How thick should I lay the glass? I am putting an Eclipse Aluminum 12 in the box powered by an alpine amp (500 watts RMS, 900 peak), in a sealed design. I want the box to be strong as h*ll, and this will be my first attempt at using fiberglass for the bottom of the box. Just trying to get the details worked out before I jump into this.

 

Depends on how well it is built - glass / resin ratio and a lot of other factors. Probably anywhere from 1/8 inch to 1 inch depending on materials and build quality. A 2 - 3 inch thick walled enclosure could be really weak and have a lot of resonance if not built properly.

 

You'll want to use as much wood as you can too. I have mine in the spare well and it's nice and thick, but it's braced with wood for some better acoustics

 

I wouldn't worry too much about hte acoustics of one material versus the acoustics of another. Cardboard has worked well in a lot of enclosures and can likely only measure differently with expensive tools, not with the ears. It's amazing when you do A/B comparisons with all other elements equal. What you think will would different definitely does sound different, unless you don't know which speaker or amp is playing. Then it's a 50/50 chance of hearing the difference.

 

So if I am careful in building it, and make sure to keep all the air bubbles, etc. pressed out and use good fiberglass cloth, 1/2 to 3/4 of an inch thick should be good right? Would the fiberglass cloth sold at H*ME D*P*T work for this? Thanks guys!

 

Make sure you have a good laminating resin with no fillers. 1/4 to 1/2 inch thick should be plenty. Use the glass cloth for the side that can be seen. Use the chopped strand mat for the rest. And you can get the shape you want with wood and fleece. Use the wood basically to make a frame. Use a good fleece that stretches equaly in both directions. You can secure the fleece in the shape you want with a staple gun and super glue. And be sure to wet out the fleece properly by useing a squeegee. Once that layer cures you can start adding body filler or mix up your own, that's the best route. Use the chopped strand mat to get the strength you need.