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Klippel, Sound Quality of Audio Systems, Part 7 Measurement of Nonlinear Parameters, 1

Loudspeaker Parts

Measurement Seminar

Klippel GmbH

Stefan Irrgang


What does this seminar offer? • Overview on loudspeaker part measurements

o B-Field Testing o Temperature / Power Testing o Suspension Part Measurement

Low frequencies (lumped K(x)) Cone break up range (distributed)

o Material Parameter Measurement o RMA – Rocking Mode Analysis

• Relation to measurements at final loudspeaker

• Theory on measurement principles

• Available Industry Standards


Measurement of magnetic Flux density


Abstract

Measurement of magnetic Flux density (B Field Scanner)

The flux density B(phi,z) in the gap is automatically measured versus angle phi and height z by using a B-Field Probe and a mechanical scanning technique. This technique is the basis for predicting the force factor Bl(x) and for detecting problems in the design, assembling and magnetization causing rocking modes and voice coil rubbing.


Example: Static Measurement of B-field in the gap and force factor characteristic Bl(x)

hall sensor

z-axis

Turntable with r-axis and φ-axis

UH

I

b

d

Hall principle

B field

Hall voltage

Neubert, Lars

Master thesis 2010


Scanning Process

Cylindrical Coordinates

Vertical

position

z

Angle


Angle (degree) Vertical position z (mm)

30

20

10

B

(Tesla)

Magnetic

flux

density

Nk

NirzB

z

ki ,...,1

,...,1),,( 0

Magnetic Flux Density on the scanned surface

maximum Angle

Vertical

position z

minimum


Force Factor Nonlinearity Bl(x) Integration of the B field versus coil length l

l

l

lz drrBeBl )(

Angle

Angle

Radius r0

Rest Position

Height

Voice coil displacement

x

zr

Voice coil

z

2nd layer

Gap width

W

w

w

w

w

N

Ni

r

N

N

r

ziD

xBrm

rdzDxBmxBl

)2

(2

),2

()(


0 45 90 135 180 225 270 315 360 -10

-5

0

5

10

Angle f

%

VB()

Asymmetrical Field Distribution

0°

90°

180°

270°

maximum

minimum

%100)(

)(z

zz

B

B

BBV

Flux Density Variation

VBl(x=0,)

%100)(

)(),('2),(

xBl

xBlxBlxVBl

2

0

),(')( dxBlxBl

Variation of Force Factor Distribution


Asymmetries of the Magnetic Field

Additional magnet

Causes:

• Geometry is not axially symmetrical

• Position of the magnet

• Position of the pole piece

• Magnetization process

Consequences:

Tilting of the voice coil former

Rocking modes

Rubbing coil Higher-order distortion damage


Causes of Rocking Modes

Mass

Unbalances

Stiffness

asymmetries

Asymmetric acoustic loads…

B field

Asymmetries

Nk

NirzB

z

ki ,...,1

,...,1),,( 0


How to assess the Force Factor Nonlinearity ?

Magnetic System

STATIC

FEM

Geometry +

Material

Static

Flux Density

)0,( coill irBParameter

Identification

Transducer

Force Factor

Bl(x, icoil>0)

+ Stimulus

Voice Coil

Force Factor

Bl(x, icoil=0)

Integration over

Coil length

Geometry

+ Material

PrototypeHall Sensor

Scanningagreement ?


Temperature Monitoring (Power Test)

KLIPPEL

0

25

50

75

100

0,0

2,5

5,0

7,5

10,0

12,5

0 250 500 750 1000 1250 1500 1750 2000 2250

Increase of voice coil temperature Delta Tv (t) and electrical input power P (t)

Delta Tv [K]

P [W]

t [sec]

Delta Tv P real P Re


Static Temperature Tests Standards:

• ALMA TM-324 (Draft): Test Method for Voice Coil Maximum Operating

Temperature (TMO):

Find ratio (K) between hot and cold DCR for coil only (DC voltage)


Conventional techniques:

Temperature Monitoring with DC source

Disadvantages:

• Requires additional hardware (large capacitor)

• Causes Offset in voice coil displacement

• Slow monitoring of voice coil temperature

• Fails in measuring drivers with crossover

• Limited in speed and AC-rejection


Temperature Measurement By Using a Steady-State Pilot Tone

Fourier

Transform

loudspeaker

system

current

sensor

U(t) I(t)

-

Stimulus

voltage

sensor

pow er

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

Not applicable for

temperature measurement

Impact of woofer, tweeter and crossover


Voice Coil Temperature Measured via Electrical Resistance Re (t)

