Best material to make a turntable plinth

[avole]

Posted elsewhere, but hopefully people here have more specialist knowledge.

The materials I have available here in Paris (well, BHV anyway) are MDF, plexiglass and plywood. I'm not going to look at other possibilities.

With the exception of the plexiglass, I'd be using two sheets of the material with foam or other plastic insulation sandwiched in between. Plexiglass would be like the Clearaudio Emotion in theory, if not in finish.

Non-suspended deck,by the way. It'll be semi-solid sandwich plinth, with a layer of foam/plastic filler for resonance purposes as well as sorbothane feet. If I chose plexiglass, which I've never worked with and about whose qualities I know little, it will be a solid sheet à la platine Clearaudio Emotion, as I said.

Running gear comes from Linn (motor, platter from a Basik) and Rega (arm).

[cafe latte]

IMO it depends what you want. My commonwealth sounds great, but from that build I think the more you deaden the plinth the more neutral it will be erasing that colour, but is that what you want? Many here dont like Technics for this reason IMO despite the fact it is probably a farly true representation of what is on the record.
Regards
CL

[avole]

Cheers CL. I've opted for two sheets of 12mm mdf with foam in between and, as mentioned, sorbothane feet. It's going to be heavy.

Biggest problem is the shape and finish. Can't spray, as it's mid winter and far to cold in my shed, which means either hand painting or veneer, which is quite expensive...

[cafe latte]

Here is an idea, how about thin ply glued to the top and bottom and a wooden strip or a bit of veneer just round the edge? This might be interesting as you will have three materials in the sandwich. Or just use thick builders ply insead as you can just varnish or oil it directly and from experience it comes up really nice (I made a desk top with it, even the edge looks nice as you see the layers)
Regards
CL

[avole]

I've bought the 12 mm mdf so will go with that. Will probably put a thin strip of veneer round the edge for decoration with veneer on top, probably wood although melamine is an option. Looks like I'll have to go with square as that's the shape in which the lids come.

[andyr]

Mmmm, given the TNT-Audio article about making up cabinets for some speakers out of several different materials and seeing how they sounded - they said hardwood cabinets sounded much, much better than the original MDF cabinets ("MDF sucked the life out of the music") - I suggest you may not get the best sound out of 2 sheets of MDF, irrespective of how much damping material you put between them.

Why don't you try stacked ply (like every other DIYer)? Or laminated bamboo, if you want to be different? Or better, slate (if it's a non-suspended deck)?

There's not much use just making one plinth and then saying ... "Wow! That sounds great!" if you haven't compared it to any other options.

Regards,

Andy

[avole]

Yet mdf is used for by far the most commonly used material for cabinets, and, let's be honest, the guys a TNT are hardly techos. If you look at the BBC papers on different materials, you'll see they went into the subject in great detail http://downloads.bbc.co.uk/rd/pubs/reports/1977-03.pdf. Convinced me enough to make my own speakers out of ply, but, frankly, next time I'll use mdf because it is so much easier to work with.

You should also consider the application of the material. In the case of turntables, you do not want materials that resonate or cause resonances within the audible spectrum, because that produces coloration. In fact, you want something pretty much acoustically dead if you're going solid plinth, so ply is not a particularly good choice, especially when bearing in mind the fact the different woods used in different plies will each produce a different effect. In other words, Beech ply is going to have different properties to Okoumi, for example. If, as you claim, people making their own turntables are using ply, then they're basically using the most hit and miss method out there. Mind you, it could also be they like the sound of the coloration as many of us do.

MDF, on the other hand, and for the reasons you cite, is eminently suitable as the basis for a turntable. You want something that is as acoustically dead as possibly, allowing the cartridge to do it's work in the cleanest possible fashion. That's why many manufacturers use MDF or variants thereof in their turntables. I have no idea why anyone would want to use laminated bamboo or slate in their turntables.

Your last comment makes no sense.

