Relation between sound transfer function from diffuse sound field to the eardrum and temporary threshold shift

Twelve volunteers with normal hearing (9 males and 3 females) participated in this work The sound transfer functions (STFS) from diffuse sound field to the subject's eardrums were measured and correlated to the temporary threshold shift (TTS) due to fiffuse-exposure.A probe tube with a miniature microphone was used for STF measurements in which successive 1/3 oct bandwidth random noise with central frequency from 0.25 kKz to 8 kHz were used. The subjects were divided into two groups, with the STF maxima at 2 kHz and 4 kHz respectively Pre- and post- exposure sweep Bekesy audiograms were recorded and the temporary thresh old shift calctilated as the difference between the two. Frequency of the maximum TTS was correlated to that of the maximum STF. The average TTS was very small or zero at frequen cies below the band noise exposure , but was noticeable even at the highest measured frequency (8 kHz) for beyond the noise band. Also individual differences in STF were found at frequencies between 2 kHz and 4 kHz

Temporary threshold shift in human subject exposed to noise

Using an audiometer, the effect of the noise level upon temporary threshold shift (TTS) for five trained normal subjects (left ear only) was studied. The measurements were carried out after 6 min exposure (in third octave band) for different sound pressure levels ranging between 75-105 dB at three test frequencies 2,3, and 4 kHz. The results indicated that at exposure to noise of sound pressure level (SPL) above 85 dB, TTS increases linearly with ths SPL for all the test frequencies. The work had extended to study the recovery curves for the same ears. The results indicated that the reduction in TTS on doubling the recovery times, for the two sound pressure levels 95 dB and 105 dB, occurs at a rate of nearly 3 dB. The comparison of the recovery curve at 3 kHz with that calculated using Ward's general equation for recovery was made. Finally, to study the values of TTS produced by exposure to certain noise at different test frequencies, distribution curves for two recovery times were plotted representing TTS values, for an exposure noise of 1 / 3 octave band and centre frequency 2 kHz, at different test frequencies.

The effects of smoking on temporary threshold shift

For studying the influence of smoking on temporary threshold shift (TTS), six normal subjects (3 smokers and 3 nonsmokers) were selected for carrying out this work. Nonsmokers were exposed separately for 7 min to 95 dB SPL in 1/3-octave band filtered noise centred at 2 kHz. Pre and post exposure thresholds (leftear) were recorded in a sound-proof booth using Bruel & Kjaer (B & K) Audiometer type 1800. For smokers, each one smoked a cigarette during the five minutes following the pre-exposure threshold measurement. All the assessments were conducted at a temperature between 22-25℃. The results indicated that smokers evidenced less TTS than did nonsmokers in the frequency range from 1 kHz to 5 kHz. At 6 kHz smokers evidenced nearly higher value. Maximum TTS was attained at frequency that was about 1/2-octave higher than that of the exposed noise. Comparison between recovery curves for smokers and nonsmokers was also made.