Where do classical vinyl records get their rumble from?

@billstevenson @lewm 

How about this for an explanation of my 6-Hz resonance with the Holbo and none with the Garrard?

1. I think the resonance is down to my sub-plinth and has nothing to do with arm / cartridge resonance. 
2. I think I hear no mis-tracking showing up arm / cartridge resonance because I am not playing the tracks loudly enough to excite enough cartridge / arm resonance to be audible.  I played loudly enough to get resonance, and stopped there.

So why is my sub-plinth resonating around 6-Hz?  I should have done some trial and error, but I went straight for the error 

To recap, my Holbo is perched on a SolidSteel S3-3 rack, itself spiked through carpet to a suspended concrete floor.  Immediately below the Holbo are two slabs of Sydney sandstone weighing about 55-kgs, separated by a constrained damping layer.  Between the rack and the sandstone are eight sorbothane 50-mm hemispheres.

I was aiming for a resonant frequency of about 4-Hz to keep well away from arm resonance.  Working with sorbothane’s technical team, a good match was six hemispheres. When it came to arranging them, I used eight, with two on the diagonals at each corner for symmetry. This keeps load away from the middle of the rack shelf, but I think I need to move two hemispheres to the middle, and discard two.  Big job for next time I get home 

There is a slightly different arrangement under the Garrard . 

Instead of suspending the whole caboodle on sorbothane, ony the plinth is suspended.

A home-made shelf has four steel tube legs onto carpet.  Two sandstone slabs sit on the shelf, with constrained layer damping in between every layer including the inner plinth.

The inner plinth is home-made from three slabs of thick MDF.  The bottom layer of the inner plinth sits on three IsoAcoustics OREA Bordeau isolators.  The outer plinth, motor-board and dust cover were made by SME.

The outer plinth and dust cover are completely air gapped from the inner plinth, except for the cables.  So  the original Garrad spring suspension has been bypassed. I suspect my Garrard is particularly quiet because most of the resonant spaces are now filled with damped MDF.

@audphile1 

what made the mat a suspect is that you mentioned the rumble had a rhythm to it

Yep, but it could also relate to record cutting lathe issues, as @hb22 says.

Each record is different, and I am not good at describing the differences!  But when the noise abates on the run-out track, that implicates the record in my opinion 

If the noise if from the tables, I would expect to hear the same noise underpinning every record, but that is absolutely not what I hear.

I will remove the mats but I have to order replacement adhesive tabs!

Cheers 

Richard,

Arm/cartridge resonance has nothing at all to do with how loudly you play your music.  In fact resonance can be measured in total silence.  It is all about how the combination reacts when stimulated by the test band, which for AnalogMagik has a frequency range of 7.5-35 Hz.  So the cantilever is vibrating, which in turn sets the arm in motion.  The target is for the arm to vibrate in a range between 8-12 Hz.  Yours is 6 Hz, which is causing something to vibrate sympathetically, probably a simple multiple of that value.  By placing a weight on the head shell and rebalancing the tonearm, you effectively increased the mass of the cartridge/arm assemblage.  I know that is counter-intuitive, but it changed your resonant frequency and got you our of that situation.  End result: it sounds a little cleaner.  

@tablejockey 

can a reflex style clamp be used on the Holbo platter?

Good to see you are still looking at buying a Holbo!  

I have never tried a reflex clamp but had a quick look at a SOTA Reflex LP Clamp. It would seem to fit, provided two conditions are met

1. The Delrin spindle must resist being pulled out of the platter
2. There must be sufficient spindle length protruding for the clamp to grip

The protrusion depends on whether you use a mat, and if so what its thickness is.

Funnily enough, I don’t know much about the internals of the Holbo even though I have one.

I probably know more about Wilson Benesch because they publish so many whitepapers and are backed by government grants and university research.  No doubt they apply for patents around the world - which is not a copy-protection mechanism affordable to most entrepreneurs.  Even patents probably don’t stop counterfeits from Asia! 

I only have one wish for a Holbo improvement, and it is a slightly longer spindle

@hb22  over to you!

I think the whole 6Hz resonance thing is a red herring.  But I am glad the problem is at least ameliorated if not solved. If the Tacet LP cannot make the SME resonate at all, like I said before, there is something fishy about it OR the resonance is below 5Hz (doubtful because it would cause havoc) or above 15Hz. Because all tonearms with all cartridges must resonate at some frequency.