# Adding a light in parallel to existing loudspeaker circuit

Discussion in 'Audio' started by gubavac111, Jun 29, 2019.

1. ### gubavac111

14
3
May 18, 2019
I work on a ship which has Public Announcement (PA) system. PA system consists of a couple of zones. Each zone has an a controller, amplifier and a loudspeakers circuit.
In our case, PA system is only used to make announcements and play alarm, not music.

What I need to do is to add a light indication which will be activated when, for example, zone A is activated (meaning that loudspeakers in zone A are producing sound).

I can definitely do it by using one of the control outputs from the controller, but it would take a lot of cable pulling. It would be much more simple if I could just
connect a light parallel to one of the loudspeakers.

Now... my concerns are:

1) When I look at the drawing of one zone, the output from the amplifier to the loudspeakers is 100V. Am I right to suppose this is 100VAC "high" frequency (by "high" I mean higher than 50/60Hz), depending on the input signal?

2) There is around 50 loudspeakers in a zone where I would like to add the light. Each loudspeaker has a marking 100V, 25W, 101dB. If I add a 220V 20W halogen light (which is purely resistive load) in parallel to the loudspeakers, am I going to disturb i any way the loudspeakers circuit or the amplifier (assuming the amplifier will not get overloaded)?

3) Is it correct to calculate the approximate current through the individual loudspeaker I = P/U = 25W/100VAC = 0.25A?

2. ### 73's de Edd

3,254
1,364
Aug 21, 2015
Sir gubavac111 . . . . .

Need more finite details .

When I look at the drawing of one zone, the output from the amplifier to the loudspeakers is 100V. Am I right to suppose this is 100VAC "high" frequency (by "high" I mean higher than 50/60Hz), depending on the input signal.

50 speakers . . .WOW! . . . .50 SPEAKERS . . . .what distance are each of them distributed apart from each other ? Over how great of an area.
Does one speaker serve one or more employees . . . . . or is the massive number, just to be able to fully cover a large spatial area ?
And where is the placement of that indicator light to be and purpose of that light.
Is it needing to be BRIGHT or just merely an indication in confirmation that your system audio is present and that those speakers are getting fed, if it is in the area that the main amplifier is located. . . . if there is no speaker being in that area ?.

The output from the amplifier to the loudspeakers is 100V.

That is somewhat of an audio related misnomer . . . . if you are suspecting some BRUTE power on that line, akin to an AC line outlets output.
That term is more of an impediance related aspect.
Should you look at the individual speaker within a location, it would be reading as being a 4 ohm or sometimes 8 ohm impediance. Should you string up all of your speaker wiring interconnections , there would be a FIERCE wiring loss attenuation with the l o o o n g wiring run lengths.
Look on that amp back terminations at its wiring output options and you should probably see the option of a 4-8-16 ohm output OR, of your interest, some 25---70.7volt ---100-volt line options of hook up.
Read this and you will be larnin' some real book smarts on the situation.

https://www.redbackaudio.com.au/understanding-100v-line-distributed-speaker-systems/

With your use of the100V line output option, you are minimizing wiring line loss.
This is akin to our power lines in avoiding power loss, whereupon the 220/120V AC power is run thru the alleys at thousands of volts and then coming to a point where ~ a transformer can be installed to feed a cluster of 4 or so side by side customers and the transformer converts that alley high voltage to 1/10th its voltage values to feed the customers houses.

Now, inside of each of the the speakers enclosures, they have a line matching transformer that will match the 100V line to the 4 ? ohms of the speaker voice, with an option of different power level tap offs.( The taps are labeled on the transformers)

If I add a 220V 20W halogen light (which is purely resistive load) in parallel to the loudspeakers, am I going to disturb i any way the loudspeakers circuit or the amplifier (assuming the amplifier will not get overloaded)?

Your . . .ahhhemmm . . ."100V" . . . . would be puny and only be on AUDIO peaks or averaged voltage, just for the bursts of speech from the announcer at his voices frequency. . . . . . NOTHING , any way like a constant 60 cycles of AC line power.

So basically . . . fill us in on
Is there just one light involved on this line.
Is it merely an indicator of audio presence of an announcement .
OR does it have to be VEWY BRIGHT, in order to alert the need for someone to shut down NOISY equipment, so that an announcement could even be known of or heard ?

I await your pending response . . . with bated breath . . . . . . . . . (unless you are an avid fisherman, and then, that would be baited breath).

73's de Edd . . . . .

EUREKA ! . . . . . I have just invented the cordless extension cord.

Last edited: Jun 29, 2019
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3. ### Audioguru

3,483
740
Sep 24, 2016
On the other website we told him that his 20W halogen light bulb is like a dead short circuit when cold so keep it away from the output of the amplifier.
He was told that the light bulb might never receive enough signal level to produce any light and if it did light then it would flicker with the words and syllables of speech.

He does not have or know that a PA speaker has a 100V to 8 ohms speaker transformer with many power taps. His 50 speakers might be tapped at 2W each then the amplifier would be rated at 100W with no extra power to drive a light bulb.

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4. ### gubavac111

14
3
May 18, 2019
First of all, thank you for your comprehensive answer. Since it seems like a lot of hustle, I am just gonna run the cable to controller and do it like that.

All the speakers in the zone act the same and are activated when an announcement is made. There is so many of them because it is a large area. One speaker covers area of approximately 30m2. If connected in parallel, the indicator light would be placed 2-4 metres from some speaker in the zone. The light itself should be bright enough to be able to clearly see it from the 10 m distance (I guess 20W bulb would be fine), so that it can be noticed by the musical band and so that they can stop playing and shut down their own speakers.

5. ### davennModerator

13,946
1,986
Sep 5, 2009
OK a couple of aggro posts removed

please guys, lets keep it civil

so it still isn't clear what you want
questions
1) ... how many zones ?
2) ... will one lamp do for each zone rather than each speaker as you hinted at ?
3) ... will more than one zone be active at the same time ?

Dave

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6. ### gubavac111

14
3
May 18, 2019
Thank you for your answer, I decided not to try to connect the light in parallel to the speaker, but rather to control output from the controller.

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7. ### hevans1944Hop - AC8NS

4,647
2,169
Jun 21, 2012
Excellent idea, except you can probably control the lights by briefly superimposing Touch-Tone signals on top of the PA audio. I have sent you a PM (Private Message conversation) on how this can be done relatively inexpensively. It might even be a project you can have completed locally. It's really that simple.