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Speaker time alignment, does it matter?

Xyrium

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#1
I posted this in a speaker review thread, and it got buried, so perhaps it was best to give it a thread of its own.

As I had mentioned, when I was getting into audio, companies and designers like Snell, Fried, and Thiel, amongst other notables, were the preeminent builders. As such, I recall them having a focus on time alignment of drivers. With many of today's powered models using DSP, I would imagine that this is a non-factor. However, does it make sense to ask Amir to measure things like step response, phase response (same? https://bksv.com/media/doc/17-198.pdf), and acoustic distance/source in the basic battery of speaker testing just to provide an additional perspective?

Also, I'm seeing lots of CSD's being posted that appear to have ringing or long settling times in the lower frequencies but no one is discussing them (or I missed it). Is the CSD plot being provided considered inaccurate, or are problems like this no longer considered a problem, audibly? https://www.audiosciencereview.com/...er-csd-waterfall-audio-measurement-png.67181/

Help a newb out! ;)
 

MZKM

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#2
Unless it’s a multi-way speaker, time alignment of drivers wouldn’t make a difference in the low frequencies.

For high frequencies, since anything <7ms is treated as a single sound, time alignment can be partially sacrificed if it leads to phase alignment.
 
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Xyrium

Xyrium

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Thread Starter #3
Thanks! For low frequencies, I was thinking that the CSD combined with the acoustic distance measurement would give us a better picture down low.

For timbral accuracy above that range, I assumed (I know, I know) that step response would be useful. So keeping with the separation of areas being measured, they still seem applicable, even today.

Don't get me wrong, I love what Amir is doing, but sometimes, reading being fundamental, can drive one crazy. Some of the articles (old perhaps, like the one referenced) seem to persuade me that there's more we can do, to understand why we hear what we're hearing. ;)
 

sergeauckland

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#4
Back in the 1980s, time-aligned loudspeakers became fashionable, such as the KEF105, KEF107, B&W DM6 (pregnant penguin) etc etc. I did a few experiments with a movable tweeter on a loudspeaker that could be moved back and forth by some 20cm/8". The idea was to hear whether there was any audible effect from moving the tweeter from behind the woofer, so late, to in-line, to forward so early.

Sadly, I and my colleagues couldn't hear any difference over that sort of distance, which was already rather more than any time misalignment due to drivers being on the same baffle.

I can imagine that if the drivers were so far apart that the time of arrival was very different, say a few seconds, then clearly there would be a mismatch between low and high frequencies. So, if a few seconds is too long, what about shorter times? Don't know at what point the two sounds will be perceived as co-incident, but certainly, over the few hundred microseconds of lead/lag I experimented with, there was no audible difference.

With my own current B&W 801s, I used the time-alignment facility on my DCX2496 crossover, just because it's there, but can't say again any difference was audible before and after.

Given the likely path differences between drivers on a typical loudspeaker, I don't see it as significant.

S.
 

pozz

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#5
Also, I'm seeing lots of CSD's being posted that appear to have ringing or long settling times in the lower frequencies but no one is discussing them (or I missed it). Is the CSD plot being provided considered inaccurate, or are problems like this no longer considered a problem, audibly? https://www.audiosciencereview.com/...er-csd-waterfall-audio-measurement-png.67181/
Those plots are affected by environmental noise in the low end. In general the on-axis FR contains the same information and presents it more accurately, without sacrificing resolution (there's a trade-off when it comes to CSDs).
 
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Xyrium

Xyrium

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Thread Starter #8
At crossover frequencies, time alignment is important. But wide band probable not.
Which brings up a good point. If folks are doing this correctly, we would see less dips in FR at the Xover freq.
 

hardisj

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#9
Between sides (left vs right) to get a phantom center, time is crucial. But in a home you are pretty much always sitting in the center of two speakers so it's of little benefit. That said, home theater setups benefit from time delay because the speakers are often not optimally placed from front to back.

As for as within a loudspeaker itself you're talking about crossovers:
Time vs wavelength is small in lower frequencies but large in higher frequencies. For subwoofer/midbass crossovers time is of less importance (assuming you're within a couple milliseconds and not off 10's of milliseconds). Here the most important feature is relative phase: crossover slopes, variable phase, all-pass filter implementation. Phase correlates with time but they are not the same thing. For high-frequencies, even 1/10 ms can alter the response at the crossover enough to where the entire sound power is effected. Now, the question here is: how much is tolerable? Luckily, this can be measured.

