I'm just wondering how big of a difference sound deadening does? Is it practically a necessity for loud subs?
how much it costs? and how heavy it is?

Bass and sub bass frequencies are absorbed by the metal panels in the vehicle and vibrate. If you can eliminate the absorption/vibration, you will gain db's. It all depends on what type of sound deadener you use. I always use Dynamat Xtreme in the trunk where my subs are and in the doors where my mids are. It isn't cheap but well worth the expense. I would say to do your trunk and doors in an average car would probably cost you "around" $300. It doesn't weigh that much, maybe adds 10lbs to your car (trunk/doors).

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Active system - Eclipse cd7000 - Focal k2p - Audison LRx 4.1k and Audison LRx1.1k - AVI sls300 x 2 in custom built spare tire well enclosure

thank you thank you, I just learned a whole lot! (I had no idea it increases db's)
any other comments?

10 lbs??? 100 sq feet is probably close to 50 lbs. and you'll need at least that to do the whole interior with one layer.

Also the search option owns you!!

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Psh, that's what every forum would love.. people to use the search..
I just feel my questions are so unique that no one could possibly have even thought of phrasing it the same.

Did you read my post???? Trunk and doors only my friend

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Active system - Eclipse cd7000 - Focal k2p - Audison LRx 4.1k and Audison LRx1.1k - AVI sls300 x 2 in custom built spare tire well enclosure

let me correct you on a few things.

it doesnt matter what kind of sound deadening you use. There are only a few types. All the ones that look the same, work the same. dynamat Xtreme is good but too expensive for what it is. You can get a much cheaper alternative that will work just as well. What you need to look for is thickness of the sound deadening material.

if you eliminate absorption/vibration you can (not will) gain db's. You can also loose alot more db's than you can gain. It all depends on how and where you apply it. IF your goal is to gain spl inside of the car by using sound deadening it will require a long period of trial and error. Blindly just applying it everywhere wont gain you anything, it will probably loose more than it will gain. If you dont know what you are doing, or dont know someone who knows what they are doing, I would not try to use sound deadening to gain spl. You will probably waste time/money and gain nothing.

if your main goal is to stop rattles on your car, then you can go ahead and blindly apply the stuff anywhere you want. Just remember, 80% of the rattles you hear outside of the car are the things like your license plate, lights, bumpers, exhaust pipe, gas tank, etc.......basically the things that are attached to the exterior of the vehicle. So makesure you have a plan of action before you begin applying the material.

I use B-Quiet, it's made in Canada and can be had on ebay for a really good deal. B-Quiet Extreme is thicker than Dynamat Xtreme and is nearly half the price.

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Team Fear Of Bass

I use B-quiet as well, IMO the best for the money. although I would recommend the ultimate over the extreme, you need to really heat up the extereme to get ot to bond well, the ultimate is very sticky at all temps.

this is correct.

we dont even use any heat in our application of B-Quiet Ultimate.

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Team Fear Of Bass

Thanks for the help once again, Ultimate seems like a winner to me.. B-Quiet - made in Canada.. Why not eh?
I'm not looking to increase SPL my subs aren't even ported .. yet..
the great thing is.. I rarely hear rattles, It's only my front doors that will ever ever rattle. my license plate used to rattle, so I unscrewed it and put three pieces of foam behind it.. the stuff that everything is packaged in.. and put the plate back on.. never rattled again.

I might dyno my trunk (maybe) and front doors then..
thank you for all the help.