06-16-09: Jrb25from my experience sometimes the original speaker feet can do a good job of keeping the floor-borne vibrations from reaching the speaker cabinet. There are a few speaker manuf who carefully select the speaker feet. Most do not perhaps knowing the customer is going to use some after-mkt solution. So, chances are very high that the speaker feet will need to be addressed.
How does a platform or brass footer "drain vibrations"? Do vibrations act like heat or fluid and flow through materials? Wouldn't footers actually prevent propagation of vibration from an external region (like the floor) to the platform and component in question? Exactly where do these vibrations originate, and what direction are they moving in? Is "isolation" a better way to think about it?
Obviously I am confused about the vibration drainage concept (and a bit skeptical). However, I have heard differences myself, but mostly for spiking speakers to a floor, where the speaker itself is doing the vibrating.
Where do vibrations originate? They originate in the electronics itself. Current flowing thru electronics generates an EMF & that causes components to vibrate which eventually couple into the chassis, CD player drive is mechanically rotating & passes its vibrations into the chassis, power xformers vibrate (& even hum), if the chassis is not isolated well then floor-borne & air-borne vibrations get coupled to it. So, vibrations are everywhere & they can be destructive to audio playback.
How does brass drain vibrations? This is my understanding - Brass is an alloy of copper & zinc & the crystalline structure of this binary pair makes it a very good electrical & thermal conductor. WHen the flat portion of the brass cone is couple/attached to the underside of the chassis the vibrations in the chassis find a low impedance path. These vibrations create heat in the brass structure that is dissipated & the rest is conducted away from the chassis by the metal into the rack shelf (the pointy end of the brass cone is coupled to the rack shelf). Since the pointy end of the brass cone has a very small surface area the vibrations from the rack shelf find it hard to enter the brass cone - it acts like a high impedance point. Hence the analogy to an electronics diode wherein the brass cone is called a mechanical diode as it allows vibrations to drain from the chassis into the rack shelf but does not allow vibrations from the rack shelf into the chassis.
If you read Audiopoints' & Mapleshade's website you'll read that the purity of brass is important i.e. the alloy should be kept binary as far as possible. The reason for this, according to my understanding, is that addition of lead or tin or nickel reduces the thermal & electrical conductivity dramatically making it less effective as a cone. The mechanical strength is increased by the addition of these other metals but it seems that varying the content of zinc alone can yield a strong enough brass for audio use.
(someone correct me if I'm wrong. Thanks.)