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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
cousinbillyl
190 posts
 
This thread is getting good. Looks like most of the trolls have jumped ship.

Timmy boy. I would like to disagree with you, respectfully. Perfect phase IS possible.

I studied Jim Thiels CS5 crossover. The man was a genius. He used an extra 10+ capacitors to phase match the signal. Let me explain; when an alternating current (sinusoidal waveform for music) goes through a capacitor, voltage lags current by 90 degrees. If a single capacitor is used on a tweeter, it's only the +ve portion of the waveform which is affected. What do we do about the -ve portion of the waveform?. Mr. Thiel was able to 'see' the phase of the music, and manipulate the -ve portion to match the positive. At this point, speaker designers will say "wait, the speaker drive is part of the circuit, and it is irrelevant where the capacitor goes". Opps, the speaker driver is not 'in circuit', but in fact is a 'load' on the circuit. Mr. Thiel understood this, and I am a fan of his speakers.

Gauder Akustic? have designed a symmetrical parallel crossover. When driven by a balanced (symmetrical) amplifier, their speaker is close to phase perfect.

A Linkwitz Riley 2nd order series crossover, with drivers acoustical centers aligned, is phase perfect.

The problem? very few people have heard these speakers. 

Timmy boy. Judging by some of your posts, you know wayyyyyy more than you are letting on. Your post on degree shifts is bang on. Too many speaker designer ignore this. Mr. Joseph of Joseph Audio also understands phase. I love his speakers.
andy2 OP
1,538 posts
 
OK, if you indeed called me "Timmy boy", you’re probably gay. Then you probably knows wayyyyy more. Then why don’t just spill the beans?

Hey you should pick on someone you're own size :-)  Mines are too big.
asvjerry's avatar
asvjerry
4,375 posts
 
@geoffkait , and time incoherence is when the clock passes through one’s head?

Just as I thought....*stare into the middle distance, drum fingers on desk....*

Ok....just to muck stuff up and soil the water...

I’ll assume the discussion is predicated on ’typical’ drivers on a vertical plane. ’Time alignment’ addressed by physical alignment of the voice coils; ’phase align(or mis-align)ment’ introduced or effected by the choice of crossover or selection of drivers characteristics to minimize or eliminate the use of a Xover...if such is possible...

Now, What If....

The driver voice coils are vertically aligned physically, ’stacked’ one above the other, drivers facing Down. Time coherence, check.

(geoff recognizes where I'm going with this...or he ignores me better than I assume...*s*....)

What happens to phase in this scenario? Will 90~180~360 be a minor/major issue? Will a Tice clock thrown at this disappear?
Will I disappear and stop being an annoyance?
(Not f’n likely, but amuse yourselves with that....)
atdavid
736 posts
 
Let’s start with your comment about capacitors. Assuming the capacitor is bipolar, which pretty much all capacitors in speakers are as well as many audiophiles, it works the same in both directions of the AC signal. Voltage lag is not 90 degrees, but may be 90 degrees at some given frequency.

On the second point, to a speaker, all amplifiers are essentially balanced. There is no ground reference in a speaker, so the speaker has no concept of what single ended or balanced is. It is getting some sort of AC signal.

On the concept of "perfect phase", it sounds like a nice concept, except the lower and upper drivers have different excursions for a given power level, the lower driver could be playing the high frequency superimposed on a low frequency that moves the speaker in and out of phase at the high frequency, etc. When you move to the digital domain, there are techniques to correct for more of the issues.
cousinbillyl172 posts10-31-2019 5:29p
Let me explain; when an alternating current (sinusoidal waveform for music) goes through a capacitor, voltage lags current by 90 degrees. If a single capacitor is used on a tweeter, it’s only the +ve portion of the waveform which is affected.
Gauder Akustic? have designed a symmetrical parallel crossover. When driven by a balanced (symmetrical) amplifier, their speaker is close to phase perfect.



andy2 OP
1,538 posts
 
physical alignment of the voice coils
a good start, but my requirement still not met

minimize or eliminate the use of a Xover
not really likely, consider xover is a necessary evil

driver voice coils are vertically aligned physically

I don't care, but sounds fantastic got my curiosity?

Will 90~180~360 be a minor/major
Too many variables, need more information to fully understand

Will I disappear and stop being an annoyance?
It's your money, your time who am I to say

  (Not f’n likely, but amuse yourselves with that....)

If f'n involved, be my guess be f'n around

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