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IEC Standard Project LOUDSPEAKER MEASUREMENTS, 1
Electrical, Mechanical and Acoustical Measurementsof Loudspeakers and Sound System Equipment
Tutorial to a new IEC Standard Project
2015by Wolfgang Klippel,
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 2
AGENDA• Limited Scope of the IEC Standard 60268-5• New requirements and challenges• Scope of new standard proposal (Part A and B)• Conditions (test signals, equipment, environment, ...)• Amplitude adjustment (umax,)• Maximal output (SPLmax, compression, ...)• Frequency Response (phase, latency, ...)• Directional characteristics (near and far field, ...)• Distortion (THD, IMD, Multi-tone, rub and buzz, ...)
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 3
SCOPE of the existing IEC 60268-5
Starting point
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 4
Characteristics defined by IEC 60268-5
1. Impedance (rated value, Z(f)-curve, Qts, Vas)2. Input voltage (rated noise, short + long term maximal)3. Input power (rated noise, short + long term maximal)4. Frequency characteristics (rated range, fs, fvent)5. SPL in stated band, Sensitivity for 1 W 6. SPL response for voltage, H(f), effec. freq. range 7. Output (acoustic) power, efficiency8. Directivity (pattern, rad. angle, index, coverage)9. Amplitude nonlinearity (THD, IMD)
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 5
Active Loudspeaker Systems
DSP Tweeterprotection
X-over
amplifiers
drivers
Digitalaudioinput
Midrangeprotection
Wooferprotection
LimiterEqualizer
GainControl
Controlinput
Integration between signal processing, power amplification and electro-acoustical conversion
Nonlinear components
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 6
New Requirementsfor Modern Audio Systems
• Audio systems become active no access to the electrical terminals of the transducer digital signal processing dedicated to the transducer amplifiers with more capabilities
• Audio systems become portable main axis of radiation, sweet point and position of the listener
are not defined battery powered
• Audio systems become personal (hand-hold devices) listener is in the near field of the source
• Audio systems become smaller, lighter using green transducer technologies (efficient, nonlinear)
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 7
Characteristics defined by IEC 60268-5can be applied, need modification, are not
applicable to Active Loudspeaker Systems
1. Impedance (rated value, Z(f)-curve, Qts, Vas)2. Input voltage (rated noise, short + long term maximal)3. Input power (rated noise, short + long term maximal)4. Frequency characteristics (fs, fvent)5. SPL in stated band, Sensitivity for 1 W 6. SPL response for voltage input, H(f), effec. freq. range, 7. Output (acoustic) power, efficiency8. Directivity (pattern, rad. angle, index, coverage)9. Amplitude nonlinearity (THD, IMD)
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 8
Need for updated IEC Standard (60268-X)
OBJECTIVES:• Applicable to all kinds of modern audio devices (active, passive) • Coping with any input signal (digital, wireless, …)• Defining new measurement techniques (e.g. Rub & buzz test)• Bridging manufacturing (QC) and system development (R&D)• Providing comprehensive information in a shorter measurement
time (e.g. directivity)• Simplify interpretation (e.g. Root cause analysis)• Increasing flexibility to consider particularities of the application
(e.g. home, automotive, personal, professional, …) • Avoiding redundancy with other standards (IEC, CES, AES,
ALMA, ITU)• Updating, merging of existing IEC standards (e.g. 60268-5)
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 9
DisclaimerThis standard provides• a physical evaluation of the sound system• no fixed values for PASS/FAIL limits and quality grading • no characteristics for assessing overall sound quality or preference of
the audio system • no modeling perceptive and cognitive evaluation of the reproduced
sound quality by user
Conclusions:• This standard describes the general framework of the physical
evaluation• Further standards are required to consider the particularities of
personal equipment, microspeakers, headphones, home-equipment, automotive, professional applications
• Perceptive evaluation requires a separate standard
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 10
How to organize the new standard ?
Problems:• An overwhelming number of meaningful and important measurements and
characteristics (not important for all users) • Measurement of transducer parameters require access to the electrical terminals
and diaphragm
Acoustical (output based) measurement (Part A)• Applicable to transducers and systems• System-oriented modeling • Input-output transfer characteristics
(distortion)• no electrical and mechanical
characteristics• Important for end-user
Electrical and mechanical measurement (Part B)• Applicable to transducers and passive
systems• Access to internal state variables of the
transducer• Model based (lumped, distributed, ...) • Essential for transducer and system design,
less important for end-user
Two basic loudspeaker standards are required !
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 11
SCOPE OF PART AACOUSTICAL (OUTPUT BASED) MEASUREMENTS
This International Standard applies to passive and active sound systems such asloudspeakers, headphones, TV-sets, multi-media devices, personal portable audiodevices, automotive sound systems and professional equipment. The device under test(DUT) may be comprised of electrical components performing analogue and digitalsignal processing prior to the passive actuators performing a transduction of theelectrical input into an acoustical output signal. The measurements presented heredetermine the transfer behaviour of the DUT between an arbitrary analogue or digitalinput signal and the acoustical output at any point in the near and far field of thesystem. This includes operating the DUT in both the small and large signal domains.The influence of the acoustical boundary conditions of the target application (e.g. carinterior) can also be considered in the evaluation of the sound system.
Note: This standard does not apply to microphones and other sensors. This standard doesnot require access to the state variables (voltage, current) at the electrical terminals of thetransducer. Sensitivity, electric input power and other characteristics based on theelectrical impedance will be described in a separate standard document IEC 60268-Xbdedicated to electrical and mechanical measurements.
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 12
SCOPE OF PART AACOUSTICAL (OUTPUT BASED) MEASUREMENTS
Evaluation is based on evaluation of acoustical output
control parameters(e.g. attenuation)
digital audio stream
Properties of theblack box depend on control parametersand stimulus
drivers
Black box
No access to internal states
Near Field Far Field
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 13
Not covered in Part A
DSP Tweeterprotection
X-over
amplifiers
drivers
Digitalaudioinput
Midrangeprotection
Wooferprotection
LimiterEqualizer
GainControl
Controlinput
no access to terminals of the
transducers
x
x
x
• No electric input power, no electric impedance• No efficiency, no sensitivity• No direct measurement of coil temperature• No lumped parameters (linear lumped T/S, nonlinear, thermal) • No distributed transducer parameters (no optical access to the
diaphragm)• No accelerated life testing and long-term measurement with on-line
monitoring to evaluate aging, fatigue, climate dependency
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 14
Conventional Characteristics applicable to active loudspeaker systems
DSP Tweeterprotection
X-over
amplifiers
drivers
Digitalaudioinput
Midrangeprotection
Wooferprotection
LimiterEqualizer
GainControl
Controlinput
Conditions:• based on sound pressure output only• ratio of acoustical output signals is considered• measurement in small signal domain (limiter, protection, nonlinearities not active)• independent of one-dimensional signal processing (equalizer)
All relative characteristics, which are
independent of amplitude, such as
• directivity index• coverage angle• radiation angle• effective frequency range
linear
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 15
KLIPPEL
-40
-35
-30
-25
-20
-15
-10
-5
0
5
10
50 100 200 500 1k 2k 5k 10k
Sound Pressure Level (rel.)
dB
- [V
] (
rms)
Frequency [Hz]
KLIPPEL
0,0
2,5
5,0
7,5
10,0
102 103
Group delay
ms
Hz
Relevant information of the Transfer Function H(f)(small signal domain)
DSP Tweeterprotection
X-over
amplifiers
drivers
Digitalaudioinput
Midrangeprotection
Wooferprotection
LimiterEqualizer
GainControl
Controlinput
1mxSPL
Input signal
H(f)
const. time delay(latency)
Phase responseGroup delay Rel. Amplitude response
Maximum SPL deviation
eff. frequency range(small signal )
Impulse accuracy
Klippel, Sound Quality of Audio Systems, Part 1 Introduction , 16
New Challenge 1:Evaluation at Small and High Amplitudes
Range of Operation
Amplitude
Large signal performance
Small signal performance
Overload
Maximal OutputDistortionCompressionStability
Linear Model
Thermaland
Nonlinear Model
Amplitude of the stimulus should be clearly defined to ensure test repeatabilityand to protect the DUT Using SPLmax as rated by the manufacturer for calibrating the stimulus
Klippel, Sound Quality of Audio Systems, Part 1 Introduction , 17
StimulusMeasured
Signal
Input Signal
OutputSignal
Linear Model
Nonlinear Model
UnpredictableDynamics
Noise
Regular linear distortion
Harmonics, intermodulations
impulsivedistortion
Accepted Large Signal Performance
Undesired Loudspeaker Defects(e.g. rub & buzz, loose particles, air leak noise,…)
Desired Small Signal Performance
New Challenge 2:Measurement of regular and irregular distortion
Which is the optimal test signal ?Amplitude of the test signal ?How to perform signal analysis ?
