This post briefly covers 3 topics: a) what kind of center channel speaker I wanted, b) why I decided on a do-it-yourself loudspeaker, and c) Troels Gravesen’s website.
A center channel speaker could be a standard vertically oriented two-way (woofer /tweeter, one atop the other) speaker. More commonly, a center channel is a horizontally oriented speaker with a central tweeter flanked by two woofers. Less commonly are 3-way W-MT-W designs where a tweeter/midrange in the middle is vertically oriented with woofers on the left/right sides.
2-way loudspeakers are the best bang for the buck – your investment goes to one woofer and one tweeter, and a simpler crossover network (circuit to divide the signal between the woofer and tweeter). Most 2- ways are meant to be oriented vertically and have good horizontal (side to side) dispersion, meaning the sound stays about the same as you move from side to side (but not as much up and down). Some designs also have good vertical (up/down) dispersion meaning they would also work well on their sides.
I wanted a high quality center channel to match my Spendor SP 2/3 speakers, and got interested in DIY because I thought it would be a fun project and I hoped it would be competitive in sound quality with much more expensive speakers. Even though DIY for me means paying retail prices for parts, and manufacturers buy parts at wholesale, a DIY speaker may use parts of a quality that are unlikely to be found in commercial speakers of reasonable price. For example, the speaker I selected uses top quality Seas Excel drivers, as well as Jantzen Audio capacitors and inductors. A pair of monitor 2-way speakers with such drivers and electronic parts may have a retail price of $4,000 or more, and many such designs are not sold as single speakers.
Troels Gravesen (http://www.troelsgravesen.dk/Diy_Loudspeaker_Projects.htm) has an amazing website full of inspiring projects, photographs, and a wealth of insights and observations from years of projects and experiments. I selected his CNO-T25 design partly because of its relative simplicity (a rectangular box, 2-way design), and the excellent measured horizontal and vertical dispersion, making this design likely to sound good even if the speaker is placed on its side or if one listens from a standing position walking around the room.