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Time/Phase Alignment, Acoustic Center, Lobing etc. - new tech note from Purifi

voodooless

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Well that, and you'll only get a square wave in one tiny spot.
Well, that depends on your speaker topology. A coaxial or especially a synergy horn will have a much larger area, which is of course the point of the damn things.

It is a good tool though, to find the sweetspot of your speakers ;) Where you’ll find the perfect square wave, you’ll have perfect time alignment.
 

fpitas

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voodooless

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Then it will depend on how low your coaxial goes,
That’s what this is for :cool::

 

fpitas

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That’s what this is for :cool::

Coaxial madness!
 

gnarly

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My understanding of FIR filtering is that it introduces a delay. When the application is different from home music reproduction, delays can be problematic. The advantage of the IIR filters + global FIR would then be that the FIR can be disabled when required by the application.
I have to admit that I am not Mr. Filter myself so apologies if I am wrong.
That's a good point. The "FIR time" latency could be switched off, to leave the IIR as the untouched low latency default.

Or, what I like to do, is just have presets that switch between IIR, and linear phase FIR crossovers.

I guess it depends on what / which of those, the processor is capable of.

Mine will do either of them, and I've found I like the straightforward crossover swap-out better, because then I can swap anything directly in one step...including different orders.
If I did the Grimm method, and changed the IIR LR4 to say a LR8, I'd have to also swap out the FIR filter to linearize the higher order.
Much easier to simply swap out whatever order lin phase LR I want to compare.
 
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gnarly

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So, who dares to show us microphone recoding of a 1 kHz square wave over his speakers?
Haha...I'll bite..

Here's a set from a while back of a prosound MTM called the PM90. Yes, on-axis no doubt, and i probably cherry picked frequencies for good looks too, Lol.
I made them when i was learning the joy and power of FIR.
I quit making them, as I learned to use an average of measurements as the base for corrections, and pay full attention to how wide an area can i get great response.
Just looking at mag and phase polars.
So nothing recent square-wave wise of any of my unity/synergy builds.
All that said, I do think fairly acceptable/recognizable square wave results are achievable within a decent sized listening window.
(Oh, and i remember 1000Hz and up aren't going to be very good no matter what, simply due to the lack of enough HF&VHF odd harmonics to fill them in...)

square wave set.jpg
 

voodooless

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Here's a set from a while back of a prosound MTM called the PM90.
These:
IMG_7132.jpeg

That’s cool :D
Yes, on-axis no doubt, and i probably cherry picked frequencies for good looks too, Lol.
I made them when i was learning the joy and power of FIR.
Well, the large horn helps a lot. If the CD is not a coaxial it should be trivial to get a nice 1kHz square wave ;)
I really love that you used a scope for this :cool:. How refreshing ;)
 

gnarly

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Yes, that's the speaker. And thx!
Well, the large horn helps a lot. If the CD is not a coaxial it should be trivial to get a nice 1kHz square wave ;)
BMS coax CD crossed at 6300Hz.

The thing I've found is, say even if it is just a single CD on a horn that easily covers 1000Hz up,
the frequency magnitude has to be made pretty dang flat with minimum phase EQ's (taking phase flat too), before getting good square waves at 1000Hz.

I mean, that's all that good square waves are saying...flat mag and phase, huh?! :)
I really love that you used a scope for this :cool:. How refreshing ;)
Thx again. fwiw, I've found REW's scope a joy to use...(other than the inability to overlay traces.)
 

voodooless

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BMS coax CD crossed at 6300Hz.
Nice! That makes it a bit more difficult :)
The thing I've found is, say even if it is just a single CD on a horn that easily covers 1000Hz up,
the frequency magnitude has to be made pretty dang flat with minimum phase EQ's (taking phase flat too), before getting good square waves at 1000Hz.
Sure, that’s a constant directivity horn, so you’ll need quite a bit of EQ anyway. And as I recall, the BMS coax isn’t exactly flat either.
I mean, that's all that good square waves are saying...flat mag and phase, huh?! :)
Only for the frequencies that they are comprised of though ;)
 

JPA

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They make huge sacrifices in directivity for meaningless gains in step response, which is moreonly only good for one listening position.
Not to mention really bad diffraction from all those disjointed cabinet edges.
 

617

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It's telling these discussions never touch on audibility, or temporal issues in recording.

Having said that, the discussion on acoustic centers was really interesting.
 

gnarly

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Only for the frequencies that they are comprised of though ;)
Aren't all frequencies in play, and comprised if not flat mag and phase?

I mean, who's to say exactly what fundamental we choose, to say a speaker can produce square waves?
If 1000Hz, then sure that frequency's odd harmonics having flat mag and phase are all that matter.
But what if we choose 1100Hz, or any arbitrary frequency.....

