Earphone sensitivity refers to the sound pressure level (the unit of sound pressure is decibel, and the higher the sound pressure is, the higher the volume is) when the earphone inputs 1 milliwatt of power to the earphone. Therefore, the higher the sensitivity is and the smaller the impedance is, the easier it is to sound and drive the earphone.

The sensitivity of the earphone mentioned in ordinary times is actually the sensitivity level of the earphone. It is the sound pressure level generated by the earphone when 1mW of electric power is applied to the earphone, coupled to the simulated ear (artificial head). The power of 1mW is calculated based on the standard impedance of the earphone at the frequency of 1000Hz.

The unit of sensitivity is dB/mW. Another less commonly used unit is dB/Vrms, the sound pressure level produced when 1Vrms voltage is applied to the earphone. High sensitivity means that the power required to reach a certain sound pressure level should be small. Currently, the sensitivity of moving coil earphones is generally above 90dB/mW. If the earphone is selected for walkman, the sensitivity should be about 100dB/mW or higher.