Nsgarch has been right in everything he has suggested.
The constrained-layer-damping is a nice touch and will certainly avoid any possible feedback problems into the shelf itself, but once you have your turntable on spikes, on a properly executed wall-hung shelf, 95% of all Structure-Bourne feedback (the real killer in audio) will be eliminated.
It helps to have metal supports from the wall and timber or timber/combination for your damped shelving.
Air-Bourne feedback is resolved in the design of the turntable/arm/cartridge themselves and will rarely be a problem if SBF is eliminated. |
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!" ;--) |
"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."
Nsgarch: Thanks very much for posting this. As I mentioned earlier, I have an older style Target wall mount that I acquired recently. The MDF shelf was warped and I've never been fond of MDF on its own anyway so ended up buying an appropriate sized piece of 3/4" baltic birch at first before experimenting with extruded acrylic as a shelf (using a Michell Gyrodec).
The acrylic had much better sound quality than the baltic birch but the plastics fabricator sold me a 3/8" inch thick piece when I probably should have gone for 5/8". In any event, the 3/8" flexed a bit under the weight of the Gryo which I was not super comfortable with.
I've always really wanted a Neuance shelf, but alas, Ken Lyon is no longer producing them, so after reading your post above I went out to an upholstery shop to seek out some high density foam. Ended up with 1/8" high density neoprene foam (it can actually be rolled up very tightly and will stay that way, almost like a piece of fabric) and then bought a piece of 3/8" baltic birch. I bought adhesive but actually never used it. The configuration is table, 3/8" acrylic, neoprene foam, 3/8" baltic birch onto the spikes of the target wall mount (metal blanks under the baltic birch at spike points).
My "sag" with the acrylic on its own has been eliminated; I was a bit surprised at the improvement in sound quality. The "constrained layer" shelf is definitely doing its job. Improved high and low frequency performance and a much more transparent and natural sounding midrange. The key words are natural sounding. The baltic birch on its own, as well as higher mass phenolic shevling were a bad match with my Gryo, "enhancing" detail but at the same time considerably hardening up the sound. Glass, marble and granite on their own all have similar, even nastier qualities.
In short, $10 for the neoprene high density foam and another $10 for the baltic birch combined with the acrylic I already had have worked together to make a very good shelf.
Thanks for the info. |
"Unfortunately, the tie-back solution is mostly effective against F/B movement. Much less L/R movement, and not at all for vertical movement."
When I've screwed fasteners from the bracket into the shelf and into the wall, and done so at either end of the shelf, f/b or l/r simply didn't occur. Might as well have been on the wall.
Also helps to mitigate vertical vibrations, but not entirely.
Total expense for this "fix" is under $10. |
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 ;--) . |
Kenny: That's too bad. That would move me very quickly away from the wall mount as well! I have an older Target wall mount, the one which Nsgarch described with triangular bracing. It is solid as a rock. Too bad that Target has cheapened the product. |
I earlier in this thread recommended the Target wall shelf, only bcause it works, and it's cheap (relatively). To level the top shelf, I placed a 3/16" thick! steel bar behind it, with a backing of sorbothane. It pissed me off, I thought the damned thing was made in England, maybe it is, but whoever built it did a piss-poor job if it.
Dan |
Hi Hdm!
Hdm -> "Kenny: When you say the Target Pro shelf "flexed under the load" are you saying that the rack itself flexed or the shelf material (MDF shelf)."
Yes, the shelf itself flexed and I was within the maximum weight load. It's possible that the shelf was defective but I did not get a response from Target. If you email me I can send you pictures.
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.
The flexing scared the "%@#!" out of me and I didn't care for the sound. I could not adjust the front leveling screws to bring the table up to level. The pictures are very revealing. |
My previous apartment had a cement floor, so I never had a problem with my TT on top of the rack, but I moved into my girlfriend's pre-war apartment and I got bad vibrations if anyone walked near the rack.
