View Full Version : The difference between "roofing products" and TRUE sound deadening.

Second Skin Rep Jon
01-16-2012, 12:24 PM
I have written several articles on sound deadening before I was with Second Skin Audio (http://www.secondskinaudio.com/) and even more recently to provide people with as much knowledge and information on this subject so that people can make the most informed decision when considering adding aftermarket sound deadening to their vehicle.
Since we are new to this wonderful forum I thought it would be as good of time as any to write another article with even more information and statistics.

So if you have ever considered or are currently thinking of installing some aftermarket sound deadening to your vehicle, whatever brand it may be, please take some time to read this and become an insanely informed consumer.

First and foremost...
In the world of sound deadening you will typically find three or four different products to use to control vibrations and panel resonance. For this article I am going to focus on the two most common types of products on the market today and those would be.

- Mass loaders
- CLDs (constrained layer dampers)

Mass loaders are exactly what they sound like, they add mass. They work on the principle that if you add enough extra weight to a panel that it's resonance frequency (the frequency at which the panel will resonate, vibrate, and make audible sound) will be lowered to the point that it's not as audible to the human ear.
Mass loading was a popular technique many many years ago and has more or less lost it's usefulness due to newer and more effective means and is now considered old technology. Why you ask? To be effective, mass loading requires approximately four times the weight of the panel to be added to reduce the panels resonance just one octave. This in not an efficient way to control vibrations, not to mention the negative impact it'll have on your gas mileage.

The next and newer form of vibration controlling products are CLDs (constrained layer dampers). Examples of quality CLDs include:
- Dynamat Xtreme
- SDS CLD Tiles
- Stinger Roadkill Expert
- Second Skin Damplifier

... as well as a few others. CLDs work on a completely different level in comparison to mass loaders. CLDs work by converting the vibrational energy into low level negligible heat through a shearing process. Because of their efficiency at controlling vibrations, these products are typically thinner and lighter than mass loaders while performing two or three times as well. Thinner, lighter, and less product needed to achieve greater results.

Roofing products are NOT sound deadener...

More often than not, a quick Google search for a cheaper alternative to automotive sound deadening results in many people suggesting or even using roofing products from their local home improvement store. But just like everything on the internet, you have to take these peoples opinions for what they are... opinions.
Materials that are usually found and used are Peel & Seal and other similarly produced roofing membranes. Quite often these products look and feel similar, if not the same as actual vibration dampers so it becomes an obvious choice.
There are still several unscrupulous companies that continue to sell these materials, just rebadged as "automotive sound deadening" and sell them at a premium.

The reason these roofing products are not an effective or efficient alternative are many.
Most roofing products are made from asphalt or a combination of asphalt, bitumen, petroleum distillates, and/or low grade rubber. These in most any combination equate to a low grade adhesive. Because of this, these products are intended for use on low sloping roofs, typically not exceeding 30, as their their adhesive is the limiting factor. If you were to apply such product to a vertical surface, such as a car door, failure can be imminent.

Another reason these roofing products are not ideal is the fact that they lack a thick enough constraining layer (foil) to do any good. Without this constraining layer the product can't withstand the shear strain of panel flex and the conversion of the vibrational energy into low level heat is lost.

Even as inefficient as mass loading is, these products wouldn't even cut the mustard as a mass loader because they are just too light weight (averaging about .30 pounds per sq. ft.).

Besides all of the reasons above, my favorite argument from these individuals (and even some companies with inferior products) is that these products are so cheap that you can get away with using two or three layers of the product and come out ahead both with your wallet and results, this is further from the truth and I can prove it!

Second Skin Rep Jon
01-16-2012, 12:25 PM
Roofing products just don't work...

To prove these people wrong that it's "cheaper" and "just as effective" to use roofing products, I set forth to put this theory to test. To do so I began with a brand new 12" x 24" sheet of 22 gauge steel which I then laid out where everything would be installed for testing.
The sheet is split in half to provide some distance between the vibration source and the equipment that will record/pickup the vibrations.
The bottom half is the testing area.
A 6" square smack dab in the middle is where the properly designed automotiove CLD vibration mat will be placed to simulate 25% coverage of a panel (such as a door, trunk lid, or even a roof).
The roofing product will be placed over the entire bottom half of the sheet metal to simulate 100% coverage.

Location for the transducer that will provide the vibrations for the test.

A better shot of the "testing area" where the products will be applied.

On the backside of the testing area is where the pickup (in this case a highly sensitive accelerometer) will be placed.

With the sheet metal panel and transducer mounted securely, an audio signal (20Hz to 250Hz sine sweep) was then fed into it, thus causing the panel to vibrate. I ran the test a total of three times and took the average of the three runs and used that as my baseline for the untreated panel, below is the graph.
The pink horizontal lines represent the highest peaks.

I than repeated the test using a well know, and properly designed, automotive sound deadener mat (around the $3-$3.50 per square foot price point):

Once again, ran the same three tests and took the average. Here is the graph for the CLD (RED) compared to the baseline untreated panel (BLUE).

So to put their theory of "it's so cheap you can use two layers and get the same results", I did just that. I applied the roofing product (U-Seal brand roofing product) over the entire bottom half, the first layer was applied horizontally, second layer was applied vertically.

Three tests were ran, and I took the average.
Below are the results of the two layers of roofing product (BLUE) overlaid with the 25% coverage CLD (RED):

As you can see, two layers with 100% coverage of a roofing product still doesn't quite beat out 25% coverage of a properly designed CLD mat. There are a few areas the roofing product did perform better, but the same can be said for the CLD.

The weight difference between the two products is quite significant, two layers of the roofing product clocked in at 9.7 ounces, where as the CLD was only 2.6 ounces.. nearly 3.75 times less than the roofing product. So for those people who believe weight has something to do with the performance of a product, think twice.

To further put a nail into the "it's cheaper to use roofing products" coffin, I took the average price in my area of your typical roofing product which is $17.45 for 12.5 sq. ft., so $1.396 per sq. ft.
The CLD I used during these tests, on the high side, costs $3.50 per sq. ft..

Now if we break that down, the roofing product per square foot costs $1.396, multiple that by two (because you need to use at least two layers to get close to the same performance) = $2.792 to treat one square foot of panel area.

The CLD on the other hand costs $3.50 per square foot, divide that by four (since it requires only a quarter of the amount) = $0.875 to treat one square foot.

$2.792 for a roofing product vs. $0.875 for a properly designed automotive sound deadener, the choice is yours.

So at the end of the day, it's your vehicle and your money. I can only help you in making an informed decision and I hope this article has.