rumble issues - see old thread update

Hi Tom,

As you know we use the same arm, cartridge and preamp. With 8-10 different UNIverses on our arm we've never had such issues with any music, at any volume up to window shattering.

Based on that experience I question the tonearm/compliance theory (assuming your cartridge has the SB option). You can test by trying a different counterweight, positioned to give you the same VTF. That will change the eff. mass slightly, which would alter the behavior if eff. mass were the culprit. Seems doubtful to me, as I said, but it can't hurt to try.

We get only minor woofer pumping on obviously warped discs, as we should. Basically it's just the cartridge, arm, preamp and and amp reproducing the warp frequency and pushing it through to the speakers, as they should. But in our setup this never results in sonic breakup or "clipping" unless a warp's so bad the cartridge mistracks. We have exactly one LP that can cause that, a nasty pinch warp. It's our torture test for vertical tracking ability. ;-)

I suspect you have some combination of room interactions reinforcing a low frequency and/or amplifier headroom issues. Both would be volume sensitive and could lead to breakup at higher SPLs.

Just for fun, try blocking the ports on your speakers and see what that does. Try borrowing a different amp too, if you can.

Koegz,

All ported speaker cones oscillate when air inside the chamber is energized at the port frequency. When air is compressed at the port waves flow back into the cabinet at that frequency. Something inside has to move and the easiest thing to move is the cone.

Dan is correct, mine do oscillate (though never to the point of audible breakup or distortion, as the OP is experiencing).

There could be many reasons why you haven't seen yours oscillate and I'm glad you haven't. Your speaker ports are certainly tuned lower than mine. Your phono stage may have a built in rolloff or filter. Your line stage or amp may not go low enough. You may not have noticed. But this doesn't change the fact that they will oscillate if excited at the port frequency.

Want proof? Try YELLING into the ports at their tuned frequency. ;-)

Tom,

If the pumping varies with volume, surely room mode interactions must be a prime suspect. My guess is that tweaking the eff. mass of the arm/cartridge may vary but will not eliminate it.

A concrete floor may dampen but it does not isolate, unless the concrete hasn't fully set and can slop around a bit. ;-) Owners of very substantial rigs on high mass stands, SRA platforms and solid concrete floors have still heard substantial improvements from adding true isolation with something like a Minus K. Not saying that would necessarily help with woofer pumping, just noting that concrete is not an isolator.

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. ;-)

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.

Agree about the Stillpoints, we both heard similar advantages/disadvantages. Like you, I'd rather not have that compliance so close to the TT. I'd ditch them too if our Salamander rack weren't so ringy (it's like your Dakota Mahogany granite, except for the good looking part!).

That's different from the sort of suspension I was referring to though. We both know people with sub-20Hz systems, very high mass tables (200+ lbs.) and concrete floors. Every one who replaced a big, high mass stand with a Minus K reported significant benefits with no loss at the bottom end. We're not talking bouncy, bouncy Linn here.

Agree there's little down low in our system vs. yours. Our speakers roll off below ~42 Hz. They can't reproduce the bottom octave no matter what we do at the source.

FWIW, our missing low end is not by choice and has little do with sonic or musical preferences. It's a function of geography and budget: we lack room for a sub and funds for full range speakers that would fit.

I'd love to try big Coincidents, which claim 20Hz without being much larger than our B&Ws. They're also easier to drive, have great crossovers and drivers (on paper anyway) and they're not ported - no woofer pumping!

That's my segue back to the topic. Sorry to Tom for threadjacking!

The key point to mention however is, that with Vibraplanes, microscope tables, etc., the entire 'table is suspended - the critical relationship between drive system and platter is still intact.

Agreed, and we go even further. In our setup the entire table + system + rack are suspended as a single entity, well away from the table and drive system. All our sorbothane floor supports see is a single, rigid mass of nearly 400 lbs. This is very different from sticking it directly beneath the TT feet or something. I tried that once, just for ha-ha's, and it sucks big time.

Agree that the connections between drive system, platter, bearing, plinth, armboard, tonearm, cartridge, LP and record clamp must be as non-compliant as one's components allow. The only compliance anywhere in our vinyl setup is Stillpoints instead of spikes beneath the plinth. As anyone who's tried them knows, they do ennable a tiny degradation of transient speed and dynamics, though most feel the reduction in sound floor makes for a worthwhile tradeoff.

It's about thoughtful implementation, as always.