SPL (dB)

1

D.I.I. - University of Parma ITALY

ASK Industries ITALY

Non Non - - linear Digital Processor for linear Digital Processor for dedicated loudspeaker systems dedicated loudspeaker systems

A. Bellini, G. Cibelli, E. Ugolotti, A. Farina, C. Morandi

1998 ICCE 1998 ICCE

Los Angeles, CA

Los Angeles, CA

Alberto Bellini

Outline Outline

z Loudspeaker physical conformation;

z Loudspeaker non-linear modeling;

z Digital audio Processor for distortion compensation;

z DSP implementation;

z Measured distortion results;

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Alberto Bellini

Basic loudspeaker Basic loudspeaker

conformation conformation

z

Electric- mechano-acoustic transducers:

– p(t) = k e(t)

z

Non-linear behavior:

– The magnetic induction B is not constant with displacement

– non ideal suspension stiffness

– R = R(T)

Alberto Bellini

Loudspeaker

Loudspeaker modeling modeling

Acoustic signal

R

R

C

M

Z

Bl:1 1:S

i(t) F(t) p(t)

Audio electric signal

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Alberto Bellini

Loudspeaker

Loudspeaker modeling modeling

Audio signal

e(t)

p(t)

) (

) ) (

ˆ

(

s e

s s p

xn

=

ϕ

) (

) ) (

(

0 ˆ

ˆ

s

s

s

n

x

x

ϕ

ψ = ϕ

z

Non-linear loudspeaker I/O relation is linearized around fixed displacements x

z

ψ

accounts only for non-

linear behavior

Alberto Bellini

Loudspeaker non Loudspeaker non - - linear linear modeling

modeling

Audio signal e(t)

p(t)

) ) (

( ) ) (

0

( n

s e

s

s p ϕ

ϕ = →

z

is similar to SPL measurements

)

ψ (n

H(n)

)

SPL

(n

ϕ

Non-linear model

displacement x(t)

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Alberto Bellini

Audio processor Audio processor

Audio signal e(t)

p(t)

z

The more critical part is the synthesis of the H(n) filter

(Non-linear model)

Audio processor

Alberto Bellini

DSP implementation DSP implementation

Audio signal e(t)

p(t) (Non-linear

model)

Audio processor

Power Audio amplifier

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Alberto Bellini

DSP implementation DSP implementation

z Audio processor implemented with a 320C54x DSK;

z 40 MIPS, 10Kword Dual Access RAM;

z Sampling frequency 23148 Hz;

z Converter resolution 14 bit.

Alberto Bellini

Multirate Audio processor Multirate Audio processor

e(t)

HPF ϕ

( n ) _Delay +

LPF

LPF

)

1(

− n ψ )

1(

SPL n ϕ −

Interpolator

{

Non-linear processing

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Alberto Bellini

Audio processor Audio processor

measurements measurements

Power Audio amplifier

Anechoic room Audio analyzer B&K 2012

Electric

signal Acoustic pressure

Audio

processor

Alberto Bellini

SPL Results SPL Results

80 85 90 95 100 105 110 115

100 1000

SPL (dB)

f [Hz]

digital pre-processed normal

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Alberto Bellini

SPL Results SPL Results

50 100 150 200 250 300 350 400

20 60 100 140 180

Distortion [mV]

f [Hz]

Amplitude input 4 V

normal digital pre-processed

Alberto Bellini

SPL Results SPL Results

20 40 60 80 100 120 140

20 60 100 140 180

Distortion [mV]

f [Hz]

Amplitude input 5 V

normal digital pre-processed

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Alberto Bellini

Conclusion Conclusion

z Definition of a non-linear model for low frequency loudspeaker systems;

z Design of a parametric audio processor for the compensation of non-linear distortion of

loudspeaker;

z Implementation of the audio processor with a low cost commercial DSP;

z Measured reduction of Distortion with the

insertion of the audio processor;