Improvements in the Acoustic Wattmeter

Abstract

In this work the acoustic wattmeter, an instrument for measuring the flow of acoustical energy, has been revised from its earlier form. The instrument has been rebuilt to transmit but a single narrow frequency band. Although in the original report the wattmeter was reported as limited to the frequency range of 100 to 2000 cycles, the variable phase shifting network and analyzer here introduced were designed to operate down to 65 cycles per second, thus increasing the usefulness of the instrument in the low frequency range. The principal error in the instrument, which was that of phase shift with a changing input level, was located and a considerable reduction in phase shift has been achieved. A method of adjusting and partial calibration of the instrument have been worked out.