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RE: Do I need feet/cones under my plinth?

Posted by mr.bear (A) on July 20, 2012 at 23:07:51

In Reply to: RE: Do I need feet/cones under my plinth? posted by Waxxy on July 20, 2012 at 17:06:11:

Just a few thoughts: The key ingredients in a vibration isolation design are 1.) The frequency of resonance of the mass-spring system comprising the TT resting on the springy support feet and 2.) the frequency of the excitation you're trying to isolate from. Consider only vertical vibration, it seems to have the most effect.

In a nutshell, no isolation is obtained for excitation frequencies far below the mounting resonant frequency. Near the resonant frequency,the response is actually amplified.

This is oversimplifying but you could say that footfall in a home have a characteristic excitation frequency of something like 4-5 HZ. To isolate from them requires a very low-tuned support system, something with a deflection of a couple INCHES! No isolation is obtained for systems with frequencies above a few Hz, per note (1). It's pretty hard to achieve isolation from footfalls. If its a problem, consider wall-mounting the TT support as the wall transmits a lot less excitation.

Structures pick up mechanically transmitted musical vibrations and also get excited by the air. This can result in feedback in the worst case, or a more subtle loss of detail from the out-of-phase, distorted vibration getting to the stylus. It seems worthwhile to isolate the TT from excitation in the audio range, so maybe a desirable resonance is around 10 Hz. You might get there with something like squash balls. I worry though that you're stabbing in the dark -- if you place the TT/support resonance too near the frequency of the footfalls in you home or up in the audio range, you'll get some amplification per note (2). You have to experiment.

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