Loudspeaker Data Reliable, Comprehensive, Interpretable...Method e.g. T/S parameter, amplitude and phase response, nonlinear and thermal parameters Psychoacoustical ... Flexible scanning

Loudspeaker Data – Reliable,

Comprehensive, Interpretable

Introduction

Wolfgang Klippel

Klippel GmbH

Biography:

1977-1982 Study Electrical Engineering, TU Dresden

1982-1990 R&D Engineer VEB RFT, Leipzig,

1992-1993 Scholarship at the University Waterloo (Canada)

1993-1995 Harman International, USA

1995-1997 Consultancy

1997 Managing the KLIPPEL GmbH

2007 Professor for Electro-acoustics, TU Dresden

My interests and experiences:

• electro-acustics, loudspeakers

• digital signal processing applied to audio

• psycho-acoustics and measurement techniques

3

Transducer

(woofer, tweeter) Perception

Audio-System

(Transducer, DSP,

Amplifier)

Agenda

1. Perceptual and physical evaluation at the listening point

perceptive modeling & sound quality assessment

auralization techniques & systematic listening tests

2. Output-based evaluation of (active) audio systems

holografic near field measurement of 3D sound output

prediction of far field and room interaction

nonlinear distortion at max. SPL

3. Comprehensive description of the passive transducer

parameters (H(f), T/S, nonlinear, thermal)

symptoms (THD, IMD, rub&buzz, power handling)

Left

Audio

Channel

Right

Audio

Channel

Final Audio Application

(Room, Speaker, Listening

Position, Stimulus)

4

Objectives

• clear definition of sound quality in target application

• filling the gap between measurement and listening

• numerical evaluation of design choices

• meaningful transducer data for DSP and system design

• selection of optimal components

• maximal performance-cost ratio

• smooth communication between customer and supplier

Transducer


Audio-System

(Transducer, DSP,

Amplifier)

Left

Audio

Channel

Right

Audio

Channel



Position, Stimulus)

5

Objective Methods for Assessing Loudspeakers

Parameter-Based

Method

e.g. T/S parameter, amplitude

and phase response, nonlinear

and thermal parameters

Psychoacoustical

Model

nonlinear

Sensations

Loudspeaker

Parameters

Room

Parameters

Loudspeaker-

Room Model

nonlinear

Distortion

Measurement

e.g. THD, IMD, rub&buzz

distortion

Perceptual

Quality Method

e.g. predicted

preference

Stimulus

e.g. music,

test signals

7

Perceptual Evaluation of Signal Distortion

Binaural

Processing

Basic

Auditory

Sensations

Loudness

Fluctuations

Sharpness S

Coloration V

Spaciousness R

Localization

Basic

monaural

processing

Basic

monaural

processing

Perceived

Defects DS

DV

DR

Ideal

Conceptions

The basic auditory sensations are

the dimensions of the perceptional

space and describe the audibility

of the distortion

+ Overall

Quality Loss

Perceived defects consider the

ideal conceptions and the impact

on quality

stimulus

reference

signal

test signal

test signal

reference

signal

distortion

distortion

10

Linear

Model

Nonlinear

Model

Unpredictable

Dynamics

Noise

Irregular Distortion

Nonlinear Distortion

Linear

Distortion

0 se )(tp)( tu

)(td lin

)(tdnlin

)(tdirr

)(tn

Model

Auralization of Signal Distortion

OBJECTIVES:

1. Virtual enhancement or

attenuation of distortion

components

2. Systematic Listening

Tests

3. Defining a value SDIS in

dB describing the

distance to the audibilty

threshold

Input

Signal

Output

Signal

11

weighted up and down method

Finding Audibility Thresholds

SDIS attenuation enhancement

histogram of the audibility

thresholds of 55000

participants of a listening

test at www.klippel.de

audibility threshold

SDIS=-15 dB

low distortion

13

Subjective and Objective Evaluation

Marketing

Management Engineering

Subjective

Evaluation

Objective

Evaluation

Listening Test + Auralization

Audibility of distortion

Perference,

SDIS

• Defining target specification

• Tuning to the market

Physical Data • Distortion, Maximal Output

• Displacement, Temperature

• Evaluation of Design Choices

• Clues for Improvements

Performance/cost ratio

Perceptive Modeling

14

Agenda











Transducer


Audio-System

(Transducer, DSP,

Amplifier)

