Electronic – Impedance of headphones


This is probably the best article for a beginner about impedance with respect to headphones.

I haven't managed to find an explanation of why the impedance of headphones is just a single, real number (like 250 Ohm). I thought impedance is a complex number, so it should have real (resistance) and imaginary (reactance) part. Maybe the imaginary part is just zero. All I know is that impedance varies with frequency.

Best Answer

Impedance does vary by frequency. However, for many things it doesn't vary very much by frequency within the expected operating frequency of the equipment, and a single number is much easier to handle than a frequency response graph. So people quote a single average number.

In fact, your linked article admits this:

Headphone impedance can vary by a factor of 10 or more over the audio band. The SuperFi 5 is rated at 21 ohms but varies from 10 ohms to 90 ohms.

That's quite a lot of variation! It also explains why this causes variation in the audio quality when driven from different sources.