Quality of Reverberation

Abstract

In observations and measurements on the acoustical properties of a number of rooms varying greatly in size, shape, ornament, and surface finish, several factors bearing on the quality of sound have been noted. The generally accepted requirements for the reverberation-time characteristic as a function of frequency are rather stringent. It has been especially evident that when the high-frequency reverberation times in a concert hall are significantly longer relative to those of the midfrequency and low-frequency range than would normally occur, the acoustical conditions are judged unsatisfactory. A specific example of this condition has recently been studied in a new concert hall. Other factors relate to directional characteristics. It is concluded that highly isotropic reverberant sound is not pleasant, but confusing. Conditions are greatly improved if the preponderance of the reverberant sound approaches the listener from directions near the plane that includes the source and the listener's ears. For longer reverberation times, the quality is enhanced when it is possible to make some judgments of distance and direction by the binaural hearing sense, provided there is ample diffusion to suppress echoing. Binaural effects produce a sense of spaciousness, and this, rather than simply a prolonged reverberation time, is probably the principal effect giving rise to the exceptional acoustical properties of many large churches.