Klippel, Sound Quality of Audio Systems, Part 1 Introduction , 18
two-dimensional
Room Interaction
Room Interaction
Room Interaction
Room Interaction
Room Interaction
Room Interaction
Room Interaction
Room Interaction
Room Interaction
New Challenge 3:Comprehensive Evaluation in 3D Space
Electro-mechanicalTransducer
i(t)
u(t)
Soundradiation
soundradiation
Soundradiation
Mechano-acoustical
Transducer
(Cone)x(t)Audio
signal
AmplifierCrossover
EQ
Multiple Outputs
Single Input
Soundpropagation
Soundpropagation
Soundpropagation
p(r2)
p(r1)
p(r3)
sound field
three-dimensional
one-dimensional
Audio System represented as a Signal Flow Chart
Conventional measurements SPL response in the far field• are not sufficient for portable devices, studio monitores, automotive• require anechoic room of sufficient size• are time consuming
Klippel, Sound Quality of Audio Systems, Part 1 Introduction , 19
CONDITIONS
The manufacturer has to specify the following Rated Conditions• rated maximum sound pressure level SPLmax or maximum input value umax
• evaluation point• rated frequency range• reference plane• reference point• reference axis• orientation vector
The measurement of the DUT is performed under Normal Conditions which define• Mounting and acoustical loading of the DUT• Acoustical environment• Positioning of DUT with respect to the measuring microphone and the walls • Ambient condition (climate, adjustment) • Test signal + amplitude • Normal position of attenuators, equalizers or any other active control elements• Measuring equipment used
To ensure reproducibility and sufficient flexibility
Depends on application
Klippel, Sound Quality of Audio Systems, Part 1 Introduction , 20
Mounting and Acoustical Loading
Mounting and acoustic loading of drive units (transducer)• Half-space free-field condition (in plan reflecting surface of sufficient size (d >> λ) • Standard baffle • Standard measuring enclosure (type-A and type-B) • Test cabinet generating used for end-of-line testing and relative measurements • Specified acoustic load generated by a defined horn, coupler, …• Plane wave tube • Free air without baffle, enclosure, horn, ...
Mounting and acoustic loading of an electro-acoustic system• Free air • State by the manufacturer
Klippel, Sound Quality of Audio Systems, Part 1 Introduction , 21
Acoustical EnvironmentAcoustical measurements shall be made under one of the following conditions, the choice being indicated with the results.
a) Free-field condition large anechoic full roomb) Half-space, field-field conditions ground floor measurement in large anechoic half
roomc) Simulated free-field conditionsd) Half-space simulated free-field conditions
a) Diffuse sound field conditions reverberant room, ISO 3741 b) Target application conditions (e.g. car interior)
gating techniques, holographic and field separation techniques
Reflections of the radiated sound on other reflecting surfaces (e.g. walls) shall sufficiently suppressed to ensure an accuracy of ±10 % of the sound pressure measurements.
Unwanted acoustical and electrical signals and noise generated by other sources shall be kept at the lowest possible level. Data related to signals which are less than 10 dB above the noise level shall be discarded. .
Klippel, Sound Quality of Audio Systems, Part 1 Introduction , 22
Positioning of DUT
z
x
yO
z
x
yO
z
x
yO
Reference plane and normal vector nref
Reference point rref
and orientation vectororef
z
x
yO
Evaluation point r
z
x
yO
Polar angle θ
Azimuthal angle
• Reference point and orientation vector are not obvious for personal sound devices• Spherical coordinates are useful for compact sources and far field data
Klippel, Sound Quality of Audio Systems, Part 1 Introduction , 23
x
z
y
Recommended Position and Orientation
normal vector nref
Reference point rref
Measurement point r
Polar angle θ
Azimuthal angle
It is strongly recommended to • to put the reference point rref in the origin O of the coordinate system, • to point the normal vector nref of the reference plan into the z direction and • to turn the audio system in such a way that the orientation vector oref points into x-direction
orientation vector oref
zyxzyx erererezeyex cossinsinsincos r
Klippel, Sound Quality of Audio Systems, Part 1 Introduction , 24
Measuring Distance between DUT and microphone
Reference point rref
Evaluation point r
Far-field conditions• sound pressure decreases according to the 1/r law with an accuracy of ±10 %.• distance >> geometrical DUT dimensions • Distance >> wavelength of the signal
Near-field conditions
• provides additional information for assessing studio monitors, personal audiodevices,
• measurements of line array loudspeakers and other DUTs of large size using multipletransducers cannot be performed in the far field of the source due to limited size ofthe anechoic room.
Evaluation distance re= | re – rref |
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 25
Definition of the Acoustical Environment
Measurement in Target Application
OUT2
OUT1
MI C1 LINE1
LIN E2 MI C2
PUSH
PUSH
I
0
(Standard) living room
Measurement under Standard Condition
transfer of the loudspeaker system
Auralization/Listening TestPerceptual Evaluation
Definition of target performance as perceived by final user
Suppressing the room influence
considering room, distance, ambient noise and other conditions
Loudspeaker Development
Physical characteristics(comprehensive, simple to interpret, comparable, reproducible)
Klippel, Sound Quality of Audio Systems, Part 1 Introduction , 26
Definition of Test Signals
• Sinusoidal chirp
• Steady-state single tone signal
• Steady-state two-tone signal
• Sparse multi-tone complex
• Broadband noise signal
• Narrow-band noise signal
• Impulsive signal
• Hann-burst signal
ttftfAtxc )(2cos))((2)(
MPt TTttfAtfAAA
tx
02cos2cos2
)( 221122
21
N
iMPiiiN
ii
m TTttffAfA
tx1
1
2
02cos)(
2)(
These terms are explained in IEC 60268-2.
1
1 02cos2)(f
NNTTttftx MP
MPs
elsewhere
ftfortftf
txb
,0
/5.602
)2sin(
5.6
2cos1
)( 000
pseudo-random phase
Instantaneous frequency
Klippel, Sound Quality of Audio Systems, Part 1 Introduction , 27
~
Amplitude Adjustment of the Input Signal
Sound pressure output
Rated maximum input value umax
• Good for DUTs with a single input and constant transfer function betweeninput and output
• Not meaningful for active systems
u
amplifier, equalizer, ect.)
Idea• Using only one single value meaningful for engineering, marketing, final user • Rating of the maximal amplitude by manufacturer based on design, target application, evaluation• Rated value can be applied to input and output• DUT will not be damaged by the test stimuli defined by manufacturer
stimulus
selected input
transducer
Rated maximum (output) SPLmax
• Universal approach for passive and active systems• Can be applied to any input channel• Can cope with gain controllers, equalizers, ect.
Klippel, Sound Quality of Audio Systems, Part 1 Introduction , 28
Rated Loudspeaker Characteristics
Manufacturer has to state (in accordance with the performance of the audio device and target application) the following mandatory characteristics:• the position of the audio device in the coordinate system used • reference point rref, reference plane and reference axis• evaluation point re or distance re from the w reference point rref
• SPLmax or the maximum input value umax
• rated frequency range
Further optional characteristics:• shaping of stimulus to simulate program material • special setting of the control parameters of the audio device
Klippel, Sound Quality of Audio Systems, Part 1 Introduction , 29
Should the manufacturer rate umax or SPLmax ?
Maximum output value SPLmax is preferred when• Using multiple input channels (digital, analog)• Using different parameter settings of the audio device (gain, equalizer,
...)• describing the physical limits and performance of the audio device • comparing competitive products• Generating useful information for the end user
Maximum input value umax
is preferred in the development and (end-of-line) testing of transducers and passive systems
Klippel, Sound Quality of Audio Systems, Part 1 Introduction , 30
What is the purpose of the evaluation point re?
• fast and easy determination of maximum input umax
• SPL response describes radiated free-field at most relevant listening position according target application
• The following properties can be assessed at a single point because they are part of the one-dimensional signal path: – regular nonlinearities caused by motor and suspension – significant rub&buzz of the transducer – thermal behavior of the transducer – protection system
Problem:• air leakage noise occuring at different sides of the enclosure can not be evaluated by a
single point measurements at multiple points required
Klippel, Sound Quality of Audio Systems, Part 1 Introduction , 31
V
Comparator
Amplitude Adjustment of the Input Signalbased on SPLmax rated by manufacturer
Evaluation point
Characteristics stated by the manufacturer• Rated frequency band defined by fstart and fend
• Rated maximum sound pressure level SPLmax
• Evaluation point re (distance, angle, …)• Properties of the stimulus used during calibration (multi-tone or pink noise with shaping, … )
Broad-band stimulus in rated frequency band
fstart fend
Note: umax depends on selected input channel, setting of control elements (gain, equalizers, ect.)
Objectives of the calibration process• Fast determination of the maximum input value umax based on SPLmax
• Using umax for the calibration of other test stimuli • Full flexibility for using any input channel of the active system (analogue, digital, ect. )
max~~ uu
Klippel, Sound Quality of Audio Systems, Part 1 Introduction , 32
V
Comparator
~~
noise
sine
Calibration of Other Test Stimulibased on maximum input umax
Evaluation point
Maximum input value
selected input channel, setting of control elements(gain, equalizers, ect.) are identical with those usedin the measurement of umax
Benefits:• Amplitude adjustment of other test stimuli• Simplifies automatic testing • Clear definition of small signal domain umax <0.1 umax
• Avoiding unintended overload of the DUT
Other test stimuli
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 33
How to rate umax and SPLmax?
