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First order/Time Phase-Coherent speakers discussions

"The game is done! I’ve won! I’ve won!"


I would like to use this thread to talk about this subject which I find rather fascinating and somewhat difficult to get my hands on. I went through a course in electromagnetism in college and I have to say this is even more confusing and you won’t find the answer in calculus, physics, Einstein relativity be damned it’s not in there either and definitely not in quantum physics. Listening to the "experts" from Vandersteens and Stereophile but ultimately it all came down to a missing link sort of argument ... something like this:
"Since if a speaker can produce a step response correctly, therefore it is time-phase coherent, and therefore it must be "good".

It’s like saying humans come from chimps since they share 90% genetic content with us, but we can’t find any missing links or evidence. FYI, we share a lot of gene with the corn plants as well. Another argument I’ve heard from John Atkinson that lacks any supporting evidence and he said that if everything else being equal, time-phase coherence tends to produce a more coherent and superior soundstage, but to the best of my knowledge, nobody has been able to produce some semblance of evidence since there is no way to compare apples to apples. Speaker "A" may have better soundstage simply because it’s a BETTER design, and the claim "time-phase coherent" is just a red herring. There’s no way one can say the "goodness" from "time-phase coherence" because you can’t compare apples to apples. Ultimately it’s a subjective quantification.

I’ve been doing some simulation and I will post some of my findings with graphs, plots, actual simulation runs so that we are discussing on subjective personal opinions. Some of my findings actually shows that intentionally making time-phase may result in inferior phase problem and NOT better! (will be discussed more in detail).

Having said all that, I am actually in favor of first order/time-phase coherent if POSSIBLE. I am not in favor of time-phase coherence just for the sake of it. It’s just that there are a lot of mis-information out there that hopefully this will clear those out. Well hopefully ...

Here my preliminary outline:

1. My "subjective" impression of what is "musicality" and how it’s related to first order filters.
2. Interpretation of step-response. I’ve read a lot of online writing with regard to the interpretations but I think a lot of them are wrong. A proper interpretation is presented with graphs and simulations.
3. A simulation of an 1st order and higher order filters with ideal drivers and why time-phase coherence is only possible with 1st order filter. This part will use ideal drivers. The next part will use real world drivers.
4. A simulation with actual drivers and how to design a 1st order/time phase coherent speaker. Discuss pros and cons. And why time-phase coherence may actually have phase issues.
5. Discuss real world examples of time-phase coherence with Thiel’s and Vandersteens speakers (and why I suspect they may not ultimately be time-phase coherent in the strictest sense).
6. I’ll think of something real to say here ... :-)
andy2
thielrules
160 posts
 
Andy2: "I’ve been doing some simulation and I will post some of my findings with graphs, plots, actual simulation runs so that we are discussing on subjective personal opinions. Some of my findings actually shows that intentionally making time-phase may result in inferior phase problem and NOT better "

Please follow through on posting these data. Why simulations and not real data from speakers.


andy2 OP
1,545 posts
 
Some of my findings actually shows that intentionally making time-phase may result in inferior phase problem and NOT better 
I think that was also what I said in my original post.  What I said that everything else being equal, then yes, time-phase coherent is a plus.  But I also said that I have seen examples in which the designers tried to make time-phase coherent at the expenses of other parameters such as phase-mismatch or frequency response that may end up creating more problem than it solves.

It seems that Thiel (an I am being VERY careful not to appear to make any false accusation) has claimed that the company's speakers have very small excess phase, which means that the phase shift of the entire frequency range (from 50Hz - 20KHz) has very minimal phase shift, and based from Tom, within a few degrees.  Now that is EXTREMELY difficult (trust me) and I do not even think it's doable or even REAL.  I tried to model one of my speakers like that and I could only achieve about +/- 25 degree but I had to bend over backward to get that done at the expense of freq. response and proper driver integration.  Therefore I really did not like the design and I think I am better off with a more conventional approach.  But having said that, there may be about 2 or 3 speakers in the world that can have +/25 degree excess phase.  John Atkinson had said that you can count will all the fingers in your hands the number of speakers he measured that can get a proper step response which is pretty hard in itself.  But having a proper step response AND having 0 excess phase is like winning the lottery every single week.

For reference, if you use 4th order (24db/octave), you automatically get an excess phase of at least 360 degree.  If you do a regular 1st order but with one of the driver inverted, you probably get about 180 degree of excess phase.  To have zero excess phase (or close to zero as claimed by some) is like hitting a bull's eyes from 7Km away.  I think you can count with five fingers the number of speakers in the history that can achieve 0 excess phase.

