rumble is the second hardware expansion module for the OP-Z.it's a built-in haptic subwoofer, using high-definition vibrotactile feedback and psychoacoustic technology,

allowing you to feel your music. when using rumble you will feel like you're holding and listening to a deep sounding subwoofer. the frequency response 10 – 150 hz is designed to maximize impact while minimizing additional energy consumption. it also features a silent metronome mode, great when performing live to always know exactly where the beat is.