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Let's talk about speaker coupling/decoupling, isolation, etc.

 

Silver Member
Username: Kbear

Canada

Post Number: 614
Registered: Dec-06
I've done a bit of reading on this subject, hoping now to set my speakers up properly on their stands. There seems to be a bit of confusion on the various forums. Specifically, do you want to couple or decouple the speakers, and how best to do it.

I think the answer is to some degree personal. It'll depend on the sound you want to achieve and the room the system is in. Generally though, from what I gather there are a couple of things you would normally want to do...

1.
Speakers should be on as stable and secure a surface as possible. This is normally done by putting them on stands that are coupled to the floor via spikes. Many online seem to think spikes decouple by making the contact point as small as possible, and of course there are many products out there sold as isolation devices that use spikes to do the job. Most discussions I've read make me lean to those who believe that spikes in fact couple, not decouple or isolate.

2.
With stands coupled to the floor via spikes, now the consideration is how to place the speaker on the stand. I gather what you want now is decoupling, but more on that a bit later.

As the woofer moves in and out, this causes some force to be placed on the enclosure and it too moves (even just if very slightly). It will move in the opposite direction of the driver, and thus any movement kind of cancels out some of what the driver is doing. Therefore, the speaker needs to be fixed in place on the stand. Spikes may do this, but spikes couple, essentially making speakers part of the stand. Any vibrations will be transmitted through the stand and to the floor (recall that the stand is coupled to the floor). Now perhaps some stands totally kill all vibrations 100%, but I'm not sure if such a stand exists.

This gets me to what I mentioned above, that you want to decouple the speaker from the stand. So we mus isolate the speaker and fix it's position on the stand, and have the stand anchored to the floor providing a solid foundation. Maybe this is overkill, most stands will do a pretty good job killing resonances after all. But why not decouple and just ensure the job is done to it's fullest potential?

I've had some decent luck with these self-adhesive vinyl pads I buy at the grocery store for about $2. They are soft and kind of rubbery and so probably do some isolating. Blu-Tac I'd think accomplishes the same sort of thing, but also provides more stickiness to the stand and so fixes the speaker in place a bit better.

But this could be taken further. What about Isonodes? They are thicker and surely isolate better, and feel like they'd fix the speaker in place quite well. Or Auralex MoPADs. To me these almost seem like they'd accomplish the job better than other options. http://www.auralex.com/sound_isolation_mopad/sound_isolation_mopad.asp I don't think the speaker is going anywhere, and surely the pad is a great isolation device.

I'd love to hear everyone's two cents about this and the methods that you personally favor.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 14804
Registered: May-04
.

"Speakers should be on as stable and secure a surface as possible.


Yes, undoubtedly so. Or, at least, according to the prevailing wisdom of the day that would be so.




This is normally done by putting them on stands that are coupled to the floor via spikes. Many online seem to think spikes decouple by making the contact point as small as possible ... "


Depending on who you ask, spikes do several things at once, which is pretty good since the requirements for most components demand several conflicting actions be performed simultaneously. Most will concede that spikes and cones "mass load" the device which they support. By placing the entire mass of the stand (in this case) on the extremely small surface area contacted by the tip of the spike the mass of the item is concentrated much like the tip of a stylus or the toes of a ballerina when she is on pointe. The supported component now increases in virtual weight by magnitudes. This concentration of mass makes for a more stable support system as any motion introduced into the system must then move the equivalent of several hundred pounds of weight concentrated on those spiked tips. In this sense, spikes couple the system to the floor or support shelf.

At the same time, spikes also decouple the stand from motion introduced by the floor itself by minimizing the footprint of the spike's tip. Not only is the mass concentrated to make the transfer more difficult but the available surface area is minimized which means there isn't much opportunity for mechanical energy to find an easy path upward. In this respect spikes and cones operate as mechanical "diodes" allowing motion to travel easily in only one direction.

To that extent spikes and cones can be made to couple the supported component to the stand. This mechanical coupling then allows for vibration and resonance to be bled away by entering the larger surface of the cone or the mechanical interface of the spike and traveling to the tip - which should be mounted on some sort of drain or sink which can remove, transfer, absorb, etc. the motion by means of a larger, less resonant surface or a surface of a differing resonant value.




