acoustical measurement of sound system equipment according ...21/e… · of sound system equipment...
TRANSCRIPT
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KLIPPEL LIVE #9: Intermodulation Distortion, 1
Acoustical Measurement of Sound System Equipment
according IEC 60268-21
KLIPPEL LIVEa series of webinars presented by
Wolfgang Klippel
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KLIPPEL LIVE #9: Intermodulation Distortion, 2
1. Modern audio equipment needs output based testing2. Standard acoustical tests performed in normal rooms3. Drawing meaningful conclusions from 3D output measurement4. Simulated standard condition at an evaluation point5. Maximum SPL – giving this value meaning 6. Selecting measurements with high diagnostic value7. Amplitude Compression – less output at higher amplitudes8. Harmonic Distortion Measurements – best practice9. Intermodulation Distortion – music is more than a single tone10. Impulsive distortion - rub&buzz, abnormal behavior, defects11.Benchmarking of audio products under standard conditions 12.Auralization of signal distortion – perceptual evaluation 13.Setting meaningful tolerances for signal distortion14.Rating the maximum SPL value for a product15.Smart speaker testing with wireless audio input
Previous Sessions
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KLIPPEL LIVE #9: Intermodulation Distortion, 3
9th KLIPPEL LIVE:Intermodulation Distortion – music is more
than a single tone
Topics today:
• Physical causes for intermodulation distortion• Measurements according to IEC Standard 20268-21• Testing with a two-tone stimulus • Testing with a multi-tone complex• Interpretation of the results• Practical demos
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KLIPPEL LIVE #9: Intermodulation Distortion, 4
Poll:
Do you evaluate the intermodulation distortion ?A. No 23%B. Yes, by listening to music 23%C. Yes, by using a two tone stimulus 33%D. Yes, by using a multi-tone complex 20%E. Yes, by other ways 0%
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KLIPPEL LIVE #9: Intermodulation Distortion, 5
Bl-Distortion in Music
Undistorted music signal
High displacement required → signal below fs → bass signalIntermodulation with signal in audioband generate roughness when fs < 100 HzHigh impact on sound quality
Distortion generated by Bl(x) only
displacement
intermodulation
Harmonics
https://www.youtube.com/watch?v=pSTLM_vCAdU&feature=youtu.be
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KLIPPEL LIVE #9: Intermodulation Distortion, 6
What causes the IM Distortion ?
pre-filterH1,1(f)
1st state variable
multiplier
distortion
fsVoltagesound
pressurehighpass
Static Nonlinearity
pre-filterH1,2(f)
post-filterH2(f)
2nd state variable
Generalized Signal Flow Modeldescribing a separated nonlinearity
The multiplication of two different state variables generates unique intermodulation distortion !
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KLIPPEL LIVE #9: Intermodulation Distortion, 7
Causes for high IM-Distortion NONLINEARITY
INTERPRETATION
PRE-FILTER H1,1(f) (output)
PRE-FILTER H1,2(f) (output)
Stiffness Kms(x) of the suspension
restoring force Low-pass (displacement x)
Low-pass (displacement x)
Force factor Bl(x) electro-dynamical force Band-stop (current i)
Low-pass (displacement x)
nonlinear damping Band-pass (velocity v)
Low-pass (displacement x)
Inductance Le(x) self-induced voltage Band-stop (current i)
Low-pass (displacement x)
reluctance force Band-stop (current i)
Band-stop (current i)
Inductance Le(i) varying permeability Band-stop (current i)
Band-stop (current i)
Mechanical resistance Rms(v)
nonlinear damping Band-pass (velocity v)
Band-pass (velocity v)
Young’s modulus E(ε) of the material
cone vibration Band-pass (strain ε)
Band-pass (strain ε)
Speed of sound c(p) nonlinear sound propagation (wave steepening)
High-pass (sound pressure p)
High-pass (sound pressure p)
Time delay τ(x) nonlinear sound radiation (Doppler effect)
High-pass (sound pressure p)
Low-pass (displacement x)
Negligible THD
Negligible THD
Negligible THDf >2fs
Measurements of Intermodulation Distortion is important !
