Interior sound deadening / Ziebart Underbody Coating

I drive a '91 Civic. There's no engine noise but plenty of road noise.

I've read about self-adhesive sound deadening interior materials like Dynamat and the stuff they sell on B-Quiet.com. A guy made his Jazz quieter with DIY-jobs at http://www12.brinkster.com/hondajazz/dead.asp I don't know the stuff he used.

And there's a Ziebart Underbody Sound Barrier thing. I'm absolutely confused about the benefits and/or side effects such as chipping and rust-proneness... And there are different opinions about the gain.

I'm definitely going for low-noise tyres like Nokians but there ought to be something I can do in addition.

Thanx for the help :)

Asphalt-based undercorating has been used as a sound barrier for decades.

As it ages it may crack or chip, allowing moisture to get behind the undecoating, next to the metal, which may accelerate rust, especially if the coating was applied to bare, unpainted metal.
Many undercoatings remain slightly flexible and do not have this problem.

Also, if you feel like pulling up the carpet and seats, undercoating can be applied to the inside of the floors, to avoid rust.

You can also put down a big plastic sheet, on top of the floor, apply undercoating to it (about 1/8-1/4 inch thick) then apply a second coat of plastic, to make a custom made acoustic mat.

The problem with this undercoating is that its a bit heavy.
A fabric carpet underpad can go under the existing carpet, to dampen sound and be lighter than undercoating.

Finally, there's fiberglass insulation. I had a '79 Mustang a while back where a previous owner had stuffed bits of fiberglass home insulation (the pink stuff) EVERYWHERE...............under the dash, behind every interoir body panel, under the carpet, in the roof panel......it made everything very quiet...............but breathing in the fiberglass dust must have been not too good........perhaps it could be stuffed in little plastic shopping bags first.

IMO the acoustic foam and mats mentioned in your link are likely the best way to go.

There is little you can really do to quiten down a 91 Civic.
Its a very small light weight car designed for cheap mass production.
The floor and fire wall already has quite thick carpet with sound deadening material behind and underneath it. Adding more to it won't make a lot of differnce, as most of the noise you here is coming from the doors which don't have sound protection, and from wind noise outside the windows.
You can't fit any material inside the door with out interfering with the door locks and windows, and there is nothing you can do about wind noise.

If you really like the car then try a nice stereo and use music to cover the noise, other wise if noise really bothers you (and you must be a little sensitive to it) then you would have to buy a heavier more comfort orintated car, which of course means losing all the advantages of the Civic.

A quick crash course in sound deadening from a car guy with a music degree :)

Those sound deadening materials work in several ways, so if you understand how they work you can maybe come up with a pleasing combination of materials that will block some sound for you.

Viscous materials like the asphalt sticky part of Dynamat converts sound waves to heat. Not really measurable heat, but the sound waves hit the stuff. In order for the sound to make it through the material, it has to vibrate the material, then in turn the material vibrates the airwaves on the other side which is how sound makes it through to the inside of the car. Using that viscous sticky stuff, the sound encounters it, tries to vibrate it, and it can't very well. The energy from the sound waves gets converted to heat and some of it never makes it past that material.

The second thing that material does is add weight to the panels it covers. The weight it adds lowers the frequency at which it vibrates naturally. Much like adding weight to a tuning fork, it will now vibrate at a much lower frequency. Most of the road and engine noise is in the higher frequency range, so the noise that hits the panel is not easily transferred.

The other kind of noise reduction that is important to you is baffling, which comes from things like carpet padding. The sound waves hit the fibers and are redirected. The short waves (high frequency) are bounced into oblivion. The long waves sneak through easier. Its the same reason that subwoofer boxes sound better with polyfill in them. The fibers fool the waves into thinking the box is bigger than it is (basically) as well as cancel out some of the higher frequencies that have no place in a subwoofer box. Its also the same reason for the little perforated steel screen in your microwave. Microwaves are damaging to you, but the high frequency waves are completely foiled by that screen in the microwave door. But the light in the microwave is low frequency, so you can see the light coming out through the holes.

Moppie is right; the civic wasn't designed to be quiet. The way the panels are joined and the design of the panels themselves were designed to be easy to assemble so that it could be an inexpensive car. But using this stuff can help you make it a good bit quieter.

First of all, check out www.raamaudio.com (http://www.raamaudio.com) . That guy makes his own version of dynamat for a fraction of the cost. His product is the same basic thing as the dynamat extreme. Buy a roll of it (I think its $75) and start stripping that interior. Seats, carpet, console, side trim panels, anything that comes out below the level of the windows basically. Cover the floor with that stuff. Pay special attention to rear wheel wells beside the rear seat well, floors, firewall, etc. Take your time and cut out for irregular corners and humps in the floor. Cover every square inch you can, and if there's any left over, do another layer on the heavy noise areas, like those rear wheel wells and the firewall. Save enough to cover things like the door panels as well.

When you replace the carpet, take note of your padding if there is any. If there isn't, you can use the thin spongey padding used for home carpet installation, but I'm pretty sure your carpet has some jute backing on it. Don't add so much padding that your carpet doesn't fit anymore, but a good 1/4" should be fine.

Hit a local swap meet and find a product (I forget the name) that looks like a big roll of 1/8" foam with foil on it. Its very light weight and works well on vertical and overhead surfaces. Get some 3M heavy duty spray adhesive and put it on door panels and the behind the headliner on the roof.

When you're all done, you'll notice a difference. It won't be night and day, but it will be much better. Total investment should be $400 or less, but its time consuming. I did one car this way and I will never do another. If the car is already completely stripped, thats another thing, but to just strip a car to do some soundproofing... never again. Way too much work for the return you get.

Potential pitfalls: If you do too much of one thing, you will in effect BOOST low frequencies inside the car. That means you may encounter drones from wheel bearings, suspension frequencies, and exhaust that you didn't expect.

The bottom line is this: You can only do so much to dampen the frequencies that Honda decided to let through. Its not a BMW or Mercedes where they spent billions of dollars designing panel orientations that cancel noises and suspension bushins filled with viscous silicone fluid to minimize vibration transfer. Its a Civic. Designed for A-B transport with lots of reliability. You can improve it, but like Moppie said, its a civic, so don't expect miracles.