Abstract: The invention is a tone producing device consisting of a tone source inside of an elongated cavity attached to at least one point of the object surrounding the cavity (such as the walls of a tube). The tone source can be any tone producing device including: (1) a length or lengths of musical string held under tension within the cavity, (2) one or more tines suspended within the cavity, or (3) an electronic tone producing device. When vibrating, the tone source transmits sound waves in four different ways: (1) sound transmitted from tone source to cavity wall; (2) sound transmitted from tone source to external soundboard; (3) sound transmitted by combination of tone source and cavity wall to external soundboard; and (4) electronic amplification to a speaker.