• Based on voltage and current

measurement

• Re (t) corresponds with mean

value of the temperature

• Local temperature varies in

overhang coils

Better cooling of inner coil

windings (Heat radiation to

the pole tips, convection

cooling, high air velocity)

Indications of a thermal damage:

• loose windings voice coil rubbing

• shortcut of windings with pole gap reduced resistance

• open coil maximal resistance limited by instrument


Pilot Tone

DA2 or PM 8

Pilot tone

Dut 1

Speaker 1Amplifier 1Power Amplifier

Signal

Source

Input Signal +

Synchroneous

Pilot tone

OUT 1

IN 1

~Internal Pilot tone

OUT 2

Speaker 1Amplifier 1Power Amplifier

Passive

Filter

Active

Filter

DA2 or PM8

Dut 2

Dut 1

Speaker 2Amplifier 2

Passive

Filter

Active

FilterPower Amplifier

~

Signal

Source

Signal

Source

Asynchroneous

Pilot tone

External

Generator

~

Asynchroneous

Pilot toneExternal

Generator

DA2 or PM8

Dut 2Speaker 2Amplifier 2

Passive

Filter

Active

Filter

Power Amplifier

Signal

Source

Synchroneous

Pilot tone

Dut 1

Speaker 1Amplifier 1

Passive

Filter

Active

Filter

Power Amplifier

Signal

SourceInput Signal +

Synchroneous

Pilot tone

OUT 1

~

Pilot tone f1

OUT 2

Input Signal +

Synchroneous

Pilot tone

~

Pilot tone f1

MULTIPLEXER

External mixing of internal pilot tone

External mixing of external pilot tone

Internal mixing of the pilot tone

2Hz for woofer

2 Hz for subwoofer

20 Hz for tweeter


Assessing Maximal Power Handling

KLIPPEL


DUT: 1 (01:35:54)

Delta

Tv [

K]

P [W]

t [sec]

0

50

100

150

200

250

300

0,0

2,5

5,0

7,5

10,0

12,5

15,0

17,5

20,0

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500

Delta Tv P

failure

Permissable increase of VC temperature Pmax

190 K

13 W


Failure Detection („Death Report“)

• High sampling of state (X, Tv) and parameters

(Kms) period just before destruction

• Allows to investigate cause of failure

-10

0

10

20

30

40

50

60

70

80

90

100

0,00

0,25

0,50

0,75

1,00

1,25

1,50

1,75

0 2500 5000 7500 10000 12500


DUT: 1 (04:04:40)

Del

ta T

v [K

]

P [W

]

t [sec]

Delta Tv P real P Re P con

25

50

75

100

125

150

175

0,25

0,50

0,75

1,00

1,25

1,50

1,75

14000 14100 14200 14300 14400 14500 14600


DUT: 1 (04:04:40)

Del

ta T

v [K

]

P [W]

t [sec]

Delta Tv P real P Re P con

Regular Sampling

Fast Sampling


Suspension Part Measurement


Abstract

Linear Suspension Part Testing for QC (LST)

http://www.klippel.de/our-products/qc-system/additional-modules/linear-suspension-test.html

The QC LST is dedicated to the quality control of suspension parts (spiders, cones, surrounds) and passive radiators (drones). Linear mechanical parameters like resonance frequency, stiffness (LST Lite) or relative mass and stiffness deviation (LST Pro) are determined dynamically from the displacement frequency response. The device under test is stimulated pneumatically while displacement is measured by a cost effective triangulation laser.

Test objects with circular geometry are easily attached to the measurement bench without time consuming mounting effort by using a set of mounting parts (rings, cones). The fast loading mechanism is designed to change DUTs as fast as possible while ensuring stable and robust measurement conditions. For quality control limits can be calculated based on reference units to provide pass/fail verdicts.













Static Suspension Measurement

Tonwel:

Elasticity of Spider

Measurement System

based on EIA RS-438

http://www.tonwel.com/b-en-t05.php

Standards:

• ALMA TM-438 Measurement of the Stiffness of Loudspeaker

Driver Suspension Components

• EIA RS-438 (ANSI C83.116-1976)


Method:

• Sample the working range

• Generate DC displacement xDC

• Measure associated state signals FDC

• Calculate instantaneous parameters

• Repeat the measurement at other working points

Quasi-Static Measurement of Kms(x)

F

x

secant

KMS(x)= FDC

xDC

Results depend on measurement time

Hysteresis has no importance for audio band

Dynamic measurement preferred


Practical Realization of Quasi-Static Method

Ringlstetter Harman Becker Straubing, Germany


Tonwell:

Compliance of Loudspeaker

Spider and Cone Test System


Quasi-Static non-linear

Measurement of Kms(x)


Dr. Kurt Müller - R&D Tester -used for the development of any kind of suspensions during early design of components.

