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Jan Vigne
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Joined: Mar 18 2006 - 12:57pm
Mass Loading

In the current April 2007 issue, MF reviews the Kuzma Stabi XL and makes the remark, " ... there's no mistaking a proper mass loaded design ... " Can someone explain just what a proper mass loaded table design is? Obviously a high amount of mass (and density) is involved, but what constitutes proper and improper mass loading? Can mass loading be applied primarily in the support stand? If so, is there an advantage to using a mass loaded or non-suspended table on such a support system or can a suspended table still work "properly" on such a support? (This mass-in-all-cases-except-Linn route seems to have been the general recommendation for turntable support systems a decade ago; but is this still what we see as "best" overall?) As a side note, why are current "suspended" tables unlike what we saw a dozen years ago in designs such as the Linn, VPI HW19 or a Sota? Many contemporary models now seem to rely heavily on the suspension capabilities of the feet rather than utilizing suspension springs or Sorbothane balls. Is this the result of simply trying to remove any pendulum effects from the modern designs?

A later comment in the review suggests the sound of the Kuzma will be somewhat determined by the stand (aren't all tables?) since "its arm tower, platter and motors will all need to share that platform." That would seem to be a specific reference to mechanically "grounding" the table under review and not necessarily a comment on all mass loaded designs. Would it be safe to assume from that remark that any mass loaded stand would be more beneficial if it had the advantage of separate support shelves - or systems - for each section of the table? Would they need to be physically separated from each other from the get go, each system being its own semi-independent massive support, or merely isolated from each other at the dense mass loaded support shelf/table interface? For the latter, I would think three separate levels of support, one for each section of the table with no common interface other than the dense top of the stand would work best.

I understand mass and density tend to act as low pass filters, which capacitively delay subsonic frequencies originating both as system resonances and externally fed motion all of which is eventually passed back through the support/table loop until they arrive out of phase with the modulations present at the stylus tip. Therefore, large, massive entertainment centers are usually horrible locations for a turntable even if the support system is not an open or closed box shape. If I understand correctly, a (load bearing) wall mounted shelf screwed into the framing studs takes advantage of the relative rigidity and stability of a massive, all but immovable support system whereas any free standing mass loaded system can suffer from low frequency modulations set off by the music playing in the room (and footfals) and further exacerbated by the physical mass and density of the support system. Obviously, the extent to which this problem impinges on the performance of the table will depend on the room construction and table location, which I assume would still be worsened in a non-suspended table despite the mass loaded stand. However, I also read into the various reviews and blurb sheets of massive, rigid semi and non-suspended tables that conventional suspended subchassis tables can never achieve the same results no matter the support system employed. In this respect, suspended subchassis tables are the CD equivalent of the analog world, convenient but never capable of the best sonic reproduction.

It is also my understanding that any random movement of any of the table's component parts in relation to the stylus' position in the record groove will result in lost information, particularly deep bass response and ambient cues, and will typically add levels of distortion, random groove noise and most likely the "hard edge" and false detail which MF surmises result from somewhat resonant bearings in the Kuzma tonearm also under review. Achieving the lowest possible noise floor from a table (in other words, having the stylus respond only to the groove modulations and not random external forces) means holding each piece rigidly in place (space?) relative to all the other parts and yet not allowing each component part to sympathetically affect the other bits while the entire system is set in motion in several different directions at once. To that affect tables such as the Kuzma have no real suspension and rely entirely on the mass and density of the support system and mass and density of the table itself to drain looped energy away from the stylus tip/record interface. (Am I correct that the Kuzma table rests flatly on its base with no intervening spikes, cones or bearings to provide further isolation? If so, why not? Wouldn't spikes effectively "ground" the table to the support system even more effectively than mass alone?) So, when is there enough mass to do this job of loading the table properly and does it depend on where that mass is located relative to the stylus tip? Would a very light table such as Rega benefit from sitting atop fifty to sixty times its own mass? I would think high mass above the stylus can only spell trouble in many different languages and dialects but is it better to place the mass as low as possible or evenly distributed through the system with the majority of the mass, and primarily the density, being at the shelf/table interface in order to mechanically ground the table and drain any motion from the table's component parts?

To put this in perspective, I have inherited an old Boos butcher block with a top "shelf" of ten inch, end cut maple forming a 24X24X10" surface which I intend to use as a turntable support. This block sits on four (spiked) legs which have been tied together for rigidity and stability. The block and its legs weigh in at just under two hundred pounds before I place any other materials on them. I'm considering placing a lower shelf on the system and using it for "in rotation" record storage which could probably add another 75 to 100 Lbs. placed close to the floor. So, about 300 Lbs. of mass consisting of fairly high density materials in order to support my lowly VPI HW19 III. From what I have read so far, I think my best route is to toss out the original suspension for the subchassis and place the working parts of the table directly on this mass loaded (?) support with independent, grounded and isolated sub-shelves for each piece of the working system. My intention in doing away with the original suspension is to minimize any motion of the separate pieces that make up the table. The motor is a stand alone component which will rest directly on the butcher block's surface and the RB300 is lightly damped in a silicone bath at the rear of the arm. I suspect this is dramatic overkill for my table but I would also assume a system hierarchy that places the support system above the value of even the table itself. I have the original motor controller for the VPI and my speakers are LS3/5a's with a small subwoofer so there are no subterranean bass notes nor high SPL's to be concerned with in playback. The floor is a pier and beam suspension but the table will in effect sit in a different room from the speakers and not tied to the same floor joists.

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