Abstract: Stringed instrument sound modification in which a specially braced soundboard is provided either for stand alone use or in cooperative combination with a plurality of vibrating reeds thereby to modify sounds produced by the vibrating strings of the instrument. The sound board includes an enlarged effective area adapted for reinforced positioning of the instrument bridge, such area being substantially defined by intersections of elements of a pair of x-shaped cross braces. Vibrating reeds are optionally provided in a removable cylindrical array of axially parallel members for further modifying the tonal characteristics of the instrument. This removable cylindrical array is adapted for mounting in the sound hole of a guitar or other stringed instrument.