Time coherence - how important and what speakers?

I have been reading alot about time coherence in speakers. I believe that the Vandersteens and Josephs are time coherent.

My questions are: Do think this is an important issue?
What speakers are time coherent?


Richard Bischoff
There are a couple of other brands too - Thiel, for one. I don't have a particular opinion on it, other than that I recently compared Vandersteens and MartinLogans, and for my tastes, it wasn't much of a contest. Whether that is because time alignment means nothign to me, or because other things about the Vandersteens were not to my liking, I can't really say.

I would have thought that the time alignment would mean better imaging, but for the music I played, that did not pan out.

Richard Hardestry (spelling?) is adamant that no speaker is worth diddly without being time aligned. I've paraphrased a little, but there are so many wonderful speakers out there that aren't (or at least do not claim to be) that one has to think that he's overstated his case ... just a bit.
Bound for Sound just wrote a piece on this in their new issue. Per the editor, Martin DeWulf, there are only three elements to sound (phase, frequency and amplitude) and time coherence is smack dab in the middle of the phase element. Low order cross-overs, preferably of the series type, now seem to be the preferred (but not sole criteria) speaker type for Mr. DeWulf. I've owned a couple of Thiel models and have to say that, to my ears, time coherence makes music palpably real.

On the other hand, that does not mean that other designs can't work. They just need to compensate, IMO, by doing other things incredibly well. Plus, first order cross-overs may lead to potential issues with being able to drive speakers within their optimal parameters. For example, first order cross-overs allow more of the midrange to leak into the bass speaker and more of the bass to leak into the midrange speaker. This could lead to a muddying effect (e.g., the doppler effect when the bass speaker is moving in one direction with deep base waves and the smaller midrange waves reproduced on that same surface are either accelerated or decelerated as a result). All in, no single criteria can be the deciding factor since every design decision is one of making trade-offs. Let your ears decide.

I'm very happy with my PBN Montana KAS speakers and must confess that I have no idea what cross-over design is being used. I do know that some time coherence is being considered in the design since the speakers are at different distances from the vertical plane.

"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.
Sure time and phase coherence are important, but these are only two aspects of many that go into how a speaker sounds. If a manufacturer achieves time/phase coherence but botches the crossover or driver integration, cabinet, etc. the result will not be pleasing. Gotta look(& listen) at the whole package, cause that's what you're ultimately hearing. I definitely hear something a little different when listening to Thiel speakers in terms of image specificity and a sense of dimension, but I don't know how much of that is due to their time/phase coherent design. Along with those mentioned above, Meadowlark is another company the adheres strongly to this design philosophy and much can be read about it on their website.
Just because a speaker system has a sloping baffle does not mean it is time aligned. 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. Also, there is the phase issue which can undue the alignment regardless of the physical alignment of the drivers. Take a look at the impulse response of speakers and it gives you a pretty good picture. Sometimes the midrange is wired out of phase to the tweeter or woofer(pick your order)This effects when the sounds arrive. I have said in many posts that accuracy is not that big of an issue it seems. Electrostatic speakers have a terrible frequency response in general. Just look at some test results. But people like them. Don't take my word, look up the test results. They also have issues similiar to what was mentioned in a post above in regards to a 6db filter requiring a broader overlap of frequencies for its drivers except the electrostatic is trying to make a diaphragm work at most frequencies equally well which it won't.
We ALL like our colorations. Pick your poison. It appears that no design has a market edge on another. Each design has its camp. However, I personally believe in time and phase coherent speakers. If you have a speaker that produces overtones that are out of phase and not arriving at the same time as the fundamentals of the sound---they call that distortion---it distorts the original waveform. I still ask the question, who has heard perfection to know what a sound should be on any speaker unless you were in the studio for the original. Even then, most of the recorded music is mixed down and altered until it is some small piece of what it started out to be.
Hell, you've got a bunch of people who like Bose cubes with a sub. Who am I to say there wrong? Man, this argument will go on until the end of time. To phase or not to phase---to time align or not time align.
Richard Hardesty has his views that have developed over many years of listening along with most people who believe in time aligned, phase perfect speakers. Technically, there is a strong argument for this. It takes a lot more to design these speakers. More is put into the drivers for the very reason mentioned above. Compare Vandersteen's frequency response curve (or any other spec for that matter) with any speaker you want and they will hold their ground easily. Any time aligned and phase perfect speaker specs out very, very well.
My bottom line here is specs and design must not be the only issue for us audiophiles chasing our tails!
Far fewer speakers are really time-aligned than you might think. For example, the Wilson Sophia has a slanted baffle, but one look at the Stereophile review's impulse response tells you that it is not even close to being aligned in either time or phase! Speakers that really come close are the Dunlavys, Meadowlarks, Thiels, and Vandersteens. The impulse response is extremely easy to measure and tells you almost everything you need to know.

And yes, it is very important, it is the difference between merely a good-sounding speaker and one that sounds like real music.
Some consider time and phase coherent extremely important especially Richard Vandersteen.

But then you hear people rant and rave about the Hyperions, the Dynaudio Evidence Master and Temptation, the Krell LAT-1 all of which are not (I believe). From what I've read and heard from others, I would probably lean toward a speaker that was time and phase coherent in design.

Don't know about the Joseph's but the Meadowlark Blue Herrons selling for $9k are also time and phase coherent. Much effort appears to have been put into the the BH's, much like the Vandersteen Model 5's.

But on paper (I've not listened to either), the Vandersteen's appear to be over the top when it comes to design and detail. And they're only $1k more than the Blue Herons.

