Paraholography—A New Method for Measurement of the Directional Distribution of Sound Waves in a Reverberation Chamber

Abstract

We describe a method for experimental determination of the various plane waves composing the sound field in a reverberation chamber. The physical quantities needed are (1) the directions of propagation, (2) the time mean of the squared sound pressure, and (3) its phase. These quantities are usually needed, for sound having a narrow band of frequencies, as running functions of time. The basic holographic principle is comparison of the actual sound field with a reference plane wave having precisely known direction of propagation, sound pressure, and phase. The reference wave is not a “real” wave but is created electronically, on the electrical side of microphones sensing the actual sound field, so as to be “parallel” to a real wave. The comparison of the paraholographic wave with the actual sound field so as to measure the latter is achieved with a least-squares principle, in which the product of the two sound pressures is time-integrated. Simultaneous integrals for several paraholographic waves may be carried out. We present the results of the analysis and some preliminary data for a standing-wave (impedance tube) for which only two paraholographic waves are needed.