A loudspeaker is a device that is used to transform
electrical energy into
mechanical energy (
sound waves). Most loudspeakers use a coil of
wire, known as the
voice coil, moving through a magnetic field, usually a
permanent magnet around the voice coil. A substance of some kind, usually
paper,
polypropylene,
composites, or
metals, is attached to the voice coil structure to push the air, making the waves that we know as
sound. This attachment is usually cone or dome shaped. The rest of the features depend on the type of speaker for the most part.
Low
frequency speakers, mainly
woofers and
subwoofers, are large and require a great deal of support to hold the parts together. A frame is attached to the magnet and the cone of the speaker is attached to the frame with a flexible baffling. A small dome is usually placed over the hole in the center where the voice coil is to protect the insides of the speaker from dust. The weight of the material that the cone is made of is very important. The weight controls the speed and frequency response that the loudspeaker will have due to the difficulty of overcoming the intertia of a heavy (high
intertia) material.
Smaller speakers, made for higher frequencies, called
tweeters are made somewhat differently from low frequency speakers. Being smaller they don't need as much baffling as the larger, heavier speakers. They are often made of metals, like aluminum. Tweeters are capable of reproducing very high frequencies and can generate a lot of heat, sometimes calling for a more
active cooling system.
There are other sorts of loudspeakers which are less common. There are
ribbon speakers that are usually used for high frequencies in place of a normal tweeter. Flat panel speakers have also made it to the marketplace to fit alongside equally flat computer monitors. Horn loudspeakers are often used for high power applications, such as
live performances as they are more robust and quite powerful.
The design of the
enclosure for a loudspeaker is nearly as important as the mechanical portion of the speaker itself. The size, shape, and venting of the enclosure effects the frequency response and loudness of the speaker. There are several kinds of enclosures:
sealed,
vented, and
transmission line are among them. Sometimes a pair of speakers will be used facing each other, with their cones together, and with inverted phase. This configuration is called
isobaric. It adds the output power of each speaker together to emulate the effect of a single
more powerful speaker.
The support electronics are just as important as the rest of the speaker. Most speaker systems are labelled as 2 way, 3 way, or more, indicating that the enclosure contains multiple actual speakers, each handling a different portion of the frequency range. An electronic circuit called a
crossover must be used to smoothly transition between the cutoff frequencies of the individual speakers. Some speakers, usually seperate subwoofers, also have amplifiers in them. The amplifier must be of
high quality or the signal may be distorted and the sound will not be pleasant.