a portable electronic device , such as a pager or a mobile station , has a housing and a vibration motor coupled to the housing for imparting vibration to it . within the device , an electronic audio signal is preferably split into high and low frequency components by parallel filters . pulses of the low frequency component are rectified , voltages of those rectified pulses are quantified and at least some are converted to pulse widths , and the train of pulse widths is amplified to drive the vibration motor , resonating the housing at in correspondence with the pulse amplitudes of at least some pulses of the original electronic audio signal . various adaptive schemes are presented to control the number of modulated pulses that drive the vibration motor to enhance the user experience . the vibration motor may act as an audible sub - woofer and / or may provide a bass effect vibration within or beyond the audible range in correspondence to certain spaced pulses of the original audio signal .