The cabinet or structure of a speaker
into which the various speaker elements (the drivers, the crossover, the
binding posts, etc.) are placed and attached.
Speaker enclosures can be essentially any shape and any size made up of
almost any material. Most speaker enclosures are made of MDF (medium
density fiberboard) and then covered in a thin wood veneer or some other
coating. Some cabinets are made of plastic or metal and some even use
concrete, Corian, or other highly rigid materials.
Enclosures generally should be very well braced with internal
strengthening members and fairly thick cabinet walls. Enclosures should be
inert so as not to color the sound by vibrating with the speaker drivers.
They must also be designed to function properly with the speaker drivers
placed in them (for example a large woofer for a subwoofer will not
perform optimally in too small an enclosure). There are as many variations
on speaker enclosures as there are speakers.
There are generally no hard and fast rules for what makes a good enclosure
other than the resulting speaker sound good (in order to accomplish this
there are certain mathematical formulas for matching a speaker driver to
the proper volume enclosure). When purchasing speakers, however, look for
enclosures that are solid and do not sound hollow when you tap them with
your knuckles. Enclosures should be sturdy and well built. A heavy
enclosure does not ensure a good enclosure, but often a heavier enclosure
is more solid and more inert and so may have some bearing on your decibels.
A type of speaker enclosure used with
subwoofers to produce large amounts of bass with minimal power input by
utilizing essentially a sealed subwoofer enclosure mated to a ported box.
A bandpass enclosure first uses a sealed subwoofer enclosure with an
outward firing bass driver. This enclosure is sealed to a second enclosure
with the bass driver firing into the second enclosure. The second
enclosure does not have its own driver only a port. The audio output
developed by the driver is reinforced in the second ported enclosure and
then emerges through the port. In a bandpass enclosure the bass driver is
not visible from outside the complete enclosure, and all the sound output
comes through the port or tube.
Bandpass enclosures maximize the output of a speaker driver over a narrow
range of low frequencies. The enclosure must be carefully designed and
built to strict tolerances in order to operate properly. Bandpass
enclosures are typically not used for high-end, high-quality subwoofers.
They are limited in the frequency band they can reproduce and their sound
quality is generally inferior to well-designed traditional subwoofer
enclosures using ported or sealed designs.
- Port Tube
Tube of a specified length and diameter
(length and diameter dependent on specific application) with one end open
to the outside of a speaker enclosure through a round hole and the other
open to the inside of the speaker enclosure. Ports are used primarily for
subwoofers and other bass speaker drivers. They allow the air movement
inside the speaker enclosure caused by the back of the speaker driver to
vent or move to the outside.
Using a port enables a speaker driver to play at a louder level than an
equivalent speaker driver in a sealed enclosure when driven with the same
power. Ported enclosures, also known as bass reflex enclosures, enhance
the efficiency of a speaker driver, but they result in some decrease in
total low frequency extension. As a compromise between ports and
completely sealed enclosures, some speaker enclosures feature passive
radiators allowing the cabinet to remain sealed while taking advantage of
some energy generated inside the enclosure.
Mechanical device used to reproduce
sound waves when a power signal is applied representing those sound waves
by vibrating some material that in turn creates vibrations in the air thus
Speakers come in many varieties and many versions suited for a variety of
tasks. The majority of speakers are dynamic designs using cones or domes
vibrated by the movement of a coil of wire near a stationary magnet (the
coil of wire generates a magnetic field that attracts it to and repels it
from the magnet thus generating motion). Electrostatic and planar-magnetic
speakers are also used along with a number of variations and other sound
Most speakers use a crossover to split up the audible frequency into a
number of bands or sections. The frequency bands are then reproduced by
different speaker drivers most capable of reproducing those sounds.
Low-frequencies use woofers that are large in size. The middle frequencies
are often reproduced with midrange drivers and the highs are handled by
tweeters. Subwoofers are sometimes used also. Subwoofers are specially
designed speakers whose purpose is to reproduce low frequency sound waves
Small speakers are typically known as satellites or bookshelf speakers
while larger speakers are known as floor-standing speakers. There are
center channel speakers designed to sit on top of or below a video display
to reproduce movie and television dialog and other effects. Surround
channel speakers are mounted high up on the walls near or behind the
listening position to create a three-dimensional, fully enveloping sound
field. Most surround speakers are dipole or bipole designs.
Dipole speakers feature speaker drivers on two opposite sides of a speaker
enclosure. Their drivers operate out of phase so that as one driver moves
in the other driver on the opposite side movies out. Dipolar speakers
create a broad sound on either side of the speaker and eliminate most
sound from the sides of the speaker.
Bipolar speakers also emanate sound from two opposite sides of a speaker
enclosure, but their speaker drivers operate in phase meaning that they
both go in and out at the same time. Bipolar speakers create a wide
soundstage with sound primarily at the front and back of the speaker but
also propagating to the sides.
Direct radiating speakers emit sound from one side with a single set of
speaker drivers. Direct radiators are easier to locate sonically. They
also provide the best imaging and space delineation, but their sweet spot
(optimal listening position) is fairly small and their soundstage is not
as wide as that of a bipolar speaker.
