Doug B's Seas Three Way Towers
These were really impressive at Arizona DIY 2005. Comments and construction pictures here are from the designer.

Woofers: SEAS L22RN4X-P
Mids: SEAS W14CY-001
Tweeters: SEAS 27TDC

Box Design Features:

• Mids/tweeters reside in a separate enclosure that is stuffed about 80% with fiberglass insulation.
• Box tuning is 25 Hz, using a 3x8" rectangular port approximately 17" long.
• Box volume is about 2-3/4 cu ft.
• Both sides and rear baffle are 1/2" MDF.
• Top and bottom panels are 1' thick.
• There are five iron-cross-style shelf braces which are tied to each other and to the top and bottom panels with a 7/8" dowel rod.
• Most interior surfaces are covered with fiberglass insulation to minimize port leakage.
• Crossover boards are mounted thru a removable back panel on separate boards to facilitate tweaking.

Front Baffle Design Features:

• Drivers are time-aligned in the baffle. Woofers are mounted on 3/4" MDF plates and tweeters are mounted on the rear of the baffle
• The baffle has a varying-pitch roundoff around the mids/tweets to minimize edge diffraction.
• The baffle uses six separate layers, including a piece of foam-backed linoleum, which acts as a constraint layer.
• Each layer of the mid/woofer opening is routed at a 45 degree angle, with each layer getting progressively larger front-to-back. (This is to minimize compression of the back wave.)
• Baffle thickness at the woofer is 2-1/4".
• Baffle thickness at the mid/tweeter is 1-1/2".
  

Crossover:

• Woofer-to-mid is second order at 400 Hz. The woofers are wired in parallel and the mids are wired in series, which provides BSC.
• Mid-to-tweeter is fourth order at 2500 Hz. There's a series LC shunt on the mids for the first cone break-up peak at 8500 Hz.
• There's a series RC contour filter across the tweeter to smooth the upper octave rise caused by the tweeter mounting method.