While I have heard speakers that I enjoyed that weren't Time coherent I am consistently attracted to speakers that are. To my ears it is important. Dunlavy, Meadowlark, Quad, Spica, Thiel and Vandersteen are. I'm not sure but I think that the ESL Acustats, Audiostatic, German Physics, Huff omnis, Original Walsh, Yankee, Museatex Mel, ESL Sound Labs, Stax, Martin Logan CLS & CLZ might be ? Does anybody know about these last possibilities?
Any single-driver speaker, whether cone, walsh, electrostatic, or whatever, is automatically time and phase aligned. That's one of their biggest advantages.
I may be wrong but I don't believe that Karl's statement is correct. Highs come at you quicker where lows are much slower. A flat diaphragm is not timed aligned by looking at its impulse response and other factors. The frequencies are reproduced at the same time but do not arrive at your ears at the same time. I am aware of only a handful of time aligned (and/or phase correct) speakers. Going back through a lot of specs, etc., nobody has ever called an electrostatic time aligned that I can find. They are certainly not phased aligned. Look at the electrostatic impulse response and phase graph. The phase angle is all over the place.
Two points for you Bigtee.

Number 1 - If the highs travel much faster than the lows, then how does aligning the acoustic centers of the drivers time-align them? Answer: The time alignment attempts to simulate a single source of the sound so that the sound emanates from the same plane. The tweeters are not moved back to compensate for the speed of the frequencies. They are moved back to align the acoustic centers of the drivers for line-source radiation from the same plane.

Number 2 - All drivers have phase charts that are "all over the place". Phase alignment does not mean that there is not phase change. Phase alignment can mean 2 things. It can mean that the multiple drivers are crossed-over in such a way that the phase changes induced by the crossover are within a certain tolerance between each driver. It can also refer to the phase relationship between the driver and the port in a reflex design, or the positioning of the speaker relative to the behind wall, in a dipole radiator speaker. Many drivers will even reverse phase, at or below the resonant frequency of the driver. Every driver that I am aware of has phase irregularities. It is inherent in the electromagnetic transducer design.

From what I have heard, generally "time-aligned" means the acoustic centers of the drivers are aligned. And "phase-aligned" means that the crossovers use a relatively phase coherent 2nd or 4th order alignment.
Some of the Audio Physics and Lowthar(?) designs might qualify.
I just came off of 2 physics websites regarding the speed of sound versus frequency. Both the Cornell physics dept. and the Nasa physics website stated that the speed of sound in air is constant, and does not vary with frequency. The only variable in the speed of sound is the density of the medium(air) which will cause variations according to altitude, and humidity, or barometric pressure. In any case, the speed of sound will be constant for all frequencies at any given condition of the air at the time.

So this idea that the highs travel faster than the lows is not borne out by fact. It seems to be an "urban legend" that grew up around the "mysterious" functions of loudspeakers, that people did not understand.

As I previously stated, the time-alignment is done to simulate a single plane radiation source.

As Karls, stated, the single driver systems, including e-stats which may use a single panel, are inherently time and phase aligned, regardless of what some are reading into some "impulse charts". Any undesirable activity shown on the impulse charts are characteristics of the particular speaker being measured, and not a function of the speed of sound vs frequency.
Twl, I'm in over my head here, but I won't let that stop me. Is it not true that for a speaker to be properly "phase-aligned" by default it almost demands a 1st order crossover?

Supposedly, that's yet another reason why the Vandersteen Model 5's are so highly rated. Time alignment being another reason.

Correct me if I'm wrong.
Stehno, the 1st order crossover alignment, which consists of a single capacitor between drivers is a 90 degree phase alignment. It allows the bass driver to run full range, to its natural limits, and blocks the tweeter from operating below the frequency specified by the capacitor value. This protects the tweeter from harmful high power that may be present at the lower frequencies, and keeps intermodulation distortion to a minimum in the tweeter. The tweeter will be rolled-off at 6db/octave, from the crossover point downward, in this configuration.

The main advantage in this alignment, is that there is the fewest number of crossover parts to screw up the signal. And the presence of crossover inductors is eliminated, which is a major cause of phase shift. For this alignment to be successful, it requires careful matching of the drivers, so that there is not a "bump" in the response where the tweeter crosses in, and the woofer does not cross out. The woofer should be naturally rolling-off on its own at around 6db/octave, right at the crossover point, in order for this alignment to be optimal. Even though this is considered a 90 degree alignment, there is much to be said for the simplicity and signal preservation of this design. There are going to be phase-shifts in any crossover, and preserving the signal integrity is a valiant thing to do, considering the necessity of having a crossover in a multi-driver system. Having no crossover in a multi-driver system, with the drivers having matching natural roll-offs at a certain point would seem to be optimal, but the protection of the tweeter is vital, and intermod is present in unacceptably high amounts, as the tweeter vainly tries to respond to low frequency information that it cannot reproduce. So the single capacitor which functions primarily as a tweeter protector is a good compromise, if you can match the drivers well enough to keep the response curve smooth. If you want to avoid the crossover phase shift altogether, you must go to single-driver, which presents its own set of difficulties.
Twl, only first order filters are phase coherent, no exceptions. First order usually refers to the electrical filter, not the inherent slope of the driver's response. Therefore a first order filter consists of one reactive element, either an inductor or capacitor, in series or parallel with the load (the driver). And the phase shift caused by the reactive element varies with frequency, as a function of the ratio of reactive impedance to load impedance. In an "idealized" first order filter, there is a woofer inductor and a tweeter capacitor, each of which has a 45 degree phase shift at the crossover frequency, but in opposite directions. Over the rest of the frequency spectrum that each driver is intended to cover, the phase shift caused by the reactive elements is less than 45 degrees. Above the woofer's crossover frequency, and below the tweeter's crossover frequency, their phase shifts gradually approach 90 degrees, again in opposite directions.

