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KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 1
Acoustical Measurement
of Sound System Equipment
according IEC 60268-21
KLIPPEL- live
a series of webinars presented by
Wolfgang Klippel
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 2
1. Modern audio equipment needs output based testing
2. Standard acoustical tests performed in normal rooms
3. Drawing meaningful conclusions from 3D output measurement
4. Simulated standard condition at an evaluation point
5. Maximum SPL – giving this value meaning
6. Selecting measurements with high diagnostic value
7. Amplitude Compression – less output at higher amplitudes
8. Harmonic Distortion Measurements – best practice
9. Intermodulation Distortion – music is more than a single tone
10. Impulsive distortion - rub&buzz, abnormal behavior, defects
11.Benchmarking of audio products under standard conditions
12.Auralization of signal distortion – perceptual evaluation
13.Setting meaningful tolerances for signal distortion
14.Rating the maximum SPL value for a product
15.Smart speaker testing with wireless audio inputAcoustical testing of a modern active audio device
Previous Sessions
1st Session
2nd Session
3rd Session 4th Session
5th Session 6th Session
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 3
8th KLIPPEL live:
Harmonic Distortion Measurements – best practice谐波失真测量 –最佳实践
今日话题 Topics today:
• IEC 60268-21定义的方法概述 Overview on Methods defined by IEC 60268-21
• 谐波失真的指标(绝对或者相对?) Metrics for Harmonic Distortion (absolute or relative ?)
• 符合IEC标准概述的测量以及其他有用测试方法Measurement according to IEC Standard Overview and other useful test methods
• 结果解读 Interpretation of the results
• 实际演示 Practical demos
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 4
非线性症状:谐波失真Nonlinear Symptom: Harmonic Distortion
frequency
Amplitudesound pressure spectrum
Nonlinear System
1f
single tone
stimulus
output Fundamental +
Harmonics +
Subharmonics +
Noise
harmonics
3rd
2nd
12 f
nth
1nf13 f
subharmonics
1/ 2f
2nd
input
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 5
单音是好的激励信号吗Is a Single Tone a Good Stimulus ?
Single-
Tone
Two-
Tone
Multi-
ToneNoise Audio
Signal
Spectral Analysis(Fourier Transform,
High-pass and bandpass filter, ...)
complexity of the stimulus
PRO:
• 易于生成 simple to generate
• 揭示谐波、DC分量 reveals harmonics, dc component
• 揭示基波压缩的最大输出 reveals maximal output of fundamental compression
• 可进行超快速扫描测量 Ultra-fast sweep measurements are possible
• 适合异音测量(参考Klippel live第10期)good for rub&buzz (see section #10 of the Klippel live)
CONTRA:
• 不产生互调成分 no intermodulation components are generated
• 对非线性行为评估不全面not a comprehensive assessment of the nonlinear behavior
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 6
Poll:
您使用哪种激励来测量谐波失真?Which stimulus do you use for measuring the harmonic distortion ?
A. 单音(稳态)Single tone (steady state)
B. 正弦步进(可变音调序列)Step sine (sequence of switched tones)
C. 正弦猝发音(整形短音+停顿)Sinusoidal burst (shaped short
tone + break)
D. 连续正弦chirp Continuous sinusoidal chirp
E. 其他 Other
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 7
如何测量随频率变化的谐波失真How to measure Harmonic Distortion versus frequency ?
Techniques Step SineSinusoidalBurst
Continuous Chirp
Distortion Separation
Spectrum (FT) Spectrum (FT) - Tracking Filter- Windowed Impulse Response (Farina)
Continous Excitation No No Yes
Steady State Yes No No
Total test duration Long Long Short
KLIPPEL modules DIS TBMTRF, TRF-steppingQC-SPL task
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 8
0.0 1.0 t / ttotal
0.5
Linear chirp
log(fmin)
log(f)
Fre
qu
en
cy
Timelog(fmax)
log. chirp
with constant
speed
Sweep Speed of the Chirp
Chirp with increasing sweep speed
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 9
Poll:
您使用哪种扫描速度配置?Which sweep speed profile do you use ?