" ... and of course there are many products out there sold as isolation devices that use spikes to do the job. Most discussions I've read make me lean to those who believe that spikes in fact couple, not decouple or isolate."


Spikes are less flexible in this respect than cones or "TipToe" like devices. Spikes can only generally be mounted in one direction depending on the orientation of the threads to which they attach (through-threads make options available). Whereas cones can be turned tip up or tip down without concern to threads.

Tip down the cone acts as a diode which decouples (in one direction only) the component it supports from the shelf or floor it rests upon. This would be your choice if the shelf or floor is somewhat too highly resonant and you want to minimize motion entering the component from the shelf or floor.

Tip up, the mass loading effect is still there to some extent but now the component has no drain available through the spike or cone. This would be your choice if the shelf or floor is not a highly resonant surface or, if the shelf or floor are resonating at a substantially different frequency than the component or stand. This has flaws, however, should the supported component produce movements which need to be drained away from the component's chassis or the component benefits from a tip down spike/cone's ability to fix the component in space.


Keep in mind there are several directions for movement to enter and exit a surface. Most physicists will talk in terms of six "vectors" of motion. Spikes and cones are only effective in one, two or a maximum of three directions depending on their number and placement.




"With stands coupled to the floor via spikes, now the consideration is how to place the speaker on the stand. I gather what you want now is decoupling, but more on that a bit later."


This becomes a "suck it and see what comes out" scenario with each speaker preferring one or the other or, occasionally, both coupling and decoupling as well as isolation from other forces.



"As the woofer moves in and out, this causes some force to be placed on the enclosure and it too moves (even just if very slightly). It will move in the opposite direction of the driver, and thus any movement kind of cancels out some of what the driver is doing."


That's the general assumption of how drivers work when they are mechanically coupled to the baffle of an enclosure. In a very few cases the drivers are intentionally decoupled by designer's use of a lossy compound placed between the driver and the baffle. Also, not all drivers sound their best when tightly coupled to a baffle by overly tight screws or bolts. Some speaker systems sound much better when the screws are backed off a few degrees which lessens the transfer of motion to and from the baffle. For all the good things MDF is capable of at a very cheap price, it also tends to kill the sound of anything attached to it. How well the enclosure deals with its own resonances might determine whether you prefer to couple or decouple the enclosure from the support surface.



"Therefore, the speaker needs to be fixed in place on the stand. Spikes may do this, but spikes couple, essentially making speakers part of the stand."


First, when you say, "spikes couple", go back to the beginning of this post. Spikes and cones offer choices and it's up to you to decide which choice is best for your speakers. However, if you make the decision to use spikes to couple the speaker to the stand and benefit from the highest degree of mass loading, then the speaker should be situated so as to make the speaker and stand appear as one. When you push on the speaker from any direction it should feel as if it is bolted to the stand. If you then choose spikes, cones or ball bearings* to mass load the stand to the floor, the same will apply to the stand. When it is properly adjusted the stand should not respond to any of your pushing and prodding, it should remain fixed in space as if it were bolted to the floor.



"Any vibrations will be transmitted through the stand and to the floor (recall that the stand is coupled to the floor). Now perhaps some stands totally kill all vibrations 100%, but I'm not sure if such a stand exists."


It's not necessary to "kill" vibrations completely in the stand. To begin with, you cannot "kill" energy, you can only convert it to another form of energy. A mass loaded stand with high damping capacity will turn the mechanical vibration into heat and as long as whatever residual is allowed to be drained to the larger surface of the floor by way of spikes or cones there should be no problem at the speakers. Proper construction of the stands permits the drain to be effective. Improper construction, of course, simply makes matters worse.

The question then becomes one of whether the speaker prefers to have the energy from its driver sent to a large mass like a fully loaded stand. Mass by itself is a selective filter which typically functions as a low pass device, whatever the mass cannot convert to another form of energy is allowed to pass through. Small, quick movements are more easily damped by sheer mass than are large, long waves which tend to remain within the mass momentarily and finally exit out of time synch with their entrance. Another way to deal with unwanted motion or resonance is to utilize light but rigid devices which allow all wave lengths to pass quickly while remaining in synch with what is then occurring in the system. Such devices normally have resonant frequencies much higher than would large, massive systems and/or lossy systems and the designer attempts to place that higher resonance in a range where it does less harm to the overall sound.




