time allignment in serial crossover

[rabbitz]

Dickason's LDC 6th edition.

See fig 7.20 B on how upward tilt works with ZDR
Section 7.23 Page 112 explains
Page 114 2nd last para explains the inverted woofer "Experts often.... blah blah".

Dickason also adds "radiating centre may be assumed to be the centre of the voice coil".

Horizontal or Hd (on my pic) if 0 has no delay but as the Hd increases then there is a delay between the woofer and tweeter due to the horizontal difference. So if a tweeter is on top and the woofer below, the sound from the woofer is delayed hence the polar downward tilt, for the inverted it's an upward tilt.

1st orders are sensitive to horizontal offest of drivers and to function correctly need to be time aligned so Hd=0.

Read LDC section 7.23 as it explains it better than I ever could.