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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
170 responses Add your response
andy2 OP
1,549 posts
 
Hi Richard,

It seems interesting that you posted with regard to the "Infinite Slope" in a time-phase coherent thread.  It's quite a different philosophical design vs. time-phase coherent with respect to phase shift.  I would assume Infinite Slope filter would have higher phase shift using very steep roll-off slope filters. vs. a time-phase coherent design that uses first order filter which has the least amount of phase shift.  "Infinite Slope" advantage is minimal over-lap in frequency response between different drivers, whereas time-phase coherent is the complete opposite being having a large overlap.  I suppose the disadvantage of "Infinite Slope" is the excess in phase shift?  

I was wondering if you could share your opinions on "time-phase coherent" as to the extend it may affect on sound quality.  Time-Phase Coherent insists that the phase of the system response (the overall response of a speaker) should be as close to 0 deg. phase shift as much as possible from 1Hz to 20KHz.  Thiel design has claimed to achieve +/- 10 deg difference.

With "Infinite Slope", I would assume it would violate the criteria of 0 deg. phase shift.  Would you share the amount of phase shift a typical "Infinite Slope" speaker.  For example, what is the typical phase shift at 17KHz vs. to something like at 270Hz?  For a time-phase coherent design, the phase shift should be very close to 0 degree.

Thanks.
kenjit
1,771 posts
 
 I would assume Infinite Slope filter would have higher phase shift using very steep roll-off slope filters. vs. a time-phase coherent design that uses first order filter which has the least amount of phase shift
Why would you assume that? 
andy2 OP
1,549 posts
 
Why would you assume that?
I was hoping you would enlighten me?  Since your post above implies you know the answer?
unsound
7,329 posts
 
https://www.stereophile.com/content/dunlavy-audio-labs-signature-sc-vi-loudspeaker-specifications
andy2 OP
1,549 posts
 
Hahaha .....  I miss the good old days.  A gigantic flag ship pair of speakers only costs $25K.  Something like this today would be $80K.  Nice square step response!  
Post removed 
unsound
7,329 posts
 
^...."....Acoustic phase response: less than +1 degrees, -2 degrees, 100 Hz -10 kHz…."...
atdavid
736 posts
 
I liked this in the review,

"
The tendency of many high-end products to attempt to "fix it in the mix," as audio engineers would say (ie, attempt to "improve" the realism of the original source material), is not in the best interests of ultimate fidelity. For audiophiles who value accuracy over euphony, products like the Dunlavy Signature SC-VI loudspeaker are a breath of fresh air in a landscape polluted by pretty-sounding panderers.
Read more at https://www.stereophile.com/content/dunlavy-audio-labs-signature-sc-vi-loudspeaker-page-6#o2Rto2F348..."

rimo
14 posts
 
Hello Andy!
I enjoy your posts. Thoughtful and intelligent; we are both music lovers and audiophiles. I need to explain again how I got myself stuck into giant speaker project as described in my very first post ever on any website, being forced into doing this by one of the four (now five!) audiophile friends who pushed me at age 81 (now) to jump into speaker design again.  After retrieval of my notes from museum and study of topology (a favorite of mine from graduate-school network-theory courses)  I tried a merger of "constant-resistance" network theory into my "Infinite-Slope" in my previous patents.  First try was a 2-way series crossover at 2KHz. Installed this into Parts-Express 2-way speaker kit with test measurements in my home lab and also in anechoic chamber of Tech Center at Binghamton university.  Waterfall plats, frequency-response, input impedance, delay response, all looked good, even surprisingly so. Even more so as I examined in detail match at the 2Khz crossover, it was seamless with no evidence of a "join" in either frequency or phase response. It was time to listen to music on this box and as in my earlier post, I burst into tears at first listen (I'm Italian!).  Never in my life did I hear that kind of sound come from a speaker box!  Emphasis needed here: I'm no genius. This result was a pure accident of discovery, nothing more, and certainly not expected. My audiophile friends came over for listen and forced me into building three Parts Express kits to listen to until I could come up with a 3-way crossover for their Joseph Pearls (Successful as mentioned in last post)!  I should mention a funny effect I observe in audio showroom where we were comparing my invention with other speaker systems, as someone wanders in and after a few steps they stop dead suddenly at the sound!  It happens every time one hears my invention for the first time.  In closing I'm actually sorry I hit upon this thing, I nearly gave up and burn my notes and abandon patent, but it's too late; I need to see this thing through. Did a public demo of invention in August before an audience of 300 at a symposium with speakers as subject with incredible results (I hope to see this publicized in Winter quarterly journal of organization which invited me), one speaker manufacturer there asked me to try my invention; gave me data on their drivers. This is a Winter project ongoing.
RIMO
rimo
14 posts
 
