Audio Impedance Meter- Testing 70/ 100 volt Speakers

G’day, Gary from Simple Audio Tips. Did you know that you can’t test the true resistance or impedance of a 70 volt speaker system with a standard multimeter like this one? Stick around and I’ll prove it with a
simple test and show you the tool you’ll need. Without getting too complicated, and
increasing the ‘yawn’ factor to about ten, I’m gonna go over some basic differences
between these two meters. A standard multimeter checks the resistance in a circuit by applying a ‘DC’ or a direct current. and displaying the result on the meter here. An impedance meter, on the other hand,
tests the circuit with the same conditions as an audio signal. And that’s by applying an alternating current. With a simple resistive circuit like a
resister inline, the results between
these two meters are going to be exactly the same. But when you introduce speakers coils and
transformers into the works, weird things start to happen with the
resistance in the circuit, especially when you’re applying an alternating current. Temporary magnetic fields produced in the coils resists current flow and in turn produces resistance. I don’t bore you with any more detail
than that but put simply a standard multimeter like this one is
unable to give you a true load reading because it doesn’t apply the same signal
to the circuit as the impedance meter. Now the audio amplifier gives alternating current, the impedance meter does the same. Now let’s look at this in practice we’ve got an audio impedance meter and
have got a standard multimeter. I’m going to connect the audio impedance meter to a standard resistive circuit that’s just a little resistor that is labelled at 470 ohms. we going to connect that up to the leads
and I’m gonna turn the meter on and it’s set to the 100 scale. It reads just below 5 That’s 5 x 100 so that’s just
below 500 ohms. Now, let’s have a look at the normal multimeter, and we’ll connect that up. Connecting that up, it’s just under 500 ohms, as well or 0.469k So, as far as these two meters a concerned, applying it to a standard resistive
circuit they see the same amount of resistance Now what happens when you test a speaker system that’s got
transformers and voice coils and things like that inline? Let’s have a look at that. Firstly what I’m going to do is connect the impedance meter to the feedline, and remember, this works on a scale, and is a multiplication scale. So whatever reading we have here, is multiplied by 100 You’ll hear a tone because that’s the
alternating current going through the system. and the reading is just under 450 ohms. Now let’s look and see what the multimeter gives Connecting the multimeter to it, 0.028 k which is 28 ohms, A big difference between
the two We’ve got 28 ohms here and when we test
with the audio impedance meter, we’ve got 450 ohms, a big difference between the two. Does it really matter that the two readings a different? Well amplifier manufacturers state the minimum impedance that can be connected before the amplifier overloads. If you overload the amplifier, you can damage it or even burn it out. Now let’s imagine an installation where you’ve got 20 or 30 speakers in a large area or even down a corridor or something like that. Without an impedance meter, you can only
make a calculation by adding each of the speaking outputs
together that’s written on the labels. But this doesn’t take into consideration any wall attenuators in separate rooms. Maybe line faults caused by damaged cables or incorrectly marked speaker outputs. There are so many different variables to take into consideration. An impedance meter tests the total load at the point where it’s connected to the
amplifier and checks that it is between the amplifiers tolerances In the next video I’m gonna take a closer look at two popular audio impedance meters on the market in Australia the “Australian Monitor” and also the “Altronics Red-back” unit which is a little more automatic If you want a reminder when we upload our next video make sure that you subscribed to our channel and if you use social media, connect with
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so stick around if you got a great question or tip of your own share it with us by typing in the comments section below. Until the next video- Catch you later.


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