Finite‐Amplitude Distortion in Air at High Acoustic Pressures

Measurements have been made at the harmonic distortion of progressive waves having initial peak pressures as high as 0.1 atm at a fundamental frequency of 445 cps. These signals were propagated in tubes of diameters 1.587, 2.66, and 5.26 cm. The tubes were terminated after seven wavelengths or before the experimental shock‐formation distance, whichever came first. Typically, twenty harmonics, whose amplitudes were within 60 dB of the initial pressure, were measured near the shock‐formation distance. The measurements of the first four harmonics are compared with an extension of a theory presented by Blackstock [Paper O15 in Proceedings of the Fourth International Congress on Acoustics, Copenhagen, 1962 (Organization Committee of the 4th ICA and Harlanz & Toksvig, Copenhagen, 1962)]. The theory is confirmed in all essential details. [Work supported in part by the National Science Foundation and by the U. S. Office of Naval Research.]