The manufacturer has freedom to rate umax and SPLmaxbut should consider the following requirements:• final target application (rated frequency range, spectrum of
typical program material, evaluation point, ect. ) • DUT can reproduce the stimulus at SPLmax for any time without
damage• sufficient sound quality for the particular application
– acceptable regular nonlinear distortion (harmonic + intermodulation)– low compression of the fundamental (heating, mechanical limiting,
protection)– effective frequency range corresponds with the rated frequency range– no rub & buzz or any other defects
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 34
How to rate the maximum input umax
or maximum output SPLmax
1. Defining a test value utest (based on information from customer, marketing or development)
2. 100 h test with the stimulus at test value utest
3. Measurement of characteristics defined in the data sheet
4. Assigning the test value to the rated maximum reference value umax =utest , if the DUT is not damaged and the within the stated specification
Repeat the test with a lower test value if the evaluation was not successful
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 35
OTHER MAXIMUM LEVELS
Long-term maximum sound pressure level SPLlongObjectives:• Maximum SPL limited by applying mechanical and thermal load without causing
damage of the DUT Method:• Conventional method defined in IEC 60268-5• Broad-band stimulus 1min on/2 min off with 10 repetitions will not damage DUT
Short-term maximum sound pressure level SPLshortObjectives:• Maximum SPL limited by mechanical load without thermal heating without
causing damage of the DUT Method:• Conventional method defined in IEC 60268-5• Broad-band stimulus 1s on/1 min off with 60 repetitions will not damage DUT
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 36
Sound Pressure in Stated Frequency Band
Characteristics to be specified:• The sound-pressure p(r) produced by a DUT at a stated measurement point r
excited with a band-limited pink-noise signal with a stated rms value αumax . • The sound pressure level SPL(r)
V
Bandpassfilter~
pink noise
slopes of at least 24 dB/octave
Application:- Sound pressure in 1/3 octave or octave band
Amplitude adjustment
refp
pSPL ~
~log20 standard reference sound-
pressure (20 Pa).
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 37
Mean Sound Pressure in Stated Frequency Band
Characteristics to be specified:The square root of the arithmetic mean of the squares of the sound-pressure pifrom all the 1/3 octave frequency bands in the stated frequency band 1 ≤ i ≤ n.
V
Bandpassfilter
pink noise
1/3rd oct.filter
1/3rd oct.filter
1/3rd oct.filter
EnergeticAveraging
slopes of at least 24 dB/octave
mean sound pressure:
2/1
1
2~1~
n
iim p
np
Amplitude adjustment
ref
mm p
pSPL ~
~log20
mean sound pressure level
standard reference sound-pressure (20 Pa).
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 38
Frequency response of the fundamental sound pressure component
2. Frequency response of the sound pressure level SPL(f) describes the output in generated by a narrowband stimulus of defined (constant) amplitudea) Direct measurement by using a single tone or narrow-band noiseb) Calculation from the complex transfer function measured by using broad-band
stimulus
Measurements at low amplitudes (scaling factor α ≤ 0.1) :- linear time-invariant modeling can be applied (nonlinearities and heating are negligible) - measurement results are independent of the stimulus properties- Transfer Function H(f) corresponds to frequency response SPL(f)
1. Complex Transfer Function H(f) between input U(f) and sound pressure output P(f) - gives magnitude response (in dB, Pascal/volt, ect.)- gives phase response (mean time delay, group delay)- Measurement by using any broad-band stimulus (shaping can be applied)
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 39
Transfer Function Measurement
Characteristics to be specified:The transfer function H(f,r) between the input signal u(t) and the sound pressure output p(t, r) at the measurement point r excited by the a broadband stimulus with rms value αumax.
V
~
ChirpMulti‐tonepink noise
FourierTransform
Smoothing
FourierTransform
Amplitude adjustment Frequency domain
• Large signal domain (scaling factor α ≈ 1) reveals linear, nonlinear and thermalproperties of the DUT.
• Small signal domain (scaling factor α ≤ 0.1) reveals the linear transfer response only.
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 40
Smoothing of the Transfer FunctionSpectral averaging of the complex transfer function
ImpulseResponse
Energy‐Time curve
RemoveTime Delay
MAXIMUM
PhaseMagnitude
SpectralAveraging
SpectralAveraging
AddTime Delay
Unwrapping
BANDWIDTH B
bandwidth B, which is typically between 1 octave and 1/24th octave, determines the spectral resolution of the magnitude and phase response
Unwrapping is a necessary butambiguous, noise-sensitive and error-prone process for frequency-discretephase data (at least in acoustics).
The frequency resolution should be highenough that the phase difference betweentwo discrete frequencies will not exceed±90 degree.
Constant time delay is estimated fromthe impulse response and removed fromthe phase response before unwrappingand spectral averaging is applied.
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 41
Direct Measurement of the frequency response SPL(f)
Characteristics to be specified:The sound-pressure level SPL(f,r) as a function of frequency, measured under normal conditions at the measurement point r using a narrow band signal at the center frequency f. The input signal u(t) has a constant rms value αumax for all frequencies f varied in the rated frequency range. The properties of the stimulus u(t), the measurement time Ts and either the rms-value or the scaling factor α shall be stated.
V
~
Single tone,Narrow band
noise
Narrow Bandpass
(center)frequency
Constant gain
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 42
Frequency response SPL(f) calculated from the transfer function H(f,r)
Method of measurement:1. Measuring the transfer function H(f,r) by using a broad-band stimulus at low
amplitudes (scaling factor α ≤ 0.1) within the measurement time Ts in accordance with clause 16.1.
2. The magnitude response is smoothed by applying a spectral averaging with a specified bandwidth B
3. The SPL(f) in dB is calculated by
V
~
ChirpMulti‐tonepink noise
FourierTransform
Smoothing
FourierTransform
rms value of the input signal
refp
ufHfSPL max
~),(log20),(
rr
bandwidth B
(α ≤ 0.1)
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 43
Short-term amplitude compression of the fundamental component
Characteristics to be specified:Short term amplitude compression Cshort(f) is the level difference between transfer function measured in the small and large signal domain
by using a broad-band stimulus with a short measurement time Ts = 1s.
V
~
ChirpMulti‐tonepink noise
Small Signal Domain
Large Signal Domain
Compression Cshort(f)
Amplitude variation
The short amplitude compression Cshort(f) reveals the nonlinear mechanisms of thetransducer, the effect of the protection system and the limiting effects from otherelectronics (e.g. amplifier).
No heating !!
),,(log20),,(log20)( maxmax ufHufHfC linshort rr
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 44
Short-Term Compressionreveals mechanical nonlinearities only (no voice coil heating )
6020 50 200 500 2k 20k
Frequency [Hz]
KLIPPEL
65
70
75
80
85
90
95
100
105
110
115
120
125
dB -
[V]
(rm
s)
system excited by a chirp (T=1 s) generating SPLmax at the evalution point
short-term fundamental (1 s)
linear prediction
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 45
Long-term amplitude compression of the fundamental component
Characteristics to be specified:Long-term amplitude compression Clong(f) is the level difference between transfer function measured in the small and large signal domain
by using a broad-band stimulus over a pre-excitation time (Tpre=1 min + short measurement time Ts = 1s )
V
~
ChirpMulti‐tonepink noise
Small Signal Domain
Large Signal Domain
Compression Clong(f)
Amplitude variation
The long-term amplitude compression Clong(f) reveals the thermal and nonlinearmechanisms of the transducer and the effect of the active protection system.
pre-excitation time Tpre=1 min heats up the DUT
),,(log20),,(log20)( maxmax ufHufHfC linlong rr
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 46
Long-Term Compressionreveals effects of mechanical nonlinearities and voice coil heating
KLIPPEL
60
65
70
75
80
85
90
95
100
105
110
115
120
125
20 50 200 500 2k 20k
dB -
[V]
(rm
s)
Frequency [Hz]
linear prediction
system excited by a chirp (T=1 min) generating SPLmax at the evalution point
long-term fundamental (1 min)
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 47
Effective Frequency Range
Method:a) The frequency response SPL(f,r) shall be measured in the rated frequency range according at resolution corresponding to narrow band filter with a stated bandwidth (typically B = 1/9).b) The mean sound pressure level SPLmean is calculated in the stated frequency range. c) The limits of the effective frequency range shall be determined where the smoothed frequency response is not more than 10dB below the mean sound pressure level SPLmean.
95
90
85
100
20 50 100 200 500 1k 2k 5k 10k 20k
dB
Frequency [Hz]
Fundamental
SPLmean
rated frequency range
effective frequency range
fl fu
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 48
KLIPPEL
0,0
2,5
5,0
7,5
10,0
102 103
Group delay
ms
Hz
Latency in the electrical system
DSP Tweeterprotection
X-over
amplifiers
drivers
Digitalaudioinput
Midrangeprotection
Wooferprotection
LimiterEqualizer
GainControl
Controlinput
p(r)u(t)
mean group delay
Phaseresponse
transfer function H(f,r)
Latency
)(rmean
cref
meanlat
rr
Latency Sound propagation
The latency of the DUT is the difference betweenthe mean group delay of the DUT and the timerequired for the sound wave to propagate from thereference point rref to the measurement point rdefined by
refrr
With speed of sound c
rref
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 49
Directional transfer function
x
z
y
Characteristics to be specified:
The directional transfer function H(f, r, φ, θ) between the input signal u(t) and the sound pressure p(t, r) of the direct sound at the measurement point r shall be specified. The measurement point r is described by the spherical coordinates distance r=|r-rref | azimuthal angle φ and angle θ in the stated acoustical environment.
