Sloped baffle

Ng... thanks for the phase coherence article. The article seems to be based on scientific controlled studies and tests. Rather than paraphrase the conclusions, I copied them here:

"So what conclusions regarding the audibility of phase distortion can we draw from the all of the above?

'Given the data provided by the above cited references we can conclude that phase distortion is indeed audible, though generally speaking, only very subtly so and only under certain specific test conditions and perception circumstances.

'The degree of subtly depends upon the nature of the test signal, the dB SPL level at which the signal is perceived, the acoustic environment in which the signal was recorded and/or played back as well as the Q & fo of any filter networks in the signal stream. Certain combinations of conditions can render it utterly inaudible.

'Room acoustics further masks whatever cues that the hearing process may depend upon to detect the presence of phase distortion."

And here's my personal bottom line. Phase coherence is just one of many variables that is taken into account when designing a speaker system ... and there are many. As many folks have said, trust your ears and audition as many speakers as you can. But ... if I was asked to buy speakers based on their phase coherence characteristics as a stand-alone factor, I personally would not.

Thanks again Ng.... Good article. It puts the issue into context.

Bruce

And here's my personal bottom line. Phase coherence is just one of many variables that is taken into account when designing a speaker system ... and there are many. As many folks have said, trust your ears and audition as many speakers as you can. But ... if I was asked to buy speakers based on their phase coherence characteristics as a stand-alone factor, I personally would not.

Bifwynne, I disagree here. Of course, you are entitled to think about this the way you choose, just as I am.
There's too much research - of the wrong type - that convinces people that time-coherence is one of the many issues/parameters to be resolved in speaker design.
After hearing time-coherent speakers vs. others, the speaker should be designed around time-coherence & issues re. that speaker's design should be solved in the context of time-coherence. When that speaker is correctly built as a time-coherent speaker it will simply be far more realistic, dynamic & accurate to the recorded music than any other speaker in its price range. From my experience, I'm convinced - there ain't no other way to go.....
Others who have also had such an experience feel the same way not surprisingly.
sorry to see that (once again) this crowd has missed the point re. time-coherence. :(
When you have a chance, listen to a time-coherent speaker (doesn't have to be Green Mtn Audio) & compare it a non-coherent speaker.....

Bif,

Don't get me wrong. Phase is taken into consideration on any competently designed speakers. My first didn't but I wasn't particularly competent then. Not yet either. Still, with four 6-1/2's per side, they sounded more dynamic than any "coherent" speakers I've heard short of the Dunlavy SCIVa. Never considered the two were related.

Time coherence implies that the first cycle of a tone is more important than the second or third. That, I'm unsure of. Really, I don't know. Low order crossovers have advantages, including transient behaviour. I like them because they're simpler and cheaper but not for all drivers and circumstances.

Here's the test... Listen to any 2.5 way speaker. By design, the woofers roll off at different frequencies and must have increasing phase separation as frequencies increase. 45 degrees by 1000 Hz is fairly typical. According to the article, where our ears are most likely to detect. The .5 woofer will be lower SPL but still audible. Can you hear any phase distortion?

Problem is that we don't hear distortion as distortion, not unless you have the trained hearing of a professional under controlled conditions. It can be measured by instruments but human brains interpret those as frequency differences and there could be any number of explanations including comb filtering, diffraction, or the driver. Almost as easily, they can be masked.

So, forget the test, it's useless. More likely that someone will misinterpret that as all 2.5's are ....

Ngjockey and Bombaywalla ... I find the issue of phase coherence to be intellectually interesting. I also find Roy's article and the article Ng... provided to be equally interesting. If I had the time, if there were more B&M stores around with a variety of speaker types, and if the salepeople were game to burn time to experiment, I'd love to build up a personal anecdotal portfolio of experiences.

To date I have only one data point, which is almost useless. I spent 90 mins about 2 years ago with Vandy Treos. They just didn't do it for me. Imagaging, soundstage and musicality were nonextant.

