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In Reply to: Re: What to put under the turntable? posted by Ray-o-Stat on August 3, 2005 at 06:53:31:
Maybe I'm not calling it the right thing...I've posted about this before, but I have a window air conditioner about six feet from the turntable mounted on the same wall - there's no way around this where I have my stuff. Normally it's fine, but when the AC unit kicks in it vibrates slightly, which winds up in the turntable. If I record an LP, for instance, and flip on the unit in between cuts, you can clearly see where it happens in the waveform, and it's not a hum or anything like that. I'm hoping the superballs will fix this.
Follow Ups:
get a thick plywood board larger than the TT by at least 4 inches in each direction (1" baltic birch if available or double up two 3/4") and hang on 4 chains from the ceiling, just make sure you anchor into joists. hang the chains at slight outward angle in all directions (joists should be 12" on center so say 24 or 36 inches apart at the ceiling) to advoid swinging. if you get J-hooks you can adjust the chains with a nut till level by drilling 4 holes at the corners of the board. depending on TT mass you might want to add some mass under the TT to add stablity but this should isolate the TT from almost anything but direct contact and insane DB sound levels. i have not tryed this myself but can not see why it would not work wonderfully, used to see it used back in the 70s. If propery anchored into joists near walls (i would go out a foot from the wall), should support 200 lbs. easily.
but why do't you try isolating the air con unit from the wall as well ? With rubber grommets & silicone etc, or even isolating the motor unit itself ? It must be bloted to something - put something rubber on the mounting points so less is transmitted to the case & the wall.
That would help at the root of the problem, making any TT support treatment more effective. + it's maybe cheaper to start there than with the TT.
This might be the solution, actually...the AC unit is just sitting in the window, no bolts or anything...I'm on the third floor, so there's no real security problem that way.
depending on how old the ac unit is, you might be able to remove the actual unit from the shell and tightly bolt the shell to the window and then reinsert the unit.just be careful the fins on those things are really sharp and will make mince meat out of your hands.
you might try mounting the A/C in a more rigid manner.
Ok.
Can your shelf support a mass-loaded turntable base? I have a DIY methos that may work for you....
I would assume; it's one piece of pine screwed into the studs and then the shelf is connected to that with large triangular brackets. I don't know that I'd trust it with a HUGE amount of wieght, but it can probably handle more than it has on it.
I'd work on the basis that the current set of brackets and shelf have to go...What you need to do is replace the existing brackets with a new set designed to hold a substantial load. The next aspect relates to how you mount the brackets onto the wall - the method, if not a brick wall (as it sounds like a wooden wall), would be to use mounting bolts that go right through and then use large diameter, thick steel washers to spread the load.
Once the brackets are installed, and before mounting the replacement shelf, mount some sorbothane (or equivalent) "bushes" on the top surfaces of the brackets and aligned with the mounting holes (light adhesive to hold them in place).
For a shelf, I'd go with a three-part "laminate" - the lower layer, a 25mm shelf made of MDF/Medite, which is drilled to match the holes in the brackets. Each drilled hole should also have a countersunk cavity bored on the top. Using countersink bolts, bolt the MDF shelf to the brackets, with nuts attached from below.
The upper layer shelf (layer 3) should be the same size as the lower, and should be another 25mm shelf of MDF/Medite.
Take a rubber bath/car mat and cut to the same size as the shelves and place on top of the lower shelf, before loosely placing and aligning the top shelf with the lower - forming layer 2 as the ham in the sandwich.
What you wind up with is a three layer "sandwich" - two layers of 25mm MDF, separated by a 3-4mm layer of rubber - and isolated (by the sorbothane) from the brackets, which are in turn mounted on the wall.
The additional rubber layer does two things:
1. Being rubber, stops the top shelf from sliding around
2. Acts as a second "isolation layer" to back-up the sorbothaneHaving no rigid connection between the two MDF layers limits the energy transfer to what can get through the rubber layer.
I don't know what the material costs would be in the USA, but could do that here in South Africa for around the equivalent of $35.00 - including brackets, mounting bolts, MDF, bath mat and sorbothane bushes..
Whew! Thanks for the in depth response...and I thought I was going to get away with superballs...let me let this sink in.
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