"This gets me to what I mentioned above, that you want to decouple the speaker from the stand."



Only in certain circumstances do you want to decouple the speaker from an effective stand. In most cases in today's market, you'll probably do better to both couple the speaker to and isolate the speaker from the effects of the stand.



"So we mus isolate the speaker and fix it's position on the stand, and have the stand anchored to the floor providing a solid foundation. Maybe this is overkill, most stands will do a pretty good job killing resonances after all. But why not decouple and just ensure the job is done to it's fullest potential?"


As I said, generally, you want to do both. Realize that should you decouple the speaker from the stand you still might not have isolated it from the effects of the stand. Remember, we talked about the many directions movement can enter the stand or speaker.




"I've had some decent luck with these self-adhesive vinyl pads I buy at the grocery store for about $2. They are soft and kind of rubbery and so probably do some isolating."


Not knowing what these pads are it's rather difficult to comment on their efficacy. However, generally speaking, "rubbery" is not what you want under your speakers. You provided the logic for this earler when you said the drivers induce motion in the enclosure. The point of anything that fixes the enclosure in space is to eliminate this random motion in the cabinet and a subsequent loss of information from the drivers. While rubber is effective at some tasks it is generally only effective in one direction at any one time. Further, once rubber allows motion to occur, it can have unpredictable damping which might allow the component it supports to continue oscillating for long periods of time.




"Blu-Tac I'd think accomplishes the same sort of thing, but also provides more stickiness to the stand and so fixes the speaker in place a bit better."


BuTak and PlastiTak do one very important thing when placed between a stand and a speaker, it restricts motional transfer in several directions at once. It first of all couples the two surfaces together by way of its molecular structure which gives it a virtual adhesive quality. The material itself is not particularly "sticky", what you are feeling is the molecular structure resisting your attempts to make it perform in ways it was not designed to operate. By the "restricted looseness" of its molecules it resists motional transfer in the vertical plane which minimizes any transfer of energy from the stand to the speaker. A speaker attached to a stand with BluTak, however, gains many of the same benefits in terms of the stand acting as a damping device as it would through the use of screws or bolts. Most importantly, it resists any shearing effects, meaning it has a strong resistance to specific types of motion in several horizontal and twisting vectors. This provides the stability the cabinet and the stand require to not be pushed around by the driver's energy. Two additional benefits are the material never completely dries out so it is as effective after years of service as it is on the first moment of contact. And, should you need to remove the material for any reason, it can be lifted with a sharp twist to the component.




"But this could be taken further. What about Isonodes? They are thicker and surely isolate better, and feel like they'd fix the speaker in place quite well."



I am unfamiliar with the specific make up of "Isonodes" but they appear to fall into the same category of materials as Sorbothane. Once the darling of audiophiles, Sorbothane has mostly fallen out of favor in many uses due to its unfortunate ability to overly damp whatever it is attached to or supports. Such materials also still suffer somewhat from the same problems as rubber in that they allow too much horizontal and shearing movement resulting from the energy of the drivers. None of that means you might not prefer the "sound" of the speakers being supported by Isonodes, but I would tend to make these devices less important in my experiments with speakers and stands. Natural cork (preferably without rubber mix ins) pads would be far and away my first choice over the more expensive Isonodes.




"http://www.auralex.com/sound_isolation_mopad/sound_isolation_mopad.asp I don't think the speaker is going anywhere, and surely the pad is a great isolation device."


The MoPads were designed to decouple near field monitors from the mixing/monitoring desk. Their benefit, as I understand it, is to keep speaker induced vibration from entering the mixing board. While this might be effective with certain small monitors, I would tend to think most speakers are going to prefer a system which couples the speaker to a drain device.




*Ball bearings have several important advantages in coupling and decoupling. Most importantly, their shape means the contact area between surfaces is similar to that of a spike's or cone's tip with only the most minimal contact at the exact tangent of the sphere. If you provide sufficient resistance to the surface of the bearing, you can achieve both coupling and decoupling at simultaneous moments. Chosen correctly, ball bearings offer options neither spikes nor cones can manage.


