What do the frequency response, sensitivity and impedance of headphones mean?

Frequency response refers to the phenomenon that the sound pressure generated by headphones increases or decreases with the change of frequency and the phase changes with the frequency when the system accesses an audio signal with a constant voltage.

The sensitivity of headphones reflects the power that needs to be input at the same loudness.

The impedance of earphone is the abbreviation of its AC impedance, and the unit is ohm (ω). Generally speaking, the smaller the impedance, the easier it is for headphones to make noise and the greater the drive.