Higher order filters add 90 degrees of phase shift per order. For example, a second order filter will have a 90 degree phase shift on both woofer and tweeter at the crossover frequency, approaching 180 degrees in each driver at the extremes. The two 90 degree phase shifts at the crossover frequency in opposite directions gives a net 180 degree phase shift between the drivers, meaning that if the drivers are wired in the same absolute phase, there will be a null at the crossover frequency. This then necessitates that the input to one of the drivers be run in inverted phase, meaning that throughout the entire range covered by the two drivers, they are operating in opposite phase. Talk about screwing up the integrity of the waveform!

Twl is right, there is no variation in the speed of sound relative to frequency. Each driver has a different "acoustical center", which is the point at which sound can be said to originate. It is not a physical property but an acoustical one, although a good approximation for any given driver is to use the point where the voice coil former meets the cone or dome.
Karls, thanks for the clarification. I was under the impression that the capacitor or coil shift would be additive to the reactive element, and not be cancelled by it, in a first order configuration. Is this fully proportional, or are there some varying degrees of shift that are not cancelled ?
I think we could discuss this subject for a long while and get very technical. I feel that anything that helps preserve the waveform is beneficial. TWL is right about the waveform. You want it all to arrive at the same time. You can go into a chamber and easily prove that a lot of speakers do not deliver the sound as a "On time" acoustical wave. This is what time alignment tries to do. Science has proven a bumble bee can't fly but it does. Acoustics has a lot of issues just like electricity. Vandersteen tries to get his speakers to perform in a manner that preserves this waveform and even though the phase angle does change, it is not going far in a positve or negative direction unlike some speakers. It is just closer to an electrical ideal. Does it make a speaker "sound " better? Well, there's your debate.
"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.
I didn't read every word in this thread, but it started by listing the Joseph speakers as being time and phase correct. I don't think so. They use patented, ultra steep slope crossovers as their main design concept, which would preclude time and phase alignment. (If someone knows something different, please post.)
Karls, I believe that John Bau of Spica designed time coherent speakers with other than 1st order cross-overs.
Well, I'm going to take one last technical stab at this. What we are talking about is the time that elapses between the arrival of the electrical signal at the input of the driver and when the acoustical signal leaves the driver. This will vary depending on the size and frequency range of the driver. This is not the time the acoustical waveform travels through the air. If it doesn't leave at the right time, it sure can't get to your ears at the right time. That is why I said that the baffle slope doesn't mean a lot, relatively speaking. We must be phase correct to assure that the amplitude of the fundamentals and harmonics are not altered and time aligned. By adjusting the acoustical centers of the drivers, we can compensate somewhat for the time alignment. It has to be precise.
The crossover network may need to be very complex to accomplish a 6db/octave ACOUSTICAL roll-off because the electrical and mechanical characteristics of the drivers must be considered. Single caps will not do the job. Phase has to be considered in this equation because phase will create acoustical timing errors. Also, we are talking about acoustical phase, not electrical phase. We are looking at wavelengths here. If you know the frequency of a sound pressure wave you can calculate the "Wavelength" of each cycle. We can also add in "transfer function."
This could be a very long discussion but I hope this gets us all on the same page.
Time coherence is difficult to achieve because the acoustical center for a moving coil driver is not a fixed physical point, but actually varies somewhat with frequency. Source - The Loudspeaker Design Cookbook, sixth edition, page 113.

Phase coherence in a multi-driver system requires first order acoustical slopes for both the low-pass and high-pass driver. The acoustical slope is the sum of the inherent driver response and the crossover response. Note that time and/or phase coherence can only occur in a single plane with a multi-driver system.

Human hearing characteristics aren't linear, but are full of thresholds and masking effects. For example, after .68 milliseconds the directional cues from a repetition of the original signal (an echo) are suppressed, and this suppression (masking effect) lasts for about 40 milliseconds. Now, if we knew precisely the thresholds that apply to time and phase coherence, we could take them into account in loudspeaker design. Alas, the published research is inconsistent on the audibility thresholds of phase and timing errors.
There may be more than one way to skin a cat. John Bau's classic Spica TC-50 claimed time and phase coherence via this arrangement: slanted baffle with cossover: high-pass slope, approximately first-order, 6 dB/octave; low pass slope, fourth-order 24 dB/octave; both drivers connected with same polarity.
Unsound---they lied! It HAS to be a first order filter period. The phase shift created by a 24 db slope would be tuff to fix. Read Richard Hardesty's issue #3 of the Audioperfectionist. You might not like his recommendations but his science is correct.
This topic comes up every few months. Designing for phase coherence may be intellectually gratifying, but here are my questions for the Phase Coherence Uber Alles crowd.

1. What does time coherence actually sound like? How could you tell a time coherent design from a non-coherent one without
looking at the measurements? Why does almost every online list of "coherent" models include some that are not?

2. If all time coherent speakers are correct, then why do they sound so different from one another?

3. If this characteristic is so important, then why do only a few companies embrace it? and why aren't those companies dominating the marketplace?

4. What about OTHER factors such as distortion, wave interference, off-axis lobing, compression etc.!? Wouldn't these have much more influence over the quality of sound?

