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In Reply to: RE: Might need to take some measurements? posted by genungo on September 06, 2014 at 10:01:36
The Alexia is not time coherent either, in fact one driver is going out while the other is going in (inverted polarity). It is far from time coherent despite the marketing BS. Compare that with a Thiel CS (any model) graph or a Vandersteen and you will see that they are world's apart.
The question of whether or not it is audible is the age old question and at least some of us are quite sensitive to speakers being coherent. My Ref 3as make a quite nice triangle and are clearly time coherent from measurements.
It is whether or not the speaker could make a credible and visually recognizable square wave as Quad used to demonstrate. Most speakers make it look like complete garbage and it is on the forgiving nature of our auditory system that allows non-coherent speakers to work properly at all.
The biggest advantage I have usually heard from coherent speakers is a much better integrated treble that seems smoother and less prominent. This leads to a more natural feel for the sounds in general as well as soundstage and imaging naturalness. This also leads to a lower fatigue factor...maybe the brain is just not working so hard to "decode" the sound waves projected its way?
What I can't understand is why Tannoy doesn't try to make drivers to use a true 1st order xover so that they can take ultimate advantage of the coincident driver concept.
The Ref 3as don't use a crossover at all on their main driver so it is possible but it has to be part of the design priority.
I would say that Tannoy is one of the most coherent sounding speakers that are not time aligned. To get them time-aligned would require a serious driver redesign though.
Follow Ups:
Despite the fact that the Alexia has one driver inverting, the ear perceives all drivers as being "time-coherent" when heard from several feet away at the recommended listening position. That is my interpretation of Atkinson's words.
Not time-coherent. I don't agree with your interpretation of JA's words. You have to think about group delay as well as phase. The order of the crossover affects both phase shift and group delay. That is why a 4th order LR crossover can be in phase but not really time coherent because the phase rotation delays the wave propagation. The Alexia even inverts polarity.
"This graph reveals that, as in the Alexandria XLF, the tweeter is connected in positive acoustic polarity, the midrange driver in negative polarity. However, with the tweeter module set up by Peter McGrath, the graph also shows that the negative-going decay of the tweeter's step smoothly blends with the negative-going start of the midrange unit's step, confirming the excellent frequency-domain integration of their outputs seen in fig.4. "
JA doesn't mention time coherence at all. He talks about frequency domain integration.
Check out square waves from the Thiel CS5
http://www.stereophile.com/content/thiel-cs5-loudspeaker-measurements-0
Not as good as the Quad 63 but not bad all the same.
.., "... the output from all the speakers drive units ARRIVE at the ear" and "the brain's temporal fusion window", etc.., would seem to be related to TIME domain behavior. That's the conclusion I was able to draw after reading the quotation in the post above.Thanks for your helpful input.
Edits: 09/09/14 09/09/14
The measurements clearly show that this speaker is like the vast majority of speakers reviewed. NOT TIME or PHASE coherent.
The reviewers words are trying to imply with separate facts a different fact that actually is not a fact.
Not saying the speaker in question is bad or the review is invalid, but it does not qualify as a type of topology that your original post was targeted against.
Well, you seem to be pretty sure about all of the above so I guess I'm willing to let the subject go for now.I would try emailing John Atkinson to ask him if he'd care to chime in but because his responses are so often met with hostility around here, I doubt that he'd feel like responding one more time.
BTW, my original post was not "targeted against" anything or anyone in particular. I'm taking a poll, that's all...
Edits: 09/09/14
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