Jumpers A and B control the bass range. A sets the lower limit and B the upper limit of the bass. On some speakers, bass boosted too far can cause distortion. To prevent distortion and limit deep bass: - Remove the cap on Jumper A to limit super-deep bass and reduce distortion. To adjust bass level: - Remove the cap on Jumper B to increase bass. - With the Jumper B cap installed, bass is reduced. Jumpers C and D control the treble range. When the caps on Jumpers C and D are on, the highs are the loudest. Practical uses - A distortion-prone speaker at high bass levels: remove A cap to tame deep bass and improve clarity. - You want more bass impact without changing other settings: remove B cap to boost bass. - You need crisper, louder highs for vocals or treble-heavy music: ensure caps on C and D are installed. Compatibility and notes - Designed for systems that use jumper caps to tune bass (A/B) and treble (C/D). Adjustments are made by installing or removing the jumper caps as described.