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Multi-Way Conventional loudspeakers with crossovers

Microphone position - theoretical phase shift delay
Microphone position - theoretical phase shift delay
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Old 6th November 2019, 11:02 PM   #11
bentoronto is offline bentoronto  Canada
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Microphone position - theoretical phase shift delay
Quote:
Originally Posted by andy2 View Post
Based on the Figures.....
We're back to 7th grade geometry.

Even if that diagram of point sources (which drivers are not) didn't excessively simplify the issue of phase, the fact that drivers "speak" at different speeds (and you don't know what speed...) needs to be remembered.

I'm not sure where the great 1970s fad for time alignment (AKA phase) stands today. On this forum, discussions of sub time-alignment seem to conclude that fine-tuning the alignment by ear and mic (which will keep you busy for a night) leads to a perceptible but rather small SQ benefit in the bass.

My gut feeling is that drivers should be within a cycle or two (360 to 720 degrees) in alignment for music to sound right. Gosh, that should irritate phase believers. I believe that based on decades of (a) sitting tweeter arrays on top of mids and not using a micrometer to position them and (b) having a big corner horn sometimes yards from the mids.

With a DSP you can fool with time-alignment (AKA phase) all you want and see if it matters.

B.
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Last edited by bentoronto; 6th November 2019 at 11:08 PM.
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Old 6th November 2019, 11:54 PM   #12
andy2 is offline andy2  United States
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bentoronto,

Sorry but I lost it after the 7th grade comment thing. And your point?
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Old 7th November 2019, 01:05 AM   #13
bentoronto is offline bentoronto  Canada
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Microphone position - theoretical phase shift delay
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Originally Posted by andy2 View Post
bentoronto,

Sorry but I lost it after the 7th grade comment thing. And your point?
My point: you can't over-simplify and "analyze" speakers as if they were Euclidian points as in the diagrams you posted.

As I specifically said, (1) drivers are not point sources in that their size is a bunch of degrees and (2) the drivers emit their sound at different latencies and polar angles.

I further provided specific comparisons that it makes no sense to talk about phase degrees because drivers and speakers are strewn about without regard to wave lengths and nobody knows or hears it and experiments with phase (AKA time alignment) do not seem too beneficial.

That is what I said in my previous post. Still having trouble getting my point?

B.
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Last edited by bentoronto; 7th November 2019 at 01:07 AM.
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Old 7th November 2019, 01:27 AM   #14
andy2 is offline andy2  United States
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Quote:
Originally Posted by bentoronto View Post
Still having trouble getting my point?

B.
Maybe.

I got the picture from D'Appolito Testing Speaker so I figure it has some merits because he's a speaker design and he might have some insights into speaker design. Now you say it's all wrong so I am kind of confused. Either he's wrong or you're wrong.
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Old 7th November 2019, 01:51 AM   #15
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by andy2 View Post
Based on the Figures, the implication is that based on the distant from the speaker to the microphone, the relative phase difference between the various drivers will change.

The other implication is the further the mic, the relative phase difference is getting smaller and smaller as calculated on the chart. Can everyone agree on this?
Yes. We may have different ways of doing it.
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Old 7th November 2019, 05:36 AM   #16
kimmosto is offline kimmosto  Finland
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Quote:
Originally Posted by andy2 View Post
Either he's wrong or you're wrong.
It's not black and white. Delay/phase calculation by distance works quite okay, but it's not accurate if shape of magnitude response changes when distance or especially off-axis angle changes, or acoustic center (at target frequency) of radiator travels while off-axis angle changes. Those depend on radiator's size and shape and wave length e.g. small radiator at low frequency is more reliable to estimate by distance only.
For example moving mic in D'Appolito's example causes magnitude and phase response changes to all drivers but mostly to woofer at HF. You could get decent result by distance, but not exact without measuring at each mic position.

As mentioned earlier, decent XO simulator is able to visualize these changes: calculate SPL change and phase summing including magnitude response and phase response and acoustic center changes if measurement data of drivers covers off-axis angle range including rotation of drivers and moving of microphone.
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Old 7th November 2019, 05:56 AM   #17
AllenB is offline AllenB  Australia
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VituixCad is easy to begin with but has advanced features as well.

Quote:
Originally Posted by bentoronto View Post
My gut feeling is that drivers should be within a cycle or two (360 to 720 degrees) in alignment for music to sound right.
Blauert and Laws had that gut feeling too. I recall Earl telling you this a couple of months back.
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Old 7th November 2019, 06:15 AM   #18
andy2 is offline andy2  United States
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Originally Posted by kimmosto View Post
It's not black and white.
I understand that but should we at least begin at some theoretical starting point even if the real world condition is a bit more complicated. The Figures I posted assumed that the xover at 500Hz and 3000Hz and the calculation was based on that assumption and the mic location. If we start to include multitude possible real world conditions, then it's hard to finish a design.

It's just simple illustration on how the phase can get affected by mic position. It does not pretend to be any more complicated than that.
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Old 7th November 2019, 07:53 AM   #19
Lojzek is offline Lojzek  Croatia
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It is exactly as you concluded and as dr. D'Appolito showed in his simple diagram. You should ignore the individuals introducing unnecessary drama whose only point would seem to be drawing attention.
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Old 7th November 2019, 11:37 AM   #20
kimmosto is offline kimmosto  Finland
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Let's go back to the first message; one tweeter at the top and another in front, offset in Z=2.7". Rotating top tweeter 90 degrees could cause about 50 degrees phase change at 5 kHz due to (magnitude) response change, if we compare minimum phase responses. Sound source at target frequency could move few millimeters closer or further due to rotation so final phase change could be e.g. 35-55 degrees + phase change due to Z difference. Without introducing unnecessary drama, I wouldn't call phase calculation by distance "exact" if radiator is rotated that much Simplifications and inaccurate approximations could be okay, but not mandatory with measurement data and decent XO simulator.
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