Absorption coefficient: The fraction of sound energy that is absorbed at any surface. It has a value between 0 and 1 and varies with the frequency and angle of incidence of the sound.

Acoustic material: Any material considered in terms of its acoustical properties. Commonly and especially, a material designed to absorb sound.

Acoustics: The science of sound that applies to noise isolation and interior performance for residential projects. It can also refer to the effect a given environment has on sound.

Ambience: The acoustic characteristics of a space with regard to reverberation (decay time). A room with a long decay time is said to be "live"; one without a short decay time is said to be "dead".

Ambient noise: The composite of airborne sound from many sources near and far associated with a given environment. No particular sound is singled out for interest.

Anamorphic: Process that horizontally condenses (squeezes) a 16:9 image into a 4:3 space. For the signal to appear with correct geometry, the display must either horizontally expand or vertically squish the image. Used on many DVDs.

Anechoic chamber: A room designed to suppress internal sound reflections. Used for acoustical measurements.

Aspect Ratio: The ratio of image width to image height. Common motion-picture ratios are 1.85:1 and 2.35:1. Television screens are usually 1.33:1 (also known as 4:3). HDTV is 1.78:1, or 16:9.

Articulation: A quantitative measure of the intelligibility of speech; the percentage of speech items correctly perceived and recorded.

Attack: The beginning of a sound; the initial transient of a musical note.

Attenuate: The lessening of sound signal level due to divergence, absorption, reflection, refraction, diffraction.

Audible frequency range: The range of sound frequencies normally heard by the human ear. The audible range spans from 20Hz to 20,000Hz

Auralization: The technique of using computer-based mathematical models of an acoustic environment and 3-D sound processing methods to make audible the sound field of a source in the modeled space. An audible acoustic model of a speaker and room acoustics that can be "played" with different audio signals.

Axial mode: The room resonances associated with each pair of parallel walls.

B

Background noise: Noise from all sources unrelated to a particular sound that is the object of interest. Background noise may include airborne, structure-borne, and instrument noise.

Baffle: A moveable barrier used to achieve separation of signals from different sources. The surface or board (front panel) upon which a loudspeaker is mounted.

Balanced Input: A connection with three conductors: two identical signal conductors that are 180 degrees out of phase with each other, and one ground. This type of connection is very resistant to line noise.

Bandpass: A two-part filter that cuts both higher and lower frequencies around a center band. A bandpass enclosure cuts high frequencies by acoustic cancellation and low frequencies by natural physical limitations on bass response.

Bandwidth: In audio, the range of frequencies a device operates within. In video, the range of frequencies passed from the input to the output.

Bandpass filter: A filter that attenuates signals both below and above the desired frequency.

Bandwidth: The total frequency range of any system. Example: 20-20,000Hz plus or minus 3 dB.

Barrier: Continuous structure that traps or stops air movement from one side of a partition to the other, greatly reducing airborne sound transmission.

Bass: The lower range of audible frequencies.

Beaming: Sound being heard in a narrow area in front of a speaker.   This characteristic becomes more acute as the frequency increases.

Boomy: This is a listening term which refers to an excessive bass response that has a peak (s) in it.

Bright: This is a listening term which refers usually refers to too much upper frequency energy.

Broad band noise: Spectrum consisting of a large number of frequency components, none of which is individually dominant.

C

Cascading Crossovers: Two crossovers used in series on the same signal in the same frequency range causing greater attenuation but sometimes with uneven response and phase shifts. For example, using the crossover in a receiver's bass management setting and the one in a subwoofer simultaneously will create an exaggerated loss of signal.

Cavity: A space between wall studs or attic joists where insulation is typically installed.

Clipping: Refers to a type of distortion that occurs when an amplifier is driven into an overload condition. Usually the "clipped" waveform contains an excess of high-frequency energy. The sound becomes hard and edgy. Hard clipping is the most frequent cause of "burned out" tweeters.

Coherence: This is a listening term which refers to how well integrated the sound of the system is.

Coloration: This is a listening term which refers a visual analog of something being not accurate and not realistic. The coloration may be euphonically pleasant, but it is not as accurate as the original signal.

Comb filter: A distortion produced by combining an electrical or acoustical signal with a delayed replica of itself. The result is constructive and destructive interference that results in peaks and nulls being introduced into the frequency response. The frequency response plot resembles the teeth of a comb.

