The equalization of headphones can force transducers to work in a non-linear condition, producing non-linear distortion. Depending on the headphone model and the reproduction level, that distortion can be audible. In this study, headphones of diverse quality and price were compelled to emulate the same target frequency response and the non-linear distortion was measured. A Diagonal Volterra model was used to simulate the different headphones with and without distortion. A perceptual test was carried out to determine the level of reproduction above which non-linear distortion is perceived for each headphone model. High correlation has been found between the level of detected distortion and retail prices of headphones.