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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
atdavid
736 posts
 
I don’t want to put words in your mouth, but I think you mean that a mid-woofer playing a 50Hz tone and a 1KHz tone will only be at the same position in space (phase-aligned) as the midrange playing a 1Khz tone, for part of the 50Hz cycle? ... or for any two speakers whose sound is integrated.
A microphone element is thin and does not move much, so alignment of the center of movement for all frequencies is most important in playback to recreate what is recorded.



timlub1,704 posts10-31-2019 2:02pmBy the way, to be clear:
Absolute phasing is IMPOSSIBLE.
You can get phasing done at the crossover point which is the goal.
a woofer playing bass at 50 cycles will move at a different rate than a tweeter playing at 15000 cycles.
When we align phase at the crossover points, that is as close as you can hope for.
I hope this helps,
Tim


andy2 OP
1,538 posts
 
Just to mention I am pretty sure Timlub has spent many years building and I think designing, and building speakers.
The only skills I need right is how to get to Ms. Kate Upton.  Now if he can get that done, he's my guy lols.


atdavid
736 posts
 
A single driver does a lot of things right, but has other issues that are hard to overcome such as doppler induced IM distortion. I.e. a 100Hz tone will modulate a 1KHz tone.

One reason that a single driver does so many things right is that there are no phase issues.
That’s not entirely true. A driver may have different phase shift at different frequencies. For example, a driver may have a relative phase of 10deg at 700Hz, but at 7KHz, it may have phase shift of 80 degrees. Not to mention different parts of the driver may not moving "at the same time".

andy2 OP
1,538 posts
 
a 100Hz tone will modulate a 1KHz tone.
I'd like to know how that feel ... errr I mean how that sounds like.
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.
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