Compression: In audio, compression means to reduce the dynamic range of a signal. Compression may be intentional or one of the effects of a system that is driven to overload. It is also the portion of a sound wave in which molecules are pushed together, forming a region with higher-than-normal atmospheric pressure.

Critical distance: The distance from a sound source at which direct sound and reverberant sound are at the same level.

Critical frequency: The frequency below which standing waves cause significant room modes.

Crossover: A component that divides an audio signal into two or more ranges by frequency, sending, for example, low frequencies to one output and high frequencies to another. An active crossover is powered and divides the line-level audio signal prior to amplification. A passive crossover uses no external power supply and may be used either at line level or, more commonly, at speaker level to divide the signal after amplification and send the low frequencies to the woofer and the high frequencies to the tweeter.

Crossover Frequency (point): The frequency at which an audio signal is divided. 80 Hz is a typical subwoofer crossover point and is the recommended crossover point in theatrical and home THX systems. Frequencies below 80 Hz are sent to the subwoofer; signals above 80 Hz are sent to the main speakers.

Crossover Slope: The rate of attenuation expressed in decibels of change for every octave away from the crossover frequency.

Cycles per second: The frequency of an electrical signal or sound wave measured in Hertz (Hz) or kilohertz (kHz).

D

Damping: Of or pertaining to the control of vibration by electrical or mechanical means.

Damping Material: Any material that absorbs sound waves and eliminates acoustic energy by converting it into a different form.  Fibrous materials, for example, turn acoustic energy into heat via friction.

dB: Abbreviation of decibel.

DB (A): A sound-level meter reading with an A-weighting is for quieter sounds.  See en.wikipedia.org/wiki/Frequency_weighting

DB (C): A sound-level meter reading with an A-weighting is for louder sounds.  See en.wikipedia.org/wiki/Frequency_weighting

Decay: How fast a sound dies off to below a fixed threshold (RT30 = 30dB, RT60 = 60db).  Live rooms have long decay times while dead rooms have short decay times.

Decibel (dB): A logarithmic measurement unit that describes a sound's relative loudness, though it can also be used to describe the relative difference between two power levels. In sound, decibels generally measure a scale from 0 (the threshold of hearing) to 120-140 dB (the threshold of pain). A 3dB difference equates to a doubling of power. A 10dB difference is required to double the subjective volume. A 1dB difference over a broad frequency range is noticeable to most people, while a 0.2dB difference can affect the subjective impression of a sound.

Delay: The time difference between a sonic event and its perception at the listening position (sound traveling through space is delayed according to the distance it travels). People perceive spaciousness by the delay between the arrival of direct and reflected sound (larger spaces cause longer delays).

Diaphragm (also diaphragmatic): Any surface that vibrates in response to sound or is vibrated to emit sound, such as in microphones and loudspeakers. Also applied to wall and floor surfaces vibrating in response to sound or in transmitting sound.

Diffraction: A change in the direction of propagation of sound energy in the neighborhood of a boundary discontinuity, such as the edge of a reflective or absorptive surface.

Diffuse field: An environment in which the sound pressure level is the same at all locations and the flow of sound energy is equally probable in all directions.

Diffusion: In audio, the scattering of sound waves, reducing the sense of localization. In video, the scattering of light waves, reducing hot spotting, as in a diffusion screen.

Diffusor: An acoustical device designed to spread sound reflections.

D-ILA: Direct Drive Image Light Amplifier. This Hughes/JVC technology uses a reflective LCD to create an image. A light source is then reflected off the reflective LCD and is directed through a lens to a screen.

Dipole: An open-back speaker that radiates sound equally front and rear. The front and rear waves are out of phase and cancellation will occur when the wavelengths are long enough to "wrap around". The answer is a large, wide baffle or to enclose the driver creating a monopole.

Directivity factor (Q): The ratio of the sound pressure squared, radiated directly ahead of a sound source, to the sound pressure squared radiated in all directions.

Dispersion: The spread of sound over a wide area.

DLP: Digital Light Processing. A Texas Instruments process of projecting video images using a light source reflecting off of an array of tens of thousands of microscopic mirrors. Each mirror represents a pixel and reflects light toward the lens for white and away from it for black, modulating in between for various shades of gray. Three-chip versions use separate arrays for the red, green, and blue colors. Single-chip arrays use a color-filter wheel that alternates each filter color in front of the mirror array at appropriate intervals.

