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The audibility of comb-filtering due to perforated cinema screens

The audibility of comb-filtering due to perforated cinema screens
The audibility of comb-filtering due to perforated cinema screens
In most professional, commercial and domestic cinemas the loudspeakers are mounted behind the screen so that the visual images on screen coincide with the position of the associated sound images. However, this requires the screen
material to be both light-reflective and acoustically transparent, which is difficult to achieve. The resultant imperfect sound transmission gives rise to the sound from the loudspeakers being reflected back from the screen and then forwards again as it reflects from the loudspeaker. The interference between the initial sound and the subsequent reflections gives rise to comb-filtering which depends upon the reflection coefficients of the screen and loudspeaker and the spacing between the screen and the loudspeaker.A change in separation will cause the respective phase difference
between the direct and reflected waves to vary, thus yielding a different resultant wave at the point of the receiver. Little research has been carried out to date on the audibility of this comb filtering, and in particular, given a certain screen/loudspeaker setup, the effect of varying the spacing has not been investigated thoroughly. By modelling the system using MATLAB, the behaviour of the perforated screen when subjected to an incident sound wave can be predicted. Once this is achieved, the effective filter for different separations between screen and loudspeaker can be used to create a database of simulated output signals that represent a portion of cinema audio being played through the screen/loudspeaker system in different geometric setups. These signals can then be used to determine the audibility of the comb-filtering effect at different separations via a comparative subjective testing technique. The results of these tests suggest that the audibility is, at the very least, barely audible at all separation distances.
Audio Engineering Society
Elliott, David
bea516fe-809c-4263-a1dc-4ccaac46d2bf
Holland, Keith
90dd842b-e3c8-45bb-865e-3e7da77ec703
Newell, Philip
f44dc810-765e-415b-b748-be31c7058a1d
Elliott, David
bea516fe-809c-4263-a1dc-4ccaac46d2bf
Holland, Keith
90dd842b-e3c8-45bb-865e-3e7da77ec703
Newell, Philip
f44dc810-765e-415b-b748-be31c7058a1d

Elliott, David, Holland, Keith and Newell, Philip (2015) The audibility of comb-filtering due to perforated cinema screens. In Proceedings of the AES 57th International Conference: The Future of Audio Entertainment Technology. Audio Engineering Society. 7 pp .

Record type: Conference or Workshop Item (Paper)

Abstract

In most professional, commercial and domestic cinemas the loudspeakers are mounted behind the screen so that the visual images on screen coincide with the position of the associated sound images. However, this requires the screen
material to be both light-reflective and acoustically transparent, which is difficult to achieve. The resultant imperfect sound transmission gives rise to the sound from the loudspeakers being reflected back from the screen and then forwards again as it reflects from the loudspeaker. The interference between the initial sound and the subsequent reflections gives rise to comb-filtering which depends upon the reflection coefficients of the screen and loudspeaker and the spacing between the screen and the loudspeaker.A change in separation will cause the respective phase difference
between the direct and reflected waves to vary, thus yielding a different resultant wave at the point of the receiver. Little research has been carried out to date on the audibility of this comb filtering, and in particular, given a certain screen/loudspeaker setup, the effect of varying the spacing has not been investigated thoroughly. By modelling the system using MATLAB, the behaviour of the perforated screen when subjected to an incident sound wave can be predicted. Once this is achieved, the effective filter for different separations between screen and loudspeaker can be used to create a database of simulated output signals that represent a portion of cinema audio being played through the screen/loudspeaker system in different geometric setups. These signals can then be used to determine the audibility of the comb-filtering effect at different separations via a comparative subjective testing technique. The results of these tests suggest that the audibility is, at the very least, barely audible at all separation distances.

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More information

Published date: 8 March 2015
Venue - Dates: 57th AES Conference: The Future of Audio Entertainment Technology, California, United States, 2015-03-06 - 2015-03-08
Organisations: Acoustics Group

Identifiers

Local EPrints ID: 410641
URI: https://eprints.soton.ac.uk/id/eprint/410641
PURE UUID: dc0431c9-cfe4-472d-954c-665c11829ef2
ORCID for Keith Holland: ORCID iD orcid.org/0000-0001-7439-2375

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Date deposited: 09 Jun 2017 09:17
Last modified: 16 Jul 2019 01:12

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