konut,
I can build the BBs into the enclosures, but as of now that's not standard. What with all the parts in this new design, I'm not looking forward to the job of finding room for them inside either.
Bill,
As always... thanks!
And I hope things work out for you. Believe me when I say - "I understand."
Chuck,
It's been a while, but sure I remember. Give me a call whenever you get a chance and stop on by. I always look forward to folks visiting. Heck... we're neighbors for Pete's sake!
Russell,
Thanks again for the support my friend!
You know me... I'll do my best to answer any questions, although you may regret asking!
OK then, what are the advantages of pushing the X-O lower? Well, there are several the way I see it.
First of all there's the issue of Time-Domain performance. "One driver does all" is the theoretical ideal in that regard. I'd reference the "square wave" comments above. Getting the fundamental tones and all of their harmonics to line up in time represents one very difficult step closer to perfection. Although even my designs don't perfectly achieve this goal, now at least we're looking at virtually ALL of the harmonics of a given instrument remaining intact with respect to each other upon arrival to our ears. Seeing our hearing is most sensitive in the "above 1kHz" range, my reasoning is that by pushing the X-O this low, at least we've covered the most critical area.
Then there's the issue of woofer/midrange cone distortion (break-up modes). A 1-inch tweeter diaphragm is simply too small for the typical "standing waves" (that we see develop in woofer cones) to propagate in. If you study the break-up modes that arise in most woofers, you'll find that they look very similar to the standing waves that develop in acoustic spaces (listening rooms). Sure, their wavelengths and decay times are shorter, but often their frequency and decay characteristics are much alike - especially the shape of their "envelopes." I once saw a review by Bruce Bartlett of an ETC measurement he did on a famous brand electrostatic speaker. The frequency and decay envelope looked just like the ETC response (RT60) of a typical reverberant room.
Well, all that "hash" is nothing more than standing waves developing in the membrane and bouncing around. The edges where the membrane is supported are the "walls" where the energy just reflects back across and around the periphery of the membrane until it finally "decays" away. As in a typical room, the number of "modes" is almost unlimited as you not only have reflections occurring across the major dimensions of the membrane, but also "orthogonal" modes where they travel around the periphery and what have you. I guess that's why I've never cared for planer speakers... they're just too under-damped for my tastes. They may be "fast" in responding to an initial impulse, but then there's a ton of energy that comes out of them later in time that has nothing to do with the original signal.
Sorry, that's not meant to be a slam to planer lovers, that's just my take on them. Although they aren't typically as bad in that regard, most cone drivers have essentially the same problem. Seeing then that a 1-inch tweeter diaphragm is simply too small physically for such modes to develop (in the midrange frequencies), if we can get it to cover more of the midrange (by lowering the crossover frequency) we should have a lower distortion reproduction.
Don't get me wrong, a tweeter diaphragm can (and virtually always does) have the same problem, but such artifacts are "pushed" well up out of the critical midrange area into the +5kHz region. Although, in the specific case of a ring-radiator there are even fewer such modes and they reside even higher yet in frequency due to the fact that they don't use a simple dome diaphragm. Also, seeing that we use rigid, "piston-like" aluminum woofer cones, this second advantage isn't as big of a deal. These cones don't flex in the way most paper, plastic and other types do, so they don't suffer from the break-up modes nearly as much to begin with. They do "ring like a bell" out around 5 kHz, but that's well above where we use them. In fact, in this newest case that's a full decade above our crossover frequency. Nevertheless... every little bit helps.
Finally, the third major advantage of lowering the crossover as far as you can go is that it reduces Inter-Modulation Distortion that arises within the woofers as a result of woofer cone excursion. The more any woofer "pumps," the more its lower frequencies "modulate" the higher frequencies it's trying to reproduce at the same time. To be sure, if you can actually "see" your woofer cones moving while reproducing music, you can figure you're hearing a significant amount of IM distortion as well.
IM distortion is particularly nasty in that the spurious artifacts generated are not harmonically related to the original tones that gave rise to them, so it definitely doesn't impart any form of "euphonic" effect. Well, if we then lower the crossover, the woofers don't operate as high into the midrange to begin with... so "modulation" and hence IM is gonna be reduced. At first listen, most folks will notice this reduction in distortion as the most prominent effect. They may not have a clue as to "why" the speaker sounds better, but it's clearly audible regardless.
So... that's my story and I'm sticking to it. You'll know better to ask another question next time.
Take care,
-Bob
