Loudspeaker

The Daleks used a loudspeaker system. (TV: Mission to the Unknown, The Daleks' Master Plan)

A Cyberman chest unit contained a small hidden "chest unit loudspeaker" which allowed them to receive audio communications. (TV: The Moonbase/PROSE: Doctor Who and the Cybermen)

A woofer was a type of loudspeaker used to render low frequencies more accurately. (PROSE: How The Monk Got His Habit)