Auditorium Wiring

[Bill K]

I been given the assignment to select audio cables for a small auditorium. All wiring will go in the walls/ceiling and terminate in boxes with appropriate connectors. NEC CM type?

I would like recomendations on:

1. Two conductor overall shielded microphone cable. Low impedance.
2. Dual channel, individually shielded cable for stereo. (L&R) Line, high impedance. Preferably this should be a single cable. This cable will carry CD, DVD and the like to a central amp.

In both cases each total accumulative run will be 300-400 ft.
There are many selections in both Belden and Alpha and it appears dificult to pick a good candidate.

Would appreciate any help.

Bill K.

 

[jaxvon]

You might also want to check out Canare. They make some quality cable. Also, you may want to check into getting a microphone snake from Canare to handle multi-channel microphone needs. What are the flamability restrictions? CL2? CL3? Plenum?

 

[BMXTRIX]

Bill - You, first and foremost, need to be looking at balanced audio cable in any pro environment where you may not have full control of electrical noise. All cabling is almost definitely going to need to be plenum rated.

So, balanced XLR for microphones, balanced cable for analog sources - converted to balanced prior to sending them several hundred feet. It will eliminate noise issues and provide a much cleaner signal.

Liberty and Belden both make excellent cables, but the type of cabling is much less important than putting a good signal down that cable that will be received clean. Shielding won't do it on an unbalanced line.

 

[Bill K]

Thanks for the quick responses.

The mike line is balanced and XLR.

The hard one is the unbalanced stereo line it starts out with and RCA jack on one end and an RCA jack on the other. I had intended to use unbalanced line for this. I will have approx 300' of this line in the walls/ceiling.

BMXTRIX suggestes this connecting line be balanced. How is this accomplished? Use 1:1 ratio transformers at each end? (10K impedance?) Will losses in the xfmrs require an active bost (preamp?) Is the effort worth the results?
I note that folks are using coax for this service. Good approach?
BTW in case there is concern this is not a commercial endeavor. I am volunteering my time to our Civic Association.

Bill K.

 

[jaxvon]

RCA Inputs? Well, this maybe a lil ignorant, but usually when you want to convert an unbalanced signal (many times high-z), one would use a direct box, or a rack mounted unit that can convert multiple signals. Since you're going to be running all balanced anyway, I'd just go for a snake with as many channels as you need. That'll allow you to have one cable for everything. Of course, I'm not up to speed on which snake models from the manufacturers are plenum rated.

 

[Bill K]

Donald:

Let me give you the rest of the story.
We have an A/V cart loaded with a CD and DVD, player, Karoke, etc. and a nice LCD projector for movies. Audio out of the cart is line level stereo, RCA jack, high impedance. This inputs to a Sony receiver with a Dolby/surround sound processor. Now according to the placment of the cart in the room it will be connected to one of 4 wall jacks. This amounts to 300 feet of unbalanced stero cable going back to the Sony.
I am looking for recomendations on two conductor individually shielded cable or a cheap way to convert from unbalanced to balance. It will take a bunch of transformers (stereo you know) and my search says this will be quite expensive. There you have it. Any ideas?

Bill K.