Jumpers A and B control the bass range. A sets the lower limit and B sets the upper limit of the bass audio range. On some speakers, distortion can occur when bass is boosted too much. Adjustment options - If distortion occurs: remove the jumper cap from A to limit super-deep bass and reduce distortion. - To increase bass: remove the cap from B. With the B cap on, bass is reduced; removing the cap from B increases bass. Jumpers C and D control the treble (highs) range. When the caps on C and D are installed, the highs are the loudest. Key benefits - Precise control of bass and treble ranges for compatible speakers. - Helps prevent distortion and tailors sound to room and listening preferences. - Simple, non-permanent adjustment using jumper caps. Compatibility and specs - Designed for compatible speaker systems that provide jumper adjustments. - Size and material are not specified. Use scenarios - Home stereo with compact bookshelf speakers: install A and B caps to limit ultra-deep bass and reduce distortion at higher volumes. - Bass-heavy music or movies: remove B cap to boost bass response while keeping overall balance. - Detailed listening in bright rooms: leave A in place and install C and D caps to maximize high-frequency presence for clearer cymbals and vocals.