More sound killing

Sorry I didn't get back to the final bit about Memorial Day weekend. I covered most of it in the last 2 posts. Today, I'll focus on additional sound dampening, but this time without the batting. There are 2 different kinds of noise we need to deal with, and I'm looking at reducing both of them but without killing my budget in the process.

Vibration Noise

I think the stuff I bought all those years ago was called Dynamat. I blew about $200 on vibration deadener, betwen this stuff and the McMaster-Carr rubber sheets. The "Dynamat" is basically a sticky asphalty black tar with a shiny foil side. The sticky side comes protected with a wax paper which peels off as you stick it. The general concept of Dynamat (or Brown Bread or any of these contact noise dampeners) is to convert the vibration into heat, reducing the noise. For it to be effective, it needs to seal with the metal as completely as possible, so really work it in when you lay it down. On the websites that I visited at the time, the manufacturers and the sound installer experts all said you only really needed to cover about 50% of the exposed steel to notice a meaningful reduction. More often than not, no sooner was this said than the poster/manufacturer shows their install, and they used 2 layers of the stuff on every square inch of metal. What gives?

I guess it all comes down to what you're trying to do. Personally, I want to be able to drive down the freeway without feeling like I'm sitting inside a jet engine. Or a diesel engine. Or any engine.

Others (like those posters I mentioned) are trying to get to an acoustic nirvana where all you can hear is the slight whistle of the road.... until your 2000watt stereo kicks in. Okay, I'll admit, I want to hear some music when I drive. One of the reasons I'm doing the TDI conversion is because driving with one ear listening for an engine failure is tiring. And its boring for your passengers who plainly don't understand the tonal changes of an air cooled engine. Pooh on them, but I guess I'm one of them now. I kinda want to hear some Jerry when I'm driving around sometimes. Anyway, on to what I did with the Dynamat I found.

First, I double-checked the exposed wall where I removed the old insulation. This was before I shot it with the rubberized under-coating. This "check" was basically light rapping on the metal with my knuckles to hear for a rattley clang. I had put Dynamat over about 2/3 of the exposed sheet metal before I'd insulated before. The knocking produced an acceptable thunk-thunk, so I left it and moved on to the rear end.

When I drove this beast to and from the muffler shop (and to/from the tow-trailer), it was loud. I mean real loud. Like "I think there's an airplane landing behind me" loud. I looked at the rear engine hatch. Dynamatted. Rear cargo access? Dynamatted (but only on the large sections of sheet metal). Top-side engine hatch? Nada. Ah ha! I covered it almost completely with Dynamat. Each time I test-closed the hatch the "chunk" became more certain and the "clatter" disappeared. Now, I can drop the lid from about 6" up and it slams shut. Then, I attacked the last 4" of rear deck from inside the engine compartment. And then the short stretch between the spare wheel well and the left side of the top-hatch opening, test knocking along the way. This should meaningfully reduce vibration noise.

Ambient Noise

So, with a well adjusted clutch, a new engine mount and a warmed up engine, how much vibration noise is getting produced compared to the racket of a 100+ HP diesel engine? My guess? Not much. So, how do we reduce the ambient noise? Well, think about your house. In the rooms with the hardwood floors or tile, everything's loud. In your carpeted rooms, its a lot quieter. This simple case explains how we can address ambient noise in a bus: carpet the bugger. We can reduce noise with a vehicular version of a carpet pad first - closed cell insulation. You can buy 1/4" reflective insulation at Home Depot or Lowes that works great for this. I can't remember how much I paid for a roll, but I don't think it was more than $20. It covers a large area. I put some of this same roll under the floor of my bus years ago (between the 2 layers of thin plywood), and it definitely helped noise-wise. I still have a bunch left. I put some in the wall where the old batting insulation was. I'll be putting more behind every spot where I put carpet: walls, ceiling, doors.

This simple step should reduce more noise than the dynamat does. Why? The dynamat enthusiasts mostly are driving cars which have little ambient noise. They have nice foam headliners and plastic interior parts which absorb sound. The 1972 VW Bus has a wood ceiling and steel walls. No wonder it sounds like I'm launching a Mars probe when I'm driving! Once the dynamat is in, followed by closed cell insulation, topped with carpet, it could be a conversational volume in there. We'll see...

More next time,

pictures:

top: top-side engine hatch with dynamat applied.

middle: behind the stove/sink unit closed-cell reflector insulation installed

bottom: behind refer/storage unit closed-cell reflector insulation installed