Facts:
1. For the same SPL excursion quadruples for each octave you drop in frequency.
2. IM distortion is a function of excursion.
3. The cross-over type determines the axis along which peak output occurs.
4. Steeper cross-over slopes reduce the effects of changing driver response beyond the pass-bind.
5. Higher order cross-overs have more ringing in the impulse response.
Opinions:
From 1+2 you need at least a third order slope so that excursion is decreasing below the cross-over point resulting in low IM distortion.
Adding 3 you need a 4th order Linkwitz-Riley XO that has its peak on-axis because this leads to the most natural sound.
4 means that the higher-order cross-over is an enabling technology that allows using stiff materials (magnesium) that are very pistonic in their passband (for low distortion) but ring like bells at higher frequencies.
5 means that you don't want to go beyond LR4.
Phase coherence doesn't matter. Time alignment at the cross-over frequency does as a tool to aim the peak response at the listening axis.
Other people have different opinions and subjectively excellent sounding speakers have been produced with all sorts of technologies.
Of course, the most important thing is what you find pleasing. If it floats your boat buy it or build it.
1. For the same SPL excursion quadruples for each octave you drop in frequency.
2. IM distortion is a function of excursion.
3. The cross-over type determines the axis along which peak output occurs.
4. Steeper cross-over slopes reduce the effects of changing driver response beyond the pass-bind.
5. Higher order cross-overs have more ringing in the impulse response.
Opinions:
From 1+2 you need at least a third order slope so that excursion is decreasing below the cross-over point resulting in low IM distortion.
Adding 3 you need a 4th order Linkwitz-Riley XO that has its peak on-axis because this leads to the most natural sound.
4 means that the higher-order cross-over is an enabling technology that allows using stiff materials (magnesium) that are very pistonic in their passband (for low distortion) but ring like bells at higher frequencies.
5 means that you don't want to go beyond LR4.
Phase coherence doesn't matter. Time alignment at the cross-over frequency does as a tool to aim the peak response at the listening axis.
Other people have different opinions and subjectively excellent sounding speakers have been produced with all sorts of technologies.
Of course, the most important thing is what you find pleasing. If it floats your boat buy it or build it.