[Elecraft] Noise Cancelling Microphones (was Re: Noise cancelling headphones)

[Jim Brown]

On 8/5/2018 10:48 AM, ANDY DURBIN wrote:
> Many/most aviation headsets use noise cancelling microphones but they are not active.  They simply sample most of the voice signal on the mouth side of the element and most of the noise on both sides of the element. Effective noise cancellation requires the microphone to be close to the lips.

Not quite -- it's the cancellation of the output of two closely spaced 
mic capsules, and as you describe operation, it depends on the mic being 
right at the lips. This is the proper definition of a noise cancelling 
microphone. Noise cancelling microphones tend to sound varying degrees 
of awful. Many years ago, Shure, one of the better mic mfrs, tried to 
build a noise cancelling mic aimed at drummers. I tested a prototype in 
a high quality recording setup, and it sounded pretty bad. They never 
marketed it.

Note that this definition is VERY different from a cardioid microphone, 
where a single capsule as two openings, one from the front and one from 
the rear, and the two types behave VERY differently.  Cardioid mics have 
a property called "proximity effect" which boosts bass response when the 
mic is very close to the sound source, making it sound rather muddy. 
When mics like this are used for singers and speech, their low frequency 
response is heavily rolled off. In some mics the rolloff is built in 
(the Shure SM57 and SM58 are examples), in some it is built in but 
switchable (the Shure SM81 is an example), while in others it is not 
built in, but applied in the mixer for sound reinforecment or recording.

I mention this because many mfrs of headset mics falsely describe their 
cardioid mic as noise cancelling, which it is NOT. It IS a directional 
mic that rejects sound coming from directions other than the front.

73, Jim K9YC