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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
timlub
2,039 posts
 
" I am still waiting for someone to tell me who can understand time-phase coherent, including all the experts in the world )-: :-("
That I can help with....
First understand "Time Alignment" 
The speed of sound moves at the same speed at all frequencies, so the first battle would be to make the sound of the tweeter,  mid,  woofer or any other driver to hit your ears at the same time.  The most common way is to align the voice coils, where the sound of the speaker originates from.  When coils are in alignment,  the sound from all drivers hit the ear at the same time.  Could be done by staggering or a slanted front etc. 
Next ... Phasing: 
One reason that a single driver does so many things right is that there are no phase issues.  A single driver does not have to move in unison with any other drivers. 
So what is phasing?  All drivers moving in perfect unison.... when one driver starts moving outward,  all drivers move outward at the same time,  when it comes back,  all drivers move back at the same time.  This helps tremendously to prevent smearing or to improve pinpoint imaging. 
So what did I mean when I said that cross overs change phasing... A single cap or 1st order crossover,  normally will cause a phase shift of 90 degrees,  so to keep the next driver moving in unison,  it must also be moving 90 degrees out of phase to stay in unison with the other driver. 
Again,  24db per octave brings you back around 360 degrees to put drivers back in phase,  but the crossover parts count, the sound of the crossover parts being used and the practice vs theory that you don't truly end of with absolute phase cause most to not use 24db per octave slopes. 
Time/Phase Coherence is just what it sounds:  Time and phase working in conjunction to form a Unified Whole.  

I hope that I have expressed this in a way for everyone of any level to understand, 
Tim 
timlub
2,039 posts
 
By 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 
marqmike
839 posts
 
Andy2 I appreciate this topic. I know very little about it. Nice to know a little more about what effects the challenges of our speakers.
Just to mention I am pretty sure Timlub has spent many years I think designing, and building speakers. He has a lot of reasonable knowledge and he is very helpful. He can help us a lot along this topic.
Thanks Timlub. And I may have short changed how much Timlub knows about speaker development and execution on a high level. If I have I am sorry.
andy2 OP
1,553 posts
 
I hope that I have expressed this in a way for everyone of any level to understand
As an anecdotal personal experience, for awhile I was learning how to cook, so either I have to take some cooking classes, or being cheap as me, I would look up at a bunch of YouTube vids and learn how they do it.  Natural I would look at vids from the famous chefs like the guy in Kitchen Nightmares and the likes.  But my results were terrible and I hated the tasting.  I then looked at the vids from regular folks figuring out they would be at the same level as I was.  But I eventually found out that most of them basically would watch some other YouTube vids and emulate them and put up their own vids without knowing if their recipes would taste any good.  I think they would just pick some random recipe, went grocery shopping, and made the vid almost like copying and pasting.  I think most of them  just want their face on YouTube and not really caring if their recipes would taste any good.  So I gave up on that too.

So I ended up deciding that I would just follow my own instincts, you know like Luke SkyWalker.  I've nailed down to a few my go-to recipes that I've developed over the years so at least I don't hate my cooking anymore.  Now I have a bunch of healthy recipes that I can use.  I actually enjoy my cookings more now than restaurant foods.  The only problem now is I still can't make my own beers or wines.  Well you can't have everything I guess.  

Damn, I thought that I would just cook like the guy in Kitchen Nightmares by just watching his vids lols.

So what's that has to do with time phase coherent?  I am not telling until I am properly wined and dined as one of my dates once told me. :-)  

All drivers moving in perfect unison.... when one driver starts moving outward, all drivers move outward at the same time, when it comes back, all drivers move back at the same time.
Physically is it possible?  For example, the woofer flapping at 70Hz, the tweeter flapping at 7KHz.  For every woofer moving forward and back, the tweeter is moving 700 time back and forth, so it's not possible right?

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".

Anyway, I spent too much time watching cooking vids to have time for time-phase coherent stuffs ... hahahahaha
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


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