Experimental and Theoretical Study of Propagation of Finite‐Amplitude Noise in a Pipe

In an earlier paper [J. Acoust. Soc. Amer. 53, 383(A) (1973)], the authors presented a computer algorithm for predicting the distortion of plane, finite‐amplitude acoustic signals of arbitrary waveform. Experimental measurements of 160‐dB periodic waves in a 2‐in.‐diam, 100‐ft‐long pipe confirmed predictions after the algorithm had been modified to account for attenuation and dispersion caused by the acoustic boundary layer at the pipe wall. The algorithm has now been used to compute the distortion of high‐intensity noise. Bursts of broad‐band noise of SPL 160 dB and higher have been used. Again, the computed time waveforms closely resemble the observed ones. Qualitatively, the noise waveform becomes simpler in appearance (for example, the number of zero crossings decreases) as the signal travels down the pipe. This change is due to the fact that as the shock waves form, grow, and decay, they “eat up” minor irregularities in the waveform. Information on the spectral content of the noise as a function of p...