The opposite of reflection. Sound absorption results from the conversion of sound energy into another form, usually heat or motion, when passing through an acoustical medium. When a sound wave encounters resistance, absorption occurs. Absorption is measured in sabins (named after Wallace Clement Sabine). One sabin is the amount of absorption offered by one square foot of open air.

Ratio of sound absorbing effectiveness, at a specified frequency, of a unit area of acoustical absorbent to a unit area of perfectly absorptive material. The portion of energy absorbed when a sound wave strikes a material. The absorption coefficient of a material is dependent on the frequency of the sound wave. An absorption coefficient of 1.0 = total absorption, 0.0 = total reflection. Note: See Area Effect for explanation of absorption coefficients exceeding 1.0.

A porous architectural material, usually constructed from fiberglass or pressed board, which is most absorptive at the high frequencies.

the residual “room sound” of a listening environment.

all pervasive noise associated with a given environment.

Test room whose surfaces absorb all sound. Note - the word anechoic is derived from the Greek words meaning without echo.

Due to exposed edges and diffraction of sound energy around perimeters, acoustical materials spaced apart can exhibit greater absorption than the same amount of material with no gaps. The surface of an anechoic wedge has a total surface area greater than the flat surface it replaces.

The room resonances associated with each pair of parallel walls (including ceiling and floor)

A device used to inhibit the propagation of sound waves. Baffles are usually suspended vertically from the ceiling to reduce reverberation time.

heavy, dense and massive material used to block sound.

A low frequency absorber. Low frequencies are particularly difficult to absorb due to their long wavelengths. Bass traps are designed and constructed to absorb these longer waves and control unwanted room resonances. Broadband absorbers extending to lower frequencies are often called Bass Traps, imprecisely. The term “bass trap” is counterintuitive since these devices eliminate low frequency room cancellations, allowing bass to be heard.

A physical gap in the assembly or construction, which acts to decouple sound vibrations from traveling through a structure.

Rates a ceiling's efficiency as a barrier to airborne sound transmission between adjacent closed offices. Shown as a minimum value, previously expressed as CSTC (Ceiling Sound Transmission Class). A single-figure rating derived from the normalized ceiling attenuation values.

An acoustical panel suspended in a horizontal position from ceiling or roof structure.

The ability of a listener to focus attention on a single talker among a mixture of crowd conversations and background noise while, at the same time, ignoring speech from other locations. Understanding is possible due to the ear / brain discrimination of unwanted sound as well as lip reading and body language. A single microphone recording of the same conversation, absent these additional factors, may be totally unintelligible and unusable as evidence in court.

The distance from a sound source at which the direct energy (energy radiated directly from the source) is equal to the reverberant energy (radiated from walls, floor and ceiling).

A metal mounting device, shaped like a D, used in conjunction with hanger wire to mount baffles.

A room with a relatively large amount of sound absorption and relatively short reverberation time.

The bending of a sound wave around an obstacle, or through an opening, such as slats. The scattering of sound waves at an object smaller than one wavelength, and the subsequent interference of the scattered wavefronts.

A sound field in which the sound pressure level is the same everywhere and the flow of energy is equally probable in all directions.

A device for the complex scattering of sound energy in all directions. Traditional spatial diffusers, such as the polycylindrical (barrel) shapes may also double as low frequency traps. Temporal diffusors, such as binary arrays and quadratics, scatter sound in a manner similar to diffraction of light, where the timing of reflections from an uneven surface of varying depths causes interference which spreads the sound.

A dense architectural wall construction material applied to wood or metal studs, A/K/A Sheet Rock or Gypsum Wall Board (GWB), useful primarily as a sound barrier but is low frequency absorber in some applications.

Reflected energy that occurs in close proximity to the source but is slightly out of synchronization (time / phase) with the source information.

An acoustical panel edge detail also known as a quarter-inch (¼") bevel.

A method used to detect objects by producing a specific sound and listening for its echo.