5. If this approach is the One True Way to superior sound, then why do people vote us Best Sound At Show?
Josephaud, to answer your questions:
(1). Time and phase coherent speakers sound as though they are "cut from one cloth" with less noticible diferrentiating sound of different drivers and cross-overs. They consistently demostrate superior sound staging and imaging.
(2). Because they uses different drivers, boxes etc. Would you ask the same question of different manufactures that share similar design priorities e.g. Acustat or Audiostatic?
(3). Perhaps it takes more talent, effort and expense in design equipment.
(4). Perhaps? Perhaps not?
(5). With all due respect not all people vote you Best Sound at Show. You have never been in the running when I vote.
I'll take a stab at Joseph Audio's post: First of all, no one ever claimed that time and phase coherence is the only important parameter in loudspeaker design (at least, no one with any sense). There are many, many factors, all of which are extremely important, and any one of which, if ignored, will detract in a significant way from the end result. THAT is the crux of the matter.

So how do you know that time and phase coherence is critical? So few speakers have these characteristics that many people are fully acclimated to the sound of noncoherent designs, and so will not notice that anything is wrong. All the individual "sounds" are there, and in the right volume proportion, and they all have excellent attack and decay, etc., but the speaker itself does not sound "coherent". I hate to use such a nebulous term, but it truly sounds as though there is not a musical whole, but rather a bunch of separate musical events occurring more or less simultaneously. It is the difference between "natural", which allows you to relax into the music, and "a really great stereo system", which may be fantastically impressive at a hifi show but never actually fools your brain into thinking that you are listening to the real thing. That is my personal opinion, but it is nonetheless exactly what I hear. When it is right, you simply forget that you are listening to speakers. And it occurs with vastly disparate design philosophies, including multiway cone/dome systems, electrostatics, and Walsh systems. Although they are instantly distinguishable from one another due to their vastly different dispersion characteristics, all of them allow your brain to relax and feel as though you are listening to real music. I have never heard a noncoherent system that could do this, not one, in over twenty years of being obsessed with hifi and music. Sure, I've heard plenty that sounded like great hi-fi speakers, but that's an entirely different subject.

That, in a nutshell, is my personal answer. Do not presume that I or others are just making this stuff up for our own intellectual masturbation. It is very real to us, every bit as real as the anechoic-frequency-response or cumulative-spectral-decay graph is to you. And every bit as important, even if it is only one of many things that are every bit as important.
In response:

Unsound: Please allow me to expand on your comments one by one:

1. I've heard this said before regarding imaging and soundstaging. But I must tell you that as I've examined different topologies, I've found that other things such as
the dispersion characteristics, smoothness of power response, and clean decay corellate more powerfully with imaging and driver integration. Indeed, our designs are almost always singled out for praise in these areas. A very steep cutoff has real advantages because the overlap between the drivers is better controlled, so you avoid the large dips and peaks in response that upset the smoothness of the power response in slow slope crossovers. If you allow the drivers to overlap over a broad range, they may add in phase at a single point in front of the system (and this can be a very very tiny point!) but they will have sharp nulls and peaks
at different points in space. This is why such systems have trouble in three dimensional space. These interdriver cancellations actually make the transition between drivers
easier to spot, at least in my experience.

2. Which leads to my larger point. There are SO many variables in loudspeaker design, from drivers to boxes to
crossover slopes to veneers . Change any of these, and the sound changes, (okay, maybe not the veneer.) Why harp on crossover design as the focal point? It's hopelessy myopic since as you admit, the speakers within the group are all different from one another.

3. Do you seriously believe that? I suppose Dr Floyd Toole, now at Harman International, formerly at Canada's NRC, must lack the resources or talent to create low order crossover based designs because his work corellates well with ours. You can read about the Harman intl facility in Stereophile, and other places.

4. Perhaps yes!

5. I didn't say everyone voted us Best Sound. You're entitled to vote for whatever system you truly loved.
However, more seasoned audiophiles voted for us at that show
than any other system.

Your belief in low order crossovers is just that. And once you've embraced a certain mode of thought, it's difficult to
consider a different one. There's a lack of supporting evidence as to the audibility of the small degree of delay associated with steep slope designs. In fact, the research seems to indicate that it needs to be 3 times the delay that exists in high order networks before it can be barely detected.
But once you believe that you can hear, it will tend to influence your opinion of whatever speakers you listen to.
And thus the belief itself can become the overiding factor in your assesment of a given system's sound.
In response:


It's possible for higher order crossover systems to sound "natural". This is one of the litmus tests for me when I'm working on a design. When you've created a system you must be hypercritical of it, and uncover any potential flaw in its sound before it goes out to the rest of the world. When I can sit in front of one of our creations, and forget about the balance, the crossover transitions, the boxes, and just IMMERSE myself in the music, I know we've done it. That, for me is the magic of this endeavor- it's like an audio seance!
You're bringing back some very talented ghosts. That's what I miss on most modern recordings - no ghosts. everything is
synthetic and processed with a plastic sheen to the sound.
Put on a simply miked recording of an orchestra with Heifitz
or a jazz ensemble with Miles or Pops, and the ghosts come back to life! It ain't the time domain, it's the whole reanimation that matters!
Man, I'd like to see Richard Vandersteen and Joseph Audio get in the ring! It's what makes this "Hobby" so great. My design is better than your design. I believe Vandersteen, Jim Thiel and a few others would debate his points. I've owned a lot of speakers over 40 years of this and maybe my ears are going bad but I never cared for the Joseph Audio sound. Once I was exposed to the time aligned and phase coherent systems, I will not be going back. But I guess there are so many speakers for the same reason there are so many cars---to be different.
By the way, I bought my first pair of Vandersteen's before I saw any specs,graphs or even knew what phase and timing were. They just sounded better to me. Isn't that what is important? I do listen to speakers every so often when I'm in a different city and stop in a store. I still don't like the Joseph Audio sound and I don't care how many "Shows" they win! Nice veneer though.
Josephaud, let me return the favor,
(1) The fact that you seem to have heard this before suggests that there is consistent consensus in this regard. I was not comparing these designs to yours or any other particular ones.
(2) I think we agree on some level here. It was however the impetus of this thread. I think that cabinet design is also a common consideration in these designs. We are now seeing drivers designed with these considerations as well. As such I don't think that were talking about a preoccupation with cross-overs. In my earlier post I mentioned that I was consistently attracted to speakers that shared this design principle. Considering the variety of speakers available and the limited time we have on this planet it would be foolish for me to ignore this consistent attraction.
(3) I believe that it's possible that some one with an extensive laboratory to miss opportunities for a variety of reasons. With the exception of the original PSB Alpha (considering it's very modest price point)I have yet to hear a product from this famed laboratory that I've enjoyed. Toole is not God and Canadas NRC isn't the only church.
(4) Perhaps is the operative word.
(5) You have no way of knowing just how "seasoned" an audiophile I am. I would venture to say that in the real voting world where votes are backed by real money on real purchases that the designers of "time coherent" speakers are enjoying greater sales and profits than you are. You state that I embrace a belief in low order cross overs despite the fact that in my earlier posts I mentioned that I enjoyed speakers that didn't confrom to these parameters and mentioned that it has been reported that one has claimed success with time coherence with a higher order cross over.

