Scott Skylane wrote:

Not necessarily true, at all. The ANR function can be tuned to any
frequency, as desired. The Telex ANR-850's that I use in the jet are
FANTASTIC at reducing high-frequency wind noise, but are totally useless
in any propeller driven aircraft.

While there is SOME ability in digital ANR headsets like the Telex to
do some SLIGHT tuning of the ANR central frequency, it is completely
incorrect to state that it can be "tuned to any frequency, as desired".

ANR works by measuring the noise with a tiny microphone and then
injecting the inverse of the noise signal into the speakers. At low
frequencies (in the 50 - 300 Hz range, or so), the wavelength of the
sound is long enough that the sensing microphone and your ear only
need to be CLOSE to each other, but not coincident, in order for the
injected signal to approximately counteract the noise.

At high frequencies (above 1000-2000 Hz), the wavelength of the sound
starts becoming very small. This implies that for the microphone to
measure (and hence cancel) the noise that the EAR is hearing, the
microphone would have to be essentially inside the ear, or else it
would be canceling something other than what the ear perceives.

Now, that's not to say that SOME amount of ANR can be done with
digital techniques at somewhat higher frequencies than analog ANR can
do with some sophisticated algorithms, but it's hardly "any
frequency". I'd be very surprised if the "wind noise" you mention is
more than a few hundred Hz, and if, in fact, the 850's are "totally
useless" in any propeller driven aircraft, then they've got pretty
poor ANR capabilities. I've never worn them, so I can't comment on
them directly.

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2006