Room acoustic and sound system design for full duplex teleconference facilities using ceiling-mounted transducers

Abstract

Room acoustics and the effects of differing conditions on performance of a full-duplex audio teleconference system, which nulls direct-path coupling, leaving only coupling by reflected energy, were studied. Room impulse responses and signal-to-noise ratios at talker locations and at transducer locations were taken for rooms with differing acoustic conditions, as were binaural recordings of the impulse response tests and of sample teleconferences in the same situations, for subjective comparison and simultaneous analysis. Long working distances from talkers to microphones offer the advantage to users of freedom of placement and movement, but at the cost of strict limits on ambient noise loudness and, more particularly, noise structure (annoyance components). Early reflections within the psychoacoustic fusion time limit described by the Haas effect were found beneficial, while reflections beyond that time proved detrimental both to intelligibility and to circuit function. Discrete energetic late reflections are especially undesirable. Optimization for various room configurations was studied, and criteria presented for obtaining subjectively high-quality teleconferences between rooms and from rooms to handsets.