Project Old School: Quiet Time

Lining the Cab With High-Tech Products from Dynamat

Jeremy Cook Jul 20, 2004 0 Comment(s)

Ever since I began driving Old School, I couldn't help feeling like I was in the center of a tin can. Granted, when I started driving the truck, it had no door glass or seals and had a bare floor, but even with the doors built out (which mostly helped with wind noise) and a makeshift piece of carpet on the floor, there was still a ton of road and engine noise in the cab. And worse yet, the reverberation off the bare roof literally makes all the noise just bounce around more. As if that wasn't bad enough, I still haven't gotten around to building a real exhaust system. So the old glass packs are still solid-mounted to the frame, and the exhaust dumps are at the worst possible place--dead-even with the back of the cab!

Being the positive-thinking guy that I am, I figured that since the cab of the truck couldn't get much louder (seriously, cutting the roof off would probably be an improvement), this would be a great opportunity to see just how much improvement some of the sound-deadening materials on the market would make. I knew they would help me, but I wanted to see an actual number. I picked up a decibel reader, set it on the seat, and got some preliminary readings. At idle at a light, with the windows up--where the engine and road noise are low but the reverb is extremely high--the meter showed 106 dB. Then, while cruising the freeway at about 80 mph--where the reverb is lower but the engine and road noise are much higher--I took another reading of 108 dB. For reference, I also sat in the truck silently, with the engine off, in a parking lot and measured 62 dB. Finally, I held the meter right next the exhaust tip at idle and got 116 dB. So what does it all mean? This is not meant to be a lesson on decibel measurement, but to help define some of the numbers I was getting, I did a little research.

The decibel scale, like the pH scale and the Richter scale, is logarithmic. The decibel scale increases ten fold for every 10 decibels measured; a decibel is a single unit of sound. It is the very limit of human hearing or the threshold point where sound can be detected by the ear. The noise produced by a leaf falling to the ground is a single decibel. A live punk rock band may produce 120 decibels. Does that mean it is 120 times more powerful than the falling leaf? No. Try a trillion times. The range of human hearing, between the softest sound you can hear and the strongest sound you can stand, is well over a hundred million times.

So with that knowledge, I was confident that if I could line my truck with something that would reduce the decibels by even three or four, it would be a dramatic difference. I contacted Dynamic Control, manufacturers of Dynamat, explained my situation, and asked if I could really make a significant difference in sound even though I would still have the metal roof when all was said and done. They were confident that their products could still work wonders, even if not in the most desirable of conditions such as these. They sent me sufficient amounts of both their Extreme liner, a patented, lightweight elastomeric butyl and aluminum-constrained-layer vibrational damper, as well as their new Extremeliner. The Dynamat Extreme is the aluminum-backed stuff that you see most commonly. Extremeliner is a four-part composite barrier consisting of an 1/8-inch layer of neoprene, 15 mils of acoustic lead barrier, an 1/4-inch layer of high-efficiency acoustic foam, and a 3-mil urethane top facing. Extremeliner works anywhere on your vehicle's floor and firewall for the ultimate barrier against road and engine noise. Extremeliner Provides Maximum Noise Control when applied over Dynamat, so that's just what I intended to do. But first I prepped the previously overlooked floor and brought the truck to Pro Design Hot Rods for some last minute welding up of various holes and even one rusty spot. Follow along as I stumble my way through the install, which was actually pretty easy once I got the hang of it. And as for the final numbers, you ask? The decibels dropped from 106 to 97 at idle and from 108 to 98 on the freeway. That was a larger noise reduction than even the folks at Dynamat predicted! More important than the numbers, though, was that this felt like a completely different truck. It is flat out more fun and less exhausting (no pun intended) to drive. Dynamat definitely made a believer out of me.

4

We ordered up two Dynamat Bulk Packs (PN 20455) for a total of 18 18x32-inch pieces of Dynamat Xtreme. It is recommended for use on rear decks, doors, and floors to lower road noise and get better sound from your stereo system. It consists of a black butyl-based core with 4-mil aluminum constrain layer and is backed with a craft paper release liner. The thickness is 0.067 inch.