Nonlinearity
Interpretation
PRE-Filter H1,1(f)
(output)
PRE-Filter
H1,2(f)
(output)
Stiffness Kms(x) of the suspension
restoring force
Low-pass
(displacement x)
Low-pass
(displacement x)
Force factor Bl(x)
electro-dynamical force
Band-stop
(current i)
Low-pass
(displacement x)
nonlinear damping
Band-pass
(velocity v)
Low-pass
(displacement x)
Inductance Le(x)
self-induced voltage
Band-stop
(current i)
Low-pass
(displacement x)
reluctance force
Band-stop
(current i)
Band-stop
(current i)
Inductance Le(i)
varying permeability
Band-stop
(current i)
Band-stop
(current i)
Mechanical resistance Rms(v)
nonlinear damping
Band-pass
(velocity v)
Band-pass
(velocity v)
Young’s modulus E() of the material
cone vibration
Band-pass
(strain
Band-pass
(strain
Speed of sound c(p)
nonlinear sound propagation (wave steepening)
High-pass
(sound pressure p)
High-pass
(sound pressure p)
Time delay τ(x)
nonlinear sound radiation
(Doppler effect)
High-pass
(sound pressure p)
Low-pass
(displacement x)
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KLIPPEL LIVE #9: Intermodulation Distortion, 8
Sparse but Comprehensive Stimulus
Stimuli
Single-Tone
Two-Tone
Multi-Tone
Noise AudioSignal
complexity
Spectral Analysis
Total Distortion2nd-order3rd-order
Amplitude Phase Intermodulation Distortion
Harmonics of the two tones
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KLIPPEL LIVE #9: Intermodulation Distortion, 9
Intermodulation distortiongenerated by Two-tone Stimulus
difference tones summed tonesharmonics
frequency
Amplitude sound pressure spectrum
IntermodulationDistortion
3rd 3rd
nth
12 )1( fnf −−
nth
12 )1( fnf −+
2nd2nd
12 ff − 12 ff +
3rd2nd
12 f
nth
1nf
“bass tone”1f
“voice tone”2f
To simplify the identification of the components:• Keep large distance between the exciting tones f1 and f2
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KLIPPEL LIVE #9: Intermodulation Distortion, 10
IM-Distortion (two-tone signal)Definitions according IEC 60268-21
Second-order Modulation
(FM + AM)2 1 2 1
22
( ) ( )20lg( )IMD
p f f p f fLp f
− + +=
Third-order Modulation
(FM + AM)2 1 2 1
32
( 2 ) ( 2 )20lg( )IMD
p f f p f fLp f
− + +=
Total Modulation Distortion
(FM+ AM)
2
2 1 2 11
1 22
( ) ( )( , ) 20lg
( )k
TIMD
p f kf p f kfL f f
p f=
− + + =
∑
The IEC 60268-21 uses relative measures (IMD component divided by carrier )The relative IMD are similar to the equivalent input distortion because the frequency distance |f2-f1|
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KLIPPEL LIVE #9: Intermodulation Distortion, 11
Contribution of 2nd and 3rd-order Components to the total intermodulation distortion
KLIPPEL
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0
5
4*102 6*102 8*102 103 2*103 4*103 6*103 8*103
Modulation distortion (U1=1 V)
dB
Frequency f1 [Hz]
Ld2 Ld3 Ldm (cumul)
Total modulation
3rd order2nd order
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KLIPPEL LIVE #9: Intermodulation Distortion, 12
Sweeping the Two-Tone SignalHow to choose the frequencies ?
f1 f2
f1 f2
f1 f2
sweeping voice tone
sweeping bass tone
difference tone measurement
f1 f2
f2-f1=const.
f1=const.
f2=const.
