Active shielding based on difference potentials

Lim, H

Abstract

Active control of sound is a technique for altering acoustic fields to wanted ones
in aimed domains by introducing controllable active secondary sound sources called
controls. This thesis describes an active shielding methodology based on difference
potentials for the control of noise and preservation of sound in domains. The main
feature of this methodology is its ability to automatically preserve "wanted" sound
within a domain while cancelling "unwanted" noise from outside the domain. This
method of preservation of the wanted sounds by active shielding control is
demonstrated with various broadband and realistic sound sources such as, human
voice, music, etc in multiple domains in a one dimensional enclosure. Unlike many
other conventional active control methods, the proposed approach does not require
the explicit characterisation of the wanted sound to be preserved. The controls are
designed based on the measurements of the total field on the boundaries of the
shielded domain only, which is allowed to be multiply connected, and the
controls are placed on the boundaries only. The cancellation and preservation
can be achieved globally over a large area of the domain. The method is tested in a
variety of experimental cases. The typical attenuation of the unwanted noise is found
to be about 20 dB over a large area of the shielded domain and the original wanted
sound field is preserved with errors of around 1 dB and less below through a broad
frequency range up to 1 kHz. This thesis reports on the results of the validation for
the methodology in detail, with particular emphasis on the volumetric noise
cancellation and wanted sound preservation offered by the proposed methodology,
which are unique features compared to other techniques available in the literature.

Citation

Lim, H. Active shielding based on difference potentials. (Thesis). Salford : University of Salford

• Thesis Type: Thesis
• Deposit Date: Oct 3, 2012
• Award Date: Jan 1, 2011