Jumper A, B are used to control audio effect of bass range. A for lower limit while B for upper limit of the bass audio range. For some speakers, when Bass 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 Bass to bring distortion lower. When we remove the cap of jumper B, Bass is increased while cap of Jumper B is on, Bass 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 , 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 air space, 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 Bass; A+C = clear Treble and Bass; A+CD = clear Treble and Bass (the overall effect inclined towards Treble); AB+CD = more mediant frequency. When Bass effect is unnecessarily high, remove cap A. Please optimize think the sound is best, and then fix the board with your speaker unit. Power: 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.