I don't pretend to have your expertise or the means and know how to actually tests the claims of of time coherence. I merely pointed out that I consistently find speakers making these claims most enjoyable.
Mr. Joseph wrote: "I've found that other things such as the dispersion characteristics, smoothness of power response, and clean decay corellate more powerfully with imaging and driver integration."

As an amateur speakerbuilder for about 20 years (who tried it all, even my own version of an ultra-high-slope crossover), and now as a dealer, I have to agree with Mr. Joseph's emphasis on radiation pattern and decay characteristics. I personally would trade off phase coherency in exchange for good radiation and decay characteristics.

I once built a speaker with true a first-order acoustic crossover (which is a helluva lot harder than it sounds). Yes it imaged quite well from the sweet spot, but the timbre wasn't very good. Recombining the same drivers (a Jordan module and an Audax woofer) with a higher-slope crossover at a much lower frequency sounded much better overall.

Ya'll remember the legendary Dahlquist DQ-10? Well, Jon Dahlquist found that he could either align the leading edge of the waveform, or the trailing edge, but not both. After listening tests, he chose to align the trailing edge, as he found that getting the decay right was more beneficial than getting the initial attack right.

Just for the record, I don't sell Jeff Joseph's speakers; he's a competitor. And a damn fine one at that.
Unsound, you may have misinterpreted a comment just as I did when I first read it: JosephAudio wrote "more seasoned audiophiles voted for us at that show than any other system". At first, I thought he meant "audiophiles more seasoned than you" but upon rereading, I interpreted it as "a number of seasoned audiophiles voted for us at that show -- more than voted for any other system". Great discussion but I wanted to help clear up one small but important misunderstanding.
I am not about to slam on Joseph's speakers, because I think that he is correct on many points and certainly the results speak for themselves: a very clean and clear decay and very flat frequency response. These are tremendously important factors, and any speaker designer that fails to perfect them is doomed to failure from the start. In addition, I would not speculate that his sales are poor either; there are few speakers in the world that perform better than his in this regard. In addition, I agree with him fully that first-order crossovers are an absolute bear when it comes to frequency response and driver integration in real space. BUT that doesn't stop me from saying that I still prefer the "sound" of a well-worked-out time- and phase-coherent speaker. Granted, there aren't many out there, but they do it for me like no others can.
Ozfly, at the risk of appearing petty, Joseph still couldn't
know how many of the audiophiles who voted for his product were "seasoned". Ironic that Joseph finds time coherent fans proccupied with cross overs when thats probably the area which sets his products apart from the rest. Like Karls I am not about to slam Josephs products. I'm sure there are alot of people who purchase his products and enjoy them. I wish that he could appreciate the fact the this holds true for other designs. There is obviously a sincere effort to produce a quality product at work. They just didn't work for me.
Time coherence is as important as the amplitude response measurements typically taken.

A time-domain snapshot would show the pressure spreading away from that cabinet- a disturbance that contains both high and low 'frequency' components, better thought of as quickly rising/falling pressures overlaid with slower rising/falling ones. When we hear them in their original sequence, we remark "what a gifted musician!"

There are serious challenges and outright limitations to achieving 'perfect' time coherence:

-We are limited by the drivers having finite bandwidths before any crossover is applied. We need perfect pistons in the treble, and response to DC in the bass.
-A driver's electrical characteristics change with the power applied (temperatures rise), which means the crossover points, thus the phasing, change dynamically.
-We have the issue of cabinet reflections. A tweeter in a large cabinetface is like putting a woofer in a corner, speaking wavelength-for-wavelength. Even if that face is beveled, or felted (felt does not absorb 100%)

How can you tell a cabinet face is a problem? Just pick any point on that face and compute the `round trip distance for sound to get over to there from the dome tweeter and from there on out to your ear. Compare that to the direct path distance from the dome to your ear. You'll see that the path-length DIFFERENCE is greater than 1/4 wavelength of any lower-range sound from the tweeter (or mid), which means the reflection smears over the direct wave- it is not coherent.

This tweeter (and mid) 'splash' off of the front panel is 'corrected'in those large cabinetface designs by crossing over the tweeter higher than the mid's crossover point (and the mid higher than woofer)- which de-focuses the image and makes the dynamics sluggish, as now the drivers are 'a little out of phase' over their ENTIRE ranges.

