THE 
PRINCIPLE
Active noise compensation is accomplished in the following manner: Each ear cup 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 ear cup resulting from both the desired radio signal from the receiver and the undesired noise that has come through the ear cup. 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 ear cup. Since the noise component of the signal is inverted, it cancels the noise signal coming through the ear cup. The radio signal remains unaffected, as it was not processed through the cancellation circuits.
Noise compensation with NoiseGard
Attenuation
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0 |
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10 |
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20 |
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| passive |
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30 |
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40 |
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50 |
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25 | 50 | 100 | 200 | 500 | 1000 | 2000 | 5000 | 10000 | 15000 Hz |
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| Frequency |
The figure illustrates the noise compensation provided by NoiseGard: A conventional noise attenuating headset provides a substantial noise reduction at frequencies above 500 Hz but not below. Unfortunately, some strong components of aircraft motor and wind noise occur at frequencies below 500 Hz. By means of active noise compensation, noise within the frequency range from 25 - 500 Hz is attenuated by about 25 dB. The combined active/passive noise compensation response of the system amounts to approximately 30 dB over the entire audio range.
A noise reduction of about 10 dB is subjectively perceived as a halving of the noise level. If the noise is reduced by additional 10 dB, this is again perceived as a halving of the noise level, etc.
ENGLISH
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