A thermophone includes an inner core and an outer shell coaxial with the inner core. The inner core and outer shell enclose a volume filled with gas. A pair of posts extend radially from the inner core to the outer shell and extend longitudinally between the inner core and the outer shell. At least one longitudinal slot is formed along the outer shell and a fluid seal covers the slot. A thermoacoustic active element is disposed in the volume and heated by modulated current to generate alternating pressure on the outer shell and produce acoustic signals.