The following article by sound engineer Jesse Warren appeared in the May 1999 issue of VIBRATIONS, The journal of microphone isolation.

You’ve heard it. Many times. It’s nasty. It’s ugly. And sometimes it drowns out everything else. Believe me, you’ve heard it. But you’ve probably have never hear of it.

It’s called Mechanical Feedback Distortion, and in many public address situations it’s the biggest source of distortion in the entire system. Sometimes MFD is so serious, it literally overwhelms the signal. And unlike its cousin, Acoustic Feedback, it is impossible to eliminate MFD with electronic filtering equipment. Mechanical feedback is caused by vibrations from PA and monitor speakers. These powerful transducers vibrate everything in their vicinity. In a typical club, for example, with music going full tilt, a table at the far end of the room can easily vibrate enough to make waves in a beer glass.

Imagine what it’s like up on the stage! The mechanical vibrations go right up the mic stands and into the mikes, and are amplified along with the signals. Sometimes the mechanical feedback is greater than the signal itself! The result? Garbage. Mechanical feedback results in sound that is muddy, unintelligible and harsh. So why not simply filter out MFD? It’s not that simple. By the time mechanical Feedback reaches the microphone, it has been travelling through all sorts of mechanical objects - speaker cabs, floors, stage supports, etc.- and naturally has become highly distorted. It bears so little resemblance to the original signal that filters will have no effect on the feedback.

The only way to get rid of MFD is to break the path of the mechanical signal itself, and that’s where Microphone Isolators or ‘shock mounts’ come in. Actually, the name ‘shock mount’ has contributed to misunderstanding of the role that Microphone Isolators have in the production of clean sound. Everyone is aware of the ugly noises that are produced by microphone handling and adjusting, and most people realize that ‘shock mounting’ prevents these sounds. The dynamic mechanical interaction between the speakers and microphones, however, is much less understood -- yet it is often the more important factor. For the sound professional, there are important implications to this knowledge. To achieve undistorted signals, Microphone Isolators are a necessity. It is not enough to isolate just the mics that are handled. All microphones in a system should be isolated!

The goal should be to have a totally ‘floating’ microphone system. This may seem a daunting task. With all the different sizes and shapes of microphones in a typical sound system, finding shockmounts for all of them would seem close to impossible. Fortunately, an elegantly simple and highly recommended product is available that simplifies this task - The Tensimount from Brewer Instruments in Newton, MA. This clever device fits most microphones, and as a bonus, it converts all mikes to fit the same standard mike clips. If all your mikes are Tensimount-equipped, it makes switching-around mikes simple and convenient since every mike fits every stand. Another bonus to Tensimounts is their low cost. For less than the cost of one microphone, a group or small studio can float their entire system. One saved take or one hassle-free gig can repay repay the whole investment. There’s really no excuse. Let’s make MFD history!

"Actually, the name ‘shock mount’ has contributed to misunderstanding of the role that Microphone Isolators have in the production of
clean sound."

"The dynamic mechanical interaction between the speakers and microphones is much less understood -- yet it is often the more
important factor."

"It is not enough to isolate just the mics that are handled. All microphones in a system should be isolated!"