An acoustic apparatus includes a vibration part configured to generate an acoustic vibration, a tube having a cavity that faces the vibration part, and at least one open tube connected to the tube via a first open end and a second open end. A length of the at least one open tube is an integer-fold of substantially a half of a wavelength of a standing wave produced in the tube. The first open end is positioned substantially at an anti-node of the standing wave produced in the tube.