How to sound deaden your car
by Patryk Rebisz

To better understand sound deadening it’s helpful to understand little bit about sound and frequencies. This might sound like a boring information, that I personally ran away from for as long as possible, but it’s vital in comprehending why certain materials and tricks are used. Sound is a vibration that travels through the air or another medium. Thus we’ll have to deal with 2 mediums: metal of our car and the air. Different solutions are used to solve those two problems.

There are 3 products to sound deaden your car. (1) Your car is made up of many relatively thin sheets of metal that produce a lot of resonance. Those sheets of metal act like a drum producing lots of low frequency noise. The whole sheets starts vibrating and thus whole air around does as well. This is where all those butyl sheets such as Dynamat come into play. They introduce obstacles in the metal’s vibration. People tend to make a mistake by covering their whole car interiors with the butyl even though only around 50% coverage is necessary (cover half of a musician's drum with some material and see if it still produces any sound…). Extra covering beyond the 50% mark hurts your pocket without producing noticeable difference in the low frequencies as the 50% coverage does enough. (2) Second step is to produce a barrier between that deadened metal and your ear. This is done with a layer of thick rubber or vinyl. This mass-loaded vinyl needs to be somehow decoupled from the sound-producing metal, it's done with a foam.

Different manufacturers produce different product to solve this mixture or problems. Add flammability and heat barrier ability and you will understand why there is no one-fits-all solution.

Pretty much all manufacturers offer some kind of butyl to adhere to the metal sheets to deaden the metal’s resonance. When you add a few of those to your trunk, hood or any metal – you almost instantly will notice the difference – when you knock on the metal the hollow metallic noise is gone. That said the noise will still travel through metal and to deal with that you will need some foam and vinyl. Some manufacturers offer the foam by itself while others couple it with a thick rubber/vinyl. As always in life both have advantages and disadvantages. The main minus of the foam+rubber/vinyl combo is the extra price and the difficulty to work with the material that isn’t as playable as foam by itself. Advantage, of course, is that it produces superior sound deadening in one package.

To summarize:
1. you NEED 50% coverage or any metal sheets that produce hollow metallic sound – usually the thicker the butyl, the better; look for the quality of self-adhesive glue if you want to deal with surfaces other than floors
2. you ALSO NEED foam or some spongy sound deadened preferably the kind that doesn’t absorb moisture AND mass-loade rubber/vinyl as the final barrier

And finally here are some options:
Dynamat produces high quality (plus very sticky glue) butyl material (Extreme). They also produce high quality foam (Dynaliner) with mediocre glue. Their foam comes with self-adhesive but don’t let this be its main selling point as the glue is weak.

Second Skin produces high quality butyl (Ultimate) with sticky glue. They also produce high quality foam (no glue backing) and high quality very playable vinyl.They also produce Luxury Liner Pro that is a composite of high quality foam with vinyl (because both materials are bonded it’s less easy to work with than foam and vinyl by itself) but saves you time as it doesn’t require double work of having to cut both foam and vinyl (and bonding those if you choose to). Another interesting material they offer is Heat Wave Pro that has very good heat absorption characteristics and excellent sound insulation. This material is made from chemically treated jute which might absorb moisture more than one would want (other than that the material would be my favorite insulator).

Noico produce high quality butyl (80 Mil) with decent glue. They also produce quality foam with very good self-adhesive. They claim that the butyl and foam is that's needed for sound control but I would take this claim with a heavy dose of salt.

B-Quiet produces quality butyl with sticky glue (Ultimate; Extreme is thin and glue is weak). They also produce good quality foam (not as moisture proof as Dynamat or Second Skin) with OK glue but with aluminum backing thus dissipating heat better than the other two. They also produce their version of SS’s Luxury Liner Pro combining vinyl with their foam.

Stinger produces high quality foam with vinyl backing. The sound deadening quality is excellent but the material does smell so you will have to leave it out for a long time if you plan to install it in places other than your trunk.

There are others but I didn’t get to test their materials.

So, now that I've tested those materials what did I end up using on MY car?
— For all the vertical and face-down surfaces I used Dynamat Extreme because it’s excellent butyl AND excellent glue.
— For non critical flat surfaces facing up I used Noico 80 Mil (because it was much cheaper than Dynamat) and for all other (like floors near the exhaust manifold) I used Dynamat Extreme.
— For can’t-smell-it flat surfaces (in the trunk) i used Stinger RoadKill carpet and for others I used Dynaliner (but could have used Second Skin Overkill Pro for similar results).
— For some surfaces I also put down mass loaded vinyl SS Luxury Liner. You can also use Luxury Liner Pro which is excellent as fantastic substitute for foam AND vinyl in one package.
— For the trunk and hood I used Dynamat butyl (again, because of its strong glue) and Dynamat Hoodliner (its glue sucks though).

If money wasn’t the issues I would just use Dynamat Extreme as butyl to deaden metal and SS Luxury Liner Pro as one-stop sound insulation on most surfaces.

Final observations:
— I didn’t particularly care for B-Quiet products.
— People blindly saying Dynamat is the best are spewing overheard gospel. Yes, they are very good but without explaining why they are good and where they are just OK it makes those people look like fools who don’t know hat they are talking about.