A. 线性时频映射 With linear time frequency mapping
B. 对数时频映射 With logarithmic time frequency mapping
C. 扫描速度不断增加 With increasing sweep speed
D. 其他 Others
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 10
Shaped Logarithmic Sine Chirp
KLIP PEL
-40
-35
-30
-25
-20
-15
-10
-5
0
5
10
15
20
50 100 200 500 1k 2k 5k 10k
dB - [
V] (rm
s)
Frequenc y [Hz]
Curve 2
Filter relative bandwidth
KLIPPEL
-75
-70
-65
-60
-55
-50
-45
-40
-35
-30
101 102 103
Spectrum of stimulus
[dB]
Frequency [Hz]
Signal lines
Filter absolute bandwidth
KLIPPEL
-20
-15
-10
-5
0
5
10
15
20
0 50 100 150 200 250 300
Stimulus (t) vs time
[V]
Time [ms]
Stimulus (t)
Amplitude spectrum
Log(f)
t
Group delay response
( )ttftfUtu )(2cos))(()( =
Amplitude depends on frequency
( ) 2 0t
start sf t f t T
=
frequency depends on time
2
1log end
s start
f
T f
=
Sweep speed
200 Hz
2 kHz
20 kHz
Time1s 2s 3s
log (f)
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 11
Property of the logarithmic Chirp
2nd3rd
1 kHz
500 Hz
160 ms
在产生谐波成分之前对其进行了测量(非因果关系)The
harmonic component was measured
before it was generated (acausal)
time
Frequency
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 12
Reproduced chirp
Total Impulse response
impulse response of the fundamental
Farina‘s Harmonic Distortion Measurement
impulse
response of the
harmonics
Energy Time Curve
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 13
More to this topic …
Reference:A. Farina, “Simultaneous Measurement of Impulse Response and Distortion with
a Swept-Sine Technique,” presented at the 108th Convention of the Audio Eng.
Soc. 2000, Paris, France
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 14
Demo: In-situ MeasurementTool: Using a dedicated software module TRF (chirp stimulus) of the
KLIPPEL Analyzer
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 15
Farina with Room Compensation
• 补偿滤波器补偿房间影响 The
compensation filter compensates for the room influence
• 减少线性脉冲响应中的振铃 reduces
the ringing in the linear impulse response
• 减少谐波脉冲响应中的振铃Reduces the ringing in harmonic impulse response
• 可应用加窗技术分离线性和失真成分(Farina技术)Windowing can be
applied to separate linear and distortion components (Farina technique)
without compensation
with compensation
FilterHc(f)
FarinaAnalysis
Results)( rfree rp
Impulse Response
Energy Time Curve
→非线性失真可以在非消声条件下测量!Nonlinear Distortion can be measured under non-anechoic conditions !
harmonicsLinear direct sound
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 16
Accurate Harmonic Distortion
以%表示的不使用补偿滤波器的总谐波失真THD显示明显误差。The total harmonic
distortion (THD) in percent without
compensation filter shows significant errors.
使用补偿滤波器的THD对应于消声环境中的预期结果。The THD with compensation
filter corresponds to the expected results found
in an anechoic environment
with compensation
without compensation
with compensation
without compensation
房间模式在基波分量中产生20 dB的误差,在总谐波成分中产生大于6 dB的误差。The room modes generate an error of 20 dB in
the fundamental component and an error of
more than 6 dB in the total harmonic
components.
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 17
Demo: Simulated Free/Far Field
Tools of the KLIPPEL Analyzer:
• Transfer Function TRF (chirp stimulus)
• In-Situ-Compensation (ISC)
• Nearfield Scanner (NFS)
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 18
0.0 1.0 t / ttotal
0.5
linear chirp
log(fmin)
log(f)
Fre
qu
en
cy
Timelog(fmax)
log. sweep
with constant
speed
Step Sine
Best chirp for end-of line testing ?
