The Suppression of Sound with Sound.
TEXAS UNIV AT AUSTIN APPLIED RESEARCH LABS
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An experiment was performed in which a finite-amplitude wave of frequency f1 interacted with a small-signal wave of frequency f2. The interaction, which resulted in an apparent excess attenuation of the signal at f2, occurred during planar, collinear propagation of the two signals in a 96 ft long, 2 in. i.d. progressive wave tube. The properties of the signals at the source were as follows f1769-1000 Hz, SPL1130-150 dB, f22800-10,500 Hz, SPL2110 dB. Propagation distances were 12.8 and 24.8 ft. A one-way modulation theory, the well known frequency modulation FM theory, and Fenlons intermodulation theory J. Acoust. Soc. Am. 51, 284-289 1972, both slightly modified to account for tube wall attenuation, were used to analyze the interaction. In one experiment, attempts to suppress the weak signal via the interaction resulted in amplitude reductions of as much as 40 dB. The results of another experiment, involving a spectral analysis, indicate that spectral amplitude predictions made using the modified Fenlon theory agree more closely with measured amplitudes than do predictions made using the modified FM theory. Author