[Elecraft] Noise Cancelling Headphones

[N2TK, Tony]

Thanks for all the feedback. I need to try out a pair of noise canceling
over the ear headset on both CW and SSB to see if it helps.
73,
N2TK, Tony

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jim Brown
Sent: Thursday, December 26, 2013 2:03 PM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] Noise Cancelling Headphones

On 12/26/2013 10:39 AM, Mark Petiford wrote:
> Re:  "Is there such a thing as a noise cancelling black box you can plug
in aheadset such as the CM-500 and get good noise canceling? No knobs. Just
anON-OFF switch like the headsets have."
>
> Well, sort of, Tony.  In the aviation world,  conversions kits have 
> been marketed for popular (in aviation circles) headsets to convert 
> them to noise canceling.  They weren't "black box" plug-in devices, 
> but rather a kit of microphones and electronics mounted in each 
> earpiece and required some disassembly of the existing earpieces.  I 
> believe they were made for David Clark and Flightcom headsets, and 
> maybe a few others.  The result was a significant improvement over the 
> original passive headset

Right.  Successful noise cancelling requires that the resulting acoustic
output AS COUPLED TO THE EAR CANAL precisely match the acoustic noise that
GETS THROUGH THE HEADPHONES TO THE EAR CANAL (caps added for
emphasis) in both magnitude and phase, and that the two acoustic signals are
out of polarity. That means that the mic picking up the noise be very close
to the headphones, the distance between the mic, the transducer, and the ear
must be compensated, and the relative response, both magnitude and phase,
must be precisely compensated.  That's a VERY difficult design problem, and
a really good solution is only practical when everything is built as an
integrated package, with dedicated mic, headphone transducers, and
electronics.

73, Jim K9YC


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