Subsonic Rumble Solution

default -- Wed, 12/17/2008 - 13:59

I've posted this question and received a lot of feedback over at Audiogon, but I'm not really satisfied with the answers:
http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1228934026
In a nutshell I'm getting woofer movement on my sub and main speakers whent he stylus hits the groove - enev in the lead in/out grooves before music is playing. I have very good rack, shelf and TT isolation. I think it is subsonics and am looking for a better way of dealing with this, short of buying/building a subsonic filter. I can live with it, mostly by turning off the sub, but would rather hear optioins on how else to deal with it.
Recently someone suggested adding some additional weight at the headshell, then rebalancing the tracing force back to 2g to see if this adjusts the resonance of the tonearm and reduces the cone movement.
Any other thoughts?
Thanks, Bob

pederb -- Thu, 12/18/2008 - 18:53

What table, arm and cartridge do you have? How close are the speakers?

Peder Beckman
Director of Sales
Musical Surroundings
www.musicalsurroundings.com

BobM (not verified) -- Fri, 12/19/2008 - 10:23

It's a custom built table using a 1" Corian plinth and a VPI MK III bearing and platter with a VPI stand alone motor. I have a Moerch DP6 red dot arm and a Dynavector 20X-H cartridge going into a Hagerman Trumpet phono stage. The TT is unsuspended and sits on a butcher block shelf, that is then supported by squash balls, sitting on another butcher block shelf in a sand box (seismic sink). The whole rack is about 200 lbs and is spiked to a cement floor.
The speakers sit in front of the racks and off to the sides, but this problem occurs without music playing (in the lead in and out grooves) and without the sub on, so I doubt that it is an isolation problem. Here's a link to a picture:
 http://cgim.audiogon.com/i/vs/s/f/1199294822.jpg
Bob

Robert Harley -- Fri, 12/19/2008 - 11:56

I suspect that the low-frequency signal that's making your woofers move is not a result of airborne or structure-borne vibration impinging on your turntable, but from record warp and groove modulation. Does it occur on all records, or just some? Is the amplitude of the woofer excursion related to the playback level?

BobM (not verified) -- Fri, 12/19/2008 - 12:15

Yes, pretty much all records, although some are certainly worse than others. Yes, the excursion seems to change with volume. At low levels I can use the sub. At high levels my ears feel the low end "whump-whump" and I need to turn the sub off.
I'm thinking the same as you and am trying to avoid building/buying a subsonic filter. If there is some mechanical solution I would prefer to try that first. If I need to put a circuit in the signal path then I am probably willing to live with the issue and leave the sub off when spinning vinyl.
There's a fairly interesting project at this link, but again, the whole signal would have to go through this filter and I am a little loathe to put it through those extra op-amps when I have taken pains to keep it as pure as possible now. They would most assuridly color the sound.
Bob

BobM (not verified) -- Fri, 12/19/2008 - 12:15

Sory - here's the link:
http://sound.westhost.com/project99.htm
 

Halcro -- Fri, 12/19/2008 - 22:51

Bob,
I suspect your problem may be related to the multitude of 'isolation' devices you have elected to place before your turntable?
Firstly, the squash balls under the butcher-block is a bizarre concept? This will allow your turntable platform to gyrate like a drunken belly dancer.
Secondly, your 'sand box' sitting on top of a flimsy steel rack on spikes? The sandbox, if properly compressed, will have the density almost equivalent to concrete. This huge mass will absorb loads of low-frequency energy from air-bourne feedback and will induce movement into the flimsy steel structure of the rack.This movement will be magnified by the large lever-arm from the sandbox to the bottom spikes and cause the entire rack to essentially 'sway'. Structure-bourne sound transmission from the floor will additionally cause your rack to 'move' again magnified by the lever-arm to the large mass of the sandbox above.
Try removing both squashballs and sandbox to see if the problems are ameliorated?

BobM (not verified) -- Sat, 12/20/2008 - 07:32

I guess you didn't look at the system picture above. The rack IS the sandbox. There is no steel at all. Each shelf is its own sandbox connected together by butcher block legs.It is very rigid and massive.
As for the squashballs, there are 9 of them in what I call a cheap man's Ginko Cloud. There is no sway or bouncing at all since they compress in half from the weight of the TT above them (it is heavy). In fact, without them any rap on the shelf is instantly and completely transferred into the cartridge and through the speakers. These squash balls do a pretty amazing job of isolating the TT from any room vibrations.
Bob

Halcro -- Sat, 12/20/2008 - 07:53

"Each shelf is its own sandbox connected together by butcher block legs.It is very rigid and massive."
Massive?.....yes.
Rigid?.....no.
There is no way that timber connections can produce 'moment' connections without serious cross-bracing. You claim to have the perfect rack with ideal isolation for the turntable yet you complain about acoustic feedback problems no-one else seems to have.
Your rack must be custom designed and built as no commercial manufacturer would be naive enough to produce such an ill-conceived notion.
Of course you could easily remove your turntable, place it directly on the floor and see if it suffers the same feed-back issues?.........but somehow I suspect you will not?

