The Harman curve is a set of target frequency response curves developed by audio experts Sean Olive and Todd Welti through extensive blind listening tests, describing the headphone sound balance that most people prefer in quiet environments. It is not a single curve but includes multiple versions for different volume levels and different headphone types, such as in-ear and over-ear models. Its core characteristics are a slight bass rise, a flat midrange, and a moderate high-frequency roll-off, designed to simulate the listening experience of speakers in a real room.
For the average user, the Harman curve provides a "mainstream taste" reference baseline: headphones that conform to it typically sound natural, balanced, and non-fatiguing, with clear vocals and good instrument separation. However, note that it does not represent "absolute correctness"—some people prefer more bass, while others favor brighter treble. When shopping, if you don't want to overthink personal preference, choosing a product close to the Harman curve is often a safer bet, especially as a starting point or for monitoring reference.
Practical advice: during listening tests, first compare the target headphones with a reference device using songs you are familiar with. If they feel "flat" or "unexciting," there is no need to force yourself to adapt to the Harman curve—your ears' preference is the ultimate standard, and the curve is just a map to help you quickly find a safe starting point.