Measurement point r
Polar angle θ
Azimuthal angle
• Direct sound radiated by a DUT into 3D space• any point near field or far field• free field or simulated free field conditions• Polar coordinate system is recommended
V
~
ChirpMulti‐tonepink noise
)(
),,,(),,,(
fU
rfPrfH
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 50
Measurement of direct sound field in 3D space
Ss
region of validity
Ss
region of validity
Far-Field Measurement- Valid measurements at a distance r>rfar
- Extrapolation based on 1/r law- Directional information is independent of distance r- Sufficient information for home, pro and other applications- Large anechoic room required
Near-Field Measurement- measured at a distance r<rfar
- Holografic wave expansion required- Extrapolation to any point outside Ss
- Important for personal audio, car, monitors- Applicable in small, non-anechoic rooms
Near field
Far field
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 51
Measurement of the Far-field Response
PUSH
AMP
InputOutpu
t
Turntable
Multiplexer Analyzer
Amplifier
Loud-speaker
anechoicroom
r
Conventional Techniques: Measurement of the sound field spherical surface atconstant distance r in the far field of the source withsufficient angular resolution
Problems:• Anechoic condition (free field, half-space condition) required• Room reflections occuring in nonanechoic conditionscan only be suppressed at higher frequencies bywindowing of the impulse response• High amount of redundant measurement dataproduced• measurement distance r should be much larger thandimensions of the radatior d • Accurate measurmeent of the phase response difficultat at large distance r
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 52
Extrapolation of Far Field data
rr1 r2rfar
Characteristics to be specified:
A directional transfer function H(f, r2, 2, θ2) between the input signal u(t) and the sound pressure p(t,r2) of the direct sound in the far field at distance r2 > rfar and angles (2, θ2) is extrapolated from a transfer function H(f, r1, 1, θ1) measured in the far field at the distance r1 > rfar at the same angles (2 = 1, θ2 = θ1)
Near field
Measurement distance
)(
2
1111222
12),,,(),,,( rrjker
rrfHrfH
Far field
Requirements:
• Direct sound radiated by the DUT • free field condition• far field (r2 > rfar and r1 > rfar )• same direction (2 = 1, θ2 = θ1)
ExtrapolationNot applicable
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 53
Evaluation of Personal Audio Equipment
d
near field
The receiving point r in targetapplication is close to the source(e.g. personal audio equipment, car, multimedia)
far field conditions:• distance r >> dimension d• distance r >> wave length λ• ratio r/d >> d/λ
far field data are lessmeaningful
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 54
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Particularities of the Near-Field
cone
baffle
Dust cap
Surround
1. High Sound Pressure Amplitudes high signal to noise ratio room reflections are neglibigle no windowing of the impulse response high spectral resolution at low frequencies Direct sound larger than room reflections Good conditions for simulated free field
condition
2. Complexity of the Sound Field not a plane wave velocity gives additional information evanescent waves (exponential decay) relationship between sound pressure of a
surface and full 3D field information holographic techniques
Sound Pressure Field at 10 kHz
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 55
Short History on Near-Field Measurement
Single-point measurementclose to the source
Don Keele 1974
On-axis
Multiple-point measurementon a defined axis
Ronald Aarts (2008)
Scanning the sound field on a surface around the source
Weinreich (1980), Evert Start (2000)Melon, Langrenne, Garcia (2009)Bi (2012)
. . ..
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 56
Holographic wave expansion
Ss
region of validity
S1
),()(),( rBCr fffH Coefficients of the expansion
transfer function
General solutions of the wave equation usedas basic functions in the expansion
Conditions to be specified
The coefficients C(f), the order N(f) depending on frequency f, the validity radius a and thegeneral basic functions B(f,r) of the wave expansion describe the directional transfer function
between the input signal u(t) and the sound pressure output p(t,r) at measurement point r at adistance r=| r –rref | from the reference point rref which is larger than the validity radius a
),()(),( rBCr fffH
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 57
Example of a Holografic Measurement spherical waves used as basic functions
1. Measurement • Scanning the sound pressure in the near field
of the source at a single or multiple surfaces2. Holografic Data Processing
• Expansion into spherical waves usingLengendre and Hankel functions
• Determination of the free parameters of theexpansion (order N(f) and coefficients C(f))
3. Extrapolation• Calculation of the transfer function H(r,f)
betweeen input u and sound pressure p(r) at an arbitrary point r in the 3D space outside the scanning surface
• Calculation of derived characteristics(directivity, beam pattern ,sound power)
monopole
dipoles
a
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 58
Expansion into Spherical Waves
tjmnn
N
n
n
nm
inmn
tjmnn
N
n
n
nm
outmn
eYkrhc
eYkrhcrp
),()()(
),()()(),,,(
)1(
0,
)2(
0,
Spherical Harmonics
Hankel function of the second kind
Coefficientsincomingwave
general solution of the waveequation in spherical coordinates
region of validity
surface
sound source
external sound source(ambient noise)
external boundaries(walls)
),,,(),,,(),,,( rprprp inout outgoing wave
incoming wave
Spherical Harmonics
Hankel function of the first kind
Coefficientsoutgoingwave
depending on frequency ω
depending on distance r
depending on angular direction
+r0 ),,,( rp
useful choice of the coordinate system results in three factors:
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 59
Angular Dependency (θ , φ)Spherical Harmonics, Legendre Polynomials
Real part Imaginary part
Bellmann 2012
),()()(),,,( )2(
0, m
nn
N
n
n
nmmnout Ykrhcrp
Spherical Harmonics
monopol
dipols
quadropols
90°
-90°
0°
90°
270°
180°
jmmn
mn eP
mn
mnnY )(cos
)!(
)!(
4
12),(
Legendre Function
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 60
Radial DependencyBessel, Neumann and Hankel functions
)()()()2( krjykrjkrh nnn Hankel function of second kind
Hankel function of first kind
)()()()1( krjykrjkrh nnn
)()(
!!)12()(
1)2( krjy
kr
njkrh nnn
kr
ejkrh
jkrn
n1)2( )(
n
r
a
10log20
kakr /log20 10
Region/1 r
20lo
g 10|
h n(1
) (kr
)/h n
(1) (
ka)|
large amplitude approximation(far field)
small amplitude approximation(near field)
Bessel function jn(kr) Neumann function yn(kr)
singularity !
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 61
Extrapolation of Near Field data
rrfar
Measurement distance
Near field Far field
Extrapolation
a1r
2r
r
Benefits of the near field measurement Comprehensive assessment of direct sound in 3D space (near + far field) High signal to noise ratio Suppression of room reflections (simulated far field conditions) Minimal influence air properties (air convection, temperature field) Low redundancy in the generated data set Spatial resolution can be controlled by order N(f) of the expansion Spatial interpolation is based on acoustical model
N > 2 N > 5 N > 10
frequency100 Hz 1 kHz 10 kHz
order of the expansion
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 62
Far-Field Characteristics
Far-Field Sound Pressure ),,( rp
dBHb ,log20),(
Beam Pattern
Directional Factor
rp
rprH
ax
,,),,(
Sound Pressure On-Axis
)0,0,()( rprpax
With P0=10-12 W
Sound Power Level
dBP
L
010log10dB
p
rprSPL
oax
)0,0,(log20)(
SPL On-Axis
With p0=20 Pa
Directivity Index
dBDDI )(log10 10
Radiation into half space (using baffle) LmrSPLDI ax )4.0(
Directivity
dSH
S
rp
rpD
S
ax
),()(
)(22
2
Sound Power
)(
),,()(
),,(1
2
22
2
rpc
S
dSrHc
rp
dSrpc
S
S
ax
S
Surface S
90°
-90°
0°
90°
270°
180°
0°
0
60°
-15 -10 -590°
-60°
-90°
-30°
dB
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 63
Sound Powerderived from the coefficients of spherical wave expansion
Far fieldcontribution of the coefficients to the radiated sound power
monopol
mismatch between position rm
of a point source and development point r0 of the expansion
+r0
rm
rr S
rr
S
dSppc
dSpv ** 1
2
0,2
0
|)(|2
1
N
n
n
nmmnC
cksee Williams, Fourier Acoustics6.113
order n of thespherical waves
With P0=10-12 W
Sound Power Level
dBP
L
010log10
n
nmmnn
S
rnn Ckrrhc
dSpc
r
2,
)2(
0
2
0
|)()(|2
11)(
Total Sound Power radiated into the far field
Apparent power of nth-order spherical wave
00
rrN
nn
Near field
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 64
Directivityderived from the coefficients of spherical wave expansion
2
2
)(
)(
rp
rp
P
PD
s
ax
a
ax as the ratio of the virtual sound power Pax generated by the on-axis response pax on the sphere in the far field and the total power Pa with
22
0
)(41
rprc
P sa
202
0,2
0
202
4|)(|
2
14
)(
r
cC
ck
r
cPrp
N
n
n
nmmn
as
where
Using sound pressure in far field kr>>1 from above we get
2
0,
2
1
0,
|)(|
)0,2/()(
8)(
N
n
n
nmmn
mn
nN
n
n
nmmn
C
YjC
D DdBDI 10log10)(
Directivity index in dB
spherical harmonics on-axis
sound power
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 65
Nonlinear Distortion Measurements
1. Harmonic Distortion (single-tone stimulus) – Total harmonic distortion– Nth-order harmonic distortion component– Maximum SPL for defined THD limit– Equivalent harmonic input distortion
2. Intermodulation Distortion (two-tone stimulus)– 2nd and 3rd-order intermodulation component– Amplitude modulation distortion
3. Multi-tone Distortion ( multi-tone stimulus) 4. Impulsive distortion (chirp stimulus)
– Impulsive distortion level– Maximum impulsive distortion ratio– Mean impulsive distortion level– Crest factor of impulsive distortion
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 66
Harmonic Distortion Measurement
Conditions:• Excitation with single tone or sinusoidal shirp• Amplitude defined as the rms input value u or by the attenuation factor α
corresponding the input value uref or Smaxax
• Short measurement time is used (1s) or stated• The sound pressure is measured at the evaluation point under normal
measurement condition
V
~
Single tone,Chirp
SpectralAnalysis
excitationfrequency
THD
nth‐HDConstant gain
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 67
Open Question:Is the SPL Level of Harmonic Distortion Components required ?
