A Computer Investigation of the Performance of Virtual Reflectors: Part II — The Effects of Room Conditions

In a companion paper [1] a technique for overcoming acoustic problems resulting from the directional nature of human speech in open stage auditoria by means of virtual reflectors has been proposed. In a following paper [2] the system was applied to a computer model of an open stage auditorium in which there was no background noise and the space was relatively dead. In the current paper the action of the virtual reflector has been systematically investigated in more realistic conditions. It is shown to be capable of functioning in conditions which are more reverberant and in conditions in which background noise is present. In all cases investigated the action of a virtual reflector results in conditions to the rear of the primary source (human speaker) being improved such that they become comparable to conditions at equivalent positions to the front.

It has been shown that the STI at the rear of a human speaker in an open stage auditorium with the virtual reflector system in operation does not increase significantly with increasing gain [2]. This is due to the Modulation Transfer Function (MTF's) being determined by the convolution of two impulse responses multiplied by a gain factor and added to a third impulse response. The resulting impulse response will therefore consists of many ‘reflections’ and hence the MTF's (and the STI values that they determine) will be adversely affected. An attempt was made to reduce the number of ‘reflections’ in the resultant impulse response by the use of a super directional microphone in order to improve the MTF's and thus the STI values. The actual improvement observed was very small and hence it would appear that the use of a super directional microphone is not particularly effective in this context.