Speakers are one of the most essential parts of any electrical audio system. A speaker or a speaker system actually comprises of electromechanical transducers that convert an electrical signal into sound. Depending on a lot of factors such as functioning dynamics and structural variations, speakers come in several types. Each type has got its own set of features and characteristics.
Loudspeakers have come a long way from the days of 1876 when Alexander Graham Bell patented the first electrical loudspeaker as part of his telephone. With the unprecedented improvement in technology since then, speakers have also evolved from a simple metal horn to the present day hi fi plasma arc speakers. But the basic technology is in fact rather simple and has not altered much for nearly 50 years. However modern speakers sound much better than they did 50 years ago.
The word loudspeaker usually denotes individual devices or drivers, and the entire system consisting of an enclosure integrating one or more drivers and additional electronics. Based on such structural qualities as well as the dynamics of working some of the popular types of speakers are as followed.
The monopole is a box speaker with its collection of speaker drivers generally set together on one side of the box. Sound transmission is achieved usually when all drivers are operated with the help of the movement of air in the same direction.
Bipole speakers have two cones, one facing the room, and the other facing backwards to produce one half of the total sound quantity as a direct sound and the other reflects off the wall.
Dipole speakers are of two types. One is physically similar to bipoles, but the speakers are out of phase, the front cone and the rear cone move in opposite directions. And the other with both speakers almost in front, but pointed 90 degree off from each other, so if the speaker is mounted on the wall, the speakers are aimed along the wall.
Speakers are also categorized based on the operating technology and other specifications as well. Accordingly there are several types available in the market.
Based on impedance speakers can be 4 ohms or 8 ohms type. Again the baffle or enclosure types are responsible for names such as sealed speaker, bass reflex speaker etc. The number of drivers a speaker has got also decides its classification such as 2 ways, 3 ways etc.
There is a full range single driver speaker, which attempts to cover the entire audible frequency spectrum with only one driver unit. Therefore, there is no need of an electronic crossover network.
The other is the midrange, which has the capability to produce frequency ranging from approximately 300 to 5000 hertz. They are also called, less commonly, squawkers.
Piezoelectric speakers are commonly found in watches used as beepers. They produce single high frequency sound.
Electrostatic loudspeakers produce sound by using high voltage electric field to drive a thin membrane between two perforated conductive plates called stators.
Ribbon speakers, just as the name suggests, consist a thin metal film ribbon suspended in a magnetic field. When electrical signal is applied to the ribbon it produces the sound.
Planar magnetic loudspeakers have flat roughly rectangular shaped radiating surfaces, with a flexible membrane and a voice coil printed or mounted on them. The current flowing through the coil interacts with the magnetic field of carefully placed magnets on either side of the diaphragm. This causes the membrane to vibrate more or less uniformly and without much bending or wrinkling.
Bending wave loudspeakers use a diaphragm that is intentionally flexible.
Plasma arc speakers use electrical plasma as drivers. It has minimal mass, but it can be charged and manipulated by an electric field, the result is a very linear output at frequencies far higher than the audible range.
Apart from the above mentioned speaker types, one can find other classifications of speakers, based on various other features and functionalities, such as woofers, subwoofers, tweeters, etc.