Film-Tech Forum ARCHIVE: Video Projector Sound Amplification

This is topic Video Projector Sound Amplification in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Robert E. Allen (Member # 1351) on 04-19-2014, 10:18 AM:

I want to use a consumer grade video projector in my small auditorium. But I have to crank the volume on my CP55 to it's max to get fairly decent sound. Is there a pre-amp or some other unit I can attach to it to give me better sound control?

Posted by Steve Guttag (Member # 268) on 04-19-2014, 10:46 AM:

Are you running any film in your theatre at this point? If not, then consider going prosumer all of the way...something like the Onkyo PR-SC5509P to do all of your video switching, sound decoding and then feed that to your projector.

http://www.onkyousa.com/Products/model.php?m=PR-SC5509&class=Preamplifier

It has both RCA and XLR outputs to feed whatever amplifiers you already have.

Posted by Robert E. Allen (Member # 1351) on 04-19-2014, 08:30 PM:

Thanks Steve. Both auditoriums are running film.

Bob

Posted by Brad Miller (Member # 2) on 04-19-2014, 08:58 PM:

Robert, are you going in through the non-sync inputs? There is a trim to adjust that. (I believe you have CP55s if I recall.)

Posted by Scott Norwood (Member # 30) on 04-20-2014, 07:48 AM:

Sort of off topic, but what video projector did you get and are you happy with the picture? (Assuming that this is the same situation that was discussed in another thread a month or so ago.)

Posted by Robert E. Allen (Member # 1351) on 04-20-2014, 03:37 PM:

Brad: It' being run through the axillary input. Yes, it's CP55. Scott: It's an Infocus and the picture is satisfactory. Better in the small auditorium than in the large. (22' vs 12')

Bob

Posted by Leo Enticknap (Member # 534) on 04-20-2014, 11:16 PM:

I once had to connect a laserdisc player (which will give you an idea of how long ago this was!) into the aux input of a CP45, and if I remember correctly I had to increase the aux gain quite a bit to get an acceptable level.

Posted by Stephen Furley (Member # 1277) on 04-21-2014, 05:00 AM:

The audio level on Laserdisc varies considerably from disc to disc, particularly with older discs.

I've run Laserdisc in a cinema not that many years ago. If the content is black and white, 3:4 aspect ratio and originated on video then it's not a bad way to do it, certainly better than the VHS tape which we were offered when we booked it.

Also once had to set up a player for a demo by a company which made or sold either players or discs, I can't remember the exact details now, but this was in the early days of multi-channel sound. We had to be able to play any type of sound from both PAL and NTSC discs. Early PAL discs had two channels of analogue sound, which were delivered on analogue outputs. On later discs there were replaced by two digital channels delivered on a S/Pdif output. PAL discs couldn't have both. NTSC discs were similar, but could have both types of tracks on the same disc. On discs with digital sound the analogue ones were often used to carry a different sound, such as a director's commentary, a very new idea then.

Then it starts to get complicated. Both Dolby Digital (ac-3) and DTS tracks were introduced, but only on some NTSC discs and in different ways. The DTS tracks, which few discs had, simply replaced the normal 2-channel PCM ones, so they were delivered on the normal S/Pdif output, and you then needed to put them through a domestic type DTS decoder. The Dolby digital tracks were recorfrf differently; the Dolby bitstream was modulated onto an RF carrier, and this was then recorded in place of the right channel analogue signal. To play this you needed a minor modification to the player to extract this signal before it received any analogue processing, then a demodulator to convert it to a standard S/Pdif signal, then feed this into a Dolby ac-3 decoder which finally gave you the six channel analogue signals. Few players had any of this built in, and neither did the older, as at the time that we had to do this demo, home cinema amplifiers. We needed a large pile of equipment to run this demo, but it did all work. If I remember correctly it was all eventually put through a CP-200.

PAL discs couldn't have DTS tracks because since they couldn't have analogue tracks as well they would be unplayable on non-DTS systems. They couldn't have Dolby Digital tracks either, since these required giving up the right analogue track, and PAL discs could not have both analogue and digital tracks. I think there was also some technical reason to do with the different RF carrier frequencies used on PAL discs.

It all worked, but was far too complicated, and expensive, for a domestic system. Not long after this DVD was introduced, and quite quickly replaced Laserdisc.

After the demo all of the equipment was donated to me. I still have both the player and the demodulator, but not the ac-3 or DTS decoders. The Dolby signal could go into a DMA now. I would have no way of playing DTS, but I might one day take the player, demodulator and a few discs in to see how it looks today on a proper digital cinema projector, something which didn't exist when the original demo was done; it used a conventional video projector, but a much more expensive one than anybody would be likely to have at home. Given that they were composite video, and with a very few exceptions widescreen films were letterboxed within 3:4 they wouldn't look so good today, but at the time they were by far the best format you could have at home. On the best examples the sound could be very good, but the picture really wasn't up to cinema use.

Posted by Gary Wachter (Member # 5833) on 04-22-2014, 12:03 PM:

You may need to raise the -10db consumer output to pro levels. The most common way is to use a Henry Matchbox http://www.henryeng.com/matchbox.html. They are under $250 new and around $50 on eBay.

Posted by Louis Bornwasser (Member # 3063) on 04-22-2014, 03:33 PM:

He has cp-55.

They are mostly the same as a cp-65. I will have to look, but on the 65, you can reverse a plug in header on the back plane or maybe on a board to get more gain on certain inputs.

Posted by Leo Enticknap (Member # 534) on 04-23-2014, 12:03 AM:

quote: Stephen Furley
Given that they were composite video, and with a very few exceptions widescreen films were letterboxed within 3:4 they wouldn't look so good today, but at the time they were by far the best format you could have at home. On the best examples the sound could be very good, but the picture really wasn't up to cinema use.

I showed quite a few laserdiscs at various City Screen sites in the late '90s, usually of rep titles and in situations where either no film print was available at all, the only print available was completely knackered, or only 16mm was available and the show had to take place in an auditorium that didn't have 16mm projection.

Agreed: they were one hell of an improvement on VHS, but the subjective viewing experience (for me, at any rate) was nowhere close to even a so-so 35mm print. It would be interesting to see what one looks like through one of today's DLP projectors, though. And yes, the DVD killed that format, almost overnight. I remember reading somewhere that Bringing Out the Dead was the final Hollywood movie to be published on LD, and that was in 2000. At that point (in Britain at any rate), only wealthy, early adopters (of consumer gadgets) had DVD players, but even at that early stage the format's success had convinced Hollywood that the laserdisc was finished.