First Order Crossovers: Pros and Cons

Well, a single "perfect" driver would be large in diameter so as to achieve good coupling with the air load so that it could reproduce low frequencies well. Unfortunately, that leads to problems with directivity and also possibly smearing of the high frequencies from widely spaced sources of the same signal. (Think panel speakers.)

So we'll go with a smaller driver and increase excursion. Then we start seeing problems with IM.

Since real drivers aren't perfectly stiff, they don't maintain pistonic motion at all frequencies. (Real drivers also have mass, and that changes things too.)

So, a cone driver will "want" to become a smaller cone at higher frequencies, and we start seeing breakup modes. This can be damped to some extent by the surround.

Ted Jordan explicitly allows for this behavior. He claims to control it in his drivers. But he's still using metal cones, and there's going to be a nasty breakup mode. the only question is how well controlled it is.

I suspect that some "full-range" drivers actually use these breakup modes to increase output at high frequencies and provide some impression of treble. Not what you'd call accuracy. :-)

So what's wrong with a multi-way system with drivers that are more likely to be able to display pistonic motion throughout their passband? Crossovers and the physical spacing of the drivers. This causes some problems and makes it harder to provide an accurate "re-assembly" of the waveform at your ear.

1st-order crossovers screw things up less than steeper slope crossovers, but place higher demands upon the drivers. (But still not as high as the demands upon full-range drivers.)

Physical placement is harder to cope with, but you can control some of it, particularly since we're only listening from one point at a time.

It's almost a Catch 22. Real full-range drivers have major problems. To solve those problems we use multiple drivers, which introduces other problems. I submit that the problems with multiple drivers can be solved more easily and more fully than those with full-range drivers, given the current state of technology.

(One possible solution is to use full-range drivers at very low power levels. This works with headphones, but not so well for normal speaker systems.)

There's just no free lunch. :-)

Cdc-- I only dimly remember the Jordan circuit, but it looked like a contour rather than BSC (it was across the driver -- but don't hold me on this!).

Skrivis:
Re: first order+ drivers. Why not use a wide-range drivers -- i.e. a 8" + supertweet, then a hefty subwoof. You'd have to biamp (at least) but, as you note, there's no free lunch!

Gregm> "Why not use a wide-range drivers -- i.e. a 8" + supertweet, then a hefty subwoof"

Well, an 8" driver is generally going to be getting pretty far away from a pure piston at treble frequencies.

Perhaps a smaller mid-woofer crossed at 3-4K to a tweeter, and then a woofer or sub below it, crossed at maybe 100 Hz?

Thanks Skrivis and Gregm. I have tried twice to respond but both times, 15 minutes into my response my computer crashes from doing Ebay auction at the same time. So I give up.

Cdc: forget the perfect piston. It'd be nice to have -- but let's just dream for now:)
An 8" driver has the advantage of being able to cope with mid & low-mid frequencies w/out extreme excursion. A smaller driver would be straining. OTOH, it WILL beam, as you hint, higher up. That'll narrow the sweet spot but, on the brighter side, IF the dispersion changes in a reasonably controlled manner, you reduce reflections... (at least that's s/thing). If the full-range can take it elegantly, I would try cutting in the tweet, 1st order, higher around 8kHz.
It's a pain to align the drivers -- but once it's done, it sounds good.
Cheers