Is that possible? I don't really feel like messing with fiberglass so would I be able to line the curves of the tC with bondo and use MDF for the straight parts for a sub box?

 

MDF is the wood product of choice for wooden boxes... bondo in those quantities may not hold together so well over time with the vibration. Plus, it will be heavy as hell! 3/4 inch MDF on its own is very heavy. A 4x8 sheet of true mdf (not chip or particle board) weighs in at around 100 lbs I believe. I used to build custom cabinets before and during part of college, and MDF is used as substrate on some types of countertops, so I can vouch for its weight. It is, however, easy to sand and work with other than that, and sounds great. I built a custom box for two 10s that is still in my saturn (mounts against the back seats in the trunk) and it works well.. but is heavy nonetheless. So, an MDF box yes, but I wouldnt try to make any of the structural parts out of bondo.

 

Bondo isn't much easier to work with than 'glass.....

 

i agree w/ engifineer bondo wouldn't hold up and it would be really heavy.. if your set on doing it in bondo i'd recommend bondoglas or duraglas. they are plastic filler like bondo except it is reinforced w/ fiberglass strainds in it

 

If you have access to a place that carries goods for cabinetry, about $35 a sheet will get you ULMDF which weighs about 1/3 less than standard Home Depot Grade MDF, which is an amalgam of many woods from many places. ULMDF is usually softwoods only, and even a full sheet of 3/4 only tips the scales around 68lbs.

I tend to use 5/8 almost exclusively, unless I have a span greater than 16" that cannot be reinforced with baffling due to location. That mere 1/8" thinner material shaves the weight of standard MDF down to around 75lbs a sheet. My last box for a pair of eD 10k.44s, fully finished, weighed only 26lbs without the subs, so it's not as if we're talking about a ton of weight.

If you want advanced contours, fiberglass is the only way to go. Of course, MDF boxes are cheaper, easier to build, and... cheaper.

 

bondo pretty much is used to fill in the holes and little gaps that isnt filled in but the fibers of the fiberglass, its merely to smooth the surface out....using to much will crack in no time

 

If you insist, use tiger hair, bondoglass, duraglass, whatever you chose to call it. I will not advocate it, but it's better than standard lightweight bondo filler. Problem people don't understand is that the bondo, nor the resin used in glass is what gives it strength. The fibers is where the strength is at.

As for MDF, use no less than 3/4 inches on any box. You could get away with 5/8 on a box for an 8, but I still wouldn't. 3/4 isn't going to flex near as much as the thinner sheets. Flexing changes box volume, and you won't get a uniform sound. I like to line the interior of my boxes with spray rubberized undercoating to reduce resonance further and further prevent flexing.