Loudspeaker types

Woofers

A woofer is a loudspeaker capable of reproducing the bass frequencies. The frequency range varies widely according to design and hence while some woofers can cover the audio band from 50Hz to 3kHz, yet others may only work up to 1kHz.

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Mid-ranges

A mid-range loudspeaker, also known as a squawker is designed to cover the middle of the audio spectrum, typically from about 200Hz to about 4-5kHz. The distinction between woofers and mid-ranges is blurred however since many woofers can operate up to 3kHz. These are used when the bass driver (or woofer) is incapable of covering the mid audio range. Mid-ranges typically appear where large (>16cm or 8") woofers are used for the bass end of the audio spectrum.

Tweeter

A tweeter is a loudpeaker which is capable of reproducing the higher end of the audio spectrum, usually from about 1kHz to 20 or perhaps 35kHz.

Full-ranges

A full-range speaker is designed to have as wide a frequency response as possible. These employ an additional cone called a whizzer to extend the high frequency response. A whizzer is a small, light cone attached to the woofer's apex around the dust cap.

Subwoofers

A subwoofer driver is a woofer optimised for the lowest range of the audio spectrum. Modern speaker systems often include a single speaker dedicated to reproducing the very lowest bass frequencies. This speaker (and its enclosure) is referred to as a subwoofer. A typical subwoofer only reproduces sounds below 120 Hz (although some subwoofers allow a choice of the cross-over frequency). Because the range of frequencies that must be reproduced is quite limited, the design of the subwoofer is usually quite simple, often consisting of a single, large, down-firing woofer enclosed in a cubical "bass-reflex" cabinet. Subwoofers often contain integrated power amplifiers that may incorporate sophisticated feedback mechanisms to assure the least distortion of the reproduced bass acoustic waveform.

The very long wavelength of the very low frequency bass sounds reproduced by the subwoofer usually makes it impossible for the listener to localize the source of these sounds. Localization starts to happen above the 150Hz point. Because of this phenomenon, it is usually satisfactory to provide just a single subwoofer no matter how many individual channels are being used for the full-spectrum sound. For the same reason, the subwoofer does not need a special placement in the sound field (for example, centered between the Left Front and Right Front speakers). It can instead be hidden out of sight. Placing it in the corner of a room may produce louder bass sounds. A subwoofer's powerful bass can often cause items in the room or even the structure of the room itself to vibrate or buzz. Extended periods of high volume bass can cause items throughout a room to "walk" on a flat surface until they fall off.

Amplified subwoofers frequently accept both speaker-level and line-level audio signals. When teamed with a modern surround sound receiver and full range speakers, they are typically driven with the specific LFE (low frequency effects) output channel (the ".1" in 5.1, 6.1, or 7.1 specifications) provided by the receiver. This is because most full-range speakers are incapable of delivering the acoustic power required by the LFE in movies or in some cases, music. When used with speakers that do not reproduce low frequencies well, a subwoofer will often be configured to reproduce both the LFE channel and all other bass in the system, the latter being referred to as "bass management".