For a special AES event we were given the chance to see how live sound is done at the Aragon Ballroom in Chicago by Geoff Gilkes with LD Audio, Friday February 20th. Geoff Gilkes and his assistant stage engineer, Giovanni, threw us in immediately to help. We set up the house woofers, which consisted of two stacks of customized JBL 2x18's for house left and right on the floor. The overhead house array was already in place from a show earlier by LD Audio. The overhead array consisted of 3 stacks of EAW's 2x15 suspended with a bottom row down tilt and wedge angles.
30,000 watts total at 2-ohm impedance from separate Crown amplifiers powered the woofers and QSC amplifiers for the high and mid drivers. Both mixing consoles (stage and house) were digital Yamaha 24x8 with an onboard effects processor. The routing cables were housed in 3 separate 48 channel digital sends, returns and matrix snakes. Geoff had 8 separate channel (subs, lows, mids, highs L/R) soft limiter, housed in the power rack. Geoff also had a stereo send going out to a camera crew from Telemundo for a Saturday broadcast.
After Geoff went over signal routing, we had the system powered up and sent pink noise blasts from the stage and Geoff went through a monitor shootout. Pulling frequencies out of thin air and hitting every single frequency on the nose by ear, his accuracy through 16 years of experience, blew us away. He attenuated and delayed the house loud speakers; there was a whopping 12 seconds of delay, especially in the lows. Geoff ran a sine wave around 80hz and set a 1.2 second delay on the low-end between the stage mics and the house system, also incorporating a .2 second delay on the highs. Reasoning for that is the acoustic transients and sustained frequencies in a live set up needs to be delayed between each other so that the acoustic frequency has time to catch up to the mic'd send frequency coming out the house and stage monitors.
Geoff put on some music over the house system and took us on a sonic tour of the Aragon showing us all the sweet spots on the floor and where the most diffractions occur. He held his hand out and felt for the end of the low-end waves and told us where to stand to "feel" the end of the low-end waveforms. You could really hear and feel it by just moving inches forward and backward.
