Cork as sound deadener? Recommend other materials to absorb noise.

nobb · 03-21-2008, 04:56 PM

I have been pretty obsessed with killing the road noise in my car, but without spending a ton.

Currently, my doors have three layers of Resisto (asphalt based roofing mat) and a layer of heavy foam based carpet underlay. The floor of my car, including the trunk floor has two layers of foam based carpet underlay. This is all on top of the stock deadener. I got the foam carpet underlay for free, which is why I have been using it everywhere. However, the stuff doesnt seem to kill road noise as much as I hoped so I am thinking maybe there is better material out there to absorb road noise.

I notice that in music rooms or recording studios, they use cork to absorb sound. Do you guys think this would be a good idea to use in the car? I always read about people using carpet underlay, peel and seel, dynamat etc... but never cork. The stuff is only about 3mm thin and fairly expensive, so I dont see myself using anymore than 3 layers on the floor and door.

Suggestions on other sound absorbing materials welcome. I dont really want to go for an aftermarket mat type material because those are expensive and seem more focused on killing vibrations, rather than absorbing sound.

greatwhite · 03-21-2008, 05:27 PM

Hmmm, seems you're trying to eliminate "sound" in the car by insulation.

Most road noise is the resonance of the vehicles metal panels. Aftermarket stuff bonds to the metal for a reason. It adds mass. This helps to keep the panel from resonating. They also have other qualities that help eliminate sound, mostly "coverting" the sound energy into a different form of energy (essentially, dampening).

By just laying foam (underlay) on the floor you've helped some, but by using the wrong mechanism.

It's doubtfull if bonding the material to the car will help much more either. You really have to add mass to the panels.

I'm not saying all your efforts are for naught, just that they aren't going to as be effective as the proper materials (as you've found out already).

But your car is probably well insulated for winter

Cheers

v8 scimitar · 03-22-2008, 06:07 AM

put the foam in your ears that will work lol. Seriously tho as greatwhite says really and the cork is to dampen reflected sound which is not what your problem is. Vibration is sound that's why Dynamat works by stopping it.

2k1Toaster · 03-22-2008, 06:20 AM

concrete?

nobb · 03-22-2008, 09:28 AM

Thats a good point about the mass loading to kill vibrations. That's why I have a layer of Resisto stuck onto the metal as the mass barrier, then I have another layer of carpet underlay foam as a sound barrier (which its not very good at).

I saw an informative thread on the civicforums about using "jute." It looks like the stuff that is used as a stock sound absorber in most vehicles:

http://www.civicforums.com/forums/21...ening-diy.html

Seems to be a promising material. Maybe I'll see if I can get it cheap somewhere.

greatwhite · 03-22-2008, 09:43 AM

Jute is ust the stuff stuck to the back of factory carpets.

Not that effective, but it is heavy.

God help you if it gets wet.................

WuNgUn · 03-22-2008, 10:22 AM

I worked at an AC shop, and they used this stuff (we called gumbo), but it's basically a type of plumbers tape, made from cork and tar and maybe rubber...
I've used that to line the panels in my car, and laid 1/2" black, closed-cell foam rubber on top of that (also from the AC shop), and the difference is amazing...especially in the doors.
I've done the trunk, rear quarters, doors, B and C pillars...
I'll be doing the front wheel wells and the bottom door sills this season...

FordNoMore · 03-22-2008, 10:26 AM

If Dynamat seems a bit expensive, you can check out some of the generic Sound and Vibration Damping Sheets at McMaster Carr. Search for catalog pg 3427. Some of them are along the lines of original Dynamat (DLF = 0.08 at room temperature). I used some a few years ago and I THINK it was 9709T39, but I can't remember for sure.

dundidit · 03-22-2008, 01:22 PM

I use spray on truck bed liner. Works great and you can put it on thick. It is a little bit expensive. For 100 bucks you get like a gallon.

Bob T · 03-22-2008, 02:08 PM

... tends to stink. That is the thick chopped cork tiles; I think the sheet stuff might be too thin to do you any good.

nobb · 03-22-2008, 02:28 PM

After doing a bit more indepth research and looking at sound absorption coefficients for materials, Ive decided to get a 100sqft 3 mil roll of fibrous carpet underlay (they call it jute in the above link for civicforums). It's supposed to be good at absorbing high and mid range frequencies. As for the low frequencies...thats what the Resisto is for. I plan on using about 4 layers of this stuff (its pretty thin) and replacing the foam underlay which I currently have on my floors. Maybe stuff some of it in the dash if I have leftovers. I hope this works.

durwood · 03-24-2008, 06:56 AM

Crap I wish I would have seen this earlier.

You need a blocker material. Not an absorber. Abosorbers are good for high frequencies, but what you are trying to do is limit the amount of road noise coming into the vehicle which is all lower frequencies. That carpet underlay is a high frequency absorber, not a low frequency blocker.

Study the differences between NRC and STC-they are different.

Mass Loaded Vinyl (MLV) is a good blocker and probably the best material you will find for the money. Deadener is good for reducing vibrations of flat unconvoluted panels-but it also lowers the resonant frequency of the panel. It is not a good blocker/barrier. The foil helps block noise, but it's much more costly to line your entire vehicle with multiple layers of it.

http://www.noisedead.com/ John is a good guy and will help you out.

Second skin also has their luxury liner pro
You might be able to find commerical places that sell it as well.

nobb · 03-24-2008, 10:35 AM

Well, I already have the wheel wells coated in about 1/2 inch of asphalt undercoating. I plan on doing the rest of my underbody with undercoating as well, so that should act as the low frequency blocker. I dont really want to tear apart my whole interior to cover everything with sticky mat based deadener so right now I'm just ripping open small areas to be able to stuff the jute sound absorber underneat my carpetting.

Is mass loaded vinyl a low frequency absorber? Could I just stick sheets of that in between the jute?

Right now I think most of the noise is from the engine and from the tires vibrating the whole metal frame. Strangely, the car feels more quiet at highway speeds then it does at low speeds.

greatwhite · 03-24-2008, 02:37 PM

Try this:

with the car a various speeds (and no traffic!) slip the transmission into neutral and let the engine idle. The noise you hear is "road noise" and possibly interior rattles. Whatch your speed and rpm before you slip it back into gear please!

Now at idle in park, slowly rev the engine up to driving rpm (around 3,000 or so) this is engine noise (well, exhaust noise is in there too). Don't get too crazy revving the engine in park either!

Now that you know which noise is which and where it is comming from, you can start attacking each source and retest the same way when you think you have it. You want to attack the the noisiest offfender first to get you best bang for the buck (IE: floor wheel wells, firewall, trunk, etc)

Keep in mind, this is just a low buck way of finding noise.

If you start laying on the dynamat (or whatever you choose, that McMaster-Carr mineralized vinyl sounds interesting) and notice a "tar like" pad on the panels, leave it there. That is the OE noise dampers and is probably there because an engineer found that was the best place for it to reduce noise during NVH testing.

Cheers.

Woofnstuff · 03-24-2008, 03:19 PM

what do you drive a battle tank? how much weight are you adding,
i was thinking of doing this sort of thing to my car but was concerned about the additional weight.