The impedance of a headphone is short for its AC system impedance, and the unit is ohms (Ω). Generally speaking, the lower the impedance, the easier the earphones are to sound and drive. The impedance of the headphones varies with the frequency of the reproduced audio signal. Generally speaking,noise cancelling earbuds and earphones， the impedance of headphones is highest at low frequencies, so there is less attenuation at low frequencies than at high frequencies, increasing the output impedance will make the sound darker and more distorted (the pa control of the headphone driver will also weaker), but some headphones require louder sound at high impedance. If the headphone sound is harsh, consider increasing the effective output impedance of the headphone jack; if the sound is dull and muddy and driven by a power-controlled amplifier, consider reducing the effective output resistance.

Headphones with different impedances are mainly used in different occasions. On desktops or power amplifiers, VCDs, DVDs, TVs and other equipment, high-impedance headphones are commonly used. Some professional headphones have an impedance of more than 200 ohms. The headphone jacks on the machine are matched. If you use low-impedance headphones at this time, you must first turn down the volume, then plug in the headphones, and then turn up the volume little by little to prevent the headphones from being overloaded, burning the headphones or deforming the voice coil and causing the sound to break. . For various portable players, such as CD, MD or Mp3, low-impedance headphones (usually below 50 ohms) are generally used, because these low-impedance headphones are easier to drive, and at the same time, pay attention to the high sensitivity. For Walkman and Mp3, the sensitivity index is more important. Of course, headphones with higher impedance will sound better when paired with a sound source with high output power.