I'm still not sure everyone is totally understanding what I did there. The object is NOT to "clamp the driver down securely." The object is to sandwich the driver so the frame makes contact all the way around the perimeter of both sides, but still allow the transducer to float inside the frame with seasonal changes of the wood. You MUST fashion an appropriate spacer between the two wood frames to allow relative movement. (The thickness of that spacer is very important.)
My setup is still working beautifully after a number of years.
Cheers,
Dave.
Not to take anything away from Dave, a gentleman named Rod Hickerson sandwiched his MMG panels several years earlier, but he used MDF. Dave's design is quite elegant. He did a fantastic job of detailing it so that others could copy it. One of the assets of his design is that it doesn't require more advanced joinery skills. Although someone who shall go nameless criticized it, I think it's a perfectly effective method. 
Guess my design is closer to Rods in that aspect (or not?), as my drivers are solid in the frames, no moment. Been that way for a few years now, and I've been happy with the results. The poplar frames were totally sealed (individual pieces, then as a whole) with a Minwax sealer, and we keep our house climate controlled, with very little variations in temperature and humidity. Matter of fact I recall a discussion on the Asylum on that subject.
IMHO, Since the driver components are placed on steel plate material, only the most extreme conditions would cause a problem.
Matter of fact, in this case, I would think the use of multiple layers of Baltic Birch plywood in a sandwich frame would have an advantage over solid hardwood. I was going to go this route at first, but was talked out of it.
At one time I entertained the idea of replacing or modifying the center wood spacer (same depth as the driver) with some sorbothane gasket material, to float the driver for more movement and hopefully better dampening results. But for now just plan to play around with some passive bi-amping, then will move on to the next speaker.
