Measurement of acoustic parameters in room at low frequency

Abstract

One of the requirements of the transmission suite and sound studios is that the sound in them should be diffuse, but since in the low frequency range the problem of poor diffusion arises, that consequently leads to discrepancies in the transmission loss measurement at various facilities. This thesis attempts to show how to achieve adequate experimental accuracy without the need for a very large room. Considerable attention has been given to the problem of understanding the performance of sound on the low frequencies range. As far as the sound and recording studios are concerned, with only a few room modes in a measurement band at low frequencies, there tends to bean irregular room response. This can change the original tonal qualities of music and also the intelligibility of speech. To avoid these problems it is necessary to treat the surfaces of the studios acoustically. The modal parameters including the natural frequencies, damping constants of a resonant mode are measurable quantities and can therefore be employed as parameters for judging the acoustic performance of a room where a particular absorbing surface treatment is applied to its boundary.In the thesis a small room is considered and the behaviour of sound in the low frequency range for various source and receiver positions has been obtained experimentally and is then compared with the theoretical analysis. The agreement and the disagreements between the coupling of the modes is applied to predict anamolies in transmission loss measurements, the design of small acoustic studios and the measurement of sound absorption coefficient.