


Statistics

• Monitor long term characeristics

• Ensure Process Stability

• Combine all measures

• Find and remove outliers

• Predict Yield for changed limits

• Determine Golden DUTs

• Calculate reliable limits

Frequency response

Average level


Online Process Control Rules

• Nelson & WECO rules – simple and common tool to check if process is under control

• Control charts – time course of scalar results (e.g. Re, fs…) based on statistical spread and moving average of past results

Upper Control

Limit

Lower Control

Limit

fs

1σ

2σ

3σ

Example: resonance frequency shows trend of six increasing values in a row


Quantitative Measures

Process capability ratio

Estimates if process is capable of producing within specification limits (LSL/USL)

LTpkpkpp withCPCP ,If process is out of control:

use process performance

2pkC

e.g. standard normal

distribution,

6σ specification:

%9999998.99)6(

DPMO002.0

6

LSLUSLCp

3,

3min

LSLxxUSLCpk

If process is off center:

?


Exploit Statistics

• Analyze large data

pools

• Filter data pool

(e.g. outliers)

• Calculate limits based

on mean or imported

reference

• Export to EOL Test

system

Cu

rve

Sta

tist

ics

...

KLIPPEL

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102 103 104

So

un

d P

ressure

[d

B]

Frequency [Hz]

KLIPPEL

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90

102 103 104

So

un

d P

ressure

[d

B]

Frequency [Hz]

new limits

log data

QC

tes

tin

g

KLIPPEL

PASSFrequence

Response

Polari ty

THD

2nd Harmoni c

3rd Harmonic

Im pedance

Re

fs


Root Cause Analysis

• Based on statistical clustering

• Assisted root cause analysis based on objective testing data

• Immediate and automatic classification – Optimize production

process to increase yield

– Feedback for R&D department improve design


Fe

atu

re 1

(

Re

)

Feature 2 (fs)

Clustering of the Tests

Fe

atu

re 1

(

Re

)

Feature 2 (fs)

Prototype

P2

P1

P3

P4

P5

Volume (deviation)

Similarity (distance)

Clustering:

- Statistical process of

separating DUTs

- Building subgroups /

classes

- DUTs in one cluster have

similar properties

- DUTs of other cluster

have distinct differences

- Prototypes represent

cluster best


Measurement

FAIL

PASS/FAIL

DetectionSelection

PASS

On-Line Off-Line Root

Cause

On-Line

Diagnostics

Clustering

Knowledge

Base

Prototype

Selection

Diagnostics

Station

Tagging

Prototypes

1st step: Automatic clustering of the raw data

2nd step: Prototype selection (best representative of the cluster)

3rd step: Human inspection and tagging of the defect

4th step: Updating the knowledge base for on-line diagnostics

Root Cause Analysis Automatic Defect Classification


Clustering of cars

Raw Measurement Data (79 cars)

KLIPPEL

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80

90

100

110

10 2 10 3 10 4

Sound P

ressure

[d

B]

Frequency [Hz]

SPL Fundamental

Rub & Buzz

20

30

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50

60

70

80

90

100

10 2 10 3 10 4

Sound P

ressure

[d

B]

Frequency [Hz]

KLIPPEL

3 Door

Std. Audio

3 Door

Std. Audio

3+5 Door

High

Level Audio

3+5 Door

High Level Audio

5 Door, Std. Audio

(low Buzz)

5 Door, Std. Audio (low Buzz)

Test of running production:

• 79 cars total

• All cars passed current EOL

• Subtypes:

3 & 5 door Compact

cars

Standard / High Level

Audio System

5 Door, Std. Audio (high Buzz)

5 Door, Std. Audio

(high Buzz)


Operator View

Defect Class with highest rank

Overall Verdict

Classification Details • List of all possible classes incl.

membership value (probability, max. 1.0)

Car Production Test Classification (On-Line)


