Just as a loudspeaker is used to produce sound in air, an acoustic projector or sound source is used to generate sound underwater. Loudspeakers convert electrical signals into sound in air. Similarly, acoustic projectors convert electrical signals into sound in water. (See How are sounds made?). Underwater sound sources (may also be called transducers) can be built in a number of different ways. Some underwater sound sources work the same way as loudspeakers in a home stereo system. They have a speaker that is vibrated using an electromagnet. Other sound sources create vibrations with special materials that expand and contract when electricity runs through them. Still other sound sources work much like a drum being played from the inside. A sound source or projector is used to create sound to do such tasks as find fish, navigate, measure water depth, and communicate underwater.
Projectors can be used in several ways. Some are placed on the seafloor. Others are placed on deep-sea moorings, with a float that holds them up and an anchor on the seafloor. Most often, projectors are mounted on a boat. A bolt through the hull or a transom can mount a projector on the hull of a boat. A projector can also be bound to the inside of the hull. The signal would then be transmitted through the hull. Finally, a projector can be lowered from or towed by a boat or placed on a trolling mount.
The performance of an acoustic projector is described by specifying its source level, the frequency range over which it operates, and its directional properties.