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 much, the speaker 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 , 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 is: A+D = better ; A+C = clear Treble and ; A+CD = clear Treble and (the overall effect inclined towards Treble); AB+CD = more mediant frequency. When 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:
2 * Frequency Divider