Quieting the Mazda 3
 

I just finished a fairly substantial project of trying to quiet down my Mazda 3. It started when the bumpy Portland streets were making my door rattle. I did a few things that took care of that and thought I was fine. Then I played some music with heavy electronic bass and all the doors rattled so horribly that I had to switch back to folk and other music with mild bass.

I had already switched out the factory stereo for a Pioneer unit, and put in a 200w power amp and subwoofer, but hadn't done anything to the factory speakers yet. They sounded okay so long as there wasn't too much bass or overall power. I bought Infinity Reference speakers to replace them. They were only like $75/pair. As always the enormous quality difference is amazing. Infinitys are not even really high end speakers, but they seem like they came off the space shuttle compared to the crappy made-in-china things that the factory puts in - the magnets are puny and the cones appear to be made out of recycled grocery bag pulp.

Anyway, the interesting part of the project is that I used a product called Quietcoat. It's basically paint thickened with ground up asphalt, I think. I painted the skins on the inside of the doors and the rear wheel well with 3 coats. It was a huge pain in the ass, especially taking off the inner plastic panel on the doors. It's difficult dealing with the window apparatus and the lock plugs. I got them half off in the back and decided not to bother with the front. Anyway, thumping on the doors only suggests a mild sound dampening from the Quietcoat.

After that, I put on the Dynamat "Extreme". I bought a kit with four large sheets. I put strips on the inside door skins, on top of the Quietcoat. Just three strips inside each door seemed to make a much bigger difference when thumping than the Quietcoat did. After that I cut the mat into strips and covered as much of the inside plastic door panels as I could, overapping some of the pieces onto the surrounding sheet metal. Then I installed the speakers.

Road noise is significantly quieter now. The doors feel heavy and solid when you shut them and the improvement in sound quality is amazing. The whole project cost about $250.

If anyone else is considering doing this, I recommend skipping the Quietcoat and just using the Dynamat. I also recommend not trying to take the inner plastic door panels off. By removing the speaker and pulling out the clear plastic insert, you can reach inside well enough to put a big strip/chunk of Dynamat on each exposed flat of sheet metal, which seems to work wonders. If I really wanted to quiet the car down more, I might consider trying to Quietcoat the underside of the car, but that seems like too much trouble.

Without the Quietcoat, the speakers and Dynamat would have cost around $200 total. In terms of sound quality, replacing the stereo is probably the most important, then the Dynamat, then the powered subwoofer, then the speakers. I estimate I have about $750 to 800 in the system overall. It's hard for me to imagine it sounding much better, so I wouldn't want to spend more for real audiophile stuff.

OK, i see it's an old post... but in any case, thanks for the tips on where you had luck with dynamat.
As for the floor - you can take the seats out and put it under the carpet, as long as it's fairly thin you shouldn't run into any carpet wrinkles or anything like that. This should be easier thatn messing around with what will stick to the bottom of the car.