THE LEVEL OF THE MUSICAL LOUD SOUND AND NOISE INDUCED HEARING IMPAIRMENT
Recently, there has been an increasing number of reports concerning hearing impairment which musical loud sound is thought to be one of the causes. We are getting more of this musical loud sound as cassette tape recorders with head phones such as Walkman and so forth get popular as well as occasions to attending rock concerts and going to discotheques increase.
This hearing impairment is generally called discotheque deafness and the following three types are considered; 1) deafness which have fixed by accumulation of loud sound over a long period of time as seen in people involved in musical performance such as rock musicians and mixing engineers; 2) abrupt noise induced hearing impairment triggered by loud sound and 3) state of deafness which is a progressing stage towards recovery of noise induced temporary threshold shift (NITTS), which occurs temporarily by a loud sound stimulus, and hearing ability recovers afterward.
However, it is considered that these musical loud sounds not only changes every moment according to method of performing or type of music, but the volume of the sound actually reaching the auditory sense differs largely by locations and direction of the ear and speakers. So it becomes necessary to measure the accumulation of the noise which each individual is exposed under over a long period of time and at the same time carry out the regular medical checkups including hearing test to check the initiation and advancement of the noise induced hearing impairment.
Then we can examine the relationship between loudness of the environmental noise and initiation and advancement of the hearing impairment. However, there has not been a device which is compact and measures noise exposure individually over a long period of time. So we have experimentally produced ultra compact noise dosimeter which we named Noise Badge, and with it we actually measured individual noise exposure over a long time in rock music, noise in discotheque and noisy factory.
Then we examined the relationship between these loud sound and noise induced temporary threshold shift (NITTS) in discotheques and noise proof room using simulation of loud sound exposure. Moreover, we measured the most comfortable loudness level of head phones in each examine and different types of music with environmental noise in consideration, thus examining the relationship between musical loud sound and the hearing impairment.