Film-Tech Forum ARCHIVE: The "Door" on Sound Heads

This is topic The "Door" on Sound Heads in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Dean Kollet (Member # 1789) on 01-12-2005, 12:30 PM:

I was wondering what the reason if for the door on soundheads, more specifically the Simplex 5-Star. I've run shows with it open and closed in both Analog and Digital (basement reader) and I didn't notice a difference. The rest of the projector and film path is opened, why would they close this? I'm guessing it's some weird engineering theory, but I guess my question if why?

Posted by Michael Schaffer (Member # 1204) on 01-12-2005, 12:37 PM:

It is indeed a very weird engineering theory behind that: to keep as much dust and dirt out as possible. Most older projectors had closed film compartments as well, not a bad idea as such. In the olden days, fire safety probably played a role too.

Posted by Mike Blakesley (Member # 26) on 01-12-2005, 12:37 PM:

- Keep dust out
- Make it look nice

Plus in the old days of flammable film, there were probably fire prevention issues.

Posted by Chris Hipp (Member # 1788) on 01-12-2005, 01:51 PM:

It could alos be to help keep out extraneous light. Run a loop through it someday and shine a flashlight and see what it sounds like. Of course a properly designed booth will not have lighting in front of the port window while the movie is running anyway so it doesnt really help.

Posted by Thomas Procyk (Member # 1170) on 01-12-2005, 02:05 PM:

But the door on the Simplex 5-Star has a clear plexiglass "window" on it. So if its job is to contain fire, it fails, and if its job is to keep light out, it fails.

I close all the "doors" whether on the projector head or soundhead, just because it looks nice and I always have that feeling that exposed moving parts are better when contained. Hate to have someone with long hair or a "required" tie sweeping around the machine... [uhoh]

=TMP=

Posted by Randy Stankey (Member # 64) on 01-12-2005, 02:17 PM:

Some older model projector heads like Century, Simplex, et. al. have doors too. Since you can mount an older sound head onto a newer model projector, it would make sense that the sound head has a door.

Keeping the door shut on the sound head keeps out a lot of stray light. Now that we have red light/electronic readers that's not so much of an issue. However, when solar cells were in use, a fluorescent light shining on the sound head could REALLY mess up the sound!

Open the door on an older (solar cell) sound head and flick a cigarette lighter in front of the cell, if you want to try a test. You'll hear a loud, "POP!!" in the speakers! [Eek!]

Most people who use electronic red readers and have never seen a solar cell would never consider problems like that. I guess it's one of those things you don't think about unless you've had to deal it before.

Posted by Stephen Furley (Member # 1277) on 01-12-2005, 02:52 PM:

quote: Thomas Procyk
But the door on the Simplex 5-Star has a clear plexiglass "window" on it. So if its job is to contain fire, it fails, and if its job is to keep light out, it fails.

I don't know what a 5-star sound head is, but if it's got a plexiglass, or similar, window in it then either it's something fairly modern, i.e. post nitrate (ok, it could still be about 50 years old!), or the original glass has been replaced. Given that few soundheads from the nitrate era are still in use today, I would guess that it's a modernised version of an old design, and thick, wired glass was no longer considered necessary.

Posted by John Hegel (Member # 628) on 01-12-2005, 04:11 PM:

On really old equipment, before solar cells, could it have helped with the tubes that were used for audio pick-up?

The tube pick-up that I found in our theater has huge optical area. I'm thinking it had to have been 1x3".

Posted by Stephen Furley (Member # 1277) on 01-12-2005, 04:37 PM:

quote: John Hegel
On really old equipment, before solar cells, could it have helped with the tubes that were used for audio pick-up?

Yes, and the old glass photocells were in use not that long ago. Quite a few places still had them until they converted to Dolby Stereo, and I seem to remember that Scott Norwood was asking recently about converting a pair of universal bases to read cyan tracks. I assume that these machines still have them.

Posted by Leo Enticknap (Member # 534) on 01-12-2005, 05:15 PM:

The most widespread fire prevention device on projector operating sides was the combination of an enclosed spool magazine and film cutting device where the film was pulled into or out of it. The cutters were so that if film in the feed spool ignited, the fire wouldn't then spread to the take-up magazine (and vice-versa).

Remember, you cannot prevent or arrest a nitrate fire by removing the oxygen supply (i.e. housing film in an airtight enclosure), because the combustion process generates its own oxygen. So whatever the reason was for enclosing projector mechs and soundheads, it wasn't nitrate fire safety. My guess would be noise suppression and/or keeping dust out. There are some mechanisms, e.g. the GK-19, which have safety magazines but the rest of the mechanism open.

Some earlier spool magazines were airtight (or very nearly so), and if the film within caught fire, the rapidly expanding combustion gases would usually cause them to explode. That's why, from the late '20s onwards, you started to see spool magazines with tapered lips facing away from the operator's side, to allow a film fire to burn itself out in a controlled way and with the smoke and flames directed away from the projectionist. Of course if this did happen you wouldn't want to stay around - one or two deep breaths of those nitric acid fumes and your lungs would be like you'd smoked 80 a day all your life - but it did buy you the time needed to get safely clear.

Posted by Ken Layton (Member # 133) on 01-12-2005, 05:26 PM:

I believe at one time the door was required for Underwriter's Laboratories approval.

Posted by Mike Blakesley (Member # 26) on 01-12-2005, 05:43 PM:

quote: Stephen Furley
I don't know what a 5-star sound head is, but if it's got a plexiglass, or similar, window in it then either it's something fairly modern, i.e. post nitrate (ok, it could still be about 50 years old!), or the original glass has been replaced.