And if the pushback is that they weren't set up correctly, or wrong cabling, wrong positoning, not leveled, and so forth, my response is .... still not impressed. Even if the Treos would have taken me to the 8th dimension if all the foregoing variables were controlled ... I am still not convinced. I want to flip the switch and listen to music. Not interested in using an oscilliscope to figure out how to enjoy music.

This is a fascinating thread. I hope it will continue to attract more comments from folks who have relevant experiences.

BIF

I believe one of the members had posted that the tweeter is 180 degrees out-of-phase in a 2nd order system.
I believe that this is wrong info. If you read Roy Johnson's 1997 article in Audio Ideas Guide he says otherwise & I quote

Contrary to popular belief, the 180-degree shift doesn't mean that the tweeter is out of phase with the woofer. It merely leads the woofer output by 180-degrees, or half of the wavelength of the crossover frequency....
Figure 5b also shows that the amplitude response (derived from steady-state tones) will have an infinite 'suck-out' Tw + W. At first glance, this cancellation does, indeed, seem exactly like that caused by a tweeter with reversed polarity. What is really true is that the time delay is causing cancellation on steady tones, because the time delay at the crossover frequency is half of a wave cycle, 1/(2f) seconds.
To 'fix' the problems of the system, a designer will often reverse the tweeter's wires to invert its polarity. Although the steady-state results shown in Figure 6a look much smoother, in reality this is because the graph for the tweeter's phase has had 180 degrees subtracted.

This seemingly minor point forms the basis for the many claims of 'phase-coherent' performance, which, at best, is a half-truth. The graph now shows 'a smooth rate of phase-angle change at the crossover point.' But it isn't smooth from the perspective of time passing by. In fact, regardless of how smooth this curve appears, the woofer and tweeter still have the same sequence of arrival as before.

Reversing the tweeter polarity only means that the tweeter is moving inward on the initial pulse while the woofer moves outward. This is evident in the square wave response in Figure 6b: The tweeter is pulling in while the woofer is pushing out. At the highest frequencies, the tweeter still arrives as before (in Figure 5), and now its absolute polarity will still be backwards.

I think that Al already provided us a link to this 1997 article so I will not repeat it here.

I want to flip the switch and listen to music. Not interested in using an oscilliscope to figure out how to enjoy music.

precisely! Even more reason to own a time-coherent speaker. Time-coherent speakers, when compared to non-time-coherent speakers, when properly designed, will be more dynamic, more true to the recorded music & simply more realistic. That's the kind of speaker to have in one's room if you want to simply "flip the switch and listen to music". With time-coherent speakers you will leave the oscilloscope on the test rack (where it belongs) & you listen to music.

Problem is that we don't hear distortion as distortion, not unless you have the trained hearing of a professional under controlled conditions. It can be measured by instruments but human brains interpret those as frequency differences and there could be any number of explanations including comb filtering, diffraction, or the driver. Almost as easily, they can be masked.

So, forget the test, it's useless.

I think that this is a bad attitude to have. Basically this says, "you are not trained to listen & you are not getting it, so drop this issue & don't make the effort to learn. keep the status quo".
I say that if one wants to become a better audiophile, a better listener, a better consumer, one should challenge oneself to reach higher & try to understand things that are at this time outside one's grasp. One should challenge one's norm or the norm & you might find out that there is indeed a better way to do things & this enlightenment might bring more satisfaction & joy in listening to music.

if you surf the Green Mtn Audio website, there are article on how to listen. http://greenmountainaudio.com/how-to-listen-to-music/

http://greenmountainaudio.com/how-to-choose-speakers/

One needs to understand that if a speaker is not time-coherent, no other parameter will make up for this. When it comes to time-coherence, you cannot juggle it/trade it off w/ other design parameters - you either have time-coherence or you don't.
Time coherence is not a 'fascinating' concept or idea. It's real & properly implemented makes the difference between enjoying music & listening to top quality sound.....