Loudspeakers have been used for many years to convert electrical signals into audio sound waves.
Although the basic principles of the loudspeaker are relatively easy to grasp, the actual design of a high quality unit is not simple: designing one and optimising it for the best sound is a difficult process.
The purpose of a loudspeaker is to convert an electrical signal into sound waves providing the most faithful reproduction that is feasible for its design.
There is obviously a very wide range in the quality of loudspeakers. Cost size, and many other factors contribute to the overall quality.
Loudspeaker frequency ranges
When looking into speakers and their technology, reference will be seen to a number of different types of loudspeaker for different frequency ranges. Often some hi-fi speaker systems are made up from a number of different speakers to enable them to cover the complete audio frequency range as it is not possible for a single speaker to cover the whole range.
- Sub-woofer: The sub-woofer loudspeaker is intended to reproduce the very low frequencies, especially giving a sense of ‘feel’ to the sound. Typically a sub-woofer loudspeaker would reproduce frequencies in the region of 20Hz or so up to just over 100Hz. Sub-woofers are present in systems where extending the bass response to very low frequencies is needed.
- Woofer: The woofer is the loudspeaker that is used in many loudspeaker systems to provide the reproduction of low frequencies. Often its range will extend down to around 30Hz or so and possibly up to 500 Hz or may be even 1 kHz.
- Mid range - squawker: As the name of this type of loudspeaker implies, it is intended to reproduce the mid range sounds A mid range loudspeaker might typically be used to cover frequencies between about 200 or 300 Hz and 5 kHz to 7 kHz or thereabouts.
- High frequency loudspeaker - tweeter: The high frequency loudspeaker is often called a tweeter in view of the fact that it reproduces the high frequencies, often above 2 to 5 kHz.
The frequency ranges for the different loudspeakers are only approximate, because different loudspeakers have different frequency ranges and different loudspeaker systems are designed in different ways with speakers covering slightly different ranges.
Loudspeaker systems vary enormously. Some only have a single drive unit or loudspeaker unit, but often these single speaker systems have limited response at the low and high frequency ends of the frequency spectrum.
As a result many systems consist of two or even three different loudspeaker drive units, each targeted at covering a different frequency range.
Loudspeaker types & technologies
There are several different technologies and approaches used within loudspeakers. As a result there are several different types of loudspeaker that can be used, and mention of these will be often be seen in the literature.
- Moving coil: The moving coil type of loudspeaker is the type that is most commonly seen. It consists of a cone attached to a coil that is held within a magnetic field.
- Horn: The horn loudspeaker type is often used for tweeters. Although it uses the same electromagnetic effect as the moving coil loudspeaker, a diaphragm held within a magnetic field that is varied in line with the audio. This causes the diaphragm to vibrate and these vibrations are then magnified by a horn.
- Electrostatic: The electrostatic loudspeaker type is uses a totally different principle to that of the moving coil and horn loudspeaker types. Instead the electrostatic loudspeaker is one in which sound is generated by utilising the force exerted on a membrane suspended in an electrostatic field.
These are various other technologies can all be used to create loudspeakers.