Hysteresis curves are basically used for interpretation or evaluation.

There are various opportunities to study the behaviour of suspension parts during their movement in a large range.

It’s an quasi static measurement and comparable with conventional tensile strength tests.

All samples have to be fixed during measurement at the neck (or inner diameter) and pressed down at the OD with pneumatic clamping force.

For analysis, the R&D-Tester has to be linked to a computer.

Weight Range: +/- 25 kg Precision: +/- 0.1 mm, +/- 1 mN Max Excursion: +/- 100mm

Quasi-Static non-linear

Measurement of Kms(x)


Dynamic, Linear Suspension

Measurement

Tonwel:

The Test System for the

Resonance Frequency of

Loudspeaker Cones


Standards:

• IEC 62459/Ed.1


Linear Suspension Test (LST) Fast quality control of suspension parts and passive radiators

• Objective: check driver and system parts before assembly (spiders, cones,

domes, passive radiators) early quality control

• Software and optional hardware set for the QC System (Basic & Standard)

• Fast and easy mounting of DUT time efficient testing

• Fits a wide variety of DUT sizes


Mounting Suspension Parts

LST Bench

Variable Ring Set Mounting Cones Free air setup

Reflective

coverLaser beamCone

Spider

Ring set

Cone

B5 B4

BoltNutStandard


Processing of displacement response

KLIPPEL

0,00

0,02

0,04

0,06

0,08

0,10

0,12

0,14

101 2*101 3*101

Dis

pla

ce

me

nt x [

mm

]

Frequency [Hz]

Displacement Magnitude

f1 fr f2

-3dB

𝑄 =1

𝐷𝐹=

𝑓r

𝐵=

𝑓r

𝑓2 − 𝑓1

Simple processing, only based on displacement amplitude response (laser signal) Assumptions • Constant driving force • Constant moving mass m

(dominated by inner clamping)

𝑓r

=1

2𝜋 𝑘

eff

𝑚≙ arg max 𝑋 𝑓

Resonance Frequency

𝑘0 ≙ 𝑘eff 𝑥

peak, 𝑥

dc = 𝑚 2𝜋𝑓

r 2 for 𝑥peak

, 𝑥dc→ 0

Stiffness (small signal)


Operator View

Control Panel

Displacement Response

Test Verdicts

Temperature/Humidity

Detailed Result Table


Testing in Operator Mode


Testing Passive Radiators

• Passive system element – difficult to test before loudspeaker assembly

• Most important parameter: moving mass

• Resonance frequency result of both suspension stiffness and moving mass

• Added mass method may be used to determine moving mass – inappropriate for QC

• Solution: monitoring relative deviation to „golden“ reference unit

KLIPPEL LST

Bench

Passive

Radiator

Fast clamper

Custom mounting

platform


Monitoring Mass & Stiffness Deviation using displacement response only

CMP

MMP

p CAB

qB qL

RAL

qqD

SPF

dx/dt

pD

ZD

RMP

Speaker Enclosure Passive Radiator

KLIPPEL

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,40

0,45

0,50

0,55

0,60

3*101 4*101 5*101 6*101 7*101 8*101 9*101

Dis

pla

ce

me

nt x [

mm

]

Frequency [Hz]

Displacement Magnitude Displacement Magnitude (Golden DUT)

Qf

fj

f

fabsfxf

Qf

fj

f

fabsfxf

fM

fM

ms

ms

11|)(|

11|)(|

)(

)(

0

2

0

2

2

0

0

2

0

2

2

0

Golden unit‘s

response

Tested unit‘s

response


Hardware Platforms

SPM Bench (RnD System)

• SPM Pro for linear and nonlinear testing

• SPM Lite for linear testing

LST Bench with internal laser

(QC System)

• Linear Suspension Test

LST Bench with external laser (RnD System)

• SPM Lite for linear testing

MSPM Bench (RnD System)

• MSPM Pro for linear and nonlinear testing

• MSPM Lite for linear testing


Non-linear Suspension Part Measurement


Abstract

Suspension Part Measurement (SPM)

http://www.klippel.de/our-products/rd-system/modules/suspension-part-measurement.html

Suspension Part Measurement features a dynamic identification of the small and large signal spider parameters (Force deflection curve, Stiffness curve, resonance, damping factor…) using an audio like ac-stimulus. This measurement can also be performed as an accelerated life test for separating fatigue from break-in and assessing the long term stability of the suspension.












