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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 14 responses by atdavid

atdavid
736 posts
 
Posted without comment:

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andy2 OP688 posts10-30-2019 10:34pm
High end expensive stuff from companies with sufficient depth to design and program signal processing electronics, i.e. like Harman companies, are doing high end in digital.

That’s not I see in REAL life. Most of the most expensive speakers on the market are analog. I can only speak with real life examples. Sure with imagination anything is possible. There are a few digital stuffs but they are few and far in between and hi-end market does not take them seriously. Like Ferrari or Porsche or Lamborghini, nobody wants to drive an electric supercar.

atdavid
736 posts
 
I think your conclusion w.r.t. filters may be a wrong conclusion based around the type of filters you were using. Different filter types have considerably different step/impulse response, independent of order.
You also have to accept that nothing in nature has 0 mass and infinite force so this concept of a pure step response is theoretical.


Add in some confusion from the likes of MQA and minimum phase filters in DACs which provide what could be considered an artificial output, i.e. they create something from the music that did not actually exist, and .... well draw your own conclusions. It is more a discussion at that point of euphonics ... what people like, not what is accurate.

Just sending a sound through air softens an impulse response. If you are recording an instrument really close to it, then adding the above minimum phase filters, you could create a very artificial response akin to having your speaker right next to the instrument, not the typical 10-10’s of feet away. What is even "natural" at that point?
atdavid
736 posts
 
There is still some or even a lot of reading on digital if you want to start pushing the limits / doing custom FIR filters, etc. 
atdavid
736 posts
 
I think you need to work on your bias as it is unjustified. More and more of the high end speaker market will go digital/active cross-over as the limits of analog cross-overs are a hard brick wall that cannot be scaled. I suggest doing some reading into it, it will likely change your bias if you keep an open mind about it.

If your turntable is only $5K, almost entry by audiophile standards today, then a good DAC, not even one that expensive streaming 24/96 or 24/192 either Qoboz or Tidal is certainly going to touch it if you compare recording to recording. So much has changed in just the last 5 years.

I will emphasize again there is distortion in dynamic speakers that cannot be corrected with an analog cross-over. It just cannot be done. In the digital domain, there is even the ability to address resonances that again, you just cannot do in analog.
I am actually working on a "DIY" 3-way right now, with Accuton mid-bass and midrange. I have not picked my tweeter yet. The level of driver integration and flatness of response after correction is just not possible with an analog cross-over.


andy2 OP689 posts10-30-2019 10:54p
I am not going to use any stinking digital with my high end drivers bought from Seas or ScanSpeak or Accuton. It’s like taking Ms. Kate Upton to McDonalds OK !!!

What am I going to do with my $5K vinyl table? Ain’t no stinking ADC will touch it lols.

Why would I want to use the same design methods we have been using for 100 years when superior ones exist? Lead, follow or get out of the way :-)

andy2 OP690 posts10-30-2019 11:22pmReal life statistics: what is the percentage of speakers sold here on Audiogon that are digital? It can’t get more real than that.

atdavid
736 posts
 
You stated that "why time-phase coherence is only possible with a 1st order filter" ... I was filling in the blanks.

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.

atdavid
736 posts
 
As someone has already done the work, I will simply post that from John Bau. By done the work, someone who has a product on the market and advertises this is what they do. It is not such an advantageous marketing thing these days.
And that is only simple analog domain in the cross-over. With a digital active cross-over, time/phase alignment becomes relatively easy.


John Bau of Spica can show you on his Tecron analyzer that the Bessel 4th-order low-pass filter he uses to cross his tweeter down to the woofer on his TC-50 and Angelus, when used with the particular drivers he chooses, is also phase coherent.
Read more at https://www.stereophile.com/content/thiel-cs12-loudspeaker-phase-coherence#J3V7cQJwU8ILdX7k.99

atdavid
736 posts
 
A lesson? High end expensive stuff from companies with sufficient depth to design and program signal processing electronics, i.e. like Harman companies, are doing high end in digital. They may not be making $100,000+ speakers that way, but that is mainly because that is not their market.
They are things you can do in digital signal processing that literally cannot be done in the analog domain. There are aspects of dynamic speaker correction that can be done in digital firmware that cannot be done in analog, and when you start talking about more sophisticated multi-driver speakers, that just compounds.

High end analog speakers are a market, but not the epitome of what is possible. That will only come with advanced digital signal processing techniques.
andy2 OP685 posts10-30-2019 10:03pm
There is still some or even a lot of reading on digital if you want to start pushing the limits / doing custom FIR filters, etc.
Digital is for low end stuffs. High end and expensive stuffs are pure analog. Consider it a lesson.


atdavid
736 posts
 
You are right that alignment between speakers in a cabinet matters, but localization via timing is based on the arrival time difference between your two ears of the same sound, whatever that sound is, even one that is not coming from a time aligned speaker.


aschuh7 posts10-30-2019 11:31pm
Inches matter. The distance between your ears or time difference of the arrival of a sound is what allows to localize the origin of a sound. Say that’s 6 inches or ~ 16 cm. Some may have bigger heads.
1 cm doesn’t matter? Think again.

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".

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


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.



atdavid
736 posts
 
Even if you have perfect pistonic motion, you still have intermodulation distortion with a pistonic driver. It is unavoidable.
atdavid
736 posts
 
I am with you midnight_rider. You can't proclaim one hypothesis to start the post that defines a holy grail, then claim that something else is too complex and variable to model .... which means no holy grail.
atdavid
736 posts
 
I liked this in the review,

"
The tendency of many high-end products to attempt to "fix it in the mix," as audio engineers would say (ie, attempt to "improve" the realism of the original source material), is not in the best interests of ultimate fidelity. For audiophiles who value accuracy over euphony, products like the Dunlavy Signature SC-VI loudspeaker are a breath of fresh air in a landscape polluted by pretty-sounding panderers.
Read more at https://www.stereophile.com/content/dunlavy-audio-labs-signature-sc-vi-loudspeaker-page-6#o2Rto2F348..."

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