Glossary Of Terms

June 5, 2005

With so many terms and acronyms used to describe the features of today's hi-performance home theater systems, we thought a comprehensive glossary of terms would be in order.

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AC Line Conditioner (Surge Protector)

A filtering product for power-line noise/interferences on alternate current, which protects any audio/video components plugged into it from voltage surges and spikes.

Active Subwoofer
A speaker designed specifically to reproduce low frequencies only, with a built-in amplifier. (See Passive Subwoofer) Go to PSB Speakers Subwoofer page
AES/EBU Interface
A connectivity standard for professional use established by the Audio Engineering Society (AES) and the European Broadcasting Union (EBU) for digital audio transmission between components. AES/EBU is carried on a balanced line terminated with three-pin XLR connectors.
Analog
A continuous movement that takes time to change from one position to another. Standard analog audio signals have an infinite number of levels between their highest and lowest value. (Note: a Digital audio signal represent only two steps: on or off or binary’s one or zero.)
Analog-to-Digital Converter
This electronic device, often referred to as A/D, converts analog signals to digital signals. (Note: a Digital-to-Analog Converter [D/A] performs the reverse function.)
Audiophile
1: Any person who has a deep affection or appreciation for audio or sound quality.
2: A connoisseur of audio. Common phrase, "audiophile-grade" meaning higher-end components capable of meeting an audiophile’s expectations.
Bass-Reflex (Enclosure)
A loudspeaker cabinet with a specifically designed port or duct that allows back-waves to be radiated in-phase with the front waves, thus eliminating unwanted acoustic phase cancellation.
Bandpass
At two part filter that cuts both high and low frequencies to leave a band in the middle. A Bandpass Enclosure cuts high frequencies by acoustic cancellation and low frequencies by natural and physical limitations on bass response.
Bandwidth
The range of frequencies that radio, TV, audio and video operate and let pass through. (Note: the wider the bandwidth, the better the A/V quality; the higher the bandwidth, the better the product performs. In a digital circuit, the bandwidth is measured in bits per second or bps.)
Bipolar
"Bipolar Speakers" A popular choice for surround speaker application and also a THX requirement. Each speaker enclosure consists of two speaker arrays facing opposite each other and are wired out of phase from one another to create an ambient and non-directional soundfield. Synchrony S Surround | Imagine S Surround | Image S50 Surround
Bi-wiring
Of or referring to a method of connecting the amplifier or receiver to the speaker in which separate wiring is run to the woofer and tweeter, or in a three-way system, to the midrange driver.
Ceiling Surround Channel/Speaker
A speaker that mounts in your ceiling and uses its height as a surround channel decoded from the front and rear channels. Its algorithm is similar to that of how center channel audio is extracted and steered front the front left and right signals.
Center Channel/Speaker
The front center speaker, placed between the left and right front speakers. Its primary function is to carry dialogue (movies), but it also carries other sounds, such as that accompanying video movement from one direction to another. It is, therefore, recommended that the center channel be of similar type and timbre as front left and right speakers and to be driven by similar amplification as well for the best clarity.
Circle Surround
This is a multi-channel surround effect produced from two channel sources, using ambient information stored in a stereo recording, a stereo recording encoded for surround, and recordings specifically encoded in Circle Surround. The surround sound information sent to the surround speakers is stereo, as opposed to the monaural approach of Dolby Pro Logic. Circle Surround creates a believable front sound stage, apportioning the stereo signal across three front channels.
Coaxial
1: A speaker with one driver in front of (and on the same axis of) another driver.
2: An audio or video cable with a single center pin that acts as the "hot" lead and the outer shield acts as the ground.
Cone
Typical shape of a speaker driver.
Coloration
Any change in the character of sound, such as the overemphasis on certain tones, that reduces naturalness.
Crossover
A component that divides an audio signal into two or more parts by frequency, sending, for example, low frequencies to one output and high frequencies to another. Crossovers are also commonly built into amplifiers and equalizers.
Crossover Network
Following final amplification in a sound-reproduction system, an outboard circuit facilitates delivery of high- and low-frequency (AF) components to correct drivers in a speaker array. (Passes correct sounds to correct speakers.)
Crossover Point
The frequency that appears in two adjacent outputs of a crossover (such as high and mid) at the same level. For example, if a two-way crossover is set for a crossover point of 100 Hz, a 100 Hz signal will be a the same level in both the high-pass and low-pass output.
Custom Installation
Any installation of home automation or theater products which requires some form of construction in order to be installed i.e. in-wall speakers, overhead projector, etc. Most often refers to the application or installation of products by a professional installer or firm.
