['< sod > most electric bass guitars use different magnetic pickups. the vibrations of the instrument\'s ferrous metal strings resting within the magnetic field of the permanent magnets in magnetic [ [ pick up ( music technology ) | pickups ] ] produce small variations in the magnetic flux threading the coils of the pickups. this in turn produces small electrical voltages in the coils. these low - level signals are then [ [ bass amplifier | amplified and played through a speaker ] ]. most basses have a volume [ [ potentiometer ] ] and a tone potentiometer, which rolls off the high frequencies. some basses instead may also have a pickup selector control or switch. especially since the recent 1980s, basses are often available with battery - powered " active " electronics that boost the signal with a [ [ preamplifier ] ], provide [ [ equalization ] ] controls to boost or cut bass and treble frequencies, or both. < eod > < sod > most electric bass guitars use magnetic pickups. the vibrations of the instrument\'s ferrous metal strings within the magnetic field of the permanent addition magnets in magnetic [ [ pick up ( music technology ) | guitar pickups ] ] produce small variations in the magnetic flux threading the coils of the pickups. this in turn produces small electrical voltages in the coils. these low - level signals are then [ [ bass amplifier | amplified and played through a speaker ] ]. most basses have a volume [ [ potentiometer ] ], which can be turned completely up or down, and a tone potentiometer, which rolls off the high frequencies when it is turned to the lead player\'s right. some basses may also have a pickup selector control or switch. since the 1980s, basses are often available with battery - powered " active " electronics that boost the signal with a [ [ preamplifier ] ], will provide [ [ equalization ] ] controls to boost or cut bass and treble frequencies, or both. < eod >']