Experiments performed to investigate the effect of ultrasonic fields on gas diffusion flames show that they can either increase or decrease the amount of flame noise generated. The studies described show that a reduction in flame noise can only be obtained with a single frequency field. The presence of a field composed of more than one frequency results in an increase in flame noise at frequencies related to the beat frequency of the applied signals. Schlieren photographs of the flame indicate a relationship between the position of its transition to turbulence and the character of the applied field.