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

Add a transformer to each speaker and leave the attenuators for zone volume adjustment. Make sure the amp is off or speakers disconnected as once you are down to the last couple the amp could damage the voice coils still connected directly

No Hal, I was sleeping in electronics class in high school

Hal -

Please correct me if I'm wrong, but 18, 8 ohm speakers connected in parallel should be as close as possible to a dead short. Therefore P=5000/.00001 (or something similar) would have to be one hell of an amp.

I have seen one rogue speaker in a run, and you're right it screwed things up monumentally. But 18!

Unless I'm missing something very basic.

Maybe they're wired in some series-parallel layout?

Sam

Sam, that's why I made the comment about speakers in series. I'm guessing 4-5 speakers in series on several runs. You'd get a reasonably high impedance, but the low end would probably be 'mushy'. The cheaper the speakers, the more like 'oatmeal'! Wait!, that was part of the problem! Oh, yeah. What Merritt said, except turn the amp OFF except when you are testing, or have eveything finished. It IS a 70 volt output and it WILL hurt if some idiot pages while you are fiddling with connections. The surprise will knock you off the ladder! John C. (Not Garand)

Please correct me if I'm wrong, but 18, 8 ohm speakers connected in parallel should be as close as possible to a dead short. Therefore P=5000/.00001 (or something similar) would have to be one hell of an amp.

0.44 ohms @70.7 volts is 11,246 watts actually. If you put that load on the 4 ohm output it will do something however.

No, I'm sure that the speakers are not in series. If they really were on the 70 volt output most likely the volume controls used presented a high enough impedance to the amp at least when they were turned down. A series resistance with the speakers connected to them actually. The amp volume had to be all the way up. I think if you turned all those volume controls up the amp would go into protection.

-Hal

I didn't go through all of the wiring or actually even count how many home runs only the speakers. But I was told all speakers were home runs and it looked like it. A 2" diameter bundle of overly tie-rapped speaker wire with two big 'ol wire nuts to a single lead to the amps 70v output.

The volume is kept very low, this maybe why the amp hasn't produced a layer 1 smoke application.

Betcha it's zip cord or Radio Shack speaker wire or Monster Cable. Those are not permitted to be used as wiring within buildings. These are ceiling speakers?

Amps are pretty well protected unless it's some piece of junk. They will just go into protection rather than go up in smoke.

-Hal

Amps tapped at 70 volts usually go into protection. Amps tapped at 25 volts just cook.
Of course, you knew that, because the volume setting was higher than your marks and the top of the amp was hot enough to fry an egg.

The K-Mart employees used to try adding 8 ohm speakers. You just went to Automotive, Sporting Goods, or receiving and asked the most likely looking dude "Who added speakers?"

Sometimes though, the problem was in the grid because the careless installer, usually me, forgot to carefully trim the tails and they were touching the hat or tile bridge and grounded to the ceiling grid :-)

However, some extra advice is don't let a colorblind person wire speakers. Violet and Black must look the same or the guy is not very smart.

Carl

I agree with Sam, a 8 ohm speaker would short out system, and the volume would be rubbish must have some transformer to remove the 70v or the speaker would lock up. It sounds like the speakers just cant handle the frequency range and you could be going to a lot of trouble for nothing, Try putting on one good 75v 1-2 watt speaker and see what it is like.You might have to replace them all

Ken

When I see ceiling speakers done by the clueless they are usually from Radio Shack or equal. They are the type that you cut a 6 1/2 inch hole for and pop them in. So if you are going to add a line transformer what are you going to do, throw it up in the hole before you put the speaker back? There is no way to mount it to the speaker.

I agree, if this is anything like this I would be replacing the speakers with JBL or TOA that have the transformers built in and will fit the existing hole. Been there, done that.

-Hal