7.4: The Speaker as a Transducer

The Speaker as a Transducer

Speakers are electroacoustic transducers. They convert electrical energy into mechanical energy (vibrations of a diaphragm) and then into acoustic energy (sound waves in the air). This conversion is fundamental to all speaker and headphone designs.

In a way, a microphone and a speaker have much in common, as they are both transducers. The mechanics of both devices are very similar—most notably in moving-coil (dynamic) designs where a diaphragm and a voice coil interact with a magnetic field. Because of this similarity, a microphone can actually function as a crude speaker, though it is not designed for that purpose. Conversely, a speaker can serve as a microphone by generating an electrical signal when its diaphragm is moved by sound waves.

While this crossover is not typically used in practice, there are specific applications where a speaker is intentionally designed or repurposed as a microphone. One example is the Subkick, a type of bass drum microphone that uses a speaker element to capture extremely low-frequency energy. The Subkick resembles a small speaker placed in front of the drum, but instead of producing sound, it outputs a microphone signal, effectively capturing the deep resonance of the bass drum.