Jump to content
Sign in to follow this  
ncc74656

spray on deadener

Recommended Posts

i decided to try some spray on deadener as opposed to stick on, i gutted/cleaned my truck before application and applied multiple layers. i found sprayed in a 1/16 inch coat with about 40% overlap a single spray has no effect, two layers is enough to stop reverberation of a smaller 5X15" panel when you tap it with your knuckle and 3+ layers is needed for larger 2X5' areas. however the peel and stick products (dynamat and mesamat in this case) not only stop the reverberation but audible lower the resonance of the panel they are applied to while the spray on does not do this, or at least not to a noticeable level.  i applied 6 coats of spray on for large areas with seemingly no audible change past the 4th layer. 

 

my question is this: so you stop the reverberation, thats good, but how does lowering the resonance of the panel effect your cabin noise when not coupled with the resonance? basically trying to separate the two effects of sound damping into quantifiable distinctions.

second, if spray on takes time to dry, time to do multiple coats, a fair amount more prep work than peel and stick... what are its advantages? why would one choose to use spray on over peel and stick?

Share this post


Link to post
Share on other sites

It isn't reverberation, but you change the Frequency, amplitude and Q of the resonance.  That is it.

Spray on's suck donkey in comparison as they do not have a constrained layer which is far more effective at making a change.

As for the cabin noise question, I am not sure I get what you are asking but it is also simple.  There are two sources of noise in the cabin; airborne noise and structure borne noise.  Any form of barrier that adds MASS will help with the airborne noise, but unless it changes the Freq, amplitude &/or Q of the resonances it won't do anything for structural noise.  The likelihood of you truly getting the resonance of your panel out of a range where your car excites those resonance modes is near nil which means you need to focus on reducing the overall response of the resonance such that it doesn't make as much audible noise.

I've moved small panels in the kilohertz range 100fm (femtometers) and it is VERY audible.  Of course the panel chosen was from a metal that made a good "speaker" but do realize that your car doors were not chosen for their acoustic properties first and foremost, but their structural to weight balance.  NVH in the era of your truck was a massive "oh shit" engineering exercise, in particular by Chrysler whom is more than a decade back in that regard.  Today it is much better as they try to model it all in software first, but FCA does the worst job of validating that what they modeled in software was right and regularly it is horribly wrong.

I tried to warn you before to skip the spray on nonsense, but you seem to like to ask questions hoping for an answer and then when you get a different one ignore the help you received. :(

Share this post


Link to post
Share on other sites

at the point i asked i already had the spray on, i had also never done it so i wanted to see what it was like first hand.  

what i noticed was about 1/2 coverage with a single layer of even mesa mat stops the tinny noise when you knock a panel and it makes the noise lower in frequency where as 6 coats of pray on with 100% coverage dosent lower the frequency but does stop the tuning fork style reverb after hitting it. 

 

so if im understanding correctly the stick on or spray on damping is more of a secondary concern and using absorptive materials will do more for internal cabin noise?  i have used MLV on my floor and rear but i didnt order anything for my doors yet. i have room to do maybe 3/4" on my doors, my understanding is as a general rule the thicker and more dense the better. i have accommodation on dynamat but looking at their dynaliner im not convinced it would be the best type of product for this as it appears to be just foam. if i were to order MLV im honestly not sure how i would secure that to teh roof with out welding studs in there o.O. all i know is i want to use what ever product is best for blocking outside noise and ill just deal with mounting.

Share this post


Link to post
Share on other sites

Don't get too hasty.  Your truck is a noise box.  The panels are designed like shit and it leaks like a sieve.  Need to treat the panels AND block the other airborne noise.  It doesn't take all that much deadener to go a long way, but MLV you need a complete cover/barrier for it to work well.


Stupid thing is that most people go buck wild on the deadener and hardly use any real blocker.

Share this post


Link to post
Share on other sites
Posted (edited)

i didnt intend to say the peel and stick deadener is useless but im thinking, if i put enough on to make the panels not vibrate (say 30-40% coverage) then my money would be better spent doing a damper after that rather than more deadener. right?

my coworker used 5 layers of dynamat peel and stick and one layer of 1/4" dynaliner. however i looked up the specs on that liner and NO WHERE do they claim it is intended to dampen anything, dynamat states the liner is intended as thermal barrier only....??

i have full coverage on the floor of mlv, i want to place it on the back wall as well but i worry its to heavy for the ceiling and doors? if its a night and day difference from an MLV style to the next step down (some type of foam) then ill figure out how to make MLV work, however if its only slightly less effective than MLV but lighter and easier to install then i think id prefer that route.

Edited by ncc74656

Share this post


Link to post
Share on other sites

It is confusing to understand what you are asking.  Deadener is a damper.

Again, it isn't about vibrating you cannot stop that you can only change the frequency, amplitude and q.

As for alternatives to MLV you can use anything that will cover the complete area and has mass.  The more mass the more effective, ie there is no "light" solution.

Share this post


Link to post
Share on other sites

ok, ill see what i can do with this MLV i have then, its fairly heavy @ 1lbs per square foot.

 

i guess my primary question is, does adding multiple layers of peel and stick dynamat do anything? my understanding is the sticky side resists the movement of hte panel and it deforms at a different rate than it returns. so if you put a layer on top could it really have any effect since its no longer attached to teh panel you are trying to dampen?

Share this post


Link to post
Share on other sites

Adding a damper to the constrained layer of another damper is not very efficient.  Multiple layers does not make sense.  Covering a quarter of the panel is enough, although I overkill EVERYTHING so even though it is a waste of money the when in doubt use a little more will at least guarantee you got the right locations.  That being said, layering over is a complete waste.  Layering a CLD on top of a spray on also doesn't really work.  Spray on deadener is a net negative.  Sucks to get off too.

Share this post


Link to post
Share on other sites

just to try it i stuck some deadener over the spray on and i could hear a drastic difference in panel noise when i tapped it so it does something, that being said i have no way to measure the loss in efficiency compared to directly on the metal.

 

i plan to stick some over the spray on and then cover that with the MLV, getting burnt out on this projecct and just to much work to redo things. at this point im going for "accecptable" over perfect

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×