DriveRack PA settings for T39s and OT212's

[Sydney]

On a related note
Refraction of Sound in the Atmosphere page 260
Sound Absorption by people page 216
The Master Handbook of Acoustics
By Frederick Alton Everest
Temp/Humidity can change things dramatically from the early morning to the late evening.
Good Chapters on Absorption and Refraction

[Sydney]

It's a great book Phil...
I broke down ( after much free preview using Google Books ) and bought the 3rd edition very cheap via Alibris.
Acoustic/Science/Tech books are very expensive new.

[Tim A]

As for aiming the array, Im sure Bill said that the array has the same vertical dispersion as one box.

No, the horizontal dispersion remains the same. Vertical dispersion narrows and extends lower as the array is lengthened.

Don't worry about the tight vertical dispersion. If you have a 6' array with the bottom 5 to 5-1/2' off the ground, which is recommended, then the top boxes are shooting out to the back, right over the close-in audience's heads. If it weren't for the narrow dispersion most of the sound would be out in the atmosphere.

I've not done any shading either, so far, no problems. My tophats are set @ 6 deg, which takes into account the 3 deg slope of the box and gives me another 3 degrees down. The next cab is aimed slightly down too, although not quite as much. With 3 cabs it will be the same. Essentially, you get to point the uppermost cab at the back of the listening area instead of off into space. Until you get in a situation where you're trying to push a lot of volume waaaaaay back in a deep venue or outdoors, shading doesn't seem to be necessary. The nearfield advantage from even the short piezo array makes a big difference.

If I were building new cabs I would absoultely use the aimable tophat that Leland sells. If memory serves they adjust in 2 degree increments. That would be very nice for any of these cabs that use a high frequency array.

After building my first DR's it was obvious that the vertical dispersion of piezos arrays is indeed tight, even when running a single cab per side. People sitting in the front row 15' or less from the stage weren't getting any highs at all, so the addditional 3 deg adjustment was made on the next cabs. Perfect.