Ambient Noise Attenuation.

TL;DRAbstract

Noise attenuation of circumaural ear enclosures is limited to low frequencies by pumping action of the earcup which generates internal noise. Theoretical study showed that this internal noise is proportional to the entrance, or inside, area of the cushion if all other variables are kept equal; thus, it is important to keep the inside area as small as possible consistent with easy insertion over the pinna. The theoretical analysis included the effect of reducing the cushion open area by reflexing the cup inwardly with a rigid flange and indicated that it is best to cover this flange with cushion material (within certain limits). For predicted benefits to accrue, the cushion must be designed to seal against the head at its inner periphery. Some experimental verification was made. A study of active noise cancellation in earcups concentrated upon the techniques of sensing cup displacement resulting from an external sound and generating an internal displacement wave of equal magnitude but o

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