Damping
Of or pertaining to the control of vibration by electrical or mechanical means.
Damping Material
Any material added to the interior of a speaker enclosure to absorb unwanted sound and reduce out-of-phase reflection to the driver diaphragm.
D'Appolito
Refers to the actual speaker array when a single high frequency driver (tweeter) is flanked by a pair of mid-range drivers to result in a well-balanced, wide dispersion of sound and increased off-axis response.
Decibel (dB)
Defined as one-tenth of a Bel (named after Alexander Graham Bell), this logarithmic ratio is used to measure power, sound pressure level or voltage. A 3dB loss or increase is considered an attenuation or augmentation of half or double its original value; 0dB is the threshold of hearing; 120dB is the threshold of pain.
Decorrelation
This technique is used in THX processors for rear speakers with the purpose of creating an ambient DSP sound field, similar in depth and spaciousness to that of a commercial theater.
Diaphragm
The part of a dynamic loudspeaker, attached to the voice coil, that produces sound. It actually has the shape of a cone or dome.
Digital Audio Inputs/Outputs
These audio jacks can be either coaxial (RCA) or optical (TosLink) and allow for the passage of multi-channel digital audio signals over a single connection. (Note: other digital audio connections for multi-channel audio include IEEE 1394 [FireWire], or the audio portions of HDMI. Digital audio connections are prone to less noise and interference than analog audio connections.
Dispersion
The degree of sound that is spread over a listening area.
Distortion
Nonlinear and unwanted changes in an audio signal, often not including the addition of noise, but including harmonic, intermodulation, transient intermodulation, phase, and frequency distortion.
Dolby Digital 5.1 Surround
A multi-channel format first introduced in movie theaters in June 1992 as Dolby Stereo Digital (or Dolby SR), this format uses five speakers (front left and right, center, and rear left and right—all 20Hz to 20,000Hz, plus a separate .1 channel for Low Frequency Effects [LFE], with a frequency range of 20Hz to 120Hz +/-0.5dB, intended to be reproduced by a subwoofer. (Note: Dolby Surround is a single-band-limited surround channel with a range of 100Hz to 7,000Hz. Dolby Digital, on the other hand, offers a full, dynamic range on five discrete main channels. And the surround channels are in stereo, as opposed to mono as with Dolby Pro Logic.)
Dolby Digital Plus
A format introduced in April 2004 at NAB for broadcasters to transmit 5.1 at 50% (192kBs) data rate of regular Dolby Digital (384kBs). Has had backward compatibility issues.
Dolby Digital Surround EX
This is a 6.1 multi-channel format that provides a third surround channel (rear center). It can be decoded by capable A/V receivers and Dolby decoders, though to maintain compatibility, no information is lost when a film is played in conventional 5.1. More realistic fly-over and fly-around effects are gained when using Dolby Digital Surround EX, creating a more stable image for atmospheres and music, and a more consistent surround effect.
Dolby Pro Logic
A matrixed surround system with four channels/speakers (left, center, right and surround) that are folded into two channels and encoded onto Left/right channels. The Pro Logic processor, in turn, extracts the four channels from the two encoded channels and directs them to the appropriate speakers.
Dolby Pro Logic II
This format creates a 5.1 surround sound field from a two-channel stereo program material (whether Dolby Surround encoded or not). Encoded material (such as movies) sounds more like Dolby Digital 5.1, while unencoded stereo material (such as music CDs) is given a wider effect and more involving sound field. (Note: Pro Logic II provides two full-range surround channels, as opposed to Pro Logic’s single, limited bandwidth surround channel.)
Dolby Pro Logic IIx
This format works with both 5.1 audio as well as two-channel material, producing up to 7.1 channels by decoding the center back and side surround channels from the left and right surround channels or Pro Logic II and 5.1 audio. Pro Logic IIx includes center channel width control and a panorama mode, as well as music, movie and game modes.
Dome
A type of speaker driver shape usually used for tweeters (convex, not concave).
Driver
A speaker without an enclosure.
DSP
Abbreviation for Digital Signal Processing.
DTCP (Digital Transmission Content Protection)
A scheme created for copy protection of digital video transmitted over the IEEE 1394 connection. Also known as 5c for the five companies that participated on the standard (Sony, Toshiba, Intel, Hitachi, and Matsushita), the format allows for copy freely, once and never as options of protection.