If it wasn't 'corrected' by staggering those crossover points, the tweeter (or mid) would measure too loud in its lower range, as the reflections boost its 'bottom end response' when measured with test tones or pink noise, or even MLSSA- which is why this phenomena is not discussed- it's not visible with std. tests. But it is audible.

To hear what really good time-alignment and lack of reflections do for the clarity of the performance and the musicality, please listen to a single element headphone- Grado's or some Stax electrostatics, etc. And listen to a single-mic recording on them, such as a Harry James Sheffield disc- you can clearly hear what each musician is doing, in any part of the spectrum, which is the benefit of a time-coherence transducer.

Then play a crummy recording and see if it is less irritating- it will be. That's because the transducer has less phase distortion, which only distorts the original distortion. You normally hear distorted distortion, which is a multiplicative process, never additive. And why it's better to improve the source components first, before say, changing the amplifier or speaker wires.

Speakers which are very sensitive to your choice of amplifiers have a phase-response that is all screwed up- which magnifys any problems the amplifier has. Also they use a wierd crossover circuit that's causing the phase problems to begin with. These circuits also put a difficult load on the amplifier, as their extra parts store energy instead of passing it on as soon as possible.

Finally, time-coherent speakers can sound great on cheap stereos, for the reasons above, but only if they employ very simple first-order crossover circuits whose few parts can actually respond to every nuance the amplifier can muster. The evidence is heard even in cheap Sony headphones (which have little phase shift) plugged into any stereo.

Also, most crossover-circuit parts cannot pass the most delicate signals, which makes the music bland. Most crossovers also use far too many of those lower-fi parts.

We don't see too much written in the press about time-coherence, as the math is confusing at first- not suitable for a casual article. I wrote one for Audio Ideas Guide magazine, and it's still hard for me to wade through without re-reading.

The best dealer has worked hard to hear `most every brand set up well, whether he carries it or not. This industry wouldn't be where it is without those retailers (which are few).

Hope this helps. Basically, trust your ears and use them to verify that a dealer knows what good sound really is.

Roy Johnson
Green Mountain Audio
Listen to Roy Johnson !
Then go listen to his speaker's.Then come back and tell us what you heard ! I think you'll find it is an important issue if your interested in true sound interpretation .
"Green Mountain Audio" are time coherent .
I don't see a web site for Green Mountain. Where can I get info?

I am buying a pair of Green Mountain C-3's, should be
here soon.
Roy is working on a website now, and should be up &
running before to long.
In the meantime you can see his speakers @

symphonysound.com, one of his dealers.

Talking to Roy is a lot of fun, and the man knows
his stuff.
The green mountain speakers look like a serious acoustics experiment, not a piece of furniture. The implication of what I read is that they can be tuned to your room, is this correct?
greenmountainaudio.com will be published in the next few weeks.
Roy Johnson
Green Mtn. Audio
They are not tuned to your room, but "focused" to your listening position via moving the mid and tweeter in the C-2 and new C-3. You are setting what we call the "Soundfield Convergence" for time coherency at your seating spot. This is done with a tape measure and takes a few minutes max.

The phase response of the C-2/C-3 will thus be- by definition- compromised everywhere else. But by many HUNDREDS of degrees less than speakers with higher-order crossovers.

We do note that with a first-order crossover, off-axis comb filtering does not seem to be an issue except on test tones and pink noise.

Moving completely up and out of the main listening plane (where off-center listening was still fine), we hear the depth of field decreasing, as the time domain becomes progressively "warped" from bass to treble. But at least there are no sudden "jumps" in the relative acoustic phase from driver to driver as there are with high-order crossovers, no "twitchiness".

Standing up, the time delay warp across the spectrum is still far less than with high-order-crossover speakers. We do not hear the soundfield degenerate into "a wall of sound"- plenty of ambience remains.

High-order designers are getting better at smoothing out the abrupt jumps in phase- for less "separate tweeter-separate woofer" effect.

They are also getting better at damping the ringing present in the highest-order crossovers, but the result is a hard load on the amplifier.

What you hear from the smoothing and damping is less image depth, less dynamic impact, and less rhythmic definition (finesse) anywhere around those crossover points. Which is why, quite often, the approved "audiophile recordings" used to demonstrate them are so bland performance-wise. Not much there to challenge the speakers. Something aggressive won't be pleasant- no Zappa allowed...

I noted in some postings above, references to the possible lack of phase shifts in minimal-driver speakers- single panel electrostats, Jordan module, Lowther, etc.

In a single driver, phase shift won't be caused by an electrical crossover- there isn't one!. The signal remains free of crossover parts distortions/haze too.

However, any driver has mass, suspension, and damping (by the suspension's resistive losses and the amplifier). Thus it is a "damped harmonic oscillator"- in a Physics 101 book.

A harmonic oscillator has a 1/4 wave's worth of time-delay down at its low-frequecy resonance, compared to the midrange tones. For a sealed woofer with -3dB at 40Hz (close-mic'd measured), that means 1/4 of 1/40th of a second, or 1/160th of a second=6.25 milliseconds. That doesn't sound like much time delay, but it is ~7 feet of distance, at the speed of sound.

Put two microphones on a piano- one for the left hand, one for the right; both equally close to the strings/soundboard. Now, impose 6.25 milliseconds delay between those two mics- that is, between the lowest notes and the mid-scale notes.

Imagine what the piano would sound like if the right hand tones got to the microphone seven feet sooner than the left hand's lowest notes, because that's what's happening as you slide down the scale for ANY loudspeaker- and it's a gradual change in phase, which is why we don't complain too much. Any driver does this- headphones, Walsh, electrostats, Lowthers...