Distribution of acoustic energy at a much greater distance from a source than the linear dimensions of the source itself.

The transmission of sound around a perimeter or through holes within partitions (or barriers) that reduces the otherwise obtainable sound transmission loss of a partition. Examples of flanking paths within buildings are ceiling plena above partitions; ductwork, piping, and electrical conduit penetrations through partitions; back-to-back electrical boxes within partitions, window mullions, etc. Flanking occurs when a free standing partition size is less than the wavelength of sound to be blocked.

A repetitive echo set up by parallel reflecting surfaces.

An environment in which there are no reflective surfaces within the frequency region of interest.

The placement of vocal or musical information ahead of (closer to) or behind (farther from) center position, front-to-back.

A freestanding device used to inhibit the propagation of sound waves. Gobos are usually employed to prevent microphone leakage between two instruments being recorded simultaneously. Typically a set of portable dividers covered with acoustical treatments.

A reactive, tuned, sound absorber. A bottle is such a resonator. It can employ a perforated cover or slats over a cavity. An acoustic guitar or violin body is a Helmholtz resonator.

A system for rating the ability of a structure to isolate impact noise (i.e. footsteps, and other vibrational disturbances). Normally used in reference to floor and ceiling constructions, the IIC method utilizes whole positive numbers for rating purposes.

A mounting fastener that is a metal plate with tines (prongs or spikes) sticking out of it. It is used along with adhesive to mount acoustical panels. The impaling clip is attached to the wall with the tines facing outward and the panel is pushed onto it (impaled).

A characteristic of the substance that sound travels through. It indicates how loud a sound will be depending on frequency and the sound source. Ratio of pressure to volume flow.

The time interval between the arrival of a direct sound and its first reflection from the surfaces of the room.

Resistance to the transmission of sound by materials and structures. The separation of airborne or mechanically transmitted energy.

A slice cut into the edge of an acoustical panel so that it can accept a spline (extrusion) to connect and mount an adjoining panel, providing a level surface at the joint or seam.

Live end, dead end. An optimal acoustical treatment plan for rooms in which one end is highly absorbent and the other end reflective and diffusive.

A reverberant acoustical condition, usually used in reference to a room whose many reflective surfaces encourage a lengthy reverberation time.

The law of physics that states that a material’s ability to reduce the transmission of sound is proportional to its weight. According to the mass law, to increase a wall’s transmission loss by 6 dB it is necessary to double the thickness (weight) of the wall. See Inverse Square Law.

A high density vinyl material that acts as a barrier to sound transmission. Directly applied to surfaces, suspended or used in wall, floor and ceiling construction. See Sound Transmission Class.

To rigidly connect two isolated objects. (Also called a mechanical “short”.) Example: Two isolated wall partitions are mechanically coupled if rigid electrical conduit is fastened to both walls. Air ducts and plumbing are prime candidates for causing mechanical shorts. When an acoustically isolated room “leaks”, it is often a mechanical short created during construction.

The elimination of mechanical shorts. See Mechanical Coupling. Typically accomplished by inserting a flexible loop between rigid components. Flexible metallic conduit (Greenfield) is used for decoupling electrical conduit, accordion shaped canvas collars decouple rigid air-ducts and flexible tubing does the same for plumbing. For structural decoupling, resilient materials are used to separate rigid components.

A raw material, made of inorganic mineral fibers, used for acoustical panels.

A non-rigid acoustical substrate (A/K/A “rock wool” or “slag wool”) made from molten rock.

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 in small rooms.

Standards established by ASTM to test the acoustics of materials by representing a typical installation. Specimens may be attached directly to the test room surface as in Type “A” Mount, spaced apart, or furred-out to produce an air space behind. (Ceiling grid test is E400 mount.)

That part of a sound field usually within about two wavelengths from a noise source, where there is no simple relationship between sound level and distance. The area in a room which is in the immediate vicinity of the sound source.

