Put one of these caps on the end of a BOOMWHACKERS tube and presto-boomo!, you?ve lowered the tone by an octave! Play the tubes as usual or hold them vertically and tap on the floor, etc., as a "stamping" tube. Placed on the higher octave tubes create the same tones as the bass octave tubes. Placed on the bass octave tubes, they go down another octave, making a 3-octave range possible.