Tutorial to a new IEC Standard Project 2016 by Wolfgang ... and... · IEC Standard Project...

IEC Standard Project LOUDSPEAKER MEASUREMENTS, 1

Electrical and Mechanical Measurements

of Loudspeakers and Sound System Equipment

Tutorial to a new IEC Standard Project

2016

by Wolfgang Klippel,


Need for updated IEC Loudspeaker Standards (60268-xx)

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)


Disclaimer

This 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 IEC 60268-21)• 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 A (IEC 60268-21)ACOUSTICAL (OUTPUT BASED) MEASUREMENTS

This International Standard applies to passive and active sound systems such as

loudspeakers, headphones, TV-sets, multi-media devices, personal portable audio

devices, automotive sound systems and professional equipment. The device under test

(DUT) may be comprised of electrical components performing analogue and digital

signal processing prior to the passive actuators performing a transduction of the

electrical input into an acoustical output signal. The measurements presented here

determine the transfer behaviour of the DUT between an arbitrary analogue or digital

input signal and the acoustical output at any point in the near and far field of the

system. 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. car

interior) can also be considered in the evaluation of the sound system.

Note: This standard does not apply to microphones and other sensors. This standard does

not require access to the state variables (voltage, current) at the electrical terminals of the

transducer. Sensitivity, electric input power and other characteristics based on the

electrical impedance will be described in a separate standard document IEC 60268-Xb

dedicated to electrical and mechanical measurements.


SCOPE OF PART AACOUSTICAL (OUTPUT BASED) MEASUREMENTS (IEC 60268-21)

Evaluation is based on evaluation of acoustical output

control parameters

(e.g. attenuation)

digital audio

stream

Properties of the

black box depend on

control parameters

and stimulus

drivers

Black box

No access to internal states

Near Field Far Field


SummaryWhat is new in IEC 60268-21 ?

• 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


Relationship to related standards projects

• electrical & mechanical Measurements IEC 60268-XX

• Microspeakers IEC 63034, TC100-2683 NP

• Standard Method of Measurement for Powered Subwoofers ANSI/CEA 2010

• Standard Method of Measurement for IN-HomeLoudspeakers ANSI/CEA 2034


Mechano-

Acoustical

Conversion

Electro-

Mechanical

Conversion

Air Load

SCOPE OF PART BELECTICAL AND MECHANICAL MEASUREMENTS

Voice

coil

radiator‘s

surface

)( cx r

)( cp rcoilF

coilx

u

i

terminals

This International Standard applies to transducers but also to passive and active sound

systems such as loudspeakers, headphones, TV-sets, multi-media devices, personal

portable audio devices, automotive sound systems and professional equipment where

the electrical input terminals and the surface of the radiator are accessible by an

electrical or mechanical sensor. The standard describes only physical measurements

which assess the transfer behaviour of the device under test (DUT). 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. car interior) can also be

considered in the physical evaluation of the sound system. The standard does not

assess the perception and cognitive evaluation of the reproduced sound and the impact

of perceived sound quality.


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)

Sound

radiation

sound

radiation

Sound

radiation

Mechano-acoustical

Transducer

(Cone)

x(t)Audio

signal

Amplifier

Crossover

EQ

Sound

propagation

Sound

propagation

Sound

propagation

p(r2)

p(r1)

p(r3)

sound

field


Black Box

Exploiting A Priory Informationfrom Physics and Psychoacoustics

Input

variablesOutput

variables

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


Normal Measurement Condition

• Mounting of the DUT and acoustical loading (baffle, clamping in free

air, coupler, horn, plane wave tube, …)

• Acoustical environment (full free space, half space, free air, target

application, …)

• Unwanted electrical, mechanical or acoustical signals (e.g. noise)

• The DUT is acclimatized to the normal ambient conditions

• Additional cooling periods are required

• Test signal (stimulus) with specified properties (spectrum, duration,

etc.) at specified rms value

• Attenuators, equalizers, dynamics and any other active control

elements shall be set to their “normal” position

• Measuring equipment suitable for determining the wanted

characteristics (accuracy


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 power

and rated impedance


~

Maximum Input and Output Signal

Sound

pressure

output

Rated maximum input value umax

• Good for DUTs with a single input and

constant transfer function between

input 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 broadband test stimulus in a frequency range 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, limiters,

ect.


How to rate umax and SPLmax?

