CP650 B-Chain Alignment for outside/open air projection

[Neal Scanlan]

Having resolved my power supply issue I am now looking at setting my CP650 sound levels for projecting films on a outside/open air screen.

As there is no auditorium, walls ceilings etc does any have a suggestion of a general setup/setting that I would apply to the B-Chain Alignment as against using the microphone/oscilloscope process described in the manual?

[Darryl Spicer]

My suggestion would be to set everything to 0db in the processors EQ settings, then run a piece of film and judge the sound by ear. Make sure your A-chain has been set correctly before doing this. If dialog sounds harsh or muffled, make adjustments to the EQ on the center channel and then copy it to the left and right. EQ settings are meant to equalize the speakers to the curve response of the room. Something that is hard to do outside since sound tends to go wild around you.

[Jay Wyatt]

Whatever loudspeaker or PA system used will be operating largely in free-space, meaning you won't benefit from the effects of boundary loading. Proper low frequency response may be harder to come by so get your low shelf filter (bass adjust on a CP650) ready if the speakers are up to the task. One positive is you're subs/LFE output won't be influenced by the room and you should get near textbook omnidirectional patterns of coverage -> less seat to seat variation. It you have multiple subwoofer elements, couple them together for free sensitivity. You also won't be challenged in getting high frequencies to cut through a perforated sheet (I'm assuming by open air screen you mean one of the inflatables that loudspeakers don't go behind?).

My advice is to start flat on the EQ but be prepared to roll off high frequencies if things seem harsh on the upper end. Again, there's no sheet in front of the speaker to naturally roll of HF so you may have to replicate that with EQ. There's no appendix entry in the SMPTE 202 spec for outdoors so all rules for system alignment still apply if you want to stay true to the mixers intent. Outdoor systems can vary from small 12" powered speakers on sticks all the way up to multi-element line arrays and everything in between. Strategies will vary depending but be realistic about the speakers you have and the audience you're trying to cover.

[Mark Gulbrandsen]

Years ago when we did a three day 70mm outdoor film fest in Chicago, There are pictires in tje Warehouse of Cinema Borealis. We had five 4675's behind the screen and so many Intersonics servo drive subwoofers that we rattled glass in a high rise a half block away. I initially set everything flat and we ran a couple reels of film. But flat sounded awful and we re-eq'd to ISO 2969 and everything sounded much better. So we ran it EQ'd that way. Mind you this was with a CP-100 and CAT 64's. You could do several sq settings in the 650 and just save them, then use what sounds the best.

[Sam Chavez]

Had the same experience as Mark states back in 1982. Started out flat. A-chain being done right with optical stereo back then is key, If the audio isn't clean going in it's not going to get any better.

[Neal Scanlan]

Hello All,

Thank you for the advise, as always a great help.