Turntable Isolation or Coupling?

Discussion in 'Audio Hardware' started by MaJoon, Jul 10, 2018.

  1. The FRiNgE

    The FRiNgE Forum Resident

    Yes! a rigid, solid piece of furniture or shelf, however its mass no influence on the turntable's performance. A mega-massive high end turntable engineered for stability would be the exception, as its mass is the plinth itself.
     
  2. sublemon

    sublemon Forum Resident

    I have two TTs, one is a very heavy mass loaded thing (acoustic signature), the other is a light one with a sort of suspension (old oracle paris). The Paris is very susceptible to foot falls, the acoustic signature never skips due to walking near it or anything, even on an ancient and somewhat bouncy wood floor. So I would say, if you have a suspended TT, you need as much isolation as you can get. But hmm, Regas are not suspended. But they are pretty light and bouncy in my experience. So I would try isolation first.
     
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  3. willboy

    willboy Forum Resident

    Location:
    Wales, UK
    If as you say, adding mass to a turntable plinth can not be accomplished by spiked feet. Can you explain how prior to replacing my turntable's compliant feet with spikes, tapping the plinth with the stylus in the groove of a stationary record produced an audible zonk from the speakers. After the spikes were fitted the same procedure resulted in very little sound coming from the speakers. The turntable, which I no longer own, was a non suspended Rotel RP-885 supported by a homemade sandbox weighing around 25lb. The top-plate of the sandbox was made out of 20mm plywood. The spiked feet actually penetrated the plywood, which I suspect may have aided coupling.
     
  4. SonOFJames

    SonOFJames New Member

    Location:
    Upstate
    Sandbox has always worked well for me with tables heavy & light. Although I will be experimenting with Maple, Bamboo, and marble this summer for a new rig.

     
    Last edited: Jul 11, 2018
  5. chervokas

    chervokas Forum Resident

    It depends on the frequency of the footfalls and the frequency at which the sprung suspension resonates, and in part that depends on the nature of the floors -- materials, how they're supported, etc. -- and the nature of how floor vibrations excite any other vibrations in the stand the turntable is sitting on. Footfall vibrations are usually very low in frequency -- 2, 4 maybe 6 Hz; that may be below the frequencies that a sprung suspension isolates at (say 7 Hz or up), or worse may be right at a frequency that the suspension resonates at. But it doesn't have a lot to do with mass or weight.

    Pneumatic isolation, including DIY setups like partially inflated inner tubes, can sometimes more effectively isolate at lower frequencies.
     
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  6. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    I don't know that one wants spiky feet on a turntable, ones that accurately transcribe any signal to the turntable above. Take instead your Technics 1200's rubber feet. Give your turntable a bump when it's sitting on the feet, and it might vibrate at 10Hz, and then the dampening of the rubber absorbs this within a few cycles. Turning the motion into heat takes a certain amount of resistance that imparts their necessary higher frequency.

    Imagine your whole stand sitting on an earthquake simulator shaker table where we can dial in any frequency of lateral motion. With slow motions of the table, the turntable is faithfully following along. However, if we turn up the frequency to where the motion starts to look more like a paint shaker hum or buzz, eventually the frequency will be one where the rubber feet will start to do their work, and the motion of the turntable will be far less - the bottom of the feet move but the turntable not as much.

    Set the whole turntable on the low-compliance isolation sandwich I depict, and start turning up the frequency of vibrations. We find a much lower frequency where the block and the turntable are not moving so much, because they are indeed acting as one mass. Above the isolator frequency but below the effective range of turntable feet the turntable is going to follow along with the isolator mass. In fact, a very close resonance of the two (such as 2Hz/3.3Hz) may let the second stage of isolation disperse the frequencies where the first stage is excited (like that frequency where shake a slinky and it goes crazy). If there was still a mechanism for audio to pass, such as resonances in a bungee-cord suspended turntable block, the feet can still do their work at higher frequencies.

    What are you isolating from, though? It can't just be some voodoo mojo that comes from nowhere, it's normally footsteps, truck drive-bys, or subwoofer infrasonics that make your floor vibrate. A pile of cinderblocks as a stand are harder for the vibration to move; an isolation system, instead, decouples your turntable from those.
     
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  7. The FRiNgE

    The FRiNgE Forum Resident

    Your observations certainly must be accepted as valid. As most of we audiophiles are not physicists (including myself) the explanations on why or how a system sounds better may elude us. I have a cheapo run of the mill Technics SL-D205 (like an SL-1200) my workhorse for test playing LP's for sale. It has reasonable isolation. It is sitting here on my computer desk, not the most stable platform for a turntable. If I tap on the desk, some of that will be audible through the speakers with the gain turned up.. at no signal of course. Likewise, when I tap on the plinth, I hear a well damped thud. (very acceptable) The turntable sounds good as is, at its location, well enough for the purpose it serves.

