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Anyone with a 2000 Si done dynamat to their car? Where do you guys suggest I should put it? I was thinking of putting it on the inside(ofcourse) of the trunk and front door panels cause that's where I get the most rattle. Also, does anyone know how to get rid of the license plate rattle? I don't have a frame and I'm not sure if I should waste my money on a dynamat one...

 
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best place is the front doors and rear wheel well areas on the sides of the trunk. you can put some on the floors too and the rear deck. it mainly improves sound quality if you put it where the speakers are installed. plate rattle, put a piece of sponge in the back. dynamat really doesnt stop rattles. they are caused by two parts touching together and can only be stopped by stuffing foam material inbetween them.

 
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That's great info Gear. What about the sound that my muffler creates interfering with my subs in the back? Do you think like a sponge-like material(i.e. whatever material they put underneath carpets) will work?

 
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yeah the factory carpet piece already has some foam but you can put more underneath if you want. if you actually want to reduce noise, you need the spongy cell-foam and partsexpress.com still has alot of that stuff i think.

 
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sorry to bring back a two month old thread but did you ever put the dynamat down in those places? did it make a big difference?

 
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i may have said this already, but dynamat is not an insulator/noise reducer. it just lowers resonant frequencies. the most difference you will notice is by putting it around speakers and their enclosures like the front doors and rear deck. and yeah its a noticable improvement in sound quality and loudness. if you want road noise reduction, you gotta look for foam composite sheets to stuff around. dynamat and foam together works best to reduce noise.

 
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i sealed off some holes in the panels with peel and seal and that helped along with rubbirezed under coating but what kind of foam do you recommend and where can i get it?

 
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partsexpress.com has acoustic damping open/close cell foam in sheets and different thickness.

 
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do you know roughly how much room there is between the window and the inner portion of the outer skin of the door? im a 6th genner so our cars are basically the same in that regard. Im just worried about getting too thick of a foam and not leaving enough room for the window. I found this insulating foam at Lowe's that I thought would work between the inner and out skin of the rear quarter panels and in the trunk. What do you think?

 
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there alot of room but also many moving parts. i opted not to put anything inbetween that space in case it got stuck or fell off. you can just cover the holes with dynamat and put some thin foam on top, then put the door panel back on.

 
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i thought about undercoating on the heat shield parts in the middle of the car the ones towards the rear, you think that will work at all? I put an *** load of peel n seal under the rear seat and that worked wonders for tire and road noise. the rear quarter panels i definately want to fill with as much material as I can. Some of the factory dynamat looking stuff is peeling off back there too.

 
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ehh that undercoating will not work on hot parts. but spraying some in the rear wheel wells will help! just make sure its the paintable version, so it dries hard. there is a regular version that stays sticky and you will have a mess. ofcourse im talking about the wheel wells OUTSIDE the car. you can put dynamat around them from the inside if you want. and stuff some insulation in the rear folding seats. they are pretty much hollow inside.

 
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ehh that undercoating will not work on hot parts. but spraying some in the rear wheel wells will help! just make sure its the paintable version, so it dries hard. there is a regular version that stays sticky and you will have a mess. ofcourse im talking about the wheel wells OUTSIDE the car. you can put dynamat around them from the inside if you want. and stuff some insulation in the rear folding seats. they are pretty much hollow inside.

 
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sweet, ill start cracking on it tomorrow and snap some photos. thanks for the input gear.

 
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It's been a while since I've posted here, but I've spent a lot time during the past 4 years studying and testing various sound deadening materials and in the past few months have actually gone into that business. All of this started when I bought a 2005 EX sedan and after a day or two realized that it was the noisiest car I'd ever been in. My car has been a test bed for every imaginable combination of materials. Here's what I have learned:

High quality vibration dampers like Dynamat Xtreme work well to reduce panel resonance. They work exactly the way the marketing hype claims they do - by converting vibrational energy into heat. They actually don't shift the resonant frequency much at all. Stiffening a panel raises the RF and adding mass lowers the RF. A decent butyl/aluminum foil material does both so the shifts are largely offsetting. The viscoelastic damping mechanism is real and does a very good job. Vibration dampers will help with noise from the panels whether they are excited by your sound system or road/engine/exhaust/traffic noise. Panel resonance adds to the overall noise levels in the car and is an important path for transmitting noise into the passenger compartment. Most panels are best treated with 25% coverage at the center. Going beyond 25% and using multiple layers runs into steeply diminishing returns.

Thin sheets of foam will attenuate very high frequency sound only. To be effective, a foam needs to 1/4 as thick as the wavelength of the frequency you want to absorb. 1/8" foam will absorb sound above the audible range and 1/4" foam just starts to dip into the audible range. Most of the objectionable noise and panel resonance is in the 50-250 Hz range and you will need foam that is several FEET thick to have any impact there. This sheets of foam are very useful to use as gasketing material for license plates and trim panels to prevent rattles. You should only use closed cell foam in a vehicle. Open cell foam will hold moisture and odors so it isn't appropriate for an automotive environment.

Take away panel resonance and rattles and these cars are still very noisy because of airborne noise - tires, engine, exhaust and traffic. The only way to effectively block airborne noise is by putting mass between the noise and your ears. This is a small scale version of the barrier walls built along highways. You need to completely shield the noise source with an unbroken layer of barrier material since noise will just bend around any gaps or openings. Mass loaded vinyl and lead sheeting are the most commonly used materials and 1 lb/ft² seems to be the best compromise between effectiveness, weight and expense. In most cases you will get the most benefit by applying the barrier material on top of a layer of closed cell foam to help with high frequency noise and decouple the barrier from the substrate.

In summary, using a product like Dynamat Xtreme alone WILL make your speakers sound better, but even completely covering every sheet metal panel in the car will only reduce nose transmission by 1-2 dBs. Using much less of a product like Dynamat Xtreme and following with complete coverage with a decoupled barrier can reduce overall noise levels by 10-20 dBs.

 
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give us an example of what materials to use like as a name brand and where to get it.

 
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My brand for one.