Phase is a out by a mile?

[Dan Twomey]

Shown here is my (unwrapped) phase. This has perplexed me from the beginning of my measurements.
With phase so far off I have no hope of correcting it?

 

[John Mulcahy]

Depends whether you have removed any time delay component, look at the group delay plot or play with the adjust t=0 control to see the effect of time delays on phase.

 

[jtalden]

This is the phase response as a result of including all room interactions. We typically correct only the direct sound response. If you are FIR EQing each channel separately then apply a heavy FDW filter to the each vector average. See what a 5 or 6 octave FDW looks like and if that is not enough to estimate the direct sound phase smoothly we can go as low as 2 octave, but that usually is not necessary and may be misleading in case where the XOs are not aligned well. All room ripples do not need to be removed. We can just ignore them and adjust the FIR phase correction filter to remove the overall smoothed shape. The 2 channels should be very similar for direct sound phase, but if they are heavily EQed independently they may deviate somewhat.
If you post an mdat containing the Left and Right vector averages (just the 2 measurements) I can take a look to see if it looks as expected.

 

[jtalden]

John is right, I now see you have FDW applied. You just need to adjust the impulse to 0 ms.

 

[Dan Twomey]

This is the phase response as a result of including all room interactions. We typically correct only the direct sound response. If you are FIR EQing each channel separately then apply a heavy FDW filter to the each vector average. See what a 5 or 6 octave FDW looks like and if that is not enough to estimate the direct sound phase smoothly we can go as low as 2 octave, but that usually is not necessary and may be misleading in case where the XOs are not aligned well. All room ripples do not need to be removed. We can just ignore them and adjust the FIR phase correction filter to remove the overall smoothed shape. The 2 channels should be very similar for direct sound phase, but if they are heavily EQed independently they may deviate somewhat.
If you post an mdat containing the Left and Right vector averages (just the 2 measurements) I can take a look to see if it looks as expected.

As requested.

Regards,
Dan

 

[jtalden]

Oh, this is the line array you previously posted. This is not the expected result from a typical 2-4 driver multi-way. It is not a settings issue within REW and the line array data I have seen from others do not look like this. I do not have any insight as why it looks this way. It may require shading or other design changes to correct this. I would not suggest trying to unwrap this phase without understanding the cause.

 

[Dan Twomey]

Depends whether you have removed any time delay component, look at the group delay plot or play with the adjust t=0 control to see the effect of time delays on phase.

 

[Dan Twomey]

In the previous post I did adjust T=0 to the highest peak in the all impulses before vector averaging. I'm assuming that's why T=0 on the highest peak on the vector averaged impulse.

Regards,
Dan

 

[jtalden]

Did you confirm that all the individual impulses were actually aligned on top of each other after selecting 'Align IR start' and before selecting 'Vector average' when creating the L and R averages?

 

[Dan Twomey]

Did you confirm that all the individual impulses were actually aligned on top of each other after selecting 'Align IR start' and before selecting 'Vector average' when creating the L and R averages?

I manually aligned the peaks of all impulses for each channel before doing vector averaging. I didn't use 'IR Start'.

Regards,
Dan

 

[jtalden]

Good, that is not the issue then.
I see now with in a quick review of the old threads that I am repeating my same thoughts - none of which have apparently helped.

 

[Dan Twomey]

Good, that is not the issue then.
I see now with in a quick review of the old threads that I am repeating my same thoughts - none of which have apparently helped.

If anything, I'm persistent? ;-)

Regards,
Dan

 

[Dan Twomey]

In another one of my threads titled, "Manually Aligning Impulses" I posted a pic of my Zu Audio Dirty Weekend speaker https://www.zuaudio.com/loudspeakers/omen-dirty-weekend-2
I also posted a quick measurement. After reviewing the measurement of this point source speaker I noticed the same phase and impulse anomalies that I'm experiencing with my line arrays.
What, if anything, can I conclude from this?

Regards,
Dan

 

[jtalden]

It suggest the issue is someplace in the measuring setup rather than the speaker itself.

I just quickly reviewed 'Dirty Weekend Apr 11.mdat' and indeed a similar excessive phase rotation is present as we noted there. I also opened 'Dirty Weekend Ndecimt Apr 12.mdat' from Post 22 in that thread and it looks believable for phase rotation (see chart). I don't remember if I opened that one before. We commented regarding the L array posted there that it was much better for phase rotation, but possibly still had some level of the issue. Maybe it is indeed the correct phase response even though it still looks to me that it has twice as much phase rotation than I expected on the mid-woofers. Are you using any shelving filters or other EQ in that L array response?

The change in Post-22 was turning off 'decimate IR'. Did you test to see if this was repeatable with this setting change? Did the phase rotation problem return later even with this setting turned off?

 

[Dan Twomey]

Depends whether you have removed any time delay component, look at the group delay plot or play with the adjust t=0 control to see the effect of time delays on phase.

The SPL and Phase plot (or Impedance and Phase for an Impedance measurement) shows the frequency (dB or Ohms) and phase (degrees) responses of the measurement. The frequency response is labelled with the measurement name, the phase response uses a brighter shade of the measurement colour and the right hand plot axis. Note that to have valid phase information it is necessary to remove any time delays from the Impulse Response. A time delay causes a phase shift that increases with frequency - for example, a delay of just 1ms results in a phase shift of 36 degrees at 100Hz but 3,600 degrees at 10kHz, because 1ms is 1/10th of the 10ms period of a 100Hz signal but is 10 times the 0.1ms period of a 10kHz signal, and each period is 360 degrees. The time delay of a measurement can be adjusted by changing the zero position of the time axis using the Impulse graph controls, or by using the Estimate IR Delay control described below.

The above quote is where John is trying to steer me in the right direction? A time delay in the Impulse response could be causing my 'excessive' phase shift?

Regards,
Dan

 

[jtalden]

Yes, that may have been the cause, but you already had the impulse at 0 ms so that was not it.

 

[Dan Twomey]

A friend of mine may have uncovered one of the issues I'm having with phase. My speakers are a two-way with both fourth order LR crossovers. The high pass filter is connected in the opposite polarity to the low pass.
It's my understanding that it's 'standard' for two fourth order LR's to be connected with the same polarity.

Regards,
Dan

 

[jtalden]

Yes, for an electrical LR24 or an acoustic LR24 rolloff then the the drivers should be the same polarity. The drivers rolloff also are involved though so the actual acoustic rolloff may be significantly different from the electrical filter. In practice it's best to choose the polarity to provide the best SPL support in the XO range. If we have DSP delay capability then we can just chose the best combination of polarity and delay; the one that provides the closest phase tracking through the XO range. This type of work in mid and higher frequency XOs is best done with the mic located approximately 1 m from the speaker. A SW XO usually needs to be measured at the LP. It all depends on the setup. The SPL chart should be the focus. The phase chart just helps us understand why the SPL may be erratic in the XO range and what change may help improve the SPL.

 

[Dan Twomey]

Thanks to a generous gift from Father Pass, I've decided to go active. It's going to take another month or so to collect more speaker and interconnect cables and then I'll go from there.
DIY biamp 6-24 crossover

It's my intention use the passive crossover specs as a starting point. Two fourth order LR's at 2500Hz. Both with the same polarity for starters.
Lots of measurements and graphs will be included. Should be a great learning experience!

Regards,
Dan