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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
(woofer, tweeter) Perception
Audio-System
(Transducer, DSP,
Amplifier)
Left
Audio
Channel
Right
Audio
Channel
Final Audio Application
(Room, Speaker, Listening
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
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)
Transducer
(woofer, tweeter) Perception
Audio-System
(Transducer, DSP,
Amplifier)
Left
Audio
Channel
Right
Audio
Channel
Final Audio Application
(Room, Speaker, Listening
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
Fund. mean (0.07 to 20 kHz)
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
Fund. mean (0.07 to 20 kHz)
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
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)
Transducer
(woofer, tweeter) Perception
Audio-System
(Transducer, DSP,
Amplifier)
Left
Audio
Channel
Right
Audio
Channel
Final Audio Application
(Room, Speaker, Listening
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
(woofer, tweeter) Perception
Audio-System
(Transducer, DSP,
Amplifier)
Left
Audio
Channel
Right
Audio
Channel
Final Audio Application
(Room, Speaker, Listening
Position, Stimulus)
50
Thank you !
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