A vibrational acoustic unit comprises a dynamic force motor (28), a power take-off spring (34) having one end attached to the dynamic force motor (28) and the other end attached to a fluid filled acoustic resonator (38). The motor (28) oscillates the entire acoustic resonator (38) so as to excite a resonant mode of the acoustic resonator (38). A method of delivering power to an acoustic resonator (38) comprises resiliently connecting a motor (28) to the resonator (38), and driving the motor (28) to oscillate the entire acoustic resonator (38) so as to excite a resonant mode of the acoustic resonator (38).
