Sabine Reverberation Equation and Sound Power Calculations

Abstract

Three reverberation time equations and three sound power equations are scrutinized for their utility in the calculation of sound power from measurements of the average steady-state sound pressure level and reverberation time in a reverberant room. It is noted that the Sabine reverberation time equation is theoretically plausible for this use, even in a moderately absorbing room, providing it can be established that the average sound energy density decays exponentially with time. The sound power calculation may also be performed in terms of the “Sabine absorption” which is simply the absorption computed (by the Sabine equation) from the observed reverberation time and room volume. The “Sabine absorption coefficient” may exceed unity; indeed, it approaches infinity as the walls of the room become completely absorbing. An experiment was performed in a concrete room of volume 1350 ft3, to which three amounts of sound absorbing material were added. Under these four conditions the appropriate measurements were made with two independent systems (one having half-octave bands, the other third-octave bands), from which were calculated the sound power spectra of a printing calculator and a unit heater. In addition to simplicity, both theory and experiment support use of the “Sabine absorption” instead of the “room constant” in the calculation of sound power.