100 %
50 100 200 500 1k 2k
Frequency [Hz]
2nd Harmonic
10 %
1 %
0.1 %
2nd-order harmonic distortion in percent
displayed versus excitation frequency
%100)(~)(~
)( 22 fp
fpfHD f
As defined in IEC 60268-5 and in new draft
SPL of spectral components
20 50 100 200 500 1k 2k 5k
dB -
[V]
(rm
s)
Frequency [Hz]
40
50
60
70
80
90
100
110
120
130
2nd order harmonic
fundamental
displayed versus excitation frequency
Not defined in IEC 60268-5 and in new draftBUT useful
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 68
H(f,r1)
NonlinearSystem
U(f)
H(f,r2)
p(r1)
p(r2)
soundfield
NonlinearSystem
NonlinearSystem
D
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 distance
Sinusoidalsweep
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
90 1 m distance 60 cm distance 30 cm distance nearfield
Sound pressuremeasurementEquivalent Input
Distortion
Independent of roomDependent on position
Equivalent Harmonic Input Distortion
Transformation to the input by inverse filtering
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 69
Equivalent Harmonic Input DistortionMeasurement
Conditions:• Excitation with single tone or sinusoidal shirp• Amplitude defined as the rms input value u or by the attenuation factor α
corresponding the input value uref or Smaxax
• Short measurement time is used (1s) or stated• The sound pressure is measured at the evaluation point under normal
measurement condition• Distortion are transformed to the input by inverse filtering
V
~
Single tone,Chirp
SpectralAnalysis
ETHD
nth‐EHD
LinearFilter
Constant Transfer Function
H(f,r) H(f,r)-1
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 70
-110
010
110
102 103
[Per
cent
]
Frequency [Hz]
0.1 m 0.5 m 1 m
3rd-order EHD measured at different point
Localization of Speaker Nonlinearity
Nonlinear distributed parameters
Nonlinearities located in one-dimensional signal path
EHD measured at different points in the sound field
h(t,r2)
N1
p(r2)u
h(t,ri)
h(t,r1) p(r1)
p(ri)
sound field
d1
N2,1
N2,2
N2,i
d2,1
d2,2
d2,i
Distributed nonlinearities(e.g. Higher-order modes after
cone break up)
Lumped nonlinearities(e.g. motor and suspension)
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 71
Intermodulation Distortion
difference tones summed tonesharmonics
frequency
Amplitude
sound pressure spectrum
Nonlinear System
input output
IntermodulationDistortion
3rd 3rd
nth
12 )1( fnf
nth
12 )1( fnf
2nd2nd
12 ff 12 ff
3rd
2nd
12 f
nth
1nf
“bass component”1f
“voice component”2f
-50
-40
-30
-20
-10
0
10
20
101 102 103
Response 1Frequency Domain
dB
u (
Uo =
1V
)
f [Hz]
spectrum of two-tone Stimulus
-50
-40
-30
-20
-10
0
10
20
101 102 103
Response 1Frequency Domain
dB
u (
Uo =
1V
)
f [Hz]
spectrum of reproduced stimulus
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 72
Two-tone Intermodulation Distortion Measurement
V~
f2
SpectralAnalysis
excitationfrequency
IMD2
IMD3
+
~
f1
Constant gainrms values
3rd-order intermodulation
%100)(~
)2(~)2(~),(
2
1212213 fp
ffpffpffIMD
%100
),(lg20),( 213
213
ffIMDffL IMD
in percent
in dB
%100)(~
)(~)(~),(
2
1212212 fp
ffpffpffIMD
2nd-order intermodulation
in percent
in dB
%100
),(lg20),( 212
212
ffIMDffL IMD
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 73
Contribution from 2nd and 3rd order modulation
KLIPPEL
-30
-25
-20
-15
-10
-5
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
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 74
Classification of IM-Distortion
Type of Nonlinearity determines Modulation Principle
Amplitude Modulation
Bl(x), Le(x)Doppler,
Sound propagation
FrequencyModulation
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 75
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
Pfa
r [
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
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 76
-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
Pfa
r [
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
Pfa
r [ N
/ m
^2 ]
Time [s]
without Doppler with Doppler
Phase variation
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 77
Two-tone Amplitude Modulation Distortion Measurement
V~
f2
SpectralAnalysis
excitationfrequency
AMD
E(t)
+
~
f1
Constant gain
Amplitude + Phase Information
envelope
Amplitude Modulation
in percent
in dB
1
01
)(1
T
dttET
E
%100*
)(2
),(
1
0121 E
dtEtET
ffAMD
T
100
),(lg20),( 21
21
ffAMDffLAMD
ENVELOPEE(t)
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 78
Contribution from Amplitude Modulation
KLIPPEL
-30
-25
-20
-15
-10
-5
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
Doppler
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 79
Modeling of Loudspeaker Defects
backplate
Voice coil
hitting backplate
Air noise
Air leakage Loose particlesCoil rubbing
vibration
Buzzing
RandomProcess
Not predictableDeterministic modulation of a random process
Semi-DeterministicProcess
DeterministicProcess
reproducible
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 80
Loudspeaker Defect: Buzz problem
Most defects behave as a nonlinear oscillator• active above a critical amplitude• new mode of vibration• powered and synchronized by stimulus• constant output power
Loose joint
(Nonlinearity)
parasitic resonator
Externally excited
spring
mass
Loose joint
(Nonlinearity)
parasitic resonator
Externally excited
spring
mass
timeone period
vibration
distortion signal
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 81
How to get Symptoms of Irregular Loudspeaker Defects
• High displacement x and/or velocity v is required Stimulus with sufficient low frequency content • Defects produce only acoustical symptoms Sensitive microphone required• Defects produce high frequency components Low-pass filtered stimulus and high-pass filtered microphone
signal • Defects are similar to ambient noise Microphone is located close to the source (near-field
measurement)
Generation of Stimulus
AnalysisMeasurement of State Variables
Symptoms
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 82
Measurement of Impulsive Distortion
60
70
80
90
100
110
120
130
100 1000 10000
Sou
nd P
ress
ure
[dB
]
Frequency [Hz]
Frequency Response
peak value
rms value
Peak value is a sensitive measure for most irregular defects such as „rub and buzz“, loose particles
~ high-pass filter
microphone
variablecut-off frequency
fc > 10f
instantaneous frequency f
squarerintegrator
peakdetector
electro-acoustical system
Impulsive Distortion
MIDrms value
IDpeak value
CIDcrest factor
chirp
dh(t)
V
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 83
Open Question:Do we need relative characteristics for impulsive distortion ?
Alternatives:
A: The ratio between impulsive distortion and the total sound pressure (in percent) • Interpretation and use for QC is more difficult• Problems with noise floor
B: The ratio between impulsive distortion and mean value of the fundamental response in the rated frequency band• Curve shape is identical with absolute level ID of the
impulsive• Applicable to QC
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 84
KLIPPEL
-50
-25
0
25
50
75
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
Distortionf
Sparse multi-tone complex
Stimulus Output signal
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 85
V
~SpectralAnalysis
excitationFrequenciesfi i=1,...N
FundamentalResponse
MDS(f)
at f requen cies f≠fi
Measurement of Multitone Distortion
Problem: Result depend on excitation lines selected Standard for multi-tone stimulus is required !!
f
Sparse multi-tone complex
f
Spectrum of distortionf
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 86
Phase of the Excitation Tones is important !!