A damped, harmonic oscillator also has a high-frequency limit, imposed by its moving mass- which equals phase shift in the highs, or time delay.
It has phase shift in the low frequencies, because it has mass bouncing on a suspension (it's a mass/spring system), as described above.
And since it cannot be an infinitely-rigid cone, it has cone breakup too, which imposes a ragged phase error across the roll-off region, a raggedness that changes with loudness too.

If it has a whizzer cone for the highs, like a Lowther, then there is a time-delay (phase shift) between cone and whizzer, seen as a wiggle in the driver's impedance curve. At that mechanical crossover frequency, the idea is that the cone stops moving as the whizzer starts moving.

Yet the amount of time delay between those two parts is far more than some electrical crossovers would've imposed. Even as the whizzer moves, the cone is also breaking up- parts of it "rattle on" in non-pistonic motion, so the phase change is not smooth with frequency.

Finally, since the forward edge of the whizzer is un-terminated (not damped or otherwise constrained), it has its own breakup modes. Which makes complex, loud, high tones sound hazy, fizzy, fuzzy or dirty (depending on the whizzer's breakup modes).

Any mechanical transistion also changes its characteristics with loudness, humidity (possibly) and aging of the materials. You are asking a piece of paper, plastic or glue joint to flex, predictably, for billions of cycles (per week), and flex in a completely linear, proportional manner on the very softest sound and the very largest- often simultaneously.

A mechanical transition is also happening at the leading and trailing edges of the ripple moving down a Walsh driver, or spreading out across the face of a Manger diaphragm. It is hard to find driver materials that do not change very much in flexiblity with age, or humdity, or loudness- which means the designers of those two drivers were truly ingenious to get as far along as they did. What those drivers offer is minimal phase shift in their mid-bands- which is good. But neither one can handle low bass, nor is very sensitive.

To check the transistion to whizzer (happens in the high-voice range), see if something abrasive such as Janis Joplin, can be tolerated in that tone range. Then listen to her on a good headphone (has no phase shift in that tone range). The whizzer transistion could be apparent on massed, loud strings- as wiry, steely, or strident- it all depends on where that mechanical crossover point is in the tonal scale, and how much you aggravate it.

No single driver can cover the whole audible range including low bass, unless it is a large single-panel driver, for which you have to sit exactly in the middle- exactly.

The Lowther drivers and Jordan 5" drivers do have some bass, but not enough to balance out the voice-range when listening > 10 feet away, and they have loudness restrictions: Their high efficiency comes from low moving mass, due to a short voice coil = minimal stroke available for midbass and lower tones. Look up the x-max specs on the drivers- you'll be surprised.

If a design has a mid cone with no electric crossover, yet the tweeter does, then at the acoustic crossover point, you have:
the electrical phase shift of that tweeter's circuit,
plus the phase shift caused by the tweeter's having its own low-end resonance,
plus the phase shift and ringing at the mid cone's breakup modes(indicated by wrinkles in the impedance curve of that mid driver),
plus the emf sent back into the amplifier from those extra cone oscillations, which gets into the negative feedback loop.

If you have ANY kind of frequency-response roll-off, then you have phase shift (time delay) that gradually comes on as you approach those roll-off points, no matter what object in your stereo, or in the recording studio you examine- amp, mic, mixer, A/D & D/A converters, analog tape recorders, disc-cutting lathes.

But all those devices have very little phase shift in the main part of the audible range. What they do impose comes on gradually, octave by octave, as you approach the devices' -3dB points, with the exception of certain microphones, like a Shure SM-57/58, that have a ragged phase shift in the sibilance range- lending a hard edge to the voice, often intentionally employed by the recording engineer.

It is the speaker's phase error vs. frequency that is much higher than anything else in the recording/reproduction chain. It is caused by high-order electrical or mechanical crossovers that "twist" or warp the phase in the mid-bass or low treble- wherever those crossover points are. It is caused by cones breaking up (or going soft, ala KEF and B&W) in the middle of their range, before they even get close to crossing over to the next driver. It is also caused by the drivers not being the same acoustic distance from the ear.

To find out what effect any crossover (mechanical or electrical, or combination thereof), has on music, listen to simple sounds that move through those frequency ranges- there you lose depth, clarity and dynamic expression. Also listen to a lot of musical instruments in person, up close, perhaps at a music store on a slow afternoon. Talk with the store's percussionist- let him show you why musicians pick certain cymbals, bell-trees, drum kits, sticks, mallets. Have the guitar person play you some differences in his gear.

Any speaker designer worth his salt needs to know, quite intimately, what goes on in the studio, in the musician's hands. After all, that's what needs to be heard on the other end.

Roy Johnson
Green Mtn. Audio
GREAT post, Roy!
I feel the need to try to set the record straight regarding our designs.

The Infinite Slope design we employ is absent of any ringing.
None. Nada. Don't believe me?
Go look at the review of the RM33si in Stereophile, see the waterfall plot of the RM33si. (it's online now)

Yet, the impedance curve is also well-behaved - not a "hard load" for an amplifier at all. Richard Modafferi is a stickler for excellent impedance curves, but then again he has the knowledge of filter theory necessary to properly implement this crossover.

The irony of all this is that initially, both Richard and I believed that phase linearity was an important factor in loudspeaker sound. Richard had concocted many experiments to examine loudspeaker phase. Richard's problem was that he had a stubborn professor who effectively debunked Richard's attempts to prove that it was significant. Richard finally had to come around to the viewpoint that it was not a serious problem. If phase is not such a big deal, then what is? Frequency response, and radiation patterns.