Bottom line, it takes flat mag and phase across the spectrum, to produce square waves across the spectrum
 

gnarly

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It's telling these discussions never touch on audibility, or temporal issues in recording.
I have to say, more and more, I view defaulting to audibility studies as a cop out.

What's audible? What i hear in nature.
Why does what i can hear with the current state of sound reproduction have anything to do with audibility,
other than how well the current state of sound reproduction can match nature.

A visual parallel. For decades, the best science grad schools taught the human eye could resolve no better than 200-300 lines per inch.
All based on exhaustive studies of photographs. Well, it turned out the best we could print was 200-300 line per inch. And when printers got better, we could see better LOL !

It's the same thing with speakers, until you've heard better, it's inaudible :D

Please give me science and products, that move the state of audio engineering forward, and let me hear how those advances sound...and understand how they measure....
without any historical audibility-anchor-dragging studies to slow them down...:)

Sorry if i've been on a bit of a rant here...it's just damn "audibility"sometimes.......
 
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617

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I have to say, more and more, I view defaulting to audibility studies as a cop out.

What's audible? What i hear in nature.
Why does what i can hear with the current state of sound reproduction have anything to do with audibility,
other than how well the current state of sound reproduction can match nature.

A visual parallel. For decades, the best science grad schools taught the human eye could resolve no better than 200-300 lines per inch.
All based on exhaustive studies of photographs. Well, it turned out the best we could print was 200-300 line per inch. And when printers got better, we could see better LOL !

It's the same thing with speakers, until you've heard better, it's inaudible :D

Please give me science and products, that move the state of audio engineering forward, and let me hear how those advances sound...and understand how they measure....
without any historical audibility-anchor-dragging studies to slow them down...:)

Sorry if i've been on a bit of a rant here...it's just damn "audibility"sometimes.......
The problem with not using audibility or perceptual science as a reference point is that it's very easy to focus on minutae which we presume to be audible, instead of things that impact sound quality. Entire careers have been spent lowering bass distortion or misunderstanding phase errors in loudspeakers and it didn't make any difference, not to mention all the audiophiles chasing their tail. Seriously, how are we to understand the careers of the great speaker designers of the audiophile era? Von Schwiekert and Vandersteen and Wilson. That wasn't engineering, and it wasn't good art, it was naval gazing.

Your analogy to the visual system is interesting, but our model of vision is arguably superior to our model of hearing. We really don't know what makes things sound real. Color perception is the opposite. As ineffable as color is, the textile industry needed a way to match thread to fabric, and this kicked off decades of research that allow us to precisely match colors made up of reflected pigment spectra, phosphors or laser beams. We have no such standard with hearing, because we don't understand how hearing works.

How did color science develop? Hundreds of tedious studies with observers looking at little patches of color under different illuminate, reporting if they are the same or different.

Worrying about crossovers and drivers brings us no closer to understanding sound reproduction. The only truly innovative loudspeaker engineering happening today is in sound bars I think.

Its an interesting engineering discipline but I've come to realize after years of building speakers and reading about them, the whole pursuit is built on a bad foundation. There is no pure phase coherent source. Vibrating bodies are not simple. A microphone (phase distorter) cannot capture them, even if they weren't in a room (phase distortor) and even if they weren't equalized and so on. The illusion is not depicted by speakers, it is synthesized by them.
 
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Curvature

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The problem with not using audibility or perceptual science as a reference point is that it's very easy to focus on minutae which we presume to be audible, instead of things that impact sound quality. Entire careers have been spent lowering bass distortion or misunderstanding phase errors in loudspeakers and it didn't make any difference, not to mention all the audiophiles chasing their tail. Seriously, how are we to understand the careers of the great speaker designers of the audiophile era? Von Schwiekert and Vandersteen and Wilson. That wasn't engineering, and it wasn't good art, it was naval gazing.

Your analogy to the visual system is interesting, but our model of vision is arguably superior to our model of hearing. We really don't know what makes things sound real. Color perception is the opposite. As ineffable as color is, the textile industry needed a way to match thread to fabric, and this kicked off decades of research that allow us to precisely match colors made up of reflected pigment spectra, phosphors or laser beams. We have no such standard with hearing, because we don't understand how hearing works.

How did color science develop? Hundreds of tedious studies with observers looking at little patches of color under different illuminate, reporting if they are the same or different.

Worrying about crossovers and drivers brings us no closer to understanding sound reproduction. The only truly innovative loudspeaker engineering happening today is in sound bars I think.

