Acoustic suspension
A type of speaker enclosure that uses a sealed box to provide tight, accurate bass response. It gives up some efficiency to provide bass that is more accurate and controlled, so compared to a bass reflex design, it may require more amplifier power to play at the same volume level. See also bass reflex.

Bass reflex
A type of speaker enclosure that includes a "tuned" port or passive radiator to increase and extend bass response (by releasing some of the energy created by the inward movement of the woofer cone).

Bass reflex designs are more power-efficient than acoustic suspension designs — they'll play louder than an acoustic suspension speaker when driven with the same amplifier power. But they may sacrifice some bass accuracy in exchange for the added bass output.

Bi-amping and bi-wiring
It's becoming more common for higher-performance speakers to include dual sets of terminals, usually binding posts (see terminals, below). Models with dual terminals almost always also feature a special type of crossover with separate "high-pass" and "low-pass" sections.

Speakers with dual sets of terminals work fine when used with a single set of speaker cables. In fact, they usually come from the factory set up for conventional operation, with "jumpers" installed between the two sets. These jumpers can be easily removed for bi-amping or bi-wiring.

• Bi-amping means that instead of driving a speaker full-range with a single channel of amplification through a single set of speaker cables, you actually connect two sets of cables, with each set carrying the signal from a separate amplifier (or amp channel). This way, both low-frequency drivers (woofers) and high-frequency drivers (tweeters) receive dedicated amplification.
• Bi-wiring involves connecting two sets of cables to your speakers, like bi-amping, but both sets of cables connect to the same set of output connectors on your receiver or amplifier. Bi-wiring doesn't deliver more wattage to your speakers, so it doesn't offer as dramatic a sonic improvement as bi-amping. Still, many audiophiles find that it offers subtle improvements in imaging and detail.

Bipole
A speaker design that uses two sets of drivers to generate equal amounts of sound both forward and backward, or side to side, with the two sounds being "in phase." In a home theater setup, bipole speakers are particularly effective at creating a full, diffuse soundfield when used as surround speakers placed behind the listening position. Some speakers offer both bipole and dipole modes.

Center channel speaker
The center channel speaker reproduces almost all of a movie's dialogue and much of the special effects. Since its purpose is to keep sound anchored to the on-screen action, a good center channel speaker is crucial for a well-balanced home theater system. It's usually mounted on top of your TV, or directly above or below it. See our article on choosing home theater speakers for more info.

Coloration
Any change in the character of a sound that reduces accuracy, such as an over- or under-emphasis of certain frequencies.

Connectors (pins, plugs, etc.) (Click for pictures)
There are several different ways to connect the cables from your receiver or amplifier to your speakers. Bare wire connections are acceptable, especially with "spring clip" terminals. However, there are other connector types that provide more solid and secure connections, especially with binding post terminals.

• Spade connectors are compatible with most binding post terminals. A spade fits around the terminal's central threaded post, allowing you to then tighten the collar down on the spade for a snug, secure connection. But keep in mind, some electronics now have terminals that prohibit the use of spade connectors.
• Pin-type connectorswill work with both spring clip and binding post terminals. This is probably the best type for connecting a thick, heavy-gauge wire to a small spring clip connector. On a 5-way binding post, this slender pin will also fit the hole that's back near the base of the central post (see binding post illustration, below). You can then tighten the collar down against it.
• Banana plugs will plug straight into the center of 5-way binding posts. They make a quick and convenient connection — nothing to loosen or tighten.
• Double-banana plugs are the same as banana plugs, except the positive and negative banana connectors are both fixed in a molded housing that spaces them 3/4" apart. (These are even quicker and easier to connect than regular, single banana plugs — as long as the terminals on your speakers and/or receiver are true 5-way binding posts with the proper spacing.)

Crossover
A circuit that divides the frequency spectrum into two or more parts. A crossover acts as a filter, allowing certain frequencies to pass through to the speaker while blocking others. It's the crossover's job to send only high frequencies to the tweeter and only low frequencies to the woofer. (And midrange frequencies to the midrange driver in a 3-way speaker.)

