Film-Tech Forum ARCHIVE: Best way to split processor outputs?

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Posted by Freddie Dobbs (Member # 915) on 01-20-2003, 05:53 PM:

I have a project where I need to "split" the outputs from a 650 processors and send each signal to a separate amp for example LEFT to amp 1 and to amp 2, CENTER to amp 3 and to amp 4. Has any one had to do this before? Any ideas? Thanks

Posted by Richard Fowler (Member # 893) on 01-20-2003, 06:09 PM:

Providing that they are the same model of amplifier the impedance problem to go to two inputs should be nil within the same rack.
Richard Fowler
Kinoton America Inc.

Posted by Greg Pauley (Member # 503) on 01-20-2003, 08:12 PM:

Hey Freddie!

I've done this on the surround channel so a seperate amp can drive the balcony surround without any problems.

Posted by Steve Guttag (Member # 268) on 01-20-2003, 09:45 PM:

Depending on your needs (as in just why they are broken up), there are different ways of doing this.

A CP-650 has a low impedance balanced output so it should drive a typical balanced input quite well, even in pairs. However, if you have one amp nearby and the other is down the hall a ways, then you should consider a DA (Distribution amp) or something like the OXMOOR 4x4.

The Oxmoor is kinda nifty since you get adjustable line amps, and summing/combining capabilities. Optional output transformers can eliminate ground loop issues and keep the two systems separate.

Oxmoor 4x4T

Now if you have the system like where you have a balcony and stall section...you can use something like the RANE RPM-26Z. It is a 2 x 6 DSP processor. This will allow you to tune each section separately for the best performance from each. The RANE has both digital (AES3) and analog inputs with analog outputs.

http://www.rane.com/rpm26z.html

So you see...the best solution really depends on what your design requires.

Steve

Posted by Freddie Dobbs (Member # 915) on 01-22-2003, 07:39 PM:

Sorry, I guess stating the specifics would have been better, What I need to do is feed L,C,R,Ls,Rs from a sound system that used a 650, DCM and QSC amps to a mixer for a private viewing booth. Looks like one of the first problems is the EQ. Does the Rane mixer have pots or controls that would affect the output of the 650 to the EQ? I’m not fond of adding another place to control levels, I believe keeping it simple would be the best way.

Posted by Jon Bartow (Member # 241) on 01-22-2003, 08:26 PM:

What exactly are you trying to do? Is this for a private seating area (VIP or something?) or just for employees or a baby "cry" room or what?
Are you going for just "sound" in this room(i.e. so people can hear and follow along)? Or are you going for the full blown "5.1" sound in this room?
Just splitting all processor outputs and running them to another set of amps for another room that is not exactly identical would yield very poor results (ok, it would sound like crap).

Posted by Gordon McLeod (Member # 33) on 01-22-2003, 08:31 PM:

The cp650 has a HI output feed that into the viewing roo

Posted by Freddie Dobbs (Member # 915) on 01-25-2003, 03:47 PM:

Jon,
It is a VIP room, that will be a 5 channel, no sub, I curious way yoou say splitting the processor outputs would cause it to sound like crap? If the processor is flatlined and the signal is split to eq's then amps there should be no problem, am I missing something?

Posted by Jon Bartow (Member # 241) on 01-25-2003, 04:53 PM:

Freddie,
Yes, that is exactly what you will need to do. All processor eq settings set to flat and output levels set for 300mv. Then a seperate set of eq's and amps for each room. Note that the master fader will affect the volume in both rooms. However, if the system is set up properly then this should not be a problem. How far away will the second set of eq/amps be? If fairly close (say less than 50 feet) then you should be fine to just split the signals. But as has been said, if farther away use a spliiter/distribution amp. also, using the same type of eq' and amps will help to eliminate potential problems.

I meant that the room would sound like crap if you used only the eq in the processor for both rooms. [Eek!]

Posted by Steve Guttag (Member # 268) on 01-26-2003, 10:37 AM:

If you really want to be slick then...go with 3 RANE RPM-26Z units. They have an AES3 input in addition to the analog inputs...get the Cat. 778 board for your CP-650 so it has AES3 outputs (keeps it in the digital domain).

Use the RANE RPM-26Z to have the two separate zones for output (even different surround delays for the two rooms). The RANE will let you add EQ and even crossover functions, if desired (you'll have an extra set of outputs on each unit since it is a 2 x 6 DSP). You will even be able to trim each output independantly to balance it all out. I believe you can even assign a remove volume control for the VIP room though I don't know if you can have one control for all three units....but maybe. I'd download the software and give it a look see to see if it would be appropriate for you installation.

If you don't have the DCM yet, you can use the RANEs to eliminate it for the crossover and then get something like the Panastereo booth monitor or the USL CM-680 to knock the costs down. I'm not trying to knock the DCM, just that if you go with the RANEs you will have the ouputs available to you. The RANE stuff is certainly more flexible.

Steve

Posted by Ray Derrick (Member # 1001) on 01-28-2003, 06:09 AM:

As usual, Steve G has posted an elegant solution to the original problem.

As a related point of interest, there are a couple of rules that can generally be applied to connecting multiple audio inputs and outputs. Most modern professional audio equipment has a high input impedance (typically 10-30 thousand ohms) and a very low output impedanace (typically 50-100 ohms). This provides the most efficient way to convey an audio signal between items of equipment, as the low output impedance serves as a sink for noise picked up by the cable and ensures that any cable resistance, capacitance and inductance has very little effect on the signal.

So, subject to some qualifications to follow,

Rule #1 is: You can connect a single output to a number of inputs without any significant degradation of the signal, provided the total parallel impedance of all the inputs is no lower than about 600ohms. So if the inputs were all 10K each you could theoretically hang up to sixteen inputs off a single output.

Rule #2 You can only connect one output to any given input. As each output acts as a sink to any other output(s), if you connect more than one output to an input, you will usually get very little signal, greatly increased noise and distortion, not to mention the possibility of some blown output stages.

Now here are some qualifications:

1. Balanced lines work best with just one input and one output connected.

2. The majority of home audio equipment has a much higher output impedance (typically around 1kHz). Whilst the audio transfer is far less efficient, it does allow uneducated, non-professionals (otherwise known as audiophiles [Smile]

) to connect two outputs to one input without destroying their sound, or their equipment.

3. Early Dolby cinema processors have a switchable Hi/Lo L-pad at the outputs which, if set to the Lo position, significantly raises the output impedance. Unless you have a very good reason to do otherwise, I would recommend always running this pad in the Hi position for best performance.

Posted by Ray Derrick (Member # 1001) on 01-28-2003, 06:48 AM:

No sooner had I posted the above than I had visions of hundreds of projectionists around the globe running around behind their CP-whatevers throwing the output pad swithes to the Hi position. If you have read the above and are contemplating this... PLEASE DON'T. It will also boost the output level from the processor and maybe blow up your speaker system. It must be done by a tech equipped with an analyser.

(Woops [eyes]

)