We also ordered 9 6-foot square sheets (measuring 24x36 inches) of Extremeliner (PN 21205). Extremeliner provides high acoustic absorption and excellent thermal insulation for a variety of automotive uses and is considered their ultimate low-frequency sound attenuator because its four-part lead septum composite acts as a sound barrier. The thickness is 0.392 inch. Dynamic Control recommends using Extremeliner with a layer of Dynamat for best results. So that's just what we did.

Dynamic Control also sent us these handy rollers and a cutting knife to help with the job. We also got out our heat gun, which we used to heat each piece of Dynamat before we laid it.

There were a lot of issues to contend with before we even began to lay the Dynamat over our neglected truck floor. The brackets at the back of the cab are now obsolete since that the gas tank has been relocated. So I removed them by grinding off each of the umpteen spot-welds. The quarter-sized rust hole on the passenger kick panel turned out to be significantly larger once I started grinding on it--so it definitely needed attention.

I'm not even sure what these holes by the steering column were for, but they made a great heater. They had to go. Over at Pro Design Hot Rods, the crew helped me out by cutting patch pieces for all the holes, and all the smaller ones that had been drilled in the floor over the years. Each piece was trimmed to fit and held in place with a magnet. Then owner Mike Filion buzzed each one in place with the MIG.

We trimmed out the small amount of rusty metal, and Mike made a quicky patch piece to fill the floor. After trimming to fit, Mike welded it in place.

He also trimmed and bent up a piece for the kick panel and welded it in place. It only took a few hours to do all this extra work, and now I'm much more confident covering the floor up forever. If I hadn't done it, I would have regretted it later.

After grinding all the welds smooth, I vacuumed everything thoroughly and even wiped the entire area down with lacquer thinner. Dynamic Control makes many mentions of working on a clean surface, so I obliged.

Instead of trying to make all the crazy bends over the center hump all at once, I opted to cut the pieces off at the hump and save the smaller pieces for later. Every square inch helps, so there should not be any waste whatsoever. I stuck mine high up under the dash. I started each piece by sticking the edge down, then rolling a little bit down at a time as I peeled back the paper.

Eventually, I came to a point where I had to begin trimming pieces prior to laying them down. Some of the pieces would bend up enough to roll out, but other areas needed a relief cut or two. If it wasn't quite right, I'd just overlap a bit or cut a small piece to fill the gap.

I removed the door panels and gave the backside the same treatment.

Okay, some might call this overkill. But hey, I wanted to quiet this thing down! Once the floor was completed, I continued right up the back of the cab wall and up the firewall. I was halfway done; now I had to figure out how to work with the Extremeliner.

For starters, Extremeliner does not have an adhesive backing, so I had to pick up two cans of 3M(TM) spray adhesive from the mom-and-pop hardware store. It also comes in much larger sheets. I started with the easiest areas again and sprayed about one-third of the sheet at a time. I worked down one side and up the other, making cuts along the way for things like dimmer switches and wire looms.

I then ran up the center using much smaller pieces. The smaller it is, the easier it is to form, but it's less effective if you cut it into a million pieces. By the time I got to the top of the hump, my pieces were getting pretty trick. I finished up with the back of the door panels and the back of the cab. I chose covering the cab wall instead of the kick panels because of the exhaust issues.

I learned this trick from my old pal and boss Brian Brennan. (He watched as someone did it on his Suburban.) After locating the seat bolt holes from the bottom with an awl, I used a 1 1/8-inch hole saw without the pilot bit to clear the areas for bolts. You just have to be careful not to drill into the floor.

All together, it took two full days to complete the job. At this point, I bolted the seat back in and went for a ride with my decibel meter. I was truly amazed at the results: about 10 full dBs on the meter, but the difference to my ears was night and day. I doubt I'll ever build another truck without using some sort of sound-deadener material on the floor.

COMMENTS

TO TOP