Jumpers A,B are used to control bass audio effects.Jumper A sets the lower bass limit, and Jumper B sets the treble limit.
Some speakers may cause the speaker to warp if the bass is too high.In such cases, remove the cap of the Jumper A to limit the ultra-bass and reduce distortion.Remove the cap of the jumper B, the bass will raise and the bass drops when the jumper B cap is on.
Jumper C and D are used for Treble range control.When both the jumper C and D caps are turned on, the treble sound is the loud.
Only cap C is turned on, the treble sound will be smaller.If Cap D only ON, it will be lowerWhen both C and D caps are removed, the treble sound will not be produced.You can adjust it to your best sound.