When you look at the step response from John Atkinson measurements, it's easy to spot if a speaker has too much excess phase.  Even if a speaker can achieve a proper step response, if the initial spike is too "spikey" vs. the rest, then it probably has too much excess phase.  I've seen various measurements of Vandersteens from Stereophile, I doubt they are qualified as "time-phase coherent" across the entire freq. spectrum.  Maybe from 50Hz to up about 7Khz but not all the way to 20KHz.  And I also posted the CS3.7 measurement and showed it to Tom and I said I doubt about the claim as well.  

I have quite a few real world data and simulations but I am waiting for better Confirmation before posting the data since I don't want to be accused of not have REAL or FAKE data.  I've heard of a lot of people including all the experts in the world talking about it but at the end you get even more confused!  Maybe it's a secret and once you know it, you don't want to share.


asvjerry's avatar
asvjerry
4,575 posts
 
"...thinking of something Real to say here..."
*mmm*
Well, if you haven’t illustrated succinctly the issues and complexity of any attempts to resolve the time/phase-coherence Gordian Knot as it relates to any speaker array, I think I’ll have to be patient to read it....
...and I will thank you for that. *S*
"...I tried to model one of my speakers like that and I could only achieve about +/- 25 degree but I had to bend over backward to get that done at the expense of freq. response and proper driver integration. Therefore I really did not like the design and I think I am better off with a more conventional approach.."
Volumes in 2 sentences...;) So, in my ’unconventional approach’ to my ’quest’, I may have to default to @cousinbillyl ’s comment:
"A Linkwitz Riley 2nd order series crossover, with drivers acoustical centers aligned, is phase perfect."
The line that follow that is also interesting....at least, to me. ;)

What I distill from your post is that if one designs to correct All that one can correct, what one May end up with...you won’t like to hear...Perhaps.

You Might get lucky.

The odds are towering against you.

Now....that’s Quixotic in the extreme.

...from @ivan_nosnibor , awhile back...
But, with active digital crossovers, there’s no need to spend all that time reading all the tea leaves (white papers, testimonials, reams of MLSSA charts, searching for who could be the most unimpeachable source of info on it, etc) in an attempt to get a handle on comparing them all from afar and then try to divine which might be best. With digital actives, you just dial it up and listen for yourself...a whole lot easier and faster that way.
I’ve got one of those...active eq as well (been doing that for decades now, like to play ’flat’ into the space as much as is practical). I think I’ll just wander off with all of this in mind and at hand...

...and see (well, hear) what I can conjure up. *S*

@andy2 ....I think that a digital Xover..."...is our only hope!" ;) *smirk*

Good variable factors, Obi Wan.
And thanks....to you, and all the posters quoted and read.
I may not have a road map, but I may have a destination to target.

[lurk mode engaged]
steve59's avatar
steve59
1,751 posts
 
My wife can't hear the difference. She thinks I'm an idiot.

trust me you don't have to be 'ocd' to fall into that camp.
hpims
129 posts
 

I recently came across a pair of vintage DCM TimeWindow 3 speakers. Phase and time aligned, by designer Steve Eberbach.

TO MY EARS, they sound great.  The usual superlatives: can hear more details, voices are more real, brushes on a drum more realistic.

I had to sell off my modest system a few years back: C22, MC275, Vandertseen 3A signatures.  Heck, I thought I was in heaven, then.


Well, I now hear at least the same detail and more, especially on the upper end from these TimeWindow 3 speakers.  (Guessing the 3As were "laid back"?) 

I pulled out my old Carver (don't laugh!) TFM-35x from the 90s.

Carver C-23 pre-amp.  Same old Rega Planet CD player! 

I did A-B testing years ago between the Carver and McIntosh amps. Very little difference.  Bass tighter with the Carver. Possibly a tiny bit better midrange with the MC275.  But one beer equalized everything!  lol!

So, if you look around what's the most traded, bought and sold  audio components?  Yeah, SPEAKERS!   Everyone looking for nirvana, since all our ears are the same, but they are all DIFFERENT, like fingerprints!  

FOR ME, I believe I am sensitive to more correct phase and time alignment factors, whatever they are, however you explain them!

If you can listen to speakers for about 4-5 hours without fatigue, they work for YOU!! 

For the record, my ears can't hear past 13K.  (going on 64 years old)

If you get yours tested, you'd be surprised how little you can hear on the upper end.  Not to mention most guys don't have a flat response curve!


Nice thread read. Never to old to learn stuff.   Now, get those ears tested and maybe you'll figure out why you prefer certain speakers over others! 

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