Left

Audio

Channel

Right

Audio

Channel



Position, Stimulus)

15

Evaluation of the Audio Product

Measurement in Target Application

O

U

T

2

O

U

T

1

MIC1

LINE1

LINE2

MIC2

I

C

P

1

P

U

S

H

P

U

S

H

I

C

P

2

P

W

R

I

0

(Standard) living room

O

U

T

2

O

U

T

1

MIC1

LINE1

LINE2

MIC2

I

C

P

1

P

U

S

H

P

U

S

H

I

C

P

2

P

W

R

I

0

Anechoic room

Measurement under Standard Condition

transfer of the

audio system

Auralization/Listening Test

Perceptual Evaluation

Definition of target performance as perceived by final user

Suppressing the

influence of

acoustical

environment

considering room, distance, ambient noise and other conditions

Loudspeaker Development

Physical characteristics

(comprehensive, simple

to interpret, comparable,

reproducible)

16

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, efficiency

8. Directivity (pattern, rad. angle, index, coverage)

9. Amplitude nonlinearity (THD, IMD)

The scope of this standard is limited to passive loudspeaker systems !

17

Sound Field

Active Loudspeaker Systems

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

18

IEC 60268-5 applicable to Active 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, efficiency

8. Directivity (pattern, rad. angle, index, coverage)

9. Amplitude nonlinearity (THD, IMD)

can be applied, need modification, not applicable

19

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)

New Requirements:

20

Integration of DSP, power amplification and electro-acoustical conversion

DSP protection

X-over

amplifiers

drivers

Digital

audio

input

protection

linearization

protection

linearization

LimiterEqualizer

Gain

Control

Control

input

Tweeter

Midrange

Woofer

Nonlinear components

• Smart technologies (DSP) saves hardware resources and energy

• more acoustical output at reduced weight, size and cost

Green Speaker Technology

21

New Standards required for Evaluating Active and Passive Loudspeaker Systems

• Applicable to active and passive systems (prototypes, final and competitive products)

• Describing the radiated direct sound at any point within the listening area (including near field)

• Consideration of room-loudspeaker interaction

• Assessment of maximal acoustical output

• Irregular loudspeaker defects (rub, buzz, leakage, particles, loose connections)

• Comprehensive set of data (low redundancy, easy interpretation)

• Bridging QC and R&D

• Bridging perceptive and physical evaluation

Currently discussed in standard committees

22

Small Signal Performance

• On-Axis Sound Pressure at reference distance rref=1m SPL(f) response

Phase response (group delay (f) response)

• Directivity a) single-value characteristics

sound power response Pa(f)

directivity index Di(f)

b) 2D far-field data

pressure distribution p(θ, ) on a spherical surface at large distance from the source p(θ, ) (balloon plot, beam pattern)

c) 3D near/far-field data

sound pressure p(θ, , r ) at any point r in the space beyond the sound source (spherical wave expansion)

Specifications for Active and Passive Loudspeaker Systems

new

23

90°

-90°

0°

90°

270°

180°

4.1 kHz at distance r=4m 6.1 kHz at distance r=4m

2D far-field data

Beam Pattern

Balloon Plot

azim

uta

l a

ngle

frequency

on-axis

SPL

Distance r >> dimensions d of the loudspeaker

Distance r >> wavelength

24

Complete 3D Information Required

Sound Pressure at 7.6 kHz

In the following application the listerner is

closely located to the source:

• personal audio equipment

(smart phone)

