[nubz69]

EPDM and contact cement seem like they would be similar to the original dynamat. I was wondering if anyone has tried using EPDM as a dampener and how it worked out. Considering you can get 1/8" EPDM and it weighs 8oz a sq ft. (half a pound) I would think it could be an option.

Opinions?

 

[FoxPro5]

Isn't the damping performance of anything directly dependent on it's ability to convert mechanical movement (vibration) to heat? If you take something that is pretty well damped (roofing rubber) and glue it down, you'd have to ensure that the adhesive is coupling the damper completely and uniformly to the surface with reliable and consistent results, right?

Seems to me that adding just the right amount of contact cement would be kind of tricky; too much would act as a decoupler when you need that rubber coupled very well; and not enough would result in no vibration loss.

EDPM sheets are probably about the right thickness at 60-75 mills, but getting the adhesive just right would be the key issue. Also, rubber varies in it's viscoelastic form and EDPM might be too elastic to elicit the type of vibration damping we need in our cars.

But I've never tried this, so this is nothing more than the voices in my head telling my hands to type this....

 

[nubz69]

Dampening is dependent on converting movement into heat (even if the heat is very minuscule) but there is more to it then this. This conversion of sound into sounds like magic to some people but it really is a mechanical force. If people thought about it in relation to bending a peice of metal till it heats up and brakes they may understand it better. Instead the dampening resists the movement of the metal and the heat is created in the dampening material. Effective dampening can also be dependent on combining two dissimilar materials with different resonant characteristics to cancel each other out. This changes the resonant characteristics of the metal + dampening as a whole. Personally I feel this plays a much larger role in sound dampening metal in a car. One last way to dampen metal is to change it's resonance with bracing. This isn't done so often in car doors for obvious reasons but if you add a brace to the center of a panel you effectively move it's resonance up higher and limit it's ability to move. You can brace a panel off center but this is less effective.

I think you are overly focusing on the adhesive, any adhesive that can bond the EPDM to the metal without loosing it's adhesion from vibration and heat would be effective. I have never hear of being to elastic being an issue before. Since we are not stretching the rubber to sound dampen and instead are using it to mass load and counteract the natural resonance in the metal with the EPDM's own resonance I don't really see this as being an issue. Is there something I am missing?

 

[nubz69]

If you really wanted to get serious couldn't you use butyl tape on the back of EPDM to make your own hardcore version of the original dynamat? It would cost more then just a regular adhesive but might be something to try.

 

[FoxPro5]

You seem confident in your ideas, so why not go for it?

AFAIK, constrained layer damper solutions need to use a constraining layer that's able to handle the dissimilarity change and resist shear forces. Not sure how roofing rubber can handle that compared to aluminum foil which is very strong horizontally (along it's length).

One thing I always think about when it comes to DIY noise and vibration control ideas is if the idea is so great, why hasn't a company in the business used it already? Why hasn't Dynamat rebadged pails of elastomeric roofing compound, called it Elasto-damp Xtreme and marked it up 17,000%??? If there are engineers out there developing the best of these products, why isn't it already being done. Just something I think about, but it's never stopped me from trying as I've come up with some pretty nutty, off the wall ****.

 

[nubz69]

I would be trying this if I wasn't a poor student right now.

Many of the products you see available are just re purposes of a different product. If you look at the products on the market whether it is second skin or dynamat extreme they are at their core a butyl adhesive layer and an aluminum foil layer. Sure their dimensions may be a bit different, one may be thicker then the other, the formula for the butyl layer may have a little bit different compound ratios, but they are 99% the exact same simple product.

I am just looking for alternatives that may work, I am sure that this could be done but will it be cost effective? Once you add up all the time invested and the materials there is no way it would be cheaper then just ordering some existing product and installing it.