Movie Theatre - Sound System Advice

[Norwalk Theatre]

Hello all!

My wife and I recently purchased the historic movie theatre in our town. The theatre was built in 1941 and is a brick/concrete art deco fortress (approximately 14k square feet). My goal is to get the (near) original sound system operational to determine if it is suitable for routine use.

The sound system is as follows:
1) The front consists of two RCA PL-301A (Ubangi?) units mounted at approximately 30 degrees to the auditorium (see line drawing). The cabinets are approximately 15' off the floor, and the dual horns are about 10' higher. All equipment is complete and in good condition. Things are (poorly) wired well enough currently to know that they work.
2) The center speaker is a third RCA PL-301A located in a "horn reverb space" (from blueprints). This area is is approximately 15' over the main stage, and is a 16' L x 9' D x 7' H concrete/brick box.
3) The two rear speakers are modern Peavey units mounted on the balcony rail.
4) The system is run by a Carver AV-405 Amplifier (5 Channel, Front 100W: 8 ohm, Center 110W: 8 Ohm, Rear 80 W, 8 Ohm) connected to a Rotel RSP-960AX Pre-Amp.

Specific questions for the experts:
1) The RCA units have the original MI-9597A Crossovers and two each of the MI-9472A Autoformers (all good condition). I would very much like some advice relative to an overall wiring diagram and specfically how to best connect to the amplifier. What taps on the autoformers are used? Any other tips to connect these units?
2) Any advice as to wire size/quality for the near 100' runs from the amp to the speakers?
3) Anything else that come to mind?

Thank you in advance!

Joe

[Lee in Montreal]

Will the equipment still be used to play movies? Old style flicks or the new stuff? I have no experience in setting an cinema system, but the usual rules do apply. Most likely the crossovers are getting old and are probably now out of specs. I'd check the condition of those woofers too. All being said, it would be interesting to contemplate a mix of old equipment and modern technology. Digital crossovers to take care o the splicing of drivers range and time alignment. You may want to add a few modern subs for modern movies. Also, I'd rather lay 100 feet of balanced XLR than speaker wires. Meaning you could have the power amps near the speakers and the crossovers/mixers are remotely. Great project you have here. Do not hesitate to keep us in the loop.

[hjames]

Interesting timing ... there is a guy on AK that is moving out in the country and needs to sell his 3 big theater system speakers ... JBL Model 4675a

No affiliation - never met the guy ... just read his posts ...

http://www.audiokarma.org/forums/sho...d.php?t=483993

[Mr. Widget]

Why do you want to continue using these vintage speakers? Is it nostalgia or economics?


Widget

[Lee in Montreal]

BTW, Eric from Ohio will literally give away 2360 horns (see my post from last week), which have a much better dispersion than those old Altec. He already shred and dumped a couple...

The Ubangi could be kept, with newer woofer. 2360 on top. Job done. The Altec horns and crossovers can probably be sold for good money to finance a few amps and crossovers.

[Norwalk Theatre]

All,

Thanks for the quick response. I knew there would be follow up questions!

My desire to hook up this system is both economic and nostaglic. We will not be going into the first-run movie business anytime soon. Our main interest is getting the theatre's stage up and running, and it would be nice to return the theatre's sound system to functionality in support of this. Everything is in place, and it only lacks some wiring at this point. Modern perfomance is not strictly required (at this time, at least). Also, the theatre was "built around" these units, and removing them would leave large, very-specifically shaped holes in the plaster.

I'd like to wire them them up to the existing equipment and see what I have, hence the request for crossover/autoformer wiring advice. If anyone can offer any suggestions, I'd appreciate (and follow) it.

There are some additional speaker mounting boxes in the front of theatre which were obviously added later. It's my plan to fill these with more modern speakers at a later date. I will certainly review the link sent in regards to this!

Joe

[Lee in Montreal]

Passive cross-overs have a finite life span. Once the capacitors' specs start shifting, it changes a lot of its original parameters. Basically, the system will most likley sound like sh.t... By the time you refurbish those cross-overs to close to original specs, you will realize you have spent more money than doing it with modern active crossovers and amps. If the sound is bad because the system is far from specs, you risk losing your audience. I have boycotted many cinemas because they had sub-par sound systems...

[Norwalk Theatre]

Lee,

I'll look into the more modern items suggested below.