.
 

Silver Member
Username: Kbear

Canada

Post Number: 615
Registered: Dec-06
The MoPads were designed to decouple near field monitors from the mixing/monitoring desk. Their benefit, as I understand it, is to keep speaker induced vibration from entering the mixing board. While this might be effective with certain small monitors, I would tend to think most speakers are going to prefer a system which couples the speaker to a drain device.

I would have thought the MoPad itself was a drain device. By preventing energy from entering the mixing board (or whatever the speaker is sitting on) hasn't it effectively fulfilled that role? Auralex recommends these devices for use on speaker stands as well. I wonder what effect using a folded up towel to rest the speakers on would have, if that would be similar to the MoPads. It costs nothing to try I guess. A towel isn't sticky like BluTak and therefore probably wouldn't be as effective against enclosure movement.

I guess my area of concern is that if the stand is there to convert energy to heat, and then pass on what it cannot to the floor, how much of that energy do we really want it passing on? After all, aren't we settling on having it pass some to the floor only because it isn't able to convert it to heat with 100% effectiveness? Is the floor an effective device against these waves? As you mentioned Jan, it would be the longer waves that reach it. I can hear this on deep bass notes. It doesn't sound bad or anything and perhaps it actually enhances the feeling of bass, but I wonder if I should strive to eliminate all of this energy from reaching the floor, rather than say 80% of it.

The other question that popped into my mind about BluTak is where you mention that it resists energy transfer on the vertical plane, and so resists the transfer of energy from the stand to the speaker. Would it not therefore similarly resist the transfer of energy from the speaker to the stand, undermining it's role as a coupler? Does the energy actually remain in the speaker then? Of course, BluTak is unlike spikes in that it does not have a larger surface area on one end and a smaller surface area on the other.

I have a set of Isonodes that I haven't used yet, that I will probably try under my amp and CD player.
 

Platinum Member
Username: Nuck

Post Number: 14900
Registered: Dec-04
As far as I can tell, the BluTak has a benign transfer of energy in the vertical, or loaded plane.
The horizontal transfer, or in a shear plane, is nulled by the makeup of the BluTak.

Taken to a Nuck level, maybe look at the way that a piece of moose is carved, with the best draw coming against the grain, as opposed to with the grain.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 14807
Registered: May-04
.

"I would have thought the MoPad itself was a drain device. By preventing energy from entering the mixing board (or whatever the speaker is sitting on) hasn't it effectively fulfilled that role? Auralex recommends these devices for use on speaker stands as well."



I suspect if Auralex thought they could sell it, they would suggest these devices for your toilet seat too. I don't know the material composition of the pads so it's difficult to say with certainty how they perform their job. They would appear to be made of the same closed cell foam material Auralex uses in their damping panels. In which case, I would expect them to have some damping effect similar to foam rubber but also possess some of the drawbacks of foam rubber. Without knowing more specifics of the material I really can't say exactly what the pads do or how they do it.




"I wonder what effect using a folded up towel to rest the speakers on would have, if that would be similar to the MoPads. It costs nothing to try I guess. A towel isn't sticky like BluTak and therefore probably wouldn't be as effective against enclosure movement."



You said it yourself, Dan, "Speakers should be on as stable and secure a surface as possible." I wouldn't consider a folded up towel to be a "stable" surface nor would I expect it to perform as a broadband filter device.





I guess my area of concern is that if the stand is there to convert energy to heat, and then pass on what it cannot to the floor, how much of that energy do we really want it passing on?"


As little as possible allowed by your budget and your aesthetics. The more you are willing to spend, the more sophisticated the stand you can afford and the better it will be at accomplishing its goal. That takes you from a pair of MFD stands screwed together by the user for $19.95 to some stands which can cost upwards of $1K. For the most part, you get what you pay for.



Earlier I posted, " Proper construction of the stands permits the drain to be effective. Improper construction, of course, simply makes matters worse."

Substitute "expensive" for "proper" and "cheap" for "improper" and the same is still true. Concrete blocks are still one of the most effective stands and one of the cheapest but not one of the most aesthetically pleasing or flexible. Sound Anchor did, and I believe still does, build stands filled with cement and a few proprietary compounds. They outperformed virtually any other stand in most cases while being more expensive also.


