Temporary Threshold Shift from Acoustic Pulses

Although some empirical laws relating temporary threshold shift (TTS) to various parameters of continuous noise (intensity, duration, temporal pattern) recently have been devised, little is known about the TTS produced by impulsive noises such as gunfire. Some preliminary studies using impulses are described. Repetitive impulses of 140- to 150-db peak SPL were generated by (a) a toy known as a “cricket” which generates acoustic pulses when a piece of metal snaps from one position to another, and by (b) a high-intensity Altec driver through which a condenser was discharged. Comparison of TTS produced by the two types of pulses shows that peak pressure, although important, is not the only relevant parameter. The correlation between the TTS produced in individual ears by the impulses and that produced in the same ears by steady noise was not significantly different from zero. This fact underscores the futility of trying to devise a simple test for “susceptibility to acoustic trauma.” (This research was supported by a research grant from the National Institutes of Neurological Diseases and Blindness, Public Health Service.)