There are three main types of headphones: Dynamic, Balanced Armature and Electrostatic headphones. Although there are several equivalent magnetic formulas in addition to these three types, they are either eliminated or used for professional purposes. The market share in Hi-Fi field is very small.

Notice the difference between resistance and resistance. In the world of direct current (DC), the effect of object on current obstruction is called resistance, but in the field of alternating current (AC), besides resistance, capacitance and inductance can also obstruct current flow. This effect is called resistance, which we call impedance everyday. It is the sum of resistance and reactance on the vector.

Low-frequency extension: refers to the lowest frequency that an audio device can reproduce. It is a scale used to determine the extent to which the sound system or speaker can descend during bass playback. For example, a small subwoofer can extend to 40 Hz at low frequencies, while a large subwoofer can dive to 16 Hz.