Im interested in building a pair of 3 pi speakers but wanted to see if there's any reason a pair of ae speakers 12 inch woofers would not be suitable for this build matching with the DE250 and your flat pack horn?
The plans show crossover components needed for the Acoustic Elegance TD-12S driver. That's the only AE part that's suitable for the three Pi model.
I would also suggest measuring the driver to check its response above 500Hz. In the past, we saw some drivers that were beautiful all the way up past 1kHz, but some people reported a cone breakup notch around 700Hz, as I recall. Not sure if that was a single batch of cones or if production changed or what.
I know I really loved the drivers I tested, but saw some others that weren't as clean up high.
As for the high-frequency components, the waveguide is our H290C and the B&C DE250-8 is the recommended compression driver. You can get the driver almost anywhere, and you can get the waveguide from us.