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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
whitestix
730 posts
 
Timlub,
I appreciate you sharing your knowledge on this vexing aspect of audio.  I can't say I understood it all, but it greatly aided my background on the topic.  

Roy at Green Mountain Audio was a big proponent of time alignment of the drivers in this speakers.  He also advocated removing ones eye glasses when listening to speakers because of the "smear" ? that they  caused in aural perception.  I built a pair of Linkwitz LXmini's a few years ago, before they came out with the companion subs for them and they were pretty sublime, but rendered my expensive 2-channel amps unusable and had limited LF response.  

I remember in 1983 when bought a pair of Spice TC50's.  I was casually listening to them one night when my neck and attention snapped to the left of the room when some violins started playing on the track... the imaging was simply unbelievable, palpably realistic.  At the time I listened to music at pretty high SPL's and went through several woofers and tweeters before moving on to JSE Infinite Slope speakers from Jeff Joseph.  They imagined quite well too, but not like the Spica's.  The Spica's were like electrostatics with a very narrow sweet spot.  
rimo
14 posts
 
Hello!
I'm inventor of well-known  (infamous?) Infinite-Slope crossover system currently marketed by Joseph Audio. My patent license agreement with them expired in 2005 and at that time I went into blessed retirement at age 67.  In 2017 I was pulled out of retirement by three audiophiles owning Joseph Audio with the question, can your invention be improved? I said no but they insisted and I gave up to shut them up and returned to my notebooks (thankfully saved and in local tech museum) to study network topology and see if I have any new ideas.
The major problem hinges on simultaneous realization of flat frequency response and uniformgroup delay in three-dimensional acoustic space of the listening room. Actually impossible but at least a good approximation is the best that we can do and I come close in with Joseph Audio's products as is well known.
Mathematically one  can achieve flat frequency response and linear phase (flat group delay) using a single very good 4" driver without crossover in a transmission-line box. This system will have nearly perfect performance over a limited frequency range and with limited  loudness capability. Next, a 2-way first-order crossover is theoretically perfect in the math, but when realized in a speaker system, it is "perfect" only in the so-called "sweet-spot"  where the sonic outputs of the drivers add correctly without acoustic wave interference.
In 2018 at age 80 I attacked the problem again. With study of my notes, I came upon an idea which may work: Combine the idea (1) of so-called "constant-resistant" network theory with my already realized "infinite-slope" theory (2) (based on high-selectivity filters in radio circuits).
I worked up a schematic-diagram of this new crossover idea using circuit-analysis models in a computer to start.  The results looked promising, and at some month's work developed a 2-way crossover model  in virtual cyberspace having both optimum frequency and delay responsesimultaneously!  Now it was time to build a physical crossover and try it in a prototype speaker system and found a quick-easy way to proceed:

I ordered the so-called "Solstice" loudspeaker kit from Parts Express , built kit, and installed my
2-way prototype crossover. At first I did not expect anything unusual, just another pretty-good sounding speaker system. I fired up my test equipment and made frequency, phase tests, and determined that system had good frequency response but surprisingly, flat group delay above the cabinet bass resonances!  A trip to the anechoic chamber at Binghamton University's Tech Center confirmed my measurements.  Now it is time to listen!

Played a CD of John Pizzarelli "Dear Mr. Cole" and the sound hit me so hard I burst into tears!Never have I heard sound like this from a loudspeaker box! The room disappeared and I heard the band!  Switching to my Pearls, I heard a good loudspeaker system. Now time to call my pesky audiophile friends, do listen with everyone astounded! We all hear something magic! I, almost with accident, had hit upon something unexpected!
We repeated test of my prototype in audio showrooms with three listeners against systems in the $30,000+ price range with same results, the little 2-way prototype was clear winner having obvious easily-heard sonic improvement. There was uniform spectral-energy sound throughout the entire listening space, with uniform sound without  "sweet-spot"  with all hearing music coming from a nearly perfect "orchestra" instead of a set of speaker boxes.

I had to develop (successfully) a 3-way crossover so invention could be installed in Joseph Pearls, with the same astonishing results. Stay  tuned everyone!
Patent on invention filed July 2019.

RIMO.
timlub
2,042 posts
 
Hi Richard,
     I have read your review on Parts Express several times as I find this speaker that you drastically changed a true bargain in the audiophile world.  I look forward to hearing the results of your constant resistant technology combined with infinite baffle.  
Just curious,  will your constant resistant technology work with any parallel or series crossovers?  Please expand on this once you are comfortable with your patents.  I appreciate you chiming in, Tim 
andy2 OP
1,555 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? 
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