Plinth mass vs. Foundation mass

Thank you, gentlemen.

My listening room has a suspended joist floor (crawl space,
floor about 30" above the dirt). Turntable will go near
an outer wall, next to the concrete foundation.

Table is an SP-10 with original obsidian plinth. SME-V arm,
but I haven't mounted the arm yet. Old Clearaudio Accurate
cart.

I had thought to put the turntable on a rather heavy little
table of some sort, on the rug, on the floor. I could
easily try some sort of soft pad/coupling between the
turntable and the table. This would be my starting point.

Another thought that came into my head is that, since the
TT is not set up yet, I could sell the whole obsidian
plinth setup and buy something even bigger and heavier,
something that would also accomodate the SME V-12 12" arm.

I guess I've been bitten by this damn bug.

The coupling between the platter and the tonearm must be exact. If the platter is moving with respect to the arm, the cartridge will interpret that as a signal and a coloration is thus introduced.

Thus the plinth should be utterly rigid and devoid of vibration. Mass is good but its better if its non-resonant, so long as rigid coupling between the elements is maintained.

However the above requirements are met is not so important as the fact that they are indeed met.

Slaw is correct.

Concrete slabs are the best place to start for isolation.

Elevated joist floors tend to be vulnerable to many vibrations and resonances. IT will depend upon construction quality to a large extent. Generally, a higher level will be more subject to these factors than a lower one in any particular building/home.

The other big mistake people make is placing a table at the top of a tall cabinet or stand. Elevation above the floor is generally the enemy of turntables in that external vibrations via the floor are amplified at greater height requiring more cost and work to isolate well. Keeping it low to the ground is best.

I am very fortunate that for the first time ever, in my current home (moved in in 1998) I was able to place my system in a basement level directly on the concrete foundation. That makes all the difference! This is the first time that I have had a near perfectly isolated table and the sonic benefits are clearly evident compared to all homes prior. It is truly a vinyl lover's dream situation that can be hard to replicate otherwise.

The overriding factor here is the construction of your home/room. Concrete slab/ floor joists. This is THE overriding factor to consider any options upstream.

These factors will help you to determine what type of tt suspension if any and so on. Start at the beginning...

A compact method of isolating is to use a wall-mount platform. In this way, floor-borne vibrations are mostly eliminated. The use of an isolation platform, such as a sand box, or other will provide mass. The secondary platform can then be isolated from the wall-mount platform, by the use of sorbothane pads, or other products available. Experimenting with different means to achieve your goal can be enjoyable, and not necessarily expensive, if you are willing and capable of some DIY.

Best of luck,
Dan

Isn't there a correlation between high mass and acoustic breakthrough, or resonance, at the low frequencies. Wouldn't that tend to thicken the sound?

I don't see how mass itself has any effect on how well a stylus tracks since the stylus is coupled to the cart and the cart to the arm which is designed to pivot in order to track a record properly.

It does make a difference in terms of isolation from external vibrations. No doubt there! A plinth alone cannot accomplish that. You also need a solid foundation. The plinth can also help isolate from motor vibrations but there are other ways to decouple a motor effectively to limit vibrations. Belt drives with separate motor components for example is one design I would tend to favor.

Also, I do not doubt that the plinth can affect the sound, but my goal would be to use it isolate the arm, cart and stylus from all vibrations, external or motor as best as possible. That would be the ideal scenario. Use the plinth as an isolation device, not as a tuning device that affects the sound in some desirable way other than its role to help isolate things (and also look nice perhaps as well while doing that). To do that effectively, mass/weight is typically required, both in teh foundation and in the plinth in order to isolate from all undesired vibrations best.

Mass can never hurt IMHO and a solid foundation is always needed for best results.

The need for mass in the plinth might vary somewhat though I would think depending on what other mechanisms might be in place to help isolate from motor noise and vibrations.

In my mind (totally un-scientifically validated though) there needs to be mass it the interface of the stylus and the record (e.g. the platter) to minimize any micro resonances that could distort that tiny signal.

Next, mass or non-resonant chacteristics in the plinth and suspension are needed to minimize larger vibrations affecting the signal.

Thirdly, mass in the stand is needed to minimize air-born and floor transmitted vibrations.

You are correct, that ideally you need all 3 to be optimal if you are using a mass loaded design.

There is of course the other camp, using rigid and light designs.