Speakers for a fire station

[Bigred]

Does anyone know how those step attenuators work on a PA system between a 70 volt amp and the transformer at the speaker?

What I want to do is allow the user to set the volume to a speaker (70V) to what they want, even off. But in case of a station page, have the volume control bypassed and apply full volume to the speaker.

What I'm thinking to to run two separate pairs to the speaker. The first pair goes through the attenuator/volume control for normal monitoring. The second pair goes direct to the speaker transformer bypassing the control. Using a relay at the amp, it would switch between one line or the other depending if the station was paged.

My question is, during an alert session with the PA going directly to the matching transformer, would the step attenuator load down the audio at all because it is also connected and several would still hooked together on the input but being open to the amp? I'm thinking an open input to the attenuator would reflect a higher impedance and not be a factor across the line direct to the transformer. Or would several inputs twisted together cause the other line to load down?
Hate to crack the old textbooks to figure this out. Anybody care to shoot from the hip?

[kb4mdz]

Seems like a kinda roundabout way to do what you want. If you can define what you want.

Just trying to understand what you're describing, it sounds like it could get complicated if you go more than about 3 speakers. And adding any more would be an additional nightmare.

What I've done, several times, if you want a guaranteed alert level, but ability to have monitor audio that station personnel can adjust volume on, is really 2 whole systems. One system of a monitor radio, to an amp, and its own set of speakers, perhaps with individual volume controls. Esp. if you want to turn it down or off at night, put a control switch to cut off certain speakers.

The other system is jusf for alerting; but put all the components in a locked box or cabinet. That way, no one can touch it and mess it up, except authorized persons. Radio, to PA, to speaker distribution, get it set up for acceptable levels & secure it.

Where you want 2 speakers, 1 monitor & 1 alert, put them side-by-side, and run 2 cables.

This is generally what I've been doing for my customers for the last few years. Alert radio system, which also trips a relay to turn on lights where they've been designated, and speakers in the Day Room/Kitchen area, apparatus bay, and dorms and maybe bath areas, with all equipment locked in a cabinet about 8 ft. up in the bay. Only radio shop guys have keys. Oh, btw, the light trip relay is a time delay off; it turns on & stays on for as long as the adjustment pot says. In our case, it's 1.8 seconds to 180 seconds; or 3 minutes. We just set it for 3 minutes.

Monitor radio is another, but sitting on a desk in the office with speakers in the Day Room/Kitchen area, and apparatus bay. We include a switch to turn off the speaker(s) in the bay, because the dorms are right next to that; that way they don't have to listen to low-level monitor audio all night long.

[Bigred]

Thanks and I understand all that. This is an existing system that will be upgraded. Only three new dorms being built will need the speakers that go to full on alert. I found that Atlas Sound makes the volume controls with a bypass relay installed. Will still need 4 wire cable to the speakers but that's in the works.

[motorola_otaku]

+1 for Atlas Sound. We use their stuff exclusively now... amps, speakers, line-level reducers, combiners, all. We're also a lot less forgiving and ordered the speakers with built-in volume controls, so if someone wants to turn it down they have to find a chair or a step-stool.

I was not aware they made a L-pad with a bypass relay built-in. Mind posting the part number? That might come in handy for a future application.

[FMROB]

So, Ill bite. Could you point me to the volume controls with the relay in them?

Thanks, Rob

[RFguy]

This one?

-Priority Paging Feature By-Passes the Effect of the Attenuator
-The SPDT Relay is Operated with 24 VDC at 10mA

10 watt: http://www.atlassound.com/at10-pa
35 watt: http://www.atlassound.com/at35-pa

[Bigred]

Tnx RFguy, that be it.

[FMROB]

Roger That.. Thank you