TT's in general, and especially ones w/ floating sub-chassis like the Linn, are always suceptable to bouncy floors. I don't care how good/expensive a rack or isolation platform, when it comes to external vibrations, they will bounce right along with the floor, period.
Unless your house has a nice thick concrete slab-on-grade floor, or you live in an old factory loft with steel-reinforced concrete floors, your best bet is a wall shelf.
And there is no way to take the bounce out of a wood joist floor except to tear out the floor ad rebuild it with deeper, more closely spaced joists, and/or provide an intermediate support beam underneath to reduce the span of the existing joists to half their present span.
Neil |
I think most folks are unclear about TT isolation/absorbtion. Things like spikes, roller blocks, Stillpoints, iso-platforms, etc. will drain away vibrations created by the TT mechanism (and I suppose the cartridge itself ;--) but these values should are hardly even measurable. Certainly not if the TT has decent bearings and motor drive. Vibes in the actual vinyl record created by the stylus should be damped by the platter (mats and/or clamps are what you want for that.) Vibes and impulse energy coming TOWARD the TT (like from foot falls, or bouncy or resonanating floors) are VERY hard to stop and here's why:
First these vibes come in all different frequencies and no one material --springs, sorbothane, hydraulic damping feet, rubber bands (like on the SME) -- can block them all. In fact, some of them can do more harm than good if they happen to naturally oscillate at one of the incoming frequencies!
And second, any mechanism that would have a low enough resonant frequency would have to be so big as to be impractical in a home environment. Just look, for example, at those HUGE spring frames in which they suspend (relatively small) microphones in recording studios. Can you imagine a turntable-sized contraption!?
That's why we have wall shelves ;--) I have seen a few audiophiles construct concrete block piers, or pillars, filled with sand, right on top of conrete slab floors in their listening space(s). However, it does require an extraordinary commitment to the location, ha, ha!
. |
I guess my point is that any top-of-shelf/under-TT treatments, if they appear to work, do so because you already have a rock solid floor, and a rock solid rack (like a Billy Bags TT stand.) But if you have a bouncy floor, it's just going to take the rack and all that other stuff with it.
To me, a solid floor is everything, and when the floor can't provide it, then you need a wall shelf (and hope and pray that the wall doesn't vibrate!) |
A couple of comments:
When I think of Target wall shelves, I'm thinking of their original design with the angled side braces. This "triangulated" design is a structurally braced shape, deriving its strength from its geometry.
The current Target design(s) use a "box" frame which is only as good as the welded connections, the shear strength of the weld itself, and the metal tubing's ability to resist bending. If I had to buy the current model, I'd take it to a welding shop and have some angle bracing installed on each side. Just look at Billy Bags designs -- every damn thing (except their little 2020 amp stand) has diagonal bracing.
Steel is the ONLY material for the BEST structural rigidity. Titanium and magnesium are better in the strength vs. weight department -- not an issue in audio (usually ;--)
A truly rigid connection between dissimilar materials is impossible because it will be mechanical, not monolithic like a weld. Further, mechanical connections almost always involve a third material like glue, or screws. This eventually leads to loosening of the joint, due to movement, structural stresses, thermal expansion, and variations in humidity. Anyone who thinks they can make truly RIGID structures out of any material that can't be welded is just nuts IMO; they are depending on intuition without knowing anything about physics and math. Intuition is useless, even when you get a lucky break, because you can't go back and figure out why it worked! (Simply PLACING a wood, corian, acrylic, granite, etc. shelf on some kind of rigid steel frame is not what I'm discussing here.)
------------------------------
Acoustic isolation of a TT or other object from airborne sound (pressure waves) is another fantasy. Oh yes, sonic pressure waves do indeed exist, but they exist in a gas (air) which means they propagate in all directions -- unless you are literally on top of the source. And they exert the same pressure on all surfaces of an object, if that object is fully inside the space where the sound occurs. Floors and walls are a different story. When they vibrate, it's because the pressure on the other side is different; usually lower.