Speaker drivers of any type are built into some form of cabinet to hold
them. Most speaker enclosures are built of sturdy materials such as MDF
and are braced internally with crossbeams and other such pieces to ensure
they are strong and do not vibrate too much with the drivers (this is
called resonance and creates a sonic distortion). The enclosures are
designed in different ways to affect the sound of the drivers mounted
within them, especially in regard to low frequency output. The most common
types of enclosures are sealed or acoustic suspension enclosures, ported
or bass reflex enclosures, bandpass enclosures, and isobaric enclosures.
Of these, the most widely used are the ported and sealed designs.
Speakers feature some type of binding that allows power from an amplifier
to be connected with speaker wire. The two primary connections are
five-way binding posts and spring connections. Of the two, the five-way
binding post is vastly superior.
Speakers all serve essentially the same function, the faithful
reproduction of sound. However, there are seemingly as many variations of
speaker design as there are sounds to reproduce. The important thing is
finding a speaker with a good quality of sound, a good dynamic range and a
reasonably flat frequency response that fills the specific needs of an
Special form of speaker used to
reproduce only the lower portion of the audible frequency spectrum usually
from 80 Hz down to or below 20 Hz. True subwoofers should be able to play
useful audible information down close to 20 Hz (the lower limit of human
hearing). Most subwoofers feature one or more speaker drivers measuring
ten or more inches in diameter (with powerful subwoofers often using
drivers of a minimum twelve inches in diameter).
There are two primary types of subwoofer – powered and non-powered.
Powered subwoofers feature their own built-in amplifier while non-powered
models need an outboard amplifier (or may be connected to the amplifier
used for the main stereo speakers using a crossover). Powered subwoofers
are by far the most popular and most versatile models.
Most subwoofers contain some type of passive or active crossover network
to separate the low bass signals (usually below 80 Hz) from the rest of
the frequency spectrum. The subwoofer then reproduces the low frequency
signals and sends the remainder on to the other speakers in an audio
Within the realm of subwoofers, there are a number of cabinet designs used
including bass reflex or ported enclosures, sealed or acoustic suspension
enclosures, isobaric enclosures, and bandpass enclosures. Of these, the
two most popular for home audio are the sealed and ported enclosures.
Sealed enclosure subwoofers feature the lowest extension (play the lowest
into the frequency spectrum) and best sound quality, but they are also the
least efficient needing additional power to reach the same output levels
(volume) as the other designs. Ported subwoofers, on the other hand, use a
port (a tube of a particular length allowing air to pass from the inside
of the enclosure to the outside through a round hole) to increase
efficiency and add around three decibels more output for a given power
input versus a sealed enclosure while giving up some ultimate low
frequency extension. Both ported and sealed box subwoofers can provide
powerful, engaging sound with excellent quality when properly designed and
Subwoofers need a large amount of power in order to optimally reproduce
low frequency sounds. Low frequency sound waves are very large (about 56
feet long for a single cycle at 20 Hz) and thus require large drivers and
large amounts of power to faithfully reproduce them. Most subwoofers
feature long-excursion drivers meaning that the speaker drivers travel a
long distance back and forth to generate sound waves (a long distance, of
course, is relative with most long-throw driver moving up to one inch or
so). As drivers become larger and they travel farther, more and more power
is required to move them and provide adequate control (damping). Most
powered subwoofers, thus, feature amplifiers of 200 watts or more,
although some subs use amplifiers of 100 watts and others use more than
Due to the nature of low frequency sound waves, subwoofers do not need to
be used in pairs or located in a specific location relative to the other
speakers in a room. Low frequency sound waves are omnidirectional and the
human ear cannot locate the origin of sound waves below 80 Hz. This
attribute allows subwoofers to be placed anywhere they sound best and
allows the use of single subwoofers. Multiple subwoofers provide benefits
of increased low frequency power and extension while helping to smooth out
frequency response in a given room making two or more subwoofers desirable
if possible but certainly not necessary in most cases.
Some subwoofers make use of a servo feedback loop allowing the subwoofer
to correct its driver motion and reduce distortion. The servo circuit
monitors the movement of a subwoofer’s speaker driver and compares it to
the input signal (what the subwoofer is supposed to output). If the two do
not match, there is distortion. The servo circuit watches for such
distortions and then adjusts the amplifier’s output to correct the
speaker driver’s motion resulting in reduced distortion.
Subwoofers are becoming increasingly important and useful in home audio
and home theater. They produce the lowest frequencies with weight and
accuracy allowing the other speakers to concentrate on frequencies above
80 Hz or so. Typically this allows the other speakers to provide better
sound quality more effortlessly since less of their input power is needed
to produce low-frequencies. Additionally, the 5.1 digital surround sound
systems allocate a specific low frequency effects channel for subwoofers.
Subwoofers produce the lowest frequencies, those below 80 Hz or so, with
the greatest detail, accuracy, ease and power adding visceral impact and
oomph to almost any audio system.