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Author Topic: Tell me what you see in these phase response graphs  (Read 9040 times)

Mike Caldwell

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Tell me what you see in these phase response graphs
« on: January 26, 2018, 09:37:11 pm »

I've been working with REW software to get an idea of what a couple speakers of mine look like at the high frequency crossover. Pictured are a couple screen shots of the response of a 12X2 and 15X2 bi-amped speaker. These are after playing with the high frequency driver polarity and time delay on the woofer.
For these test the 12X2 crossover is 1700hz and the 15X2 is 1600hz.
Set up outdoors, measurement mic on axis between woofer and horn about 8 foot from the speaker.

Mac Kerr

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Re: Tell me what you see in these phase response graphs
« Reply #1 on: January 26, 2018, 10:03:43 pm »

I've been working with REW software to get an idea of what a couple speakers of mine look like at the high frequency crossover. Pictured are a couple screen shots of the response of a 12X2 and 15X2 bi-amped speaker. These are after playing with the high frequency driver polarity and time delay on the woofer.
For these test the 12X2 crossover is 1700hz and the 15X2 is 1600hz.
Set up outdoors, measurement mic on axis between woofer and horn about 8 foot from the speaker.

It's hard to imagine what you're doing to get 16 phase wraps in 1 octave.

A shot of the screen with full bandwidth might be more enlightening.

Mac
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Mike Caldwell

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Re: Tell me what you see in these phase response graphs
« Reply #2 on: January 26, 2018, 11:44:43 pm »

Here's a couple shots of the 12X2 that show more bandwidth. No EQ was active.

I got about the same phase response when measuring a small powered speaker a few days ago.

I'm thinking the couple deep notches are from my less than perfect testing location.

I should have saved some of the shots before and during the measurement process.
« Last Edit: January 27, 2018, 08:49:29 am by Mike Caldwell »
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Merlijn van Veen

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Re: Tell me what you see in these phase response graphs
« Reply #3 on: January 27, 2018, 01:49:39 am »

If this was Smaart I would recommend setting the delay locator which effectively takes out all constant delay caused by latency and / or time of flight.
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Mike Caldwell

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Re: Tell me what you see in these phase response graphs
« Reply #4 on: January 27, 2018, 10:12:57 am »

If this was Smaart I would recommend setting the delay locator which effectively takes out all constant delay caused by latency and / or time of flight.

REW does not have set or find delay like Smaart, it does have loop back delay finder or a use acoustic source to set delay, using both showed the same results.

For what it's worth I'm using a small Allen Heath ZED10 mixer as the IO via it's USB connection.

I was primarily interested in the phase response at the crossover and if I'm looking at it right I think it is at least somewhat "flat" through the crossover point and the area around it.

I really should have taken a screen shot of the before adjustment.

Mac Kerr

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Re: Tell me what you see in these phase response graphs
« Reply #5 on: January 27, 2018, 01:42:24 pm »

I was primarily interested in the phase response at the crossover and if I'm looking at it right I think it is at least somewhat "flat" through the crossover point and the area around it.

I really should have taken a screen shot of the before adjustment.

You're not looking at it right. That sawtooth display at the bottom is the phase response. It is about as far from "flat" phase response as it is possible to get.

Ideally it should be a flat horizontal trace, not a sawtooth showing dozens of 360 phase wraps in a single octave. As Merlijn said, your reference and test signals are in totally different time zones.

Mac
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Ivan Beaver

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Re: Tell me what you see in these phase response graphs
« Reply #6 on: January 27, 2018, 03:36:36 pm »

You are going to to have to set the receive delay (or whatever it is called in that software) properly.

There are simply to many phase wraps to get any useful information.

It is possible to have a wrap or two, depending on the speaker.  Better ones will have fewer wraps.

A perfect phase response would be a flat line.  So that is the "goal", but rarely achievable-especially at a decent distance away, due to reflections.
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Marc Sibilia

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Re: Tell me what you see in these phase response graphs
« Reply #7 on: January 27, 2018, 04:02:27 pm »

It's hard to imagine what you're doing to get 16 phase wraps in 1 octave.

Mike,

If you open up the measurement again, in the upper right, there is a button for Controls.  Open that, and press Estimate IR Delay.  After you adjust the Impulse Response, you will have the phase plot you expect.

What you are looking at is the phase wrap of the delay caused by the travel time through the air between your speaker and microphone (as well as any measurement latency).

Marc
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Mike Caldwell

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Re: Tell me what you see in these phase response graphs
« Reply #8 on: January 27, 2018, 04:09:08 pm »

I know the bottom trace is the phase, and after looking at is why I wanted some other opinions.

I got to dig into the software deeper and see what's going on with the delay offset.

Thanks
Mike C.

Mike Caldwell

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Re: Tell me what you see in these phase response graphs
« Reply #9 on: January 27, 2018, 04:11:02 pm »

Mike,

If you open up the measurement again, in the upper right, there is a button for Controls.  Open that, and press Estimate IR Delay.  After you adjust the Impulse Response, you will have the phase plot you expect.

What you are looking at is the phase wrap of the delay caused by the travel time through the air between your speaker and microphone (as well as any measurement latency).

Marc


Thanks for that info!
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