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)
Time signal (logarithmic sweep)
f
Phase spectrumKLIPPEL
-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)
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
-40
-30
-20
-10
0
10
20
30
40
0 50 100 150 200 250 300
[V
]
Time [ms]
Time Signal (Multi-tone complex)
f
�Phase spectrum
KLIPPEL
-40
-35
-30
-25
-20
-15
-10
-5
0
5
10
15
20
20 50 100 200 500 1k 2k 5k 10k 20k
[dB
]
0 d
B =
1 V
Frequency [Hz]
Amplitude spectrum
random
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 87
Defined Properties of Multi-tone Stimulus
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 ,...,12int
1 /
m
ii
ma
mmod
2
*21
N
iiii tffUtx
1
2cos)(
Frequencies of the sparse line spectrum logarithmically spaced Pseudo-random phase
Amplitude spectrum
Max. Number of frequencies a=48271, m=231-1 and 1=1 Starting
frequencyduration
resolution
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 88
Multi-tone Distortion Measurementcompared with traditional THD, IMD
THD
MTD
IMD
IMD:f1 = 50 Hz @15 V + sweep @ 3V
MTD:Multitone @ 15V
THD: sweep @ 15 V
10 %
1 %
0.1 %
KLIPPEL
-80
-70
-60
-50
-40
-30
-20
-10
0
50 100 200 500 1k 2k 5k 10k 20k
[dB
]
Frequency [Hz]
MTND THD IMD
600 Hz40 Hz 600 Hz
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 89
SummaryWhat is new in Part A ?
• updating measurement techniques using new stimuli (chirp, multi-tone complex, burst)
• (“Comprehensive”) physical evaluation of the acoustical output• A single value (Umax or SPLmax) rated by the manufacturer to
calibrate the rms value of the stimulus • Assessing large signal performance (considering heating,
nonlinearities) • complete assessment of the 3D sound field radiated by the
loudspeaker in an anechoic environment (near and far field)• physcial measurement of impulsive distortion in the time domain
to assess rub & buzz and other loudspeaker defects
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 90
Mechano-AcousticalConversion
Electro-Mechanical Conversion
Air Load
SCOPE OF PART BELECTICAL AND MECHANICAL MEASUREMENTS
Voicecoil
radiator‘s surface
)( cx r
)( cp rcoilF
coilx
u
i
terminals
This International Standard applies to electro-acoustical transducers and passive andactive sound systems such as loudspeakers, headphones, TV-sets, multi-mediadevices, personal portable audio devices, automotive sound systems and professionalequipment. The device under test (DUT) allows access to electrical signals at theterminals or to the mechanical signals of the transducer. The measurements usephysical models describing the transduction process, modal vibration and soundradiation while considering nonlinear and time-variant properties of the DUT.
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 91
IEC 60268 PART BElectrical and Mechanical Measurement
LIST OF CONTENT:• Measurement of the electrical signals at the terminals (u, i)• Electrical characteristics (input impedance, power, …)• Efficiency, sensitivity, …• Lumped parameters (TS, other linear, nonlinear)• Coil and magnet temperature, thermal parameters• Mechanical characteristics and distributed parameters (cone) • Long-term testing • Time varying parameters (aging, fatigue, …) • Climate impact• …
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 92
Not covered in Part B
• Radiation and propagation of sound into 3D space• Black box modeling of DSP, crossover, amplification • Linear and nonlinear distortion in the output signal
Room Interaction
Room Interaction
Room Interaction
Room Interaction
Room Interaction
Room Interaction
Room Interaction
Room Interaction
Room Interaction
Electro‐mechanical Transducer
i(t)
u(t)
Soundradiation
soundradiation
Soundradiation
Mechano‐acoustical Transducer
(Cone)
x(t)Audiosignal
AmplifierCrossover
EQ
Soundpropagation
Soundpropagation
Soundpropagation
p(r2)
p(r1)
p(r3)
sound field
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 93
Black Box
Exploiting A Priory Informationfrom Physics and Psychoacoustics
Inputvariables
Outputvariables
state variables parameters
Structure
Model
1. Structure, Relationship, Operators (e.g. equivalent circuit)
2. Parameters (e.g. moving mass Mms, ...)
3. State variables (e.g. displacement x, ...)
„Grey“ Model
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 94
1. State Variables
• describe the instantaneous state
• vary with time
• depend on input variable (stimulus)
• large amount of information
Black Box
Inputvariables
Outputvariables Structure
state variables parameters
„Grey“ Model
• Current i(t)
• Sound pressure p(t)
• Temperature T(t)
• Displacement x(t)
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 95
2. Structure of the Model
• shows the relationship between the state variables
• gives general description of the physical mechanisms
• depends on the scope (micro or macroscopic view)
Black Box
Inputvariables
Outputvariables Structure
state variables parameters
„Grey“ Model
MMSCMS(x) RMS
b(x)
LE(x)RE(TV)
v
Fm(x,i)
i
b(x)v b(x)i
L2(x)
R2(x)
u
Lumped Parameter Model
1. Linear vs nonlinear2. Deterministic vs. stochastic3. Static vs. dynamic4. Lumped vs. distributed parameters
Distributed model
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 96
3. Model Parameters
Parameters of the model (Exogenous variables)
• should be independent of stimulus and measurement conditions
• are constant values or functions of one or more variables
• describe the properties of the particular unit
Black Box
Inputvariables
Outputvariables Structure
state variables parameters
„Grey“ Model
•Material parameters•Geometry•Transfer functions•Thiele-Small Parameter•Nonlinear Parameter
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 97
Electrical signals at the terminals (u, i)
• Measurement voltage and current– Four wire sensing– Peak and rms values
• Maximum Input Voltage Characteristics– Rated noise voltage– Short term maximum noise voltage– Long term maximum noise voltage– Rated sinusoidal voltage
Related to maximum input powerand rated impedance
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 98
Rated Noise Voltage
Characteristic to be specified:The voltage of a noise signal, simulating normal program, whichthe loudspeaker can handle without any thermal or mechanicaldamage shall be specified by the manufacturer.
Method of measurementSee current standard IEC 60268-5 section 17.1• Applying pink noise shaped and clipped by a network under controlled
climatic condition for 100 h test at a rated voltage• 24 storing under normal climatic condition• Testing electrical, mechanical and acoustical characteristics• TEST fulfilled if there are no defects and no significant changes
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 99
Electrical Input Impedance
Definition– Ratio between complex voltage spectrum and current spectrum (transfer
function of a linear system)
Condition– Sufficient spectral excitation– small signal domain (distortion THD < 1 %)
General Characteristis:– Magnitude and phase response
Transducer Characteristics– Rated Impedance (based on minimum electrical impedance)
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 100
Input Electrical Power
Definition of Input Electrical Power – Real input power – Power dissipated in DC resistance Re
– Power dissipated at nominal impedance
Maximum Input Power Characteristics– Rated noise power (power handling capacity)– Short term maximum noise power– Long term maximum noise power– Rated sinusoidal power
T
real dtituT
tP0
)()(1
)(
)()()( 2Re tRtitP erms
nom
rmsnom Z
tutP
)()(
2
Related to maximum inputvoltage and rated impedance
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 101
Electrical Lumped Parameters
• Small Signal Parameters (based on linear modeling)– DC resistance Re(Tv)– Equivalent circuit of the mechanical resonator– Lossy inductance parameters (Wright, Leach, LR2,...)
• Large Signal Parameters (based nonlinear modeling)– Inductance Le (x) versus voice coil displacement– Inductance Le(i) versus input current– Nonlinear variation NL(x,i) of impedance representing lossy inductance
)0,0(
),(
)0,0(
),(
)0,0(
),(
2
2
2
2
ixR
ixR
ixL
ixL
ixL
ixL
e
e
LR2-Model)0,0(
),(),(
ix
ixixN
L
LL
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 102
KLIPPEL
0
10
20
30
40
50
60
70
1 2 5 10 20 50 100 200 500 1k
Magnitude of electric impedance Z(f)
[Ohm
]
Frequency [Hz]
Measured Fitted
Interpretationof the Electrical Input Impedance Ze(j)
)(
)()(
jI
jUjZe
voltage
current
Electrical Impedance at the Terminals
Re
ZL(j)
Resonance Frequency
cesmesmsmss LCMC
f1
2
11
2
1
Electrical Quality Factor
emess
sms
ees RCf
fBlC
RQ
2
22 esmess
smsmsms RCf
fRCQ
2
2
1
Mechanical Quality Factor
fs,Qes,Qms
Cmes
Re(TV)
i
ZL(j )
u Lces Res
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 103
Mechanical Measurements
Displacement x(t,rc) at arbitrary point rc on the radiatior surface• Non-destructive, non-contact measurement without additional
load optical sensor• Dynamic measurement required (full audio band)• Scanning technique provides sufficient spatial resolution• Forces are difficult to measure ( x, v, a)• Measurement of displacement x provides dc-component
generated dynamically by transducer nonlinearities
RadiatorMotor Air LoadVoicecoil
radiator‘s surface
)( cx r
)( cp rcoilF
coilx
u
i
terminals
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 104
Voice Coil Displacement
Mean coil displacement xcoil averaged over coil
N
nnc
L
c
coil txNL
drtx
tx1
,0 ),(
1),(
)( r
r
RadiatorMotor Air LoadVoicecoil
radiator‘s surface
)( cx r
)( cF rcoilF
coilx
u
i
terminals
Measurements at 4 points
x
x
xx
Voice coilRadiator‘ssurface
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 105
Identification of Mechanical Parameters
• Requires second measurement with additional mass or enclosure
• Based on impedance measurement• No mechanical sensor required• Time consuming• Problems with mass attachment, box
leakage
• Requires mechanical (acoustical) sensor (e.g. Laser)
• Only one measurement (fast)
• Driver in free air or in enclosure
• Reliable and reproducible data
• Can be applied to tweeters
Direct Measurement of a Mechanical Signal
Known Perturbation of Mechanical System
(traditional technique)
We need more information about the mechanical system
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 106
Mechanical Lumped Parameters
• Small Signal Parameters (based on linear modeling) Transducer operated in free air (#=s), box (#=c) or vacuum (#=d)
– Moving mass Mm#
– Force factor Bl(x)– Stiffness Km# and compliance Cm# of the suspension– Creep parameters (Knudsen, Ritter)
• Large Signal Parameters (based on nonlinear)– Force factor Bl(x)– Stiffness Km#(x) and compliance Cm#(x) versus voice coil displacement– Mechanical resistance Rm#(v) versus voice coil velocity v
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 107
Mechanics Separated from Air Loadby performing a measurement in vacuum
moving air mass air
Cavities
radiationresistance +turbulences
air leaks
pure mechanical elements measured in vacuum
electro-dynamical transducer operated in air
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 108
Example: Micro-speaker (3)
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 109
Acoustical Lumped Parameters
• Small Signal Parameters (based on linear modeling)– Nominal effective radiation area Sd(f=fs)– Mechano-acoustical transduction factor Sd(f) versus frequency– Acoustical compliance CAB of the enclosed air– Acoustical mass of the air in the port– Equivalent air volume VAS of loudspeaker compliance
• Large Signal Parameters (based on nonlinear modeling)– Mechano-acoustical transduction factor Sd(f,x) versus frequency f and
displacement x corresponding to effective radiation area Sd=Sd(f=fs,x=0)– Acoustical compliance CAB(p) of the enclosed air depending on sound
pressure
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 110
Effective Radiation Area SD
SD
• is an important parameter of the lumped parameter model• describes coupling between mechanical and acoustical domain• determines the acoustical output (sensitivity, efficiency)• affects the precision of the lumped parameter measurement if the test box
perturbation technique is used (Mms, Bl, Kms, Cms)
Precise Measurement of SD is important !
