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Content archived on 2024-04-16



The directive on the protection of workers from the risks related to exposure to noise at work (86/188/EEC) requires that workers should be provided with hearing protectors if the noise exposure is greater than 90 dB(A) or, in the case of impulsive noise, the maximum sound pressure level is greater than 200 Pascal.

The current standard, ISO 4869, determines the noise attenuation of a hearing protector as a function of frequency by measuring the human threshold of hearing with and without the hearing protector: the difference between the two thresholds is defined as the attenuation of the hearing protector. This method present two major problems. Firstly, it cannot be used with non-linear or amplitude-sensitive hearing protectors which provide increasing attenuation with increasing noise level so as to allow speech communication whilst at the same time attenuating hazardous noise. Secondly, irrespective of the linearity of the hearing protector, it is not possible to determine the attenuated maximum sound pressure level in the case of impulsive noise.

The answer to these problems lies in the use of acoustic measurements in the ear under the hearing protector when using realistic noises. Initially, hearing protector characterization methods will be developed that use test subjects, but ultimately it is intended to extend them to head simulators in order to be able to conduct tests that would otherwise expose subjects to potentially hazardous noises.


Two pilot studies are currently underway to investigate the feasibility of making appropriate measurements at a rate location in the ear under the hearing protector and to establish a suitable set of standard impulsive noise sources for laboratory tests.


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TNO Institute for Perception
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