We have a 5-star, purchased new in 1980. It came with a plexiglass window in the door (as did the Simplex projector). I always figured that the door was an old design, but the plexiglass was a newfangled post-nitrate feature.

Posted by Dean Kollet (Member # 1789) on 01-12-2005, 06:04 PM:

So besides fire prevention for Nitrate films, the really isn't a reason for it. I've seen booths running 5-Stars without the door attached and they all seemed fine. I'm guessing it just evolved into an asthetic thing then.

Posted by Chris Trainor (Member # 9) on 01-12-2005, 06:49 PM:

The door wasn't really to prevent nitrate fires, but to prevent the fire inside from getting outside. Little bits of burning film could've easilly fallen out of the projector onto the floor, etc if there wern't any doors. Also back in those days the operators were in the booth while the film was running, so it kept burning pieces of non-extinguishable film from landing on them too.

--Chris

Posted by Bruce Hansen (Member # 281) on 01-12-2005, 06:52 PM:

BTW: the LED readers still use solar cells to convert the light into an electrical siginal.

Posted by Monte L Fullmer (Member # 2797) on 01-12-2005, 08:05 PM:

..yet kinda funny seeing that pic in the "picture warehouse" in this site, of a machine in 1975, that had a nitrate fire which travelled up to the upper magazine and cooked everything from the machine (an XL setup without magnetic penthouse) on up. And this setup had the firetrap rollers in the upper magazine and prob the magazine door was even closed.

This really makes one wonder if these safety devices really worked or not.

Going back to the Simplex "5-star" head: We can remember the SH-1000,("4-star") head with that stud mounted in the middle in the inside of the door, when the scanner drum lateral roller wasn't closed, the soundhead door could be shut as well.

Old picts that I've seen of nitrate days: sand buckets, carbon tetrochloride filled glass bottle extinguishers, port hole shutters with lead chain breaks, film cabinets in separate rooms away from from the machinery, plus, operators with fire department approved licenses.

Lotsa fun - Monte

Posted by Randy Stankey (Member # 64) on 01-12-2005, 08:44 PM:

I thought modern electronic red light readers used CCD chips, not CdS solar cells so that the CCD can be tuned to respond only (or chiefly) to the wavelength of light emitted by the LED.

Is this not right?

Posted by Steve Guttag (Member # 268) on 01-12-2005, 09:36 PM:

This topic has generated this much discussion? [Roll Eyes]

Older Simplex soundheads (SH-10XX) had a much smaller window and indeed part of the door's job was to keep the light out of the optics (mirror too) as well as for nitrate reasons.

When the 5-star was introduced, the door did not have the plexiglass openening that we see today...it was a solid piece of cast aluminum.

The opening appeared later.

Remember the 5-star may be mated with a PR-1014, PR1020, PR-1030 projectors...all of which have doors on the projector themselves. The doors provide a degree of cleanliness and sound isolation. For those installations where the projector has a door, the soundhead should have a door.

I would say that for a turreted machine that does not have a door, the door on the soundhead is mostly superfelous. I know many operators that have removed them from both Simplex and Century soundheads.

Steve

[ 01-13-2005, 07:43 AM: Message edited by: Steve Guttag ]

Posted by Frank Angel (Member # 248) on 01-13-2005, 02:29 AM:

I can understand why one would ask how come the soundhead has a door when the turret head is opened....basically doorless. But now I have ask, why would anyone take the time and go through the trouble of actually removing the soundhead door that's already there? What does THAT accomplish? I mean, you've got find the time to dismantle it and then find a place to put it, which is usually going to wind up in the spare parts cabinet right? So now you've got a door sitting in a cabinet taking up room that everyone know is way too limited in the first place, so now you've got this THING sitting there for no good reason when it had it proper storage space ON the soundhead not getting in anyone's way! Am I right?

(Can this thread get any more Seinfieldian?).

Posted by Leo Enticknap (Member # 534) on 01-13-2005, 04:22 AM:

quote: Monte L Fullmer
..yet kinda funny seeing that pic in the "picture warehouse" in this site, of a machine in 1975, that had a nitrate fire which travelled up to the upper magazine and cooked everything from the machine (an XL setup without magnetic penthouse) on up. And this setup had the firetrap rollers in the upper magazine and prob the magazine door was even closed.

This really makes one wonder if these safety devices really worked or not.

As Chris pointed out, the reason for the traps and magazines was to contain the fire and prevent it from spreading beyond the affected projector. So if only that projector was cooked and the projectionists got out unhurt, they worked.

The main safety regs in Britain (which were introduced in the 1909 act and theoretically still apply to any theatre licensed to show nitrate) are that the booth must have two separate exists, one of which must lead directly to the exterior of the building (in our case one of these is a large ground floor window); safety shutters on the portholes and a 'rewind room' separated by a fire door from the main booth, in which most film is stored. Only the reels being carried to and from the projectors should be in the booth itself. We follow exactly the same principle in our archive workroom: we don't allow any more than 5,000 feet to be present in there at any one time (and only that much very rarely, e.g. when we're comparing two or three elements side by side for technical selection). The rest stays in the vault.

The idea is that you can only stop a nitrate fire by not allowing it to get started. If for whatever reason it does get started, all you can do is to let it burn, but manage the situation so as to minimise the risk and damage caused by the fire.