A Sound Deadener that Hardens? Need to stiffen up rear deck for subwoofer

[nobb 10+ year member]

Im running a small 8" subwoofer in my rear deck (OEM location) as an infinite baffle to save room in my coupe. Problem is that this subwoofer has so much power that it is enough to noticeably shake and vibrate the rear deck.

Standard stick-on type sound deadener will not really dampen things much, so I'd like to possibly try other methods to stiffen up the rear deck. MDF boards are too thick and clunky to work with so I am wondering if anyone knows of a liquid that will harden (and not crack over time) and that I could use as a type of deadener for the rear deck?

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[goingdef 10+ year member]

fiberglass maybe? you might be able to laydown a good amount and still get the cover back in place easier then mdf because you can pick and choose how thick you want each area.

 

[Moble Enclosurs 10+ year member]

Yea, I would say fiberglass it. You can deaden it from the bottom if possible. Or top, whichever will work best for your layout of the rear deck.

 

[Bettr n' Revrse 5,000+ posts]

Pics of the rear deck? I have to do soemthing about this in a friends Maxima as well...

 

[Bettr n' Revrse 5,000+ posts]

I was thinking a couple layers of liquid deadener

 

[Linkz 10+ year member]

Spectrum sludge?

 

[Rudy 10+ year member]

I did the same thing with a 10 on my rear deck. Since there wasn't a flat surface I built one up using fiberglass. I bolted the mounting plate to the rear deck with butyl adhesive between them. It made the entire structure much stronger and completely non-resonant. Also built a fiberglass cover for the empty stock speaker hole on the other side of the deck and mounted it the same way. Added more strength.

Lousy photo:

 

[nobb 10+ year member]

Nice, thanks for the advice guys. Never worked with fiberglass before but that's a great idea. Do you just slather it on the rear deck and layer it like you would sound deadening? Im assuming it will bond to the metal deck pretty decent?

All the liquid deadeners I've seen are flexible to prevent cracking. That will not work as there is more to it than just adding mass. The rear deck needs to literally be physically strengthened.

 

[Kangaroux 5,000+ posts]

Is the deck flexing a lot or just structurally weak? I'd be weary about adding fiberglass to something that is flexing a lot as it could crack.

 

[nobb 10+ year member]

It literally flexes maybe 1cm both ways. The rear deck actually looks and feels stiff at first....until you put an aftermarket sub in there.

 

[murph 10+ year member]

Deadening the bottom will help a lot. Put a few layers and it will decrease the vibrations and flex a lot.

 

[Kangaroux 5,000+ posts]

My vote is deadener to cut down on the flex...unless you load up that thing with fiberglass I have a feeling it might end up cracking

 

[Rudy 10+ year member]

Never worked with fiberglass before but that's a great idea. Do you just slather it on the rear deck and layer it like you would sound deadening? Im assuming it will bond to the metal deck pretty decent?

You want to mask the area and use wax and a release agent so that you can remove the fiberglass piece and finish it outside of the car. Mine varied in thickness for .5" - 1". It's not going to crack. Vibration damper isn't a very good stiffening material. An alternative to fiberglass would be a heave steel or aluminum plate or maybe even plywood. Depends on how flat the deck is to start with and your fabrication skills.