Dolby Digital: An encoding system that digitally compresses up to 5.1 discrete channels of audio (left front, center, right front, left surround, right surround, and LFE) into a single bitstream, which can be recorded onto a DVD, HDTV broadcast, or other form of digital media. Five channels are full-range; the .1 channel is a band-limited LFE track.

Dolby EX: An enhancement to Dolby Digital that adds a surround back channel to 5.1 soundtracks. The sixth channel is matrixed from the left and right surround channels. Often referred to as 6.1.

DTS: Digital Theater Systems. A digital sound recording format, originally developed for theatrical film soundtracks, starting with Jurassic Park.

DTS ES: An enhanced version of the 5.1 DTS system. Like Dolby's Surround EX, a sixth channel is added. In some cases (DTS ES Discrete), the sixth channel is discrete. Software is backwards-compatible with 5.1 systems, but requires an ES or 6.1 processor to obtain additional benefit.

Dynamic headroom: The ability of an audio device to respond to musical peaks. For example, an amplifier may only be capable of a sustained 100 watts, but may be able to achieve peaks of 200 watts for the fraction of a second required for an intense, quick sound. In this example the dynamic headroom would equal 3 dB.

Dynamic Range: The difference between the lowest and the highest levels; in audio, it's often expressed in decibels. In video, it's listed as the contrast ratio.

E

Echo: A sound wave which has been reflected or otherwise returned with sufficient magnitude and delay (typically >50 milliseconds) to be perceived as distinct from that directly transmitted.

Energy-Time Curve (ETC): In FFT measurements, a display of all the energy returned during a specified time span. Time is displayed on the abscissa (x axis) and energy on the ordinate (y axis). An ETC reveals how energy is released from a system or room or device after it is hit with a sudden application of input energy confined to a given frequency band.

Equalization: Any type of relative frequency adjustment.

ETC: Energy-time curve.

F

Far field: The distribution of sound energy at a great distance from the source in which the sound waves can be considered to be plane waves.

Flanking noise: Transmission of sound from the source to a receiving location by a path other than a direct obvious one.

Fletcher-Munson Curve: Our sensitivity to sound depends on its frequency and volume. Human ears are most sensitive to sounds in the midrange. At lower volume levels humans are less sensitive to sounds away from the midrange, bass and treble sounds "seem" reduced in intensity at lower listening levels.

Flutter echo: A series of specific reflective returns caused by large surfaces being parallel to each other.

FFT: Fast Fourier Transform. An iterative program that computes the Fourier Transform in a shorter time.  Used in sound analysis.

Fiberglass insulation: An energy-efficient glass fiber insulation used to ensure the best thermal and noise control performance available.

Free field: An environment in which a sound wave may propagate in all directions without obstructions or reflections. Anechoic rooms can produce such an environment under controlled conditions.

Frequency Response: A measure of what frequencies can be reproduced and how accurately they are reproduced. A measurement of 20 to 20,000 Hz ± 3dB means those frequencies between 20 and 20,000 Hz can be reproduced no more than 3 dB above or below a reference frequency level.

Fundamental: The lowest frequency of a note in a complex wave form or chord.

G

Gain: To increase in level. The function of a volume control.

Gray Scale: The ability for a video display to reproduce a neutral image color with a given input at various levels of intensity.

Grain: This is a listening term which refers a sonic analog of the grain seen in photos. A sort of "grittiness" added to the sound.

H

Harmonic: One component of a complex tone whose component frequencies are all integer multiples of a common fundamental frequency.

Haas effect: Also called the precedence effect. Delayed sounds are integrated by the auditory apparatus if the fall on the ear within 20 to 40 msec of the direct sound. The level of the delayed components contributes to the apparent level of the sound, and it is accompanied by a pleasant change in character.

Hard room: A room in which the surfaces have very low values of sound absorption and are therefore highly reflective.

Helmholtz resonator: A reactive, tuned, sound absorber.

HVAC: Abbreviation for heating, ventilation and air conditioning.

I

Imaging: The ability to localize the individual sound sources in three-dimensional space.

