rumble issues - see old thread update

hi guys

just reading your insightful posts

latest update

less woofer excursion after using granite slab under table on craz rack - it eliminated or greatly reduced isolation
slightly warped records set it off, but most have much more minimal speaker pumping (I can live with if not damaging cartridge)

craz platform is floating and works great with electronics but not with turntables - I could tap it and get noise through the speakers - not now as I replaced it with 3cm granite

pumping is more pronounced on outer portion of record which fits with the warpage scenario
so I may have similar observations as what you saw at Doug's (room and port elements may add to this)

the arm is still resonating (as seen on the scope) - calculations and your experiences as well as Mehran's and Thom Mackris say this should work and it seemed to till I got a low end pre amp -the doshi

weight 1.75 ish - have the shim and adding a quarter on top of the cartridge didn't work either
I tried the mass counterbalance variations along the arm

room 15 by 27
I have system/speakers on long wall using Cardas nearfield setup
There is a dip in volume om the back wall behing the couch - increases two feet into the room
speakers 3 feet into room. CD's sound great in the room with no noticable freqency humps

haven't tried the speaker placement
do have some echo buster type iso panels I could stick between speakers and equipment

alignment is dead on as shown by scope with test records and hearing music

I have a heavy anvil I can use on the top of warped records
is the clamp more effective

the pumping at present isn't really audibly effecting the sound anymore or minimally except for warped records

Richard is also going to bring over a few other cartridges with lesser compliance and see if we can remove resonance

this may be as dan and bob suggested - live with it

I think I'm getting closer, just want to isolate this and tweak everything out of my system

enjoy music tolerate equipment ...

thanks for all the helpful insight,
much appreciated

Those resonance figures you posted are absolutely fine. This is not, IMO, a tonearm/cart resonance issue. That combination is used by many people with no issues. Now, if one is using the Universe without one of the plates, 5 grams may be too light.

I have no idea what you mean by low end preamp.

Doug's B&Ws do not pump in the least with almost every record we played. There were maybe 3 times over a 6-7 hour session that I noticed woofer excursion out of the norm. We have also mounted his Universe on my TP and had no problems.

But it sounds to me like you are getting to the issue. I think you're rack, or what is under the table, is the problem. The granite shifted the resonances up higher. I know because I also have granite under my table as the shelf for my sandbox. It sucks because it does cause smearing in the midrange. I use Stillpoints between my plinth and the granite to remove the ill effects from the granite.

FWIW, I can tap on my stand and hear it through the speakers. That proves absolutely nothing about how the table is performing, IMO. Well, unless one tends to tap their stand while they listen to music.

No offense, but who is Richard and why is he intent on proving your arm/cart match is wrong?

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.