Sound Insulation - Keep Quiet!

Readers may recall seeing Andrew Borodin's red '70 GTO on the cover of our April 2003 issue. More recently, Andrew and his GTO competed in Car Craft's Real Street Eliminator. What follows is a first-person account of how Andrew tackled a very crucial part of his build-up: sound insulation. We all love our g-Machines, but at times they can be unbearable on rough roads or long trips. Since we know you love to drive 'em as much as possible, keeping quiet can be a good thing--especially if you want to live peaceably with your car, your family and friends. Andrew used Cascade Audio products, but know that there are plenty of top-quality products from others such as Dynamat and Mr. Gasket (under the G Muff line). --Johnny Hunkins.

When I built my GTO, I wanted a car that felt modern, not some drumming, clanging, tinny, prehistoric beast. After having gone to all the trouble to have the body E-coated, and lovingly sprayed with Viper Red paint, I wanted a taut, quiet, and civil ride I could enjoy for hours without needing earmuffs and ice packs. Along with performance and handling goals, I wanted a comfortable cruiser that I could take on long trips. When I speak of comfort, I am talking about a nice airtight cabin that is well insulated from the elements, as well as engine and road noise. A well-insulated interior will also make your stereo system sounds much better. It's very important to make plans for a comfortable cabin before the car is completed. These things should not be afterthoughts, but should be integrated into the build-up at an early stage. This will allow you to easily integrate the right products in the right places and at the appropriate time of the build up. These steps can be implemented as part of a ground-up restoration or as part of an interior make over.

Thermal Control
Let's start from the inside out and look at the various goals that we want to achieve. When you have a bare shell or a car with a gutted interior, you have the perfect opportunity to use modern products to insulate against heat. As you all know, headers and large exhaust pipes are notorious for heating up the foot wells on muscle cars. There are various ways to insulate the floor pans against header heat. I chose a spray product from Cascade Audio, called Thermaguard (TG-1). This product is easy to apply with a special, inexpensive spray gun, the SG-1. Thermaguard is a mixture of microscopic, air-filled glass beads that are held in suspension by a latex emulsion. two thin layers (15 mil each totaling 30 mil) yields a theoretical R20 thermal control rating. This is equivalent to about 3 inches of solid foam block. Try lining your floor pans with that!

Vibration Damping
The next thing that you want to consider is how you plan on controlling the vibrations of various body panels. One technique that I am sure most of you are familiar with is the use of rubberized undercoating. There are some inherent drawbacks to using undercoating. One is that undercoating gives off a rather strong odor of freshly laid asphalt. It can also stain clothing and upholstery, so it's not really suitable for use on the inside of the car. Once again I turned to Cascade Audio for modern products that would dampen the natural vibrations of various body panels. The first product that I used was VB-1X. Much like Thermaguard, VB-1X is a spray-on product. It goes on easy, using the SG-1 gun that was used for the Thermaguard. VB-1X dampens body panels by increasing their "mass" and converting the vibration energy into thermal energy. It also has unique color-shifting properties. When first sprayed, it appears purple. As it dries, it turns black. This allows you to see when you are ready for more coats.

Another damping product that I used on my GTO is VB-2HD. This product is absolutely the coolest. It is a lightweight, vinyl-based vibration damping sheet that offers awesome fit and finish. It was used on the interior side of the door panels. The VB-2HD serves a dual purpose: It acts as both a vibration damper and a vapor barrier. One side of VB-2HD has a very aggressive acrylic adhesive that will bond to most any surface. By using a heat gun, VB-2HD can be molded to the exact shape of the door panel.

The last damping product that I used was VMax. It is a layer of thin, black aluminum that is covered with a layer of non-curing butylene rubber. Think of it as heavy-duty aluminum foil with a layer of bubble gum on the back. It sounds rather strange, but the results are remarkable. I used VMax to cover about 90 percent of my interior roof panel. Before the application of VMax, tapping on the roof would produce a sound much like a tin can. After the installation, the roof sounded like it was made out of plastic. It was amazing. Rain drops sound like quiet "thuds" (Yes, I have driven my car in the rain!) Noise Barriers

So far we have covered two aspects of assembling the perfect interior. The last item to consider in your battle against road noise, are "barrier" products. These products go on the floor pans, between the pan and the carpeting. VB-3 is a sheet product made of 15-mil thick layer of lead, sandwiched between two layers of eighth-inch thick layers of neoprene foam. Per Cascade Audio's recommendation, I used the VB-3 sheet as a "floating" floor barrier on the transmission tunnel and right under the driver and passenger feet. The lead layer allowed me to mold the VB-3 to the exact contour of the transmission tunnel. By layering the VB-3 over the sheetmetal floor, an additional air layer is created that further helps to insulate against heat, just like layering your clothing on a cold day.

The last product that went between the carpet and VB-3 is VB-4. VB-4 is a heavily mineral-loaded, vinyl barrier that is bonded to a .25-inch thick layer of acoustical foam. It is designed to work best for flat areas such as interior cabin floors, trunk floors and footwells. I laid a large sheet of VB-4 from the front to the back of the interior floor pan. [It should be noted that Cascade Audio recommends that VB-3 be used exclusively on irregular or curved shapes, i.e. transmission tunnels. VB-4 is likewise recommended for flat surfaces only. Cascade Audio states that it is not necessary for the two products to be used in conjunction with each other in the same area of the car.--ed.]

So what does all this mean for your ride? You can actually talk to your passenger as you drive down the road! I can't tell you how many people have commented on how quiet my GTO is when they rode inside it. No longer does my head feel like it's about to explode after driving the car on the highway for three hours. This is not to say that all noise is completely blocked. The sounds of a muscle car are all there. The great exhaust note can still be heard and the stereo sounds great. What is gone is the droning and resonance that is common in most muscle cars. The rattles and squeaks are all but eliminated. I urge everyone doing a ground-up restoration or an interior make-over to consider using some of these modern, high-tech products on your vehicle. Then maybe your special someone will actually want to take a ride with you.

HOW QUIET IS IT?
Here is a before and after comparison graph. The vehicle that was tested is a 2001 Toyota Tundra V-8, access cab with a TRD package. VB-2HD was applied to all interior door skins, replacing the stock vapor barrier. VB-2Max was applied to the back of all outer sheet metal, such as the doors and the back wall of the cab. VB-3 was applied to the transmission tunnel and the front floor pans. VB-4 was installed behind the seats and up the back wall of the cab. The microphone was placed at ear level on the driver's side and the truck was driven on pavement at 55 mph with the ambient temperature at 65 degrees. The "after" measurements were taken the following day, on the same road, same time of day and relative temperature.

In the frequency band of 100hz to 1Khz (the three octaves most obtrusive to the human ear) there is an average sound reduction of 10 dB, which to the untrained ear equates to a reduction in noise of about one half.