I've been using the Theater 4's since midsummer with a pair of Welborne Labs Laurels (300Bs - c. 8W). The Laurels are beautiful amps, but they either roll off or lack the muscle to get the full bottom end out of Theater 4's (compared, for example, with my Assemblage ST-40). Casting about for my next project, I figured what the heck, I'd try a subwoofer and after searching around settled on the Tempest driver with Adire's 250W plate amp, downfiring in a sealed 21.5" box, the design right off Adire's site.

To make a long story short, the Tung oil finished drying and I hauled the finished box upstairs this morning, stuffed it, screwed in the plate amp and driver and fired 'er up.

What a hoot! The most surprising thing is that the greatest effect of the subwoofer isn't increased bass per se - though it's there in spades - but rather that it seems to allow the Theater 4's to do their beautiful thing even more effortlessly than before. Individual notes and instruments - a stray, haunting background flute - are more distinct than they were before. I can only guess that the Pi's are benefiting from the fact that the Laurels are no longer straining to power the drivers all the way down. I'd also say that the Pi's are playing louder, presumably for the same reasons, although it could be that the additional bass makes the total output seem subjectively louder.

My woodworking skills are pretty rough, but I tried a few nice touches: Cherry veneer from Constantine's, five coats of Tung oil, both driver and amp are attached to the box with machine screws in threaded inserts, so that they can be repeatedly removed without weakening the attachment.

I sometimes forget how much fun this hobby can be! Jimi's playing Voodoo Chile now and I'm laughing again.