0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

10 1 10 2 10 3 10 4

[mm

/V]

f [Hz]

measured

• Different approaches to describe this effect

Magnitude o f Transfer Function X(f)/U(f)

estimated without creep

Problem: Suspension at Low Frequencies

Mmd Cmd(f) Rmd(f)-1

Bl

Re

V=dx/dt

i

Blv

Bli

U

ZL(f)

Kundsen and Jensen, JAES

1993

𝐶 𝑓 = 𝐶0 1 − 𝜆 log10𝑗𝑓

𝑓s

𝐶 𝑓 = 𝐶0

1 − 𝜅 log10

𝑗

𝑓𝑓min

𝑒−𝑗 tan −1

𝑓𝑓min

1 + 𝑓

𝑓min

22

Ritter, 2010

• compliance Cmd(f) and resistance

Rmd(f) increases to lower frequencies

below resonance f << fd

DC Audio Band


Static and Quasi-Static Measurement of Kms(x)

Disadvantages:

• Stiffness measured at very low frequencies is much smaller than the stiffness found in the audio band

• Static displacement of the suspension affects the rest position

• Creep, relaxation, hystereses only occur at low frequencies

• Time consuming


Method:

• Excite speaker with large AC-signal

• Measure a state variables XAC(t) and FAC(t)

• Estimate KMS(x) to describe relationship between input FAC and output XAC

Full dynamic Measurement F

x

secant

KMS(x)= F

X

FAC(t)

XAC(t)


How to measure the Large Signal

Parameters of Suspension Parts

Advantages:

• dynamical method

• vertical operation

• robust, easy to use

• inexpensive Set up according to IEC Standard 62459

Example: SPM System


Dynamic Measurement of the Mechanical

Stiffness of Suspension Parts


Need for a Dynamic Measurement

of Suspension Parts

significant variation of Kms(x=0) at the rest position x=0

small variation of Kms(xpeak) at the maximal displacement Xpeak

500

1000

1500

2000

2500

3000

3500

4000

4500

-15 -10 -5 0 5 10

[N/m]

displacement x [mm]

500

1000

1500

2000

2500

3000

3500

4000

4500

-15 -10 -5 0 5 10

[N/m]

time

displacement x [mm]

500

1000

1500

2000

2500

3000

3500

4000

4500

-15 -10 -5 0 5 10

[N/m]

time

displacement x [mm]

500

1000

1500

2000

2500

3000

3500

4000

4500

-15 -10 -5 0 5 10

[N/m]

time

displacement x [mm]

Measurements in

15 min intervals

Kms(x)- versus time

Generation of a

dc component

by stiffness

asymmetry

Small variation at

maximal

excursion


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


Accumulated 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


Example: Poor Spider Suffering from Long-Term Fatigue

1,1

1,2

1,3

1,4

1,5

1,6

1,7

K(W)

[N/mm]

0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35 0,40 0,45 W [kWh]

measured

fitted

• 50% of initial stiffness

decay during life-cycle

• Only 50% of stiffness

decay during break in

• High fatigue ratio -

permanent but slow decay

of the stiffness


Measurement Technology Suspension Parts

Res

Laser

Sensor

Analyzer 2

suspension

loudspeaker

enclosure

inner clamping

System

Identification

K(x)

P

Fitting Algorihm

Parameters

of the Aging

Model

X(t)

Measurement of spiders, surrounds and passive

radiators using a laser sensor and system identification

dt

tdxtxxKtP

)()()()(

apparent mechanical power

nonlinear

system

identification

displacement

sensor


How to measure Micro Suspension Parts

Preparation

• Diaphragm glued or clamped in panel

• Diameter < 40mm

Measurement

• Passive excitation by pressure chamber below

• Laser measurement of displacement

• Microphone measurement of pressure

Laser Sensor

Microphone

Panel with DUT

Loudspeaker

Pressure

Chamber


Linear Parameter Identification

Calculation of Results

• Mass perturbation with known mass

• Fitting modelled Transfer function to the measurement

Measurement Signal

• Sweep Signal

• Measurement of Transfer function H(f) = X(f)/P(f)

KLIPPEL

0,00

0,01

0,02

0,03

0,04

10 2 10 3

Input Curves

Ma

gn

itu

de

Frequency [Hz]

Curve 1 without mass Curve 2 without mass

Curve 1 with mass Mean Fitted Curve Without Mass

Mean Fitted Curve With Mass Fitting Range

Added Mass

No Mass

H(f) = X(f)/P(f) 𝐻 =𝑋

𝑃=

𝑆𝐷𝐾

1 + 𝑠 ∗𝑅𝐾+ 𝑠2 ∗

𝑚𝐾


Nonlinear Parameter Identification

Calculation of Results

• Model Force FDUT from the measured Displacement

• Minimize error between measured Force (𝑃 ∗ 𝑆𝐷) and modelled Force

• Verification: Fitting Error <20%

Measurement Signal

• Low frequency Multitone signal

• Measurement of displacement

• Generated distortion results from nonlinear K(x)

