Full circumferential geometry voice coil bobbin made with non-metal or metal

An electromagnetic loudspeaker transducer; where its voice coil bobbin has a fully circumferential geometry to provide increased mechanical strength. When the bobbin to be made with sheet metal and sheet metal deep drawn it further provides a stiffened construction by work hardened metal during the process. The full circumferential bobbin made with metal also serve as a one turn coil to short out the induced current from back electromotive force due to the voice coil moving under the magnetic field from the audio transducer's motor structure. The bobbin also allows a support feature for the transducer diaphragm to attach to and avoid leaving a dent mark on sheet metal diaphragms.