On Frequency Modulated Signals in Reverberation Measurements
Frederick Vinton Hunt · The Journal of the Acoustical Society of America · 1933
A point-by-point curve tracer, similar to that described by Norris and Andree [J.A.S. 1, 366 (1930)] but permitting a longer period of decay to be traced, is employed to study the reverberant decay of pure tones and tones having various degrees of frequency modulation (so called “warble” tones). Straight lines (db vs. time) are fitted to the decay curves by the assumption that the slope determined by every pair of points should be weighted in the average according to the decay time included between the two points. This leads to a simple numerical procedure when the points are equally spaced on the time axis. The deviations of individual points from the best straight line are computed and found to fall into regular and consistent time patterns, from which large group deviations can be seen to gradually disappear as the degree of warble is increased. These time patterns differ from point to point in the sound chamber but the magnitude of the deviations and the slope of the decay curves (within a limit of accuracy consistent with the deviations) is practically independent of position. Conclusions are drawn regarding the accuracy with which decay rates can be determined using pure and warble tones.