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jimmy mac

In article ,
(David Platt) wrote:

I was thinking of putting foam
under the speaker which would be easy and perhaps even a soft foam block
under the turntable as well but I'm afraid that trying to support and
level a turntable supported like this could be a nightmare. Does anyone
have any ideas? Thanks, Lenny

One approach I've seen used is to add both mass, and decoupling, to
the turntable.

Mass: go buy a sheet of rock. Stone. Cement. Something like that.
If you want to be elegant, go to a stonecutter, pick out a piece of
marble or limestone or granite whose color appeals to you, and have a
slice cut and polished which is just the size of your turntable base.
If you're on a budget and don't care terribly about looks, get thee
hence to a home-improvement/garden store and buy a concrete or brick
"paver" roughly the size of your turntable base (18"x18" is a good
size to look for). All else being equal, thicker is better than
thinner.

Decoupling: go to a bicycle store, and buy a small-diameter heavy-duty
bicycle inner tube. If you bought an 18"x18" paver or marble slab, a
16" inner tube would be a good size to try. You want it to be just a
bit smaller in diameter than the smaller side of the stone slab, so
that the slab will sit on it in a stable position without the tube
"bulging out" in any direction.

Partially inflate the inner tube. Lift your turntable out of position
(unplug first, of course). Put the partially-inflated inner tube in
its place. Put the stone slab on top of the inner tube, and put the
turntable on the stone. If it doesn't sit entirely level, lift the
turntable and slab and try moving an inch or so in each direction to
get it to level out.

If the weight of the slab makes the cabinet collapse and dump your
turntable onto the floor... oops :-( Sorry about that.

This approach will greatly reduce the amount of structure-borne
vibration which gets up to your turntable through the cabinet or
shelf.

It won't do anything much to reduce airborne vibrations (acoustic
pickup). Removing the dust cover entirely when you're playing music
can help to some extent.

A somewhat similar approach involves building a heavy platform for the
turntable to sit on, and suspending it from above using rather long
springs.

In either case, you want the resonant frequency of the mass/spring
system (whether it's a metal spring, or the "air spring" of an inner
tube) to fall below the lowest bass frequency from the speakers. This
creates a "low pass" filter which will tend to attenuate the bass
before it feeds back into the turntable system. It's also good if it
falls below the resonant frequency of the arm/cartridge system, so
that the two resonances don't reinforce one another and cause
excessive stylus "wobble". If you can get it to the point where it
"bounces" 2-3 times per second and no faster, it should help stabilize
the turntable's playback quite a bit.

Thanks for some good advice!

--
jimmymac

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