Here's a good site to give you an idea of time (speed of sound) vs wavelength:
http://www.sengpielaudio.com/calculator-waves.htm
 
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Xyrium

Xyrium

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Thread Starter #10
Between sides (left vs right) to get a phantom center, time is crucial. But in a home you are pretty much always sitting in the center of two speakers so it's of little benefit. That said, home theater setups benefit from time delay because the speakers are often not optimally placed from front to back.

As for as within a loudspeaker itself you're talking about crossovers:
Time vs wavelength is small in lower frequencies but large in higher frequencies. For subwoofer/midbass crossovers time is of less importance (assuming you're within a couple milliseconds and not off 10's of milliseconds). Here the most important feature is relative phase: crossover slopes, variable phase, all-pass filter implementation. Phase correlates with time but they are not the same thing. For high-frequencies, even 1/10 ms can alter the response at the crossover enough to where the entire sound power is effected. Now, the question here is: how much is tolerable? Luckily, this can be measured.

Here's a good site to give you an idea of time (speed of sound) vs wavelength:
http://www.sengpielaudio.com/calculator-waves.htm
I didn't realize (never considered it I suppose) that even humidity can impact the FR. I suppose it makes sense since the air is literally "thicker".

For relative phase, I was under the impressive that the shallower the slope in the xover, the better the phase and time alignment (or at least the easier to achieve). I've noticed some measurements that indicate a steep rolloff in the bass could also increase ringing, or settling times in the CSD plot. That's why hand tweakers seem to get a cleaner CSD (aka: Dennis Murphy in the AAM model).

Edit: Speakers such as the acclaimed Amphions seem to find a unique combination of these traits: https://www.resolutionmag.com/wp-content/uploads/2017/03/Amphion-Two18.pdf

As mentioned, it's all a compromise, but these time-related perspectives are overwhelmingly curious to me. More reading to do....
 

Inner Space

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#11
I did a few experiments with a movable tweeter on a loudspeaker that could be moved back and forth by some 20cm/8". The idea was to hear whether there was any audible effect from moving the tweeter from behind the woofer, so late, to in-line, to forward so early.
I remember Paul Klipsch reporting a similar experiment, in an issue of "Dope from Hope", around the same time, as I recall. He used a thing like a pizza oven paddle that moved the tweeter +/- yards, relative to the bass bin. Listeners were blindfolded, and noticed no difference until the tweeter was practically in their faces.

Methodology seemed solid, but I discounted the results somewhat, because I felt the genre of multitrack recording used was likely to be hopelessly time-smeared anyway, and because I sensed Klipsch desperately wanted the result he got, as he was then under attack from a newer generation of critics.

I once made a classic crossed-pair Blumlein recording of a simple solo instrument in an uncomplicated space, and it was a spectacular proof of concept, but very loudspeaker-dependent upon replay - sometimes fantastically real, sometimes blah. I assumed all of amplitude, phase and time alignment were critical. But commercially, almost zero such recordings are available, so I stopped worrying about it.
 

gene_stl

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#12
the first time aligned speakers I remember were from Technics , a three way with the voice coils lined up in the same plane.
At the time I doubted it made an audible difference but I never heard the speakers except in a store show room. Probably mid seventies.
One of many audio myths in my opinion. There are lots of others.
 
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KaiserSoze

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#14
I am new here and have been very impressed with all I've seen, especially compared to other audio forums. I am wondering how time alignment and phase alignment are intertwined, and a few related questions. I will appreciate informed responses. I will make a few naive statements as ask for informed persons to either agree or disagree, and to explain why.

1. Phase misalignment generally implies misalignment or offset in the time domain?

2. The greater the wavelength at which a given amount of phase misalignment occurs, the greater the time offset?

3. If 1. and 2. are correct, then it follows that time misalignment is more likely audible when it associated with a given amount of phase offset at low frequency vs. the same amount of phase offset at high frequency?

4. Group delay may be understood as a frequency-dependent shift in the time domain?

5. A comparatively large value of group delay (at low frequency) implies a comparatively large amount of time offset between closely spaced (low) frequencies?

6. If the above perspectives happen to be approximately correct, then does it not follow that the most likely scenario for time misalignment to be audible should occur with the group delay associated with bass in ported speakers? Would it be correct to say that deep bass in ported speakers is time-smeared to an extent that is potentially audible?

