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Original Message
Probably the vast majority of multi-way speakers ever made . . .
Posted by Brian H P on March 12, 2021 at 11:59:58:
. . . cross too high from the mid to the tweeter, and hence exhibit dips in the off-axis response in the crossover region. Even expensive, well-regarded models. Many of them also have too much distance between the acoustic centers of the drivers (greater than one wavelength at crossover frequency), exacerbating the problem. They don't even pretend to follow Toole rules.
And yet, lots of people love and enjoy their imperfect speakers. With proper toe-in toward the listening sweet spot, good distance from reflective side walls, and maybe some absorbtive/diffusive treatment on those walls, the hole in the off-axis response is not notable enough to be bothersome. Perfectionists like you and me will hear it, but most people won't.
To avoid the problem, particularly with larger diameter midrange drivers (which have their own sets of advantages and drawbacks), you need to use a ROBUST tweeter (Fs below 800Hz, high rated power handling) and cross it LOW -- not much more than an octave above Fs. Also, get the driver centers as close together as possible on the baffle. Truncated frame drivers are useful for this purpose.
Coaxial drivers, which I have not experimented with, probably offer the best solution to aligning acoustic centers, but probably introduce other compromises unique to them.