Damping and plinth improvements

[Bob in STL]

This is such a great forum for learning and sharing experiences. I am reading a lot on this subject and I have a little experienced firsthand on the benefits of dampening. Seems like one very easy way to improve platter performance is to make a cork mat to replace the standard issue rubber mat. Other mats and solutions are discussed here including the use of "dynamat" and other materials that can be added to the bottom of a platter to "carefully" add damping while (hopefully) not changing the balance.

Plinth improvements would seem to provide a similar benefit as platter improvements. I am looking for proven methods to make a stock plinth better?

Two specific questions:

On my TD-160 (or any wood/ particle board type base) it is common knowledge to replace the plinth bottom with 1/2 plywood or MDF. Similarly, can the sides of a wood plinth be improved by gluing more wood (or MDF) to the inside walls, or maybe by gluing cork to the insides?

I also have two decks with plastic plinths (Technics Sl-1300 and Yamaha P751). What can be done to add good mass that actually helps. The Yamaha is running great right now and I am thinking of adding mass to the inside of the base. I just read about plasticine (modeling clay) but not sure I want a bunch of Play-Doh inside my deck? I am trying to squeeze a little more performance out of it but maybe good enough is ok? Will plasticine really help? Can I glue cork to the inner structure and improve things?

Onto the SL-1300, this deck was a freebie and is in my “to be repaired” backlog but the same questions remain. Technics decks are hugely popular and I am wondering what is done, if anything, to improve the existing plastic plinth?

Thanks, Bob

[dlaloum]

I have 3kg of plasticine in my JVC - difference was very noticeably better...

[Fishtails]

Adding things to the plinth is tricky as every turntable is different.

The best thing to do is go by trial and error.

To,do,this you need to,fimd a way to add material in a non permanent way. If you glued a material on and it didnt sound good then you ar estuck with a mess trying to get it off.

So try a few different materials. Then permanantly attach the one you like the best.

Material for the plinth may include rubber, sorbethane, cork, foam etc.

It is my persomal opinion that the rubber mat has always sounded best and i am dubious about a cork mat.

I wouldnt use clay or anything that will eventually crumble for damping material.

Also pay attention to the feet that your tt sits on. They should be fairly rubbery too.

I had an old turntable with a wooden base. Imadded wood tomthe outside of it , stained it and laquered many times and it game up nice and i feel i produced a nicer sound.

Hope this helps!

[cats squirrel]

I agree totally with dlaloum, I would also advise adding 'non-hardening clay', like plasticine, or a better alternative is 'Newplast', which has even better damping properties. Note, play doh is not the same thing, being water based. I have experimented with plasticine type recipes, and have obtained very impressive results, although my products are not for sale.

Adding anything other than these materials is not going to get you to where you want to be. Also, be ware that you are going to add 8-10 times the mass of the object you are trying to damp. And IMHO, money would be better spent on replacing the top plate, sub chassis and arm board with much more suitable materials.

Just adding mass is not the answer, either, see my web site for full info on this.

[rkay5]

Hi,
If you want to better the Thorens TD160 plinth it's best to build or buy a new hard wood plinth to get better SQ that is what I did with my TD150 and TD166mkII.

[dlaloum]

I strongly recommend cats squirrel's website as a source of valuable information with regards to plinths, the science behind them, damping abilities of differing materials, combinations of materials etc...
It is quite an eye opener.

Mass loading the turntable is a way of getting its suspension / mountings resonant frequency down lower... - so the higher the mass the lower the resulting frequency (until you totally compress the springs / elastomers, and then suddenly there is no damping/isolation at all!).

This can be a good way to adjust things... if your current resonant frequency is coinciding with some environmental vibrations in your setup (eg: footfall) then shifting it down can sometimes resolve the problem.

Some plinth materials are also good dampers - but they have that effect at a specific range of frequencies - nothing is totally generic across all frequencies.

Layered wood products (Panzerholz, glued plywood layers, densified wood, bamboo timber) tend to be good dampers, but primarily at higher frequencies - not much effect in the subsonic range.

Plasticine is an effective damper in the 300Hz to 3kHz range (especially if sandwiched making a constrained layer) - but is a very easy to use, and reversible way of adding mass to adjust springing... so it can be used both for midrange frequency damping, and for low frequency resonance adjustment. (it is also dirt cheap!)

Hardwoods and any solid natural woods, tend to have specific damping frequencies and resonance frequencies (which will differ along the grain and against the grain) if the resonance frequency coincides with a frequency at which some other aspect of the tables design is a very effective damper - the combination can be very effective - otherwise it is likely to add that resonance frequency to the mix as a colouration.

When layered, subsequent layers are layed down with the fibres in differing directions - taking advantage of the differing damping/resonance linked to fibre direction - the glue between the layers also acts as a constrained layer damper (effectiveness depends on the type of glue...). As a rule this means that laminates of wood are far more effective than solid sheets of hardwood.

If you are serious about controlling resonances and improving SQ via plinth changes/tweaks - the starting point should be to measure the current resonances.

Your simplest measuring implement is your stylus, sitting either directly on the plinth or via a solid connector (in my case a spare counterweight did the job).

Then you can record the output using any computer and soundcard, and take a look at the frequency spectrum to see what comes up.

For mid to high frequencies, recording the plinth, while having the turntable in front of a set of speakers spouting high SPL pink noise should give you a fairly clear picture of what is going on.

For subsonics - It is more often related to isolation from the environement (stand/rack/feet) - and I tested it by recording, and walking around the room and house in a heavy stomping manner on my suspended wooden floors...

Measurement then allowed me to tweak and adjust my suspension and isolation to achieve a 20db reduction in LF "noise" at the plinth (problem zone was 2Hz to 10Hz) - the effect was very noticeable!

The plasticine in my plinth helped in terms of mass with the LF adjustment, but also helped in the midrange and highs which are now cleaner as well.

Other parts of my solution included mag-lev feet, concrete paver and sorbothane pads... I really would like to built a complete new plinth for my JVC, but I am not quite mentally up to the task yet... I have not (yet) worked out a design for the plinth that can house the electronics of the Servo arm, look good, and also provide improved functionality over the OEM plinth....

bye for now

David

[Bob in STL]

Wow. Thanks to all for the informative replies.

For my TD-160, other than the simple mod of replacing the bottom board I was not planning on touchng the plinth and I can see that the best solution for it is to replace it with a more substantial wooden one. The other TD 150/160 mods are well documented and i am studying them.

My other two decks have palstic plinths so that is why I was wondering about the plasticine or cork. I went to an arts and crafts store today. They have modeling clay that will dry out, get hard, and will not adhere to a plastic surface.

I will visit those websites and keep reading.

Thanks for the info.

Bob

[megatrends]

I use these that I came across. They make so many cool patterns, I have a monogrammed one with the turntable name lol.






Which are radio station leftovers, the radio station I do shows at got a whole bunch of these. I really like them much much better than the rubber mats that come with the turntables.

[dlaloum]

I went to an arts and crafts store today. They have modeling clay that will dry out, get hard, and will not adhere to a plastic surface.

Plasticine and the other brands of non-hardening modelling clay or Oil Clay are commonly used in kindergarten's, childcare, and pre-schools.

I found 500g blocks of it at an office supplies store, and I purchased some from a pre-school supplies wholesaler - price either way was around $4 per block (a bit more from the office supplies store, a bit less from wholesaler, either way it's cheap!).
One thing to watch out for - it softens with heat - so if it is near circuitry that gets warm it will be softer (and it's damping will be altered by that as well...)