Sloped baffle

"I still wonder out loud whether speaker inductance as a function of frequency response in fact remains constant within the speaker's pass band. Indeed ... even if speaker inductance remains constant as a function of frequency, wouldn't that also impact phase coherency?"
Speaker inductance is one of the main factors that we measure to build a impedance/phase correction circuitry. The more that impedance and phase can be controlled, the easier it is on amplifiers (especially tubed).. Tubes can handle inductive loads reasonably well, but crap on themselves trying to drive capacitive loads.
Here is a thread where Al does a good job of explaining it...
http://forum.audiogon.com/cgi-bin/fr.pl?htech&1377551562&read&3&zzlMesch&&

Hi Timlub,
Ok, no problem.

I believe his real question is "do all frequencies move at the same speed"

yes, all freq travel at the same speed. But the answer to his question is still "No, they do not arrive at the listener's ear at the same time". I tried to explain that in my post - looks like you missed it? I'll cut & paste here again for your convenience:
" the acoustical center of the 18KHz driver would be in front of the acoustical center of the 30Hz driver. Due to this, the 18KHz signal would get a head-start & would reach your ear 1st."
if you do nothing to compensate for the fact that the acoustical centers of the 2 drivers are different, the highs arrive earlier.
hope that this clarifies.

07-07-14: Bifwynne
.....I still wonder out loud whether speaker inductance as a function of frequency response in fact remains constant within the speaker's pass band. Indeed ... even if speaker inductance remains constant as a function of frequency, wouldn't that also impact phase coherency?

Bifwynne, here is some more material for you to read that will address the phase coherency question you had yesterday (7/6/14):
http://greenmountainaudio.com/speaker-time-phase-coherence/
this is an article that Roy J wrote for Audio Ideas Guide back in 1997. A small cut & paste from this article:

"The causes of phase distortion

Time delay is the natural consequence of making something vibrate, whether it's electric fields or material objects. In speakers, only three things can cause time delays:

◾The moving elements (the drivers -- woofers, midranges, tweeters);

◾Their distances through the air to the listener; and

◾The crossover circuit.

Let's go over the cause of motion-based time delays first. Different drivers (round, square, flat) have an inherent amount of phase shift, related only to each one's natural resonant frequency. One analogy is a weight hanging from a spring. If you move the other end of the spring up and down very slowly, the spring does not stretch and the weight follows your motion exactly. The phase shift between your applied force and the weight's motion is zero. The moving system is in a 'minimum-phase' mode. If you move more rapidly, the spring starts to stretch and contract -- and the weight no longer follows your driving force. It moves with a different phase.
......"

there's a lot more to read but I believe that you should read the section "The Causes of Phase Distortion" to answer your question....

I have never heard Roy's speakers, but I would love to, I've never seen any speaker that was plus or minus just a few degrees throughout its frequency range... It would probably be easier to read a book than try to get all the info from a forum, so much skipped over, so many half truths... very difficult... We have only really discussed baffle step compensation... I have tried several times to electrically time align a woofer rather that the tweeter. It can be done, but throws so many other things out of wack that I've never really been successful.
One thing that I would say... it is possible to get a great sounding speaker without very good alignment, but most speakers that "just aren't right" do not have good alignment characteristics.... Any speaker that has very good alignment characteristics, you will find very listenable, it may not be your cup of tea, but it will do most things well. At least that is my experience.
Tim

Thanks again Bombaywalla. I caught the article. It doesn't speak to the impact of the speaker's electrical characteristics on phase coherence. Maybe it's just a non-issue.

@Tim ... based on the various posts in this thread, I gather there are not very many conventional speaker brands that are time and phase coherent. Vandersteen, Thiel and GMA come to mind.

As to your point about flat impedance and phase angle plots, take a look at the stats on the Magico S5 here:

http://www.soundstagenetwork.com/index.php?option=com_content&view=article&id=1043:nrc-measurements-magico-s5-loudspeakers&catid=77:loudspeaker-measurements&Itemid=153

Not saying the S5 is an easy speaker to drive because its impedance plot ranges for the most part between 3 and 4 ohms and its phase angle goes negative in the low bass, but overall pretty flat plots. I think my ARC Ref 150 could drive it ok off its 4 ohm taps, especially since my amp has a pretty muscular power supply - 1040 joules. OTOH, I would not try to drive the S5s with a low power SET amp. :)

I find the phase coherence issue to be extremely interesting. It's frustrating because without doing critical listening, it's hard to get one's "ears" around the issue.

Thanks Psag for bringing this important issue to our attention. Just not sure what to do with it. :)

BIF