Random Phase Reversals?

[lanetim]

Hi,
I'm scratching my head over this one!

In measuring my speakers in my media room to ensure the crossovers are wired and performing correctly, I am getting phase reversals in the tweeter region (2.2K Hz+). The microphone is at the listening position, ~ 10 feet from the speakers. I'm measuring them one at a time, then calculating and presenting minimum phase. Sometimes the phase reversal happens at ~2kHz, 7 kHz, etc. I am repeating measurements without any changes to setup - I get perfect results, then? Using a MacBook laptop running REW and a Umik 1 mike plugged into the USB port on my laptop. Two examples here of the same speaker, one measurement made right after the other...

Any help greatly appreciated!!

Many Thanks
Tim

 

[sm52]

This is normally. The reason is extraneous sounds, vibrations that you are used to and do not pay attention to. Or interference in the measuring path. Therefore, measure several times and take as a basis the graph that repeats in most measurements.

 

[John Mulcahy]

That's not a reversal, it is a 360 degree rotation, often found where the response passes through a null.

 

[lanetim]

Hmmm, getting my head 'wrapped' around this. The presented phase curve is unwrapped. In another example below, the phase curve goes from -397 deg @ 1.9k Hz to -763 deg. @3.6k Hz, a difference of 366 deg. So the phase is still the same, it has just rotated in a complete circle. I still don't quite understand why it does this...a transient?