A high-pass crossover allows only frequencies above the "crossover frequency" to pass through, while a low-pass crossover (common in powered subwoofers) allows only frequencies below the crossover frequency to pass through. A "bandpass" crossover combines a high-pass and a low-pass so that the driver (often a midrange unit) only sees a restricted band of middle frequencies.

Decibel (dB)
The standard unit of measure for expressing relative power or amplitude differences. With audio, it represents loudness. One dB is the smallest change in loudness most people can detect. A 1 dB difference is barely noticeable, but a 10 dB difference is big — a speaker playing at 10 dB higher volume will sound roughly twice as loud.

Another amazing dB fact: For any given set of speakers, each 3 dB increase in volume level requires a doubling of the amplifier power.

Diaphragm
The part of a speaker driver that moves, producing the sound. Each diaphragm is directly connected to a voice coil. The diaphragm for a woofer is a cone, while for a tweeter, it's often a dome.

Diffusion
The scattering of sound. Diffusion reduces the ability of a listener to pinpoint the actual location of a speaker, a useful quality in surround speakers. Diffuse surrounds create a wraparound soundfield that draws you into the on-screen action.

Dipole
A speaker design that uses two sets of drivers to generate equal amounts of sound both forward and backward, or side to side, with the two sounds being "out of phase." Dipoles are often used as surround speakers, and are very effective at creating a diffuse soundfield when placed on the sides of the listening position. Some speakers offer both dipole and bipole modes.

Direct and reflected sound
The sound that you hear from your listening/viewing position is a combination of the direct sound that travels straight from your speakers to your ears, and the indirect, reflected sound — the sound from your speakers that bounces off the walls, floor, ceiling or furniture before it reaches your ears.

Dispersion
The degree to which a speaker's sound is spread over the listening area.

Driver
Any individual diaphragm (cone, dome, etc.) within a speaker that compresses and rarefies the air to create sound waves, such as a woofer, tweeter, midrange, etc.

Dynamic range
The difference between loud and soft sounds. A speaker with wide dynamic range — one that can reproduce the sudden and wide changes between loud and soft sounds in music and video soundtracks — will sound more realistic (all other things being equal).

Efficiency
Although a speaker's efficiency rating is almost always correlated to its sensitivity rating, it is actually a different measurement. The efficiency rating for a speaker is a measure of how well a speaker converts watts of electrical power into watts of acoustical power. Most speakers have a very low efficiency rating — between 1% and 10% — so manufacturers rarely provide this information, choosing instead to list sensitivity ratings.

Flat
When a speaker's response is described as "flat," that's a good thing. It means that the speaker can accurately reproduce a signal that is fed to it without adding unnatural coloration to the sound. Specific frequencies don't sound too loud or too soft.

Frequency response
The human ear responds to frequencies from approximately 20 to 20,000 cycles-per-second, or Hertz. A speaker's frequency response indicates how much of that range can be reproduced.

Front speakers
In home theater, the front left and right speakers deliver a wide soundstage that blends with the video to create a more realistic and exciting movie experience. In addition to reproducing the musical score, front speakers work with your center channel to reproduce the special effects, along with any on-screen action that moves left to right or vice versa. The front left and right speakers in your home theater system also act as the left and right stereo speakers for listening to music. See our article on choosing home theater speakers for more info.

Hertz (Hz)
The unit of sound frequency; one Hz is equal to one cycle per second. The range of human hearing is 20-20,000 Hz. Points of reference: low "E" on a bass guitar is 41 Hz; middle "C" on a piano is 262 Hz; cymbals can go out to 15,000 Hz.

Imaging
The ability of a speaker to reproduce spatial information in a recording so that you can visualize the relative positioning of individual voices and instruments as you're listening.

