[catastrofe]

From my turntable that is. . .

Anyone available to come by and provide some input on reducing tt rumble?  Here's how I have it
situated. . .it seems pretty well isolated but I guess not.  Very noticeable rumble on lead-in grooves and quiet passages.  I was able to reduce it somewhat by adding a low pass filter on my Behringer inputs at 20HZ, but it's still present and I'd rather treat the cause, not the symptom.

[Scott F.]

Bob,

Let's start at the beginning. What arm and cart are you using. better yet, if you have the compliance figures on these, post those. I'll plug them into a spreadsheet I've got and calculate the resonant frequency and see if it's in accepted norms.

I'll need;
Cartridge compliance (mn/N)
Cartridge mass (g)
Tonearm effective mass (g)
Headshell/screws mass (g)

[catastrofe]

Scott, all should be good based on the Vinylengine resonance calculator.  Here goes:


Cartridge compliance (mn/N)  15 (DV 17D3)
Cartridge mass (g)  5.8
Tonearm effective mass (g)  14 including headshell (SME 312S)
Headshell/screws mass (g)  1 or 2

The sandbox has 75 pounds of lead shot in it, with the maple plinth sitting on Herbie's Iso balls embedded in the shot.  The entire box sits on a slab of soapstone, which in turn sits on 4 isolation feet attached to the aluminum framing.

[KenSeger]

Scott,

That is so cool that a program like that exists.

At the old Bang and Olufsen turntable clinics they had a special record (which they would only play on the testing turntable *IF* the stylus was in good shape via examination with a Wild microscope) that had a series of horizontal tones and a series of vertical tones at very low frequency. I guess that would be R-L and then R+L starting at 200(?) Hz and going down to 5(?) Hz.  I remember on a particular tonearm in Mpls., a Transcriptor tonearm, the one with the short vertical at the end of the tonearm pivot and the string connected counterweight, had a resonance at 185 Hz.  It was assumed that its jeweled bearings were cracked!

Considering that the distribution of the tonearm mass, (its inertial polarity) can effect the resonance, I assume that that is the difference between tonearm mass and tonearm effective mass?  Though I don't see how such modeling would work.  I assume the program needs both vertical and horizontal compliance?

While the turntable support looks nice and sturdy, it might be transmitting feedback infrasound from the vibration of the floor from your speakers.  Is the rumble noticeable only when the speakers speakers are playing?  I.E. with a given record, can you measure the same amount of rumble when the speakers are on as when the speakers are off?

These are about infrasound from a completely different topic, but it shows how tricky it is to measure infrasound properly.
http://oto2.wustl.edu/cochlea/wind.html  http://oto2.wustl.edu/cochlea/windmill.html and http://en.wikipedia.org/wiki/A-weighting

and why idiots and imbeciles that pretend to make 'scientific' medical assertions should be kept far away from measuring equipment, if they don't understand how it works.

http://www.bwea.com/ref/noise.html

Ken

[Scott F.]

Yep, looks like it. Using 1g for screws gives you ~9Hz resonant frequency. That's well within the (recommended) 8-12Hz range.

....hmmm, before we look at anything more drastic, why don't we try a different phonostage. We're headed to the Fox today and dinner afterwards with Bryan and Sue. I don't think we can stop by (I know Sue's schedule) but maybe we could meet on the way down or back somewhere and I could give you the Slee Jazz Club to try. I'm just going on a hunch.

Gemme a buzz if that sounds like it will work. We'll be buzzing by 40/270 area about 12:30 on the way in and about 6:00 on the way out.

[catastrofe]

Thanks Scott.  We could connect, but I don't think it's the phono stage.  I have Chris' GCPH and a DV P75 and the rumble is present with both.

Maybe I should move the table off its "pedestal" and down to the main rack area?  I do find that the plinth of the sandbox isn't "dead", so maybe a more mass-loaded approach (like right on the soapstone) would help?

Ken, I don't think it's speaker feedback. 

[Scott F.]

If it's doing it with the DVP75, the phonostage isn't the issue. I'm with you, get the table off the elevated stand. That was going to be my next suggestion. I'd try it with and without the sandbox. It should be better with but if you can tap on the outside of the box itself (not the top), the filler material you are using isn't doing its job...or something. I can't imagine the lead shot not diffusing/absorbing vibration...but weirder things have happened 

Rather than the sandbox sitting on the soapstone, try some points of some sort (coupling).

[Blackmore]

I think I'm right in saying that your TT is rim drive.  Could you try sliding an old spongy mouse pad under the motor section and still have the rim drive work?   If it changes the amount of rumble, then you are on the right track to get the table down off the pedestal.

[blakep]

Seems you have properly matched cartridge/arm with respect to compliance/effective mass.

The next line of attack is, as others have mentioned, isolation of the table. Ideally, this would be a wall mount on a load bearing wall that also takes the table into an area where it is least likely to be confronted with any air borne vibration from actual sound from the system.

Sometimes, due to room constraints, an ideal situation is not possible and even if it is the problem may persist. A lot of records will have substantial subsonic information cut into them and there are very few perfectly flat records. Combine this with the fact that (I believe) you are using speakers with a passive radiator design-many ported designs will have problems with subsonics as well-and this may well be a problem which is most effectively dealt with using a high quality subsonic filter.

If you were using an acoustic suspension or sealed design speaker chances are you would not have the issue.

You constantly read on these forums that a subsonic is a band-aid and that it is masking the problem, not transparent, etc. but my (and many others) experience in playing vinyl with non-sealed design speakers is that a subsonic filter is necessary and a welcome additon if a high quality one is implemented. Attempting to reproduce that subsonic info is not good for either your speakers or your amplification.

If you have to end up with a subsonic filter, just make sure it's a good one and don't sweat it. Either that or sell your speakers and buy a sealed design .

[Scott F.]

Bob,

Did you have any progress?

[catastrofe]

Hey Scott.

First, thanks to all who offered suggestions.  My initial course of action was to remove the Iso balls from under the sandbox plinth.  This placed the plinth directly on the bed of lead shot.  There is a significant improvement (reduction) in the amount of rumble.  The plinth also sounds much more dead when tapping on it, but it still "knocks" like wood.

There is still some rumble, so my next step may be to replace the maple sandbox plinth with some type of stone.  If that doesn't resolve the issue, I'll look at moving the table off the pedestal and down lower on my rack.

[Mitsuman]

Hey Scott.

First, thanks to all who offered suggestions.  My initial course of action was to remove the Iso balls from under the sandbox plinth.  This placed the plinth directly on the bed of lead shot.  There is a significant improvement (reduction) in the amount of rumble.  The plinth also sounds much more dead when tapping on it, but it still "knocks" like wood.

There is still some rumble, so my next step may be to replace the maple sandbox plinth with some type of stone.  If that doesn't resolve the issue, I'll look at moving the table off the pedestal and down lower on my rack.

That 80/20 aluminum extrusion stuff is great, but I wouldn't think it would make a very good isolation frame. It rings like a bell. 

[gooberdude]

I always had a TT on concrete floors & subfloors & never had a positive experience with pure isolation.  Doin' the Mapleshade 'drain & then isolate' set-up eliminated many issues.

You might try coupling the TT to the sandbox to allow the energy to flow....then isolate the sandbox if possible.

Bob, I have all sorts of Mapleshade goodies you can use including 3 difft types of their footers and their 4" thick TT platforms, isoblocks and all that.   


Just my 2 cents, but I wouldn't put hard surfaces like stone, tile, etc anywhere near a TT.  You need the vibes to flow away from the needle, not hit a brick wall & retreat back into the TT.

matt