In the effort to reduce noise inside my cargo van (part of a stereo/sub installation) I'm doing several steps. I'm lining the steel panels with butyl foil (like Dynamat), then putting a layer of acoustic foam sound absorber, then making the interior panels from pegboard covered with carpet.
The question is about the foam. I'm sure I could buy some fancy super studio viscous foam panels for $50 sq ft, but will they be notably better than, say an eggcrate mattress topper? What qualities (closed cell, open cell, density, etc) should I look for in the foam to make it work well?
I'm just thinking if some free foam from CL will work well instead of the pro stuff, that would be a bonus.
I don't know what it is made of, but acoustic foam is amazing stuff. I would substitute with the highest-density closed-cell foam you can get. Maybe find a used memory-foam mattress?
In my experience working with studios and recording engineers the eggcrate foam doesn't lower volume levels much at all. What it does do is reduce sound reflections, which is why you see it primarily in the engineer booth at recording studios.
Wikipedia said:
The objective of acoustic foam is to improve the sound quality by removing residual sound in any space. This purpose requires strategic placement of acoustic foam panels on walls, ceiling and floors, effectively eliminating all resonance within the room.
It won't do much to lower overall sound levels if that is what you are looking for.
Acoustic foam is an open celled foam
Insulation behind van walls? Just use rolls of the pink stuff (home insulation). Stuff in in your side and rear doors too before putting panels over it. Gets rid of that echoey metallic sound when you close the doors, replacing it with a nice thud. Also good for temperature control if you ever plan on sleeping in the van. Even if you dont, it still does keep the inside of the van from getting so damn cold in the winter and so damn hot in the summer.
Ive been told make the insulation stop about 6 inches above the floor, so if there is ever any moisture back there it doesnt absorb into the insulation.
Since its going behind a wall of pegboard and carpet, why use acoustic foam?
Yeah, open cell foam, and eggcrate shapes stop sound from reflecting, since the open cell/wavy shape create little pockets for the sound waves to get trapped in. Covering it up with paneling will negate a lot of the eggcrates ability to deaden sound. Id bet the dynamat stuff and the carpet will go a long way towards quieting road noise by themselves. If youre really bent on lining the backs of the panels, get 1/2 blue builders foam panels from the big box home store, or cheap white styrofoam sheet from the craft store. It will help stop vibration of the steel from turning into noise inside the cabin.
I have an unused roll of Brown Bread you could have for the cost of shipping (I'm in SW CT)...
http://www.b-quiet.com/brownbread.html
failboat wrote:
Since its going behind a wall of pegboard and carpet, why use acoustic foam?
I was thinking that any sound coming in from the outside would be partially diffused/deadened by the foam before making it into the cabin, and the pegboard would allow some of the sound waves to make it into the foam and hopefully not come back out.
So what it sounds like you all are saying is that the foam would make it "dead" inside like a studio, but not really prevent outside noise intrusion? I like the idea of the fiberglass, I was just thinking that foam would carry less moisture and have less of a chance of growing mold in the case that condensation happens back there. (which is another reason for the pegboard... to allow sufficient air flow to keep it dry)
Should I skip the pegboard and just use hardboard? That might block more sound from getting in, but also renders the diffusion properties of the foam useless.
4cylndrfury wrote:
, get 1/2 blue builders foam panels from the big box home store, or cheap white styrofoam sheet from the craft store. It will help stop vibration of the steel from turning into noise inside the cabin.
I've tried that before with catastrophic results. Maybe its my installation, but styrofoam has no place in my vehicles anymore. Ever travel with a styrofoam cooler in the back seat? Imagine 200 of those coolers and you get the idea of how badly the last one turned out 
In reply to curtis73:
I can imagine loosing my mind with all of that squeaky din
All I knows is, conversion van walls are simply made out of plain old wood paneling, covered with foam backed upholstery. if you are doing carpet, you can stick a layer or two of regular carpet padding on it so it has some give to it. Behind the walls conversion I pulled apart, there was regular old fiberglass insulation.
Most people I have talked to that did their own interiors did it pretty much the same way in regards to paneling and insulation. I helped a friend strip out the interior in his 79 chevy van that he owned since new and had a DIY interior done with paneling and fiberglass insulation, it was fine, no moisture issues appeared to have developed like mold or rust, although it had been sitting in his garage for a few years and a mouse found its way into those insulated walls.