Results of Root Cause Analysis

Re-Design

Production

Testing

Production Lot

Golden units

Golden Defects

Defect

Classification


Auralization

Listening Tests

Perceptual Analysis

Objective Measurements


Basic Idea of Auralization

• Sdis>0 dB Distortion emphasized

• Sdis<0 dB Distortion attenuated

• Management: acceptable scaling of distortions

• Engineers: selection of critical stimulus

MIXER

SEPARATOR

xRef

ddis GD

Test Signal

1st input file

2nd input file -

d dis

Reference Car

Test Car

yAur

Output wave file


Audio Sdis/dB Signal

-∞ Reference (optimal quality)

-18

-15

-12

-9

-6

-3

0 Original test signal (current quality)

3

6

9

12

15

18

Systematic Listening Tests Audio Examples (Car Audio System)


Perceptual Evaluation Simulation of Human Auditory system

• Excitation patterns for auralization output

• Simultaneous and temporary masking

[ITU-R BS.1387]

Calculation of Meaningful Perceptual Metrics

• Distortion to mask ratio

• Loudness

• Treble stressing

• Bass enhancement

• Discoloration

• Roughness

• Modulation

• …


Limits

as tight as possible to get high quality

as wide as possible to reach maximal yield


Rub&Buzz limit (1/2) Spec definition

• „Hard“ limit that must not be violated

• Relative to average level „clearance“

• Consider headroom (defects are instable!)

• Collect Data first

• Start with relaxed limit

KLIPPEL

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40

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100

120

10 2 10 3 10 4

Sound P

ressure

[d

B]

Frequency [Hz]

Frequency Response Response Max

Response Min Rub+Buzz

Rub+Buzz Grades Max Rub+Buzz Max

Level Level

Avg. Level

Rub&Buzz

Limit

R&B Clearance

Rub&Buzz

Example:

R&B Headroom


KLIPPEL

20

40

60

80

100

120

10 2 10 3 10 4

S o u n d P

r e s s u r e

[ d

B ]

Frequency [Hz]

Rub&Buzz limit (1/2) Spec definition

• „Hard“ limit that must not be violated

• Relative to average level „clearance“

• Consider headroom (defects are instable!)

• Collect Data first

• Start with relaxed limit

Avg. Level

Rub&Buzz

Limit

R&B Clearance

Rub&Buzz

Example:

R&B Headroom


Rub&Buzz limit (2/2) Internal definition

• „Soft“ Limit for internal analysis

• Detect and analyse stray units

• Relative to reference car

KLIPPEL

20

40

60

80

100

120

10 2 10 3 10 4

Sound P

ressure

[d

B]

Frequency [Hz]

Frequency Response Response Max

Response Min Rub+Buzz

Rub+Buzz Grades Max Rub+Buzz Max

Level Level

• Consistency of production

• Use warning grades

• Record critical responses

Avg. Level

Rub&Buzz

Limit

R&B Specified

Clearance

Rub&Buzz

Rub&Buzz

Grades

Example:


How to tune limits

Left

Audio

Channel

Engine

Right

Audio

Channel

Database

End-of-line testing

Definition of

Production Limits

Off-line Processing

Root Cause

Analysis

Door Buzzing

SDIS = 24 dB SDIS = 12 dB SDIS = -6 dB SDIS = 0 dB SDIS = -12 dB

Test with sweep for loudspeaker

defects and parasitic vibration

Recording of reproduced music

stimulus if defect is detected Auralization +

Perceptive

Evaluation

Reference

Measurement

results

Music recordings

in defective cars

CLUSTER

ANALYSIS


Learning form End-of-Line Testing

Valuable information for Design and Manufacturing

R&D

Statistics

Production

Design Customer Pass

Automatic

Defect

Classification

Fail Re-Design

Production

Control

Golden

Defect Unit

Root Cause Analysis

Golden

Reference Unit


Summary

• Customers expect high quality

• 100% testing of the components is not sufficient

• Parasitic vibrations are most critical for sound quality

• Fast, reliable detection of defects can be provided in a noisy production environment

• Start with relaxed limits!

• Exploit EOL for root cause analysis (localization and detection of the cause) and process control

• Close the loop from production back to design


Thank you!

in-situ production test car audio systems - aes.org production test of car audio systems , 5 causes...

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