ACTIVE CONTROL OF SOUND Professor Mike Brennan Institute of Sound and Vibration Research University of Southampton, UK - PowerPoint PPT Presentation

1 / 59
About This Presentation
Title:

ACTIVE CONTROL OF SOUND Professor Mike Brennan Institute of Sound and Vibration Research University of Southampton, UK

Description:

(dropping the explicit dependence on frequency) Optimal controller ... automobile. Combination of acoustic and vibration control maybe seen in. the future ... – PowerPoint PPT presentation

Number of Views:464
Avg rating:3.0/5.0
Slides: 60
Provided by: SueBr9
Category:

less

Transcript and Presenter's Notes

Title: ACTIVE CONTROL OF SOUND Professor Mike Brennan Institute of Sound and Vibration Research University of Southampton, UK


1
ACTIVE CONTROL OF SOUNDProfessor Mike
Brennan Institute of Sound and Vibration
ResearchUniversity of Southampton, UK
2
Active control of sound
  • Active control of sound in ducts
  • Single secondary source
  • Two secondary sources
  • Where does the power go?
  • Control of harmonic disturbances
  • Control of random disturbances
  • Single channel feedforward control
  • Constraint of Causality
  • Active control of sound in enclosures
  • Cars
  • Aircraft
  • Active head sets
  • Vibroacoustic control

3
Passive Control of Sound
?
Sound source
Observer
Passive control relies on barriers, absorption
and damping. It works well when the acoustic
wavelength is short compared with typical
dimensions ? Higher frequency solution.
4
Active Control of Sound
?
Sound source
Observer
Acoustic or structural actuators are driven to
cancel waves It works well when the acoustic
wavelength is long compared with typical
dimensions ? Lower frequency solution.
5
Patent for Active Control of sound by Paul Lueg
1936
Active Control of Duct-Borne Sound
6
Loudspeaker source in a duct
If the frequency of interest is such that the
acoustic wavelength is greater than twice the
dust cross-section then it can be modelled as a
pair of massless pistons forced to oscillate
apart with a fluctuating volume velocity q(t)
between them.
7
Loudspeaker source in a duct
For x gt 0 the complex pressure and particle
velocity fluctuations can be written as
8
The plane monopole source
9
The plane monopole source
We define the source strength as
So
10
Cancellation of downstream radiation using a
single secondary source
Secondary source
Primary source
11
Cancellation of downstream radiation
Secondary source
Primary source
This requirement is
that is the secondary source is a delayed
inverted form of the primary source.
12
The net sound field in the duct
The field between the primary and secondary
sources is give by
Upstream of the primary source it is given by
Downstream of the secondary source it is given by
13
The net sound field in the duct
Note that when Ln?/2 the pressure upstream of
the primary source 0
14
Time domain interpretation
Secondary source
Primary source
15
Cancellation of downstream radiation using a pair
of sources
Primary source
Secondary sources
16
The net sound field in the duct
The field upstream of the secondary sources is
given by
Between the secondary sources it is given by
Downstream of the secondary sources it is given by
17
The net sound field in the duct
18
Time domain interpretation
19
Time domain interpretation
Secondary sources
Primary source
20
Sound absorption by real sources
Electrical power supplied
The acoustical power can be negative in such
cases less electrical power will be required to
sustain a given piston velocity u
21
The influence of reflections from the primary
source
Absorbing surface having a complex
reflection coefficient R
Secondary source
Primary source
22
The influence of reflections from the primary
source
Secondary source
Primary source
23
Adaptation in Feedforward Control
Active Control of Transformer Noise, Conover 1956
An error microphone is introduced to monitor the
performance. Changes in the disturbance and plant
response, from loudspeaker to the microphone,
require adaptation of the feedforward controller.
24
Single channel feedforward control
Periodic Primary source
Error sensor
Secondary source
Electrical reference signal
Electronic controller
(Unaffected by secondary source)
25
Single channel feedforward control
26
Control of random noise in a duct
Sound from Primary source
Error sensor
Secondary source
Detection sensor
Electronic controller
There are two main differences between the
control of random and harmonic disturbances
  • The detected signal x(t) is generally influenced
    by the
  • electroacoustics of the feedback path

