First Order Crossovers: Pros and Cons

All designers are trying to make intelligent choices in trying to work around the problems associated with crossover design. It's just that the priorities and trade-offs are different. Some designs use but one driver, such as the Lowthers, or Quads, so no crossover is used at all. Some run the woofer full-range, without any crossover and only use a simple crossover on the tweeter, such as Epos. At the other end of the spectrum, the much-misunderstood Bessell alignment is maximally phase coherent and has very steep slopes, the older conrad-johnson Synthesis and Spica speakers are good examples. The infinite-slope crossover has extremely steep slopes as well, currently it is used by Joseph Audio. There's a lot of great ways to skin this cat! The reason that first order slopes are generally best integrated in the far-field is that at a wide range of frequencies around the crossover frequency, both drivers are contributing a large amount of energy. This leads to complex interference patterns between the two drivers that are very dependent on the position of the drive units, the size of the drive units, the listener and the placement in the room. Generally, this interference smooths out in the far-field, the sound arriving at the listening position being the sum of the direct and reflected sound and averages the dispersion patterns of the drivers as well. The crossover is but one element in what should be an integrated design. The drive units themselves, the cabinet and the room being at least equally important.

Viridian. Your explanation is helpful but leaves me wondering--Why would a speaker designer want to allow each driver in, say, a three way design want to "bleed" into the frequency spectrum of the nearby driver(s) rather than use a steep slope (is this sometimes called a third or fourth order crossover? I need help with the terminologies!) to prevent interference between them? What is to be gained from using first order designs that allow the bleeding to take place? Do the advantages of the first order design depend upon drivers of sufficient quality to be able to blend accurately? Which of the designers using first order designs do the best job getting the blending to occur seemlessly? Sorry for all the questions but your post raised more questions for me than answers gave!

I don't have the technical chops to make a great contribution to this discussion, but my understanding is this: first-order crossovers confer benefits in terms of maintaining phase accuracy (coherency?) across the drivers. The price for doing this is as Vridian stated, the need to have all the drivers operate well beyond their prime frequency range. Which means that driver selection becomes especially challenging.

And why would you want to maintain phase coherency? I'll leave that for someone else.

Great thread, Dodge.