Impedance
The load value (in ohms) that the speakers present to the amplifier — the amount of resistance to the flow of current. While playing music, a speaker's actual impedance constantly fluctuates; however, speakers are usually given a single nominal impedance rating for easy comparison. Low-impedance speakers (4 ohms or less) can cause problems with receivers or amplifiers that are not designed to deliver large amounts of current.

Kilohertz (kHz)
One thousand Hertz.

LFE input
Found on some powered subwoofers, this special preamp-level input accepts the "Low Frequency Effects" signal that's output by digital 5.1-, 6.1-, or 7.1-channel home theater receivers, ensuring proper bass reproduction. This type of input doesn't route the signal through any processing inside the sub which could potentially interfere with the low-pass crossover built into the receiver's bass management circuitry.

Some powered subs feature an unfiltered LFE input/output — the output sends full-range signals minus the low frequencies back to a receiver or preamplifier's "main in" jacks for even more precise sonic control.

Midrange
Generally considered to be the range of frequencies above bass and below treble that our ears are most sensitive to, which includes most vocal and instrumental sounds. Sometimes refers to a driver designed to reproduce these frequencies.

Motor structure
The part of the speaker that moves a diaphragm to produce sound. The motor structure basically consists of a voice coil that sits inside a cylindrical magnet. Alternating current is pumped through the voice coil, which constantly changes its magnetic polarity. As the voice coil alternates between being attracted to and repelled by the magnet, it moves the attached driver to create sound.

Neodymium
A material used in some speaker magnets. Neodymium magnets are smaller and more powerful than conventional speaker magnets.

Passive radiator
A type of bass reflex speaker enclosure that includes a "passive" woofer in addition to the main woofer. The passive woofer isn't powered, but moves in response to changes in air pressure inside the cabinet that are caused by movement of the main woofer. Passive radiators are often used in speaker cabinets too small for a properly tuned port. Plus, they avoid some of the issues associated with ports such as port turbulence, which can sometimes lead to a low-pitched whistling noise coming from the port. However, passive radiators tend to be more complex to design, so you'll typically pay more for speakers with passive radiators than similar ported models.

Phase
Refers to the timing relationship of two or more signals or sound waves. It's especially important to be sure that your stereo speakers are playing "in phase." This means that the drivers (woofers and tweeters) of your right and left speakers are moving in and out at the same time.

If your stereo speakers are "out of phase" — that is, with one set of positive and negative leads reversed — you'll hear significantly less bass, and instead of producing a strong center image, the sound tends to stay localized at the speakers. To learn how to be sure your speakers are in phase, check the Home Speakers FAQ).

Phase control
A 2-position switch found on some powered subwoofers that lets you delay the subwoofer's output slightly so that it is in phase with the output from your main speakers.

Power handling
A measure of how much amplifier power, in watts, a speaker can take before it is damaged.

Resonance
When a component or system vibrates more at a certain frequency than at any other frequency. In a speaker system, resonance with the speaker enclosure or any of the components can lead to colorations in the sound.

RMS
A term used to indicate the average level of power that a receiver or amplifier can sustain over a given period of time. Average power ratings (ex: 100 watts RMS) provide a more realistic assessment of your amp's performance than peak power (ex: 400 watts peak/dynamic power) since an amp can only sustain peak power for a short period of time. (RMS stands for "root mean square," which is one of the mathematical methods used to calculate an amp's average power output. While it isn't an accurate descriptor of the measurements themselves, it's commonly used throughout the industry to denote the average power rating.)

Satellite speaker
A small speaker with limited bass response that's often designed to be used with a matching subwoofer.

Sensitivity
A sensitivity rating tells you how effectively a speaker converts power (watts) into volume (decibels). The higher the rating, the louder your speakers will play with a given amount of amplifier power. Sensitivity is often measured by driving a speaker with one watt and measuring the loudness in decibels at one meter.

The chart below illustrates that a few dB in sensitivity can make a big difference:

Soundstaging
A stereo or home theater system's ability to present music, dialogue, and other sounds as taking place within a physical space with definite width, height, and depth. The individual vocal and instrumental "images" are part of the "soundstage."