DTS (Digital Theater Sound)
This originated as a digital 5.1 surround scheme developed for the movies by MCA/Universal and Steven Spielberg. DTS was first employed in Spielberg’s Jurassic Park film (Summer 1993). DTS Coherent Acoustics Coding (CAC) maps discrete 6-channel, 20-bit encoded data onto the 16-bit PCM digital audio stream, which is found on either a laserdisc or compact disc. DTS' CAC signal is passed via the digital output (either coaxial or optical) present on many laserdisc, CD and DVD players. (Note: While Dolby Digital uses perceptual coding to reduce the bit rate, DTS uses compression technology and the CAC algorithm with a higher bit rate than Dolby Digital.) The compression ratio is 3.75:1 of a 20-bit PCM digital audio stream with an eight times oversampling rate. It has a typical data rate of 1,411kBps (as opposed to 384kBps of Dolby Digital). The CAC algorithm is a scaleable digital coding methodology which operates on a multirate filterbank. It has been designed to filter the audio signal into frequency bands, which match the critical perceptual bands of the human ear. Within each frequency band, the signals are re-quantified at a variable resolution. This is determined by the available bit-rate and an analysis of the long/short periodicity of the audio signal in each frequency band. Essentially, this allows six channels of transparent quality 24-bit recorded material at 48kHz with less digital compression.
DVD-Audio
A multi-channel surround sound format of 24-bit/96kHz or up to two-channel 24/192. Sampling rates of 48kHz, 88.2kHz and 176.4kHz, as well as DTS and Dolby Digital data streams are also included on this format. A single layer, single-sided DVD-Audio disc holds 4.7GB (for up to 40 minutes of 6-channel audio at 24/96). Six channels of uncompressed 24/96 audio data require 13.8Mbps data speed while the DVD standard allows for up to only 9.6Mbps (the reason for which a lossless form of data compression was needed (Meridian Lossless Packing).
Dynamic Range
Audio range expressed in dB and measured between low-level noise and overload distortion; also defined as the range between the softest and loudest sound passages.
Efficiency Rating
the loudspeaker parameter that shows the level of sound output when measured at a prescribed distance with a standard amount of energy fed into the speaker. Efficiency rating standard is 1-watt at 1-meter and is measured in decibels.
Ferrofluid
A synthetic fluid with excellent cooling and lubricating properties. Most often injected into the "gap" (space between the voice coil and magnet) to prevent overheating and ultimately failure of the motor structure.
Flat Response
The reproduction of sound without alternating the intensity of any part of the frequency range.
Frequency
Audio frequencies are commonly defined as ranging from 20 to 20,000 cycles per second (Hz), assuming that the air pressure 20 or 20,000 times each second can be heard.
Frequency Response
A measure of what frequencies can be reproduced and how accurately they are reproduced.
Fs
Frequency resonance of a driver in free-air.
Harmonic Distortion
This is distortion caused when audio equipment adds unwanted overtones to an original signal.
HDCP (High-Bandwidth Digital Content Protection)
A content protection system developed for DVI. The HDCP 1.0 specification was developed by Intel, with contributions from Silicon Image in February 2000 to protect DVI outputs from being copied by providing a secure digital link between a video source and a display device. HDCP offers authentication, encryption and renewability.
High (frequencies)
Treble frequencies; those over approximately 3,150 Hz. Typically produced by the tweeter in a speaker array.
Home Theater
Encompasses all types of multimedia equipment that make up an entertainment center or room. Typically refers to surround sound (5.1 or greater) speakers, A/V receivers, display and source units ranging from DVD players to computer or gaming devices but can also include video capturing devices, media servers and other related items.
Hz
Short for Hertz; cycles per-second. Something that repeats a cycle once each second is moving at a rate of 1 Hz.
Interconnects
Also called RCA plug and phono plug. A plug or cable designed specifically for the quick connection between various audio and video components.
Imaging
The ability to reproduce sound so accurately that listeners can imagine the sound sources (such as musicians) sharply, clearly, accurately and their correct placement in a recording.
Impedance
a measure of how much something resists (impedes) the flow of electricity. Large numbers mean more resistance. Measured in Ohms.
In-Cabinet Speaker
A self contained speaker designed to be installed into a cabinet (entertainment center) or other enclosure to be concealed from sight. Typically any speaker designed void of aesthetic appeal for the purpose of being concealed. PSB Speakers In-Cabinet Speaker page
In-Room Speaker
A self contained speaker designed for the purpose of either floor-standing or to be placed onto a bookshelf or speaker stand.
In-Wall Speaker
Any speaker designed for the purpose of being installed into a wall or ceiling. Typically uses the wall cavity as the enclosure unless noted as a "self-contained" in-wall, in which case it has a full enclosure. PSB Speakers In-Wall Speakers
kHz
One thousand Hz; 1 kHz equals 1,000 Hz and 20 kHz is 20,000 Hz.
