A portable electronic device comprising: an enclosure having an enclosure wall that forms an interior chamber and a sound output port to an ambient environment; a transducer positioned within the interior chamber and dividing the interior chamber into a front volume chamber coupling a first side of the transducer to the sound output port and a back volume chamber coupled to a second side of the transducer; and an electromechanical valve comprising a number of flaps operable to open and close a vent to the interior chamber, the front volume chamber or the back volume chamber.