This past weekend I put up a Target Pro shelf and it works great- you can jump up and down and nothing happens. I recommend going back to the shelf. |
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! |
Having faced this issue countless times, the only technique that consistently works is to fasten a 90 degree shelf bracket (which you can buy or fabricate yourself) to the top shelf at the back and to the wall. This will cure 95% of the problem.
Failing that, even wedging something between the wall and the back or the rack/shelf can help a bit, until it falls. :)
A vertically suspended turntable such as a Linn on the top shelf that is susceptible to footfalls is actually having to contend with some horizontal movement, which it cannot handle. |
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.)
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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!
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Kenny: When you say the Target Pro shelf "flexed under the load" are you saying that the rack itself flexed or the shelf material (MDF shelf).
If it's the rack itself that's flexing, I'd say dump it. If it's just the shelf material you could experiment with a number of different types of shelf materials (some more expensive than others-but some very cheap) that will give you different sound qualities and definitely will not flex.
The MDF is pretty crappy and a definite weak point with the Target rack, both from a structural and sound quality standpoint. |
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Just my opinion of course, but if you have a suspended floor, it is going to be awfully difficult for you to obtain the performance you were achieving with the wall mount, so my suggestion is, unless it is impossible, go back to it.
Secondly, my experience is that with a suspended table you want light and rigid for the shelf material. With non-suspended tables massive like the granite may be ok, but granite rings like crazy so it should be damped if used at all. Personally I don't like what it does to the sound, especially without damping.
If you want to create a shelf for your rack, given the suspended table, I would look at having a shelf cut from 5/8" extruded acrylic. If it can be placed directly on the rack (replacing the existing glass or mdf shelf) you could try that. Alternatively you could try the vibrapod sandwich, with vibrapods under the acrylic shelf on the top shelf of the rack but that would be my second choice (third actually, as going back to the wall mount-with a custom acrylic shelf for it-makes the most sense.) |
Thanks for all the great responses.
Buconero117: I am fortunate that the turntable is in a closet so in room vibrations, especially airborne are probably less of an issue
Nsgarch: I whole heartedly agree with you in regards to wall mounted tables. The change from going from the Target shelf to the rack is the source of all this heartache. If i was not so stubborn i would remount the wall shelf in a second. As it is i am going to try to work through the rack positioning to hear if i can improve anything. My strategy is to position the TT on the granite slab which in itself is mounted on 4 isopads placed on the top shelf of the rack.
I know from experience that increasing the mass on the top shelf of a structure / rack helps to dampen lateral forces.
I will report back once i have given it a try |
A lot of good comments, but one is missing, so I will add it. Acoustic shield around the table. The sound engery that is in the room will directly impact the table, arm and cartridge. Play some music in the room from a different source and put your finger on the pith, arm and cartridge. You are bound to feel the vibration the acoustic engery that is flowing all over the TT. Just think what is happening when you are actually playing a record, the speakers vibrate via acoustic engery everything. In the interest of full disclosue, I am in the process of marketing 'acoshield', the solution to fixing this problem. |
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!) |
All very good points, Ns. The wall mount is the easiest, most effective (for the price) solution. I considered it worth a try in Neil's situation, first without the wall-mount. I have seen this method used on top of racks and table supports that were located on the floor. The supplier of the information insisted the isolation was effective. I know only that with my installation, the results have been superb, the arm and plinth drain into the Brightstar, and the springs isolate the table. The wall mount is however, a major contributor to its sucess.
My judgement is that it is worth a try, not much cost involved, and may be retained and used in the final solution.
Regards,
Dan |
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!
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I have a modest analog front end, but I have been able to maximize it's performance with isolation. You may be able to use your granite slab to do this. I use a Brightstar Audio BigRock2, (a sandbox, basically), which is supported by four steel coil springs. I am using a wall-mount support, but I believe it will work on your stand. I installed brass spikes to drain vibration into the box, but in your case, more isolation between the plinth and sandbox might be the better approach. It sounds strange, your table being supported on springs, but you soon get used to the motion when touching the table. I do think in your case, the sandbox might be indispensable.
If you try it, I think you may be surprised at how much relief you will get.
Regards,
Dan |
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 |
