Posted by Dave Rat on April 02, 2002 at 12:51:29:
In Reply to: Re: boxes posted by Ron S on March 28, 2002 at 20:49:13:
In a true line array there are maximum angles between boxes, usually a few degrees, and beyond that the HF decouples and interferes at unacceptably lower frequencies. The Tall Fills use a somewhat conventional horn (90 degree waveguide). When using multiple in the vertical array the opposite is true. There is a minimum angle between boxes, so stacking them is not really a good idea. Flown you can get enough angle between the boxes to minimize the overlap between horns but regardless, they operate as a "splay" rather than a line array in the HF region.
The spacing between the horns is not the big issue you will run into. With a conventional flat front horn the distance that the sound travels to the center of the horn is shorter than the distance traveled to the edges of the horn. In line arrays, a variety of different methods are used to try and solve this issue. The goal is to have the sound leave the center and edges of the horn at exactly the same time. The better a design accomplishes this, the higher usable frequency the line array will reproduce without destructive interference.
If you do a search on uspto.gov you can find Christian Heil's patent on the V-Dosc horn as well as Clair brothers and I think the Adamson and JBL patents as well.
Two main methods have evolved for solving the "time of exit" issue with line array horns. 1) the V-Dosc and similar where the sound of the horn driver is forced through a longer path to center of the horn and a shorter path to the ends. The path lengths are set so all sound leaves at the same time. 2) the Clair and JBL Vertec method where the uses multiple long skinny horns stacked on top of each other so the sound from the edges vs. the middle of each horn leaves at very close to the same time. This pushes the frequency the mismatch in timing occurs up to a very high frequency.
Ribbon drivers are perfect for line array applications and don't suffer from the "time of exit" issue but they are still very new and have other issues like low efficiency, reduced dynamic range and non linear sensitivity.
Companies are striving to resolve these points and depending on you application there may be ribbon drivers available that will perform acceptably
: I see in your tall fills box which by the way is pretty much what Im looking at doing you use a round flare. With everyone talking about keeping the vertical as small as possible yours was probably a 60 or a 90. I was looking at a 60 x 40 and when stacked these would be spaced by approx 1"to the outside of the flare. Those ribbon tweeters at 1000 watts from Holland are expensive but a consideration , have you tried them?
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