The magnetic transducer is similar to the magnetic buzzer, but it does not have a 0scillating circuit, so it will not make a sound when connected to a direct current. But alternating current can drive electromagnetic transducers. The alternating current is driven through a voice coil to produce a magnetic field. When a voltage is applied the coil generates a magnetic field and then allows the diaphragm to vibrate and produce sound.
Therefore, it is alternating current instead of direct current that drives the electromagnetic transducer. From your driving method, you can determine whether you need to buy an electromagnetic transducer or an electromagnetic buzzer.