Artificial Heads for High-Level Impulse Sound Measurement

摘要

If the Insertion Loss (IL) of hearing protectors has to be determined with very high impulse or continuous noise levels, the acoustic insulation of the Artificial Test Fixture has to exceed at least the Insertion Loss (IL) of the hearing protector. An another requirement when evaluating ear muffs, is an adequate reproduction of the pinna and the circumaural area. For the evaluation of ear plugs and hearing protectors using Active Noise Cancellation (ANR) the impedance of the eardrum must be properly reproduced. These requirements have not been always fulfilled by commercially available artificial heads. Therefore, a special device for this type of measurement has been designed and built in our laboratories. The head has been molded with Polyurethane material in a way, that the HEAD Acoustics external ear and circumaural area could be fit. In order to simulate the acoustic impedance of the human ear, a Bruel & Kjaer ear simulator has been used. The acoustic insulation of the ATF is better than the requirements of the different standards. The Transfer Function of the Open Ear (TFOE) is very close to the data published by Shaw. The device is linear up to peak pressure levels of 190 dB. It is possible with this ATF, to evaluate the IL of all types of hearing protectors up to pressure levels of 190 dB.