In addition to the horizontal/vertical lobing issue, a 2-way ribbon will have huge distortion or directivity issues at the crossover anyways. Pairing it with woofer will likely require an unusually high crossover point, both drivers will likely distort at that level, and both drivers will probably be beaming. This would leave you with a narrow listening window on top of whatever other lobing issues occur. It's super tough to make a good 2-way like that.
My favorite designs for a center are a decent two-way with flanked woofers, WT/MW style. Get a nice midrange or midwoofer and cross it so the midrange takes the majority of the vocal range, 300-4000hz, get some fun/price effective drivers to do the rest. This is especially important when using a center for home theater, where most voices come directly from that channel. Having a strong 3-5" mid fill the room, unobstructed by cancellation is the goal, IMO.
My favorite designs for a center are a decent two-way with flanked woofers, WT/MW style. Get a nice midrange or midwoofer and cross it so the midrange takes the majority of the vocal range, 300-4000hz, get some fun/price effective drivers to do the rest. This is especially important when using a center for home theater, where most voices come directly from that channel. Having a strong 3-5" mid fill the room, unobstructed by cancellation is the goal, IMO.