KLIPPEL

-510

-410

-310

-210

10 2 10 3

Distortion in Frequency Domain

Fo

rce

[N

]

Frequency [Hz]

Fundamental (F_Stim) E_F(f) Distortion

KLIPPEL

0,5

0,6

0,7

0,8

0,9

1,0

1,1

1,2

1,3

-0,5 -0,4 -0,3 -0,2 -0,1 0,0 0,1 0,2 0,3

K(x) over Displacement

K(x

) [N

/mm

]

Displacement [mm]

K(x) Extrapolation K(x)

𝐹𝐷𝑈𝑇 = 𝑃 ∗ 𝑆𝐷 = 𝐾 𝑥 ∗ 𝑥 + 𝑅 ∗ 𝑥′ +𝑚 ∗ 𝑥′′


Comparing LSI vs. MSPM Results

Small differences possible

• Different time and temperature conditions – LSI: 5-10min

– MSPM: 2-5s

• Different application of force – LSI: at voice coil position

– MSPM: distributed over membrane area

diaphragm

backplate

magnet

pole plate

coil

Microspeaker

diaphragm

backplate

magnet

pole plate

coil

Force Force

Diaphragm

KLIPPEL

0,4

0,5

0,6

0,7

0,8

0,9

1,0

1,1

1,2

-0,4 -0,3 -0,2 -0,1 0,0 0,1 0,2

K(x) over Displacement

K(x

) [N

/mm

]

Displacement [mm]

MSPM LSI

LSI Microspeaker

MSPM Diaphragm

Softer due to

temperature and time


Application


MSPM in Operation Laser positioning by clamping MSPM bench at

LST or SPM Bench

SCN - Scanning Vibrometer

Pro Driver Stand


Challenges in Suspension Design

Critical examples are flat and slim transducers used over the full audio

band (headphone, micro-speaker, TV-Speaker)

PROBLEMS:

1. Suspension centers the coil in the gap sufficient clearance to

avoid coil rubbing

2. Suspension determines the rest position of the coil in the gap coil

offset

3. No spider is used or distance between spider and surround is small

Rocking mode coil rubbing

4. Surround contributes significantly to the effective radiation area Sd

acoustical output

5. Suspension determines the peak displacement xmax required for bass

reproduction large geometry significant material deformation

6. Air pressure in the enclosure affect the stiffness of the suspension

7. Displacement (bass) affects modal vibration of the surround

strong intermodulation


Objectives of the Suspension

voice coil

former

diaphragm

frame

spider

diaphragm

backplate

magnet

pole plate

coil

microspeaker

Centering

Defining coil‘s

rest position

Suppressing tilting and rocking

Conclusion:

• Decreasing stiffness in the direction of intended

coil movement !

• Increasing stiffness in all other directions !

Solved by nonlinear

control with active

stabilization

Unsolved problem !


Suspension Characteristics for describing optimal properties in the particular application

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

-10,0 -7,5 -5,0 -2,5 0,0 2,5 5,0 7,5 10,0

Mechanical compliance Cms(X) vs displacement

Cm

s [m

m/N

]

Displacement X [mm]

more linear progressive

Compliance XC(x=0) at rest

position which is important for

resonance frequency fs

Maximal Excursion Xmech

which is important for

mechanical protection 25 %

Displacement limit XC

generating 10 % harmonics 75 %

Note: Symmetrical nonlinearities of the suspenion are usually beneficial


What is a Bad Suspension Part ? Properties which are not acceptable – k.o. criteria

500

1000

1500

2000

2500

3000

3500

4000

4500

-15 -10 -5 0 5 10

[N/m]

displacement x [mm]

500

1000

1500

2000

2500

3000

3500

4000

4500

-15 -10 -5 0 5 10

[N/m]

time

displacement x [mm]

500

1000

1500

2000

2500

3000

3500

4000

4500

-15 -10 -5 0 5 10

[N/m]

time

displacement x [mm]

500

1000

1500

2000

2500

3000

3500

4000

4500

-15 -10 -5 0 5 10

[N/m]

time

displacement x [mm]

K(x=0)

Significant loss (> 30 %) of stiffness K(x=0,t) versus time after break-in

Ak Stiffness asymmetry Ak (> 20 %) measured at high excursion

Significant dc displacement generated dynamically by stiffness asymmetry

12 mm -17 mm


Bad Spider Suffering from Long-Term Fatigue

1,1

1,2

1,3

1,4

1,5

1,6

1,7

K(W)

