Time coherence - how important and what speakers?

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

Roy, that's okay to dominate the thread, I think we are all learning a lot. At least I am. One note though. Thiel speakers uses metal drivers and are first order (time coherent?).
Would a single driver be better still than 1st order crossover? I've got a 5" single driver speaker for a week. But it has a plastic "whizzer cone" glued on it. So I'm not sure if this counts as a true crossoverless design. Maybe mechanical, not electrical. Female vocals with acoustic instruments sound very different than my 4th order speakers. There seems to be more ambience to the music. But for some reason the single driver speakers don't have the pinpoint imaging.

ALso...Spica tc-50s were designed and marketed as a truly time and phase correct speaker...I know there is alot of jargon these days..."phase correct","phase coherent",etc...but the spicas...like Vandersteen, meadowlark,Thiel,etc...were the real deal...with that said...they were not a perfect creation...the highs were rolled off, they had very little bass, and were not very efficient...however...their 3-d imaging&spacious qualities as Roy mentioned were their claim to fame...and why they still fetch 3-$500 used almost 20yrs later...not much more than they retailed for back in the day...a great speaker during its heyday...and a fine value...but a bit outclassed today...especially in the detail department...at even at the $500 level...

Roy...do you have a dealer in the midwest?...I would love to audition the Europas...cheers...or do you have any b-stock/demos available?

Cdc- Thiels use a complex crossover circuit to force first-order acoustic rolloff responses from the drivers, because of their driver choices and cabinetry. Dunlavy and to some extent, Vandersteen employ similar approaches.

Your question about a single driver- if there was one with a perfect cone, free of breakup, the end result would be little bass response and very narrow dispersion in the highs. To widen dispersion in the highs and extend high-frequency response, a whizzer cone is attached, driven through a mechanical crossover (the adhesives used) between it, the voice coil, and the main cone. Those type of crossovers at best are 2nd-order, which means there's 1/2 wave-period of time delay at the crossover point. There are cone breakups usually still present. There are standing waves in the whizzer, reflected from its un-terminated outer rim. Those all are responsible for less than pinpoint imaging. At least their designers get to leave off any electrical crossover, which is a good thing, considering how much information is lost in most of circuits. Whizzer-cone drivers are not time coherent, but just less imperfect that most speakers that do use a crossover.

Phasecorrect- just remember that "phase correct" and "phase coherent" do not mean "time coherent". The converse does. See my first 02/12/03 post above.

Best,
Roy