Thanks for the feedback.
I don't feel bad about answering- I just don't want to dominate this thread. And it would be more fun to ask the questions. But you're right, this is my profession. Much of what I learned came through sharing, so I'm glad you appreciate the information.
My words here have not been about reaching perfection- speakers are man-made devices, and I am not going to give away any trade secrets on how to better approach perfection. My intention is really to tell you about certain design pitfalls that could be avoided, except "the math's too hard!".
And out of respect for your and everyone else's intellect, I try not to make unqualified statements- so you see the reasoning behind my logic and of others, and in 20 years come up with a new way to drive the air. Mostly, I would hope any reader leaves with enough knowledge to recognize when "marketing" is disguised as engineering. Like the claims of cones dissipating energy. The lack of educational/technical writing in the press over the last 20 years is one of the main reasons hi-end has become a confusing, poor-value hobby, full of frustration for most participants.
Anyway, thanks again to you and the others for your interest and insightful questions. So I do not repeat myself for related topics, such as why a cone breaks up in the first place, please look at my posts at "the Vinyl Engine" at
http://www.nakedresource.com//yabb/cgi-bin/yabb/YaBB.pl?board=general;action=display;num=1038342561
About the Spica? It's been a long time since I studied some of what he claimed, but I do have several AES papers on similar computer simulations done in the early eighties that do not support that claim of virtually no phase anomalies. Actually his claim could be true- because of the word "phase". Remember though, that "lack of phase anomalies" does not mean "time coherent" nor "no time-delay differences", an important distinction. See my 2nd-to-last post. Phase is not time. Phase is relative; time is absolute.
Chances are that Mr. Bau was among the first to combine the 4th-order filter with the supposed "perfect" second-order mechanical rolloff of that soft-coned woofer, plus combine a 1st-order electrical filter with the natural second-order "sealed-box" rolloff of the tweeter:
That would be 6 x (-45 degrees) shift on the woofer (-180 degrees), and 3 x (+45 degrees) shift on the tweeter, (+135 degrees). Which means they are 315 degrees out of phase- only 45 degrees away from 360 degrees- near the same as from two 4th-order acoustic-rolloff filters. That remaining 45 degree discrepency? If one considers that the woofer's cone will not be breaking up in a "perfect manner", which is true, then that 45 degree differential can be easily "added back in" from the woofer's non-perfect cone breakup. So you come up to a total of ~360 degrees phase shift- which is indeed "no phase anomalies", as they are "in phase". But not in sync.
The main reason Spicas were so spacious has to do with
a) being a two-way with good drivers,
b) the felt-work around the tweeter,
c) the shape of the cabinet,
d) the slant-back of the cabinet,
e) the lack of resonance/echo inside the cabinet,
f) there was only one cap on the tweeter, in the days of poor capacitors.
g) he was among the first not to let the woofer-cone breakups interfere with the tweeter.
Smart guy. An inspiration.
Best regards,
Roy
