PA system for Openair Cinema


I am working on a Open Air Cinema. The field is 19 meters deep. Max 450 visitors will sit in a 80 degree "fan" from the screen. The speakers have to be set up every night. No possibility to rig them, they would be gone the next day...

My initial idea to get at 85dB @2/3 of the field with 20dB headroom: A pair of 18Sound Coax 15NCX750 drivers in a ported cabinet -3dB 50Hz. And a QSC RMX 4050A amplifier 2 x 850Watt @8 Ohm, to power the speakers. I have an Oppo to take care of the signal processing aka make stereo from the LCR signal. And protect the speakers from anything below 50Hz. If the Cinema is succesfull, i can add a center channel and a subwoofer. For now i am looking for a basic way to get decent sound. I am a bit of a fullrange & coax nut. So i would like it to sound like a very good fullrange speaker. Danley would be way to expensive...

Any comments or suggestions?
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Joined 2007
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Just throw plastic sheeting over them if it starts to rain? Some drivers are coated to make them water resistant but I'm not sure the general wooden construction of DIY speakers lends itself to getting wet. When I see outdoor line arrays they usually have some effort put in to stop rain directly falling on them.
Joined 2008
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Looking at the price of the 18Sound coax, I think it should be possible to use a 12" coax, maybe something like 12FCX76 and 15" BR subwoofers below that. If there should be any kind of bass, a single 15 coax will not do it. Edit: What is the total budget for speakers and amp(s) excluding the wood work?
Thanks for the bin bag tip!

Budget is between 2.000 euro for L+R + 1 amp and 3.000 for LCR & Sub + amps. The idea is to play outdoors 12 weeks @ 3 nights a week. So lots of setting up and breaking down. Compact, reliable, not to heavy, sound quality as high as possible. System as simple as possible, so others can set it up too.

LCR 15 or 12 inch Coax, -3dB point around 65 Hz for the 15's. Or higher for the 12's.
Sub 2 x 18 vented or single 18 in a horn.
An Oppo Blu Ray player will handle the x-over. And limit subbass excursion for the L+R.

Would be nice if the coax 15's L+R can manage the complete sound. So i have a fallback option if one of the amps or sub in the LCR + Sub system goes poof. Another + for the L+R as 15's would be headroom.
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Joined 2007
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The short list:

15 inch coax speakers that can handle high spl and bass with a highpass:
18Sound 15NCX750
B&C 15CXN76
Celestion FTX 1530

12 inch coax speakers, that need a sub:
18Sound 12NCX750
B&C 12CX32

2x 18 inch subwoofer ported. Push push. Both woofers opposite to each other to cancel out enclosure noise. Or a single 18 in a (tapped) horn.

The Faital 10HX230 and 12HX230 model well too. But don't come with a stock crossover intended for PA use. The 18 sounds, B&C's and Celestion do. I don't have time to work out a crossover for the Faital's if i want to open this summer.
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Still working on permits for the Open-air Cinema. Looks good, there is a chance i can get a bigger plot of land. Thinking of using a 20 feet shipping container as a base for the screen. My questions:

What if i integrate the horn opening in the 20 feet shipping container? Opening in the middle, as close to the ground as possible. Would be nice to know a bit more about pro's and con's.

In bafflestep. Does anyone know of a bafflestep calculator that will handle 20 feet baffles?
So...anybody running target SPL vs distance vs speaker efficiency calculations here? More important than the -3dB down point...just sayin....

How/why are you getting maximum SPL at 127dB with a reference of 85dB and 20dB of headroom? Where's the extra 22dB of SPL coming from and why? Trying to hurt people? Get the permit pulled? If it takes 300W to get 105dB (85+20dB), it will take nearly 50kW to get the next 22dB, and nothing, no speaker made...will take that kind of power even if you could afford to deliver it.

Now, returning to earth...

I don't see any reference to seating area, distance from screen, angles...nothing. I also would STRONGLY suggest the center channel right away. Big venue systems do not work in stereo, might as well do dual mono because only the few seats on the center line will get any semblance of stereo. The center channel fixes all of that.

I know picture is off topic, but where are you getting the power to run the 6kW lamp?