使用扫频增速的chirp Chirp with increasing sweep speed
( )2 max( ) log 1 1 / ( )t Q f t = +( )2 max 0log 1 1 /
.
Q f
const
= +
=
使用恒定扫频速度的对数chirp Logarithmic chirp with constant sweep speed
Chirp with increasing
sweep speed
使用固定周期数的正弦步进Step Sine with fixed number of periods
模态共振的最大品质因数Qmax maximum quality factor Qmax of the modal resonances
max1 .8
i
QP const
= + =
起始频率f0 Start frequency f0
Step sine contains
fixed number of
periods at each
frequency
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 19
0.0 1.0 t / ttotal
0.5
linear sweep
log(fmin)
log(f)
Fre
qu
en
cy
Timelog(fmax)
log. sweep
with constant
speed
Step Sine
10
0.1
1kH
z
0.9
waveform of
log. sweep
with speed profile
log. sweep
with speed profile
ms
产线上的超快速测试 Ultra-Fast Testing in Production
扫频速度增加的对数chirp Logarithmic chirp with increasing sweep speed
High
sweep
speed
low
sweep
speed
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 20
Sweeping Up or Down ?Ultra short testing < 0.5 s
振铃的问题 Problems of ringing:
• 高Q共振需要的衰减时间>50ms High Q resonances need decay time of >50ms
• 基波被解读为谐波 Fundamental interpreted as Harmonics
→ 极快速测试使用向上扫频 Use UPWARDS SWEEP for extremely fast testing
Upward Sweep
Downward Sweep
30 dB
0.2 seconds total sweep time
ringing
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 21
More to this topic …
Reference:
S. Irrgang, W. Klippel, “Fast and Sensitive End-of-Line Testing,” presented at the 144th
Convention of the Audio Eng. Soc., May. 2018, preprint 9927
• EOL测试的目标和特点 Targets and Particularities of EOL Testing
• 限制测量速度的物理原因 Physical reasons for limiting measurement speed
• 寻找最佳激励进行EOL测试 Finding best stimulus for EOL Testing
• 嘈杂环境中的快速测试 Fast testing in a noisy environment
• 从生产中学习 Learning from Production
• 结论 Conclusions
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 22
谐波失真的解读Interpretation of the Harmonic Distortion
目标 Objectives:
• 用一个指标描述失真的特性 Describing the properties of the distortion by a metric
• 理解与非线性的关系(根本原因)Understanding the relationship to nonlinearities (root cause)
• 评估对感知音质的影响 Evaluating Impact on the perceptual sound quality
诊断利用以下特性 Diagnostics exploits the following properties
• 偶次和奇次分量(2阶、3阶)Even and odd-order components (2nd, 3rd)
• 失真分量的能量总和THD Energetic sum of the distortion components (THD)
• 谐波失真的频率依赖性 Frequency dependency of the harmonic distortion
• 谐波失真的幅值依赖性 Amplitude dependency of the harmonic distortion
• 低阶和高阶失真 Lower-order and Higher-order distortion
• 所选失真分量的加权能量和(高阶失真IEC 60268-21,HI-2失真)Weighted energetic sum of selected distortion components (higher-order distortion IEC 60268-21, HI-2 Distortion)
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 23
符合IEC 60268-21的谐波能量和Energetic Sum of the Harmonics according IEC 60268-21
问题 Problems:
• THD(f) 绘制成与激发频率f相关的曲线 THD(f) is plotted versus excitation frequency f
• THD通常由2阶和3阶分量主导 THD is usually dominanted by 2nd and 3rd-order components
• THD取决于pref(f) 的定义(总信号、基波、指定频率范围的平均基波)THD
depends on definition of pref(f) (total signal, fundamental, mean fundamental in stated frequency range)
谐波分量的能量和(绝对值)Energetic
Sum of the Harmonic Components (absolute)总谐波失真(相对值)Total Harmonic Distortion (relative)
2
2
( ) ( )N
TH nf
n
p f p f
=
=
in sound pressure
0
( )( ) 20 lg TH
TH
p fL f
p
=
in decibels:
=
%100lg20)(