Impact Isolation Class (IIC): A measure or specification of isolation effectiveness of building structures from impact noises such as slammed doors, dropped objects, footfalls, shuffled furniture, etc. The higher the IIC rating, the better such isolation (in dB). Impact noises can be transmitted through walls, floors, and ceilings throughout a building and re-radiated at distant locations. Careful design and special construction materials (floating floors, isolation pads, resilient channels, spring rails, flexible connectors and hangers, for example) can help improve IIC ratings.

Impulse response: A measurement of sound pressure versus time, showing how a device responds to an impulse.

Intensity: The name given to the physical energy with which a sound is present. It contrasts with "loudness," which is the perceptual experience approximately correlated with that physical intensity.

Insertion loss, IL: Of a silencer or other sound-reducing element, in a specified frequency band, the decrease in sound power level, measured at the location of the receiver, when a sound insulator or a sound attenuator is inserted in the transmission path between the source and the receiver.

Inverse-square law: Under far field/free field conditions, sound intensity varies inversely with the square of the distance from the source. In pure spherical divergence of sound from a point source in free space, the sound pressure level decreases 6 dB for each doubling of the distance.

Isolate: A dampening mechanism made a part of the assembly or system, which reduces structure-borne vibrations from passing through the structure.

K

Keystone: A form of video image distortion in which the top of the picture is wider than the bottom, or the left is taller than the right, or vice versa. The image is shaped like a trapezoid rather than a rectangle.

L

Localization: The judgment of the place of spatial origin of a sound.

LFE: Low Frequency Effects track. The .1 channel of a Dolby DigitalThe LFE is strictly low-frequency information (20 to 120 Hz, with 115 dB of dynamic range) that's added to the soundtrack for extra effect. This track does not inherently contain all the bass of the soundtrack.

Line-Level (Low-Level): A level of electrical signals too low to make the average speaker move sufficiently. Amplifiers receive line-level signals and amplify them to speaker level.

Loudness: A subjective term for the sensation of the magnitude of sound. The subjective response to a sound level.

Low Pass: Filters that lets low frequencies go through but doesn't let high frequencies go through. Same as high cut.

M

Masking: The process by which one sound affects the threshold of audibility of another sound when played at the same time. More intense sounds mask less intense ones.

Mass law: An approximation that describes the Sound Transmission Loss (TL) of a limp, flexible barrier in terms of mass density and frequency. For each doubling of the weight or frequency of a partition, mass law predicts a 6 dB increase in TL.

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 used as a term for loudspeaker drivers designed to reproduce both bass and midrange frequencies.

Midrange: The middle of the audio frequency range. Also used as a term for loudspeaker drivers designed to reproduce this range.

Mode: A room resonance. Axial modes are associated with pairs of parallel walls. Tangential modes involve four room surfaces and oblique modes all six surfaces. Their effect is greatest at low frequencies and for small rooms.

Monopole: Any speaker that encloses the back-wave of the speaker device even though part of this back-wave may be released via a port or duct. The primary radiation at most frequencies will be from the driver front. If the driver is not enclosed it becomes a dipole.

Muddy: Listening term. A sound that is poorly defined, sloppy or vague. For example, a "muddy" bass is often boomy with all the notes tending to run together.

N

Near field: That part of a sound field, usually within about two wavelengths from a sound source, where there is no simple relationship between sound level and distance.

Noise criteria (NC) curves: A measure of background noise in rooms. The lower the NC rating, the lower the background noise level.

NTSC: National Television Standards Committee. Government-directed committee that established the U.S. color TV standard in 1953. Also known, sarcastically, as Never Twice the Same Color or Never The Same Color due to the inherent difficulty in achieving proper color calibration.

Near field: Locations close to the sound source between the source and the far field. The near field is typically characterized by large sound pressure level variations with small changes in measurement position from the source.

Null: A low or minimum point on a graph. A minimum pressure region in a room.

O

Octave: One of the pitch intervals in music. Physically, a note that is an octave higher than another has a frequency that is twice that of the lower one.

Off-axis: Not directly in front of a microphone or loudspeaker.

Octave: The difference between two frequencies where one is twice the other. For example, 200 Hz is an octave higher than 100 Hz. 400 Hz is one octave higher than 200 Hz.

P

Parametric: Equalizer with adjust-able parameters, such as center frequency and bandwidth (Q), as well as amplitude.

Passive absorber: A sound absorber that dissipates sound energy as heat.

