Rational Acoustics

Andrew Lye
July 27th, 2016, 06:27 AM
Hi all,

I'm seeking advice from those in the know on some phase measurements I made of a line array earlier this week.

There are 6 elements per side in the array. This measurement was made approx 8-9m from the array on a mic stand approx 1.5m off the ground. Subs and all other components in the system were turned off. I made a total of four measurements at different locations around the room and all showed similar behaviour in the low-mids.

On the magnitude graph you can see a large peak occurring between 100 - 200Hz, whilst on the phase graph there is a jump that corresponds with a dip in frequency response at 205Hz. If I turn smoothing down to 1/24 Oct, I can observe a jump of -140 to +18 degrees in phase at 205Hz.

In what scenario would you usually see this behaviour? Is this typical of line array behaviour due to the different arrival times of the dozen mid bass drivers, or is it likely that there is an element misconfigured within the array? (Each element contains it's own DSP)

Could this just be a reflection hitting the measurement mic?

I do know that having mixed in this room that this is a problem area within the system, subs sound indistinct around their crossover point and low-mids are a little murky.

Any suggestions would be greatly appreciated :D



July 27th, 2016, 10:33 AM
In my opinion, the phase jump and FR dip you are seeing is caused by a reflection hitting the mic, as can be inferred by the dip in coherence at precisely the same place. the LF peak you are seeing is probably because the LF summation of the multiple array elements. It is normal line array behavior to have their LF energy raise as more and more elements are added to the array. That's assuming everything is ok on the DSP side of it. Having individual DSP for each cabinet is a blessing, but can be a curse if it is not used correctly.

In any case, it is common to see differences in HF eq on individual cabinets, but not on LF as you can't do an individual change there and expect not to affect the whole array. Because of the wavelengths involved, you should treat LF in a line array the same in all cabinets.

I hope this helps.