THDfLTHD
in decibels:
%100)(~
)(~
)(2
2
fp
fp
fTHDref
N
n
nf=
=
in percent
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 24
Causes of THD in Sound Pressureof an electro-dynamical loudspeaker
KLIPPEL
50
60
70
80
90
100
110
120
130
50 100 200 500 1k 2k 5k
dB - [V] (rms)
Frequency [Hz]
Fundamental THD
Total Harmonic Distortion (THD)
FundamentalFundamental
Kms(x)
Bl(x)
L(x)
L(i)
Cone Vibration
resonance frequencyCone Vibration
L(i)
Bl(x)
Kms(x)
L(x)
excitation frequency
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 25
广义信号流模型 Generalized Signal Flow Model
描述分离的非线性 describing a separated nonlinearity
pre-filterH1,1(f)
1st state variable
multiplier
distortion
fsVoltagesound
pressurehighpass
Static Nonlinearity
pre-filterH1,2(f)
post-filterH2(f)
2nd state variable
feed-back loop
distortion added to the inputpost-shaping
post-
shaping
pre-
shaping
Current
displacementL(x)
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 26
The Particularities of Each Nonlinearity
NONLINEARITY
INTERPRETATION
PRE-FILTER H1,1(f) (output)
PRE-FILTER H1,2(f) (output)
POST-FILTER H2(f)
Stiffness Kms(x) of the suspension
restoring force Low-pass
(displacement x)
Low-pass
(displacement x) 1
Force factor Bl(x) electro-dynamical force Band-stop
(current i)
Low-pass
(displacement x) 1
nonlinear damping Band-pass
(velocity v)
Low-pass
(displacement x) 1
Inductance Le(x) self-induced voltage Band-stop
(current i)
Low-pass
(displacement x) differentiator
reluctance force Band-stop
(current i)
Band-stop
(current i) 1
Inductance Le(i) varying permeability Band-stop
(current i)
Band-stop
(current i) differentiator
Mechanical resistance Rms(v)
nonlinear damping Band-pass
(velocity v)
Band-pass
(velocity v) 1
Young’s modulus E() of the material
cone vibration Band-pass
(strain ) Band-pass
(strain ) 1
Speed of sound c(p) nonlinear sound propagation (wave steepening)
High-pass
(sound pressure p)
High-pass
(sound pressure p)
differentiator
Time delay τ(x) nonlinear sound radiation
(Doppler effect) High-pass
(sound pressure p)
Low-pass
(displacement x) differentiator
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 27
More to this topic …
Reference:W. Klippel, “Loudspeaker Nonlinearities – Causes Parameters, Symptoms,” J. Audio Eng. Soc. 54,
no. 10, pp 907 – 939 (oct. 2006)
Get a free poster for your
workshop
Attend the annual three day block seminar (March 2019)
Lecture „Sound quality of Audio Systems“ at the
University of Technology, Dresden, Germany
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 28
Demo: Interpretation
Tools of the KLIPPEL Analyzer:
• Transfer Function TRF (chirp stimulus)
• In-Situ-Compensation ISC)
• Nearfield Scanner (NFS)
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 29
Poll:
您是否更喜欢呈现和解读相对度量的失真?Do you prefer to present and to interpret the distortion on a relative metric ?
A. 不是(绝对分量和基波分量刻度相同)No, (absolute components on the same scale as the fundamental)
B. 对,参考于基波幅值响应Lfund(f) Yes, referred to the fundamental amplitude response Lfund(f)
C. 对,参考于基波均值(在频段上的平均)Yes, referred to the
mean value of the fundamental (averaged over the frequency band)
D. 其他方法 Other methods
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 30
Harmonic Distortion – Absolute or Relative ?
