Loudspeaker types
Multi driver systems
Home loudspeaker systems are generally multi-driver
systems. 'Multi driver' refers to any speaker system that contains two or
more separate drive units, including woofers, midranges, tweeters, and
sometimes horns or supertweeters. In loudspeaker specifications, one often
sees a speaker classified as an "N-way" speaker where N is a positive whole
number greater than 1, indicating the number of separate frequency bands
into which the system divides the sound (not the number of drivers, as one
frequency band may be handled by more than one speaker driver). A 2-way
system consists of
woofer(s)
and tweeter(s)
sections; a 3-way system is constructed as a combination of woofer(s),
tweeter(s) and
mid-range speakers, etc. The frequency bands are separated and routed to
the correct driver by an
N-way crossover defined in the same manner, most usually a
passive crossover within the speaker system, but in
audiophile systems, sometimes an
active crossover placed before the
power amplifier stages.
Woofers
-
A woofer is a loudspeaker capable of reproducing the bass
frequencies. The frequency range varies widely according to design. Whilst
some woofers can cover the audio band from the bass to 3 kHz, others only
work up to 1 kHz or less.
Mid-ranges
-
A mid-range loudspeaker, also known as a squawker
is designed to cover the middle of the audio spectrum, typically from about
200 Hz to about 4-5 kHz. The distinction between woofers and mid-ranges is
blurred however since many woofers can operate up to 3 kHz. These are used
when the bass driver (or woofer) is incapable of covering the mid audio
range. Mid-ranges typically appear where large (>16 cm or 8") woofers are
used for the bass end of the audio spectrum.
Tweeters
-
A tweeter is a loudspeaker capable of reproducing the higher end of the
audio spectrum, usually from about 1 kHz to 20 or 35 kHz.
Full-ranges
- Main article:
Full-range
A full-range speaker is designed to have as wide a
frequency response as possible. These often employ an additional cone called
a whizzer to extend the high frequency response and broaden the high
frequency directivity. A whizzer is a small, light cone attached to the
woofer's apex around the dust cap. The use of a whizzer requires that the
main cone decouples from the coil at high frequencies such that most or all
of the motion at those frequencies is imparted to the whizzer, which then
acts like a second smaller coaxial loudspeaker. This gives many of the
benefits of a tweeter without the additional expense or circuitry that is
required. A whizzer might not be necessary if the diaphragm is small, stiff
and light enough. There exist full-range drivers which are capable of
reproducing a frequency range from 50 Hz to 20 kHz and higher without a
whizzer cone. These drivers are often quite small, typically 2" to 5" (5 to
13 cm) in diameter.
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 ensure 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 60Hz
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 enhancement) 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".
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