It's really important to understand the theory behind constrained layer damping before building one. I've tested several butyl formulations alone and they do almost nothing without constraint. The magic happens at the interface between the viscoelastic adhesive and the constraining layer. The ideal constraining layer would be the same as the substrate - if you are trying to damp 22 gauge steel, the theoretical ideal would be a 22 gauge steel constraining layer. Since that isn't practical, foil is used as a reasonable compromise. EDPM rubber wouldn't make a good constraining layer because it is too elastic - it would just return all of the energy it receives.
Whatever you use, you want it to resist the strain force it receives from the viscoelastic material. This is why applying a liquid applied material on top of a thin foil CLD improves its performance - it reinforces the constraining layer. It really isn't an extensional damper at this point. Anything that increases the foil's rigidity would do the same thing.
I realize this is sort of obscure stuff, but it's important if you want to make your own vibration damper. Constrained and non-constrained damping work in completely different ways. In a constrained layer system vibrations travel from the substrate into the viscoelastic medium. The ve medium is deformed and the vibrations are converted to heat by strain forces between the ve medium and the constraining layer and the substrate itself. Extensional or non-constrained systems work by resisting deflection of the substrate. These approaches require very different material properties. In practice a CLD uses a much more easily deformable material. Adding a constraining layer to an extensional damper won't do anything and using a CLD adhesive without a constraining layer is just as pointless.
EDPM might make a pretty good barrier based on mass. At .5lb/ft² at 1/8" thick, you'd have to accommodate twice the thickness of MLV to achieve the same mass/area (and many times the thickness of lead). There's a theoretical disadvantage to an elastic barrier but I doubt it would be a problem in reality. This seems like the best potential use for rubber sheeting to me.
When I mentioned the apparent correlation between a butyl compound's heat tolerance and its damping performance, I should have been more specific. I was talking about temperatures in the 400°F+ range. Any product with a butyl base should be able to handle 180°F - although I've seen several that just barely made it.
I guess the most important points are that as useful as butyl is as a chemical compound, it isn't necessarily a good vibration damper and it isn't one at all without a constraining layer. It is inherently more stable than asphalt so it is much less likely to melt or fall off when used in a vehicle. Not melting or falling off is the lowest possible standard and has nothing to do with vibration damping except that nothing will damp vibrations if it doesn't maintain its contact with the substrate. Unfortunately, melting and falling off has been a problem in this market because some sellers haven't cared enough to meet this absurdly low requirement.
A manufacturer sent me a few dozen butyl samples a while ago - different formulas and different thicknesses. All of these materials easily met the 180°F test. All of them had reasonable adhesive bond strengths. Only two had good vibration damping characteristics when a constraining layer was added. That's something like a 5% shot at getting a good ve damping medium if you just specify butyl.
I'm not suggesting that everything being sold as a butyl vibration damper has been optimized for that purpose. In too many cases "looks like Dynamat Xtreme" is all that matters. Even so, something is going to be at least marginally better than nothing. Many products get great testimonial support because the users mistake isolating adjacent panels with vibration damping - it stopped my rattles - not realizing that a single strip of duct tape would do exactly the same thing.
The way to save money on vibration damping, whether you are making your own or buying it pre-assembled, isn't to compare price/ft². The least expensive product is almost certainly going to be the the one that will do the job with as little material as possible. You're much better off with 25-50% coverage at the center of a panel using an effective product than you are with multiple layers covering everything in sight. Less cost, less work, less weight added and less chance of making future maintenance difficult or impossible. The difference between a poor and a good product can easily be 6-10/1, meaning you would need 6-10 times as much of an inferior material to equal the effectiveness of one that works well. This makes price/ft² a completely meaningless metric.
Part of the problem when comparing CLDs is the severely diminishing return you get with additional layers. You'll often hear people say that because of the price differential it's cheaper to add multiple layers of an inexpensive material. Here's what the "Bible" on vibration damping says:
Vibration Damping - Ahid D. Nashif said:
Multiple constrained-layer treatments are often used to increase damping of structural applications. Usually, by increasing the number of layers, more damping can be introduced for a given mode of vibration. However, as a result of many tests on the performance of multiple constrained layers, it has been found that most of the shear deformation occurs in the first damping layer, closest to the structure. In other words, all subsequent layers work mainly to increase the stiffness of the constraining layer to which the first damping layer is subjected.
I'm not trying to discourage the experiment and I'm obviously suggesting a higher standard than is used by all but a few sellers of these materials, but if you are going to do it, you may as well do it right