Mmd Cmd Rmd-1Bl
Re
V=dx/dt
i
Blv
Bli
U Sd Cabp Ral
qa=Sdv
qlqbpSd
ZL(f)
Map
Electrical domain Mechanical domain Acoustical domain
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 111
Effective Radiation Area Sd
1. Geometrical Definition• based on surround geometry• Easy to use• Applicable to woofers (surround area is much smaller than cone
area)
2. Acoustical Definition• Based on voice coil displacement and acoustical output• Required for headphones, microspeakers
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 112
A Good Approximation ?Calculation of Effective Radiation Area SD based on measured diameter
22
0
22
424
34
ddd
ddddddS
i
ioiioiD
R. Small: less than 1% error if 0.8 d0 < di)
Assumption:
• displacement decreases linearly over the surround
• displacement in constant in the inner part
d0
d
di
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 113
Limits of the Approximation
• No linear decay of displacement in the surround area
Voice coil
In headphone, micro-speakers, tweeters, compression drivers :
• No constant displacement in the „piston area“
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 114
replaced by
)(
),(
)(
coil
cc
SD v
dSv
S c
r
using mean voice coil velocity
2
),,(
)(
2
0
drv
vcoil
coil
)(q
),( cv r
Radiator‘s surface
coilr)(q
)(DS
)(coilv
Rigid piston
The effective radiation area SD is an important lumped parameter describing the surface of a rigid piston moving with the mean value of the voice coil velocity vcoil and generating the same volume velocity q as the radiator‘s surface. The integration of the scanned velocity can cope with rocking modes and other asymmetrical vibration profiles.
Effective Radiation Area SDDefinition
)( 0DD SS Reading the absolute value at fundamental resonance
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 115
Predicting the Acoustical Output at higher frequencies based on effective radiation area SD(f)
useful for transducers having• high complexity of the mechanical vibration• low complexity of the acoustical system (ka < 1)e.g. (in-ear) headphones, microspeaker application
radiatedsound power, (SPL in a duct) )(
0AR fS
cR
d
using effective radiation areaSD(f) as a function of frequency f
KLIPPEL
0
100
200
300
400
500
600
700
800
900
1000
102 103 104
Effective radiation Surface (Sd)
Sd
[cm
^2]
f [Hz]
Sd
30
40
50
60
70
80
102 103 104
Total Sound Pressure Level
SP
L [d
B]
Frequency [Hz]
Total Sound Pressure Level
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 116
Relative Small Signal Parameters
• Transducer operated in air (#=s), enclosure (#=c) or vacuum(#=d) (2nd order system)– Resonance frequency f#– Total quality factor Qt#
– Electrical quality factor Qe#
– Mechanical quality factor Qm#
• Additional Resonantor (4th order system)– Resonance frequency fp of the additional resonator (port, passive radiator)– Quality factor Qp of an additional mechanical or acoustical resonator
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 117
Parameters at x=0
Overview on Single-Valued Parametersderived from loudspeaker nonlinearities
ElectricalParameters
ee LR ,
RelativeParameters
bbesmstss QfQQQf ,,,,,
MechanicalParameters
msmsmsms KCRMBl ,,,,
10 % distortionin IMD or THD
NonlinearParametersat x=xpeak
Compliance limited displacement xC
Force factor limited displacement xB
Voice Coil Offset xoffset fromreference DUT
Stiffnessasymmetry AK
Mms Cms(x)Rms
Bl(x)
Le(x,i)Re (Tv)
v
Fm (x,i)
i
Bl(x)v Bl(x)i
L2(x,i)
R2(x,i)
u Sd Cabpbox Ral Map
Sdvqp
Symmetry point in the Bl(x) curve
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)
0
1
2
3
4
5
-5,0 -2,5 0,0 2,5 5,0
Kms(x) N/mm
x mm
xpeak
KMS( -xpeak)
coil in
-xpeak
KMS( xpeak)
coil out
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 118
Characteristicsderived from Nonlinear Curve Shape
NONLINEAR FORCE FACTOR• Force factor limited displacement XBl generating 10 % distortion• Symmetry point Xsym(Xac) depending on AC amplitude Xac• Offset xoff of the voice coil from a defined reference rest position
NONLINEAR STIFFNESS Kms(x)• Compliance limited displacement Xc generating 10 %
distortion• Suspension asymmetry Ak
NONLINEAR INDUCTANCE Le(x)• Inductance limited displacement XL generating 10 %
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 119
Force Factor Limited Displacement xBl
defined according IEC standard 62458
0,0
1,0
2,0
3,0
4,0
6,0
-5,0 -2,5 0,0 2,5 5,0
Bl N/A
<< Coil in X mm coil out >>
Blmin=82 %
Bl(x=0)
Bl(xBl)
xBl
Steps:
1. Operate transducer in large signal domain
2. Read displacement XBl
where force factor Bl(xac) decreases to 82 % of the value Bl(x=0) at rest position
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 120
Compliance Limited Displacement xCdefined according IEC standard 62458
Steps:
1. Operate transducer in large signal domain
2. Read displacement XC where compliance value Cms(xac) decreases to 75 % of the value Cms(x=0) at rest position
0
0.2
0.4
0.6
0.8
1
-5,0 -2,5 0,0 2,5 5,0
Cms(x) mm/N
x mm
xC
coil in coil out
CMS(x=0)
0.75CMS(x=0)
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 121
Peak Displacement limited by Nonlinearities
Xmax,10%Generating not more than 10 % THD or 10 % IMD
minimum
XcX limited
by Cms(x)
10 % THD
KLIPPEL
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
-4 -3 -2 -1 -0 1 2 3 4
N/A
<< Coil in X [mm] coil out >>
Bl(X)
Clim = 75 %
Compliance
XBlX limited by Bl(x)
10 % IMD
KLIPPEL
0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9
-4 -3 -2 -1 -0 1 2 3 4
mm/N
<< Coil in X [mm] coil out >>
Cms(X) Cms (-X)
Bllim = 82 %
Force Factor
XDX limited
by Doppler
10 % IMD
Doppler
XLX limited by Le(x)
10 % IMD
KLIPPEL
0
5
10
15
20
25
101 102 103 104
Magnitude of electric impedance Z(f)
[Ohm
]
Frequency [Hz]
x= 0 mm x = - 4 mm x = + 4 mm
Zlim = 10 %
Inductance
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 122
0
1
2
3
4
5
6
7
-5 -4 -3 -2 -1 0 1 2 3 4 5
Force factor Bl(X)
Bl [
N/A
]
<< Coil in X [mm] coil out >>
Reference
KLIPPEL
0
1
2
3
4
5
6
7
-5 -4 -3 -2 -1 0 1 2 3 4 5
Force factor Bl (X)
Bl [
N/A
]
<< Coil in X [mm] coil out >>
How to check the
Voice Coil Rest Position
Offset from Symmetry Point Offset from Reference Curve
KLIPPEL
0
1
2
3
4
5
6
7
-5 -4 -3 -2 -1 0 1 2 3 4 5
Force factor Bl (X)
Bl [
N/A
]
<< Coil in X [mm] coil out >>
• Reference curve is required (Golden Reference DUT) • Coil height and gap depth are constant• Important for QC end-of-line testing• can cope with asymmetrical curve shape
Symmetry
Induction B
pole piece
pole platemagnet
voice coil
displacementx=0
Induction B
pole piece
pole platemagnet
voice coil
displacementx=xb
voice coil rest position
• Can not cope with B field asymmetry• No reference curve required• Important for product development• Transducer diagnostics
Symmetry pointOffset
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 123
0,0
1,0
2,0
3,0
4,0
6,0
-5,0 -2,5 0,0 2,5 5,0
Bl N/A
<< Coil in X mm coil out >>
Blmax
Symmetry point Xsymdefined according IEC standard 62458
)()( acsymacsym xxBlxxBl
Definition:Symmetry point xsym is the centre point between two points having the same Bl value at a distance 2xac
0,0
1,0
2,0
3,0
4,0
6,0
-5,0 -2,5 0,0 2,5 5,0
Bl N/A
<< Coil in X mm coil out >>
2xac
0,0
1,0
2,0
3,0
4,0
6,0
-5,0 -2,5 0,0 2,5 5,0
Bl N/A
<< Coil in X mm coil out >>
xsym
xac xac
x1 x2
Blmax
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 124
Stiffness Asymmetry AKdefined according IEC standard 62458
Steps:
1. Operate transducer in large signal domain
2. Read stiffness values Xms(Xpeak) and Xms(-Xpeak) at maximal peak displacement
3. Calculate stiffness asymmetry according
0
1
2
3
4
5
-5,0 -2,5 0,0 2,5 5,0
Kms(x) N/mm
x mm
xpeak
KMS( -xpeak)
coil in
-xpeak
KMS( xpeak)
coil out
%,100)()(
)()(2)(
peakMSpeakMS
peakMSpeakMSpeakK xKxK
xKxKxA
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 125
Electro-acoustical Efficiency
1. Efficiency in a specified frequency band (e.g. pass band)– Ratio between measured electrical nominal input power Pnom
and measured acoustical output power Pnom
– Based on lumped parameter modeling
2. Mean Efficiency in a specified frequency band– Average of efficiency measured in third-octave bands
nom
a
P
P0
c
S
MR
Bl d
mse 2
)( 20
2
2
0 for f >fs and ka<1, radiation on one side considered
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 126
Sensitivity
Calculated from the frequency response and effective frequency range, as the sound pressure level produced at 1 m on the reference axis by an applied voltage of 2,83 V.