The manufacturer has freedom to rate umax and SPLmax

but 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 withoutdamage

• 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

• Durability of the loudspeaker shall be tested by a 100 h test using this stimulus


How to verify the maximum amplitude ?

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


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


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


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 maximum noise power (power handling capacity)

– Short term maximum noise power

– Long term maximum noise power

– Rated sinusoidal power

NZuP /~2

maxmax

NNE ZtutP /)(~)( 2

,

)()(~

)( 2 tRtitP ERE

dtituT

tPREAL )()(1

)(


Complex 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 %)

Single value Characteristic:– Rated input impedance (based on minimum electrical impedance)

)(/)()( fIfUfZ E


Mechanical Measurements

Vibration x(t,rc) at arbitrary point rc on the radiatior surface

• Non-destructive, non-contact measurement without additional load optical sensor

• measured in the direction of the normal vector

• 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-componentgenerated dynamically by transducer nonlinearities

RadiatorMotor Air LoadVoice

coil

radiator‘s

surface

)( cx r

)( cp rcoilF

coilx

u

i

terminals


Positioning of the Radiator

z

x

yOro

rn

refr ,r

Reference plane and normal vector

The reference plane with the normal vector nr shall

be used to define the reference axis and the

reference point rr,ref.

Reference point

The reference point rr,ref shall be a point on the

radiator’s surface cutting the reference plane. The

position of the reference point rr,ref shall be

specified by the manufacturer.

Orientation vector

The orientation vector or defines the orientation of

the radiator within the reference plane and the

direction of azimuthal angle =0 in spherical

coordinates.

Rated conditions used to describe the geometry and

position of the radiator in the coordinate system


Mean Voice Coil Position

Mean coil displacement xcoil averaged over coil

N

n

nc

L

c

coil txNL

drtx

tx1

,0 ),(

1),(

)( r

r


coil

radiator‘s

surface

)( cx r

)( cF rcoilF

coilx

u

i

terminals

Measurements at 4 points

x

x

xx

Voice coilRadiator‘s

surface


Voice Coil Position

KLIPPEL

-5

-4

-3

-2

-1

0

1

2

3

4

5

0 100 200 300 400 500 600 700 800 900

Voice coil displacement00:15:30

[mm]

t [sec]

Xpeak Xdc Xdcmax Xbottom

Dynamic

DC displacement XDC

Coil‘s rest position X0

displacement xrel

Only AC component xAC generates sound pressure output

Absolute voice coil position is

determined by

),()()( 0 DUTtXtxtx relabs

Voice coil rest position X0 depends on time t

and the device under test (DUT)

)()()( txtxtx DCACrel

Voice coil displacement DC displacement XDC depends on the audio

signal and transducer nonlinearities

rest position of

the voice coil

Upper boundary

Lower boundary

overload overload


-310

-210

-110

10 20 50 100 200 500 1k 2k 5k 10k

Magnitude of transfer function Hx(f)= X(f)/U(f)

[mm

/V]

Frequency [Hz]

Displacement Transfer Function

VibrationMotor Radiation

F

V

X(r)

F(r)

soundfield

u

near

field

far

field

fs

12 dB/octave

compliance dominant mass dominant

Hx(0)

creep

Log-Model

)0(

)(

x

sx

tsH

fHQ

Total quality factor

voltage

displacement

Qts > 1

)(/),(),(, fUfXfH rrUX rr


Small Signal Lumped Parametersbased on linear modeling

Electrical Parameters– DC resistance Re(Tv)

– Lossy inductance (Wright, Leach, LR2,...)

– Electrical representation of the fundamental resonator (capacitor CMES,

inductance LCES and resistance RES )

Relative lumped parameters– resonance frequency

– mechanical quality factor, electrical quality factor, total quality factor

Mechanical lumped parametersmoving mass, stiffness, compliance and mechanical resistance


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(jw)

)(

)()(

w

ww

jI

jUjZe

voltage

current

Electrical Impedance at

the Terminals

Re

ZL(jw)

Resonance Frequency

cesmesmsms

sLCMC

f1

2

11

2

1

Electrical Quality Factor

emess

sms

ees RCf

fBlC

RQ

2

22

esmess

smsms

ms RCffRC

Q

22

1

Mechanical Quality Factor

fs,Qes,Qms

Cmes

Re(TV)

i

ZL(j )

u Lces Res

w


Mms Cms(f) Rms(f)-1

Bl

Re

V=dx/dt

i

Blv

Bli

U

ZL(f)

