Low Frequency Modeling and Experimental Validation of Passive Noise Attenuation in Ear Defenders

Abstract

Circumaural ear cups have been used for decades as an effective way of protecting users from high noise fields. Over the decades, a number of researchers dedicated their time to understanding the dynamics that govern the attenuation of hearing protectors. This thesis duplicates some of this work with newer technology and better data processing ability. In addition to revitalizing the accepted knowledge of hearing protector technology, this thesis is the first documented effort to show how the previously ignored air leak, known to exist between the ear cup and the head, has a profound effect on the low and mid frequency attenuation of a circumaural hearing defender.

Past research focused on the mechanical vibration of the cup on the seal as the main source of noise within the ear cup. This mechanical vibration, known as the piston resonance exists, and affected noise attenuation within the ear cup. A reasonably sized air leak of 160 e-7 m2 however, overwhelmed the piston resonance. An air leak of this size was shown to degrade noise attenuation by over 50 dB at 40Hz and 30 dB at 200 Hz when compared to a no-leak case. Further testing also suggested that the air leak has the ability to continue adding energy into the cup up to 3000 Hz.