If you can literally anchor the top plate into (not sitting on top of) a 3" box of sand, you'll have a very effective device. It might prove too much for some speakers but you'll only know that after you try it.



The point is effectiveness costs money or ingenuity or both. If you have the money, buy very good stands, they will pay off in ways no other investment can. If you have a budget, then accept that some energy will exit the stand and your job is to select the stand that does the best job for the available money.




The other question that popped into my mind about BluTak is where you mention that it resists energy transfer on the vertical plane, and so resists the transfer of energy from the stand to the speaker. Would it not therefore similarly resist the transfer of energy from the speaker to the stand, undermining it's role as a coupler?"



"By the 'restricted looseness' of its molecules it resists motional transfer in the vertical plane which minimizes any transfer of energy from the stand to the speaker."

I thought that statement might get some questions. You're misreading the statement, Dan. What BluTak accomplishes is to become a very thin layer of "adhesive-like" material between the mating surfaces. At most you neeed about a pea sized blob for any speaker or component which will spread out to about the thickness half that of a Kleenex. This thin layer of material is an effective damping device as it doesn't transfer energy through its depth with ease. Therefore, any energy moving upward from the stand to the speaker is damped before entering the speaker. Likewise, in the opposite direction, energy at the speaker enclosure is damped as it passes through to the stand. This makes the BluTak unlike rubber in that it damps energy but does not allow for a spring effect between the surfaces. That's not to say BluTak damps all energy, it cannot in most speaker/stand applications. (Keep in mind this material was sold originally for mounting photos to paper, not as a damping material.) It secures a bond between the two surfaces which allows for the transfer of energy from speaker to stand. It then relies on a well designed stand to remove the energy sent there by the speaker.

A well designed stand resists transfering energy back into the speaker by acting as a drain in one direction only while (usually) adding internal damping material(s). It also resists airborne excitation by employing a powder coated damping material on the surfaces of the stand. IOW a good (preferably spiked) stand does not transfer energy back into the speaker.


You can try a sheet of drawer liner if you care to. Buy the thinnest material you can find, about the thickness of a few sheets of paper. It has many of the same properties (without the science of course) as does BluTak. It damps and it couples without the spring effect of foam rubber or incomplete action in the horizontal direction of thick rubber pads. You can buy it at the hardware store where it is sold to hold work pieces in place while you use a router, if that gives you an idea of how effective it can be. As shelf lner it should cost you about a buck at the $1 store to try. If it doesn't work under your speakers, you'll probably find another use for it in the system somewhere.


Remember, Dan, there are no absolutes I can give you. Each speaker and stand combination will require your exprimenting with various techniques to ascertain which works best for your application. Sometimes speakers work best when they are secured to a stand with spikes or somtimes BluTak and sometimes they are better left undamped and quick to diminish energy in their own way. If there were only one answer, Dan, I would be happy to provide it. But there isn't and that's why there are numerous devices sold and DIY'd for just such applications.

As usual the "suck it and see what comes out" advice remains the most effective answer to all the possibilities of speaker/stand interfaces.



My op was meant primarily to clear up the confusion regarding what spikes do.




.
 

Silver Member
Username: Kbear

Canada

Post Number: 616
Registered: Dec-06
Thanks Jan, this has been very informative. I think Nuck, you alluded to the same answer that Jan later gave.

My first pair of speakers came with those vinyl pads, I had to stick them on myself but they came with the speakers. They may have been included as a convenience to protect furniture or something, and not for sound quality reasons. My second pair did not come with them at all and so I when I found them at the store I purchased them and thought they did a pretty good job. Of course, I didn't have proper stands at that time. The desk I used them on isn't very resonant.

I've tried BluTak under my Quads but felt the speaker sounded better without it. Maybe that's as you said Jan, that some speakers will sound best if you let them pass along energy in their own way. Unlike my previous speakers, the Quads already came with pads stuck on the bottoms, so I would think this is as Quad intends them to be placed. The pads aren't sticky at all though. When using the BluTak I used it right under the pads, so that's two damping materials placed together, perhaps not a good idea. BluTak may work better on a speaker that comes with nothing on the bottom.
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