rumble issues - see old thread update

Great post, Dan. I agree on nearly all points (except I believe you got it just half right on the granite).

Tom,

If changing your craz shelf to granite reduced the pumping then it's likely the additional mass lowered the resonance frequency and amplitudes of the shelf/table system taken as a whole. Thus less pumping.

However, as Dan noted, granite can also be problematic because its higher frequency internal resonances often introduce smearing, ringing or shouting into the audible band. Listen carefully for that. If you don't hear any, great. If you do, consider isolating the table from the granite as Dan suggested or (ideally) trying different support solutions that might lower the shelf/table system's resonance frequency without introducing ringing at higher frequencies. The Minus-K stands come to mind.

...the arm is still resonating (as seen on the scope)

Of course the arm is resonating. All arms resonate. At what frequencies? Under what conditions? What exactly are you measuring? What does it have to do with woofer pumping? The statement as posted lacks meaningful content.

...slightly warped records set it off, but most have much more minimal speaker pumping...

Good! You're building a system designed to reproduce everything that's on a record. "Everything" includes warps. If one's woofers are susceptible to pumping then on certain warps they in fact ought to pump. If they didn't, it would mean the LF signal generated by the warp was not reaching the speakers.

The solution is not to install LF filters, nor to worry about what is in fact an indication of good LF system capability. The solution is to flatten or replace warped records and perhaps to consider woofers which don't pump.

Vacuum hold-down would eliminate all but the severest warps. Center clamp + periphery ring would be next best. The Anvil may help on some records, but on others its weight can actually cause a flat record to dish upward. An adjustable clamp like Teres uses is more effective on a broad range of records. Further, each time I've heard the Anvil it also caused upper midrange smearing or glare, whereas the Teres cocobolo clamp actually reduces smearing and glare.

Sadly, there are no perfect solutions. We're just groping our way blindly from equipment toward music!

Doug

P.S. Your friend Don Ricardo seems like a man tilting at a phalanx of windmills with but one lance in his armory. ;-)

Yep, the oscillations of the craz were in my brain, but my fingers don't move as quickly as my thoughts. I tend to leave out parts. In this case, skipping ahead to the problems with granite.

Adding a suspension under a non-suspended table is not the way to go, IMO.

Oops! Dogma demolition time!

"Adding a suspension beneath a non-suspended table" is exactly what devices like the Minus K do. Chris Brady and others have found that it provides major benefits beneath even the heaviest (unsuspended) tables and is markedly superior to the best 300+ lb. unsuspended stands. My poor man's equivalent (sorbothane hemispheres between our equipment rack and the floor) also add a suspension to a suspended table.

Yes, our Teres is ultimately sitting on a compliant suspension. So was your Galibier both times you brought it down. I trust you didn't hear any softening of dynamic impacts, murky bass or other effects attributed to lightly suspended tables. The trick is to do the suspending effectively, with awareness of certain unavoidable contradictions.

A. The main reason to suspend a TT is to isolate it from floorborne vibrations.
B. The main reason NOT to suspend a TT is to allow the table's mass to resist being displaced by big transients.

These goals are self contradictory, so we address each while trying to minimize impacts on the other.

In our setup the non-moving mass of an 80 lb. TT is pretty tightly coupled to the ~300 lb. mass of our equipment rack and other gear. Except for the tiny amount of movement allowed by the Stillpoints (which do slightly diminish dynamics, as you know), we effectively have a ~380 lb. plinth to resist transient-induced displacements. So far, so good.

To avoid floorborne vibrations, this entire mass is sitting on weight-specific compliant bits to create a tuned system. The compliant layer sees all ~380 lbs. as a single mass and has a resonance frequency of < 10 Hz. If I could afford a Minus-K large enough to suspend the entire rack I could get that down to around 2 Hz.

To get a ghostly low sound floor and big dynamics too, we must suspend, but not too much. The devil's in the details.

I also have a Galibier (Stelvio) table and have had a friend's ZYX mounted on my Triplanar. We did not experience the woofer pumping you are experiencing. Your CRAZ rack is an amazing product. I wonder if it would be worth a call to Kevin; perhaps he could point you in the right direction. As an aside, my turntable sits on a GPA Monaco platform on a EquaRack. Perhaps the EquaRack product might be worth exploring.

BTW, great information on this thread.

Nope, no dogma here. I specifically included this is my opinion.

The granite was added on top of the craz, if I read Tom's post correctly. If that extra mass reduced oscillations getting to the speakers, something is moving too much. I didn't mean to point directly at the Craz, just whatever the table is sited on. But if that is the Craz, well not everything works in every application.

The Stillpoints are the limit I will go with compliance under my Gavia, and even then I know it is a compromise to the sound I could get with a braced, aluminum shelf on my sandbox. If I ever grow tired of that beautiful Dakota Mahogany granite it will be gone along with the Stillpoints. Remember, I'm coupled to a concrete sub-floor so I don't have the issues of a suspended floor. If I did I might own something other than what I now own. Suspend away if you want or need to. I don't find it necessary or desirable under my table to get a low enough noise floor.

Yes, there are things I hear in the mid and upper ranges differently in your system and mine. But down low is a different issue, and that's what where talking about here. I dont hear any down low in your system, I never have. I have to extrapolate what I think it would sound like. But I realize you do have your system tuned for a different sound than I based on our different preferences. Even as close as our systems are, they are still as different as the music we each prefer.