It is generally acknowledged that the sound pressure level (SPL) of air-modulated speaker (AMS) will finally reach the level of saturation when the chamber pressure increases to a certain degree. As a new approach to obtain higher SPL output, supersonic flow modulation was discussed in which the flow speed of nozzle exit was increased from sonic to supersonic. Results from the quasi-steady theory proved that, when the chamber pressure is high, the SPL in the supersonic case is higher than that in the sonic case. Larger SPL increments generally appear at smaller nozzle area ratio. The improvement of the source intensity was validated by the comparison of sound measurements between the sonic and supersonic cases in low frequency modulation. But in high frequency modulation, due to the transient flow effect, the SPL in the supersonic case is the same as that in the sonic case while the air jet is considered to be not fully developed or sped up to be supersonic.