Propagation of spherical acoustic noise of finite amplitude

Some theoretical and experimental aspects of a practical problem concerning the wave motion of spherically spreading acoustic noise of finite amplitude in freefield have been treated. This deals with the changes of noise spectrum with increasing propagation distance. The theoretical analysis is based on Burgers' equation and Banta's expansion, and a stationary Gaussian noise of zero mean is assumed as an initial signal. The power spectrum of sound pressure is considered on the acoustic axis of a loudspeaker (tweeter) in an anechoic room. The source radiates 13-octave band noise with center frequency 5 kHz, and noise level at 1m from the source is 111 dB (re 20 μPa). Regarding the spectrum envelope, the experimental data obtained by digital computational technique agree well with the theoretical results.