• multimedia (tablet,

notebook)

• studio-monitor

• car audio

far field data

are less

important

Near Field

loudspeaker

25

Holografic Measurement of the radiated direct sound in the complete 3D space

Loudspeaker microphone

1. Scanning the sound

pressure in the near field of

the source

φ

z

r

),()()(),,,( )2(

0

, m

nn

N

n

n

nm

mnout Ykrhcrp

Spherical Harmonics

Hankel function

Coefficients

3. Results:

- frequency dependent set of coefficients

- point r0 of expansion

- radius rs of validity (scanning surface)

- order N of expansion

)(, mnc

2. Expansion in spherical waves

monopol

dipols

quadropols

26

Practical Realization near field scanning by using robotics

Example of a Near-Field Scanner

Objectives of the robotics: 1. Acoustical properties

• transparent,

• low noises

2. Flexible scanning grid

• scanning close to the source

• accurate positioning on multiple layers

• 2 π half-space (driver in baffle)

• 4π full-space (compact sources)

3. High-Speed measurement

• simultanous positioning in 3 coordinates

• multiple channel aquisition (mic array)

4. Wide range of application

• from smart phone to line array

• heavy systems (> 500 kg)

• slim system (> 4 m)

• cost effective, portable

scanning in various

coordinates (cylindrical,

spherical, cartesian)

27

Evaluation of a Notebook Application of Near-field Acoustical Holography

far field

near field

r

sr

0r

1. Measurement of the sound

pressure distribution

scanning surface close to the

source

2. Expansion into spherical waves 3. Extrapolation of the sound pressure at any

point outside the scanning surface

28

Line Arrays in Professional Audio Application of Near-field Acoustical Holography

a

1) Near-field Measurement large dimension a of box

anechoic room is too small for far field condition:

distance r >> dimension a

distance r >> wave length λ

2) Comprehensive 3D data coefficients of spherical wave expansion

direct sound in near and far field (any distance)

no redundancy (angular resolution at minimal data

size)

more information provided by GLL files

3) Input for Numerical Simulation Tools superposition of wave expansions

design and evaluation of line arrays

room interaction

29

Large Signal Performance

• Maximal SPLmax at reference point (1 m, on-axis), in rated frequency range

• Effective frequency range (Upper and lower limits flower,l < f < fupper,l )

• Compression of fundamental component (thermal and nonlinear effect)

• Harmonic distortion (Equivalent input distortion)

• Intermodulation distortion (IMD, MTD)

• Impulsive distortion (PHD, CHD) indicating rub&buzz, loose particles

• Modulated noise (MOD) indicating air leakage

• Durability verified in accelerated life test

Specifications for Active and Passive Loudspeaker Systems

30

sound field

Condition for Large Signal Measurements new IEC TC100 standard project “Output-based Evaluation of audio systems”

control

parameters*

drivers

active audio

system

(no access to internal states)

*conditions defined by

manufacturer

re

evaluation

point*

Output*

SPLMAX

~ test signal*

(chirp in rated frequency

range)

maximal input

value umax ?

optical

analogue

wavefile

wireless

gain ?

u(t)

gain and umax

depend on

measurement

setup !

31

Interpretation and Benefits of SPLMAX

Example as specified by a manufacturer:

SPLMAX, =108 dB for 60 Hz < f < 3kHz

(default test chirp, 1m on-axis)

SPLMAX

• is a single-valued characteristic describing the limit of the acoustical

output (but not sound quality of the system)

• is rated by the manufacturer considering target application

• depends on rated conditions (working range, reference point, stimulus,

...)

• can be generated by the audio system without damage

• provides a fast way for adjusting the input level of any stimulus during

measurements

32

-20

0

20

40

60

80

100

120

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

dB

- [

V]

(rm

s)

Frequency [Hz]

Fundamental

THD

Fund. mean (0.06 to 3 kHz)

Definition of SPLMAX

SPLMAX

fl fu

rated frequency range

SPLMAX is the mean short-term SPL in the rated frequency range generated by a sinusoidal chirp at the reference point.