Sweeping two tones f2/f1=const.
not very usefulExploit information for f2 ≠ f1 !!! f1
f2
20 kHz
20 kHz
20 Hz
20 Hz
f2/f1=const.
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KLIPPEL LIVE #9: Intermodulation Distortion, 13
Poll:How do you set the frequencies of the two tones in the stimulus for the testing ?A. None 41%B. Fixed setting two tones (f1 > f2) 19%C. Sweeping the Bass tone f1 (fixed f2 > f1) 9%D. Sweeping the voice tone f2 (fixed f1 < f2) 25%E. Sweeping two tone sweep with constant
frequency ratio f2/f1=const 13%F. Other 0%
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KLIPPEL LIVE #9: Intermodulation Distortion, 14
Setup for IMD in Sound Pressure bass sweep technique
Optimal Stimulus:Two-Tone stimulusVarying frequency of bass tone about resonance 0.5fs < f1 < 2fsConstant frequency of voice tone above resonance f2 =7fs
Requirement:2 sinusoidal generators, Spectrum analyzer
Bass tone f1
Loudspeaker~
FT
Microphone SpectrumAnalyzer
Amplifier
~voice tone f2
Amplitude response versus frequency f1 :
2nd-order IMD3rd –order IMD
frequency
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KLIPPEL LIVE #9: Intermodulation Distortion, 15
Causes of IMD in Sound Pressure Output using bass sweep technique
Cone Vibration
L(i)
Bl(x)
L(x)
Doppler Effect
L(i)
Bl(x)
L(x)
L(i)
Cone Vibration
Doppler
IMD%
fs
30
f1bass tone
voice tonef2=10fsdistortion is minimal
above fs
IMD generated by voice displacement
Kms(x) negligible
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KLIPPEL LIVE #9: Intermodulation Distortion, 16
Demo: Intermodulation Distortion2 tone stimulus with bass sweep
Tools of the KLIPPEL Analyzer: • 3D Distortion Measurement (DIS)
http://www.klippel.de/products/rd-system/modules/dis-3d-distortion-measurement.html
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KLIPPEL LIVE #9: Intermodulation Distortion, 17
Measurement of IMD in Sound Pressure voice sweep technique
Optimal Stimulus:Two-Tone stimulusVarying frequency of voice tone above resonance 5fs < f2 < 20fsConstant frequency of bass tone below resonance f1 < 0.5fs
Requirement:ALMA Test CD, 2 tone generators, Spectrum analyzer, Microphone
Bass tone f1
Loudspeaker~
FT
Microphone SpectrumAnalyzer
Amplifier
~voice tone f2
Amplitude response versus frequency f1 :
2nd-order IMD3rd –order IMD
frequency
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KLIPPEL LIVE #9: Intermodulation Distortion, 18
The Causes of IMD in Sound Pressure Outputvoice sweep technique
Cone Vibration (at maxima of AAL)
L(i) (rising with f2 )
Bl(x) independent of f2
L(x) (rising with f2 )
Doppler Effect (rising with f2 )
Bl(x)
L(x)
L(i)
Cone Vibration
Doppler
IMD%
f 220f s7f s
20 -
variable voice tone
fixedbass tonef2=0.5fs
independent of frequency
distinct frequencies
L(x) ,L(i) and Doppler
Bl(x)
Cone Vibration
Kms(x) negligible
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KLIPPEL LIVE #9: Intermodulation Distortion, 19
Demo: Intermodulation Distortion2 tone stimulus with voice sweep
Tools of the KLIPPEL Analyzer: • 3D Distortion Measurement (DIS)
http://www.klippel.de/products/rd-system/modules/dis-3d-distortion-measurement.html
