NoiseGard active noise compensation is achieved by generating a signal identical in sound pressure level but exactly reversed in phase to the noise signal, the effect being that the
Active noise compensation is accomplished in the following manner: Each earcup includes a microphone, a feedback control circuit, and a transducer to reproduce both the communication and the noise cancelling signal. The feedback control microphones sense the total sound pressure within each earcup resulting from both the desired radio signal from the receiver and the undesired noise that has come through the earcup. The microphone signal is amplified and the radio signal is subtracted from it. The remaining signal (noise) is then filtered and inverted and the radio signal is added back in. Eventually, the entire signal is amplified and fed back to the transducer in each earcup. Since the noise component of the signal is inverted, it cancels the noise signal coming through the earcup. The radio signal remains unaffected, as it was not processed through the cancellation circuits.
The diagram on the left shows noise compensation with NoiseGard: Passive hearing protectors effectively attenuate noise from the middle and upper frequency range, the effect decreasing sharply in the lower range. However, active noise compensation with NoiseGard combined with passive hearing protectors results in a reduction of noise of approx. 25 dB in the
A 10 dB reduction in noise is perceived subjectively as a halving in volume. A further reduction in noise of 10 dB again results in a decrease in unwanted noise by 50 %.
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