Reverberation enhancement for small rooms

Abstract

Reverberation enhancement is a technology which allows the reverberation time of a room to be increased through the use of an electronic system. These systems have traditionally been applied to improve the acoustics of large concert halls but the technology can also be used in smaller spaces with several possible applications. Previous uses of reverberation enhancement in small rooms have largely consisted of direct transplants of systems designed for large concert halls. This work investigates the complications which arise when using reverberation enhancement in a small room due to the differences in the acoustic properties of the space and also the restriction on the channel count of the system due to physical constraints.

The first part of this work deals with increasing the resultant reverberation time of the room without requiring additional system channels. This is achieved through the use of processing within the system. Two methods have been investigated. The first extends the resultant reverberation time without changing the feedback gain. The processing used for this purpose is either electronic reverberation or simple delay, both of which have been shown to allow significant increases in resultant reverberation time. These changes can be predicted accurately using diffuse field theory. The other method uses time-varying processing to increase the maximum stable feedback gain. This has been shown to allow increases in resultant reverberation time but also causes undesirable artefacts which limit the usability of this technique.

The second part of this work focuses on the differences in the acoustic properties of small rooms and especially the ways in which these rooms differ from a diffuse field. This includes the consideration of the modal properties of the room at low frequency which are insignificant in a large room. It has been shown that the spatial and frequency variations of the room at low frequency can be reduced through numerical optimisation of the processing within the reverberation enhancement system. Finally, the diffusion of the sound field and the early energy in the impulse response have been considered. It is shown that restrictions on the resultant reverberation time may be required in order to create a subjectively acceptable acoustic response. Overall, this work has shown that by accounting for the properties of the room, excellent performance of the system can be achieved.

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Identifiers

ORCID for D.J. Thompson: orcid.org/0000-0002-7964-5906

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