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KLIPPEL LIVE #9: Intermodulation Distortion, 20
Sparse but Comprehensive Stimulus
Stimuli
Single-Tone
Two-Tone
Multi-Tone
Noise AudioSignal
complexity
Spectral Analysis
Time Domain Analysis EnvelopeCalculation
Phase Modulation
Amplitude Modulation
Total Distortion2nd-order3rd-order
Amplitude Phase Intermodulation Distortion
Harmonics of the two tones
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KLIPPEL LIVE #9: Intermodulation Distortion, 21
Amplitude Modulationtwo-tone stimulus f1 < fs, f2 > fs
-5,0
-2,5
0,0
2,5
5,0
0,05 0,10 0,15 0,20 0,25 0,30
Sound pressure Pfar(t) in far field vs time
Pfar [
N / m^2
]
Time [s]
Pfar(t)
SymmetricalForce factor
Bl(x)
Cycle
peak
Rest positionKLIPPEL
0,51,01,52,02,53,03,54,04,55,0
-5 -4 -3 -2 -1 0 1 2 3 4 5
Bl(x)[N/A]
[mm] x BottomMean
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KLIPPEL LIVE #9: Intermodulation Distortion, 22
-10,0
-7,5
-5,0
-2,5
0,0
2,5
5,0
7,5
10,0
0,08 0,09 0,10 0,11 0,12 0,13 0,14
Sound pressure Pfar(t) in far field vs time
Pfar [
N / m^2
]
Time [s]
without Doppler with Doppler
Phase (Frequency) Modulationcaused by Doppler Effect
-7,5
-5,0
-2,5
0,0
2,5
5,0
7,5
10,0
0,106 0,107 0,108 0,109 0,110 0,111 0,112 0,113
Sound pressure Pfar(t) in far field vs time
Pfar [
N / m^2
]
Time [s]
without Doppler with Doppler
Phase variation
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KLIPPEL LIVE #9: Intermodulation Distortion, 23
Phase of Intermodulation Distortion
Amplitude Modulation Frequency Modulation(Phase Modulation)
variationof envelope
12 ff − 12 ff +
phase variation
1f 2f
Lamplitude spectrum
2f
in-phase
12 ff −12 ff +
90 degree phase shift
2f12 ff −
12 ff +
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KLIPPEL LIVE #9: Intermodulation Distortion, 24
Audibility of Intermodulation DistortionJust-noticeable degree of amplitude modulation (AM) and just noticeable index of frequency modulation (FM) of a 1-kHz tone at 80 dB SPL, as a function of modulation frequency
„Bass tone“
Critical condition:modulation frequency of the „bass tone“ is sufficiently low (fB < 200Hz) the intermodulation
distortion are within a critical band rate
AM modulation (e.g. force factor distortion) are audible at 3 % and perceived as roughness
Threshold of FM modulation is 20 dB higher
Doppler distortion are not critical
„Voice tone“
fc = 1kHzLc = 80dB
100
%31.6
3.16
0.316
8 32 128 512
Modulation frequency fB
degr
ee o
f am
plitu
de m
odul
atio
n, m
inde
x of
freq
uenc
y m
odul
atio
n, n
AM
Zwicker, Fastl, 1999
FM
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KLIPPEL LIVE #9: Intermodulation Distortion, 25
IM-Distortion (two-tone signal)Definitions according IEC 60268-21
Second-order Modulation
(FM + AM)2 1 2 1
22
( ) ( )20lg( )IMD
p f f p f fLp f
− + +=
Third-order Modulation
(FM + AM)2 1 2 1
32
( 2 ) ( 2 )20lg( )IMD
p f f p f fLp f
− + +=
Total Modulation Distortion
(FM+ AM)
2
2 1 2 11
1 22
( ) ( )( , ) 20lg
( )k
TIMD
p f kf p f kfL f f
p f=
− + + =
∑
Amplitude Modulation
(AM only)∑=
=K
kkE
KE
1][1
( )%100*
][21
2
