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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

Showing 2 responses by midnight_rider

midnight_rider's avatar
midnight_rider
5 posts
 
I can see there is no point in going any further. 

Nobody in their right mind would attempt to fully model a physical system when a perfectly good approximation will get you 98+% of the way there with a fraction of the work. Simple harmonic oscillator and rigid rotor are perfect examples of this. Yes, the electron probability density function is infinitely more complicated than our simple model, yer we are still able to predict with stunning accuracy observable properties using these simple models. This extends to many, many practical examples.

Granted, with access to a supercomputer, it can be fun to attempt to add as many perturbations as one can, but that's an entirely different exercise.

I leave you to it, as you are obviously very capable.
midnight_rider's avatar
midnight_rider
5 posts
 
EDIT: Woah! I typed this earlier and did not post. The got home and hit "post" and see that it's waaay outdated. This was in response to a definiteion of T/Φ coherence.

Let me preface this by saying that I am not an audio engineer, so I don't know how meaningful anything I say can actually be. What I AM is a fully trained physical chemist, specializing in quantum mechanics and neutron crystallography. I have a tremendous amount of training in wave mechanics and the theoretical mathematics behind it.

If we are concerned with the time/frequency domain, we must first agree on a mathematical definition of how to represent a sound wave propagating through atmospheric medium. Once we establish this, we can discuss things without any subjectivity. Of course, we will also need data to use with our expressions, and as we are dealing with wave functions, we will likely want a periodic eigenfunction of some sort, a la sine or cosine or perhaps e^(x), which gives a better representation, but is less well-defined when deriving or integrating with it.

This is my recommended starting point for a meaningful discussion absent the subjectivity or ambiguity that inevitably arises when talking Hi-Fi sound. It’s actually not as daunting as it sounds, and we could easily develop a simple system from first principles.

You have given a terrific definition above, now let’s quantify it! This is a fascinating thread. Thanks for this!
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