How much sound deadening is enough?

[bigmack2007 10+ year member]

I have 6 layers or so of dynamat on my roof in my jeep grand cherokee. I dont hear rattleing inside but the roof still flexes alot. Is there like a certain point where dynamat just stops really benefiting as you put more on? Thanks

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[jfsh90 10+ year member]

Isn't flex different from rattle?

 

[hazardous0388 10+ year member]

theres never enough

 

[twisztdauthorit 10+ year member]

Isn't flex different from rattle?

x2

 

[WrenchGuy 10+ year member]

Sound deadening adds mass to large flat vibrating surfaces. Your roof will flex until you put supports in it. Rattles are from 2 objects vibrating against each other. The cure for that is to stick something between them.

 

[WOT]

I wedged wood shims in between my roof and the cross bars in the BIG spaces where there was no support or stitch welding, my roof doesnt move, but I need to deaden it more, only used about 15 sq feet up there, all I had left

 

[WrenchGuy 10+ year member]

2 layers on the roof should be plenty. Deadening doesn't stop flexing.

 

[MyFartsStink 10+ year member]

I have 6 layers or so of dynamat on my roof in my jeep grand cherokee. I dont hear rattleing inside but the roof still flexes alot. Is there like a certain point where dynamat just stops really benefiting as you put more on? Thanks

holy shit

 

[bigmack2007 10+ year member]

alright cool so i really dont have anything to gain from adding more? i definitely have 2 layers. Really between 4 and 6 over everything.

 

[Eugenics 5,000+ posts]

first off, mass loading will not solve your flex problems.

 

[Eugenics 5,000+ posts]

any more layers than two will be useless. i would explore other options. Secondskin has some. if foxpro says something. avoid him.

 

[audioholic 5,000+ posts]

For roof flex, I recommend fiberglassing it. That will stiffen it up nicely. Then lay mat over the top of that. Done.

 

[FoxPro5 5,000+ posts]

any more layers than two will be useless. i would explore other options. Secondskin has some. if foxpro says something. avoid him.

//content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif How come whenever you read what Degenics says you feel super unintelligent?

You need to add cross-bracing to the roof to prevent it from flexing.

Your deadening mats that contain a layer of foil (CLD) on butlyene rubber convert mechanical energy to heat. The math equations used to model this type of damping (called hysteretic structural damping) don't factor in weight. Therefore, most of this "mass loading" you read about on forums is just incomplete, limited thinking at best.

CLD works better on stiffer structures to begin with or situations were shear force along the substrate is high. A flexing roof is one of those situations, partly. It's also a situation where the metal flexes back and forth...or pulsates. In this case, it's better to use an extensional damper (ED) like a liquid, as it has a better ability to counter flexing deformation stress.

A good solution would be CLD + ED plus additional cross-bracing perpendicular to the lines of shear, particularly in the center of the roof where the summation is the highest.

A good analogy that sort of disqualifies this "mass loading" business would be the resonant action of an undamped snare drum.