Rational Acoustics

Rasmus Rosenberg
November 13th, 2010, 12:04 PM
So I had a fun one a couple days ago. Two positions on stage, with one monitor same type singing mic. One starts to feedback at 1khz'ish before the other but witch one are actually working proberly :p


Dr. J
November 13th, 2010, 11:22 PM
So -- you are saying you use the exact same monitor & microphone BUT two different positions on the stage for your monitor? Just want to clarify.

Rasmus Rosenberg
November 14th, 2010, 09:10 AM
Hey J,
No not the same, but "matched". A x wedge and a 58, its the SR (White) and SL (Blueish) position (singing gtr and bass player). I start at the SR (white) position and get it up and going. When pushed it starts to feeds back a 1khz'ish. So I take out 3db on the graphic Eq and go to the other position. Here with the same channel EQ, but the graphic flat, I can't get the 1khz feed back, at the same level,Lucky me no nasty feedback? All good? No...
I all ready had Smaart hooked up to my cue bus. So instead of starting a heated discussion with the house tech, that some thing might be wrong somewhere. And instead of running around like a chicking with out head, comparing the two positions with my voice. I quickly measured the two positions and as the picture shows, I could with confidence tell the house tech that the SL monitor's horn had inverted polarity. Checked the cables (they where all good) then opened the box up (wire blue + and white - was crossed) changed it (re meassured, all good) and had a great show.
My moral here was just that, I was very very close to call it good and go on, when there was no feed back, but it puzzled me too much. With Smaart it was quite fast to get settled if there was a problem or not.

Arthur Skudra
November 14th, 2010, 10:50 AM
Another perfect example of solving the problem at the source! Great post illustrating the concept.

Telltale signs to look for when a driver is out of polarity (Comparing a known "good" loudspeaker to one that is questionable):
180 swing in phase at the crossover region
A very deep notch in the magnitude response in the crossover region

Dr. J
November 15th, 2010, 11:59 AM
Nice Ras -- great example. Thanks.