2. There is a constraint of causality on the
controller
27
Control of random noise in a duct
Measurement noise at detection sensor
Primary path
Signal at detection sensor
Signal to secondary source
Controller
Error signal
Error path
Signal due to primary source
Feedback path
Measurement noise at detection sensor
28
Optimal controller
disturbance and measurement noise
The block diagram becomes
Primary and measurement noise
Error signal
Controller and feedback path
Error path
29
Optimal controller
Power spectral density of the error signal is
where E is the expectation operator and
denote complex conjugation
30
Optimal controller
The power spectral density of the error signal
can be written as
31
Optimal controller
To find minimum error substitute
into
32
Optimal controller
Controller
Error signal
Error path
Feedback path
33
Digital implementation of the controller
Sound from Primary source
Secondary source
Error sensor
Detection sensor
Electronic controller
34
Digital implementation of the controller
The overall frequency response of the controller
is
Sampling time
Frequency response of filters and data converters
Digital filter
Causality condition
Approximate delay through an analogue filter is
roughly due to 45 phase lag or 1/8 cycle of
delay at its cut-off frequency, fc Total delay
through two filters which have a total of n poles
is n/8fc The cut-off frequency is typically 1/3
the sampling frequency (fs1/T), so that
fcfs/31/(3T) Allowing 1 sample delay for the
data converters and the digital filter means the
total delay is given by
35
Causality condition - example
Sound from Primary source
Secondary source
Error sensor
Detection sensor
Electronic controller
Rectangular duct with largest dimension D0.5m
single channel control can only be achieved
below about 300 Hz
Sampling frequency 1kHz (T1ms) Two 4th order
analogue filters (n8) Delay in analogue path is
about 4ms
36
Active control of sound in a duct experimental
work (Roure 1985)
37
Active control of sound in a duct experimental
work (Roure 1985)
Amplitude spectra of the fan noise at the error
microphone with a mean duct velocity of 9m/s
Active control off
dB
Active control on
Frequency (Hz)
38
Active control of sound in enclosures
Electronic Sound Absorber H.F. Olson and E.G.
May, Journal of the Acoustical Society of
America, pp. 1130-1136, 1953
39
Active Control of Sound inside Cars
Low-frequency engine noise in the car cabin can
be controlled with 4 loudspeakers, also used for
audio, and 8 microphones, also used for
hands-free communication (Elliott et al. 1986).
40
Initial Demonstration Vehicle
41
Measured Results in a Demonstration Vehicle
A-weighted sound pressure level at engine firing
frequency
42
Active Sound Control in Propeller Aircraft
System is standard fit on Dash 8 Q400 (Stothers
et al. 2002)
43
Active Sound Control in Propeller Aircraft
www.bombardier.com Periodic excitation generates
intense harmonic soundfield inside cabin
44
Active Sound Control in Propeller Aircraft
Spectrum of Pressure Inside Propeller Aircraft
45
Active Sound Control in Propeller Aircraft
Control System for Propeller Aircraft Active
Noise System
Centralised digital system made by Ultra
Electronics controls 5 harmonics with 48
structural actuators at 72 acoustic sensors,
distributed throughout cabin.
46
Active Sound Control in Propeller Aircraft
Typical Performance of an Active Aircraft System
Single multichannel centralised digital
controller used with 48 actuators and 72 sensors
distributed throughout the cabin
47
Feedback control of Sound
Active Headset using Feedback Control
If no external reference signal is available,
conventional feedback control can be used to
control sound at low frequencies.
48
Feedback control of Sound
Active Headset using Feedback Control
Active control off
dB
Active control on
Frequency (Hz)
49
Feedback control of Sound
Active Headset using Feedback Control
www.Bose.com
50
Active headrest
51
Active headrest zones of quiet
kL0.2
KL0.5
10dB
20dB
KL1
KL2
52
Active Vibroacoustic Control
53
The Problem
baffle
Incident sound power
Transmitted sound power
Simply supported panel
Objective To minimise the transmitted sound power
54
The Active Control System
Panel
Accelerometer
Piezoceramic actuator
Analogue controller
55
Piezoceramic Actuators
56
Active Control Performance (simulations)
57
What Happens to the Panel Vibration?
Integrated from 0-1kHz
Piezoceramic Actuators
Kinetic energy (dB)
Force Actuators
Feedback gain
58
Experimental Result (after Bianchi et al)
Pressure (dB re arbitrary units)
  • Gain limited by accelerometer resonance
  • Compensator used in feedback circuit

59
Concluding Remarks
  • Active sound control is being used as an
    alternative to passive
  • control in many different applications
    especially at low
  • frequencies
  • ducts
  • aircraft
  • automobile
  • Combination of acoustic and vibration control
    maybe seen in
  • the future
Write a Comment
User Comments (0)
About PowerShow.com