Just need to rotate the button of the controller, easy operate. | Used to adjust amplifiers power level, stereo, equalizer or crossover volume from the dashboard or other remote locations. | Universal fit for most of car, simple in and out connection, no additional wiring need. | Two adjust way - adjust by gain, adjust by frequency. | Different frequency can make the song feel different. Adds subwoofer level controls or balances a multiple amplifier installation.