Compressed air acoustic sources for active noise control
Compressed air acoustic sources for active noise control
An analysis is presented of an acoustic source which operates by the release of compressed air through an aperture, the area of which is made to vary with time. A distinction is made between sonic and subsonic compressed air sources, and in both cases simple equations are derived that describe the acoustical behaviour of the devices. Sonic sources are linear but inefficient. Subsonic source are much more efficient that sonic sources but their output is generally no longer a linear function of aperture opening. A numeric comparison between the performance of compressed air sources and electrodynamic loudspeakers shows that the former appear to be well suited to active noise control applications.
The design of a subsonic source is described, in which a sliding plate driven by an electrodynamic shaker modulates the air flow. An experimental analysis of the laboratory subsonic source is carried out. The acoustic pressure at the source output is measured for various conditions. The experimental results are found to be in good agreement with the theoretical predictions. Predistortion of the subsonic source to produce a sinusoidal output is considered. A predistortion processor is placed in series with the electrodynamic shaker, the output of which is computed on the basis of the fundamental equation of the subsonic source. This predistortion processor is shown to be quite successful in producing controlled acoustic waveforms. The measurement of the pneumatic efficiency of the laboratory source is also considered and the measured efficiencies are close to the predicted values.
The possibility of using the subsonic source as a secondary actuator for active control of period primary sound fields in ducts is investigated. The nonlinear behaviour of the source is shown to be reduced when the acoustic pressure at a location close to its output is cancelled. An harmonic controller is discussed that accounts for the residual nonlinear behaviour of the subsonic source and such a controller is implemented on a signal processing board. A linear model for the plant under control is shown to be accurate enough for modelling the system under control, since the harmonic controller is found to converge. Experiments with the automatic controller reveal that the attenuations measured at the monitor microphone are around 25 dB, for sinusoidal primary sound fields.
University of Southampton
1998
Blondel, Laurent Armand
(1998)
Compressed air acoustic sources for active noise control.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
An analysis is presented of an acoustic source which operates by the release of compressed air through an aperture, the area of which is made to vary with time. A distinction is made between sonic and subsonic compressed air sources, and in both cases simple equations are derived that describe the acoustical behaviour of the devices. Sonic sources are linear but inefficient. Subsonic source are much more efficient that sonic sources but their output is generally no longer a linear function of aperture opening. A numeric comparison between the performance of compressed air sources and electrodynamic loudspeakers shows that the former appear to be well suited to active noise control applications.
The design of a subsonic source is described, in which a sliding plate driven by an electrodynamic shaker modulates the air flow. An experimental analysis of the laboratory subsonic source is carried out. The acoustic pressure at the source output is measured for various conditions. The experimental results are found to be in good agreement with the theoretical predictions. Predistortion of the subsonic source to produce a sinusoidal output is considered. A predistortion processor is placed in series with the electrodynamic shaker, the output of which is computed on the basis of the fundamental equation of the subsonic source. This predistortion processor is shown to be quite successful in producing controlled acoustic waveforms. The measurement of the pneumatic efficiency of the laboratory source is also considered and the measured efficiencies are close to the predicted values.
The possibility of using the subsonic source as a secondary actuator for active control of period primary sound fields in ducts is investigated. The nonlinear behaviour of the source is shown to be reduced when the acoustic pressure at a location close to its output is cancelled. An harmonic controller is discussed that accounts for the residual nonlinear behaviour of the subsonic source and such a controller is implemented on a signal processing board. A linear model for the plant under control is shown to be accurate enough for modelling the system under control, since the harmonic controller is found to converge. Experiments with the automatic controller reveal that the attenuations measured at the monitor microphone are around 25 dB, for sinusoidal primary sound fields.
This record has no associated files available for download.
More information
Published date: 1998
Identifiers
Local EPrints ID: 463352
URI: http://eprints.soton.ac.uk/id/eprint/463352
PURE UUID: 52959981-e9a0-4623-ad73-e4e7e1c91f31
Catalogue record
Date deposited: 04 Jul 2022 20:50
Last modified: 04 Jul 2022 20:50
Export record
Contributors
Author:
Laurent Armand Blondel
Download statistics
Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.
View more statistics