How dose your plinth sound?

I realize that there are many variables in design and suspended is one that im not about to attack(build). In general im referring to the “slab o plinth” type of table. So if i understand right whether its a light or a heavy plinth the ideal material would be one that absorbs vibration without vibrating its self, and/ or transmits vibrations away from bering/ arm(one way) to another location?. Question ... can you induce sound to travel in one direction. Say with different layers of materiel with the most resonant being the farthest away(or some other arrangement)?
As for the mass issue i have a hard time believing that the “more mass is better “ argument. All mass is not created equal. Some would absorb and some would reject sound. I believe how you use the mass is the most important thing. Also a 300 lbs. turntable is not an option!(for me at least)...... On the other hand ... anybody know were i can get my hands on a few hundred lbs. of depleted uranium? .. ; ‘ ) ...

All we are dealing here is physic. Very simple.
It takes high mass and density to combat vibration.

Of all the best turntable available now, the Rockport is 600lbs, the Walker is 300lbs??!!!. And there is a reason behind it.

Yes, depleted uranium is probably the best material. But it is hard to find and you might get radiation sickness or cancer from it!!!

But if I can find a way to seal the plinth completely. I think mercury is the next best material......

Cheers.........

I am building a turntable now and using two pliths using Lexon(bulletproof plexy) I am going to fill with lead shot and try this. The platter will be of Lexon also(All 1" thick). Let you know later. Gets the parts back on Monday.
Dale

Bill, you pose a good question. There are some significant misconceptions about the resonant properties of different materials. Acrylic is NOT non-resonant at all. It does in fact have a significant low frequency resonance. When you tap on it there is a "bong" resonance that often is thought of as being dead. This is actually good and bad news. A low frequency resonance is much more benign and even can be a little euphonic, sounding warm. But it clearly does obscure detail and adds coloration. The bad news is that a low frequency resonance is nearly impossible to control. Adding damping helps little. The only way to effectively control a low frequency resonance is to add rigidity. Mass loading can easily make things worse.

Very hard, dense woods like cocobolo have a pronounced high frequency resonance. When you tap it is "pings". In spite of the resonance it sounds surprisingly good as is. Can't say that I understand why. Unlike acrylic a little lead completely eliminates the resonance. Tap on a lead loaded cocobolo base and it is really dead, as opposed to the "bong" that you get from acrylic. As TWL so generously has pointed out, the sound of a wood/lead base is significantly better.

I should also point out that I have tried lead loading an acrylic base. It does help a small amount. However, with a wood base adding the lead is a major transformation.

Metals, like wood are rigid with a high frequency resonance that is likewise easy to control. But for reasons unknown to me they don't sound all that good. I have tried using very well damped aluminum and steel. Steel usually sounded better than aluminum but neither were very satisfying. Clearly there are important factors other than simple resonance that are not understood, at least not by me.

I mostly agree with Edle's point that a heavier base is better. Just adding more mass is not a good idea. But if you add both mass and rigidity at the same time the results are very good. The upcoming Teres 340 has a 80 lb. base and does sound considerably better. However, it adds a lot of extra rigidity along with the mass.
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Chris

Why not use ironwood? Very hard to work with but can be possibly better than cocobolo.