    Consider this same turntable placed on a sandbox. The physics of resonance can be complex. The assumption is, the mass of the sandbox (although not coupled entirely to a desk or shelf) should deaden any tap of a finger on the sandbox, and the desk. (or shelf)

    Your setup sounded better through coupling, an improvement over not using a sandbox. However the stock rubber feet do not isolate entirely, some engineered better than others. Some vibration gets through, just less of it, and at a lower frequency bandwidth. (stock feet do nothing at sub-sonic) Isolation covers the full frequency spectrum, but concern mostly at low frequencies and sub-sonic. A tap of the finger on a computer desk such as the one I have, produces a strong 250 Hz -400 Hz sound thereabout. The turntable should be isolated from these frequencies too. Sound energy from the speakers excite all surfaces in the room. Every part of the turntable will be subject to compression and rerefaction of air molecules, and set into motion. Coupling could in some cases, worsen this problem. The platter and arm should ideally resonate as a single piece.... although never entirely in practice. The arm has its own mass and resonant frequency which "decouples" from the pivot and platter, but only AT its resonant frequency. (edit: I refer back to my original comment on turntable design as the root cause of resonance problems, and the degradation of clarity and transient response .. see comment below)

    So this bears the question, what frequencies does a sandbox or butcher block help deaden? Some frequencies may be absorbed and dispersed, others could be amplified.

    Air filled isolators or well damped springs tuned to about 2Hz take care of subsonic resonances (converts this energy into heat)
    The turntable plinth itself needs to be anti-resonant. If it "rings like a bell", then perhaps spikes would help to disperse resonances into an acoustically dead platform. The "problem solved" in this instance isn't resolved entirely. The problem is the turntable.

    I go back to my original comment. Coupling is most important in the closed loop of the record groove to the cartridge body. We want as little compliance as possible. The closed loop mechanical system of the platter, platter bearing, the arm pivot bearings, and arm, should be well isolated from outside vibration. For the non-suspended turntable or suspended, (either type) the plinth should be massive as practical and acoustically dead.
     
    Last edited: Jul 12, 2018
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  8. Guth

    Guth Member: Slink Rand Fan Club

    Location:
    Oregon
    In my experience if you want to hear the Rega at its best then save up the extra money to purchase the Rega shelf along with the turntable.

    For what it's worth, I actually can jump up and down on my floor during vinyl playback without problem but look even more goofy than normal while doing so. So I mostly just remain seated on the couch.
     
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  9. chervokas

    chervokas Forum Resident

    Obviously, swapping spikes for original rubber feet only adds mass to the extent that the feet may weigh more and be more massive than the rubber feet. If they add mass at all it's a tiny amount and it's all actually below the turntable not part of the turntable. So, no, adding mass to a turntable can't be accomplished by swapping rubber feet for spiked feet. Tighter coupling between the table and the surface below it is what's accomplished.

    The more tighter coupling you got between the spiked feet and your sand box below it, which presumably was pretty inert and, because it's made with compliant sand, converts some frequencies of movement to heat loss, may well have been the source of whatever improvement you heard in terms of terminating plinth resonances, which is a positive thing, but which is different isolating the table above from structure borne vibrations. I don't know what frequencies a sand box is dampening, I suspect not down to 2-4 Hz, where footfalls could be a problem for someone with springy floors.

    Spiked feet, I have heard asserted, can be like a mechanical high pass filter, passing high frequencies but blocking low frequencies, I don't know if that's true, but if so maybe that can help

    Adding the sandbox to the shelf below it almost certainly mass loaded that shelf below it though.

    As @harby asks above, the salient question is "What are you trying to isolate the turntable from?"

    BTW, you're not really testing a table's isolation from it's environment by tapping on the plinth, you're just testing they length of the ringing of the plinth/arm resonance.
     
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  10. missan

    missan Forum Resident

    Location:
    Stockholm
    The difference was down to the plinth rigidity. The spiked feet added rigidity by help of the plywood. Tapping at a corner of a TT will normally be audible, when resting the needle on a record. It will take a really well designed TT, if tapping at the corner of the plinth, isn´t audible.
    Sand is very good by not having any own resonances, only it´s mass can be seen as part of a resonance; everything else is dampened, by the sand´s motion, to heat.
     
