engine and drivetrain 2 layers of FatMat Too Much?

[justinevert]

Over bought the stuff and have another roll left.

I had put down Dynamat (a gift) on the Firewall and rear bulkhead and coated that with the FatMat, and then put down the remaining on the floorboards.

Since I am going to run a hotter engine and SS manifold/SuperSprint resonator and exhaust, you think it would be necessary or overkill?

Justin

[elementfmfl]

No the one should do it, sell me the excess!

[72Fjord02]

I would think the one is good. I have a single layer of dynamat on everything but the roof and roof pillars, and it is pretty quiet at all speeds with a hotter engine and high flow exhaust with headers.

Plus the stuff is heavy, more weight = more slow, so try the single layer, if you aren't happy just take out the seats and roll back the carpet and add another layer if needed.

[milfweed]

Jus:

I say overkill. not because I know about sound & reverb, though.

Dad was an architect & there's little gain to dbl. R-value temp insulation.

but-- I make my stuff up.

[Colin]

If you're really trying to quiet down the car, plugging all the "leaks" is the first and most effective course of action.

Having said that, though, in my experience, adding a second layer of fatmat does quite a lot. It adds a lot more mass and kills a whole lot of resonances.

The weight penalty is negligible for a street car.

[shipm_8]

As Colin said, I can't imagine weight would be an issue.

As a reference, a 36sqft roll of dynamat is 15lbs, as is a 50sqft roll of fatmat. It takes what, a couple of rolls to do the car? If you are replacing the old tar stuff with the dynamat/fatmat the net is probably a loss in weight.

William

[nbcbird]

Two layers is too much. Now that you have it installed, I would have suggested using the material with the aluminum backing on the firewall and other areas above the exhaust system. I think regular Dynamat just has a plastic film for backing.--Jim

[BLUNT]

lots of different opinions on this. i have 2 and 3 layers in my car. while there is an added weight penalty it isnt significant. my exhaust seems to be getting louder as time goes by but the sound deadening i did made my car very tolerable to drive and allowed me to have a conversation at speed without yelling.

[Colin]

lots of different opinions on this. i have 2 and 3 layers in my car. while there is an added weight penalty it isnt significant. my exhaust seems to be getting louder as time goes by but the sound deadening i did made my car very tolerable to drive and allowed me to have a conversation at speed without yelling.

Same experience here. Adding mass does a lot in these sort of situations. I kept adding layer after layer under my rear seat until I ended up with 4. I would put a layer on, drive it around, then add another until the SPLs were satisfactory.

I am an audio engineer and used to build recording studio. Really, the only ways to stop "noise" from coming in are decoupling the sources of vibration, making everything as "air tight" as possible and then by adding mass. At some point, adding more mass isn't going to do anything, but honestly, 2 layers does quite a bit more than 1 as does 3...

And I don't sell the stuff or anything.

The trick is positioning it strategically. It does not need to cover every square inch!

[Squatch Pads]

For my project I had purchased Fat Mat, but then changed direction due to a friend suggesting another alternative.

Since my interior was gutted, I sprayed two gallons of Quiet Coat throughout the entire car. The weight was significantly less and it covered really nicely.

Now for the test. I just got the motor fired the the other weekend, and currently am just dumping out a Stahl header. My build partner was checking for volt charge and it was just too dang loud, so I closed the door and rolled up the window. In an enclosed garage with a just a header and no carpet yet, it was tolerable. I was quite surprised that it was so quiet.

So short story shorter, if the interior is bare, why not spray and get every little hiding spot.

No one is right, just opinions, possible lessons learned.

[justinevert]

I was thinking maybe 2 layers on the floors and one layer on the sides. I will be doing the doors and rear quarters when I finish welding in the trim holes.

Justin

[Maceo23]

Dynamat, fatmat, or whatever other brand you go with, they are sound dampeners. They are designed to stop panel vibration, not block noise. Its a common mistake to just put layer upon layer of dynamat to try to block unwantred road or engine noise. After a ton of research, it looks to me that the best strategy is to start with a layer of dynamat ( or whatever ) then follow it with a layer of closed cell foam, and top it off with a layer of Mass Loaded Vinyl. The dynamat stops the resonant vibration, the foam is a decoupler, and the MLV is a sound blocker. It comes out much cheaper than shelling out for multi layers of dynamat. Heres a link to a site that knows a little more about it. http://www.sounddeadenershowdown.com/cgi-bin/index.cgi

[Colin]

Dynamat, fatmat, or whatever other brand you go with, they are sound dampeners. They are designed to stop panel vibration, not block noise. Its a common mistake to just put layer upon layer of dynamat to try to block unwantred road or engine noise. After a ton of research, it looks to me that the best strategy is to start with a layer of dynamat ( or whatever ) then follow it with a layer of closed cell foam, and top it off with a layer of Mass Loaded Vinyl. The dynamat stops the resonant vibration, the foam is a decoupler, and the MLV is a sound blocker. It comes out much cheaper than shelling out for multi layers of dynamat. Heres a link to a site that knows a little more about it. http://www.sounddeadenershowdown.com/cgi-bin/index.cgi

Mass Loaded Vinyl isn't so different from fatmat, really. That stuff is HEAVY at about 1lb per sq ft which doesn't really make it practical.

Fatmat, as you said, does lower the resonance of a panel, but it also adds mass which will, in fact, lower the amount of "noise" that gets into the cabin.

We do the same thing in recording studio construction except you would use extra thick drywall, or two layers, which get a fully air tight seal and are "de coupled" from the floors. The only de-coupling you can do on a 2002 has already been done by the factory via the rubber mounts, guibos, etc. Sealing all the air gaps should be done by replacing all the factory seals, especially around the holes in the pedal box and the dounut under the gear lever. This will make a big difference.

The fatmat will stop panels from resonating but as I said, will provide more mass which means it takes more energy for a sound wave to travel through. It helps.

The next step would to fill cavities, such as under the seat, with a rigid fiberglass insulation such as Owens Corning 703 or generic rockwool. You could seal it in a plastic bag to keep water out and it will still absorb the low frequencies from the exhaust rather well. Again, the insulation converts the sound waves into heat and helps tremendously to lower the SPLs inside the cabin.

This is all really a diversion, and like many things on the internet, there are more "myths" about this stuff than truths, but I can say that, for sure, 2 layers of fatmat, or any similar product, will definitely quiet your car down more than a single layer.

If your seals are shot, though, the net effect of the fatmat WILL NOT be that noticeable.

[robsanab]

well said colin... I can concur... I just did my car with fatmat (mostly fatmat and some damplifier i think).

If you rap on the panel before you start and then add a layer and rap, another and rap... you can hear the difference. Now there were some areas that didn't resonate much to begin with... but in the wide open areas in the middle of the panel even 3 layers made a difference. The way i ended up laying it out was that I sort of started each piece in the middle of a panel or highly resonate spot... so I have even 4 layers in some areas... once you're in there doing it, it's no big deal to add one more.

I have no actual comparison between one versus two versus three layers... also I did a pretty complete resto with new seals, fixed holes in the floor, 5 speed etc. But I am very happy... dramatically quieter.