100
%
50 100 200 500 1k 2k
Frequency [Hz]
2nd Harmonic
10 %
1 %
0.1 %
Content of distortion in total signal
displayed versus excitation frequency
100%=n
t
dp
np
Rms-value of nth-order
harmonic component
rms-value of total signal
Amplitude of spectral components
20 50 100 200 500 1k 2k 5k
dB
-[V
] (
rms)
Frequency [Hz]
40
50
60
70
80
90
100
110
120
130
2nd order harmonic
fundamental
displayed versus excitation frequency
Be careful - difficult to interpreterecommended - easy to interprete
15 % distortion ?
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 31
Room Influence2nd-order harmonics measured at 8 locations
Variation
40 dB
-110
010
110
210
102 103
[Per
cent
]
Frequency [Hz]
1 2 3 4 5
6 7 8 1 m
100
0.1
1
10
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 32
相对谐波失真 Relative Harmonic Distortion
参考于总输出信号的失真 distortion referred to the total output signal
缺点Disadvantages:
• 线性响应H(f,r) 导致高复杂度 Linear Response H(f,r) causes high complexity
• 不同阶次的谐波无可比性 Harmonics of different order are not comparable
• 解读困难 Interpretation is difficult
• 没有精确考虑掩盖效应 Does not consider masking effect precisely
优点 Advantages:
• 失真分量参考于总输出 Refers distortion component to total output
• 解释由单音产生的谐波的可听度比绝对分量好(但不适用于音乐)Explains audibility of harmonics generated by a single tone better than absolute components (but not for music)
更加强大的扬声器诊断 More powerful for loudspeaker diagnostics:
• 将基波和谐波显示为绝对信号分量 Display fundamental and harmonics as absolute signal components
• 将谐波转换为扬声器输入(等效谐波失真IEC 60268-21)Transform harmonics to the loudspeaker input (equivalent harmonic distortion IEC 60268-21)
• 用感知模型评估失真的掩盖 Use perceptional modeling to evaluate the masking of the distortion
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 33
H(f,r1)
Nonlinear
System
u(t)
H(f,r3)
p(r1)
p(r3)
Nonlinear
System
Nonlinear
System
D
H(f,r2)p(r2)
H(f,r1)
Nonlinear
System
u(t)
H(f,r3)
p(r1)
p(r3)
Nonlinear
System
Nonlinear
System
d(t)
H(f,r2)p(r2)
H(f,r1)-1
H(f,r2)-1
H(f,r3)-1
u (r1)
u (r2)
u (r3)
u (t)
KLIPPEL
50 100 200 500 1k
3rd harmonic distortion in voltageSignal at IN1
dB -
[V]
Frequency [Hz]
-45
-40
-35
-30
-25
-20
-15
-10
-5
0nearfield 30 cm 60 cm 1 m dis tance
Sinusoidal
stimulus
KLIPPEL
50 100 200 500 1k
3rd harmonics absoluteSignal at IN1
dB -
[V]
Frequency [Hz]
40
45
50
55
60
65
70
75
80
85
901 m dis tance 60 cm dis tance 30 cm dis tance nearfield
Harmonic Distortion
Independent of linear
properties
(radiation, position,
room, sensor, …)Distortion depends on
linear transfer function
等效谐波输入失真 Equivalent Harmonic Input Distortion
在声源处确定失真 Determine the distortion at the source
Inverse filter
Sound field Equivalent
harmonic input
distortion
Distorted input signal
u‘(r1)≈ u‘(r2)≈ u‘(r3)≈u‘(t)
nearfield
1m
30cm
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 34
多路径中的非线性 Nonlinearity in Multidimensional Path
非线性音盆振动示例 for example nonlinear cone vibration
H(f,r1)
p(r1)
H(f,r1)-1
u(r2)
u(r1)
H(f,r2)-1
Out of axis
On axis
p(r2)
U1, U
2, U
3
Nonlinear
System 2
Equivalent
Input distortion at
Point r1
Equivalent
Input distortion at
Point r2
disagreement
Nonlinear
System 1
U1, U
2, U
3
H(f,r2)
x
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 35
- 110
010
110
102 103
[Perc
ent]
Frequency [Hz]
0.1 m 0.5 m 1 m
3rd-order EID
扬声器非线性定位 Localization of Speaker Nonlinearity
