History:
The first experimental moving-coil (also called dynamic) loudspeaker was invented by Oliver Lodge in 1898. The first practical moving-coil loudspeakers were manufactured by Danish engineer Peter L. Jensen and Edwin Pridham in 1915, in Napa, California.
A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer,[1] that is, a device that converts an electrical audio signal into a corresponding sound.[2] A speaker system, also often simply referred to as a "speaker" or "loudspeaker", comprises one or more such speaker drivers, an enclosure, and electrical connections possibly including a crossover network.
In order for a speaker to efficiently produce sound, especially at lower frequencies, the speaker driver must be baffled so that the sound emanating from its rear does not cancel out the (intended) sound from the front; this generally takes the form of a speaker enclosure or speaker cabinet, an often rectangular box made of wood, but sometimes metal or plastic. The enclosure's design plays an important acoustic role thus determining the resulting sound quality. Most high fidelity speaker systems include two or more sorts of speaker drivers, each specialized in one part of the audible frequency range . The smaller drivers capable of reproducing the highest audio frequencies are called tweeters, those for middle frequencies are called mid-range drivers and those for low frequencies are called woofers. Sometimes the reproduction of the very lowest frequencies (20Hz-~50Hz) is augmented by a so-called subwoofer often in its own (large) enclosure. In a two-way or three-way speaker system (one with drivers covering two or three different frequency ranges) there is a small amount of passive electronics called a crossover network which helps direct components of the electronic signal to the speaker drivers best capable of reproducing those frequencies. In a so-called powered speaker system, the power amplifier actually feeding the speaker drivers is built into the enclosure itself; these have become more and more common especially as computer speakers.
Smaller speakers are found in devices such as radios, televisions, portable audio players, personal computers (computer speakers), headphones, and earphones. Larger, louder speaker systems are used for home hi-fi systems ("stereos"), electronic musical instruments, sound reinforcement in theatres and concert halls, and in public address systems.