A Study of the Acoustic Significance of the Amplitude and Phase of Harmonics Present in a Source of Sound in a Room

Abstract

This investigation is pointed toward obtaining some further measure of the acoustic properties of a room. First, a brief subjective study is made of listener response to sounds which have various degrees of modulation on their decay curves and to alternate sounds which differ only in the phase relation of one of the harmonics with respect to the fundamental frequency. Second, an objective study of the modulation of sound decay curves is carried out for rectangular rooms, with emphasis on the effect of the phase and amplitude of harmonics present in the source of sound. In this study, the sound source consisted of a Complex Wave Generator, a power amplifier, and a loudspeaker. The Complex Wave Generator provides output terminals for the fundamental frequency and for the first four harmonics at controlled phases and amplitudes. The power amplifier is a conventional resistance-coupled amplifier combined with a device designed to cut off the output at any predetermined phase of the fundamental frequency and with a minimum switching transient. The loudspeaker and the complete recording system are conventional.