Originally in my search for another speaker project to work on I came across this thread about "Econowave" speakers. The idea behind them is to use a compression driver with a waveguide paired with a large woofer, resulting in high sensitivity that allows playback at reference levels with low power requirements. Additionally, the waveguide controls the directivity of the tweeter, narrowing it to reduce unwanted reflections, especially in the vertical plane.
Another resource I found as I was looking at these kind of speakers was the Pi Speakers website which uses the same idea although arguably in a more polished form.
Once I had decided that the constant directivity (CD) speaker was the way to go, the next step was to start figuring out what I wanted out of them, and from there which components to use.
Really my only requirement is that the speakers play low enough to crossover to a sub at 80Hz, which even with a sealed design should be doable. Since I don't plan to listen at reference levels (peaks up to 105dB from the main speakers and 115dB from subwoofers), that is a secondary concern, but with the high sensitivity of constant directivity speakers, it's a very achievable goal. Finally, since my goal is to never have to replace these, I set the budget to around $300 per speaker for electronics.
With that said, here are some of the options I considered when choosing components for this project:
QSC PL-000446GP Replacement Waveguide Horn for HPR152i ($35)
SEOS ($30) (http://www.diysoundgroup.com/waveguides/seos/plastic-seos-matte.html)
Dayton H6512 ($7)
B&C DE250 ($130) (http://www.parts-express.com/pdf/294-605.pdf)
Denovo DNA 360 ($75) (http://www.diysoundgroup.com/drivers/tweeters/dna-360.html)
Denovo DNA 350 ($57) (http://www.diysoundgroup.com/drivers/tweeters/dna-350.html)
Selenium D220Ti ($50) (http://www.parts-express.com/pdf/264-270s.pdf)
Eminence Deltalite-II 2512 ($150) (http://www.eminence.com/pdf/DeltaliteII_2512.pdf)
Eminence Delta Pro 12A ($135) (http://www.eminence.com/pdf/Delta_Pro_12A.pdf)
Eminence Delta 12LFA ($100) (http://www.eminence.com/pdf/Delta_12LFA.pdf)
Dayton Audio PA310-8 ($65) (http://www.parts-express.com/pdf/295-032s.pdf)
The Dayton woofer and Selenium compression driver were used in quite a few of the Econowave designs, which is why they show up here along with the QSC horn. That pairing would have been my initial choice based on their price and the success people have had with them in the past, but after looking around some more I came across the SEOS project. The waveguide measured very well, and the DNA compression drivers offered alongside them are very comparable to the much more expensive B&C DE250.
With the SEOS and the DNA-360/350 looking like the best option for the high end, I wanted to find a woofer that could keep up, so I finally settled on the Eminence 2512 which offers better sensitivity, power handling, and extension than the Dayton (or some of the other Eminence offerings).
As of right now I've ordered the SEOS and DNA-360 as well as the 2512s (which just came in), and I'll be starting measurements and modeling the speakers so I can begin designing the crossover.
That was a pretty dense post, since I had to cover a lot of progress all at once, but it'll be a little more broken up in the future (and there will be more pictures once I get my camera from home).