Film-Tech Forum ARCHIVE: CP65 with mono surround channel

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Posted by Tom Wienholt (Member # 1510) on 12-12-2011, 06:03 PM:

I am installing 2 cp65's with no digital sound so split surrounds are not necessary. Can I just use the left or right surround output to feed all of the surrounds for a mono surround channel? This way I can avoid the need for an additional amp channel at this point.

Posted by Mitchell Dvoskin (Member # 751) on 12-12-2011, 06:21 PM:

No. The mono surround channel in analog Dolby stereo is 180 degrees out of phase between the front left and right. The processor removes the out of phase information from the front channels and moves it to the rear outputs.

Posted by Tony Bandiera Jr (Member # 2365) on 12-12-2011, 06:38 PM:

Bzzzzzttttt..wrong answer Donovan. (You are correct in what you said in that the surround information is ENCODED on the optical track out of phase, but the OUTPUT of the processor is IN PHASE with the rest of the speakers.)

You can most certainly use either output if you so desire, as the surround information for SR or A type, even though it is mono, is fed equally to both outputs. (With the CAT 441 card installed and it's jumper J3 set to stereo.) If the processors do NOT have the CAT 441 installed, you would use ONLY the LS output to feed a MONO surround array.

With digital, yes you can have phase and level differences which would result in some very odd results.

The question I have is why would you use only one of those outputs if you are NOT sure you're NEVER gonna add any digital or external 5.1 sources?

The smart move is to wire the surround array in stereo split up left and right and feed it with a stereo amp. Set the CAT 441 J3 jumper to stereo (don't worry, SR and A tracks will still output correctly) and that way you'll be future-ready.

Tom, the CP-65 Installation manual is available here on F-T, download and read it carefully before you install those CP-65's.

MANUAL LINKY

Posted by Mitchell Dvoskin (Member # 751) on 12-13-2011, 12:13 PM:

I never meant to imply that the surround output is out of phase with the front channels. That obviously would make for a bad sounding system. What I said was that the surround information is removed from the front channels and moved (in corrected phase) to the rear.

Who is Donovan?

Posted by Sam D. Chavez (Member # 1841) on 12-13-2011, 01:31 PM:

Regarding phase of surround speakers; it's pretty random as speaker brands are often different from front channels and no one can really hear the difference in phase relative to the front channels.

Not to say you should not strive to wire everything correctly.

Posted by Tony Bandiera Jr (Member # 2365) on 12-13-2011, 07:51 PM:

quote: Mitchell Dvoskin
..... What I said was that the surround information is removed from the front channels and moved (in corrected phase) to the rear.

Who is Donovan?

Donovan was my misinterpretation of your last name, by the time I caught it the edit time limit expired. [Big Grin]

And that was not what you said (might have been what you meant) but it most definitely not what you said:

quote:
No. The mono surround channel in analog Dolby stereo is 180 degrees out of phase between the front left and right. The processor removes the out of phase information from the front channels and moves it to the rear outputs.

What you wrote in bold was misleading and gave the impression that what Tom was asking could not be done. [thumbsup]