声场中不同点处测量EID EID measured at different points in the sound field
Distortion depend on measurement point
Nonlinearities located in
one-dimensional signal path
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 36
Active Speaker Linearization
H(f,r2)
Nonlinear
System
p(r2)
u
H(f,r3)
H(f,r1)
p(r1)
p(r3)
sound
field
uD
Nonlinear
System
z
uD
-
Active Control Loudspeaker
主动控制系统只能补偿等效输入失真(EID)! Only the
equivalent input distortion (EID) can be compensated by an active control system !!
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 37
等效谐波输入失真 Equivalent Harmonic Input Distortion
IEC 60268-21
好处 Benefits:
• 在主要失真产生处描述它们 Describe the dominant distortions where they are generated
• 与换能器、房间、距离、传感器等的后整形无关Independent of the post-shaping from transducer, room, distance, sensor, …
• 现场(办公室)、QC测试箱、消声室测量的结果相同same results measured in-situ (office), QC-test box, anechoic room
• 易于解读(平滑曲线、输入信号的百分比)Simple to interpret (smooth curves, percent of the input signal)
• 可以通过主动线性化(DSP)消除 Can be cancelled by active linearization (DSP)
实用建议 Practical Tip:
• 通过近场测量保证足够的SNR!Ensure sufficient SNR by performing near-field measurement !
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 38
Demo: Equivalent Input Distortion
Tools of the KLIPPEL Analyzer:
• Transfer Function TRF (chirp stimulus)
• TRF Voltage Stepping STEP
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 39
Poll:
您使用2次和3次失真分量用于扬声器诊断吗?Do you use the 2nd- and 3rd-order distortion components for loudspeaker diagnostics ?
• Yes
• No
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 40
40
50
60
70
80
90
100
0 250 500 750 1000 1250 1500 1750 2000
Spectrum Pfar
[dB]
Frequency [Hz]
Distortion Fundamental
Root Cause of the HarmonicsSymmetrical Nonlinearity
Symmetrical nonlinearity
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0
4,5
5,0
-10,0 -7,5 -5,0 -2,5 0,0 2,5 5,0 7,5 10,0
Force factor Bl vs. displacement X
Bl [
N/A
]
Displacement X [mm]
Bl(X)
odd-order distortion
3rd
3rd 3rd
5th
5th 5th
2nd 4th 2nd 2nd4th 4th
fundamentalfundamentalStatic
nonlinearity
feed-forward system
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 41
40
45
50
55
60
65
70
75
80
85
90
95
100
0 250 500 750 1000 1250 1500 1750 2000
[dB]
Frequency [Hz]
Distortion Fundamental
Root Cause of the HarmonicsAsymmetrical Nonlinearity
2nd2nd 2nd
4th
4th 4th
fundamental
fundamental
Asymmetrical nonlinearity
0
1
2
3
4
5
6
7
-10,0 -7,5 -5,0 -2,5 0,0 2,5 5,0 7,5 10,0
Force factor Bl vs. displacement X
Bl [
N/A
]
Displacement X [mm]
Bl(X)
even-order distortion
2nd,4th,6th-order component
Staticnonlinearity
feed-forward system
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 42
40
45
50
55
60
65
70
75
80
85
90
95
100
0 250 500 750 1000 1250 1500 1750 2000
[dB]
Frequency [Hz]
Distortion Fundamental
Root Cause of the HarmonicsAsymmetrical Nonlinearity
3rd
3rd 3rd
5th
2nd2nd 2nd
4th
4th 4th
fundamental
fundamental
Asymmetrical nonlinearity
0
1
2
3
4
5
6
7
-10,0 -7,5 -5,0 -2,5 0,0 2,5 5,0 7,5 10,0
Force factor Bl vs. displacement X
Bl [
N/A
]
Displacement X [mm]
Bl(X)
even and odd-order
distortion
Staticnonlinearity
loudspeaker is a
feedback system
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 43
Poll:
您是否评估高阶失真分量?Do you evaluate the higher-order distortion components ?
