Sub to Midbass Crossover Blend
Watch the low-pass, high-pass, and acoustic sum interact. Chase a flat handoff with no dip or bump.
Delay offset shifts the sub in time relative to the midbass, which rotates phase at the crossover. A small offset or a polarity flip is usually what turns a dip into a flat blend.
An all-pass leaves the sub level alone but rotates its phase around the center frequency. It bends phase locally near the crossover instead of adding a fixed time shift everywhere, so it can fill a stubborn dip that plain delay cannot fix without wrecking alignment elsewhere. Watch the green sum, not the amber curve: the all-pass is invisible on a magnitude trace by itself and only shows up in the sum.
Matched puts both corners at the same frequency. With the right polarity this is the flattest, most predictable handoff and it is what most installs should run.
Staggered sets the sub low-pass below the midbass high-pass, so each driver is doing less work in the overlap. People reach for it to keep the sub from playing up into a boomy region or to dodge a cabin peak. The cost is that the wider the stagger, the more you risk a gap between the two corners where neither driver is at full output. Use the green sum to see whether your offset is filling in or leaving a hole.
On the "half octave" label: a true half octave is a frequency ratio of 1.41 (for example 80 Hz down to 56.6 Hz). The popular chart that lists pairs like 80 / 67.3 Hz is actually a quarter octave (ratio 1.19), even though it is labeled half. The offset slider here shows the real octave value so you can set whichever you actually want.
Dip at the crossover (matched mode) means the sub and midbass are arriving out of step. Flip polarity first, then walk the sub delay offset a few tenths until the green sum fills in.
Bump at the crossover means too much overlap energy, usually phase-aligned but with one side too hot. Pull the louder side down a dB or two, or steepen the slope.
LR2 (12 dB) sums flat only with one side inverted. LR4 (24 dB) and LR8 (48 dB) sum flat with normal polarity. The tool models that, so the polarity button shows you the real acoustic result.