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  11. willboy

    willboy Forum Resident

    Location:
    Wales, UK


    I was just experimenting. I had read that coupling with spikes can reduce the noise floor by transferring internal resonances made by the turntable's motor, bearing, etc down through the spiked feet into the sandbox. With the spikes fitted there was a definite change to the sound, which became more focused, clearer and with a quieter background. It did however lose some body and warmth, which may have been the result of spikes blocking the lower frequencies as you mention. That said, the positives outweighed the negatives for me and I did prefer the sound that the spiked feet produced, though I'm sure some people would think differently. Interesting that you mentioned ringing in the plinth. The DC motor and main bearing on the Rotel RP-855 were very quiet indeed, and I did have my suspicions that most of the resonances were coming from the chipboard box type plinth
     
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  12. sublemon

    sublemon Forum Resident

    true, it depends on a lot of things. But I can say from my experience, at least with less advanced suspended turntables like the Paris and maybe say an AR-XA, that they are more susecptible to footfalls on a variety of typical residential wood floors (wood flooring over wood joists) than non-suspended turntables. Pretty much regardless of the staad they are on. I think it is because if the floor moves enough, the whole stand will move, and the simpler suspension, while being effective maybe in a purely vertical plane, don't work as well if the direction of movement is more angular. or something.
     
  13. Pastafarian

    Pastafarian Forum Resident

    When I had a LP12 the best table was light and rigid. On a wooden floor the test would be jump as high as you can and land as close to the table as possible. The effect on the turntable none, however that didn't mean it was immune from the frequencies your Hi-Fi is pumping out.

    Now I isolate my equipment using the Bamboo shelf and inner tube method, to great effect. In terms of material which is effective PEEK Polyether ether ketone - Wikipedia

    I've heard very good reports for these cones: MusicWorks P-Cone equipment isolation

    My advice would be try the inner tube under the Bamboo, that should be a total cost of around £10 and don't have it on that piece of furniture if at all ppossible
     
    Last edited: Jul 12, 2018
  14. KT88

    KT88 Forum Resident

    That sounds like what should occur with typical tables. The box type "plinths" of many designs can resonate, and using spikes on the base couples and increases energy transfer efficiency back and forth between the stand. Having sand under the stands top shelf soaks that energy away from the table and also prevents a lot of HF energy from reaching the table through the stand. Extemely low frequency energy should just move the entire stand, sand box and all, so the arm and record interface could be effected by that energy. It's way better than not using the sand in most situations.
    -Bill
     
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  15. Paully

    Paully De gustibus non est disputandum

    Location:
    Alabama
    Attaching a shelf to the wall was mentioned. I did it this way and have been very happy with the results.

    [​IMG]
     
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  16. Guth

    Guth Member: Slink Rand Fan Club

    Location:
    Oregon
    I mounted the Rega shelf to a nice solid piece of oak that I had painted black to match the rest of my audio shelving setup. That way I was able to mount the piece of oak directly to the wall studs to make things extra solid. If I owned a turntable other than a Rega I might have gone about things differently, but in this case Rega themselves provided me with the best way of managing things so I went this route. I too am very happy with the results, and that's what it's all about.

    [​IMG]

    [​IMG]
     
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  17. JOnny Cox

    JOnny Cox Member

    Location:
    Bridgend
    I’ve just put an IKEA Aptitlig board under my table and isolated from my oak unit with cork dots. Wondering how much isolation is best? I’ve got approx 15mm at back but only 3 mm at front (to get table perfectly level). Is this enough. I’ve not actually listened to it yet either.
     
  18. Madness

    Madness Forum Resident

    Location:
    Maryland, USA
    I have a sort of combination of coupling and isolation. I have a wood shelf unit with isolation pads under the feet, but my turntable has the spiked feet. Should I isolate the turntable as well, or am I good?
     
  19. Jeffreylee

    Jeffreylee Rock 'n' Roll Typist

    Location:
    Louisville
    The "hi-fi kind" are common industrial vibration control pads. They're available on Amazon or eBay for a fraction of what they cost when rebranded by an audio manufacturer. I've had some luck using them, although they aren't helping much underneath a bamboo cutting board that's holding an AR table.
     
  20. willboy

    willboy Forum Resident

    Location:
    Wales, UK
    Well worth a read..... Technology: Drainage and Isolation/The Cone
     
  21. Gibsonian

    Gibsonian Forum Resident

    Location:
    Iowa, USA
    I like to isolate from things that move and couple to things that don't move.
     
  22. Ilovefooty

    Ilovefooty Forum Resident

    I recently bought myself the Auralex Iso-Tone Turntable Isolation Pad. It worked wonders on my Kuzma Stabi Reference.
     

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