[JaS]

MDF, on the other hand, and for the reasons you cite, is eminently suitable as the basis for a turntable. You want something that is as acoustically dead as possibly, allowing the cartridge to do it's work in the cleanest possible fashion. That's why many manufacturers use MDF or variants thereof in their turntables.

I haven't got a great deal of experience in this area, but I made a few plinths for my SP10 and I would avoid using too much MDF in a plinth in future. In a layered structure, or a lightweight plinth it seems to work OK, but when I used it for a high mass plinth (around 100mm deep glued and screwed layers) it added an obvious colour to the sound. I got better results by layering different materials, but isolating the layers as you seem to be suggesting should work too?

FWIW In the end I got an original Technics plinth which uses a 5mm layer of rubber under the motor unit and armboard, then a layer of cast, powdered obsidian, then 25mm of high grade ply, all sitting on sprung feet. I'm not suggesting you use this, just citing an example of a plinth design that IME works very well.

Regards,
JaS

[andyr]

Yet mdf is used for by far the most commonly used material for cabinets

Yes it is ... and - I'm asking here - you can't guess why, avole?

Because it is cheap, yes it is relatively dead ... and it machines well. Mass market speaker mfrs do not use it because it is sonically beneficial.

Regards,

Andy

[avole]

andyr, we're talking about turntables here, not speakers. Also, speaker manufacturers do take into account the properties of the material they use to construct cabinets when they make their speakers.

JaS, I'm making a sandwiched high mass plinth using acoustic foam in between the two layers of MDF plus using sorbothane feet to try to avoid any possibility of resonance, but we shall see. The Linn Basik, from which the running gear mostly comes, uses veneered chipboard of 15mm depth if I remember correctly, and it's their feet that seem to be designed to damp any resonance. The Linn motor uses foam glued strips for mounting, so I'll do that, too.

[JaS]

JaS, I'm making a sandwiched high mass plinth using acoustic foam in between the two layers of MDF plus using sorbothane feet to try to avoid any possibility of resonance, but we shall see. The Linn Basik, from which the running gear mostly comes, uses veneered chipboard of 15mm depth if I remember correctly, and it's their feet that seem to be designed to damp any resonance. The Linn motor uses foam glued strips for mounting, so I'll do that, too.

Sounds good to me. I have some Linn/Roksan/Rega parts I've been thinking of turning into a turntable, so I'll be watching your progress with interest

Regards,
JaS

[cats squirrel]

ca va, Avole,

if you have limited yourself to those materials, choosing just one is not going to provide much damping for that motor noise. And making a sandwich of it with a foam in between will just isolate the upper panel, and the lower panel will be irrevalant.

My suggestion is for you to consider a sandwich with perspex (plexiglas) facings and either an mdf or plywood core, the latter being better.

Best of all would be a simple panel made of a material with good intrinsic damping, or a sandwich using a similar material as a core and metal sheet facings.

There is much more info on my web sites on this.

[avole]

The motor is attached by foam strip, à la Linn and Rega, so I'm fine there.

I can't agree with you about the plywood, as it doesn't, from what I've read, have optimal qualities for turntables. I'm not going with plexiglass partly because I could find little about its acoustic properties, and partly because I've never worked with it before.

Haven't mentioned construction deliberately at the moment, because I'm still working out feasibility, but hopefully it will have damping covered.

[cats squirrel]

The motor is attached by foam strip, à la Linn and Rega, so I'm fine there.

foam strip? if you isolate the motor, it will vibrate more, not less.

I can't agree with you about the plywood, as it doesn't, from what I've read, have optimal qualities for turntables. I'm not going with plexiglass partly because I could find little about its acoustic properties, and partly because I've never worked with it before.

if you are looking at 'optimal' properties, then none of your materials (on its own) is anywhere near.

Haven't mentioned construction deliberately at the moment, because I'm still working out feasibility, but hopefully it will have damping covered.

I thought you mentioned a sandwich construction, with a foam core? This will have only minimal damping, and probably nowhere near enough to cope with the buzzing motor.