mdf box or fiberglass box?

i built a model for my subs, 2 12" infinity. i would rather build a fiberglass one because it looks bettern than a box i think. i have a few questions though. seeing how it is my first time playin with fiberglass should i try and build something else first instead of the box? how do you go about figuring out the volume of a fiberglass box with curves and stuff or do you just sort of guestimate? how long does it usually take to make a fiberglass enclosure, before painting?

You could make a box , or box's out of mdf, then make a fiberglass covering over the box's and flow it the way you want to.

Someone did a civic like that about a month or so ago, , , search back see if you can find it.

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You have to try to guess when building. After building you can measure fairly accurately with foam peanuts or like.

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Any flat portions of an enclosure should be made of MDF. It is stronger and lighter than fiberglass. It does depend on the vehicle it is going in, though. If you can make all but the top of an enclosure in MDF, then the top can be fiberglass to give you that custom work, without the custom budget. And it is quicker, too.

Good luck,
DXAV

MDF isn't lighter than fiberglass but it is stronger in flat areas. Definitely recommended for extensive flat areas.

An MDF box with a fiberglass top is an excellent starter project. Most folks will have some experience in enclosure building before working in fiberglass. That type of project makes an excellent transition between the two.

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MDF is lighter than fiberglass. 1 sq ft flat piece of 3/4" MDF is much lighter than 1 sq ft flat piece of 3/4" fiberglass. Why do you think it is not?
Also, the same piece of MDF board is stronger than the flat piece of fiberglass. But with 2 curves, 1/2" fiberglass is stronger than 3/4" MDF of the same size, the only problem with that relation is that with the curves of fiberglass you have consequently increased the surface area and made a piece bigger than the original 1 sq ft piece. You can make a 1/4" piece of fiberglass stronger than 3/4" MDF, but just think how much larger it has to be....

Or am I completely wrong here?

DXAV

Not wrong at all. For a given thickness, MDF is indeed weaker, but it is also about half as massive. For a given strength, FG will be thinner in most circumstances. Fiberglass loves to be strong, and it does it best with compound curves and multiple layers. Curves are easiest with fleece or foam on which to place the FG mats, and if you're careful with the laminations and keep the air bubbles away, you'll get a super strong box.

That said, I almost always build boxes with MDF for the flat parts and braces/splines, mainly because it's easy, and none of the subs I build need to be that strong. If they do, MDF gets replaced with 13 ply Baltic Birch plywood (which is itself 'glassed), and the fiberglass that needs to be structural is laminated to 1/2" or more, instead of the usual 1/4".

-dave

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Good explanation dpaton. There are many variables to consider when comparing MDF, fiberglass or any other material in terms of strength. That's why I always hesitate to give specifics to questions like, "How many layers of fiberglass should I use". It all depends on the specific situation.

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