atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Security, Alarms and Paging 70v BGM system

If you've only cut a 6 1/2" hole in the tile, then it's gonna be hard to fit the Quams in the space..it might be time to try those Bogen ones that you just pop into the tile.

I love your idea of the 110v AC on the grid to pop out bad speakers, Hal. I don't think I have enough nerve to do it, but it might be fun to try.

Carl

Yeah, I'd be afraid of the sparks setting fire to all the garbage and dust up there.

Regular 8 inch speakers and baffels need a larger hole, you can just make the hole bigger. Even with a quality speaker like the Quam 8C10FEPAX and TBH70 transformer they are about half the cost of something like the JBL Control 24CT (that pops in a 6 1/2 inch hole) and can sound very good. But the nice thing about the JBL is that you are getting a "known quantity" in that they are a system and will sound the same regardless of how you install them. Speakers and baffels can lose a lot on the low end if you install them with a small back can.

-Hal

I noticed that our systems here use 25V and not 70V. Is this so they get around having to run conduit?

Jeff -

If your local codes require conduit for circuits >50 Volts, then yes. That's what they were designed for.

Sam

That's how the 25 volt system came into being. Some municipalities still insist on it based on their code that was probably written 75 years ago.

This actually goes against the NEC because pulling a low voltage speaker wire into conduit is not a class 1 wiring method which is what I assume they are after.

-Hal

But with 25V you would need to use larger wire to cover a longer distance, right? What about the tap settings? Would they be the same as on a 70V system?

Larger wire generally yes, depending on distance and wattage.

There are different transformers for 25 volt, 70.7 volt and 100 volt (yes there is a 100 volt system popular in Europe). Sometimes you will find "combo" transformers with the taps marked for one wattage at 25 volts and another wattage at 70.7. I know that most speakers that have the transformer built in, like the JBL Control series give you a rotary switch with which to select the wattage taps. There are settings for all three voltage systems.

Except for those instances you mention, 25 volt systems are not really used.

-Hal

I used some excellent speakers on the last big job - Tannoy - a British company. They came with built in transformers that offered taps for 25, 70 & 100 volt taps (I've been told that in Europe they also have 200 volt speaker systems, but haven't seen them myself).

Some of the taps offered double duty - x watts if used at 70 volts, y if used at 100, etc.

One tap was 15 Watts at 70 volts and only 2 watts at 25!

Sam

Some of the Quam transformers list the 25 and 70 volt tap values, and the Bogen trumpets do also.

They are sort of inverted. In the Bogen, there are some settings that are invalid for 25 volt or invalid for 70v sources.

Carl

a transformer can be used on any voltage as long as you don't over power the amp or speaker. The power difference between 25 and 70 volt is about 8 times the difference. a transformer marked at 1 watt 70 volt would give you about 1/8 watt at 25 volt.

here is some info
and some more