Time coherence - how important and what speakers?

http://sound.westhost.com/ptd.htm

"Do think this is an important issue?"
Its certainly something to strive for and can be easily attained. However, when price becomes a factor it may not be something one should get hung up on- as there are other things to the speakers performance that are also important. Ozfly says it right in the next to last sentence of the second paragraph.

"What speakers are time coherent?"
Any speaker with a sloped or staggerd baffle has the voice coils (acoustic centers) of the drivers lined up and this is time-aligned, a starting point (assuming the xover also keeps the drivers in phase--fortunately they usually don't go through the trouble of staggering their baffles and then ignoring the xover). Full-range loudspeakers are also time-aligned by default. And to a lesser extent in population, systems with the tweeter below the mid/woof but still on the same plane are also physically time-aligned. Thiel, Wilson, Dunlavy, Biro Technology, Spica, Vandersteen, Avalon acoustics (pretty sure), Audio Physic, Lowther, Full-range Electrostats, Martin-Logan above the bass driver (not sure what they do w/ xovers), Vienna acoustics (pretty sure) etc. to name a few off hand. Drivers can still be time-delayed electronically too, so the speaker may look conventional but still compensate for it.

"Science has proven a bumble bee can't fly but it does"

While I won't disagree with most of your statments, science never proved a bumble bee can't fly. Technically, science can't prove anything. We/science never proved all objects fall to the ground at a constant speed (or that they'd all even fall to the ground) since we can't possibly drop all the objects. An assumption is finally made that the hypothesis being tested is 'true' when nothing disproves it after a certain number of experiments (and we decide when enough experiments is enough). And this is why we also create the null hypothesis for the sake of formality/consistency and this is called the falsification principle that science progresses under (Wasn't it Popper who write of this?). Helicopter's fly, and do so in a completely different manner than airplanes do-and we have explanations for both. Dragonfly's create little tornadoes under their wings by disrupting the air current, a completely different manner of flight than most birds. The Bumble flies and for a reason--we just may have not found a way to explain it yet. But nothing in science says a bumblebee can't fly, because this would be defeating to the whole purpose of what science is about: to know why everything around us is the way it is-to understand all of cause-and-effect. (I don't know what's in the literature about bumblebee flight).

Returning to Science & Audio:

"Just because a speaker system has a sloping baffle does not mean it is time aligned."
My bad, this is a correct statement. If there's a new generalization to be made, possibly: a slightly sloping baffle is usually not time-aligned, but one of a greater/steeper angle is.

"There are a few manufacturers who would like for you to think there speakers are time aligned. This has been noted in Stereophile's reviews of speakers from time to time"

I'm not sure about the first sentence-it gets into other peoples' intentions and I can't live in someone else's head. But then again I don't know what all the manufacturer's out there are doing so you may be right-there may be some doing it. Ruark had a little floorstanding model years ago in a Stereophile review that was alluded to as not being time-aligned. However I didn't think anyone was insinuating that Ruark wanted you to think it was. If anything it cost more money to make a cabinet with a sloping baffle and why a manufacturer would do it but not go through with the xover design is a little weird. Especially, since xover design is *simplified* (I believe) once the acoustic centers have been lined-up. But I'm thinkin, maybe, in the case of the Ruark its baffle was slightly sloped just to get the sound up to the listeners ears (and maybe add a little visual appeal), so Ruarks intentions may have been sincere. 30" is pretty short for a floorstander and while some drivers are better listened to off-axis, 28" above the ground tweeter might be a little low regardless. And it may be effective in getting rid of internal standing waves which become a big problem with many floorstanding designs (although cabinet stuffing is the most effective way). But, there maybe alot of models out there marauding/falsely advertising as 'time aligned' creatures. I don't read the fashion rags because they're still recommending $10k speaker cables with $12k speakers. Although from what I hear there may be an article or two in there I wish I had read--Stereophile reportedly had a good one on Opamps.

Incidentally, BigTee, some of Bose's models are, more or less, time and phase coherent. My clock radio is.