Artificial Head (ATF) for Evaluation of Hearing Protectors

In order to measure the Insertion Loss (IL) of hearing protectors in high levels of steady-state or impulse noise, the acoustic isolation of an Acoustical Test Fixture (ATF) has to exceed the Insertion Loss of the hearing protectors. As the acoustic isolation of commercially available artificial heads does not meet this requirement, a new device has been designed and built. The artificial head, made of hard polyurethane, is designed to fit the Head Acoustics^® external ear and circumaural region. An ear simulator from Brüel & Kjær is used to simulate the acoustic impedance of the human ear. The isolation of this ATF is better than 70 dB in a large frequency range (even when exposed to shock waves). The transfer function of the open ear is in close agreement with the experimental data published by Shaw and is linear up to 190 dB (peak pressure). This ATF allows the evaluation of all kinds of hearing protectors from the lowest to the highest (190 dB) levels.