The Oasis Bass Humidifier uses a completely new suspension system and generates a great deal more daily humidity than most humidifiers. It’s ideal for use on 3/4 double basses and some 1/2 size and smaller (it’s designed to fit inside the double bass through the F-holes, which must be equal to, or larger than, 1 ¼”.) An elastic cord slips over the neck of the humidifier and is held in place by tension and the humidifier cap. The cord extends through 2 pieces of felt (user installed), and knots at the end. One piece of felt is round and fits in the F hole; The other is rectangular and fits outside the bass, preventing the humidifier from falling inside. Because of the large air capacity of the double bass, two humidifiers are generally needed to supply sufficient humidity and both should be refilled with distilled water every three days.