Phase: The phase is the particular point in a wave that is passing a position in space at a certain instant of time. Phase is measured in units of degrees, with 360 degrees representing one complete cycle of the wave. If two tones have the same period and are occurring at the same time, the temporal lag of one with respect to the other can be described in terms of phase. If two waves are out of phase by 180 degrees, the later one is lagging by one-half a period.

Phase shift: The time or angular difference between two signals.

Phon: The unit of loudness level of a tone.

Pink noise: Noise with a continuous frequency spectrum and with equal power per constant percentage bandwidth. For example, equal power is any one-third octave band.

Pitch: A subjective term for the perceived frequency of a tone.

Plenum: An absorbent-lined cavity through which conditioned air is routed to reduce noise.

Polarity: The positive or negative direction of an electrical, acoustical, or magnetic force. Two identical signals in opposite polarity are 180 degrees apart at all frequencies. Polarity is not frequency dependent.

Pressure zone: As sound waves strike a solid surface, the particle velocity is zero at the surface and the pressure is high, thus creating a high-pressure layer near the surface.

Precedence effect: An effect in which the human auditory system suppresses early reflections of a direct sound, i.e., it "fuses" the direct sound and its early reflections and localizes the source on the basis of the earlier (i.e., direct) sound. The basis for the distinction is that the reflections arrive with a certain delay compared to the direct sound. Precedence effect is sometimes referred to as the law of the first wavefront or the Haas effect.

Psychoacoustics: The study of the relationship between physical measures of sound (e.g., amplitude and frequency) and the perception of them.

Pure tone: A tone with a sinusoidal waveform is called a pure tone because it is considered to be the simplest form of tone. Lacking any harmonics.

Q

Q: The magnification or resonance factor of any resonant device or circuit. Also the width of affected frequencies in an equalizer. Shaped somewhat like an adjustable width bell curve.

R

Rarefaction: The portion of a sound wave in which air molecules are spread apart, forming a region with lower-than-normal atmospheric pressure. The opposite of compression.

Ray: At higher audio frequencies, sound may be considered to travel in straight lines like a light ray.

RC (Room Criteria) curves: Undesirable rumble can result if NC curves are determined mainly by low frequency noise. Similarly, a hissing effect can result from NC level being controlled by higher frequency sounds. To achieve a better balance between low frequency and high frequency components, RC curves have been established for which the objective is to design spectra that meet an RC curve within + 2 dB at all frequencies.

Receiving room: In architectural acoustical measurements, the room in which the sound transmitted from the source room is measured.

 Re-EQ: Short for Re-equalization. A feature found on THX-certified receivers and pre/pros. Movie soundtracks are mixed for theaters or far-field monitors with an expected high-frequency roll-off. If these soundtracks are not re-mixed for home use, they will sound too bright when played back through home speakers or near-field monitors.

Reflection: For large surfaces compared to the wavelength of impinging sound, sound is reflected much as light is reflected, with the angle of incidence equaling the angle of reflection.

Refraction: The bending of sound waves traveling through layered media with different sound velocities.

Reverberation time (RT): The time it takes for a loud sound to decay to inaudibility after its source is cut off..

Room criteria (RC) curves: A measure or specification of background noise from HVAC systems according to measured sound pressure level at 10 octave-band center frequencies: 16, 31.5, 63, 125, 250, 500, 1000, 2000, 4000 and 8000 Hz. Room Criteria curves were derived for use in office spaces and are more demanding than Noise Criteria curves at low frequencies.

Room modes: Frequencies at which sound waves in a room resonate (in the form of standing waves.

RFZ: Reflection-free zone.

S

Sabin: A unit of absorption equal to the absorption of 1 square foot of surface which is totally sound absorbent.

Sone: A unit of loudness. Defined as the loudness of a 1000 Hz tone 40 dB above threshold.

Sound absorption: (1) The process of dissipating sound energy. (2) The property possessed by materials, objects and structures such as rooms of absorbing sound energy. (3) The measure of the magnitude of the absorptive property of a material, an object, or a structure such as a room.

Sound power level, Lp: Of airborne sound, ten times the common logarithm of the ratio of the sound power under consideration of the standard reference power of 1 pW. The quantity so obtained is expressed in decibels.

Sound pressure level (SPL): Given in decibels (dB) is an expression of loudness or volume. A 10 dB increase in SPL represents a doubling in volume.

