Originally Posted by Boostedrex View Post
That confuses me a bit Brian. Fiberglass will be stronger than MDF while remaining thinner and lighter. Just lay it up where it doesn't have any large flat areas and you'll be good to go. Though I'm sure you're no rookie at laying glass. I avoid MDF as much as possible because fiberglass is so much stronger and easy to mold to specialized shapes.
I don't mean to hijack this thread, but there's some good reasons to use MDF *and* fiberglass. Here's why:

When you make a loudspeaker enclosure, you basically have two ways to make it work properly. The first way is to make the walls strong enough that they don't flex. For instance, you could use 1.5" MDF, and it will flex less than 3/4" MDF.

But there's another approach that works too, which is to have a stiff layer, then a soft layer, and then a stiff layer. What happens is that the stiff layer flexes, and the soft layer absorbs the energy.

This is constrained layer damping, and with this approach you can create a material that is better damped than lead.(!)

I've been following this approach for a few years now, and it seems to work well. I stole this idea from Geddes, who used this construction on the Summas that he built for me. (My Summas are carbon fiber - MDF - carbon fiber.)

I use this on my bikes too. Very time consuming, but effective.

One of these days I'm going to try replacing the MDF with cardboard. Basically make a poor man's version of Nomex. (The wheels on my bicycle are carbon fiber - cardboard - carbon fiber.)

It might seem a bit silly to use foam or cardboard in a loudspeaker enclosure, but it's really effective. By themselves, they're not ideal, but sandwich them together and they're greater than the sum of their parts.

The Airbus A380 is also built with the same construction. (fiberglass-aluminum-fiberglass-aluminum-fiberglass-aluminum-fiberglass)