A. 不 No
B. 是,4阶和5阶 Yes, 4th and 5th order
C. 是,指定高阶分量的能量和(如6阶至20阶)Yes, energetic sum of higher-order components of specified order (e.g. 6th …20th )
D. 是,加权高阶失真(HI-2、blat失真)Yes, weighted higher-order distortion (HI-2, blat distortion)
E. 是,其他方法 Yes, other ways
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 44
Root Cause of the HarmonicsHard or soft limiting nonlinearity
0
10
20
30
40
50
60
70
80
90
100
0 500 1000 1500 2000 2500 3000
[dB]
Frequency [Hz]
Distortion Fundamental
0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
1 0 0
0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0 3 0 0 0
[dB
]
F re q u e n c y [ H z ]
D i s t o r t i o n F u n d a m e n t a l
0.0
1.0
2.0
4.0
5.0
-7.5 -5.0 -2.5 0.0 2.5 5.0 7.5
Bl
N/A
Displacement mm
equal-length
soft limiting nonlinearity hard limiting nonlinearity
0.0
1.0
2.0
4.0
5.0
-7.5 -5.0 -2.5 0.0 2.5 5.0 7.5
Bl
N/A
Displacement mm
overhang
equal-length
high 2nd- and 3rd order distortion Large amplitude of all components
Spectrum of sound pressure signal (two-tone stimulus):
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 45
高次谐波失真 Higher-Order Harmonic Distortion
HOHD as defined in IEC 60268-21
2( )
( ) 100%( )
l
N
nf
n N
ref
p f
HOHD fp f
==
=
%100
)(lg20)(
fHOHDfLHOHD
State:
• Lowest order Nl
• highest order N
Weigthed harmonic Blat DistortionHI-2 (KLIPPEL application note AN7)
( )10
2
2
2 2
( ) ( )
10 lgnf
n
HI
ref
w n p f
Lp
=
−
=
𝑤(𝑛) = 4𝑙𝑑
𝑛
4
Blat失真是由设计特征引起的,而不是单元缺陷的摩擦、嗡嗡声或嘀嗒等类型的异音 Blat
Distortion results from a design characteristic rather than a rub, buzz or tick type of unit defect
建议 TIP: • 测量期间保证足够的信噪比SNR Ensure sufficient signal to noise ratio (SNR) during measurement
• 在近场测量声压!Measure the sound pressure in the near field !
• 与脉冲失真测量相比,HOHD对异音的灵敏度较低 HOHD are less sensitive for rub &
buzz than impulsive distortion measurement
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 46
Poll:
您是否在不同的输入电压下测量谐波失真来研究幅值压缩?Do you measure the harmonic distortion at different
input voltages to investigate the amplitude compression ?
