Shhhhhhhh.....mass loaded vinyl and sound deadening

Yup. As long as the original deadening is still in good shape, leave it. Carpet will help immensely as well. So will jute.

I Would say, as long as the original stuff is not rock hard, you can leave it. Just make sure any rubber/asphalt on top of is very well glued to it (so it can move with it).

I also used the reflective bubble wrap stuff. It seems to do a decent job of absorbing some higher frequencies and of course reflecting a bit of heat. Not sure it is an ideal soundpfoofing material, but it is thin and very light.

Another material that does a good job in certain circumstances and is cheap is fiberglass insulation. Very bulky of course and can get very itchy. Good for larger "void" areas like under fixed seats though.

rslifkin wrote: You can probably leave the original sound deadening material in place and just add additional in the places that need it. Carpet with a good backing does cut down on noise quite a bit.

I use moving blankets/old sleeping bags in the RX-7 to mitigate its lack of a carpet and giant holes in the floor where the suspension comes through. Helps phenomenally.

'peel and seal' way cheaper than dynamat from Lowes worked for me. (Home Depot did not have it when I sound deadened my civic.)

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5 years later none of it has moved through several 100f episodes and it never stunk though maybe the volatiles in this stuff dont stink so dead brain cells might still be happening. 5 rolls or so for total of 20 lbs ish acroos the whole interior floor pan. I also shoved as much recycled denim insulation matt into spaces behind panels as I could. The car went from crazy making to tolerable for 100 bucks and a long day.

Second Skin Audio has some good products / system for this. Check out this link for their approach and products.
http://store.secondskinaudio.com/how-to-insulate-your-ride/

I was just looking for this stuff today, literally 3 hours ago. The Peel and Seal product is going to get tried just because it is half the price of other things. I can appreciate the effectiveness of the layering approaches but due to time and budget I'm going to do floors and trunk pan with this stuff and see how it goes.

Although this stuff looks appealing and is also economical: http://www.lobucrod.com/

The king of solutions here is a set of Winchester shooters' earplugs.

Plugs out, it's a '91 CRX with a noisy exhaust and unbalanced wheels, about 95 dB at 80 MPH.

Plugs in, it's a Lexus LS400, about 70 dB at 80 MPH.

Earplugs do work, but handing them out to the kids before we go to soccer doesn't seem like a great solution. This is just a situation where one car is clearly better, so now I want another car to be better too and I wonder if I can.

Peel and seal only works well at nearly 100% coverage. And then not as well as dynamat. Or mastic from McMaster-Carr. I will say that peel and seal is a good primer for another product, as the adhesive-backed stuff sticks well to the aluminum, and peel and seal sticks well to air and water, let alone metal.

I've used Peel and Seal (Lowes), and it was better than nothing, but not great.. I also tried (with limited success) to make/apply my own Lizzardskin using Henry's roof paint and adding glass beads (Google poor man's lizzardskin)- but not worth the effort in the end.. I needed to just bit the bullet and spend the $$ on the real thing..

I was very happily surprised when I tried Dynamat Extreme.. I drive a BEC, so it's buzzy and noisy by the nature of the engine, but Dynamat made a huge diffence in the end.. I was really surprised at how very effective it is. For me, from here out, I'm just going to ignore the cost and weight penalty and apply it in all my projects (I recommend 100% coverage, even though they say 30% is enough).. It's so much nicer to drive a sound treated car

RealMiniParker wrote: This is a good study guide. Sound Deadener Showdown EDIT: 8th post in point's link has this site linked.

This is where I learned things for the Motovan. I didn't follow that plan but at least I learned things.

For what it's worth, Peel & Seal and other hardware store alternatives are asphalt-based and some people have complained about odor emissions from it. Dynamat, Damplifier etc. are butyl-based and scent free, though some say they don't stick as well as the Peel & Seal. I'm going for butyl myself when I do the Fit just to be safe, though a lot of people seem to be perfectly happy with the asphalt-based products. Something to think about.

All these choices that mount on the inside of the body does help. Each to varying degrees. Haven't tried it yet but been told that coating the underside with bedliner paint helps. Supposedly quiets down more than just the sound deadening material alone. Have to use both for maximum effect.

anybody have thoughts/experiences using Kevlar?

I realize this is a 'more permanent' installation... but I recall it being used quite a bit for kit aircraft cowlings because of the noise attenuation. Could have similar benefits in a car? {aside from being messy and nasty to install }