Narrow-band sensitivity: the test signal is 1/3-octave filtered noise centered at 1 kHz, or at the geometricmean of the limit frequencies of the effective frequency range if different from 1 kHz. The frequencyshall be stated.
Broad-band sensitivity: the test signal is 2-octave filtered noise centered at 1 kHz, or at the geometricmean of the limit frequencies of the effective frequency range if different from 1 kHz. The frequencyshall be stated.
Reference: AES recommended practice Methods of measuring and specifying the performance of loudspeakers for professional applications Part 1: Drive units, AES2 -1-R
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 127
Mechanical Distributed Characteristics
• Set of transfer functions between input voltage u(t) and displacement X(t,rc) at arbitrary point rc on the radiatior surface
)(
),(),(
fU
fXfH C
Cx
rr
RadiatorMotor Air LoadVoicecoil
radiator‘s surface
)( cx r
)( cF rcoilF
coilx
u
i
terminals
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 128
Mechanical and Acoustical Characteristicsderived from Displacement Transfer function
• Predicted Sound Pressure Level SPL(f,r) • Accumulated Acceleration level AAL(f,r)• Relative Rocking Level RRLn of the nth rocking mode• Lowest radiation efficiency ηrad
• Acoustical cancellation distance Lcan
• Cone break-up frequency fbreak-up
Scanning Vibrometer )(
),(),(
fU
fXfH C
Cx
rr Diagnostics
On Cone vibration
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 129
Accumulated Acceleration
Rigid body modes
30
40
50
60
70
dB
90
100 1000 10000f [Hz]
Accumulated Acceleration Level
Integral of the absolute value of weighted cone acceleration
1078,1 Hz
)( ca r
)( ca r
with reference sound pressure p0
dBp
pAAL
o
aaaa
2
)(log20)(
rr
c
S
caaa dSaWpc
)()( rr
and a useful scaling W to comparable ALL with SPL output
ca
Wrr
20
cone‘s surface Sc
ca rr ar
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 130
Accumulated Acceleration Level (AAL)
Acceleration level
Total sound Pressure levelRigid body modes
30
40
50
60
70
dB
90
100 1000 10000f [Hz]
SPL
AAL
Rigid body mode
• describes total mechanical vibration• is comparable with SPL • is never smaller than SPL • predicts potential acoustical output • neglects acoustical cancellation• is identical with SPL for a rigid body mode
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 131
Characteristics for DiagnosticsSingle-valued parameter derived from AAL (5)
0
10
20
30
40
50
60
70
80
100 1000
dB
f [Hz]
Total AAL
Circular Component (AAL)
1. Search for first maximum in quadrature component in AAL-on-axis !
Quadrature Component (AAL)
3. rocking mode is negligible if RRL< -5dB
RRL(frock)=AALquad-AALin
2. Determine the relative rocking level RRL defined by
RRL
frock
How critical is the rocking mode ?
Woofer A with paper cone
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 132
Thermal Measurements
• Increase of mean voice coil temperature ΔTv based on monitored DC voice coil resistance Re(t)
• Increase of magnet temperature ΔTm
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 133
Temperature Measurement By Using a Steady-State Pilot Tone
FourierTransform
loudspeakersystem
currentsensor
U(t) I(t)
-
Stimulus
voltagesensor
poweramplifier
PilotTone
TemperatureCalculation
Resistance of coldspeaker
Conductivity of CoilMaterial
Increase of VCTemperature
Transducer: 1- 4 HzSystems: 0.01 ... 3 kHz
Benefit of adding an additional tone:
•Quasi-dc measurement with ac-power amplifier possible (f < 4 Hz)•High speed monitoring of variation of Re(t)•Long term averaging using low amplitude•No external stimulus required •active during cooling phase (OFF-cylce)•Impedance measured at one frequency• power of pilot tone is negligible
KLIPPEL
5
10
15
20
25
30
35
40
45
50
2 5 10 20 50 100 200 500 1k 2k 5k 10k
Magnitude of electric impedance Z(f)
[Ohm
]
Frequency [Hz]
Measured
Most accurate measurement for
transducer
Impact of woofer, tweeter and crossover
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 134
Thermal Characteristics
Basic Characteristics• Parameters of a thermal model
Derived Characteristics• Effective total thermal resistance Rtherm= ΔTv/Preal
• Thermal time constant of the voice coil τv and magnet τm
• Bypass factor to assess convection cooling and heating by eddycurrents
Rtv
RtmCtv Ctm
TvTm
Ta
Rtc(v)
Peg
Rtt(v)
CtaRta(x)
Pcon
Ptv Pg
Ctg
Rtg
Tg
Pmag
Pcoil
TgTvTm
Can be used to predict heatingand cooling for any stimulus
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 135
Voice Coil Heating depends on the Spectral Properties of the Stimulus
VocalPopClassic
6,8 K/W 4,6 K/W 7,5 K/WTv/Preal=
Music: Thermal resistance is not constant !!
High voice coil displacement gives high Convection cooling
KLIPPEL
- 10
0
10
20
30
50
70
80
90
100
0
5
10
15
25
30
0 250 500 750 1000 1250 1500 1750 2000 2250
[K] [W]
t [sec]
Delta Tv
P Re
t 3t 2t 1
40
Preal
T V
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 136
Rtv
RtmCtv Ctm
TvTm
Ta
Rtc(v)
Peg
Rtt(v)
CtaRta(x)
Pcon
Ptv Pg
Ctg
Rtg
Tg
Pmag
Pcoil
TgTvTm
Nonlinear Thermal Model
Air convection
coolingDirect heat
transfer
coil
dome
v
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 137
Time Variant Parameters
• Shift of resonance frequency• Shift of the voice coil rest position • Electrical characteristics (input impedance, power, …)• Efficiency, sensitivity, …• Lumped parameters (TS, other linear, nonlinear)• Coil and magnet temperature, thermal parameters• Mechanical characteristics and distributed parameters (cone) • Long-term testing • Time varying parameters (aging, fatigue, …) • Climate impact• …
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 138
Variation of Suspension Stiffness K(t)versus Measurement Time t
Disadvantages of :• measurement results depends on the
properties of the stimulus• assumes constant excitation during
power test• can not be transferred to other stimuli• neglects the slope of the stiffness
variation
)h1(
)h100(h100
tK
tKR
break-in
fatigue
accumulated load
Stiffness ratio after 1 h and 100 h power testing
Idea:Replacing time t by a quantity describing the dosage of the mechanical load
Performing a power test with pink noise of constant amplitude
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 139
Mechanical Load Model
Measurement Condition:same stimulus of constant amplitude during the power test
N
i
wWi
ieCWK1
/1)(
)()0()(ˆ WKWKWK
Stiffness of loudspeaker suspension versus accumulated work W
N=2 sufficient for most cases
loss of stiffness
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 140
Your feedback is appreciated
There are the following opportunities:• Join or contact your national IEC committee• Attend the AES standard group SC-03-04• Attend the ALMA symposium 2015 (before CES)• Contact the German standard group
([email protected])• Or just contact me ([email protected])
IEC Standard Project LOUDSPEAKER MEASUREMENTS, 141
Thank you !