E
EkEK
d
K
kAMD
∑=
−=
=100
lg20 AMDAMDd
L
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KLIPPEL LIVE #9: Intermodulation Distortion, 27
Contribution of Amplitude Modulationto the total intermodulation distortion
KLIPPEL
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0
5
4*102 6*102 8*102 103 2*103 4*103 6*103 8*103
Modulation distortion (U1=1 V)
dB
Frequency f1 [Hz]
AM distortion (Lamd) Ldm (cumul)
Total modulation
AM modulation(force factor, inductance, cone vibration)
Doppler
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KLIPPEL LIVE #9: Intermodulation Distortion, 28
Demo: Amplitude Modulation2 tone stimulus with voice sweep
Tools of the KLIPPEL Analyzer: • 3D Distortion Measurement (DIS)
http://www.klippel.de/products/rd-system/modules/dis-3d-distortion-measurement.html
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KLIPPEL LIVE #9: Intermodulation Distortion, 29
Intermodulation Measurement using a Two-Tone Stimulus
Disadvantages:• Frequency of excitation tones have to be set carefully
Advantages:• Simple generation (by using two sinusoidal generators)• Separation of noise and distortion• Easy to interpret• Good for loudspeaker diagnostics in R&D• Sensitive stimulus also for listening tests
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KLIPPEL LIVE #9: Intermodulation Distortion, 30
Universal Stimuluscomplex, steady-state, like an organ tone
Single-Tone
Two-Tone
Multi-Tone
Noise AudioSignal
Spectral Analysis
complexity of the stimulus
sparse excitation
Amplitude and Phase response
Fundamental Components Multi-tone Distortion(harmonics, intermodulation)
some frequencies are not excited !!!
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KLIPPEL LIVE #9: Intermodulation Distortion, 31
KLIPPEL
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2 5 10 20 50 100 200 500 1k 2k 5k 10k 20k
Spectrum p(f) of microphone signal
[dB]
Frequency [Hz]
Signal lines Noise + Distortions Noise floor
Signal level MTND
Multi-Tone Distortion (MTD)
MTD don‘t show the generation process in detail
„Fingerprint“ (good for quality control)
• distortion at fundamental frequencies• harmonic components• difference-tone components• summed tone components
intermodulation
DistortionfSparse multi-tone complex
Stimulus Output signal
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KLIPPEL LIVE #9: Intermodulation Distortion, 32
Poll:Do you evaluate the distortion generated by a multi-tone stimulus ?
A. Yes 25%B. No 75%
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KLIPPEL LIVE #9: Intermodulation Distortion, 34
Phase of the Excitation Tones is important !!
KLIPPEL
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101520
0 50 100 150 200 250 300
Stimulus (t) vs time
[V]
Time [ms]
Stimulus (t)
Time signal (logarithmic sweep)
f
Phase spectrum
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0
5
10
15
20
50 100 200 500 1k 2k 5k 10k
dB - [V] (rms
)
Frequency [Hz]
Curve 2
Amplitude spectrum
At any time there are multiple frequency components
interacting !!!
Intermodulation + Harmonics
At one time there is only one frequency component !!!
