Rumbler Fretted Acoustic-Electric U-Bass Natural Mahogany. The Kala Rumbler is the latest model in Kala Brand's distinctive line of award-winning portable U-Bass instruments. The Rumbler takes the U-Bass into a new dimension with the addition of custom engineered electronics and new proprietary strings, at an economically friendly price. The Rumbler design integrates a specially designed Kala electronic system with a piezo pickup and is equipped with an active EQ with built-in tuner. Each bass is strung with Kala Silver Rumbler Strings which are proprietary U-Bass strings designed and manufactured exclusively for Kala Brand Music by Aquila strings. Padded gig bag included. Die-cast U-Bass tuners, Laminate mahogany construction, mahogany neck with rosewood fingerboard and bridge.