• Yes
• No
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 47
Compression of 3rd-order Harmonic
K LIP P E L
0
10
20
30
40
50
60
70
80
4*10 1 6*10 1 8*10 1 10 2
T hird-order harm onic d istortion in percent (IEC 60268)S ignal a t IN1
Perce
nt
Frequenc y f1 [Hz]
0.50 V 1.57 V 2.64 V 3.71 V 4.79 V 5.86 V 6.93 V 8.00 V
Voltage
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 48
Compression of 2nd-order Harmonic Distortion
K LIP P E L
5
10
15
20
25
4*10 1 6*10 1 8*10 1 10 2
Second-order harm onic distortion in percent (IEC 60268)S ignal a t IN1
Percen
t
Frequenc y f1 [Hz]
3.71 V 4.79 V 5.86 V 6.93 V 8.00 V
• 非线性失真取决于频率和电压 Nonlinear Distortion depend on frequency and voltage
• 复杂的幅值特性(压缩、减少)Complicated amplitude characteristic (compression, reduction)
• 还需要测量与幅值的关系(3D测量)Measurement versus amplitude also required (3D measurement)
reduction
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 49
0
10
20
30
40
50
60
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
%
displacement mm
equal-length
overhang Total harmonic distortion (THD)
in percent
(peak)
Compression in THDHard or soft limiting nonlinearity
0.0
1.0
2.0
4.0
5.0
-7.5 -5.0 -2.5 0.0 2.5 5.0 7.5
Bl
N/A
Displacement mm
overhang
equal-length
Steep but
late increase
early but
slow increase
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 51
Demo: Amplitude Compression of the
Harmonic Distortion
Tools of the KLIPPEL Analyzer:
• Transfer Function TRF (chirp stimulus)
• TRF Voltage Stepping STEP
• 3D Distortion DIS
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 57
Discussion
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 58
Summary
Harmonic Distortion
• 谐波失真测量揭示了系统非线性的有用症状Harmonic distortion measurement reveals useful symptoms of system nonlinearities
• 通过使用扫频速度增加的对数chirp信号进行超快速测量Ultra-fast measurements can be performed by using logarithmic chirps with increasing sweep
speed
• 等效输入谐波失真(EIHD)简化了结果的解读The Equivalent Input Harmonic Distortion (EIHD) simplifies the interpretation of the results
• 在不同幅值处的测量(电压步进)提供重要信息Measurement at different amplitudes (voltage stepping) provides important information
• 近场测量提高SNR Measurements in the near field improves SNR
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 59
Open Questions
谐波失真测量很方便,但不能全面反映非线性失真!Harmonic distortion
measurements are convenient but don’t give a comprehensive picture of the nonlinear distortion!
第九期KLIPPEL live主题 The next 9th KLIPPEL live webinar entitled
互调失真 –音乐不仅仅是单音信号Intermodulation Distortion – music is more than a single tone
将讨论 will address the points:
• 如何按照IEC 60268-21用双音激励测试?How to test with a two-tone stimulus according IEC 60268-21 ?
• 为什么互调失真通常比THD大?Why are the IM Distortion usually larger than the THD ?
• 为什么幅度调制比相位调制重要?Why is amplitude modulation more critical than phase modulation ?
• 如何简化互调测量?How to simplify the intermodulation measurement ?
• 如何进行多音测试?How to perform multi-tone testing ?
• 如何解读结果?How to interpret the results ?
KLIPPEL LIVE #8: Harmonic Distortion Measurements - Best Practice, 60
1. Modern audio equipment needs output based testing
2. Standard acoustical tests performed in normal rooms
3. Drawing meaningful conclusions from 3D output measurement
4. Simulated standard condition at a single evaluation point
5. Maximum SPL – giving this value meaning
6. Selecting measurements with high diagnostic value
7. Amplitude Compression – less output at higher amplitudes
8. Harmonic Distortion Measurements – best practice
9. Intermodulation Distortion – audio is more than a single tone
10. Impulsive distortion - rub&buzz, abnormal behavior, defects
-- small break ---
11.Smart speaker testing with wireless audio input (July 22nd)
12.Benchmarking of audio products under standard conditions
13.Auralization of signal distortion – perceptual evaluation
14.Setting meaningful tolerances for signal distortion
15.Rating the maximum SPL value for product
Next Section
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