They use very complex and hard to get right all pass ladder networks to get this delay to get things in phase. Tannoy and a few others used similar systems. But it cost a lot, takes a lot of knowledge, time and trial and error to get it right, so nobody does that anymore. Later, people used bbb analog delays in an active crossover to match phase, and now most use dsp as it's cheap, easy to use and calibrate and reliable. The disadvantage (for me and many others) is that it's digital processing. But sometimes you can't have all what you want and digital processing is getting much better every day so...
Well I think I’m going to get some plywood cut up tomorrow and put some boxes together. I’ll order drivers over the weekend. I’m going a bit bigger than absolutely necessary to lower the qtc and ensure some excursion headroom for eq. I’m looking at about 36l gross in a 12x15x17” enclosure. The driver will be on the the 12x15 side and biased to the top to prevent vacuum cleaner impacts. By mounting on the narrow side I can nest them close to the tv table and optimize space.
