Loudspeakers - Multiple Inputs

[Morydd]

In our black box theater, which is used as a classroom, the school failed to include speakers for the school Public Address system, which also includes bells between classes. The solution that someone before my time came up with was to run a line to the audio rack, and run it through the audio system in the theater. However, this means the amps have to be powered up any time school is in session. This seems wasteful to me both in terms of power consumption, and the life of our components.

What I'm wondering is, if there is a way to add a small, low-power always-on amp to the system, and route it through the speakers, and then have some sort of relay that switches between the school audio and the theater audio automatically when the theater sound system is powered up.

Is this a reasonable way to do this, or am I just better off adding a separate set of speakers and amp just for the school feed and putting a kill switch on it up in the booth?

[headcrab]

It would probably easier and cheaper to tap off the existing PA system, and add the kill switch like you said, provided the school's existing PA is a high-voltage system. Those PA speakers aren't all that expensive, certainly less than a new amp.

[DuckJordan]

and really an amp only draws power when its in use, not when its on, sure theres a little loss but not really all that much. considering we run our line aray system off of 3 phase with less than 20 amps per phase. and that fills a 1500 seat grand hall.

[museav]

It would probably easier and cheaper to tap off the existing PA system, and add the kill switch like you said, provided the school's existing PA is a high-voltage system. Those PA speakers aren't all that expensive, certainly less than a new amp.

That might often be true but since they noted that the line from the PA/paging system currently feeds into the rack and that they have to have the room amplifier on, then it sounds like it may be a line level signal feeding the room. That line level feed could be direct or via a step down transformer giving you a line level output from a 70V line, which it is might lend itself to different solutions. For example, if it is a 70V line coming in then a autoformer volume control or a switch and one or two inexpensive dedciated speakers might be an option.

Another possible consideration is that while it used to be common to have 'kill' swicthes on paging feeds to some rooms, with many newer systems that may also be used for emergencies that may not be desired. You seem to currently have the ability to turn up or down the paging level and may or may not want to keep that functionality, maintain the paging feed at all times or have any switch be able to be overridden from a remote location.

[Morydd]

I believe that it is a line-level input and it is _probably_ from a 70V system. (It's from Simplex and it's less than 10 years old if that makes any difference.) Our current "kill" system is that we open up the back of the rack and physically disconnect the line coming in from the wall. As near as I've been able to determine, the line coming into the theater is a feed off the "general" feed, rather than one of the classroom feeds that's addressable. (At the other school I can shut down the feed from the school PA from my computer.) The people using the PA system have never been trained to utilize the setup that allows different levels of paging groups. They use All Call for everything. I'll keep mulling over the options. I don't get to spend any more money till July, so I'm in no rush.