Hello Andy,
Thanks for Interesting recent post. Both you and I find my results with invention crossover a mystery.  Earlier infinite-slope crossovers worked nearly "perfectly" (maybe just OK) inside each other's band-pass, as characteristic to "brick-wall" filters make each other's loads (the drivers in speaker system) operate completely independent from each other. There is no acoustic interference among drivers in infinite-slope systems which eliminates  "sweet-spot"  errors acoustically. Amplitude response is flat all over listening space, dependent only on the polar response of each driver. However phase response is another problem which in my earlier work I either ignored or tried to fix with only slightly improved results. FFT analysis showed group-delay "bumps" at crossovers over a narrow frequency range around each crossover, I left things alone  as an unsolvable problem believing error was inaudible. Many nears ago in Grad School during a course in acoustics I attempted to devise an experiment to determine if we were able to hear "phase" as we hear "amplitude". It became a difficult problem; I could not even devise a methodology to formulate an experiment which would result in useful data. I got a "B" for trying!  Thus I became sure that we were "deaf" to absolute phase, or phase errors in reproduced sound over speakers. I know we hear relative phase in midrange very well with out 2 ears, as God designed us.(to avoid danger, etc.)  However FFT analysis on my new invention reveals clean waterfall plots and seamless amplitude and delay at crossovers!  I assume without proof that accidental combination of constant-resistance with infnite-slope compensates for "bumps" at crossovers. Everyone who listens to invention describes sound as "coherent" or "all-there", etc. Everyone listening for first time immediately states that they have never heard a speaker system sounding like real music as this one! Square waves maybe??? System test reveals good square-waves well over range 150Hz to 2.5Khz, at higher frequencies the 3rd and 5th harmonics become weak and waveform degenerates into sine wave. Square waves not too pretty having ragged edges due to edge diffraction from box.

A weak hypothesis regarding loss of group-delay "bumps" is somehow due to an adjustment of "overlap" at crossover frequency which compensates for delay bumps. Maybe you have an idea in this regard! If so your name can go on patent!

RIMO.

andy2 OP
1,549 posts
 
Hi Richard,

Thank you for your posts and your unique perspective. For now, I would like to take a rain check as for a proper response from me since it may require a bit more thinking from me.

The only thing I want to say now is that, after listening to different types of speakers with different design philosophies, some being optimized for freq. domain and some being optimized for time domain, I think a well designed speaker all sound very good regardless of the underlying design philosophy.

Some one once told me all women are beautiful. If she doesn’t look beautiful, it just means that she does not know how to put on make up. Same with speakers. If a speaker does not sound good, it probably because it was not well optimized for its purpose - however different in design philosophy.

I would like to stop for now, but without trying to sound too general, I think ultimately, either you gain in frequency domain or time domain but at least for now, I don't know of a way to have both.  God does not seem to give us human any free lunch.  


unsound
7,329 posts
 
^ https://www.stereophile.com/content/dunlavy-audio-labs-signature-sc-vi-loudspeaker-specifications

…"...Frequency response: 25Hz-20kHz, +/- 0.5dB (approx. -3dB at 20 Hz)."...
prof
3,473 posts
 
Well, Richard's input in to this thread is fascinating!

I personally have nothing technically useful to add, just personal anecdote.

I own both Thiel speakers (had the 3.7s, now own the 2.7s), with their concentric drivers and time/phase coherence, AND I own the Joseph Audio Perspective speakers (Infinite Slope).

