Jumper A, B are used to control audio effect of range. A for lower limit while B for upper limit of the audio range. For some speakers, when is turned up too much, the speaker will show distortion. When that happens: we remove the jumper cap of jumper A to limit super low to bring distortion lower. When we remove the cap of jumper B, is increased while cap of Jumper B is on, is decreased. Jumper C and D are used to control Treble range. When cap of both jumper C and D are on, the sound of treble is loudest. When only cap C is on, the treble sound is lower. When only cap D is on, further lower. When both caps of C and D are removed, there is no treble sound. (Generally speaking, with the four jumpers, you'd sooner or later find your best sound effect. Anywya, all effects still depend on your actual test.) How to use the splitter board: First connect as per our diagram above (Treble, Low, Input), connect to speaker, seal space, we can begin to hear music while optimize. Normally we use jumper A and let B idle. For jumper C and D: we need to hear the actual effect of treble. A general formula is: A+D = better ; A+C = clear Treble and ; A+CD = clear Treble and (the overall effect inclined towards Treble); +CD = more mediant frequency. When effect is unnecessarily high, we can remove cap A. Please optimize until you think the sound is best, and then fix the board with your speaker unit. : 400W or lower Resistance: 4-16ohm Frequency: Adjustable Colour: red Material: PC+metal Package Contents: 1 * Frequency Divider Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.