I intended to use a 3rd-order Butterworth alignment on the woofers in order to solve the vertical lobing issues with this design, and suppress break-up as much as possible. With the center-to-center distance being 7-1/4" (adding in the 3/4" MDF strips), the maximum acoustic crossover point from the woofers to the tweeter would have to be 1875 Hz. For the woofers, the electrical filter is actually 2nd-order with a conjugate network. The acoustic roll-off is close to a 3rd-order Butterworth alignment. On the tweeter side, a 3rd-order electrical filter and L-pad are used to achieve an acoustic 4th-order Linkwitz-Riley roll-off with the actual acoustic crossover point of both drivers being 1500 Hz. The tweeters have their polarity reversed relative to the woofers in order to tilt their radiation pattern upwards.