Speakers Glossary
Acoustic suspension
A type of speaker enclosure which uses a sealed box to provide accurate, tight 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 which includes a "tuned" port 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 when driven with the same amplifier power. But they may sacrifice some bass accuracy in exchange for the added bass output.
Bi-amping
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, low frequencies and high frequencies each receive dedicated amplification.
Coloration
Any change in the character of a sound, such as an over- or under-emphasis of certain frequencies (tones), that reduces accuracy.
Decibel (dB)
The standard unit of measure for expressing relative power or amplitude differences. With speakers, it's a measure of 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 twice as loud.
Another amazing dB fact: for any given set of speakers, each 3 dB increase in volume level requires double 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 sense of direction of a sound source, a useful quality in surround speakers.
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 speaker within a system, such as a woofer, tweeter, midrange, etc.
Efficiency (Sensitivity)
Indicates how well a speaker system converts input power into sound. Efficiency is usually measured by driving a speaker with one watt of power and measuring the loudness (in decibels) at one meter. The higher the number, or sound pressure level, the more efficient (i.e. louder) the speaker. Efficiency measures the quantity of sound — not the quality.
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 any unnatural colorations 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 accurately reproduced.
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. Low-impedance speakers (4 ohms or less) can cause problems with receivers or amplifiers which are not designed to deliver large amounts of current.
Midrange
The range of frequencies above bass and below treble that our ears are most sensitive to, which includes most vocal and instrumental sounds.
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 (cones and domes) of your right and left speakers are moving in and out at the same time.
If your stereo speakers are "out of phase" you'll hear significantly less bass, and instead of producing a strong center image, the sound tends to stay localized at the speakers.
Phase control
A control 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. This control may be a 2-position switch or a variable control.
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, resonances in the speaker enclosure or any of the components can lead to colorations in the sound.
Sensitivity in dB
The sound pressure level, in decibels, produced by the speaker. The higher this figure, the louder your speakers will play.
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 level of sound (measured on the dB scale).
Subwoofer
A speaker specially designed to reproduce a range of very low frequencies only. The typical range for a subwoofer is about 20-200 Hz.
A "powered subwoofer" includes a built-in amplifier to drive the speaker.
Surround speakers
Speakers located beside or behind the listening/viewing position. They help create an enveloping three-dimensional soundstage by reproducing the surround information on video soundtracks and music recordings encoded with surround sound.
Timbre
The quality of a sound related to its harmonic structure. Timbre is what gives a voice or instrument its sonic signature — why a trumpet and a saxophone sound different when they play the same note.
Transducer
Any device that converts information 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 for reproducing the highest musical frequencies of violins, cymbals, female vocals, etc. The typical range for a tweeter is everything above 2,000 Hz or so.
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-matched
Speakers that are "voice-matched" have a similar timbre or tonal quality. Voice-matched speakers in a home theater system will result in more seamless, consistent, convincing wraparound sound.
Woofer
This driver uses a large cone to move the large volume of air necessary to reproduce long-wavelength bass frequencies.
Glossary
