UNDERWATER SOUND PERCEPTION AND THE DEVELOPMENT OF AN UNDERWATER NOISE WEIGHTING SCALE

The sensitivity of human hearing underwater for a 'wet' ear has been measured. A total of 21 subjects underwent an underwater audiogram in an acoustic water tank at DRA Alverstoke. A high quality underwater loudspeaker provided pure tone sound stimuli at the third octave band centre frequencies from 25 Hz to 16 kHz. The results have enabled the underwater threshold of hearing to be defined. The most sensitive hearing frequency was 800 Hz, and at a level of 41 dB SPL re.20 mu Pa. There is a general loss in hearing sensitivity underwater, which is most pronounced at frequencies above 2 kHz and as a consequence, low frequency sound plays the greatest role in underwater sound perception by divers. Consequently, a higher level of noise is permissible underwater than would be permissible in air. An example is presented of the use of a new underwater weighting scale, the dB(UW), as a means of assessing underwater noise hazard.