So if a TT is "dancing to the music" it's because the structure that it rests upon, (along with everything ELSE one has contrived to stick under it,) is all already resting on a moving platform: the floor!
. |
Hornguys, you are talking about what's generally referred to as a "tie back"; tying the top of something that's swaying, like an equipment rack or a tall panel speaker, to something that isn't swaying (we hope) like a wall! This can be a good solution. It depends.
Let's take racks first. If a rack is on a concrete slab floor and it still sways, it is a poor design. The worst offenders are the threaded rod type, because the rods themselves aren't fat enough to resist bending and there's virtually no moment resistance in the rod/shelf connection. There is a way to cross brace these racks, but for the time and money involved, sturdier racks are available for less money.
If the rack is quite sturdy like a cheap Studiotech, or a pricey Billy Bags, it can still sway left-right, or front-to-back on a joisted wood floor. L/R if the joists run perpendicular to the wall behind the rack, and F/B if they run parallel; ditto for loudspeakers.
Speakers should not be allowed to sway F/B even a millimeter (at the top) because it can ruin transient response. If a speaker sways a little bit L/R (joists running perpendicular to the wall behind) it's not a big deal performance wise.
Unfortunately, the tie-back solution is mostly effective against F/B movement. Much less L/R movement, and not at all for vertical movement. I have my MartinLogan panels on Sound Anchor stands which have triagulated bracing (see system) but before that, I had their tops tied to the back wall by a 6 foot length of 3/4 inch white PVC pipe. The improvement in soundstage and lyrics intelligibility was amazing! |
Previously, I had used an older Target shelf with a SOTA table but I needed the Pro shelf to accomodate my new table. The old Target shelf never flexed but it was designed differently. Kenny, that's exactly what I was referring to 6 posts ago ;--) The original version IS BETTER As for leveling the shelf surface itself, before installing the wall shelf against the wall, put a 3 foot or longer carpenter's level against the wall (vertically) and check to make sure the wall isn't leaning in or out!! It's a lot easier to shim the whole shelf (frame) at the wall than it is to try and level the (horizontal) shelf surface later on. Dan, for what it's worth (and I've been using Target wall shelves since 1990 ;--) one of the best (and easiest) mods one can make to the MDF shelf that comes with the unit is to make a "constrained layer" damped shelf out of it. Start with a second sheet of denser material the same size as the MDF shelf. I use 1/4" glass, but you can use Corian, acrylic, granite, aluminum -- whatever, as long as it's a harder than the MDF. Then get a sheet of 1/8" - 3/16" thick (maximum) dense foam or sheet sorbothane. Spray the bottom surface of the MDF and one surface of the second material with 3M 88 Spray Adhesive and press the sandwich together, place it on a flat surface and set a couple of cinder blocks, side-by-side on top for 8 hours (you want the adhesive to dry out under pressure!) You now have one of the best constrained layer damping systems in the world! If you can use spikes under your TT, that will increase performance even further. How it works, is that the vibes drained off the bottom of the TT (by the spikes or feet) travel more or less straight through the MDF (and are just partly absorbed by it) but the MDF itself can't vibrate because it's sitting on something hard and unyielding. When the vibrations exit the MDF and hit the constrained (i.e. mostly squished) layer, they are forced to travel horizontally through the foam or sorbathane until they dissapate. You can pay more but you can't get a better shelf. All by itself, the MDF shelf will bounce (too little for us to see or feel) but it won't absorb! It will transmit the vibes to the metal structure and possibly refelect some back to the TT. That is NOT what you want ;--) . |
HDM, it's very nice of you to confirm my advice ;--) I'd further suggest that you get a thicker piece of acrylic (definitely 5/8 or even 3/4), and do bond the sandwich together under pressure. If you do that, then try flipping the sandwich over (birch on top thicker acrylic on the bottom) and see which you like best. Not saying that it will be better (having the birch on the bottom right now may offer just a little more flex resistance when using it with just the 3/8 thick acrylic) ) but I always say (especially with audio), "Leave no turn un-stoned!" ;--) |
