TheAlarmTech.com

How do you calculate the load of a speaker circuit.

You can use a Volt meter to calculate the load of a speaker circuit, but it is not easy.

This is because you need to read the Impedance not the resistance, you can not use the ohm scale on your meter.
also keep in mind that fire alarm speakers are a step down transformer with a capacitor in series.

how to use Impedance meter
zero out meter, use meter to get Impedance of circuit
Is it a 25 or 70 volt speaker system.
then
E / R = I 10 amps / 25 volts = 2.5 amps
then 2.5 amps* 25 volts = 62.5 watts
or
P = E 2 / R




The load of a coil is measured in Impedance. The easiest way is to buy an Impedance Meter.


This is the one I bought - about $300 - TOA ZM104 Impedance Meter

To use your meter to measure the load of a speaker circuit.
You will need to know the volts and amps.
1. Put a 1k signal into preamp of the amp.
2. measure the ac volts on the speaker circuit.
3. Put your meter in series with the speaker circuit and measure the amps.
4. Do the math Volt * Amps = power
- this is a pain in the ass, good luck.

When I used the Impedance Meter on a site that uses centrally bank audio I found a lot of speaker zones that were over loaded and under used.

It cleaned up a lot of problems that I did not know I had, it was a big help