Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

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Explanation

Posted by Allan Moyse (A) on June 11, 2002 at 13:49:09

In Reply to: Question posted by bdiament on June 11, 2002 at 11:43:22:

Barry, you are exactly right. Anything that conducts vibration one way will also conduct it the other way. This is a fundamental example of Newton's Third Law, one of the most basic components of physics. If someone tells you that they have a "magic" rack that drains vibration out of a component one-way only, that is just marketing hype. It's IMPOSSIBLE.

When it comes to racks, etc, there are two different things you can do:

1. You can ISOLATE a component. This is where you are trying to prevent vibration from traveling between the component and it's surroundings. An ideal, but impossible, example of this would be if you could magically "float" a component with nothing actually touching it. Vibrapods, the "inner tube" trick, etc, are all forms of isolating.

2. You can COUPLE a component. This is where you are trying to rigidly connect the component to the stand. Spike feet are an example of coupling.

Ususally, if you have a component that generates it's own mechanical noise (vibration), such as a turntable, CD player, etc, you want to couple it to something. Coupling will reduce the self-induced vibration of the component, by channeling a lot of it into the floor. It will also transfer some of the floor's vibration into the component. When you do this, you are betting that the component's own vibration is worse than what it will get from the surroundings (floor, usually)--and that is usually true. You can also reduce the magnitude of vibration in this manner. For example, the motor in your turntable might have enough vibration to move the turntable slightly. However, if your turntable weighed several tons (which you are approximating by coupling it to the cement slab under your floor), there is no way that little motor can make it vibrate that much.

You use isolation whenever you want to stop room (floor-borne) vibration from effecting the component. Since isolation does nothign to control intrinsic vibrations in the component, it usually works best for things like amps which have no moving parts.

If you work in industry, you can see this everywhere you look. When somone has machinery that vibrates a lot and you don't want that vibration transferred elsewhere, that machinery is mounted on springs or rubber bumpers. Examples are pumps, vibrators, rock crushers, tumblers--and even your washing machine.

Another well-known vibration control trick is mass loading a component. Technically, this has nothing to do with isolation or coupling. Mass loading works like this: Every mechanical system has one (or more) freqencies at which it "likes" to vibrate. This freqency is based, in part, on the mass of the component. The higher the mass, the lower the freqencies. What this means is that if you stack weights on top of a component, you are FORCING it to vibrate at a lower freqency. This usually makes it sound better since lower frequencies are less likely to affect sound quality.

Mass loading can also be used to "improve" the effectiveness of a coupling setup. By increasing the weight of a component, you are also increasing the force with which the component's feet contact the shelf it's mounted on. This allows for a stiffer coupling, which transfers vibration better. Again, this works both ways! It will better conduct vibration out of the component, and room vibration into the component.

Allan

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