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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 7th November 2019, 02:20 PM   #21
weltersys is offline weltersys  United States
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Quote:
Originally Posted by andy2 View Post
I post here two figures from D'Appolito book Testing Loudspeaker to more specifically illustrate the intent of my question.

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?
The chart exactly represents what I wrote in post #7, so I agree.
The chart represents reality as can be measured or heard at the various vertical off-axis listening positions.

The phase angle changes with the relative vertical off-axis angle.
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Old 7th November 2019, 03:54 PM   #22
bentoronto is offline bentoronto  Canada
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Microphone position - theoretical phase shift delay
Quote:
Originally Posted by weltersys View Post
....The phase angle changes with the relative vertical off-axis angle.
Back to drama.

Yes, some simple parameters in acoustics work just like 7th grade geometry, for example, weltersys's comment.

But this thread started with a question about the coordination of two drivers. And I said, without any intention of being dramatic, that you can't over-simplify the sound output of drivers in this case as if they obeyed simple Euclidean rules.

If they did, when you ran FR plots you'd have hideous nulls showing up when the Euclidean moon crosses the acoustic sun. In fact, you do get interference by the interaction of phases but you don't get nulls.

B.
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Last edited by bentoronto; 7th November 2019 at 03:58 PM.
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Old 7th November 2019, 04:42 PM   #23
andy2 is offline andy2  United States
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Originally Posted by Lojzek View Post
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.
OK. Thanks. Some have made it more complicated than needed to be.
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Old 7th November 2019, 05:26 PM   #24
weltersys is offline weltersys  United States
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Quote:
Originally Posted by bentoronto View Post
And I said, without any intention of being dramatic, that you can't over-simplify the sound output of drivers in this case as if they obeyed simple Euclidean rules.

If they did, when you ran FR plots you'd have hideous nulls showing up when the Euclidean moon crosses the acoustic sun. In fact, you do get interference by the interaction of phases but you don't get nulls.
Ben,

In the polar response charts below, it is easy to see the null in the crossover range deepening between 1kHz and 2kHz as the vertical angle increases thereby increasing the arrival time of the woofer in relation to the tweeter, while the horizontal dispersion, equidistant between the two drivers, stays consistent over the same range.

At a 30 degree angle up from "on axis", that null is around 6 dB deep- whether that is "hideous" is a subjective observation, but it is certainly measurable and can be heard when listening that far off the vertical axis. With the speakers oriented "normally", tweeter over woofer, not a problem when moving laterally, but if the speakers were turned "sideways", the response "suckout" would "suck" by comparison.

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Old 7th November 2019, 06:53 PM   #25
kimmosto is offline kimmosto  Finland
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Quote:
Originally Posted by andy2 View Post
OK. Thanks. Some have made it more complicated than needed to be.
How you gonna use that information, and why you just picked the simplest answer?

I'm asking this because measuring tape is not valuable (to me) for measuring distance difference of assumed acoustic centers or distance from assumed acoustic center to mic. It's more valuable (to me) for measuring distance from mic to timing origin of driver's measurement data i.e. selected rotation center while off-axis measurement sequence. That is physical origin XO simulators with 3D driver geometry parameters use for timing/phase and SPL simulation of each driver.
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Old 7th November 2019, 07:20 PM   #26
bentoronto is offline bentoronto  Canada
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Microphone position - theoretical phase shift delay
Quote:
Originally Posted by weltersys View Post
Ben,

In the polar response charts below, it is easy to see the null in the crossover range deepening between 1kHz and 2kHz as the vertical angle increases thereby increasing the arrival time of the woofer in relation to the tweeter, while the horizontal dispersion, equidistant between the two drivers, stays consistent over the same range.

At a 30 degree angle up from "on axis", that null is around 6 dB deep- whether that is "hideous" is a subjective observation, but it is certainly measurable....
You are making two mistakes.

First, "Null means having no value; in other words null is zero"

Second, although there are dips (of course), but that doesn't mean you or anybody can predict them with a tape measure (AKA Euclidean-like distances), as kimmosto wisely posts and for the reasons I earlier provided.

But your charts do have a dip (reminiscent of stuff Linkwitz published when developing his theories). However, testing two tweeters comes as close to the reductionist situation where even I would expect simple geometry to have a bit of value.

B.
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Old 7th November 2019, 07:32 PM   #27
ctrlx is offline ctrlx  United Kingdom
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Quote:
Originally Posted by andy2 View Post
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.
Thanks.

anyone who has done actual tests will confirm that the phase between the drivers will change when measured at 50cm and then again at 75cm.

unless you have access to a large space measuring an 8ft is not possible.
as a compromise, measure the tweeter at 60cm (or so to get enough data) then lower the mic down to the next driver (whislt maintaining same baffle distance)
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Old 8th November 2019, 01:47 AM   #28
Rick PA Stadel is offline Rick PA Stadel  United States
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Perhaps Dr D'Appolito intended those two figures as a starting point to explore the complexities of any math solution -- and didn't intend to imply that there is an exact, comprehensive mathematical solution.

In any case, it is certainly easy to get lost in the trigonometry ...

If you're still bothered by all this -- that an oversimplification might confound more than illuminate -- keep in mind that Dr's diagrams are only valid if all 3 drivers are getting phase-matched stimuli at all frequencies that they reproduce!

+1 Lojzek

Cheers,
Rick

Last edited by Rick PA Stadel; 8th November 2019 at 02:03 AM.
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Old 8th November 2019, 02:37 AM   #29
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by Rick PA Stadel View Post
lost in the trigonometry ...
I think vector summing the height and distance is all that's needed on this level.
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Old 8th November 2019, 07:13 AM   #30
Juhazi is offline Juhazi  Finland
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I am very much challenged in trigonometry and geometry. But I like pictures

Tolvan Data Edge (you can have several sources of same size, same phase), variable baffle, source location, mic position)
Tolvan Data XDir

Click the image to open in full size.
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Last edited by Juhazi; 8th November 2019 at 07:18 AM.
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