Noise cancelling headphones

[Jim Brown-10]

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


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[Christopher Hoover]

Automatic noise cancelling microphone *systems* for consumer devices
typically involve 3 carefully placed DMIC's (digital microphones) and a lot
of DSP.    73 de AI6KG



On Sun, Aug 5, 2018 at 2:09 PM, Jim Brown <[hidden email]> wrote:

> 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
>
>
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>
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