?? regarding fiberglass and Brahma...

Heck, I wouldn't mind knowing, either. I have a 12" gti (very beefy) I'd like to put in a 'glass enclosure to cut down on weight (gas = $2.53/gallon...every bit helps) and give me a little more room behind my seats.

Geo...mmats...?

 

Based on personal experience with my Brahma 15, I would not consider this sub as an extreme driver... Very clean sounding and decent SPL but hardly extreme. Like with any other high excursion sub, a rigid and substantial (like in heavy) enclosure will this sub much good... I use 1inch MDF with 1.5 top plate for my little thing with 1200 watts of power and it is sounding greaat... I would say, a 1in MDF mounting rings would be a must for starters. If it was me, I would 3/4 MDF for at least a part of your enclosures and for the parts requiring composite shapes 3-4 layers of mat and resin plus bracing... The biggest problem I found with my Brahma I found out was not a problem with the box but rather with surrounding areas in the car and way to stop them from rattling. <_<

 

First off - use solid MDF wherever possible, any flat surface.

As far as building up fiberglass, the best stuff that I've used is a specialized filler mat that Select Products sells - it's very cool, called I-beam mat I believe.
I tried it after watching their first fiberglassing video, it works real well.

Essentially, you prep the area to be 'glassed... tape, mold release wax (or WD-40 I've heard, but haven't tried), etc.

Then, you brush on some resin.... stick some chopped mat strips down.. more resin... saturate it. Basically one good decently thick layer here.

Next is the I-beam mat. It's thick, about 1/4", cotton/foam like, and with small holes perforated in it. Get that down there, saturate it as best you can.

Next, the final layer of chopped mat. Another good, thick layer here.

The structure will have a good build thickness, and the perforations bond the outer layer to the inner layer, giving that I-beam strength. Cool stuff.

1/2 cube for each is tiny, I'd go bigger if the space isn't a factor - and just turn the gains down on the amps, so you aren't giving them each 1000w! B)

It isn't as though they won't be as loud - they'll be every bit as loud. Maybe louder, since you can effect a larger difference in output by changes in enclosure size than you can by changes in electrical power. Not a bad strategy for SPL.
But your electrical system won't be taxed, your amplifiers won't be working as hard, all your distirtion specs will be improved, etc. Not a bad strategy for SQ.

And definitely - listen to what Peter says - you'll have more worries about how to quiet your car, with all that bass in there.

 

This link (which is actually a broken-out frame from the SP website... navigate "products A-Z" and then "fiberglass"):
http://selectproducts.com/shopsite_sc/store/html/page1.html
What I was calling I-beam mat is what they have listed there as "Fiberglass 4mm filler mat", model number FGFILL4M.
It's the best for doing what you are doing. B)

...and they sell that mold release wax, that's what I use, even though its pretty hard and difficult to rub on some times.

 

when we build enclosures at the shop... we often get the how thick or how many layers question. there is no real answer because the mat is sold in diffrent thickness. so what may only be 3 layers for me ... may mean 15 layers for someone else.
the standard complete audio test....
so when we think a glass enclosure is thick enough... we simply stand on it and jump up and down... proves the point real quick. once that is complete... then its thick enough.

 

so are you more concerned with strength or mass? I would think you have to obtain some sort of mass in enclosure to get good sound...

 

Both! But what's important is not mass in terms of weight, but rather mass in terms of density.

That's why that I-beam mat is so cool.
It lets you quickly build up a piece so that it is both rigid, and dense. Walls end up around 1/4" thick with just one layer of chopped mat or medium woven, the I-beam mat, and another layer of chop or woven.
How cool is that? B)

Rigidity is important because you don't want your enclosure's walls to flex - you'll suffer dB losses, and possibly rattles, and even potential structural cracks down the road.

Density is important because of the very fundamentals of what an enclosure does...
The sound off the rear of the speaker is exactly 180 degrees out of phase with the sound off the front of the speaker.
If the walls are thin enough that the sound from the rear of the speaker can leak out, that causes cancellations - again, dB losses.

Some home audio cabinets use 1.5" thick MDF, with another layer of some exotic cabinet material... piano-finish exotic hardwoods, carbon fiber or fiberglass composites... and those aren't even bass cabinets.

Keep both things in mind... but also keep in mind that fiberglass is naturally much denser and more rigid than wood (in fact, it is so dense it can be reflective - that's not a good thing - but not really harmful for subwoofer frequencies).
So, where 3/4" MDF is pretty much a minimum spec... minimum spec for fiberglass is more like 1/4" to get equal performance, as long as you have shape, or bracing to keep it rigid. B)

 

i also slap some damping material on the inside of my glass enclosures.