Thanks for the advice!

Joe

[Lee in Montreal]

BTW Those Ubangi look great. There are a few fans on this forum. I am persuaded they will do the job.

[Earl K]

Hi Joe,
> Shoot Steve Schell a PM ( Private Message , assuming he's accepting them ) .

> Steve is a co-founder of this web-site and has always been crazy about old RCA stuff ( such as you have ) . He'll set you straight about the relative quality of the components that you've inherited .

> He even has some the old PhotoPhone (??? ) operators manuals ( & installers notes ) which detail the setup & wiring of these systems .

A couple of notes ;

(1) The horns & drivers ( if original ) are all made by RCA ( not Altec , I don't know where Lee contrived the Altec connection, considering he owns some JBL 2350s which were direct developments of these very same horns ) .

(2) Assuming all the drivers ( woofers & compression driver types ) work , I would strongly consider Lees good suggestion to update the system to some newer amps ( & crossovers ) all placed closer to the speakers and driven by line level signals originating from the projection booth .
- The older method of using Tube Amps feeding AutoTransformers that maintain a high impedance all the way to the speakers Passive Crossovers was necessary ( in the day ) when all pertinent stuff was located near the projectionist in the booth ( in case he needed to replace an amp tube during the run of a movie ) .
- This approach is archaic and really quite unnecessary with today's low-maintenance ( solid state ) amplifiers .


(3) I briefly looked at the drawing that you made ( detailing the horn coverage ) . It seems real odd to cross-shoot ( across the room ) and lose the "reach" of these horn loaded systems ( unless the acoustics of the place are soooo live that the horns were purposefully aimed away from the nearby walls to minimize exciting room reverb ) .
- That top tier horn would appear to be aimed only at an upper side walls ( which is only good for kicking off the room reverb , raising more questions ?? ) .
- If reverb times are indeed bad / I'd be treating the place with some acoustic treatments to bring down the RT60 times to something more reasonable ( once you have the money ) .

In summary , see if you can get Steve to add his 2 cents here .

[Lee in Montreal]

(1) The horns & drivers ( if original ) are all made by RCA ( not Altec , I don't know where Lee contrived the Altec connection, considering he owns some JBL 2350s which were direct developments of these very same horns ) .

He, he. You are 100% correct. I have no clue why I mentionned Altec. I think it probably was from doing some reading this morning on Altec stuff. Sorry about the misinformation.

[louped garouv]

a great project!

and great advice with respect to seeking out Mr Schell.....
and at the least investigating acoustic treatment ....

[Norwalk Theatre]

Earl,

That's the place! Nice find on the photo.

Will do on the PM. I can confirm that all the equipment is RCA, as I've been rooting around on them.

As to the front cabinets: your comment may explain why the cabinets are rotated in their niches to better face the auditorium. Looks like somebody manually pushed them to about 45 degrees. The 30 degrees I noted is the position they started in.

The speaker over the stage is a mystery. The room is clearly listed as "horn space" on the drawings, but it doesn't appear that the speaker was ever hooked up to the system (no wires). I wonder if it would be better to leave this unit out of the mix for now?

The entire auditorium (924 seats, 714 down, 210 up) has large art deco arches that are completely covered in acres of carpet (luckily in very good condition). We've been told by previous performers that the place has excellent acoustics. Certainly seems so.

Joe

[Lee in Montreal]

Hi Joe

To start acertaining the condition of your audio system, and get a feel of how it will sound, you could purchase a cheap $120 Behringer 2/3 way active crossover and a pair of power amps. That shall allow you to power up the Ubangis and mids.

iPod ---> mixer/preamp---> crossover ---> power amps ---> drivers.

Set a crossover frequency between 500 and 800Hz between Ubangis and mids. Then play with individual volumes. No need to get powerfull amps to do the tests. 100wpc on bass and 30 wpc on mids shall get you a good taste of thigs to come.

On the long run, you can get decent digital amps that weight nothing, stay cool all the time and of decent quality. I am sure you already have the basic kwoledge to do the tests and set your system up...

[Mike F]

That is quite the project you have going there! As previously mentioned, upgrading to modern amplification and signal processing and adding subwoofers would yield positive results.

Question for the members: Can the RCA cone and compression drivers be substituted for something more "expendable"?