Thiel Owners

"Since if a speaker can produce a step response correctly, therefore it is time-phase coherent, and therefore it must be "good" - is not something I hear him saying. He does say that "all else being equal, phase coherent speakers tend to produce exceptional imaging". (My semi-quote)

Yes, I think that's what he said.  I may have mistaken "exceptional imaging" for what he felt as "good".  I think I've read the same article that you read and he did say "exceptional imaging".  It's been awhile since I've read the article (and I can't seem to find it anymore), but I also believed he said something to the extent "if everything else has been taken care off", that is if a speaker was well designed in other regards, then "time-coherence" may have an advantage of providing "exceptional image".  

Anyway, what I will write probably won't be based on my personal opinions but more based what I've seen from simulations with actual real world data.  Others will have to draw their own conclusions.  I only used John Atkinson's statement as an "introduction", but I will try to stay clear of using my own subjectivity.  

I think that phase coherence (as an objective or success) increases the difficulty of making a good speaker by a large multiple, and that many attempts fail in many ways, including Thiel's attempts.

I agree that time-coherence is not easy and that's why besides Vandersteens, I don't know of anyone else.  I have seen a few measurements from Stereophile done by John Atkinson and he did question the validity of some of the claims of being time-coherent (not Thiel though).

My document is not meant to be a vehicle for judging anyone's work, but it is meant to discuss "time coherence" in a objective way with actual simulation using real measured data (when possible), plots and graphs, and as I said, I will not include any of my subjective opinions.

And for whatever reasons, this topic is weirdly fascinating to me, and I probably won't sleep well until I put the document together :-)

I also find the topic of phase fascinating, including the auditory neurology and learning that helps us hear, as I have expounded on this thread.

There are some confusing terms. Time alignment is a great term, but was trademarked by Ed Long around 1980, which is weird. Time coincident means the same thing, and I recommend it. Time coherence merges two concepts, leading to confusion. Also, Atkinson and others have hijacked "coherence" to include the smooth phase transitions in non-coincident systems with large phase shift - as long as the phase transitions are smooth, some call it phase coherent. Thiel, Vandersteen and many physicists reserve the term "coherence" to mean that the phase response remains minimum, ie. it does not depart from flat. A good measure is "excess phase" approaching zero. When terminology is scrambled, concepts are harder to define. 

Tom, 

Thanks!

George

George - I always wonder whether my comments are clarifying or just muddy the waters darker. My survey of the web suggests that there are strongly held but contrary opinions on the subject. I, as you might guess, have paid attention from various angles including music playback and record production. I take comfort that my opinions align with the best of the bunch, those recordings that play well on all systems.

Here's a link to a good explanation of the territory. It demonstrates the 'stealth phantom' of linear phase filters, whether they are analog or digital.

https://www.audiomasterclass.com/newsletter/the-difference-between-minimum-phase-and-linear-phase-eq...

Atkinson and others have hijacked "coherence" to include the smooth phase transitions in non-coincident systems with large phase shift - as long as the phase transitions are smooth, some call it phase coherent

That is certainly what I understand as one class of "phase coherence".

Thiel, Vandersteen and many physicists reserve the term "coherence" to mean that the phase response remains minimum, ie. it does not depart from flat.

I look at some of Vandersteen designs and I am not sure how he could achieve that.  

A good measure is "excess phase" approaching zero.

Yes, in the strictest of the definition, that is true.  But in reality, I am not sure if any speakers can meet that definition but I could be wrong since I have not seen all the designs out there.  The latter Thiel speakers use coax drivers so maybe "time coherence" can be achieved without excess phase on the tweeter as it approaches 20KHz.  In the case of Vandersteens, he uses conventional drivers with the tweeters offset from the midrange so I am not sure how he could do that without some amount of excess phase.  So it's possible he could be sacrificing "smooth phase transition" at the expense of the tweeter excess phase?

I've seen John Atkinson measurement of the CS2.4 step response, and the peak on the step response does suggest that the tweeter response as it approaches 20KHz may not meet that "strictest of definition" as you pointed above.  If a speaker meets the "strictest of definition" of "phase coincidence" , then the step response should be "smooth" on top of the step response where there lies the tweeter phase vs. the rest of the frequency (for example below the tweeter cross over point).

For example, if you take the phase at the cross-over point to be the reference, the tweeter phase will always deviate from that reference as it approaches 20KHz and therefore the speaker does not meet your claim of "phase coincidence" and therefore by definition, the tweeter response will not be "phase coincident" with the rest of the frequencies.  And of course, some speakers are the worse offenders than others with this respect.