Development of an Active Noise Cancellation Hearing Protector: How Can Passive Attenuation Be Retained?

Abstract

The modest low-frequency attenuation of the conventional passive hearing protector can be improved electronically by active noise cancellation techniques. This paper presents the theory and some of the actual limitations of an active noise cancellation hearing protector. Three prototypes with similar types of controller, but with different mechanical construction were made and their performance was measured. The electronics of the system were implemented using analog electronics and feedback construction. The measurement results were compared with the results of an equivalent passive hearing protector with no internal electronics and with an intact earcup. The results show that the integration of the controller inside the earcups degrades the passive attenuation of the hearing protector at frequencies below 200 Hz. With proper design, an active noise cancellation hearing protector can still have 15 dB more noise attenuation at 100 - 200 Hz range than an equivalent passive hearing protector.

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