The difference I hear between the two designs is that the Thiels have an imaging precision and density none of my other speakers have ever had, including the Joseph speakers.  They "disappear" just that much better than most speakers, but without sounding ghostly or insubstantial in the imaging.  Tonally they sound very "right" to my ears.  And I would but the Thiels as the most coherent multi-driver speakers I've ever owned (or, I think, heard).

The Joseph speakers though seem to offer even lower apparent distortion in the signal, with a sense that a fine layer of "hash" heard in most speakers seems removed, so the timbral quality of instruments seems even more revealed.  (They are also very punchy and fun and image/soundstage great!).

As for other time/phase coherent speakers, the old Dunlavy's also impressed me, doing something very similar to my Thiels.

And yet, having also heard the newer Kii Audio Three speakers a couple of times (DSP speakers time/phase coherent), I didn't find they had the same magically believable tone as I hear in either the Thiel or Joseph speakers.   I found myself having to "work" to unravel various instrumental timbres in the mix, where with the Thiels and especially with the Joseph speakers, this is effortless.   Don't know why.


andy2 OP
1,549 posts
 
So it looks like the Dunlavy Audio Labs Signature SC-VI was designed by God after all.  Only HE can give us the cake and we can eat it too.  Perfect time/frequency response!  
unsound
7,329 posts
 
^ Perhaps he just tweaked it a bit further than a few others had.
andy2 OP
1,549 posts
 
Perhaps he just tweaked it a bit further than a few others had.
I am sure he can do more than "tweaked".  With a simple wave of a magic want, voila, a perfect speaker.  If I were him, why do any work and just wave my magic wand.  

Conservation of energy be damned!  


unsound
7,329 posts
 
John Dunlavy passed away in January of 2007.
May he rest in peace.
andy2 OP
1,549 posts
 
I've created a thread at DIYaudio.com.
https://www.diyaudio.com/forums/multi-way/345669-exercise-converting-speaker-time-phase-coherent.htm...


contrastaudioua's avatar
contrastaudioua
12 posts
 
Contrast audio loudspeakers.
Own designed parts. Only from naturall materials.
Only single one capacitor in crossover-network! Frequency response of tweeter 10 KHz!

If to say about 3-band  speakers, situation more interesting. WITHOUTT FILTEREDDD BASS DRIVER.... 





rimo
14 posts
 
Hello!

Audiophile friend urged me to jump into this discussion with some of my ideas.  Here goes my take on phase-coherent speakers and first-order crossovers:
A perfect transition from an electrical signal to acoustic sound is defined by the simple so-called all-pass transfer function defined by:                  
                    -St
(1) f(s) = Ke          (note: this dumb website does not allow math symbols, sorry)

For perfect fidelity in acoustic space this equation defines it, where S is the complex frequency variable S = p+jw  and K,T are real positive constants and =2.718......
One can realize a loudspeaker crossover in Laplace-Transform form by expanding (1) in an infinite series and taking only the first term in (2) to yield (3), as:
                                                       2
(2)   F(s) = e        = 1/(1 + St + (St)    + etc.......)
Taking just the first term yields

(3)  f1(S) =  1/ (1 + St)
Laplace transform of (2) represents circuit consisting of a coil of T Henries in series with a 1-ohmresistor. (You need to imagine circuit because website cannot draw schematic symbols!)
Replacing variable S with its inverse 1/S in (3) yields St/(1 + St) or, a single capacitor and resistor in series:

(4)  f2(S) = St/(1 + St)
Equation (3) is transform of a woofer crossover in circuit, equation (4) is transform of a tweeter in
a crossover circuit. Now add (3) and (4) to obtain:
(5)  f1(S)   +  f2(S) = 1/(1 + St) + St/(1 + St) = 1.
Sum adds to a constant, the number one! The crossover is perfect, a constant. No variables are present. Speaker will be flat in amplitude and linear in phase!!!! Crossover uses one coil and one capacitor!!!!  Simple!!!!

Here I show why people are in love with first-order crossovers.  Realized carefully, a first-order crossover system will work reasonably well and satisfy almost anyone with decent sound.


RIMO
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