LFE (Low Frequency Effects)
This is the .1 channel in Dolby Digital or DTS 5.1/6.1/7.1. The LFE channel contains low frequency effects in the range of 20-100Hz, intended to be reproduced by a subwoofer.
Low (frequencies)
Bass frequencies; those below approximately 200 Hz.
Midbass
The middle of the bass part of the frequency range, from approximately 50 to 100 Hz (upper bass would be from 100 to 200 Hz). Also drivers designed and used produce both bass and midrange frequencies.
Midrange
The middle of the audio frequency range, from approximately 200 to 3,150 Hz. A "midrange driver" typically produces the "voice" or vocals in music or cinema.
Octave
The difference between two frequencies where one is twice the other. For example, 200 Hz is one octave higher than 100 Hz.
Ohm
A measure of how much something resists (impedes) the flow of electricity.
On-Wall Speaker
A self-contained (fully enclosed) speaker typically designed with a low-volume (low-profile) enclosure intended to be installed (or hung) onto a wall.
Passive Subwoofer
A speaker designed specifically to reproduce low frequencies only, which requires a separate amplifier to drive it. (See Active Subwoofer)
Passive Radiator:
An undriven loudspeaker cone that is mounted in a bass-reflex (sealed) enclosure with other, actively driven speakers to aid in the tuning of output.
Polarity
The 180-degree difference in the phase of audio signals that must be observed when wiring speakers.
Port
An aperture in a loudspeaker enclosure used to help tune the output. A ported enclosure is also called a vented or bass reflex.
Power
Should be well-balanced and clean (free of noise or interference) in any audio/video system, for optimum performance. Components experience degradation in power quality when sharing electrical circuits with appliances or other devices. It is recommended that a separate electrical circuit be used for A/V components, as well as the use of an A/C line conditioner/surge protector.
Q
The magnification of the resonance factor of any resonant device or circuit. A driver with a high Q is more resonant than a driver with a low Q.
Qes
The electrical Q of the driver.
Qms
The mechanical Q of the driver.
Qts
The total Q of the driver at fs.
RMS (Root Mean Square)
A measurement of the continuous power output produced by an amplifier. The higher the RMS number, the cleaner and louder (without distortion) the sound will be. (Note: one of the primary specs on which to base an amplifier purchase.)
Sound Field
A volume of space or material containing sound waves. Commonly refers to the area in which a speakers or speakers direct sound.
Soundstage
The area that seems to be occupied by sonic images. Like a real stage, a soundstage should have width, height and depth.
Subwoofer
A speaker designed and dedicated to reproduce low frequencies (bass) from the .1 LFE Dolby Digital or DTS channel, and/or from the bass received from other channels if their lower frequencies are crossed-over to the sub with a low-pass control. Bass being non-directional, placement of the subwoofer can be anywhere in a listening area. Subs (or woofers) can range in size from five to 18 inches in diameter and come in active or passive applications. Some of these enclosures are ported (with a hole on the side or bottom), which helps to add a thump to bass response. PSB Speakers Subwoofers page
Surround Channels/Speakers
Typically placed to the sides or rear of listening area, these speakers carry directional effects (Dolby Digital/DTS) or sound field enhancements (Dolby Digital, DTS, Pro Logic, Circle Surround). Surround channels/speakers can also be placed in the rear as an additional center speaker or in the ceiling for added surround effect. Speakers for discrete, full-bandwidth surround formats, like Dolby Digital/DTS, should be capable of handling a full frequency response of 20-20kHz and be sufficiently larger to handle loud passages. Rear surround speakers are either bipole or dipole, by design. Dipoles produce sound from the rear and front speakers out-of-phase from each other. For bipoles, the front and rear speakers are in-phase and sound equal.
THX
A license that identifies and certifies compliance with high performance color and sound parameters for home theaters.
Timbre
This is the tonal characteristic of a sound determined by its harmonic structure.
Transient Response
A term frequently used to describe a driver's (speaker's) time measurement for peak to peak movement; the distance at which a speakers maximum and minimum excursion and incursion begin.
Treble
The higher part of the audio signal range, approximately 3,150 Hz and up.
Tweeter
A speaker driver designed to reproduce very high frequencies, those over approximately 5,000 to 10,000 Hz.
VAS
The volume of air that offers the same degree of restoring force on the cone as that of the cones suspension.
Woofer
A speaker driver designed to reproduce low frequencies.

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