In this episode of Ask The Expert we address a follow-up question to our episode on impedance.
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When you are measuring the loudspeaker with a multimeter, you are actually measuring what's called DC resistance. This is the resistance or impedance at 0Hz and – as we explained in an earlier episode – impedance varies by frequency.
When we specify impedance, we do so based on the lowest point, which might be different to that of the DC resistance i.e the 0 Hz resistance.
In this specific case, you have a loudspeaker that measures 8 ohms at DC, but that goes lower (4 ohms) at a different place in the frequency response.
This is why we specify this speaker at 4 ohms, even though the DC resistance is 8 ohms.