PHD
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- Mar 15, 2023
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Sorry, but I assumed that Erin has some knowledge of basic electricity. Have a look at this:
He's advising people to use a DMM to measure the speaker's impedance? DMMs Ohm measurements are a simple DC measurement, not actual impedance.
Even with an LCR meter, you'll probably get the speaker's impedance wrong because a speaker + passive crossover is a complex circuit which have inductance, capacitance, and stray resistance.
It also has an induced back EMF, which together with the drawn current forms the main portion of the Ohmic (real) part of the impedance. The back EMF depends on the output power of the speaker and of course, the frequency.
When you measure the DC resistance of a commercial loudspeaker, all you get is the static equivalent resistance of the crossover + voice coils of the woofer and midrange drivers (not the tweeter because of the DC blocking capacitor).
I've just measured the resistance of my Forac Aria 906 speakers using a DMM and got a value of 3.6Ohms which isn't even close to the nominal 8Ohms.
I always assumed that to measure nominal impedance you need to drive the speaker near rated power using an amplifier and a tone generator, measure voltage and current per frequency, and then calculate the impedance and stage an average. I'd expect the Z(f) graph to change if you change the power because the higher the motor's excursion, the higher the back EMF would be.
I'd love to learn how exactly impedance graphs are generated.
He's advising people to use a DMM to measure the speaker's impedance? DMMs Ohm measurements are a simple DC measurement, not actual impedance.
Even with an LCR meter, you'll probably get the speaker's impedance wrong because a speaker + passive crossover is a complex circuit which have inductance, capacitance, and stray resistance.
It also has an induced back EMF, which together with the drawn current forms the main portion of the Ohmic (real) part of the impedance. The back EMF depends on the output power of the speaker and of course, the frequency.
When you measure the DC resistance of a commercial loudspeaker, all you get is the static equivalent resistance of the crossover + voice coils of the woofer and midrange drivers (not the tweeter because of the DC blocking capacitor).
I've just measured the resistance of my Forac Aria 906 speakers using a DMM and got a value of 3.6Ohms which isn't even close to the nominal 8Ohms.
I always assumed that to measure nominal impedance you need to drive the speaker near rated power using an amplifier and a tone generator, measure voltage and current per frequency, and then calculate the impedance and stage an average. I'd expect the Z(f) graph to change if you change the power because the higher the motor's excursion, the higher the back EMF would be.
I'd love to learn how exactly impedance graphs are generated.