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    In reply to Angier Ames, yes there is technology out there to design and
install active noise cancellation systems in various sorts of enclosures,
including aircraft cockpits.  My wife suffers from a hearing disorder
(technically severe tinnitus with recruitment), which effectively keeps her
out of any small airplane.  In hopes of building a quiet airplane, I
researched this topic a couple of years ago.  There are some companies out
there, mostly oriented toward noise reduction in the industrial workplace.
Unfortunately, active noise cancellation systems are very complex (read
expensive) and have to be tailored to each situation.  The headset folks
have an easy chore, really, because they deal only with a small, defined
space:  the volume inside the earcup.  In addition, the passive noise
reducing elements already simplify their job.  For an aircraft cockpit,
there would first have to be careful studies of the intensity, frequency
distribution, and spatial orientation of sound through the operating
envelope of the plane.  Then appropriate cancellation algorithms have to be
worked out, taking into account the performance of the sound-producing
elements required for cancellation.
    Bottom line:  No one has an off-the-shelf solution, and one engineer I
spoke with guessed that $50K, perhaps much more,  was a reasonable estimate
of what it would cost to develop a system for a small aircraft!  Sigh.

Jim Cameron    LNCE N82500

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