7. If it happens to be correct that group delay is greater for steeper crossovers compared to less steep crossover, then does it also follow that using a steep crossover at the subwoofer-woofer or woofer-midrange handover is more likely to introducing audible time smearing as compared to a more shallow crossover at those same points?


Now, if I've implied things that some people disagree with vehemently I apologize. Also for displaying my ignorance. But hopefully there will be some replies that will help to improve my understanding of this important aspect of loudspeaker behavior.
 

echopraxia

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#15
Unless it’s a multi-way speaker, time alignment of drivers wouldn’t make a difference in the low frequencies.

For high frequencies, since anything <7ms is treated as a single sound, time alignment can be partially sacrificed if it leads to phase alignment.
Wow, I just tried adding a 5ms delay to one of my Genelecs and the soundstage changes HUGELY. What was pinpoint imaging of a voice in front of me became smeared wider, and shifted to the side. It's hard to describe, but it felt like the voice shifted in position to my right (I delayed my left speaker), but without the same precise pinpoint imaging that it had before -- sounds almost like an echo or larger/wider soundstage, weirdly enough.

I tried with 1ms, and it's also extremely easy to perceive the difference. So what does this mean when you say "anything <7ms is treated as a single sound"? I am also confused by this statement of what it's trying to imply -- are you saying time domain is important, or is not?
 

echopraxia

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#16
Between sides (left vs right) to get a phantom center, time is crucial. But in a home you are pretty much always sitting in the center of two speakers so it's of little benefit.
Now, the question here is: how much is tolerable? Luckily, this can be measured.
I'm currently sitting dead center between my Genelec 8351Bs. If I add a 1ms time delay to the left speaker (via GLM software), I can hear an extremely obvious difference in soundstage shift and smearing. To my ears, it is not subtle at all and I have no doubt at all I could discern them in a blind test. Is this to be expected, or counter to existing psychoacoustics?
 
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Xyrium

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Thread Starter #17
I was under the impression that such measurements are important for the overall picture. Particularly step and phase....but certainly also acoustic distance.
 

RayDunzl

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#18
Wow, I just tried adding a 5ms delay to one of my Genelecs and the soundstage changes HUGELY.
That's like moving the speaker about 5 feet farther away from you on that side.

Two ways to create "stereo" is to make one side louder or one side later, for a particular part of the material.

I tried with 1ms, and it's also extremely easy to perceive the difference.
The difference can be even less. the width of your head (about .5ms) comes into play. Inter-aural time difference.

https://en.wikipedia.org/wiki/Interaural_time_difference

---

The time alignment of speakers being discussed can concern a single speaker - or both equally in a pair - like "bass comes later than treble", not left/right time offsets.
 

hardisj

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#19
I'm currently sitting dead center between my Genelec 8351Bs. If I add a 1ms time delay to the left speaker (via GLM software), I can hear an extremely obvious difference in soundstage shift and smearing. To my ears, it is not subtle at all and I have no doubt at all I could discern them in a blind test. Is this to be expected, or counter to existing psychoacoustics?
1ms ~ 13 inches. That kind of left/right difference is certainly expected to be noticed between stereo speakers; you're essentially shifting the phantom center 13 inches in one direction or another.

My comment regarding how much is noticeable is in regards to inter-driver time delay. An A/B test will more easily yield audible differences than not. That would be a relative test. In terms of absolute (i.e., you buy the speaker, you take it home and you don't have the luxury of futzing with inter-driver delay) then you won't know for sure unless the delay is off considerably... smaller delay values are noticeable in mid-to-mid/high frequencies than they are in low frequencies. And in high frequencies, amplitude takes over. You can blame the size of your head.

I made this video a few months back explaining the basics of time delay and providing an example of how to use my website to calculate delay values need for active speakers. It might help you make a bit more sense of things.
 

MZKM

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#20
Wow, I just tried adding a 5ms delay to one of my Genelecs and the soundstage changes HUGELY. What was pinpoint imaging of a voice in front of me became smeared wider, and shifted to the side. It's hard to describe, but it felt like the voice shifted in position to my right (I delayed my left speaker), but without the same precise pinpoint imaging that it had before -- sounds almost like an echo or larger/wider soundstage, weirdly enough.

I tried with 1ms, and it's also extremely easy to perceive the difference. So what does this mean when you say "anything <7ms is treated as a single sound"? I am also confused by this statement of what it's trying to imply -- are you saying time domain is important, or is not?
That’s time alignment of the pair of speakers. I was referring to the window of time when the direct and reflected sound reach your ears.
 
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