Features: Just gently rotate the button of the controller. Different frequencies can make the audio output vary. It feels smooth and is very convenient. Connect the RCA from the output of this controller to the amplifier, and connect the car stereo output to the RCA input of this unit. Ideal for sub amplifier volume control. Used to adjust an amplifier's power level, stereo, equalizer, or crossover volume from the dashboard or other remote locations. Adds subwoofer level control or balances a multiple amplifier setup. Compact housing allows the unit to be mounted virtually anywhere for easy access. Fine tunes the volume of any RCA line level signal. Simple input and output connections; no additional wiring required. Connect the RCA from the output of this controller to the amplifier, and connect the car stereo output to the RCA input of this unit. Specification: 4 RCA: 2 RCA input & 2 RCA output Level control knob Frequency Range: 150Hz - 40Hz Volume Gain Range: 0dB to -12dB Dimensions: 48x56x41mm / 1.89x2.2x1.61 inch Material: Plastic Color as shown Package Contents: 1 x Controller Only the above package content; other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture to appear slightly different from the actual item. Measurement allows an error of +/- 1-3cm.