Sloped baffle

^Again good step and square wave response are indications of wave form fidelity (time and phase). Again, as to it's importance, well that's up to debate, with opposing opinions prevalent on both sides. I will say when I first began seriously auditioning speakers and without any real technical knowledge I was consistently drawn to those speakers that unbeknownst to me at the time shared those design properties, and those speakers designs continue to favorably impress. Others don't always seem to share the same sensitivity and/or priorities that speakers with these design priorities share. Only by listening to them yourself will you know for sure if it's important to you. Oh, btw, they usually share the similar quality of steady impedance loads, a subject of which I'm confident you will recall being discussed previously here on Audiogon.

Hi Bif, I've found that time alignment is certainly worthwhile, but let me just say that all you may need is a way to visualize how and why it would be important. I'm not technically as well versed on the subject as some, but I do have some direct user experience with it. I'm in the process of triamping my rig. Each amp I have (and will be adding) will have a suite of (digital) tools which include a pair of xovers, EQ and time delay. Each pair of tweeters, mids and woofers will have their own amp...and each of those frequency bands can be delayed the appropriate amount - dialing in by ear alone, at the lp, is sufficient. I can tell you that in practice that process is far from complicated and can be done in a couple minutes by anyone. It just may seem impossible to grasp for you at the moment because (understandably) you don't have any way to vary the control over your time alignment one way or the other so there is no way for you to realize its effects at this point. But, try to visualize it in terms of what you may already have some ordinary experience with. Try this: turn on a TV in one room of your home and then turn on another TV in a different room, but turn that one up loud enough to hear it while you're in the other room listening to the 1rst TV. Make sure they are both on the same channel. You can't help but notice the substantial time delay - like a rather serious echo, but in a nutshell, that's really all there is to time alignment. You've likely heard this effect countless times before without thinking about it at places like car dealerships, fire halls, etc...places where a PA system is using more than one loudspeaker in different places outside (usually on the other side of the building), creating the very noticeable amount of delay. Now, the big difference (apart from the sheer amount of time in the delay) is the fact that, like with the TV example, all of the frequencies overlap...hence the echo effect, naturally. But, with HiFi speakers (except to a degree at the xover regions, which we'll ignore here) the frequency groups are largely separated in their delay. What this means is that (with any conventional, flat baffle arrangement, anyway) the highs reach your ears first, then the mids and then the bass. Basically it means that the highs are simply being projected out into the room and are imaged a little closer to you (in soundstage distance) than the mids, which are in turn projected a little farther into the room than the bass...it simply becomes apparent to you that the higher frequency band seems physically imaged a little closer to you. Time alignment resets this effect, moving the imaging of the higher band back into place with the frequency band below and gets all the instruments and voices that much more correctly positioned from top to bottom in the frequency range...a very nice and more realistic or natural presentation - definitely worthwhile. Once you've ever heard the effect for yourself it takes all of about 5 seconds to solve the mystery as to how and why it might be useful, but, with speakers if you visualize the difference in terms of the distance of the soundstage image from you with each driver's operating range, then you just may at some point be able to recognize just how most speakers have somewhat less than ideal time alignment. And some will seem a little worse or better than others. If you use subs, however, it is always recommendable to take time alignment into consideration along with the other factors concerning placement, but I don't believe perfect time and phase alignment has ever been done in any speaker and I may never see it in my lifetime. But, triamping in this way for me is giving me the opportunity to pretty much 'fix' the time-alignment problem, which won't hurt me at all. Apart from building your own speakers though, it seems there are not too many designs that have actually tackled the problem, as near as I can tell. Until more makers become convinced there is a market for time-aligned cabinets (expensive because it's so labor intensive), then there may be only a handful of alternatives for us. Other problems for manufacturers include that in designing cabinets for true time alignment (meaning driver offset at something close to the correct distance) they start getting into a world of cabinet diffractions and reflections - not easy enough to successfully solve, particularly in any aesthetic sense. It's not horribly critical to get the distance precisely right, but the closer the better up to a point...like trying to position both your speakers the same - it might be quite good to get them within, say, a 1/4" of each other, but under an eighth of an inch??..at some point there ceases to be an improvement, but then again, with time alignment you would notice generally a better sense of scale and improvements in the macro areas of the soundstage...while the soundstage details would remain largely unchanged. Hope this helps.

Do not pick a speaker based on crossover slope, sloped baffle or not, type of driver, or any other feature or set of features. There are plusses and minuses of every design under the sun. Don't even be influenced by things such as this. Pick a speaker based on your ears.

Bruce (Bifwynne), thanks for the summons. I haven't yet taken the time to read the links Bombaywalla was good enough to provide, but I am pretty much in agreement with all that has been said by the various posters above. Including the comment by Kiddman just above, which I believe to be a correct statement of the bottom line. And also including the comments by others to the effect that speaker technology is not one of my areas of expertise :-) And in that connection I'll say also that over the years I have found Tim's (Timlub's) posts concerning speakers to be highly knowledgeable, credible, and informative.

Another member whose inputs I suspect would be particularly valuable on these issues would be Duke (Audiokinesis); perhaps he'll spot this thread.

Regarding your basic questions about about how to gauge time and phase coherence, and about how important it may be among the innumerable tradeoffs that are involved in speaker design, I think that Unsound summed up the answers very well when he said:

Good step and square wave response are indications of wave form fidelity (time and phase). Again, as to it's importance, well that's up to debate, with opposing opinions prevalent on both sides.

Realize that a theoretically ideal square wave (which does not exist in the real world, of course), having infinitely fast transition times between its two states (i.e., risetimes and falltimes of zero), perfectly flat tops and bottoms, and no overshoot or ringing, consists of the summation of an infinite number of sine waves, one being at its "fundamental frequency" (the frequency with which its pulses repeat), plus others at every odd multiple of that frequency (i.e., the 3rd, 5th, 7th, etc. harmonics). The amplitude of each harmonic decreasing as its order (i.e., its frequency) increases.

In order for a real-world approximation of that square wave to be reproduced accurately by a speaker, at a given listening position, all of those harmonics (which collectively are generated by a combination of all of the drivers in a multi-way speaker) have to arrive at that listening position properly timed and phased relative to one another. No speaker will do that perfectly, of course, but results will vary widely among different designs.

In the measurements section of most of the speaker reviews which appear in Stereophile, John Atkinson presents and discusses the speaker's step response (which is pretty much as meaningful as the square wave response, a square wave consisting of a continuous series of positive-going and negative-going steps). For example, Figure 9 here is the step response for the (very expensive) Vandersteen 7, measured at a certain height and distance. The step response shown is probably about as good as it gets. (Keep in mind, btw, that the step response of any speaker will not **look** like a step because, among other reasons, for it to do so would require that the speaker's frequency response extend down to close to zero Hz).

So perhaps some degree of insight into the importance of time and phase coherence could be gained by comparing that measurement for speakers whose sonics one is familiar with and that have been reviewed by Stereophile, and trying to judge the degree of correlation that exists between the quality of that measurement and one's subjective preferences among those speakers. Although to be meaningful, that would have to be done by a given listener for a considerable number of speakers.

I've never done that, btw, and unfortunately I don't think that such measurements are available for most of the speakers I've owned or extensively heard over the years.

Best regards,
-- Al

Bifwynne, if you don't mind a little more reading, I suggest Time and Phase Coherence by Roy Johnson from his website. This is very informative with illustrations, and you don't have to sort through confusing comments as in the threads from the links that were provided previously.

Hope this helps.