In my house I would like to have speakers in garage, mud room, few hallways, power rooms, closets, etc.
I don't need nor want to change sources, volumes, etc.

What I do want, is to control when each zone turns on/off based on occupancy, time of day, etc.

The easiest way to do this, as I see it, is to use 70V setup.

Even though the rest of my house is 8Ohm setup, for these support areas I'm thinking of going with 70V, that way I don't have to worry about impedance, and I don't have to 'burn' a bunch of zones on my Russound C5.

I'm thinking of taking Z8 pre-amp outs from the C5, run them into a 70V amp and then feed that into a multi out relay module which will give me the control above mentioned locations.

Has anyone done anything like that or am I on my own?

Mario,

Would these rooms be stereo or mono?

It's easier to find attractive home audio speakers than 70V speakers. To me 70V or Ohms does not matter much, is just different math -- there is always an impedance issue. The 70V speakers usually incorporate multiple taps on a control that is mounted on the speaker. This is a great feature in commercial applications because one usually wants uniform acoustic levels and any adjustment is usually a one time event. The 70V scheme implies less current which allows longer wire runs and much less wire because I don't home run to each speaker and there are very few (if any) wall mounted volume controls.

If you want mono in these rooms, placing a simple mixer or building a summing network ahead of a dedicated amplifier is the best plan. It is a lot of trouble to sum left and right at the speakers.

A central relay box could work. How will you control to this box? How will you send occupancy data back to your control system? Of course, you would need to home run each speaker back to the central location.

Be sure to check your relay specs. Many are spec'd at 32VAC.

buzz,
I would sum both channels for mono.
70V grills are the same as 8Ohm grills.
I'm not looking at architectural or invisible speakers.
I've been using Proficient 600TT and 800TT in my house, and would replace few of those while adding several more of 70V flavored speakers.

As for there not being an issue with impedence: most D/A amps are only stable down to 4Ohm -- some are good down to 2Ohm.
So depending whether I have 1 speaker on, two or more, I would need to mess with the impedance on the 'fly'.
70V doesn't care whether I have 1 speaker on or 100. As long as amp and speaker wire can drive it, I'm fine.

In my case, say I tapped each speaker at 7W.
Also, lets assume that I have 10 locations, each with single speaker.
With 20% overhead, I can easily get away with a single 100W amp and almost any relay block.

From there, I could use a ridiculously small gauge to feed each speaker. BTW, my house is already wired with 16/4 to most of the above mentioned locations.

As for control -- no volume CTRL is needed.
On/Off would be based on events, logic done by HAI, feeding relay board.

You could do a dead simple system by having all speaker zones run through volume controls in those zones. Go into a room, turn up the music. Leave it, turn it down. Want the house silent? Turn off the amp.

Everything you propose is very simple until you get to that last sentence. Suddenly you need a control system!

I would get two Xantech CC62s and change their addresses. Each one gives you IR control of six DPDT relays. Since you have rather low current, you could just use the relays in the CC62 as your speaker switches.

You could diode-logic a local pair of push buttons, one to turn a zone on and another to turn it off.

The last CC62 I used runs a screen down, the screen up, turns on and off two fireplaces... and I forget what else. It's been seven years!

Mario,

If I was working on a 100 speaker system I would go 70V (and a commercial amplifier and processor) in a blink. For your scale of system I would want in-wall volume controls and I'd probably use home speakers unless I had a bunch of 70V speakers that I needed to recycle.

Given what you have on hand, go with whatever you are comfortable with. The 8-Ohm scheme will result in more current in the speaker wire legs, otherwise the only real difference is the physical location of the matching transformers. (included with the speaker, in-wall volume controls, or at or inside the amplifier) OK, some 70V amplifiers might not include a matching transformer. They are becoming harder and harder to find, but there are matching transformers (KEF offered one of the last that I've seen, but Russound and Sonance offered them too) designed for 8-Ohm amplifiers and a bunch of consumer speakers. (This is really the 70V mindset with a different label)

I do NOT want any local control.
No On/Off switches, no volume controls.
The idea is to have the music start automatically in rooms where people only pass thru and not spend much or any significant amount of time in.

Think of pulling into a garage* at the end of the day.
You open car's door and are greeted by nice music.
No need to get out of the car, walk over to music keypad.

Same with hallways, mud room, etc.

In shitters, I don't need people to change music/volume.
All I'm trying to provide is soothing music and some privacy.

*Garage is used for parking car only. No storage. No car washing. No working on the car. I have other spaces for those tasks. This garage is for in/out in under 60 seconds.

This is even simpler.

Install PIR sensors in each room that you want to perform that way. Alarm suppliers have time delay modules, so you can create a relay closure for a certain amount of time after the last trip of the PIR. Say, 30 seconds.

Each PIR plus delay circuit controls the ON state of a relay and thus the sound. Or, if the PIR output is a relay that can handle the current of the 70V signal, just put the audio through the time delay's dry contact.

Speaking up, summing the output to mono is simple. Many mixer amplifiers on the market have consumer rca left and right inputs summed to mono.

Going to a prioritizing vc used for page over ride is an option as well...