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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
andy2 OP
1,554 posts
 

For the record, my ears can't hear past 13K. (going on 64 years old)

That's true.  I can't hear past 15KHz.  But I am pretty sensitive to speakers with high frequency issues.  Why? (Read below)

If you get yours tested, you'd be surprised how little you can hear on the upper end. Not to mention most guys don't have a flat response curve!
But not to worry.  Most of meaningful music lies much below that.  My speaker has a rising freq. from about 7KHz.  At 15KHz it's 5db above the rest! and I swear it doesn't sound bright at all.  And I am listening almost on-axis with toe-in.  

But IF that 5db was around 3KHz, you'll or I'll be running for cover.

Treble starts at much lower frequencies than people think.

People hearing is very sensitive around 1KHz - 3KHz.  A slight bump in this freq. range will be very audible.  It's like running fingers on chalk board.

In general, 6KHz - 8KHz is sibilance if the speaker is excessive at this freq range.  A bit high will make the  neutral ssssshhhhh to ssssssshhh.  If too high will be like sssssssssh.  When you hear actual people talk, you don't hear sibilance unless they talk straight into your ear.  

8KHz or above, we call "air" or whatever that is.  After 10KHz, unless it's very excessive, most people probably can't hear.  I guess young people could.  And I am sure some people are more sensitive than others, but in general, most people especially old are not very sensitive above 10K.  

Some tweeters are designed intentionally to have a bit lift above around 13Khz to artificially give an extra "air" to the sound.  I actually hate that they do that.  I prefer a more neutral freq. response.  If I need more air, I can do that myself thank you.  
asvjerry's avatar
asvjerry
4,680 posts
 
[lurk disengaged} @andy2 ....I won't disagree with you as to the 12:51 pm 11/3 post; all of which is generally acceptable.  As for your personal hearing range, lucky you. *S*

As for how you can discern that I'm drunk or under some sort of influence over and through this medium that we're engaged in....*hmm*
That will take a certain amount of explanation on your part to the viewers of this forum as to how you've arrived at that observation.
I'll leave that issue for you to explain to the viewers here.

Personally, I've been called worse.  How far you care to sink is your call.
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!
andy2 OP
1,554 posts
 
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.
I am pretty sure that you're pretty intelligent and capable but this time-phase coherent thing is a lot more complicated than quantum physics and I am not kidding.  

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.
The problem is not about the mathematics.  As a matter of fact, the mathematics are rather simple.  

Once we establish this, we can discuss things without any subjectivity.
I agree in general but the problem is how to identify which part is objective and which part will always be subjective and you just have to deal with it.  For example, it's difficult to say which is better sounding since it's also dependent personal tastes.  No mathematical modeling can sort that out.

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.

Again, the problem is not the mathematics on the objectivity side of thing.  In term of measurements, simulations and so on, all these are fairly well established.  The problem is that our hearing is very complicated and no amount of mathematics can figure it out.  I don't mean to obfuscate the issue.  It's really true that nobody has been able to model our "hearing".  Not even close.

It's actually not as daunting as it sounds, and we could easily develop a simple system from first principles.
Already you have under-estimated the complexity of our hearing.  "A simple system" will not do it! 

let's quantify it!
Amen .....

While I can't say which is better, whether time-phase coherent matters or not, I can give a clear definition of what is time-phase coherent is.  Soon I hope!



andy2 OP
1,554 posts
 
Personally, I've been called worse. How far you care to sink is your call.
It depends on the level of weirdness of your posts.  If there are more than three run-on sentences and more than three random thoughts randomly put together into a sentence, then that would be qualified as being "drunk posting".

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