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Author Topic: phase alignment between two speakers  (Read 12607 times)

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phase alignment between two speakers
« on: June 01, 2010, 11:17:25 AM »
First, I am an engineer, but do not pretend to be anywhere near an expert in sound or wave
theory. So please feel free to comment openly if I appear to have made a bad conclusion in my question
below. I am working on a proof of concept and this is a first stage.

One of my immediate needs is to measure the phase variance/alignment from a
single audio test signal coming from two speakers at various distances apart.

If the two speakers are in sync then there should be no variance in
the plane perpendicular and intersecting the midpoint between the two
speakers. If I move outside that plane (when the speakers are in sync)
there should be some recordable variance. Is your software (and the
iphone) able to detect this variance?

As I add a delay (resulting in a phase shift) to the signal from one
speaker to the other, I should see that the phase shift is constant all along
the mid plane mentioned above and the two signals should be in sync
somewhere along a hyperboloid either left or right of the center plane. I would
like to be able to not only move my iphone to that
hyperboloid region and detect that the signals are phase aligned but
also generate the two misaligned signals (hopefully from the same iPhone) and send them to external stereo speakers. Alternately, I could generate the two signals from a common audio file but played
in or out of phase from two iPhones/iTouch devices if it is not possible to do a stereo phase shift from a single device

How much of this is possible with one (or two or even three) iPhones/iTouch using
this software?

Finally, is it possible for this software, via the iPhone, to
generate/detect signals in the UltraSonic (above 20 Khz)?
If the answer to any of the above is yes can you please explain how it
could be done and what specific tools and/or additional HW I would need to do it.



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Re: phase alignment between two speakers
« Reply #1 on: June 01, 2010, 12:42:23 PM »

Can you provide a higher-level description of what you're trying to accomplish? It feels a little like we might get lost in implementation details that may or may not make sense for what you are trying to do.

Phase is a relative quantity. When you produce sound from two loudspeakers, your microphone only detects a single acoustic pressure signal, so it won't enable you to directly measure relative phase between the two loudspeakers.

You could use IOScope on the iPhone to measure the phase of each loudspeaker, independently, and then compare results.

Are you performing your tests in an anechoic environment?

Finally, is it possible for this software, via the iPhone, to
generate/detect signals in the UltraSonic (above 20 Khz)?
Current hardware effectively limits the software to a sample rate of 48 kHz, which means that the maximum theoretical bandwidth would be 24 kHz.



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Re: phase alignment between two speakers
« Reply #2 on: June 03, 2010, 11:20:30 AM »
I understand your point, unfortunately I can't provide a higher level description on a public domain but your information was useful.

Ben is there any way I can email you directly and in confidence?
« Last Edit: June 03, 2010, 11:46:41 AM by kdavis45 »