 Soundstage: A listening term that refers to the placement of a stereo image in a fashion that replicates the original performance. A realistic soundstage has proportional width, depth and height.

Sound transmission class, STC: A single-number rating for the sound blocking ability of a structure. It provides an estimate of the performance of a partition

Sound transmission loss, TL: The reduction in sound level when sound passes through a partition or ceiling system.

Spaciousness: A room is said to be "spacious" if the music performed in it appears to the listener to emanate from a source wider than the visual width of the actual source. The listener is noticeably enveloped by the ambience of the room.

Specular reflection: A mirror-like reflection of sound from a flat surface; reflections that do not spread out.

Speed of sound: In air, approximately 1130 feet per second at 68 degrees F.

Speech intelligibility: A measure of sound clarity that indicates the ease of understanding speech.

SPL: Sound-Pressure Level. Measured in dB.

Standing wave: An apparently stationary waveform created by multiple reflections between opposite room surfaces. At certain points along the standing wave, the direct and reflected waves cancel, and at other points the waves add together or reinforce each other. These are sometimes called room modes.

STC: Sound Transmission Class.

Subwoofer: A speaker designed exclusively for low-frequency reproduction

T

Tangential mode: A room mode produced by reflections off four of the six surfaces of the room.

Timbre: The quality of a sound that distinguishes it from other sounds of the same pitch and volume. The distinctive tone of an instrument or a singing voice.

3:2 Pulldown Recognition or 3:2 Inverse Telecine: Film is usually recorded at 24 frames per second. NTSC video (North America) is 30 frames (60 fields) per second. In order to get smooth motion, the film frames are broken into video fields in a 3-2-3 sequence. 3 fields for the first film frame, 2 fields for the second film frame, and so on. If a line doubler doesn't compensate for the extra field during playback on a progressive-scan display, the image will have noticeable motion artifacts. A line doubler with 3:2 pulldown recognition or 3:2 inverse telecine can see this sequence in the signal and correct for it by making sure the last field in the first frame isn't mixed with the first field of the second frame.

Threshold of pain: The sound pressure level that makes the ears tickle, located about 120 dB above the threshold of hearing.

THX: Certification program for home theater equipment. Uses some proprietary features, but mostly assures a base quality level for a given room size. (See THX Select or Ultra.) Is compatible with any and all soundtrack formats. Stands for either Tom Holman's eXperiment, after the engineer who drafted the original standard, or is named after the company's founder George Lucas' first movie, THX 1138. Nobody agrees on which.

THX Select: Certification program for speakers and receivers that assures a base level of quality and performance when played in a room that's between 2,000 and 3,000 cubic feet.

THX Ultra: Certification program for speakers, receivers, and amplifiers that assures a base level of quality and performance when played in a room that's greater than 3,000 cubic feet.

THX Ultra 2: The newest certification from THX, THX Ultra 2 requires amplification for seven channels, boundary compensation for subwoofers, and stricter requirements for amplifiers and speakers than THX Ultra. Dipole speakers are used for the side surround channels. Monopole speakers are used for the surround back channel and are placed next to each other. The Ultra 2 processor accommodates both 5.1 EX/ES soundtracks, as well as multichannel audio recordings by directing ambient sounds to the dipole speakers and discrete effects/sounds to the back channels.

Transient response: The ability of a component to respond quickly and accurately to transients. Transient response affects reproduction of the attack and decay characteristics of a sound.

W

Warmth: This is a listening term which refers to the range from approx. 150Hz-400Hz. A system with the "proper" warmth will be preferred within this range and is usually slightly louder in this frequency region.

Wavelength: The distance the sound wave travels to complete one cycle. The distance between one peak or crest of a sine wave and the next corresponding peak or crest. The wavelength of any frequency may be found by dividing the speed of sound by the frequency. (speed of sound at sea level is 1087.42 feet/second).

Weighting: Adjustment of sound-level meter response to achieve a desired measurement.

White noise: Noise with a continuous frequency spectrum and with equal power per unit bandwidth. For example, equal power in any band of 100-Hz width.

Z

Zone: One or more rooms powered by one or more amplifiers, which are all fed by one source. A home can be divided into multiple zones, which can play multiple sources, even though several rooms (say, the kitchen, dining room, and living room) all play the same source.