Frequently Asked Questions - MicMuff® Microphone Cover

Good question! The short answer is that in a noisy airplane, a MicMuff® Microphone Cover enables a noise canceling mic to do its job. But here’s the complete explanation.

Aviation microphones are noise canceling mics, built with two microphone cartridges aligned back to back with a common output membrane. Look at your headset mic. It has openings for sound to enter on both the front and back of the microphone body.

Cockpit noise enters both sides of the mic and cancels itself at the output membrane because this membrane must resonate to put out a signal. By allowing the same sound to enter both sides of the mic, the microphone cancels the cockpit noise effectively. When you speak into the mic, your voice mostly enters one side of the mic, causing membrane to resonate, which creates the output signal (your voice) without much of the ambient noise (cockpit sound). The output signal-to-noise ratio (your voice vs. cockpit noise) is quite good.

This technology works well until the ambient noise level exceeds 97dB of sound pressure. This sound pressure level is exceeded easily by the noise of a large engine, insufficient sound insulation, an open cockpit, or an open ventilator, doors or windows.

When the cockpit noise entering the microphone exceeds 97dB, it causes the membrane to resonate harmonically to the cockpit noise.This resonation makes a noise that sounds like the "shhhh" of wind. The harmonically vibrating membrane creates this noise, much like drawing your finger over a phonograph needle (remember those?) creates a "shhhh" noise.

Unfortunately, when the mic resonates, it (1) fails to cancel cockpit noise, (2) transmits the noise, and (3) creates additional noise! Your voice is lost in this chaos. The signal (voice) to noise (other sound) ratio is now reversed — there’s more noise than signal.

The MicMuff® Microphone Cover is a two-part device. The first part is an ordinary foam sleeve placed over the mic. You probably have something similar on your mic now. These sleeves are commonly called "wind screens." They are not wind screens; they allow wind to pass right through. The foam sleeve is really an "anti-sibilant" which is meant to reduce the "sssss" and popping sounds caused by pronouncing "S" or "P" when speaking into the microphone. Oregon Aero uses the foam to produce a chamber around the mic.

The second component of our MicMuff® Microphone Cover is a solid leatherette sleeve with two small holes and an elastic cord to fasten it onto the mic. This is pulled over the foam sleeve and the two small holes are aligned with the front and back openings on the mic. This combination creates a small chamber around the mic with limited access for cockpit noise to enter the mic cartridges. What is created is an acoustic baffle around the mic which reduces the noise level at the mic to less than 97dB. This allows the noise canceling mic to do the job it was designed to do.

Yes, easily. Look at your cell phone mic opening; it’s probably smaller than the head of a pin.

Probably. Most intercoms make all the headset mics hot at the same time so any mic without a MicMuff® Microphone Cover will create noise in the whole system. Like a bucket with two holes, plug one hole and the other still leaks; you must plug both holes. Make sure all headsets installed on the intercom have the MicMuff® Microphone Cover.

Aviation mics come primarily in three types:
The small "Electret" type uses a #90015 MicMuff® Microphone Cover, the larger "Dynamic" mic uses a #90010 MicMuff® Microphone Cover, and the "M-87 Military" mic uses a #90020 MicMuff® Microphone Cover..