Equivalent Circuit of a electrodynamical transducer operated in free air

Electrical domain Mechanical domain

Electrical dc

Resistance

Impedance describing

lossy inductance

Force factor

LossesMoving mass

compliance

Voltage

current

Back EMF

Driving

force

velocity

mechanical admittance (Mobility, Fi) Type Analogy

hres(f)

representing mechanical elements

including air loadrepresenting voice coil

residual

admittance


Lossy Inductance ZL(jw)measured curves fitted by an ideal inductance

0.1

1

10

40

50

60

70

80

90

100

1 2 5 10 20 50 100 200 500 1k

[Oh

m]

[de

g]

Frequency [Hz]

Magnitude

(measured)

Magnitude (fitted)

Phase (measured)

Phase (fitted)

6dB/octave

90 degree

• 1 Parameter only

• Large deviation

• limited use

Le

Mms Cms(f) Rms-1

Bl

Re

V=dx/dt

i

Blv

Bli

U

ZL(f)


Models for Electrical Impedance ZLEddy currents cause a „lossy inductance“

• Leach

ZL(jω)= Krm·ωErm + j·(Kxm·ωExm )

• Wright

• LR-3 (shunted inductance)

• and more (e.g. Thorborg)

Le

R2

c)

L2

R3

L3

ZL(jω)= K·(jω)n ; ω= 2πf

a)

ZL(jw,x)

ZL(jω) = Le·jω + (R2·L2·jω ) / (R2 + L2·jω)

• LR-2 (shunted inductance)

Le

L2

R2

b)

Mms Cms(f) Rms-1

Bl

Re

V=dx/dt

i

Blv

Bli

U

ZL(f)


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


Perturbation Method: Sealed Test Box

Technique:A second measurement is performed while a

known air stiffness Kair is added to the

suspension

Advantages:• simple technique

• Cms is measured primarily

Problems:• depends highly on precise value of effective

radiation area Sd

• residual air volume (inside the transducer)

can not be considered

• requires sealed diaphragm

• cannot be used to measure mechanical

mass without air load

•Time consumingSd

Air volume Vbox

generating an

additional stiffness Kair


Perturbation Method: Added Mass

Technique:1. In a first measurement the resonance frequency fs

of the transducer is measured

2. In a second measurement the resonance

frequency fm of the transducer is measured while

a known mass Madd is added to the cone.

3. The moving mass may be calculated by two

methods

ring of clay used as added mass Madd

1

2

m

s

addms

f

f

MM

1

mes

sem

addms

fQ

fQ

MM

Bl is constantCms is constantAssumption:

Advantages:• Simple technique

• Mms is measured primarily

Problems:• cannot be applied to tweeter and microspeakers

• Time consuming

• Mechanical Resistance or stiffness are assumed

as frequency independent parameters


Direct Parameter Identification using an optical laser sensor

Technique:

In addition to the voltage and current also

the voice coil vibration (e.g.

displacement) is measured by using an

optical sensor

Advantages:

• Fast (one step technique)

• Simple to use

• Bl is measured primarily

• Most precise results

• Can be applied to most transducers

Problems:

• Optical problems (angle, surface)

• Coil displacement is not axial-symmetrical

Laser

triangulation

sensor


Pure lumped mechanical parameters measured in vacuum

Mair Cair Rair hres(f)Mmd Cmd(f) Rmd(f)-1

Bl

Re

V=dx/dt

i

Blv

Bli

U

ZL(f)

moving air

mass air

Cavities

radiation

resistance +

turbulences

air

leaks

pure mechanical elements

measured in vacuum

Mms

Cms(f) Rms(f)-1

Bl

Re

V=dx/dt

i

Blv

Bli

U

ZL(f)

hres(f)

electro-dynamical

transducer operated in air


0 ,0 0 0 0 0

0 ,0 0 0 2 5

0 ,0 0 0 5 0

0 ,0 0 0 7 5

0 ,0 0 1 0 0

1 0 1 1 0 2 1 0 3 1 0 4

M e c h a n ic a l c o m p l i a n c e (d ri v e r i n v a c u u m )

[m

m/

N]

F r e q u e n c y [H z ]

C o m p lia n c e C m d ( f) fm in

M in im u m c o m p lia n c e C m d 0

Mechanical Compliance Cmd(f)

fmin

EFFECT:

compliance

increases to lower

frequencies

CAUSE:

viscoelasticity of

the material

CONSEQUENCES:

more displacement

than predicted by

traditional modeling

creep factor or

describes relative

increase of compliance

per decade

fd

creep factor or

Cmd(fd)≈Cmd0 (Ritter)

Cmd(fd)

2

min

min10min

/1

/log1)(

ff

ffCfCMD


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


Acoustical Lumped Parameterssmall signal parameters based on a linear model

– Mechano-acoustical coupling function Sd(f)

– Nominal effective radiation area Sd(f=fs)

– Acoustical load impedance ZAL(f) describes the air load on

the radiator’s surface and effect of the acoustic system

(port, enclosure, horn) versus frequency.

