TUTORIAL IEC Standard Project 60268-5 A and B AES 2015€¦ · · 2017-08-23SCOPE of the existing IEC 60268-5 Starting point IEC Standard Project ... electrical impedance will be

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,


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, ...)


SCOPE of the existing IEC 60268-5

Starting point


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)


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


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)


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)


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)


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


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 !


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.


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


Not covered in Part A


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


Conventional Characteristics applicable to active loudspeaker systems


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


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)


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


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 ?


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


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


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


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. .


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


x

z

y

Recommended Position and Orientation

normal vector nref


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


Measuring Distance between DUT and microphone


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 |


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)


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


~

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.


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


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


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


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


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


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


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


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


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).


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).


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)


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.


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.


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


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

~


FourierTransform

Smoothing

FourierTransform

rms value of the input signal

refp

ufHfSPL max

~),(log20),(

rr

bandwidth B

(α ≤ 0.1)


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

~


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


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


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

~


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


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)


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


KLIPPEL

0,0

2,5

5,0

7,5

10,0

102 103

Group delay

ms

Hz

Latency in the electrical system


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


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

~


)(

),,,(),,,(

fU

rfPrfH


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


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


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


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


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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


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)

. . ..


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


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


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:


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


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 !


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


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


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


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


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


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


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


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

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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


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


-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)


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


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


Contribution from 2nd and 3rd order modulation

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-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


Classification of IM-Distortion

Type of Nonlinearity determines Modulation Principle

Amplitude Modulation

Bl(x), Le(x)Doppler,

Sound propagation

FrequencyModulation


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


-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


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


Pfa

r [ N

/ m

^2 ]

Time [s]

without Doppler with Doppler

Phase variation


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)


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


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


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


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


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


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


KLIPPEL

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-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


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


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

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-35

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-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

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-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

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-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


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


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

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-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


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


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 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• …


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


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


1. State Variables

• describe the instantaneous state

• vary with time

• depend on input variable (stimulus)

• large amount of information

Black Box

Inputvariables

Outputvariables Structure


„Grey“ Model

• Current i(t)

• Sound pressure p(t)

• Temperature T(t)

• Displacement x(t)


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



„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


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



„Grey“ Model

•Material parameters•Geometry•Transfer functions•Thiele-Small Parameter•Nonlinear Parameter


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


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


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)


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


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


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


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


)( cx r

)( cp rcoilF

coilx

u

i

terminals


Voice Coil Displacement

Mean coil displacement xcoil averaged over coil

N

nnc

L

c

coil txNL

drtx

tx1

,0 ),(

1),(

)( r

r



)( cx r

)( cF rcoilF

coilx

u

i

terminals

Measurements at 4 points

x

x

xx

Voice coilRadiator‘ssurface


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


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


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


Example: Micro-speaker (3)


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


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


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


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


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“


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


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


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


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


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 %


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


Compliance Limited Displacement xCdefined according IEC standard 62458

Steps:


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)


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


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


[Ohm

]

Frequency [Hz]

x= 0 mm x = - 4 mm x = + 4 mm

Zlim = 10 %

Inductance


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

]


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

]


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

]


• 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


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


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


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


xsym

xac xac

x1 x2

Blmax


Stiffness Asymmetry AKdefined according IEC standard 62458

Steps:


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


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


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


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



)( cx r

)( cF rcoilF

coilx

u

i

terminals


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


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


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


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


Thermal Measurements

• Increase of mean voice coil temperature ΔTv based on monitored DC voice coil resistance Re(t)

• Increase of magnet temperature ΔTm


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


[Ohm

]

Frequency [Hz]

Measured

Most accurate measurement for

transducer

Impact of woofer, tweeter and crossover


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


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


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


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• …


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


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


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])


Thank you !

Documents

TUTORIAL IEC Standard Project 60268-5 A and B AES 2015€¦ · · 2017-08-23SCOPE of the existing IEC 60268-5 Starting point IEC Standard Project ... electrical impedance will be