The off axis comb filtering of low order crossovers is a serious problem, which is why companies that employ that method often require the listener to tilt or "focus" the main lobe towards the firmly dictated listening position.

The broad overlap between the non-coincident drivers will create large peaks and dips in response if one moves from the optimium spot. This flaw in the radiation pattern of
slow slope crossover designs may be what certain listeners are accustomed to hearing from a stereo system.
That energy does not disappear into the sunset, but rather is bounced around the room, scrambling the magic "phase coherence" that the designer so carefully
struggled for.

Once I had lived with speakers that are free from this artifact, I found it impossible to go back. Whenever I listen to slow slope crossover designs, I find that I'm easily distracted by the large changes in tonality observed with small shifts in listening position. Which listening axis is correct? And if you can contort yourself into that position, can you stay there and refocus your energies on the music? And if you should stand up, the stark balance shift reminds you that what you're hearing is fake and unnatural.

While the idea of filtering bad recordings through such a speaker may have merit, it's more likely to be dynamic compression and radiation pattern that is taking the edge off the ol' Janis Joplin records, not superior phase response. Remember you're talking about a multi track phase scrambled recording played into a phase scrambled listening room. It's too bad that filter is not defeatable. Anyone who's visited us at shows knows that our speakers are equally at home with Louis Armstrong, Frankie Laine, Bill Evans, Nirvana, Norah Jones, Cassandra Wilson, Elvis Costello & the Soggy Bottom Boys.

Happy Tunes to you!
Now we're getting somewhere. Designers sharing the merits and compromises they have to deal with in a decorous forum. As I have previously stated, I am consistently attracted to time coherent designs. How ever, the thought of lobing effects have caused me concern. Perhaps the experts would shed some light on the subject.
Every speaker design is a compromise. The perfect solution is not available and probably never will be. I'm sure that every speaker manufacturer feels "His" design is the best solution.
I prefer the 6db designs and I use Vandersteen 3A Signatures with a pair of matching 2wq subs. This has provided me with the best sound "I" have ever had in my dedicated listening room.
On the test bench, these speakers are about as good as any out there (testing wise using Stereophiles reviews and in Richard Hardesty's reports and comparisons in The Audioperfectionist) Obviously, there is more to speakers than what shows up on a test bench, eg:room acoustics.
I feel Jeff is trying to "Sell" his design. I'm sure his speakers are liked by some(most manufactures are) but I personally did not favor the sound. Is his solution the answer? I don't think so.
I do agree that 6db speaker designs are a little harder to set up and do have a limited "Sweet spot." But to be honest, in 40 years of being in this hobby, I have not heard a speaker that didn't take time to set up and was somewhat limited to a "Sweet spot." Vandersteen's have an area where the sound doesn't change and unless you are moving around listening to music, then, this is really a non issue. I haven't heard a speaker thats sound didn't change when moving around. I usually stay put.
I have owned probably in the neighborhood of 30 pair of different speakers over the expanded course of my trial and tribulations with this stuff. My final solution has been---If it sounds good then stick with it! I'm through spending my money chasing my tail for the "Perfect sound." And by the way, NOBODY KNOWS WHAT PERFECT SOUND IS!

I agree that there are trade offs in every design, but for me the trade off's in low order crossover designs are too great to allow me to enjoy listening through them. I should mention one exception, however- the Quad ESL 63 with Crosby mod's was
within its limitations a very satisfying speaker. Just don't turn them up too loud, and place them very carefully.

One needs to be able to interpret the test data correctly, in order to identify what is significant and what is not. If you are willing to ignore peaks and dips of 10-14 dB off axis, I suppose that's your perogative.

I'm not laying claim to "PERFECT SOUND". Just "TRUER SOUND".
The problem with "if it sounds good, stick with it" is that
I couldn't find a speaker that I was completely satified with. Each system pointed out flaws in the others. That's why I went into the loudspeaker business to produce Richard Modafferi's Infinite Slope designs. These systems managed to
get more things right to my ears than any other system. And the measurements happen to bear that out.

Jeff, The last statement you made about "truer" sound is where the problem lies. What is truer? Is it based on measurements or are you ears "truer" than mine (which could be the case considering the age factor!) My point was that to each individual,truer takes on a different opinion. No speaker is perfect, as I said, and therefore is not truer unless you use a subjective analysis(as in your case---your ears.)
I actually talked to Richard Vandersteen at some length about his design and, like you, he could not listen to anything but a "slow slope.")Is he wrong in his opinion? To his ears, it was "Truer." He also believes in the "Baffleless" design. I definitely feel that speakers with a large area surrounding the tweeter and midrange affects the sound negatively.
I have listened to your speakers extensively. I do know set up affects them and they do have a sweet spot. I also find them somewhat analytical with a slightly dry sound. I hate to say this but they sound somewhat similiar to the B&W Nautilus line(which I owned for a while--805's and 802's)which i feel ARE excellent speakers but not for me.
I'm certainly not going to tell you your design is wrong and that your speakers don't sound correct to you. I'm sure your speakers are well built and deserving of the interest they get. However, I am going to tell you they do not sound truer to me for whatever reason. I find the Vandersteen to be as dynamic and accurate as sounding as any speaker system I have owned. They may truly be +- 10db off axis but they sound damn good on axis where I listen.
I don't have the means or ability to test my listening impressions. With that said, I have found the sweet spot of low impedance speakers to be wider in the horizontal plane and narrower in the veritcal plane. Despite the fact that my mother used to teach ballet, I'm not prone to dancing. I usually listen alone. As such it's an easy compromise to live with. Interestingly, the Dunlavy's seem to have overcome a bit of this vertical sweet spot compromise.