A point or line where minimal air motion takes place.

A filter of extremely narrow bandwidth used to eliminate discrete frequencies. Notch filters are usually tunable, and can be used to eliminate specific room or instrument resonances.

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

A sound absorber that dissipates sound energy as heat.

The difference in time/distance of source energy from reflected energy.

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.

Reflection-free zone.

A decrease in density and pressure in a medium, such as air, caused by the passage of a sound wave. Opposite of compression.

A silencer in air-conditioning systems that uses reflection effects for its action.

A sound absorber, such as the Helmholtz resonator which involves the effects of mass and compliance as well as resistance.

A room that is designed to cause even distribution of the sound field. Reverberation rooms often have very hard exposed surfaces that are not parallel.

Bouncing back of wave energy such as light or sound. - when a wave reaches a new material part or all is reflected.

Free from rigid contact, such as a spring-mounted floating floor. Resiliency reduces the transfer of noise and vibration from one structure to another.

The exposed edge at the side of ceiling tile that is at right angles to the general face of the ceiling, visible (revealed) below the supporting grid.

The area in a room in which the multitude of decaying reflections has created a reverberant and diffuse condition.

A test chamber so designed that the reverberant sound field within the room has an intensity that is approximately the same in all directions and at every point. It is commonly used to measure sound absorption, ASTM C-423 and transmission loss, ASTM E-90.

A sheer, loosely woven fabric used as “backing” for acoustical panels.

A thin layer of material between two layers of absorptive material, such as foil, vinyl, lead, gypsum, steel, etc., that prevents sound wave from passing through absorptive material.

An apparent shift of the position of an instrument or voice in the stereo image due to a discrepancy in the phase relationships of the signals from either side. See Image Shift.

A discrete reflection from a nearby surface.

The degree of acoustical separation between two locations, especially adjacent rooms.

A room or studio that is usually soundproof, used for the production of movies. Or: The psycho acoustic phenomena where a two-dimensional image (left-to-right and front-to-back) is created in the mind suggesting the physical relationship of the listener to the individual performers. A well designed listening space will create the impression of a much larger sound stage than the physical placement of the speakers, or the size of the room would otherwise allow.

The conduction of a sound wave through air. The speed of airborne sound transmission varies with temperature and humidity, and is 1130 feet/second in air at 70°F.

Ratio of sound energy emitted by an acoustical material or structure to the energy incident upon the opposite side.

A single number rating for describing sound transmission loss of a wall or partition. A rating system designed to facilitate comparison of the sound transmission characteristics of various architectural materials and constructions.

The conducting of a sound wave through a physical structure (such as a wall, floor, ceiling or door). Because of the increased speeds of sound through common building materials (wood @ 11,700 feet/second, steel @ 18,000 feet/second) as well as the physical connection of such materials in the structural framework of a building, structure borne sound transmission is much more difficult to stop than airborne sound transmission, and thus requires special measures to be dealt with effectively.

Walls are splayed when they are constructed at angles of varying degrees from normal rectangular form.

An attachment method and related hardware for acoustical wall panels that works in conjunction with kerfed edges. Similar to a tongue and groove application. See Kerf.

The underlying material to which a covering is applied, or by which it is supported. A substrate (sometimes referred to as “core”) can also have important functional characteristics such as acoustical performance, impact resistance, and tackability.

A basic acoustical design to create a desirable balanced listening environment.

Any metal member of the “T” cross section used in ceiling suspension systems.

Edge detail on ceiling panels allowing a panel to hang flush or partially below a suspension grid.

The propagation of sound through a medium or barrier. (See Sound Transmission.)

The number of dB by which a barrier reduces the transmission of sound. Transmission loss varies significantly with frequency. For an accurate representation of soundproofing ability, Transmission Loss should be indicated at several frequencies for any given barrier.

The portion of sound energy transmitted through a material.

A two piece metal clip, one sliding over the other, used to attach panels to a wall (removable).