Its an interesting engineering discipline but I've come to realize after years of building speakers and reading about them, the whole pursuit is built on a bad foundation. There is no pure phase coherent source. Vibrating bodies are not simple. A microphone (phase distorter) cannot capture them, even if they weren't in a room (phase distortor) and even if they weren't equalized and so on. The illusion is not depicted by speakers, it is synthesized by them.
This is good context.

I would add that, for the article, its aim doesn't seem to be new technical insights or a guide for better audible sound. I think the aim is to be a note for manufacturers and DIYers who misunderstand the concepts and end up having silly design priorities for their speakers. Those two groups are their main market, and Purifi aims not only to sell them product but educate them about how to use it. If we look at all of the designs that have come out using Purifi drivers, I can't think of one that uses DSP. So the content makes sense.
 

617

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This is good context.

I would add that, for the article, its aim doesn't seem to be new technical insights or a guide for better audible sound. I think the aim is to be a note for manufacturers and DIYers who misunderstand the concepts and end up having silly design priorities for their speakers. Those two groups are their main market, and Purifi aims not only to sell them product but educate them about how to use it. If we look at all of the designs that have come out using Purifi drivers, I can't think of one that uses DSP. So the content makes sense.
The directiva used a dsp crossover, although passive designs exist. I think the purifi woofers lend themselves to dsp since the output potential is so high, you can get a lot out of a small cabinet by boosting the bass.

It's an excellent article.
 

gnarly

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The problem with not using audibility or perceptual science as a reference point is that it's very easy to focus on minutae which we presume to be audible, instead of things that impact sound quality. Entire careers have been spent lowering bass distortion or misunderstanding phase errors in loudspeakers and it didn't make any difference, not to mention all the audiophiles chasing their tail. Seriously, how are we to understand the careers of the great speaker designers of the audiophile era? Von Schwiekert and Vandersteen and Wilson. That wasn't engineering, and it wasn't good art, it was naval gazing.

i agree with that. I have no regard for chasing minutiae, especially for minutiae's sake, which most often means for marketing's sake.
And frankly, the audiophile era (which I blindly followed for a few decades), kinda disgusts me.
I view very few conclusion and impressions formed in that era, as science.


Your analogy to the visual system is interesting, but our model of vision is arguably superior to our model of hearing. We really don't know what makes things sound real. Color perception is the opposite. As ineffable as color is, the textile industry needed a way to match thread to fabric, and this kicked off decades of research that allow us to precisely match colors made up of reflected pigment spectra, phosphors or laser beams. We have no such standard with hearing, because we don't understand how hearing works.
Yes agree again, we do not come close to fully understanding how hearing works.
That's a big part of my admitted faith...that there is significant room for further speaker development.

But we do know how sound works, and I think ignoring principles of time and phase with speakers, is a form of reverse subjectivism/faith, given what we don't understand about hearing.

How did color science develop? Hundreds of tedious studies with observers looking at little patches of color under different illuminate, reporting if they are the same or different.
Reminds me of an old joke about color scientists...."what's a sure-fire way to start an argument?" ask 2 color scientists what color something is ..
sorry, couldn't resist


Worrying about crossovers and drivers brings us no closer to understanding sound reproduction. The only truly innovative loudspeaker engineering happening today is in sound bars I think.

I really disagree with respect to xovers. Lobing can be substantially reduced for wider listening areas, by paying attention to xover order, time and phase alignment.
Sound bars, with their horizontal driver arrangements, have the most acute need to pay attention to these factors.

Even if one thinks phase at the ears is inaudible, the reduction of lobing produces better polars/spinorama results....
which many audio buffs seem to be accepting as the be-all /end-all needed re speaker measurements. (i don't accept that idea obviously :))

Drivers are more like nuts and bolts to me, just parts that need to meet certain engineering tasks....
Its an interesting engineering discipline but I've come to realize after years of building speakers and reading about them, the whole pursuit is built on a bad foundation. There is no pure phase coherent source. Vibrating bodies are not simple. A microphone (phase distorter) cannot capture them, even if they weren't in a room (phase distortor) and even if they weren't equalized and so on. The illusion is not depicted by speakers, it is synthesized by them.
Agreed as to how unlikely a pure phase coherent source exists, with music. Sources in 3-d space, even a single instrument, of course have multiple sound emanating surfaces and regions.
And then a mic collects all those and crams it into 1-d space. And then our speakers try to take that 1-d summation and re-emanate it, as at least 2-d, some will wax on about 3-d.. Impossible task to recreate the real life 3-d musical experience imo...no matter how few or how many speakers are used.

(Recordings of birds, or better fireworks with their full range stimulus , things like that, where natural phase coherence is much more possible,...... are the test signals I'd like to see used in studies of phase audility, with single speakers.)