[N/mm]

0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35 0,40 0,45 W [kWh]

measured

fitted

• 50% of initial stiffness

decay during life-cycle

• Only 50% of stiffness

decay during break in

• High fatigue ratio -

permanent but slow decay

of the stiffness


Spider - Weakest Part of the Loudspeaker

Research activity: Replacement of impregnated

fabric by new materials

Tupperware® gives lifetime warranty

KLIPPEL

0,0

0,5

1,0

1,5

2,0

2,5

3,0

-10 -5 0 5 10 15 20

Stiffness versus Displacement

Stif

fne

ss [N

/mm

]

Displacement x [mm]

Kms(x) after 10 min

Stability of a

Tupperware lid

over time


How to Specify the Suspension Part

R&D Measurement (e.g. SPM module)

• Vertical operation

• Clamping similar to final application

• Dynamic measurements

• Small and large signal domain

• Long-term Measurement (ageing, fatigue)

Important Characteristics

• Dynamic stiffness K(x=0) measured at small amplitudes

• Loss of stiffness K(x=0,t) versus time t

• Stiffness asymmetry Ak measured at high excursion

• DC-displacement generated dynamically

• Maximal peak displacement Xc giving decay of compliance to 75 %

More details in IEC Standard 62458 and 62459

QC

R&D

End-of-line Testing (QC System)

• Horizontal operation

• Minimal clamping

• Dynamical Measurement

• Small Signal Domain

• Fast measurement (< 1s)


Material Parameter Measurement

2014

Stefan Irrgang

Klippel GmbH


Abstract

• Temperature Monitoring (Power Test)

• http://www.klippel.de/our-products/rd-system/modules/power-testing.html

• A fast and reliable measurement of the instantaneous voice coil temperature of woofer, tweeter, micro-speakers and active systems can be realized by using a small ac pilot tone added to the stimulus. This technique reveals the thermal dynamics (heating and cooling process) of voice coils with a small or large thermal capacity.


Measurement of Young‘s E-modulus and loss

factor of material samples

X/P [dB]

f [Hz]

- 3dB

0 dB

∆f

f 0

𝜂 =∆𝑓

𝑓0

𝐸 = 38.29𝑚𝑙3

𝑏𝑑3𝑓0

2

… mass

… width

… height

… length

m

b

d

l

Requirements: • Planar (flat) material samples

• Isotrophic material

• Constant thickness and density

Modal loss factor

Youngs E-modulus

Application: • Communication between driver and softpart manufacturer

• Checking production consistency

• Not applicable to FEM at high frequency

Method: • simple beam technique (Standard ASTM E 756-93)

• acoustical excitation (applicable to thin foils)

http://www.klippel.de/our-products/rd-system/modules/power-testing.html








Operation of the MPM Measurement hardware


Dustcap

Cone

Surround

Problem: • FEM requires accurate material material parameters for simulation • Compound materials are used in loudspeakers • Influence of glue and processing (variation of thickness and density) Table or standard values for materials are not applicable

• Material parameters are highly frequency dependent (factor 10 over audio band) The first prototype of the transducer is the best test measurement setup for

exciting the material and measurement the mechanical vibration at high frequencies.

Measurement of Youngs modulus and loss factor by

fitting FEM to Scanner


Vibration Data FEM

Calculation of modal Parameters FEM

Calculation of differences in modal Parameters

Calculation of modal Parameters SCN

Optimized material parameters

Parameter optimal?

No

Yes

Identification Process


KLIPPEL

100

105

110

115

6*10 2 8*10 2 10 3 2*10 3 4*10 3 6*10 3

AAL

AA

L/d

B

f/Hz

SCN FEMKLIPPEL

100

105

110

115

6*10 2 8*10 2 10 3 2*10 3 4*10 3 6*10 3

AAL

AA

L/d

B

f/Hz

SCN FEM

Iterations

Error

Optimal „fitting“ of the material

parameters by minimizing the error

between FEM and SCANNER

Iterative Parameter Identification

Residual modeling error

caused by

• Geometry (cone

thickness)

• Density variation

Optimal values of E-modulus

And modal loss factor

Mismatch between FEM

and scanner


Results

Frequency

E-Modulus


Scanning Vibrometer System


Abstract

Scanning Vibrometer System

http://www.klippel.de/our-products/rd-system/modules/scanning-vibrometer-system.html

The SCN Vibrometer measures the vibration and geometry of radiators, enclosures and mechanical structures used in loudspeakers, micro-speakers, headphones and other electro-acoustical or electro-mechanical transducers. The SCN Analysis Software performs visualization, animation and a modal analysis of the mechanical vibration using the scanned data which is provided by the vibrometer.


