First Order Crossovers: Pros and Cons

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.

Ahhh, but it would seem you do have the phase chops for this Drubin...coherency (is that how it's spelled?) is what we are all after and why some turn to single driver systems...they can hear the X-over.

Dave

To answer your questions, the general benefits of a 6db per octave crossover design are claimed to be first that, at the proper listening distance, the drivers blend better, seeming more like one, seamless driver. This is because the transition from one to the other happens more gently, with the drivers sharing the spectrum over a greater span. Also, as mentioned by Drubin, these 6db per octave slopes confer good phase integrity as measured by good step and impulse responses. The price to pay is that the drivers must be linear over a much larger passband than with higher order crossovers. Many drivers behave badly when hit with suffient energy at the top, or bottom of their intended ranges. Tweeters have trouble with the large excursions required for them to play loudly at lower frequencies. The large cones of mid-bass drivers often have audibly annoying resonances at the top of their range. As it is, with most two way speakers, the woofer is operating in controlled breakup at the top of its range. This actually is a trade-off that generates much greater dispersion in this area. The result is that most of these drivers are, in and of themselves, not really phase coherent when employed in this manner. The logical thing seems to be to add more drivers, each having less bandwidth to cover. New problems arise. Is it hard to make two drivers blend? Well then, try three, four or.... For a given price point as you add drivers you split your budget, and the quality of the driver. Some designers, and listeners like the sound of this trade-off and some do not as it is realized in specific speakers. I would ask you what models of speakers you have heard, and like with this topology? It does up the complexity of the task. That said, there are really excellent examples of speakers using all different types of crossovers. They coexist in the market because different listening biases, rooms and musical tastes can cause one to be favored over the other. Much of the magic also lies in the drivers (can't make a silk purse out of sows ear) and the cabinet. Good luck in your journey.

Time/phase coherance is the primary advantage of a first order design. There was a thread here about this topic from Roy Johnson of Green Mountain Audio a while back. Look here:
http://forum.audiogon.com/cgi-bin/fr.pl?cspkr&1032037028&openusid&zzgma@pcisys.net&4&5#gma@pcisys.net