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Author
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Topic: Laser fixture for aiming HF horns
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John Walsh
Film God
Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999
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posted 12-23-2003 01:16 AM
I noticed that at theaters our company had previously built, the high-frequency horns were usually poorly aimed. We mostly use the JBL 4675’s and the usual procedure to aim them is to look through the horn throat prior to installing the HF driver, and aim the horn at the center of the auditorium, 2/3’s to the rear of the seating area. When looking through the horn throat, the aperture is very narrow, but tall. This makes it easy to correctly position the horn left-to-right, but leaves a lot of room for error when tilting the horn up-down.
Whenever a new theater is in the process of being constructed, the trades really do want to do things the right way, but are pressed for time. I felt it could help if there was a tool to help them aim the HF horns. I had an idea using a laser, but I needed help making such a tool. I needed a machinist, who knew about lasers, and would understand about theater sound. Where would I find a specialist like that? Well, for once I had an easy answer; Greg Mueller of course!
I sent him a drawing I made, and in no time I had a working laser fixture, just in time for a new theater we were building. I had originally thought about just a sleeve I could put an Align-O-Tron into, but Greg went the extra mile and not only made the whole thing, but also put a battery and switch inside.
I added a lanyard so it could be hung around a person’s neck to leave their hands free. The boss on the laser end fits into the opening in the back of the horn. I would imagine this would fit any of the JBL horns that used the 2446 driver.
The rear of the HF horn before the driver is installed.
We set up a cardboard dude and placed him on the seat in the ideal location. One person would stand in the auditorium to warn away people, so they wouldn’t get “shot” and also tell the “aimer” where to move/tilt the horn. It’s hard to see when aiming; the large horn and the baffle wall block the view.
The 9v battery lasted the whole time; about 3 weeks of “turn on-turn off” use. So, a battery-operated Align-O-Tron or this “speaker Align-O” might be a good option. Greg already thought about turning down the face of Align-O-Trons to match different driver openings.
Obviously, this is not much good if the screen is already hung. I would think the holes in the screen might deflect the laser beam as it passed through, but I haven’t tried it. For new theaters, I felt it was well worth the time using this fixture; it made the job go quicker with more accuracy.
Many thanks to Greg for a very handy tool!
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John Walsh
Film God
Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999
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posted 12-26-2003 04:53 PM
I set up the laser and put some screen material in front. Although the light was reduced, it still seems like it will work, although having to take the drivers off would still be a major pain. I could make some kind of large fixture to hold the laser on the outside, but the baffle wall blocks much of the area. As with most of these kind of things, I'll have to wait until some special circumstances force me into designing a solution.
To hold the fixture up to the horn, we just wrapped the lanyard through the mounting hole on the top, above the holes for the driver. The boss could be extended more like a "tube" to stay in the throat, but the inside of the throat flares inward so the tube would have to be cut inward also.
THX wants the bass cabinets to be placed flush with the outside of the baffle wall, so you are forced to point them on the same plane. We usually curve any screen over apx. 30 ft wide, so the "faceting" of the baffle gets the bass cabinets generally pointing in the right direction.
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![[Cool]](cool.gif)
....we did something similar with a maglite and wooden plug for the horn and a clamp for small horns with existing drivers. The Laser set up would be more precise and work under a higher light level. Our "kit" did not solve the occaisonal paper safety cover on the opening of the driver that was not removed when the driver was bolted on by a rushed crew ![[Confused]](confused.gif)
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