Sound Deadener Showdown
Version 2 Updated: October 19, 2005
Products Reviewed: B-Quiet Extreme and Ultimate, Brown Bread, Cascade Audio Engineering VB2, Dynamic Control Dynamat Original and Dynamat Xtreme, Elemental Designs eDead v1 and eDead v1SE, FatMat, RAAMaudio RAAMmat BXT, Second Skin Damplifier and Damplifier Pro,
Why Do It?
Before I found the solution I didn't know I had a problem. My new car didn't have any of the rattles the car I traded in had. The engine had a nice smooth sound and I was quite pleased. I did notice that cell phone conversations required more effort than I cared for and that the stock sound system was typically unrewarding to listen to. Like every one else, I had noticed that many luxury cars provided a completely different interior experience. Quite ride, better stereo and a really satisfying thump when you closed a door. I always thought it was nice, but never considered it a big deal.
I don't think that most people, myself included, have ever really considered just how noisy most cars really are. That's just the way it is.
The only thing I really wanted to do was slightly improve the sound of the car's stereo. Nothing big, maybe an amplified subwoofer in the trunk. I looked into the possibilities, stumbled on to sound deadening, and here we are.
Most cars are inherently very hostile acoustical environments. Engine noise, road/tire noise, wind noise and the cacophony generated by nearby vehicles combine with light weight sheet metal, plastic trim and lots of glass to create an extreme challenge to anyone looking for quiet or sound quality on the road.
There are two basic concepts that need to be addressed. First, reduce the level of noise coming from outside the passenger compartment. This is the noise "floor" with which the sounds you want to hear must compete. Conversation or your audio system must be loud enough to be heard above this noise level.
Second, control the reflections, resonances and rattles that are generated by the the noises comprising the noise floor and your sound system itself.
Sound deadening is the first, most basic step toward controlling vehicle acoustics.
The principle is simple. Vast areas of our vehicles consist of highly resonant expanses of sheet metal and plastic. Hit them with a sound wave and they start vibrating. These vibrations are distorted versions of the original sound and propagate throughout the car adding to the overall noise level.
Just as you can stop a tuning fork's vibration by touching it with your hand, sound deadening does the same thing with vibration prone panels. When you touch the tuning fork two things happen. First, your hand adds mass, lowering the resonant frequency of metal. Second, your flesh is resilient and damps the vibration through resistance. This second effect is called viscoelasticity. If you poke your hand with your finger, the flesh is compressed and then rebounds to its original shape. The adhesive layer of a deadening mat works in much the same way. When the surface to which it is attached vibrates, the viscoelastic adhesive is moved and then returns to its original shape more slowly than it was displaced. The vibrational energy is converted to a very small amount of heat and dissipated. When you see a product described as viscoelastic, remember that the term describes a property, not a particular composition or material.
Applying a damping mat to the sheet metal of a vehicle has a second significant benefit, it reinforces the surfaces to which it is attached, making them more rigid. As hard as it can be to visualize, our sound systems can cause significant changes in air pressure inside a small, closed environment like a car or truck. Especially at high volumes, these pressure changes will actually cause the vehicle's sheet metal to flex in and out in reaction. The energy that is used to flex the sheet metal is energy lost from the audible range. The flexing action will add distortion to the audible frequencies that are not lost.
Both of these fundamental benefits reduce noise and and preserve the sound waves we want. Very good things indeed.
There are two bonus effects that come along automatically. Since we have already dealt with the transmission of noise via vibration of the vehicle's sheet metal and trim, we need to consider the other ways we can stop noise from entering the passenger compartment. We can block them and we can absorb them. We block them with a barrier - a wall that sound has trouble penetrating. We absorb them with material that acts like a sponge, except that instead of soaking sound waves up and holding them inside, it gradually slows then down until they no longer exist.
The barrier and absorption properties of the products reviewed here are significant, but generally not a complete solution by themselves. We will need other products to fully achieve our goals. These properties are often exaggerated by the marketing hype put forward by those selling damping mats to the point that you could reasonably expect their product to change your Toyota into a Lexus all by itself. Not so. None of the additional steps are difficult and a great deal can be accomplished without drastically increasing the cost of your project. While I can't find any reliable data on the barrier and absorption properties of these damping mats, I believe that they are better barriers than they are absorbers. In most situations the best step after damping unwanted energy transfer with our mat is adding some sort of absorbing material, both on top of the deadening material and in places that adding weight will not help. Acoustic foam is the usual way go. The object is to absorb those unwanted sounds that are not blocked or damped by the previous step and to reduce sound reflection inside the vehicle, resulting in a more inert environment. We will deal with these topics more in the <a href="/howto/index.shtml">How To</a> section., just keep in mind that your sound deadened efforts will be greatly enhanced with this multi-stage approach.
OK, so that's the theory, but will you really be able to hear a difference in real world application? Oh my, yes. I took an unreasonably enthusiastic approach to this which provided a more dramatic demonstration of the change than I would have seen with a more practical approach.
Instead of doing this in phases - which I would very much recommend - I decided to do it all at once. Step one: completely gut the car. Everything out of the car and in to the house. I effectively made it unusable until it was done.
So there I was, several long days of hard work done and the car back together. I was almost afraid to go for a drive. If I had done all of this and there was no improvement, I would truly be the stupidest man on earth. Actually, now that I think about it, just taking that risk pretty much makes me the stupidest man on earth - but that first drive was rewarding beyond anything I would have thought possible.
I drove around for hours on all sorts of roads at all speeds, no stereo on, nothing, just listening. I could still hear the engine, I could still hear some tire and wind noise, but at a fraction of the level it had been before. Traffic noise all but disappeared. Absolutely amazing. The previously tinny sounding doors closed with an authoritative thump.
Then I turned on the factory sound system. Again, amazing. Suddenly I could hear things in the music that I never even knew were there. I found myself looking over my shoulder because my brain couldn't process the fact that what I was hearing was coming from inside the car. The bass response was astonishing. The mid range and high frequency were clear and defined. With sound deadening, my factory sound system sounded better than some multi-thousand dollar systems I had heard in other people's cars. Gulp.
I could suddenly hear the other party on my cell phone without straining and could be heard when I spoke in a normal voice. I could play the stereo at the threshold of pain and people outside the car could barely hear it.
You would be right to wonder if this wasn't just a case of wishful thinking and self deception. If it was, it was contagious. My girlfriend came home from a business trip to find my brand new car's interior in the living room. She could not begin to understand why I would do such a thing. She accused me of loving my car more than I loved her and got no comfort from my assurances that I loved her and the car equally. This poor exasperated woman asked me if I could put some of this stuff in her car after just one ride. I promise you, there was no one in the world less inclined to acknowledge any benefit from this project.