Time coherence - how important and what speakers?

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

I dont believe Vandy or THiel use "complex" x-over circuitry...these are afterall pioneering first order time and phase correct speaker designers...both Richard and Jim...and as RIchard V has openly stated...there are only a handful of truly time and phase correct speakers on the market...SPica would be the one that fall into a more complex x-over category...

I'm not sure about the Vandersteens, but, I do think some of Jim Thiel's crossovers are quite complex. I suspect his goal of amplitude coherence has something to do with this. I suspect that the complexity of his cross-overs is what accounts for the low yet narrow impedance of his speakers. Have you ever seen the one Thiel used in the CS-5. Some have criticized him for this, complaining that his cross-overs suck the energy out of the performance and add a veil to the sound. Yet others critcize his products for being too "analytical" and "clinical" sounding. Go figure? Of course due the the mechanical cross-over nature of some of his new co-axial drivers, the electrical crossovers have simplified. On the other side of the spectrum I think that the Meadowlark offerings use a different set of priorities and accomplish their results with a simpler crossover. Mind you I enjoy all of the above manufacturers products. In as much as one can readibly identify from whose pen what product came from, I still think they have more in common than not. To me, there is something that just sounds more "right" about them.

Look at a Vandersteen crossover and decide for yourself. There is a lot more to the crossover than most other speakers. As for being complex, I have always thought the more pieces parts the more the complexity. You can get a glimpse on his website.

The simplest electrical crossover on a speaker is an inductor placed in series to the woofer, and a capacitor to the tweeter. The amplifier drives into both simultaneously. If they are perfectly equal and opposite in "reactance", then they cancel out, as far as the amplifier is concerned. This cancellation is what makes this the only dividing network without time-delay distortion.

This is a first-order network. Its two components can be used only when the drivers and cabinet designs are "perfect".

Not bloody likely.

More complex circuits are usually required, whether using two or ten more parts. The result can still be a "measured" first-order acoustic rolloff. The extra parts "modify" driver non-linearities and "make up" for cabinet reflections. Which they cannot- but they can fool the microphone. Of course, extra circuit-parts cannot be perfect either. Reductions in transparency and dynamics are givens.

To keep the number of crossover parts to the barest minimum, one has to use the most linear drivers- which are relatively few. However, not that few: specific examples include tweeters from Morel, Dynaudio, Foster, Stage Accompany, Pioneer TAD, and Scanspeak. Certain mids from Audax, Eton, Davis Acoustics, Bandor, Jordan, Foster, Peerless and Aurasound. Specific woofers from Scanspeak, Davis, PHL Audio, Volt, Audax, Peerless, Pioneer and Aurasound. There are others.

And every one of them is far more expensive than the drivers used in most designs.

For a commercial designer who wants to use the simplest crossover, it's hard to find the best drivers under deadline conditions. But by using the most linear drivers, within proper cabinetwork and correct bandwidths, the crossover circuit can be reduced to just a handful of parts, for clarity and for time coherence. The converse is entirely true.

Best,
Roy