– Lumped parameters of the acoustical load (e.g. vented box)


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-1

Bl

Re

V=dx/dt

i

Blv

Bli

U Sd Cabp Ral

qa=Sdv

qlqb

pSd

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 conearea)

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

2

2

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

)(

),(

)(w

w

wcoil

cc

S

Dv

dSv

S c

r

using mean voice coil velocity

w

w

2

),,(

)(

2

0

drv

v

coil

coil

)(wq

),( cv rw

Radiator‘s surface

coilr

)(wq

)(wDS

)(wcoilv

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

)( 0wDD 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

radiated

sound power,

(SPL in a duct) MMD CMD RMD-1Bl

Re

v=dx/dt

i

Blv

F=Bli

U Sd(f)p

qa=Sd(f)v

pSd(f)

ZL(f)

)(

0AR

fS

cR

d

using effective radiation area

SD(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

SPL

[dB

]

F requency [ Hz]

Total Sound Pressure Level


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


coil

radiator‘s

surface

)( cx r

)( cF rcoilF

coilx

u

i

terminals


Mechanical and Acoustical Characteristicsderived from Displacement Transfer function

• Accumulated Acceleration level AAL(f,r)

• Relative Rocking Level RRLn of the nth rocking mode

• Modal Expansion (Eigenfunction, natural frequencies, lossfactor)

• Rocking Mode Parameters (Imbalances of mass, stiffness and Bl)

Scanning

Vibrometer)(

),(),(

fU

fXfH C

Cx

rr

Diagnostics

On Cone vibration

Applications:

• Sound pressure prediction (system design based on measured vibration)

• Verification of FEA

• Optimization of modal vibration and sound radiation

• root cause analysis of rocking modes rub and buss


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 acceleration1078,1 Hz

)( ca r

)( ca r

with reference sound pressure p0

dBp

pAAL

o

aaaa

2

)(log20)(

rr

c

S

caaa dSaWp

c

)()( rr

and a useful scaling W to

comparable ALL with SPL output

ca

Wrr

2

0

cone‘s surface Sc

ca rr ar


Relationship between AAL(f,ra) and SPL(f,ra)

Acceleration level

Total sound Pressure levelRigid body modes

30

40

50

60

70

dB

90

100 1000 10000

f [Hz]

SPL

AAL

Rigid body mode

Accumulated Acceleration Level

• 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

The Rayleigh Integral is a useful approximation for

the sound pressure output.

The definition of the AAL(f,ra) corresponds with

Rayleigh Integral but neglects the phase information


Natural

Function

30

40

50

60

70

dB

90

100 1000 10000f [Hz]

Acceleration Level

Natural

frequencies840 Hz 3,8 kHz 8,1 kHz70 Hz

Experimental Modal AnalysisExpansion into a Series of Orthogonal Modes

displacement:

11,2 kHz

Completely different mode shapes (orthogonal) ! nmT

nm 0ΨΨ

Frequency response

for each mode

mm

M

m

jj Ψx )()(1

ww

Natural Functions

describing mode shape


Modalanalysis of a Microspeaker

Rocking mode

Rocking mode

RRL = -30 dB

1 2 3

10

17

Total Vibration


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


Desired and Undesired Vibration

timeone period

impulsive distortion

Voice coil

gapvoice coil rubbing

piston mode generates the sound output

F0

rocking modes generate no output but impulsive distortion

µ1


What Causes Rocking Modes ?

