User manual SENNHEISER HMEC 222-III

[. . . ] Investigations have revealed that noise affects the nervous system, causing e. Cockpit noise amounts to about 80 dB (A) in jets and to 90 up to 97 dB (A) in turboprops. [. . . ] The overall noise level is reduced so that the radio volume can be turned down but enough noise still remains for the pilot to safely monitor the aircraft engines. 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 out-of-phase signal cancels most of the noise signal. Noise compensation with NoiseGard 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. 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. [. . . ] ACX-11 ACX-22 Adapter cable for the power supply of only one headset Adapter cable for the power supply of two headsets HEADPHONE Transducer principle Coupling to the ear Frequency response Nominal impedance active Nominal impedance passive Attenuation active + passive Operating voltage Current consumption dynamic, closed circumaural 45 - 15. GENERAL Caliper pressure Weight without cable Subject to alterations 18 approx. [. . . ]