33

Short-Term Compression reveals mechanical nonlinearities only (no voice coil heating )

60 20 50 200 500 2k 20k

Frequency [Hz]

KLIPPEL

65

70

75

80

85

90

95

100

105

110

115

120

125

dB

- [V

] (

rms)

system excited by a chirp (T=1 s) generating SPLmax at the evalution point

short-term fundamental (1 s)

linear prediction

34

Long-Term Compression reveals 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

] (

rms)

Frequency [Hz]

linear prediction

system excited by a chirp (T=1 min) generating SPLmax at the evalution point

long-term fundamental (1 min)

35

-20

0

20

40

60

80

100

120

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

dB

- [

V]

(rm

s)

Frequency [Hz]

Fundamental


Harmonic Distortion

3rd Harmonic

2nd Harmonic

THD

system excited by a chirp (T=1s) generating SPLmax at the evalution point

36

-20

0

20

40

60

80

100

120

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

dB

- [

V]

(rm

s)

Frequency [Hz]

Fundamental


PHD limit (-40dB)

Higher-Order Distortion for assessing rub&buzz and other irregular loudspeaker defects

Absolute PHD peak value of higher-order

distortion

system excited by a chirp (T=1s) generating SPLmax at the evalution point

38

Agenda











Transducer


Audio-System

(Transducer, DSP,

Amplifier)

Left

Audio

Channel

Right

Audio

Channel



Position, Stimulus)

39

Interfaces between Signal Processing, Electronics, Transducer, Acoustical Environment

DSP

HP

LP

BP

amplifiers

Digital

input

software transducer

Example: Active Loudspeaker System

x

x

x

enclosure

sound field

horn

x

x

x

x

electrical

measurement

mechanical

measurement

acoustical

measurement

40

How to Specify the Optimal Transducer ?

1. Parameters (independent of stimuli) • Acoustical transfer functions (from near-field holography)

• Mechanical transfer functions (from laser scanning)

• Small signal parameter T/S

• Large signal parameters (thermal, nonlinear)

2. Stimulus-based Characteristics • Maximal SPL

• Nonlinear distortion (THD, IMD, XDC)

• Symptoms of irregular defects (rub, buzz, leakage,...)

• Coil temperature, compression, Pmax

Should be

transformed into

parameters

Parameters give a

comprehensive

set of data !!

41

Important Transducer Parameters

1. Linear parameters of Motor and Suspension

T/S parameters (Re, Mms, Rms, ...), lambda (), electr. impedance

2. Nonlinear lumped parameters of motor and suspension

Bl(x), Le(x), Kms(x), Le(i)

3. Thermal parameters

thermal resistances Rtv, Rtm and capacities Ctv, Ctm 4. Linear distributed mechanical parameters

mechanical transfer function Hx(rc,j), cone geometry z(r), AAL response

5. Sound pressure responses (transducer in infinite baffle)

spherical wave expansion, on-axis response, directivity

6. Mechanical or acoustical load

Mechanical Admittance Y(j) of the coil

49

Conclusions

1. Development of modern audio system requires different kinds of models, characteristics and measurement techniques

2. Perceived sound quality depends on the final audio application, perceptual processing, training and expectations of the customer

3. Output-based evaluation of active audio-systems is under discussion (join the IEC or AES standard groups)

4. Parameters (independent on the stimulus) play an important role in tranducer design and system integration

Transducer


Audio-System

(Transducer, DSP,

Amplifier)

Left

Audio

Channel

Right

Audio

Channel



Position, Stimulus)

50

Thank you !

Documents

Loudspeaker Data Reliable, Comprehensive, Interpretable...Method e.g. T/S parameter, amplitude and phase response, nonlinear and thermal parameters Psychoacoustical ... Flexible scanning