Tuning device with combined backflow function

A supercharger has an inner wall defining an inner cavity for receiving lobed rotors for rotation therein, a low-pressure inlet and a high-pressure outlet. A sound attenuator is associated with the housing and located adjacent to the high-pressure outlet. The sound attenuator has a tuner chamber and circumferentially spaced tuner ports fluidly connecting the tuner chamber with the internal cavity of the housing to define a Helmholtz resonator. A land is defined between the circumferentially spaced tuner ports such that the high-pressure outlet and low-pressure inner chambers defined between the rotor lobes and the inner wall are fluidly connected when the rotor lobes are in alignment with the land to reduce the pressure differential between the high-pressure outlet and the low-pressure inner chambers.