OBJECTIVETo evaluate the sound pressure level at outlet of external auditory canal and eardrum, and to observe the range of maximum frequency of sound effect of outlet ear canal, so as to provide exact data for designing personal noise rating instrument and studying the effect of environmental noise on human body, and to provide basis for calibration of noise sound pressure level.

METHODSound pressure level at eardrum and outlet of external auditory canal in 30 young people (60 ears) were measured by Audio Scan RM500 at 50 dB SPL narrow band noise with different frequencies (0.25 - 8.00 kHz).

RESULTSAt the same frequency, sound pressure levels at eardrum were less than (0.6 +/- 2.6) dB SPL, at outlet of outlet ear canal less than (0.2 +/- 1.8) dB SPL, there were no significant differences between both sound pressure levels (P > 0.05). There were significant differences in sound pressure levels between both places at 1.50 - 8.00 kHz (P < 0.01). The maximum difference was (10.5 +/- 3.4) dB SPL at 2.00 kHz, and the minimum was (0.5 +/- 6.2) dB SPL at 0.50 kHz.

CONCLUSIONThe effects of increased sound pressure should be considered in the evaluation of environmental noise and the design for individual noise rating meter when the noise frequency was >or= 1.50 kHz.