ABSTRACT
A dynamic microphone can function as a loudspeaker, and vice versa. The basic design of dynamic loudspeakers has been around since before 1900, though modern versions are, of course, greatly improved and have much higher fidelity. In a dynamic loudspeaker, the permanent magnet has north and south poles that never change, while the electromagnet created by current through the voice coil changes in step with the audio. An un-mounted dynamic loudspeaker suspended in free air sends sound more or less equally out the front and rear. A loudspeaker’s woofer cone must be large enough to move a lot of air to fill a room with bass. The common practice of putting loudspeakers behind the projection screen can reduce higher frequencies even more. Most earphones contain very small dynamic loudspeakers, though some models—mostly sold to the audiophile market—use electrostatic drivers. Sealed earphones are usually preferred in recording studios because less sound escapes to be picked up by the microphones.
