Effects of cup, cushion, headband force, and foam lining on the attenuation of earmuffs

Abstract

The essays were undertaken using an artificial head and a diffuse sound field, according to DIN ISO 4869-1. Increasing the cup mass improved the noise attenuation by 17 dB at 100–300 Hz. The coherence function between cup vibration and sound pressure inside the cup has shown that a great amount of sound energy is transmitted to the inside of the cup, at low frequencies. The foam lining of the cup clearly attenuated the sound in the frequency between 2000 and 8000 Hz. Increasing absorbent mass improved attenuation because resonances could be damped. The attenuation measured with a complete earmuff, and the same without the cushion, have shown that sound leakage occurs at frequencies ranging from 100–2000 Hz. The vaseline coating between the skin and the cushion improve the attenuation by less than 5 dB (100–200 Hz). As the headband force increases to a maximal deformation of the cushion, attenuation reaches 20 dB at 200 Hz. The increase in the headband force is, however, a limiting factor in the use of the earmuff, as it becomes too uncomfortable. The same conclusion applied to the increase in the mass of the cup.