Film-Tech Forum ARCHIVE: Need Suggestion regarding Stereo System using CP45

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Posted by Demetris Thoupis (Member # 833) on 04-08-2009, 02:15 PM:

I have a request from a small village at a sound upgrade and I would like to hear peoples' opinion on the following. The cinema has no budget for a full Surround system and I don't want to use a conventional home theater amp with mixer. I have a few CP45 to spare and I was thinking of using the CP45 Left/Centre/Right outputs to a preamp mixer and pan the left channel to the left output, the right channel to the right and the centre channel to both and the outputs to go to either two active speakers or passive speakers via separate amp. I believe the configuration will work but my worry is will I have too much delay of the sound reaching the speakers and have lipsync problems? The mixer pre/amp considered is a PR4092 from Italy company RCF which has balanced inputs and outputs. What do you people think?
Demetris

Posted by Joe Tommassello (Member # 4632) on 04-08-2009, 02:31 PM:

Maybe I am over simplifying this but wouldn't you get a similar effect from just taking the signal from your sound reader, pre-amping it and using a stereo amplifier or receiver as a power amp to the two speakers? You might also want to use an equalizer to adjust for the loss of noise reduction. Hardly a professional setup but surely an economical way to get a similar effect. Other more technical advice is surely imminent.

Posted by Demetris Thoupis (Member # 833) on 04-08-2009, 02:37 PM:

I want to use something decent for noise reduction that is why I want to pass it via the CP45.
Demetris

Posted by Marin Zorica (Member # 1716) on 04-08-2009, 03:10 PM:

CAT 222SR/A [Razz]

Well....you might try to pass decoder, just take Lt and Rt signal after cat 222?

I think it would be much better than mixing C to L&R, and because of decoding and phase difference you might get bad sound in that, use stereo only from CP!

Posted by Brian Guckian (Member # 1678) on 04-08-2009, 05:21 PM:

Is the idea for two channels purely for cost reasons, Demetris?

If so you could push for just L/C/R. Otherwise it might actually be worth sticking with good old fashioned Mono, on the basis of that being better than a compromised stereo setup.

Also..."the cinema has no budget"...to quote Obi Wan in Star Wars, "that's what your uncle told you"! Surely they could do L/C/R only with one of your CP45s and some appropriate reconditioned speakers and amplifiers?

Posted by Louis Bornwasser (Member # 3063) on 04-08-2009, 06:45 PM:

Should work fine; only problem is the delay on voice from two point sources. You'll know right away; voices will be hard to understand unless you are in the center seat. Louis

Posted by Kenneth Wuepper (Member # 1174) on 04-08-2009, 07:59 PM:

Demetris,

Try this in one of your other working screens:

Turn off the center channel and surround amplifiers.
Listen to a known section of film with just the L & R channels.
You will notice that it is like the old disco recordings played through the solo removal box and the center channel information is gone.
Reverse the phase of one of the channels, L or R.
Notice that now there seems to be a phantom center channel?

This is not a good way to operate, it is cheap and dirty sound. The center channel caries the dialog and without it there is no story.

KEN

Posted by Demetris Thoupis (Member # 833) on 04-09-2009, 03:12 AM:

Playing a system out of phase really isn't ideal is it! [Big Grin]

Posted by Tony Bandiera Jr (Member # 2365) on 04-09-2009, 01:52 PM:

Guys, while the replys so far are very true in what you all are saying, it seems as though you didn't read the opening post carefully and understand the setup:

Outputs of Left, Center and Right of CP-45 to go to a mixer;
Mixer will output Left and right to speakers behind the screen;
The outputs of the CP-45 will be assigned as follows, using the mixer:

Left to Left;
Right to Right;
CENTER will Be sent equally to Left AND Right.

Will there be delay/lip synch issues? NO.
Phase issues? NO, unless he connects one of the speakers backwards
Dialog intelligibility issues? Slight. This is not an optimum set up but it WILL work well, I have done it several times on temp shows with no ill effects.

Some important things to do though:

Both speakers MUST be placed EXACTLY with their faces on the same plane (or line if you prefer) as if one is even slightly forward or back from the other things can get a bit weird;

Bot speakers MUST be the exact same make and model, and the gain (level) from each speaker MUST be the same within 1dB or less;

If the auditorium is wide it would help a bit to toe each speaker in toward the center slightly while maintaining alignment in the same plane;

Most importantly; set the CENTER channel output of the CP-45 to 3-4dB HIGHER than Left and Right, and make sure that gain follows thru the mix to the output.

As pointed out, this is NOT an optimal setup but in can and will work well until the theatre can upgrade and get the dedicated center channel speaker and amp.

Martin, taking the Lt and Rt signals WILL have the phase and decoding (or lack of) issues that you speak of...if the OUTPUTS of L,C,R are taken from a PROPERLY aligned (A and B chain wise) processor there better NOT be any phase or delay issues or the processor has issues!

Remember, like Ken pointed out and you all should know by now, even in optical the decoder matrix in the processor strips virtually all of the center channel information from the Left and Right outputs, that's why you would not be able to hear the dialog if you just ran Left and Right outputs from a processor.

Posted by Louis Bornwasser (Member # 3063) on 04-09-2009, 08:22 PM:

This is a standard "condition" in drive in theatres.

If you take any mono signal, especially dialog, and send it to 2 sources, you will have articulation issues if the path lengths are not the same. This is why old style church/school P.A. systems with a speaker on each side are so hard to understand. So it will be with your system.

It will sound "good;" but will be hard to understand, especially if you don't lip read. Louis

Posted by Kenneth Wuepper (Member # 1174) on 04-09-2009, 10:33 PM:

Demetris,

Since we all seem to agree that the center channel is most important, how about this idea?

Take the center output to a center channel amplifier and speaker. Now we have dialog as it needs to be. Then take the left and right channels and wye them together into a second amplifier and speaker. Now the compromise is in the left & right channel sounds rather than the dialog in the center.

Save the mixer expense altogether.

KEN

Posted by Demetris Thoupis (Member # 833) on 04-10-2009, 03:28 AM:

Actually I seen the application I suggest done at a Drive In theater with a CP500 and the signal was routed to the mixer with the configuration I mention above and then to an FM transmitter and we had no problems. Considering this is a village at the mountains with 200 sear capacity and only to be used for childrens shows and some festivals. I have an open air cinema which is free for use and I might pop there and do some testing with the system and see or rather hear how it sounds.
Demetris

Posted by Demetris Thoupis (Member # 833) on 05-01-2009, 12:51 AM:

Ok guys, it's been a while so I made several tests and actually did put this in a small village cinema. A 200 seater with a decent upgrade. The real trick to get this right is that you need to have the same EQ on the CP45 for all screen channels exactly the same. 300mV if I remember correctly was the output set on each channel from the CP45 and then down to the stereo mixer as I described before. I saw or rather heard no lypsinc problem during projection of various films and trailers throughout. The clients are so pleased they are thinking of adding a subwoofer in the near days which shows that they really liked the improvement. They also have received great comments from the clients about sound improvement (hey it's better than 100V line speakers right!!) When I was doing my tests in the open air cinema I refered in a previous post, I tried to bypass the CP45EQ and passed it through an external EQ after the stereo mixer. Unfortunately there was lipsync problems so I stayed with the original solution I suggested. It worked out fine and I believe that if you people run some kinds of festivals here and there and need a decent sound with 2 speakers this is the way to go.
Demetris