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 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