More Comprehensive Assessment

VibrationMotor Radiation

F

V

X(r)

F(r)

soundfield

u

near

field

far

fieldVoice

coil

Cone‘s

surface

Electrical

Measurement

Mechanical

Measurement

Lumped Parameters Distributed Parameters

electrical

Hx(f)=X(f)/U(f)

mechanical

Acoustical

Measurement

Cone Vibration

+ Geometry

mechanical acoustical

Far Field SPL

Response

Impedance

Ze(f)=U(f)/I(f)











Cone Scanning Techniques

Doppler Interferometry

(Polytech, 1995)

Frankort 1978

Olson, 1950

Triangulation Laser Scanner

(Klippel, 2007)

geometry

displacement

Velocity destribution on the cone

intensity

Amplitude+ phase Amplitude Amplitude + phase

+ geometry


Triangulation Laser

Features: • measures reflected laser light

• provides displacement

• Also black, transparent surface

• 0 Hz ... 25 kHz (dc component !!!)

• robust

x

Vb Va

Vl

Target surface

transmitting point receiving

point

receiving point

transmitting point

LASER

LASER

Vd

PRO • cost effective alternative to the Doppler

Interferometry

• Accurate measurement of cone geometry

• dc component generated by driver nonlinearities

Cons • Short working distance • Needs robotics for scanning


Measurement of Cone Displacement ?!

KLIPPEL

-610

-510

-410

-310

-210

-110

500 1k 2k 5k 10k

[mm

/ V]

Frequency [Hz]

surround dust cap

-100 dB

Transfer function between electrical input voltage and displacement of a point on the diaphragm


How to measure displacement at 20 kHz ?

Sweep Shaping Averager

Amplifier Displacement

Sensortransducer

X(t)U(t)

-10

-5

0

5

10

0 10 20 30 40 50 60 70 80

[V]

Time [ms]

Stimulus (t)KLIPPEL

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 10 20 30 40 50 60 70 80

[mm

][e-3

]

Time [ms]

Y2 (t)

Amplitude of displacement is almost constant (less than a micro meter)


z

phi

r

SCN Scanning

System

Mechanical scanning system with one

rotational (φ) and two linear actuators (r, z)

Automatic Scanning Process

• Special control software

• Secure scanning of unknown

driver geometry

Start

Finish



Sd Scan (100 points)

Good for

measurement of

effective radiation

area and other

lumped parameters

Rectangular Scan (2000 points)

Good for TV and

microspeakers

Profile Scan (27 points)

Assuming

axial-symmetrical

vibration

Explore Scan

(226 points)

Good for vibration

analysis and sound

pressure prediction

of round speakers

Detailed Scan (2900 points)

Good for searching

for irregularities

Scanning Time

8 min 1 hour 8 hours

Resolution of the Scanning Grid


3D Animation Cross-sectional Cut

Amplitude Distribution

Visualization of Vibration Data

Phase Distribution


Sound-Pressure-Related Decomposition

generates sound reduces sound no sound

)()()()( cquadcanticinc vvvv rrrr


KLIPPEL

50

60

70

80

90

100

101 102 103

Sound Pressure SPL @ 1m, 1V Accumulated Acceleration (AAL)

Power Level +47 dB @ 1V

@ 0.4m

Three Important Responses

Power

On-axis

Example: woofer

Piston mode

AAL

Maximal possible

sound pressure

output

Acoustical

cancellation

Directivity

Index

Displacement is in-phase

Omni-directional behavior

(like a point source)


Practical Examples

discussed in Journal AES 2008

Woofer A with paper cone

Woofer B with magnesium cone

Woofer C with flat radiator


Smooth On-axis SPL Response ?

Woofer A with paper cone

KLIPPEL

40

45

50

55

60

65

70

75

80

10 2 10 3

SP

L [d

B]

f [Hz]

-30 degree

on -axis

+30 degree

Woofer B with magnesium cone

KLIPPEL

20

30

40

50

60

70

80

90

10 2 10 3 10 4

SP

L [d

B]

f [Hz]

-30 degree

on -axis

+30 degree


KLIPPEL

20

30

40

50

60

70

80

10 2 10 3 10 4

-30 degree

on -axis

+30 degree


Sufficient Cone Vibration ? KLIPPEL

50

55

60

65

70

75

80

10 2 10 3

SP

L [dB

]

f [Hz]

Total SPL

acceleration level

Woofer A with paper cone:

low Q factor of cone resonances

KLIPPEL

50

55

60

65

70

75

80

85

90

10 2 10 3 10 4

SP

L [d

B]

f [Hz]

Total SPL

acceleration level Woofer B with magnesium cone:

natural modes cause high peaks in SPL

KLIPPEL

30

40

50

60

70

80

90

10 2 10 3 10 4

SP

L [dB

]

f [Hz]

Total SPL

acceleration level


dips are not visible in AAL

AAL cause peak at 0.8 kHz

Compare SPL and AAL !