Harmonics only
KLIPPEL
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0 50 100 150 200 250 300
[V]
Time [ms]
Time Signal (Multi-tone complex)
f
Phase spectrum
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[dB] 0 dB = 1 V
Frequency [Hz]
Amplitude spectrum
random
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KLIPPEL LIVE #9: Intermodulation Distortion, 35
Defined Properties of Multi-tone Stimulusaccording IEC 60268-21
Objective:- ensure comparability of the results measured by different instruments- easy to generate (by software implementation)- Modification of the stimulus should be possible (bandwidth , resolution R)
( ) NiwithfTT
f Ristarti ,...,12int1 / =⋅⋅=
=+ m
ii
mam
mod2
*21 π
ϕπϕ
( ) ( )∑=
+=N
iiii tffUtx
12cos)( ϕπ
Frequencies of the sparse line spectrum logarithmically spaced Pseudo-random phase
Amplitude spectrum
Max. Number of frequencies Seeds (a=48271, m=2
31-1 and ϕ1=1) Starting frequency
Duration(periodicity)
resolution
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KLIPPEL LIVE #9: Intermodulation Distortion, 36
Interpretation of the Distortion
KLIPPEL
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60
70
80
90
100
110
120
50 100 200 500 1k 2k 5k 10k
[dB]
Frequency [Hz]
Fundamental Multi-tone Distortion
Distortion
Fundamental
frequency of the spectral components
Total Harmonic Distortion (THD) Multi-tone Distortion
Sound pressure spectrum
KLIPPEL
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60
70
80
90
100
110
120
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50 100 200 500 1k 2k 5k
dB - [V] (rms)
Frequency [Hz]
Fundamental THD
Total Harmonic Distortion (THD)
FundamentalFundamental
frequency of the fundamental tone
THD
Benefit: Distance between fundamentals and distortions is meaningful for perceptualmasking
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KLIPPEL LIVE #9: Intermodulation Distortion, 37
KLIPPEL
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0
50 100 200 500 1k 2k 5k 10k 20k
[dB]
Frequency [Hz]
MTND THD IMD
Multi-tone Distortion Measurementcompared with traditional THD, IMD
MTD
IMD:f1 = 50 Hz @15 V + sweep @ 3V
MTD:Multitone @ 15V
THD: sweep @ 15 V
600 Hz40 Hz 600 Hz
THD0.1 %
IMD10 %
1 %
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KLIPPEL LIVE #9: Intermodulation Distortion, 38
The Causes of Multi-Tone DistortionKLIPPEL
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60
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90
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110
120
50 100 200 500 1k 2k 5k 10k
[dB]
Frequency [Hz]
Fundamental Multi-tone Distortion
Distortion
Fundamental
resonance frequency Cone Vibration
L(i) (rising with frequency)
Bl(x) (independent of frequency)
Kms(x)
L(x) (rising with frequency)
Doppler (rising with frequency)
Kms(x)
Bl(x)
L(x)
L(i)
Cone Vibration
Doppler Effect
Rms(v)Rms(v)
frequency of the spectral component
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KLIPPEL LIVE #9: Intermodulation Distortion, 39
Exercise: WooferAnalysis of Multi-tone Distortion
KLIPPEL
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20
40
60
80
100
120
102 103
Spectrum sound pressure output
[dB
]
Frequency [Hz]
fundamental components
Bl(x)Kms(x)
Le(x)
Rms(v) Le(i)Bl(x)Kms(x)Le(x) Doppler Effect Cone Vibrationcauses:
total distortion
fs=60 Hz
out of band distortion
Le(i)
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KLIPPEL LIVE #9: Intermodulation Distortion, 40
Exercise: MicrospeakerAnalysis of Multi-tone Distortion
KLIPPEL
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50
60
70
80
90
100
110
120
130
Distortion Components
[dB]
Le(i)
fundamental components
20102 103 104
Frequency [Hz]
Bl(x)
Kms(x)
Le(x)
Rms(v) Le(i)Bl(x)Kms(x)Le(x) Doppler Effect Cone Vibrationcauses:
out of band distortiontotal distortion
Rms(v)
fs=600 Hz
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KLIPPEL LIVE #9: Intermodulation Distortion, 41
Measurement of Multi-Tone Distortion
Disadvantages:• Amplitude and phase of stimulus have to be defined by standard• no separation of odd- and even-order distortion components• does not reveal the asymmetry of the nonlinearities• no separation of harmonics and intermodulation• fundamental components are also distorted
Advantages:• Considers intermodulation components• Audio-like signal • Separation of noise and distortion• fast (perfect for quality control)
This measurement is very powerful in loudspeaker diagnostics !
