The Subjective Evaluation of Sonic Bangs

An experiment is described in which 61 subjects used the method of direct magnitude estimation to judge the relative annoyance of sonic bangs, explosions and jet aircraft noise. Artificial white noises were included to test the subjects' performance for individual consistency and to compare their results with the established relationship between subjective magnitude and objective level.

The annoyance of sonic bangs is shown to correlate closely with calculated loudness level, nearly as well with perceived noise level but poorly with peak overpressure. Conventional methods of calculation for steady sounds have to be modified to take account of the predominance of low frequency energy and of the short duration of sonic bangs. The appropriate band pressure levels are derived from the Fourier transform of the waveform by averaging band energies over the auditory critical time of 70 ms. The same procedure is applied to the explosions. The relative annoyance of the transient sounds and of the jet aircraft and white noise are then correctly predicted.

The octave band sound pressure spectrum of the theoretical waveform for a ground-reflected N-wave is shown to agree with measured spectra of sonic bangs.

The subjective results are consistent with those of a laboratory experiment using recorded sonic bangs from a similar aircraft, the present results showing that a peak over-pressure of 1.4 mb measured at ground level is as annoying as jet noise at 110 PNdB. For sonic bangs of different rise time this result would not apply.

The listening tests were repeated outdoors and indoors, and showed that subjects were about 5 phons more severe in their judgements indoors, in conformity with previous results on conventional aircraft noise.