BobM (not verified) -- Sun, 12/21/2008 - 08:59

Halcro - I did a few tests this morning. I bumped into Michael Fremer yesterday and explained my dilemma. He suggested adding some Moretite/Bluetac to the headsheel to see if there might be a resonance problem with the tonearm and cartridge compliance. I tried 1, 2, and 3 grams, but alas, the problem still persisted.
So then I tried your suggestion (Why so hostile? I'm just looking for suggestions from others who may have additional insight, and I am willing to try most anything within reason). Unfortunately it made no difference (the floor is concrete, so it's not springy). I would hardly say that nobody else has this problem. I also spoke with Wes Bender, who knows a thing or two about analogue and has a VERY high end system (Hansons, Redpoint TT, etc.). He gets this pumping action also and basically just ignores it, saying that it is just a fnction of the medium.
So I'm back t square one. Any other suggestions?
Thanks,
Bob
 

Steven Stone -- Sun, 12/21/2008 - 11:40

 I agree with Robert Harley's answer - record warp may be a likely suspect.
 
While your turntable is on the floor, which may be Halcro's preferred position, try different records and see if the problem varies. Also take note of the tonearm's movement to see if it corresponds with the low frequency pumping.
 
You may find that a low frequency subsonic filter is your best solution. It could be set as low as 15 HZ and be VERY effective at reducing your problem without having a negative effect on your audible low frequencies.

Steven Stone
Contributor to The Absolute Sound, EnjoytheMusic.com, Vintage Guitar Magazine, and other fine publications

SundayNiagara -- Sun, 12/21/2008 - 14:26

"Why so hostile?"
I was wondering the same thing myself!
 

Halcro -- Sun, 12/21/2008 - 22:19

Bob,
Sorry if the written word appears 'hostile'?........it's not meant to be. I simply have a problem with your rack......and the floor certainly is not my preferred location for your turntable. I simply wanted to remove the rack from the equation to see what would happen?
It may be that Steven Stone is right about the subsonic filter?
One further thing you might try if you can borrow phono leads long enough..........is to move the turntable to another room or as far from the speakers as possible and see if the problems persist?

Cemil Gandur -- Mon, 12/22/2008 - 10:01

Also, as far as the squash balls are concerned, I am not sure if it is a good idea to diss this right from the bat. Ginko uses those in their Cloud series of isolation platform to pretty good effect. Yes, the whole thing wobbles if you put a side pressure on the table/platform, but noone does usually, and it seems to tighten up things very successfully (tested with a VPI)

Halcro -- Mon, 12/22/2008 - 19:33

The problem with squash balls (or any rubber-type isolation feet) IMO are twofold:-
1. They move. This movement may be microscopic but then so too is the tracking and retrieval of the information buried in the vinyl grooves.
The movement in the squashballs is not caused by the absorption of energy within the balls themselves, but in the absorption of feedback energy in the base and plinth of the turntable which rests on the balls. The more massive the base and plinth are, the more energy they can store and this energy is converted into heat and vibration. The vibrations will cause the base and plinth to 'release' this energy via the 'movement' that is allowed in the squashballs.
You will notice that all speaker manufacturers 'isolate' their speakers from 'movement', via the use of spikes......NOT rubber?
2. Any compressible material will alter its density the more it is compressed and the denser a material becomes, the more it can absorb feedback frequencies and 'pass' them directly into the base and plinth sitting upon them. Hence the heavier the weight placed on the squashballs, the more the compression and the less effective they become as an isolation device?
The effectiveness of the Ginko system is debatable and I don't know which VPI deck you tried it with? It's interesting that the majority of audiophiles seem to prefer the 'unsprung' VPI decks like the Super Scoutmaster over the 'sprung' TNT or HRX models?

Cemil Gandur -- Tue, 12/23/2008 - 04:19

I've tried it (and am using it now) with the Super Scoutmaster, 10.5i arm, super platter. It tightened the bass and opened up the soundstage a bit more, both side and depth. Detail retrieval is a touch improved. The Ginko is sitting on a Finite Elemente Pagode ref stand.

SundayNiagara -- Wed, 12/24/2008 - 15:09

Could this problem this gentleman is having be caused by DC leakage?

BobM (not verified) -- Sat, 12/27/2008 - 22:35

Interesting question. I'll test it with a voltmeter and see if I'm getting any.
 

Pete Wilson -- Fri, 01/02/2009 - 23:35

BobM
 What happens if you use headphones?
-- Pete

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