Growth of TTS as a function of the peak level of impacts noises of long duration

Abstract

The Concept of critical level for impulse noise [H. McRobert and W. D. Ward, J. Acoust. Soc. Am. 53, 1297–1300 (1973)] was tested using impact noises of long duration. Fifteen normal listeners were exposed to repeated series of 30 impact noises presented one every 3 s at peak levels ranging from 106 to 136 dB SPL. The duration of the impacts were approximately 500 ms each. TTS2 at 4 and 6 kHz in both ears was measured following each series of 30 impacts and the peak level was increased by 3 dB steps until a TTS2 of 15 dB at any frequency was observed. The peak noise level producing the 15 dB TTS was identified as the critical noise level (CL). Results indicated that growth of TTS was not linearly related to the peak level of the noise. For the 13 subjects who reached the target amount of TTS, the CL's ranged from 118 to 136 dB SPL, In 8 out of 13 subjects, the target amount of TTS could be observed following a single series of 30 impacts presented at individuals CL. However, exposure to 120 impacts at 6 dB below the CL also induced the critical amount of TTS2, suggesting that the equal energy assumption may be partially correct for establishing a trading relationship between peak level and number of impacts.