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Project Old School: Quiet Time

Lining the Cab With High-Tech Products from Dynamat

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.

Use this handy chart to help make some sense of how sound is measured
Type of Sound Units or Individual Decibels Decibel Scale Value

Rustle of Leaves

10 10

Whisper

100 20

Soft Conversation

1,000 30

Average Residence

10,000 40

Average Office

100,000 50

Telephone Conversation

10,000,000 70

Heavy Traffic

1,000,000,000 90

Subway Traffic

10,000,000,000 100

Airplane Engine,Jackhammer, Punk Rock Band

1,000,000,000,000 120
SOURCES
DYNAMIC CONTROL OF NORTH AMERICA, INC.
3042 Symmes Rd., Dept. CT
Hamilton
OH  45015
PRO DESIGN HOT RODS
2020 S. Susan St., Dept. CT
Santa Ana
CA  92904
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