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PSW: What problems does the KF900 solve or stadium tours?
EAW's David Gunness: The unique challenge in stadiums is accounting for air losses. With the distances involved (up to 700 feet), the air attenuates the 8 kHz by 20 dB in addition to the more familiar inverse square law. To make music sound like music at that kind of distance, you need a tremendous amount of high-frequency projection. The entire KF900 design hinges on achieving the required HF projection without frying the people right under the stacks.
PSW: Why is it not a “one box” type system.
D.G.: The part of the high-frequency beam directed at the farthest listeners is 30 dB louder than the part directed to the nearest listeners. That means any "sidelobes" spilling downward from the long-throw part of the beam have to be down more than 30 dB. You can only achieve this if the HF horns are adjacent. In a system that arrays horizontally, you can't have a full-range box without introducing gaps, vertically, in the HF array.
Everything in the system sort of progresses from this one overriding requirement. It has to - if we didn't recognize this up front, there would have been no way to fix it later.
PSW: What is F-Chart and what does it do?
D.G.: Making all the HF energy go straight out is easy. Keeping most of it going "out", while establishing an "underside" to the pattern with flat, musical response is hard - very hard. It calls for very precisely determined DSP processing, and can't be done by the seat of the pants. FChart is the tool we used to develop the steering algorithms that make the system work.
PSW: What does it feel to see someone like Clapton using something you built?
D.G.: It's tremendously gratifying. During the development process there were a lot of speech-oriented events, festivals where nobody got a sound check, and a lot of mix engineers getting their first chance on a large system. There were some great shows too but when you have an artist like Eric Clapton, and a guy like Robert Collins has a chance to really get comfortable with the rig and what it can do, then you get to be part of something really special.
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Clapton KF900 Rig.(Dave's Engineering Drawing)
Some points of interest:
- The magenta boxes are KF914's, which were developed specifically to give HF coverage to the people who sit above the rig on the sides. The dark boxes next to them are KF910's, which face the far end of the venue.
- The KF930's are all the way at the top. They will quite often be flown at the bottom of the array, but Robert felt that it was important to reduce the bass buildup underneath the stack. I think this helped keep the acoustic guitar sound from becoming boomy in the front rows.
- The KF913's are below the KF920's, while the KF910's & KF914's are above the KF920's. This allows the long-throw and downfill sections to be separately aligned with the KF920's.
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