I'm making a snake for intercoms when doing organ recording. I'm going to have a 50 meter 4ch snake for the main mics, but I want talkback to the organist so I was thinking maybe I should do a dedicated snake for that. Here's what I thought of so far.

What do I need?
1 ch loudspeaker for overall talkback
1 ch mic for the organist's talkback to me
2 ch for organist stereo headphones

Feel free to expand this for me! I was thinking that maybe sometimes it'd be useful to have two mic channels for organist's monitoring when doing organ + tape concerts and using close mics for the monitoring. I could use the channel for the loudspeaker of course.

I was looking at either using the same 4ch sommer cable I have for the mics now, or using a sommer cable that also carries power for the loudspeaker. Advantage: I can use it where the churches lack easily accessed power next to the organ. Disadvantage: it's expensive as all h*ck. Like 590€ compared to 150€ for just audio. Money's not really a problem, but that's a bit on the extravagant side, yes?

Couple of quick comments-
If you're planning to do more than chamber music (groups with conductors) you will want a telephone as well as a talkback speaker (For those comments that you don't want the orchestra as a whole to hear...). The final option is for a red light/green light system. Each of these takes a shielded twisted pair (Not common ground!!!).
Out standard communication package includes Talkback, Telephone and Redlight. Studio program feed is normally carried in the audio snake, but there is no reason to not put it in the communication snake if you have the capacity.
As to the lack of electricity near the console, we have 2 solutions. First is a small speaker with a built in 5 watt amplifier that runs on +9 to 20vdc. You can buy these in kit form from a whole bunch of sites on the internet. We actually switch the power along with the single ended audio so there isn't current running in the line except when we are talking. (We do this with a pair of relay's in the talkback unit itself). The other way to do it is with a battery powered speaker, but these are typically wimpy sounding and have trouble getting over the noise in the hall.

All the best,
-mark

Why not just buy an inexpensive 50' (15m) "standard" audio snake (like: Hosa Technology | SH 8X0 25 8-Channel Sub Snake | SH-8X0-25)... sorry... that was a 25' (8m) snake... dedicate channels 1-4 as mic sends to you (if you're concerned about the quality of the cable, order 8- or 12-pair Mogami and build your own... soldering connectors is a skill you need, if you haven't already acquired it) and the other four as dedicated talkback/handset/AC or DC power. Change out the connectors if you are concerned your markings won't be adequate (XLRF panel jacks for comms at the box; XLRM-4 for Ac or DC power; etc) and be done with it.

FWIW, I just built a 16x3 passive split from an abandoned fan-less Rapco stage box (cut down to about 35 feet/10m) and some surplus (it helps to have a friend in the audio installation business) 8-pair cable. Appropriate connectors (line and panel), strain relief, shrink... my total out-of-pocket was somewhere around $120, and my time investment was 6 or 7 hours, mostly spent waiting for video projects to render. That's $45 more than it cost to rent a "professional" passive box with massive multi-con connectors (to allow the company to supply 5m/10m/25m/50m I/O as needed) for ONE night ($75). It was a nice split... but it wasn't THAT nice. Since I built it, I've billed rental to one client three times at $30. The May gig will see it completely paid for, and it will become yet one more income-generating asset, as well as the convenience of an "in-house" split that I trust.

Here's a photo... house snake runs into the box; blue lines 1-8 and 9-16 connect to the house console; the 16-pair black snake runs to my Mackie Onyx 1640i console, or interface, depending on the gig.

Thanks for your informative and inspiring replies!

Telephone and redlight is actually a good idea. I considered phone briefly before and thought it was excessive but it might be useful in the future. I should expand to six or eight channels then. I think I'll go for a separate power cord as well, it seems a bit expensive just to have it included - cool as it may be though.

I'm buying bulk cable and soldering my self.

My own talkback snake consists of:-

Balanced pair for talkback loudspeaker (K+H M51)
Stereo pair for headphones
Balanced pair used as a DC switch for turning on red lights

I normally rely on the recording mics to listen to what is going on, but an extra pair for a reverse mic. may be useful.

Good suggestions, all. Final tally looks like this at six channels:
2ch headphone
1ch talkback speaker
1ch talkback mic
1ch red/greenlight
1ch video

Looks like?

Edit: just struck me that I'll get by with one channel for headphones. Have to test if my uln-8 can run headphone hot enough over 40 m of wire. Leaves one channel for other fun stuff. Like what? Telephone for conductor is covered with this channel, I figure.