Rattling 6x9s, should I use CLD? Help me learn about Compressed-layer damping.

[crashprime 10+ year member]

Alright, I have a project ahead. I am going to be installing 6x9's in the rear decklid of a 5th generation Camaro.

The stock speakers ALREADY cause some rattle when you get some bass thumping. This can be seen here:



I know how to bolt things up and plug them in, but controlling rattles is beyond my knowledge base. To install the 6x9's in this car, it requires you remove the back seat, and all the paneling from the seatbelt back. It's a royal PITA that I don't want to have to do twice, so I want a plan of attack here.

This leads me to my question. What's the best way to control this type of rattle?

I know a lot of times people automatically think Dynamat. I did, because this is what it's been marketed as. It's the solution to every problem! Road noise? Dynamat. Rattle? Dynamat. Panel vibration? Dynamat... Spend more than a few minutes on the internet car forums and the more boutique branded Second Skin will be recommended. It's better made stuff than Dynamat, but it's Damplifier (Pro) is still compressed-layer damping.

Is it really the solution? I'm not sure.

And while I am asking about it, I want to learn a bit if I could. The theory of CLD's is that you bond a viscoelastic material (in the case of high quality brands this is a butyl rubber compound), to the substrate (aka the car, be it the floor, trunk, or in my case decklid/parcel shelf), and with a constraining layer a-top (in the case of high quality brands this is >4mil thick aluminum foil).

So, bottom layer = car, middle = butyl rubber, top = aluminum foil. Apparently it works because the low frequencies of the speaker cause the substrate to flex/resonate, causing shear strains to develop in the viscoelastic butyl rubber.

What I don't understand is the importance of the constraining layer (the aluminum foil), and specifically the importance of it's thickness. If the shearing and energy exchange happens in the butyl, why is it beneficial to have a thicker constraining layer? This is the major difference in pricing when comparing brands. It's all about the thicker constraining layer. It's what differentiates Second Skin's Damplifier and Damplifier Pro products.

Is the thicker constraining layer just doing the job of mass loading? When speaking in terms of mass loading, I was under the impression that it was it's own product, typically taking the form of Vinyl loaded with Barium Sulfate.

I really hate how there is so much misinformation and general lack of information when it comes to WHY these sound deadening/damping products work.

I mean heck, over a different camaro centric forum, I've read about folks using bungee cords to pull down on their decklid to stop it from rattling. I've read about folks screwing up from the bottom of the decklid into the speaker mounting bracket. Everyone seems to have some "trick" or band-aid, and I just want to do this the RIGHT way.

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[trumpet 5,000+ posts]

It's not just a thicker foil, the adhesive compound varies from manufacturer to manufacturer as well. Different fillers may be added to reduce the weight and lower the cost, plus the adhesive can be whipped to force air bubbles to form. The foil does a lot of the work, but it's no good without a good viscoelastic adhesive compound that sticks for years throughout a wide range of temperatures.

If you have rattles they should be stopped with a decoupling layer. I use CCF from Sound Deadener Showdown to do this, as it's thin yet resistant to compression. This is something you can secure with hot glue here and there and then forget it about it.

 

[crashprime 10+ year member]

Close cell foam decoupling layer. This is something I can't seem to find a lot of information about.

Does this mean I am covering the parcel shelf entirely in something like Ensolite (raamaudio has a peel and stick application that's priced nicely)? Would I still benefit from 25% coverage of CLD, or will the Ensolite be enough?

Am I just using a small piece around the mounting bracket for the speaker? Am I cutting little stand offs to place under the speaker mounting bracket?

 

[trumpet 5,000+ posts]

Close cell foam decoupling layer. This is something I can't seem to find a lot of information about.

All of these concepts related to vibration damping, decoupling, and making a noise barrier are discussed in depth here: Sound Deadener Showdown

Does this mean I am covering the parcel shelf entirely in something like Ensolite (raamaudio has a peel and stick application that's priced nicely)? Would I still benefit from 25% coverage of CLD, or will the Ensolite be enough?
Am I just using a small piece around the mounting bracket for the speaker? Am I cutting little stand offs to place under the speaker mounting bracket?

Do what's necessary depending on the vehicle and what is actually rattling. If the entire cosmetic cover over the metal deck is rattling then put foam over the entire metal deck. If the speaker bracket is rattling, such as with a cheap plastic factory bracket, then you can make a foam gasket to completely follow the shape of the bracket. Sometimes you might find a poorly mounted wire bundle that can rattle, so what I've done is wrap a small piece of CCF around the area that I suspect is striking the nearby panel. CCF can be used under plastic clips as well.

 

[bmk6795 10+ year member]

I used a combination of audio technix deadener, great stuff (expanding foam), and weather stripping. The great stuff went in between panels to keep them from pretty much moving at all, and the weather stripping went in between metal pieces, or moving pieces to keep them from whacking against each other. Then the deadener went on pretty much any metal surface where i had rattling and now i have almost 0 rattles. The only things that rattle anymore are the back bumper and the doors on occasion. Keep in mind that if you use great stuff it is pretty much permanent. However if you plan on putting a layer of cld on top of the metal anyway no one would ever know its there. Just be careful not to use it near moving parts, and wear gloves cause if you get it on your hands its gonna be there for a few days.

Ive also used Fatmat deadener and its no where near as good as the AT. The at went on nicely and is staying put while the adhesive from the fatmat is actually melting and running. Im not recommending a brand in particular but dont cheap out on it or its not gonna last nearly as long, and you'll have to do it again rather soon. I put the fatmat on about a year ago and the AT on about 8 months ago and the AT is doing better by quite a large margin.

 

[crashprime 10+ year member]

I'm strongly considering going with audio technix for my CLD needs just because they're closing out that branded stuff so cheaply to make way for their companies new logos. Damplifier Pro B-Stock is tempting as well ... but I think I'd get better results from the 80mil AT stuff.

That Sound Deadener Showdown site is great. Looks like he sells the stuff too but there isn't any cart system to buy the stuff, so I'd imagine its all custom assembled kits and what not.