I know there are products out there that are similar to Dynamat and cost considerably less..

such as:

Polymeric Mastic

Peel & Seal

Ice Gaurd

Rubberized Undercoating

etc..



I am wondering if any of you have used any them or could suggest some ideas/alternatives to me to "de-rattle" my trunk lid (and other things)..

i have already taken care of the license plate with some semi-carefully placed foam weather-stripping but the trunk lid itself (i think mostly the tail light housings but i'm not 100%) rattles considerably.. and i HATE it.

the rattle subsides considerably if i push down on/hold the top part of the lid assembly (just above the tail lights on the rear of the lid where it makes that sloped vertical transition)


just wanted some input before i go wasting money on Dynamat..


Also what's your opinion on sheet material (like the mastic stuff) vs. spray on material.. equally as good ? one better to use? use both in combination?


Thanks in advance,

~Moddage

 

GAD DANGETT I typed all this stuff only to have my mouse slide of my lap and hit the close button. Basically what I said was that the only important thing is how dense it is. The more mass the better. What is happening is when you add mass to the sheet metal you are bringing the resonant frequency down stopping the rattle. So if you can find one cheaper, and has about the same mass and density as dynomat it will work the same. I only have experience with dynomat brand, so others may have a better opinion.

 

If you're cheap, carpet padding and liquid expanding foam insulation have worked wonders for people.

 

The only thing I can see expanding foam working on, is getting between two layers, like a door. And the foam will just physically not allow the metal to move, over time I think it will start to vibrate. Carpet padding is used by car manufactures for deadening, and does work for stopping road noise I don't think it will work well getting rid of rattles from bass, if at all.

 

I agree completely. But, as long as my box is wedged between the trunk floor and the rear deck, I get little to no rattling.

 

@t00fatt

That sucks man! i hate when stuff like that happens.. just out of nowhere.. Poof.. GONE... but anyway that's about what i gathered last night from searching the web.. basically what you said.. add mass.. stop vibrations.. or at least put them below the human hearing threshold..

@19Accord97
apparently FatMat is basically pretty much Peel & Seal.. they are both Asphalt based.. and from some guy's personal testing of each material in small samples.. he said they appear EXACTLY the same as well.. and have similar enough characteristics to not make a difference..

@finch13

I heard carpet padding was pretty good for reducing/removing road noise.. only problem is sticking it up to places... i suppose a few cans of 3M Super-77 might do the trick...



thanks for the replies!


I'm going to keep looking into this some more and hopefully by spring time i'll know where to go from there..


~Moddage

 

This was a good post that never proceeded on..

 

As an Acoustics Engineer I spend my days developing noise control and vibration damping solutions for a very wide range of applications. Coupled with over a decade experience with sound deadening products - i can say you get what you pay for. There is a bit of a brand name markup on Dynamat, but there are other companies putting out awesome product. Raammaudio and Second Skin are two of those.

The cheap asphalt alternatives mentioned are a waste of money for several reasons.
1. The weight to benefit ratio is terrible - just adding mass isn't the goal. Adding viscoelastic damping is the goal. you want vibrations and resonance to be converted to low level heat - something asphalt cannot do.
2. Asphalt does not stick. It loses adhesion in cold temps and hot temps. I have easily removed asphalt based "deadener" from cars - true sound deadening does not come off easily. This goes for peal-n-seal and Fatmat.
3. Asphalt products stink. literally, they smell. the smell is bad and comes back whenever it's hot. that alone makes it undesirable.

I never recommend asphalt based deadening products. They are not designed for viscoelastic damping and cannot perform the function.

It is true you can increase transmission loss (TL) of the vehicle metal by adding mass - something asphalt based products can do. But you need 100% coverage. just putting patches won't increase TL. just putting patches of asphalt products won't do anything except add weight and change the frequency of resonance (by creating new modes on the panel). patches of viscoelastic damping products can be effective by truly absorbing vibration. the most benefit is found with as close to 100% coverage as possible.

the most effective method of reducing road noise is creating a mass-decoupler-mass assembly. the vehicle metal (with or without deadening added) is one mass layer. you'll need a decoupling foam/rebound layer - carpet padding can work for this on a budget. carpet padding alone will do nothing. you'll then need a mass layer on top of the foam/padding layer. Mass Loaded Vinyl (MLV) is the product to use if tomb like silence is your goal. it comes in several thicknesses and weights (rated lb/sf ... pounds per square foot). there are several distributors of MLV - and other acoustical products. however, just like before, you need 100% coverage. this gets expensive and tedious. without 100% coverage it's like the crack under the door letting all of the sound through. the transmission loss of an assembly is only as good as the weakest part.

the cheapest way i've incorporated mass-decoupler-mass is carpet padding and the thickest vinyl "fabric" we could find. we covered a 2002 Tundra floor with this and it did make a difference. We also sealed and covered the doors with Fatmat. The result was a reduction in road noise and while we weren't lowering door resonance we did create a sealed cavity for the Image Dynamics midbass which was an improvement over stock. This was a pretty cost effective application; however, I don't recommend Fatmat.

For reducing road noise in a vehicle you have several locations for noise
1. wheel wells - this is a major source
2. doors - front and rear they let a lot of road noise through
3. floor - while being the thickest metal with the most padding, it's a huge surface
4. roof - a large source of ambient noise ingress
5. trunk - without an adequate barrier the trunk becomes a noticeable source after treating areas 1-4.
6. windows - the glass has limited TL and this is your limiting factor. your only solution for increased TL would be laminated glass for the windows.


you get what you pay for. The cheapest yet effective sound deadening i've found and used is Raammaudio BXT and BXT II. BXT II is awesome for the price.

you can get 1/8" 1 lb/sf MLV for about $1.00 per SF a few places. you'll still need your own decoupler (foam is sufficient, quilted fiberglass is best)

 

as it was mentioned, the goal of sound deadening is to lower the resonance of the vehicle metal. this is huge when wanting good performance from your sound system. rap your knuckles on a factory door or rear quarter and it sounds like cheap, thin metal. put a layer or two of viscoelastic damping products and then rap your knuckles - now it sounds like a concrete block. that's when you know you've done something worthwhile.

trunk latch rattles are not helped by deadener. the sound is from the trunk being pressurized and the actual latch rattling. most trunks have play in the latch. wrapping the latch (mounted to the bottom of the trunk not the lid) with tape will squelch the noise... for a while. eventually the tape is worn through. the type of tape has a difference in longevity.

other rattles happen from panels on metal. thin strips or layers of foam can help silence those panels. you want something soft between the metal and plastic. well made luxury cars already have this foam. newer Honda and Toyota have this to some extent.

For a very detailed build log of two sound deadening projects of mine, look no further than here:
https://www.hondaaccordforum.com/for...ad.php?t=32679

 

FWIW, I completely respect the engineered approach. Very cool. I've enjoyed reading up on the placement and quantity required (vs. the blanket approach) that is discussed here:

http://www.sounddeadenershowdown.com/cgi-bin/index.cgi

However, with all that said, I had a serious NOISE and HEAT and BUDGET issue in my old hot rod. I cheaped out and blanketed the entire floor pan, rear seat back, and side panels with something very close to Peal N' Seal from the store with the orange sign... I doubled up over my headers and mufflers. I then went with a layer of jute padding under the carpet.

It made a HUGE difference. I went from having to shout to have a conversation with my passengers, to being able to talk normally (with the windows up). The heat improvement was less impressive, but still better.

And if there was a smell, it went away QUICKLY. I can get in that car after it has been sitting (closed up) and it smells fine.