Various implementations include loudspeaker drivers. In some aspects, an electro-acoustic driver includes: a cup section; a core section at least partially housed in the cup section, the core section including: a primary magnet; and a coin adjacent to the primary magnet; a bobbin surrounding the core section between the cup section and the core section, where the bobbin and the core section define an inner magnetic gap; a coil surrounding the bobbin and a portion of the core section; and a ferrofluid located at the inner magnetic gap, where the driver has an outer diameter less than or equal to approximately 10 millimeters.