Vibration isolating rollerballs

[JohnSwenson]

Hi YashN,

 

With a flat surface, neither will isolation happen. The bowl is *necessary*.

Try it and see.

 

Best regards,

Barry

Soundkeeper Recordings

http://www.soundkeeperrecordings.wordpress.com

Barry Diament Audio

 

Hi Barry,

the bowl shape is not necessary for the isolation to happen, however without it the system is like a pencil sitting on its point. If the system is not PERFECTLY level gravity will cause the top to just roll right off. The bowl shape adds some restoring force to keep the top centered.

 

John S.

[JohnSwenson]

John,

 

If the bowl is unnecessary, and there is no slope for the ball to push against, where is the isolation occuring ?

 

Somewhere in the 4 tiny contact points ?

 

 

Fine Forth,

Dave

 

Go back and read the thought experiment post I had in the big thread.

 

The basic idea is that if you have two slabs with zero resistance between them, the bottom slab can move around from side to side as much as it likes and there will be NO transfer to the upper slab if there is no resistance. The top's own inertia will keep it from moving. A hard ball between two hard surfaces comes pretty close to that. It has very low resistance in the horizontal direction and very high resistance in the vertical direction.

 

The two flat slabs have a problem, if they are not perfectly level, the top will just slide right off the bottom due to gravity, you need some sort of weak restoring force to keep the top from falling off the bottom. The more the restoring force the worse the isolation, the isolation works better the lower the connection between the surfaces.

 

The bowl is how the restoring force is applied. As the ball rolls up the sides gravity is applying a force to push it back towards the center. The shallower the slope the less coupling there is (and greater isolation) but it is easier for the top to fall off. So in general you want as shallow a curve as you can get and still keep the gear from falling off when you touch controls etc.

 

The bowl shape is essentially a necessary evil to get the concept to work in the real world, it is NOT the primary reason there is isolation.

 

Notice from the above that this provides essentially no isolation in the vertical direction, so other methods need to be used to get vertical isolation.

 

John S.