SPL (sound pressure level)
The intensity or volume level of sound (measured on the dB scale). See sensitivity, above.

Subwoofer
A speaker specially designed to reproduce a range of very low frequencies only (the bass). The typical range for a subwoofer is about 20-200 Hz.

A "powered subwoofer" includes a built-in amplifier to drive the speaker.

Surround
Connects a driver's diaphragm to its basket. The two most common surround materials are rubber and foam. Rubber typically lasts longer than foam, especially in warm, moist climates, but tends to cost more.

Surround speakers
In a home theater system, the speakers located beside or behind the listening/viewing position. These speakers can be mounted on the walls, placed on stands, or set on bookshelves. They help create an enveloping three-dimensional soundstage by reproducing the surround information on video soundtracks and music recordings encoded with surround sound. For details, check out our nuts and bolts discussion of the different surround sound formats.

Some multichannel movie soundtracks also take advantage of surround back speakers. These speakers are used in addition to the regular surround speakers mentioned above, and can either be a pair of speakers placed behind and slightly to the sides of the listening area, or a single speaker directly behind it. You'll need a six- or seven-channel receiver for this type of setup, but adding surround back speakers can give you even more convincing wraparound effects. See our article on choosing home theater speakers for more info.

Terminals
You probably don't think about the connectors on the back of your speakers until you go to hook them up. There are two basic types: spring clips and binding posts.

• Spring clip terminals are usually found on lower-priced speakers, and low- to medium-priced receivers. They work best with bare wire connections with small-gauge speaker wire, or pin-type connectors (see connectors, above).
• Binding post terminals are a sturdier, more versatile type of speaker jack, often found on higher-quality speakers and receivers, and on most amplifiers. They're threaded, so you can tighten them down against the wire or connector for an extra-snug connection.

A common variety of binding post, especially for speakers, is known as a "5-way" binding post. This type accepts bare wire, pin connectors, spade connectors, banana plugs, and double-banana plugs.

Timbre
Pronounced "tam-burr." The quality of a sound related to its harmonic structure. Timbre is what gives a voice or instrument its sonic signature — for instance, why a trumpet and a saxophone sound different when they play the same note.

Transducer
Any device that converts a signal from one physical form to another. Examples: a phono cartridge (mechanical to electrical); a speaker (electrical to mechanical).

Transient
A short-lived aspect of a signal, such as the attack and decay of musical tones. A speaker that can react quickly to rapid changes in the music is said to have good "transient response."

Tweeter
A small, lightweight driver that reproduces the highest musical frequencies, like violins, cymbals, female vocals, etc. The typical range for a tweeter is everything above 2,000 Hz or so.

Unfiltered LFE input
See LFE input.

Video shielding
A way of containing a speaker's magnetic energy inside its enclosure. This is usually achieved by placing another speaker magnet back-to-back with the existing one so that the two magnetic fields cancel each other. Shielding may also be achieved by lining the inside of the speaker cabinet with metal.

Video shielding is important for home theater speakers — especially the center channel speaker — because if an unshielded speaker is placed too close to your TV, the magnetic energy can cause picture distortion and even permanently damage the TV's picture tube.

Voice coil
The cylindrical coil of wire that moves in the magnetic field of a dynamic driver. The voice coil is bonded to the diaphragm, which actually produces the sound.

Voice-matching
When speakers possess a similar timbre or tonal quality. Voice-matched (or timbre-matched) speakers in a home theater system will result in more seamless, consistent, convincing wraparound sound. A good way to get voice-matched speakers is to stay within a family or series of speakers from a single manufacturer, or to get a pre-matched multi-speaker system.

Watt
A unit of power. Named after James Watt for his contributions to the development of the steam engine.

Woofer
A type of driver that features a cone-shaped diaphragm, commonly used for producing the mid- and low-frequency portions of the music signal.