A whistle for producing resonant frequencies comprising a body which includes a mouth piece having an inlet, and at least two sound chambers to which inlet air is blown from the inlet. The whistle further includes air passageways for communicating inlet air from the inlet to the sound box and sound chambers. The body further includes at least two exhaust ports in communication with the sound chambers for discharging air and sound. The two sound chambers are dimensioned to create peak principal frequencies which interactively produce a pulsating sound having a periodic pulse frequency of less than 100 hertz. The whistle preferably includes air intake ports for communicating additional port air into the sound box.