Sound deadening is an important step to improving audio quality, as well as driver comfort. This does not apply to car audio alone. If you’ve ever been in a luxury vehicle, you may be surprised by how little you hear of the outside world when the doors/windows are closed (even when the car is moving). While we all might like our Nissans, I seriously doubt anyone would call them a luxury vehicle. Adding sound deadening material works to eliminate noise from entering the cabin, as well as reducing the amount of music leaving the cabin to the outside world (trust me, no one wants to hear your stereo from outside your car – if you’re looking to let people outside your car hear your music, put some speakers in the grille for them).
First, there are many different brands of sound deadening materials. The most commonly known is Dynamat. That name has become synonymous with sound deadening (like Kleenex with facial tissue). However, that does not mean they are the best. In fact, Dynamat is frequently one of the more expensive materials, and other brands can match the performance (if not exceed it) for less cost. I’m not here to plug any brands (I wish they would pay me to do so, but they don’t), so investigate yourself. I have used or heard good things about the following: Second Skin Audio, B-Quiet and eDead. For information and a comparative test on these materials, check this out. There is a bunch of information there on choosing sound deadening materials, as well as performance results.
Applying sound deadener is a time consuming task. It will require you to remove all of the interior of the car. I know it seems like a daunting proposition at first, but once you get going you will realize how simple it is. The first thing I would recommend (and I cannot stress this enough) is pick up the service manual for your car. This will generally tell you how to remove the entire interior of the car to get to the sheet metal. I am not going to give you a link to the service manuals (as they cost money and I’m sure that would have legal ramifications), but you should be able to purchase them somewhere. Also, make sure you do your work in a covered area (you probably don’t want pieces of your car sitting outside in the rain). Additionally, you may want to do this in a heated area, or when it is warm outside. I have personally cracked plastic interior trim pieces, and the string of profanity that follows is inevitable. Then, you have to go and purchase new pieces to replace them. When warm, the paneling is much less likely to crack as it is more flexible.
Sound deadening works by reducing the ability of your body panels to vibrate. Large pieces of sheet metal can bow and flex easily. This will negatively impact the audio performance of your vehicle. Applying these materials adds weight to the body panels, making them more rigid. Most of these products are a rubber adhesive with a foil-like backing. They will easily stick to the metal of the car. Be prepared to cut yourself on the aluminum backing (kind of like a paper cut but thicker). This will definitely happen (likely on multiple occasions), but the finished product is well worth the time and slight discomfort (oh yeah, you’ll probably have to contort your body in ways you never imagined to get to those tough to reach spots). I would not recommend having a shop do this step, as it is relatively simple but time consuming. They will charge an arm and a leg for this, and it can easily be done on your own during free time (I did my car on weekends only over the course of about a month). When installing, the goal is to get as much contact as possible between the deadener and the metal of the car. I’ve found it is easiest to cut the sheets into small pieces when applying. Some people may try to use large sheets, but this can entrap air that will hinder the ability of the material to work. This may not make an audible difference (theoretically, there is definitely going to be a difference in performance, but you might not hear it), but if you’re going to do it you might as well take your time and do it right. Start slow, and once you’ve figured out what you’re doing you will be able to pick up the pace.
After deadening the sheet metal, it is a good idea to add closed cell foam (closed cell means that water cannot enter the foam and be entrapped, later resulting in mold which will make the car smell awful). The brands listed above all sell this material as well. This will help block noise and some vibration between body panels and the frame/sheet metal of the car. It will also dampen the vibrations the sound waves make when hitting the body of the car (resulting in less echo-effect so there is less cancellation of frequencies that you hear).
If all of these things are added, you will be amazed at how quiet the car sounds without the radio on. Road noise will be severely diminished, and obtrusive sounds from the outside world will as well. This can be an expensive step if done correctly as these materials are not cheap. However, why would you want to run an expensive setup and not get the best performance possible? Ask anyone who as deadened their car, and they will tell you it is well worth it.
The area of primary importance will most likely be the trunk. If you are installing a subwoofer, there will be a great deal of pressure build up in the trunk that will make it noisy. I’m sure most of you have heard a car with a sub or subs in the trunk that sounds like rattling cans from the outside. This car is almost certainly not sound deadened. Also, if you can hear those noises outside the car, you’ll be able to hear them inside as well. The stereo may seem to cover a lot of it up, but listen closely and you’ll hear that it is still there. Since the goal here is accurate sound reproduction, this bit of noise is costly in terms of the whole system performance.
By now, you are probably wondering how much material this will take. The closed cell foam, when applied liberally throughout the interior cabin of the car will maybe take 50-75 square feet. The rubber adhesive-type deadener will be applied over much more of the car, so the requirement will be higher (for the coupe I would recommend 200 square feet and about 250 square feet for the sedan). Again, these estimates are for a liberal application. The doors of the car have an outer skin (this is the metal that is painted on the exterior of the car) and an inner skin (the metal that the door panels are mounted to). Both of these sections should be deadened for optimum performance. I have always found it is better to order more material and have some left over; you never know what rattles you might pick up on after your complete installation. If you have extra material, you can then easily go back and re-apply deadener to those problem spots.
Modified by AppleBonker at 1:44 AM 8/2/2008