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KLIPPEL LIVE #9: Intermodulation Distortion, 42
Demo. Multi-tone DistortionTool: Using a dedicated software module Multi-Tone Measurement (MTON) of the KLIPPEL Analyzer
http://www.klippel.de/products/rd-system/modules/mton-multi-tone-measurement.html
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KLIPPEL LIVE #9: Intermodulation Distortion, 43
Discussion
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KLIPPEL LIVE #9: Intermodulation Distortion, 44
Summary
• IM-Distortion give valuable diagnostic information not provided by harmonics
• IM-Distortion is the only symptom for L(x) nonlinearity (reduced by shorting rings)
• Multi-tone measurements gives a comprehensive fingerprint of all nonlinear distortion components
• Multi-tone testing shows the impact of the program material
• Two-tone stimulus gives more detailed information and is the most critical signal for listening
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KLIPPEL LIVE #9: Intermodulation Distortion, 45
Open Questions
How to evaluate the irregular properties of the audio device ?
The next 10th KLIPPEL live webinar entitled Impulsive distortion - rub&buzz, abnormal behavior, defectswill address the points:• Need for special measurements more sensitive than the
human ear• What the Time-Frequency analysis shows• Inspecting the fine-structure of impulsive distortion in the
time domain • How to find the root cause of the irregular behavior• New solutions provided by IEC 60268-21
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KLIPPEL LIVE #9: Intermodulation Distortion, 46
1. Modern audio equipment needs output based testing 2. Standard acoustical tests performed in normal rooms3. Drawing meaningful conclusions from 3D output measurement4. Simulated standard condition at a single evaluation point5. Maximum SPL – giving this value meaning6. Selecting measurements with high diagnostic value7. Amplitude Compression – less output at higher amplitudes8. Harmonic Distortion Measurements – best practice9. Intermodulation Distortion – music is more than a single tone10. Impulsive distortion - rub&buzz, abnormal behavior, defects
-- small break --11.Benchmarking of audio products under standard conditions (July 22nd)12.Auralization of signal distortion – perceptual evaluation 13.Setting meaningful tolerances for signal distortion14.Rating the maximum SPL value for product15.Smart speaker testing with wireless audio input
Next Section
Acoustical Measurement �of Sound System Equipment �according IEC 60268-21 Previous Sessions9th KLIPPEL LIVE:�Intermodulation Distortion – music is more than a single tone��Poll:Bl-Distortion in MusicWhat causes the IM Distortion ? Causes for high IM-DistortionSparse but Comprehensive Stimulus Intermodulation distortion�generated by Two-tone StimulusIM-Distortion (two-tone signal)�Definitions according IEC 60268-21Contribution of 2nd and 3rd-order Components �to the total intermodulation distortionSweeping the Two-Tone Signal�How to choose the frequencies ?Poll:Setup for IMD in Sound Pressure �bass sweep techniqueCauses of IMD in Sound Pressure Output �using bass sweep techniqueDemo: Intermodulation Distortion�2 tone stimulus with bass sweepMeasurement of IMD in Sound Pressure �voice sweep techniqueThe Causes of IMD in Sound Pressure Output�voice sweep techniqueDemo: Intermodulation Distortion�2 tone stimulus with voice sweepSparse but Comprehensive Stimulus Amplitude Modulation�two-tone stimulus f1 < fs, f2 > fs Phase (Frequency) Modulation�caused by Doppler EffectPhase of Intermodulation DistortionAudibility of Intermodulation DistortionIM-Distortion (two-tone signal)�Definitions according IEC 60268-21Contribution of Amplitude Modulation�to the total intermodulation distortionDemo: Amplitude Modulation�2 tone stimulus with voice sweepIntermodulation Measurement �using a Two-Tone Stimulus Universal Stimulus�complex, steady-state, like an organ toneMulti-Tone Distortion (MTD)Poll:Phase of the Excitation Tones is important !! Defined Properties of Multi-tone Stimulus�according IEC 60268-21 Interpretation of the DistortionMulti-tone Distortion Measurement�compared with traditional THD, IMDThe Causes of Multi-Tone DistortionExercise: Woofer�Analysis of Multi-tone DistortionExercise: Microspeaker�Analysis of Multi-tone DistortionMeasurement of Multi-Tone Distortion Demo. Multi-tone DistortionDiscussionSummaryOpen QuestionsNext Section