Phase Coherency & the Inter-driver Phase Difference
When the woofer and tweeter acoustic phase are in close agreement with each other, the two drivers vibrate in "lock step", and the sound improves.
This is known as phase coherency. Voices lose any trace of grain; the image becomes more focused and slightly deeper, while sound sources become more pinpoint. In short, imaging and definition improve, while the handoff between woofer and tweeter becomes indiscernible.
Unfortunately, since the woofer voice coil is deeper on the baffle than the tweeter's, additional acoustic delay is introduced to all sounds coming from the woofer. The same effect is seen by a clockwise rotation of the phase vs. frequency curve. If the phase of the woofer and tweeter do not precisely match each other throughout the crossover region, the sound becomes "smeared", i.e. less distinct.
To counteract this effect, all Bamberg crossover networks employ various types of proprietary circuitry that rotate the woofer and tweeter phase back into alignment with each other. We indicate the success of this process by the Inter-driver phase difference parameter in the Specifications section. Always expect to see a phase difference of less than 5 degrees at the cross frequency, 10 degrees within an octave on either side of crossover, and typically less than 35 degrees over a four-octave span centered at the crossover. Another quality check is by inspecting the low-pass, high-pass, sum, and difference SPL curves around the cross point. When these four curves trace a wide, symmetric "diamond" centered at the cross frequency, and with a deep null in the difference curve, we can be sure that the phase performance is excellent.
All Bamberg passive crossovers employ various forms of proprietary phase compensation circuitry.