Headphone impedance is often treated as a simple indicator of how difficult a pair of headphones is to drive. It matters, but impedance alone does not tell the whole story.
What is headphone impedance?
Impedance is the opposition a headphone presents to an alternating audio signal and is measured in ohms. Common headphones range from below 20 ohms to several hundred ohms.
Lower-impedance headphones generally require less voltage but may draw more current. Higher-impedance headphones typically need more voltage to reach the same output level.
Sensitivity matters too
Sensitivity tells you how much sound pressure the headphone produces for a given electrical input. A relatively high-impedance headphone with high sensitivity can be easier to drive than a low-impedance model with low sensitivity.
This is why two pairs of headphones with the same impedance can behave very differently when connected to the same source.
What works with a phone or laptop?
Portable devices are usually designed around lower-impedance, reasonably sensitive headphones. They may still play a higher-impedance model loudly enough, but the available headroom can be reduced.
The H2 Closed-Back Headphones, for example, use a low nominal impedance intended to suit a wide range of sources.
When is a headphone amplifier useful?
A dedicated headphone amplifier can provide more voltage, more current and a lower output impedance than a basic device output. It can be useful with insensitive planar magnetic headphones, high-impedance dynamic headphones or whenever the existing output cannot reach clean listening levels.
A DAC/headphone amplifier such as the D4 combines digital conversion and a dedicated headphone output stage in one component.
What about output impedance?
The amplifier’s own output impedance also matters. A low output impedance generally gives more predictable frequency response across different headphones and better electrical damping of the driver.
How should you choose?
Look at impedance and sensitivity together, then consider your source. If the headphones reach comfortable volume with clean dynamics and no obvious strain, extra amplification is not automatically necessary. Browse the Fred.Audio headphone range to compare different driver types and impedance values.