Impedance
Definition
The total opposition a circuit presents to alternating current, measured in ohms. In audio, impedance matching between devices — microphones, headphones, amplifiers, and speakers — determines signal transfer efficiency, frequency response, and potential for noise or distortion.
In Simple Terms
Electrical resistance that affects how audio devices work together. Low-impedance headphones (32 ohms) are easy to drive from a phone. High-impedance headphones (250+ ohms) need a dedicated amplifier. Mismatched impedance between gear causes volume loss, tone changes, or noise.
In Practice
A 250-ohm studio headphone connected directly to a smartphone produces significantly lower volume and altered frequency response compared to the same headphone driven by a dedicated headphone amplifier designed for high-impedance loads.
Common Confusion
Impedance is not the same as resistance, though they are related. Impedance varies with frequency; resistance is constant. This is why a headphone's published impedance is measured at a specific frequency (usually 1 kHz).