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In Reply to: Vertical array vs trap arrays posted by DSM on December 8, 2004 at 09:43:47:
Trouble with most trap boxes is the coverage angle varies with frequency, especially around the crossover point. When trying to horizontally array them it is impossible to prevent overlap at some frequencies causing cancellations (dropouts) and dead areas at other frequncies where there is a gap in coverage. The effect is VERY noticable when walking across the front of the stacks. The only way to horizontally array is to have very tight dispertion control ie, well designed waveguides (therefore horn loaded boxes). Martin got it very close with their W8 system, but the Funktion-One Resolution boxes have perfected it. To get high spl, the coverage pattern of each box must be narrow, which is difficult to DIY (the Resolution boxes get 25degrees ! - I'm currently trying to get down to 40degrees and that is hard enough).The vertical array works easier as off-axis (in the vertical plane) cancellations get swamped by the summation of close drivers. Only thing is the horizontal dispertion is only as good as one box, which quite often is not wide enough.
Both systems have their merits and applications but require good design to achieve best results - the vertical array is probably easier with DIY boxes.
Cheers
Graeme
Follow Ups:
Hi Graeme, Thanks for the reply. I guess its lesser of the two evils. Most of my mobility FOH entails walking toward the stack then back to the desk as opposed to walking across. Not that I don't walk across to listen but, since I have been using a vertical array I am always aware of the comb lines in the HF. The bandwidth where the driver or horn mouth size prevents close enough spacing to prevent interference lines. Its been awile since I horizontally arrayed. I just seem to recall it being easier to rig. Oh, if I had the money for a few TD-1s or Function-Ones wouldn't life be just too easy?
I have been using around 12 ten inchers closely spaced in vented boxes <1.2K. I picked up a bunch of these cheapies just to play around with the line array idea a few yrs back. Turns out a stack of 12 sounds decent. I had plans to rebuild the box and use better drivers but have been unable to settle on a decent HF waveguide. So, its been on hold for a yr or so. Now I'm starting to think if I lay out enought cash for a bunch of decent drivers, horns,and after reading Jim Griffins paper on spacing... I might as well just build a few trap boxes "throw in the line array towel" and get it over with and never walk across. But then again...
How well will your Alpha 6 horn array? Now you got me thinking 3-way LA.Dan
BTW, the outdoor venue where the system is mostly used is 200'wide x 300'deep with a gentle rise towards the rear. L/R spacing is about 45'.
Dan, the Alpha6 experiments did steer towards a line array for a while, but I found that getting a wide dispersion was not as easy as it seemed. Due to requiring a vertical diffraction slot, the initial horn expansion to the slot was very steep, causing path length cancellations in this area. A trial split throat arrangement seemed to work better, but would neccessitate a complex fibreglass moulding to achieve in practise.After re-reading various line array theory papers, and writings from Tony Andrews and others, plus taking into account the proposed line array would only cover 90 degrees horizontally, I am going back to the trap box idea. Currently working on confining dispersion to 40 degrees horizontal by as narrow as I can get vertical. If the box is built right, one inverted box on top of the first could give a psuedo line for extra spl in the top end in each direction. Still looking at the box running two 1" drivers, two Alpha 6 and maybe two Beta 8 or one Kappa 12 for low mids.
Lots of money certainly would make things easier - I would probably go Resolution 5s over EAW KF940 subs (dream, dream....) :)
Cheers
Graeme
Funny how the Res 5 has the two 1" spaced what looks to be far apart to me. I can't tell if they are "splayed" or not.
Maybe the two spaced this distance is how Mr Andrews achieves 25 degrees.
I understand the complex nature of phase issues in the throat when trying to get the last bit of bandwidth. Damn physics. How about casting a DPRWG?Keep me posted on your progress. It seems our goals are similar.
Dan
Check this out... it should solve your problem.
It's a good idea to use a cabinet that can stand alone in a small gig and can be arrayed vertically when you have a large venue. I can heartily recommend the DR250a as an unbeatable cabinet in either stand alone or line array duty. It has average SPL of 106dB and the HF horizontal dispersion is unmatched by anything else, period. Check it out here:
http://www.billfitzmaurice.com/plans/product_info.php/products_id/3
How many of these DR-250s have you used in your line array? Did they array well?
We actually use only one DR250a per side, above Tuba 24s, for our PA. But we have a total of 3 DR250a boxes (one I use normally for my bass) and we did set up the three of them in a vertical array this past summer for an outdoor party, playing CDs, and they worked great, really long throw, very clean.
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