HowToAV explains how to measure the speaker load connected to an amplifier on a 100v line installed audio PA system or background music systems.
100 volt line (or high impedance) audio systems are the most commonly used for commercial and large scale public address and background music.
If you need to add more loudspeakers to an exisiting system, you should first check the amplifier can take the additional speaker load. The installer will need to measure the speaker load beforehand when planning to add more speakers (or alternative speakers) to an existing system.
When working on a public address system there are many times that having a method of measuring the speaker load connected to an amplifier comes in very handy and can also be a lifesaver.
These can include amongst others...
Having the correct test meter for the job will save you time and money and could even prevent damage to expensive equipment.
As an installer, having a meter to measure the speaker line is an invaluable tool! And the meter used for this task is an impedance meter. It's a simple, cost effective solution to make your work easy.
You simply disconnect the speaker line you need to check from the speaker terminals on the amplifier. Connect the impedance meter to the twin speaker cable you have just disconnected. Press the test button on the meter and an impedance reading in ohms will appear on the display.
This reading can then be used to determine the speaker load connected by either cross referencing your reading to an impedance-to-watts chart, or performing a simple maths calculation. Another way is by checking the reading against the minimum impedance displayed on the back of the public address amplifier.
Job done, all in a few minutes!
To calculate the required value of a 100v line amplifier power, simply add together the power of each loudspeaker.
The simple answer is no. You cannot use the resistance range on a standard electrical multimeter as this will only give you the DC resistance of the speaker line. Using a DC resistance reading will not work!
A loudspeaker line is driven by AC voltage from the amplifier. An impedance meter will test the line using an AC waveform normally at a frequency of 1KHz. A standard electrical multimeter willn't perform this test.
So measuring 100 volt line loudspeaker lines is relatively simple and is going to save you time and trouble to ensure a reliable PA system.
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