KLIPPEL

30

40

50

60

70

80

90

10 2 10 3 10 4

SP

L [dB

]

f [Hz]

Total SPL

acceleration level


What Causes Excessive Peaks ?

• low modal density reduce bending stiffness (cone thickness)

• low loss factor apply damping

• longitudinal mode increase longitudinal stiffness

Search for peaks in AAL !


Sufficient Damping of the Material ?


Increase loss factor of material

Read 3dB bandwidth in AAL !

1.0840

80)(

1

1111

f

fff


Where to apply additional damping ? Woofer C with flat radiator

820,3 Hz 12398,4 Hz

65

70

75

80

85

90

102 103 104

Total Acceleration Level

ACC

[d

B]

F re qu e nc y [H z ]

Find places of high deformation !

View the shape of the modes !


Where to apply additional damping ? Woofer B Magnesium cone

KLIPPEL

50

55

60

65

70

75

80

85

90

100 1000 10000

AA

L [dB

]

f [Hz]

Acceleration Level

10 5.01

01.02

11109,4 Hz

Rubber surround has sufficient losses Cone requires damping

0


replaced by

)(

),(

)(

coil

cc

S

Dv

dSv

S c

r

using mean voice coil velocity

2

),,(

)(

2

0

drv

v

coil

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 SD Definition

)( 0DD SS Reading the absolute value at fundamental

resonance


0,5

1,0

1,5

2,0

2,5

3,0

cm2

1 10 Frequency [kHz]

)( 0DS

f0

Voice coil

)( 0DD SS

Reading the absolute value at

fundamental resonance gives

)(

),()(

,,

coil

icic

Dx

SrxS

Method:

1. Measurement of vibration and radiatior‘s geometry

2. Integration over surface and voice coil position

3. Calculation of effective radiation area SD()

4. Reading SD(s) at fundamental frequency s

Problems:

• Surface is covered by grill (surface is not visible for laser)

Effective Radiation Area


Benefits

• Measurement of geometry and mechanical vibration

• Visualization of vibration behavior

• Shows contribution to sound pressure output

• Directivity pattern

• Accurate Sd calculation

• Analysis of actively radiating cone regions


Vibration and Radiation Analysis Overview on Models, Parameters, Characteristics

3937,5 Hz

Radiator (cone, diaphragm, panel)

Drive Unit (woofer, tweeter, ...)

Geometry

Boundary

Element

Analysis

Finite

Element

Analysis

Sound Pressure •of total vibration

•of separated components

•on-axis

•directivity

Vibration

Material

Parameters

E,

Acceleration (accumulated level)

•of total vibration


enclosure,

horn, room

Modal &

Decomposition

Analysis

System (enclosure, horn, room)

Geometry

Shape of Components •natural modes

•radial/circumferential

•related with SPL output

•irregularities

Sound Power •of total vibration


3937,5 Hz


Root cause analysis of

Rocking modes

Scanning Vibrometer can make Rocking Modes visible

But it gives no clue on the root cause of the Rocking Mode

Klippel, Sound Quality of Audio Systems, Part 7 Measurement of Nonlinear Parameters, 95 William Cardenas – Klippel GmbH

Imbalances?

KLIPPEL

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

100 200 500 1k 2k

Instantaneous crest higher order distortion (ICHD)

Sig

na

l a

t IN

1

[V]

Frequency [Hz]

-29

-27

-25

-23

-21

-19

-17

-15

-13

-11

-9

-7

-5

-3

-1

1

3

5

7

9

1112

13

35

40

45

50

55

60

65

70

75

102 103

Total Acceleration Level

AC

C [

dB

/ 1

V]

Frequency [Hz]

Total Acceleration Level Total Sound Pressure Level

PROBLEMS:

- Mechanical limit due to rub&buzz

- Reduction of the acoustic output

- Can be highly excited at large amplitudes

- Asymmetric radiation pattern

0°

330

300

270

240

210

180°

150°

120°

90°

60°

30°

-15 -10 -5


ER1,E

ER2,E

IRE

Root Causes Where are the asymmetries and Inbalances located? Example:

Dominant Stiffness Asymmetry is causing rocking mode

Direction of

Mode 1

Direction of

Mode 2


• For more details on RMA, see separate presentation on ALMA 2016

loudspeaker parts measurement seminar - alma · pdf fileklippel, sound quality of audio...

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