All that that said, it doesn't mean we throw up our hands and quit, ime. My experience is that time and phase alignment matter. Clarity and transient response are defintely improved.
Whether the improvement is due to having also achieved exemplary frequency magnitude response on-axis, or an improved set of polars off-axis, or having a better impulse and step response arriving at the ears...I dunno...haven't been able to differentiate the partials yet.

I will say this though....it seems pain silly to me to discard the idea phase and time matter. If for no other reason than, making them matter is probably the easiest way to achieve excellent frequency magnitude spinorama results. And why the heck not, when it's so easily doable (if one is willing to use DSP)
Hey, it certainly has more potential to matter, than differences in electronics' sinad ...speaking of minutia lol

Hey, sorry for long post...hope it's all well taken
 

IPunchCholla

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A visual parallel. For decades, the best science grad schools taught the human eye could resolve no better than 200-300 lines per inch.
This is misleading, at best. First off, you can’t define it the way you have, so I doubt the best science grad schools ever said such a thing. If you’re going to define resolution by inches you have to do so for a particular viewing distance. Secondly, we have had ways of creating high resolution images (far higher than inkjet printers, for a very long time, so the better printers leading to better tests is probably apocryphal.

A quick survey of human generated literature puts the ability to resolve at about 120 lines for ever degree of arc. The 200 to 300 number comes from translating that number to lines per inch at a typical viewing distance, with different viewing distances chosen.

None of the major players in inkjets are competing on resolution anymore. They’ve long since passed the point where it matters. And there is still no point in sending a file at anything higher than 360 dpi as that is what all these printers interpolate to anyway.

Where canon and Epson compete is in color gamut, by always adding more inks. The crazy resolution numbers are obtained by multiplying the number of ink channels by the interpolation resolution of the printer. Which is pretty much a made up meaningless metric as it has nothing to do with either the resolution of the source, nor the resolution of the print.
 

617

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I agree we shouldn't throw up our hands and quit! My point is that chasing after engineering metrics is not going to work.

Perceptual metrics need to be developed. Geddes developed one for distortion, which isn't perfect, and is incredibly complex, but it works better than THD. David Griesinger has a concept he calls 'presence' iirc which is a notion of intelligibility, and of course there are industrial metrics for speech intelligibility.

The problem is that it's much, much harder to design a speaker, even conceptually, which excels at these metrics, when you could just devote your career to achieving another 1mm of xmax or another 2% of second harmonic, or nicer looking square waves. The problem with these synthetic metrics is that they achieve nothing, and we have long since gone past the point where they mattered.

In the 50s, when we simply couldn't reproduce loud bass or get decent treble dispersion, the engineering of this kind mattered a lot. Leo Fender, Neville Theile, Henry Kloss, Don Keele, Linkwitz, all those guys made an impact. It's the second and third generation of audio designers which got lost in the weeds, and you can see this by looking at the health of the science they pioneered. Audio is not attracting the best engineers, and the best audio engineering is probably in sound bars and noise cancelling headphones and smart speakers. Look at Vandersteen - look at their website. Does that look like an organization built for the future?

This 'scientism' isn't limited to boutique audiophile companies making speakers covered in lacewood veneer, it's also the most advanced outfits. I love what Genelec has done with cardioids and their most recent speaker is incredible - but is it a step forward in audibility? I see no evidence that it is. It probably sounds incredibly impressive, but I bet a Westlake Audio system does too.
 

617

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This is misleading, at best. First off, you can’t define it the way you have, so I doubt the best science grad schools ever said such a thing. If you’re going to define resolution by inches you have to do so for a particular viewing distance. Secondly, we have had ways of creating high resolution images (far higher than inkjet printers, for a very long time, so the better printers leading to better tests is probably apocryphal.

A quick survey of human generated literature puts the ability to resolve at about 120 lines for ever degree of arc. The 200 to 300 number comes from translating that number to lines per inch at a typical viewing distance, with different viewing distances chosen.

None of the major players in inkjets are competing on resolution anymore. They’ve long since passed the point where it matters. And there is still no point in sending a file at anything higher than 360 dpi as that is what all these printers interpolate to anyway.

Where canon and Epson compete is in color gamut, by always adding more inks. The crazy resolution numbers are obtained by multiplying the number of ink channels by the interpolation resolution of the printer. Which is pretty much a made up meaningless metric as it has nothing to do with either the resolution of the source, nor the resolution of the print.
The fact that we have a concept of color gamut, and well defined perceptual metrics to transform one gamut into another, speaks to the maturity and effectiveness of visual science compared to audio. Imagine if we could translate the 'control room' audio into 'headphone' audio as well as we can translate pigments into light.
 
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