DIY Turntable Isolation Sand Box

[NBPK402]

I am in the process of building a sandbox out of Teak, and MDF. I am using 3 1/2" x 3/4" teak pieces of wood for the basic frame work. The plan is to make a MDF, or plywood base that would seal the bottom of the box off, and then attach that to a piece of slate. The top piece would be MDF with a 1/8" clearance all around. The top piece would have 1" holes drilled in it for tennis balls to rest in. I would make 2 of these MDF pieces with the holes lined up. The first one would set on the sand bed, and the 2nd one would be glued to a piece of slate that would be the size of the entire box. Once the first MDF layer is laid in place, and leveled the tennis balls wpuld be inserted, and the top layet of MDF, and Slate would be set on top of the tennis balls.

One other thing I am thinking of doing is... notch the rear corner of the platform for the motor on our Pro-Ject RPM 1.3 Turntable. I am thinking that the lower piece of slate could extend far enough to support the motor assembly. I was thinking of building a platform of different materials to bring the motor back up to the stock height via glueing different materials together (or just build another platform, maybe of Teak, and or slate for the motor). My reasoning is that the motor would then be damped separately than the turntable, and the connecting area would be at least 3 1/2" below the motor just like the turntable is. This would give better isolation I am thinking.

Any comments or insight? I would eventually like to expand on this idea, and make a turntable stand that would have the arm, at one level, motor, and another, and the table on the upper most top portion, but for now I want to see how this idea goes.

 

[Matthew J Poes]

Not a lot of design comments, but be careful in separating the platform that the table and motor sit on. The motor should sit on the same rigidly attached platform as the table. Any separation can allow independent movement, this can allow the motor to wiggle and slightly change the tension of the belt. This can cause wow and flutter, precisely the thing we want to minimize in a turntable. Any improvement in damping is potentially undone by this effect.

What you might consider instead is a constrained layer top plate. You can still use Slate if you wish, but adhere another material, MDF, more slate, whatever to the bottom of the Slate with a lossy adhesive. The damping layer needs to be very thin (It can be a bit counter-intuitive, CLD actually needs a very thin layer to sheer, not a big thick layer). The reason why this could be good is that the vibrations won't move through the Slate as readily as the damping will dissipate them before they can transfer very far.

While I don't use a sandbox for my turntable, I did create a CLD top plate for my stand. I bought a set of Audio Advisor racks and combined two shelves for top and bottom, adhering them with the lossy adhesive. I have some measurements I took of the test panel clamped to a subwoofer with an accelerometer adhered to its surface. The difference is easily measured.

Also, I've talked to some guys about this before, the idea of pneumatic isolation. I don't fully know why, but this guy told me that racket balls are better than tennis balls for objects the weight of a typical turntable. He was an engineer at Purdue and maintained the scanning electron microscope, he also developed vibration isolation stands for smaller microscopes. He preferred these racket balls and suggested them to me.

 

[Todd Anderson]

I'm out of the vinyl loop... but this looks like an interesting project. Curious to see some pics!

 

[ddude003]

Call me crazy and I would not like any sand near anything electrical or mechanical... No thank you... Various kinds of rock can "ring"... So, I only use solid blocks of hard wood for isolation for my tube preamp to help with microphonics... Air dried Maple from a local Amish saw mill...

I do wish you luck with your project and hope it works out well for you...

 

[NBPK402]

Not a lot of design comments, but be careful in separating the platform that the table and motor sit on. The motor should sit on the same rigidly attached platform as the table. Any separation can allow independent movement, this can allow the motor to wiggle and slightly change the tension of the belt. This can cause wow and flutter, precisely the thing we want to minimize in a turntable. Any improvement in damping is potentially undone by this effect.

What you might consider instead is a constrained layer top plate. You can still use Slate if you wish, but adhere another material, MDF, more slate, whatever to the bottom of the Slate with a lossy adhesive. The damping layer needs to be very thin (It can be a bit counter-intuitive, CLD actually needs a very thin layer to sheer, not a big thick layer). The reason why this could be good is that the vibrations won't move through the Slate as readily as the damping will dissipate them before they can transfer very far.

While I don't use a sandbox for my turntable, I did create a CLD top plate for my stand. I bought a set of Audio Advisor racks and combined two shelves for top and bottom, adhering them with the lossy adhesive. I have some measurements I took of the test panel clamped to a subwoofer with an accelerometer adhered to its surface. The difference is easily measured.

Also, I've talked to some guys about this before, the idea of pneumatic isolation. I don't fully know why, but this guy told me that racket balls are better than tennis balls for objects the weight of a typical turntable. He was an engineer at Purdue and maintained the scanning electron microscope, he also developed vibration isolation stands for smaller microscopes. He preferred these racket balls and suggested them to me.

Would Green Glue be good, or is there a specific one you would try? I will look at racquet balls too.

 

[NBPK402]

I'm out of the vinyl loop... but this looks like an interesting project. Curious to see some pics!

I will post some pics up as soon as I get the joints made. I wanted to get the equipment to make my own fancy joints, but I am unsure how much room I will have for woodworking in our new house. I am looking for a good carpenter now to make some nice joints for the sandbox. I will post pics up when I have completed it.

 

[NBPK402]

Call me crazy and I would not like any sand near anything electrical or mechanical... No thank you... Various kinds of rock can "ring"... So, I only use solid blocks of hard wood for isolation for my tube preamp to help with microphonics... Air dried Maple from a local Amish saw mill...

I do wish you luck with your project and hope it works out well for you...

Some people put a layer of plastic to seal it off, and others use weather stripping to seal off the box. Once you have it made there really is very little chance of sand leaking out. BTW this technique is used world wide, and you can buy these already made. I even read where one person said they have used these for over a decade in radio stations.

 

[ddude003]

I understand that many of these sand boxes are made and used and over the years have studied finished products and DIY plans... And a lot of folks use slate, granite, quartz etc which can "ring" like a bell... I prefer tone woods + cork + and felt... Just my POV...

Again, I wish you luck with your project and hope it works out well for you...

 

[NBPK402]

This project has been moved to the back burner until I get the speakers, amps, and room treated. Once that is done I will continue on it...one reason is the turntable will be downstairs, and I need all my speakers in place before I decide how much space I need to do this. I hope to have 4 Belle bass bins, 4 biamp amps, and whatever Dirac I end up with completed around Xmas this year. Then I will work on room acoustics, black electric stage curtains, k402 synergy horns, and possibly 3 class A amps for the horns in addition to 3 more B&O amps for the bass drivers, and of course the cabinets for the synergy horns. This next year I am hopefully going to make some good progress with a ton of DIY projects.