Mass Imbalances

Force Factor Imbalance

µm

µk

µBl

Stiffness Imbalances

Which root cause excites the rocking ? mass, stiffness, force factorWhere is the root cause located ? angle showing the direction

How to assess the magnitude of the excitation ? moments


Rocking Mode Analysis

Modal

Resonator

Modal

Expansion

µnxn(rc)

Modal

ExcitationΔn

Φn(rc)

τn

Root-causes

(imbalances)

Boosting Mechanism

one piston modes,

two Rocking Modes

SCANNER

Total VibrationAccumulated Acceleration Level (AAL)

System Identification

DIAGNOSTICS

Mode Coupling


Excitation

total:

CFRT= 1.6 % (295°)

components:

CFRM= 1.4% (299°)

CFRK= 0.07 % (296°)

CFRBl= 0 % (-°)

Mass Imbalance Experiment modified loudspeaker with additional mass

lighter

AAL ~ Energy

CFR in %

CF

R i

n %


Electro-acoustical Efficiency

1. Efficiency in a specified frequency band (e.g. pass band)

– Ratio between measured acoustical output power Pa and measured electrical nominal input 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

)( 2

0

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

geometric mean of the limit frequencies of the effective frequency range if different from 1 kHz.

The frequency shall be stated.

Broad-band sensitivity: the test signal is 2-octave filtered noise centered at 1 kHz, or at the

geometric mean of the limit frequencies of the effective frequency range if different from 1 kHz.

The frequency shall 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


Advanced modeling

of an electro-dynamical transducer

using on lumped elements where some parameters

• are time variant ( due climate, aging, heat)

• are frequency dependent

• have a nonlinear dependency on state variables (displacement, current )

mechanical admittance (FI) type analogy

MMS CMS(ω,x,t) RMS(ω,x,v)-1Bl(x,t)

RE(t)

v

i

Bl(x,t)vu p

LE(ω,x,i) F=Bl(x,t)i

p

q

FA

SD(ω,x)

Zload(ω)

pout(r)

Frel(x,i)

RL(ω,x,i)

dL(q)

electrical domain higher order

modesacoustical

domain

mechanical domain

(fundamental mode)


Ranking List of

Transducer Nonlinearities

1. Force Factor Bl(x)

2. Compliance Cms(x)

3. Inductance Le(x)

4. Flux Modulation of Le(i)

5. Mechanical Resistance Rms(v)

6. Nonlinear Sound Propagation c(p)

7. Nonlinear Cone Vibration

8. Doppler Distortion (x)

9. Flux Modulation of Bl(i)

10. Port Nonlinearity RA(v)

11. many others ...

horns

tweeter

woofers

microspeaker

microspeaker

Full band microspeaker


Full Dynamic Measurementof transducer and system nonlinearities

described in IEC Standard PAS 62458:2008

Noise or

musiccurrent

voltage


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 xC


Steps:


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)


Peak Displacement limited by Nonlinearities

Xmax,10%

Generating not more than 10 % THD or 10 % IMD

minimum

Xc

X 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

XBl

X 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

XD

X limited

by Doppler

10 % IMD

Doppler

XL

X 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


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


Stiffness Asymmetry AK


Steps:


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

peakMSpeakMS

peakKxKxK

xKxKxA


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

Fourier

Transform

loudspeaker

system

current

sensor

U(t) I(t)

-

Stimulus

v oltage

sensor

power

amplif ier

Pilot

Tone

Temperature

Calculation

Resistance of cold

speaker

Conductivity of Coil

Material

Increase of VC

Temperature

Transducer: 1- 4 Hz

Systems: 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


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

Rtm

Ctv

Ctm

Tv

Tm

Ta

Rtc(v)

Peg

Rtt(v)

Cta

Rta

(x)

Pcon

Ptv

Pg

Ctg

Rtg

Tg

Pmag

Pcoil

TgT

vT

m

Can be used to predict heating

and cooling for any stimulus


Rtv

Rtm

Ctv

Ctm

Tv

Tm

Ta

Rtc(v)

Peg

Rtt(v)

Cta

Rta

(x)

Pcon

Ptv

Pg

Ctg

Rtg

Tg

Pmag

Pcoil

TgT

vT

m

Advanced Nonlinear

Thermal Modeling

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

1000 8060 12020 40 160140 180

K(t=1h)

K(t=100h)

K(t)

hourt

Speaker 2

Speaker 1

)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

0

K(W=0)

K(W)

WW90%W50%

K(W)

K

P=const.

N

i

wW

iieCWK

1

/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 2017 (before CES)

• Contact the German standard group ([email protected])

• Or just contact me ([email protected])


Thank you !

mailto:[email protected]

Tutorial to a new IEC Standard Project 2016 by Wolfgang ... and... · IEC Standard Project...

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Transcript of Tutorial to a new IEC Standard Project 2016 by Wolfgang ... and... · IEC Standard Project...