Studio Acoustics & Soundproofing Glossary

A| B| C| D| E| F| G| H| I| J| K| L| M| N| O| P| Q| R| S| T| U| V| W| X| Y| Z

[A]

Absorption: Quality of a surface or substance to take in, not reflect, a sound wave.

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 dealing with sound and it's physical properties.

Airborne sound: Sound that arrives at the point of interest, such as one side of a partition, by propagation through air.

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.

Ambient Field / Reverberant Field: The area away from the sound source where the reverberation is louder than the direct sound.

Ambient Micing: Placing a microphone in the reverberant field where the reverberation is louder than the direct sound so as to do a separate recording of the ambience or to allow the recording engineer to change the mix of direct to reverberant sound in recording.

Amplitude: The depth, or excursion of a vibration or wave. In audio waves, it translates to loudness.

Anechoic: Without echo.

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

Artificial reverberation: Reverberation generated by electrical or acoustical means to simulate that of concert halls, etc., added to a signal to make it sound more lifelike.

Attenuation: Reduction of electrical or acoustic signal strength.

Audio: All vibration that falls between the frequency range of 20 to 20K Hz, and therefore detectable to the human ear. Often used in recording to mean the desired sound of the recording as apposed to undesired noise.

Audiophile: A person who is interested in sound reproduction.

Average room absorption coefficient: Total room absorption in sabins or metric sabins, divided by total room surface area in consistent units of square feet or square meters.

Average sound pressure level: Of several related sound pressure levels measured at different positions or different times, or both, in a specified frequency band, ten times the common logarithm of the arithmetic mean of the squared pressure ratios from which the individual level were derived.

A-Weighted Sound Level: A measure of sound pressure level designed to reflect the acuity of the human ear, which does not respond equally to all frequencies. The ear is less efficient at low and high frequencies than at medium or speech-range frequencies. Therefore, to describe a sound containing a wide range of in a manner representative of the ear's response, it is necessary to reduce the effects of the low and high frequencies with respect to the medium frequencies. The resultant sound level is said to be A-weighted, and the units are dBA. The A-weighted sound level.

[B]

Baffles: Sound absorbing panels used to prevent sound waves from entering or leaving a certain space.

Bandwidth: The range of frequencies over which a tape recorder, amplifier or other audio device is useful, the range of frequencies affected by an equalization setting.

Barrier: Anything physical or an environment that interferes with communication or listening. A poor acoustical environment can be a barrier to good listening and especially so for persons with a hearing impairment.

Bass: The lower range of audible frequencies.

Beaming: The phenomenon of sound being emitted within a comparatively small solid angle. This characteristic becomes more acute as the frequency increases.

Beats: Periodic fluctuations that are heard when sounds of slightly different frequencies are superimposed.

Block: Building a continuous barrier that traps or stops air movement from one side of a partition to the other, greatly reducing airborne sound transmission.

Boomy: Listening term, refers to an excessive bass response that has a peak(s) in it.

Bottom: Bass frequencies (bottom end).

Bouncing: Playing several tacks with sync playback through a console to mix them together and record them on an open track.

Break: A physical break in the assembly or construction which acts to decouple sound vibrations from traveling through the structure.

Bright: Listening term. 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.

Bus: Also referred to as sub-mix. A group of tracks routed to a bus for processing as a mixed group. Usually added back into main mix post processing. Busses can also be as separate outputs from a mixer to a soundcard.

[C]

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

Cancellation (phase cancellation): The energy of one waveform significantly decreasing the energy of another waveform because of phase relationships at or close to 180 degrees.

Center frequency: Frequency of the audio signal that is boosted or attenuated most by an equalizer with a peak equalization curve.

Channel balance: In a stereo system, the level balances between left and right channels. Properly balanced, the image should be centered between the left-right speakers. In a home-theater system, refers to achieving correct balance between all the channels of the system.

Clean: A distortion free sound.

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. Even a low-powered amplifier or receiver driven into clipping can damage tweeters which would otherwise last virtually forever.

Close Micing: Technique of placing a microphone close to the sound source (within one foot) in order to pick up mainly the direct sound and to avoid picking up leakage or ambience.

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: Electronic filter in a sound system that routes sound of the correct frequency to the correct part of the speaker system (active crossovers split the signal from the mixing desk into high, mid and low frequencies which are then sent to three separate amps.

Crossover frequency: Frequency that is the outer limit of one of the bands of a crossover.

[D]

Damping: The dissipation of energy with time or distance. The term is generally applied to attenuation of sound in a structure owing to the internal sound-dissipative properties of the structure or to the addition of sound-dissipative materials.

db (decibel): Numerical expression of the relative loudness of a sound difference in decibels between two sounds is ten times the common logarithm of the ratio of their power levels; Relative measurement for the volume (loudness) of sound.

Delay: Sound equipment that can momentarily stores a signal being sent to part of a P.A. system so that delayed reinforced sound reaches the audience at the same time as live sound from the stage, effect used to create echo.

Diffraction: Breaking up of a sound wave caused by some type of mechanical interference such as a cabinet edge, grill frame, or other similar object.

Distortion: Usually undesirable result of overloading sound equipment.

[E]

Echo: A delayed return of sound that is perceived by the ear as a discrete sound image.

[F]

Feedback (acoustic): Unwanted interaction between the output and input of an acoustical system, e.g., between the loudspeaker and the microphone of a system.

Field sound transmission class (FSTC): Sound transmission class calculated in accordance with Classification E 413 using values of field transmission loss.

Flutter: A repetitive echo set up by parallel reflecting surfaces.

Free sound field (free field): A sound field in which the effects of obstacles or boundaries on the sound propagated in that field is negligible.

[G]

[H]

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

[I]

Impact insulation class (IIC): A single-number rating derived from measured values of normalized impact sound pressure levels I accordance with Annex A1 of Test Method E 492. It provides an estimate of the impact sound insulating performance of a floor-ceiling assembly.

Impact sound: The sound produced by the collision of two solid objects. Typical sources are footsteps, dropped objects, etc.., on an interior surface (wall, floor, or ceiling) of a building.

Impedance: The opposition to the flow of electric or acoustic energy measured in ohms.

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.

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

[J]

[K]

[L]

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

[M]

Mass: The fundamental property of a material relevant to sound transmission loss through that material. Generally, the more massive the material, the greater the sound transmission loss.

Monitors: Speakers created specifically for the purpose of recording and mixing. Very flat uncolored frequency response with a highly directional sound pattern. Highly recommended gear for setting stereo field and hearing how well a mix of tracks work together.

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: 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.

Noise: Interference of an electrical or acoustical nature. Random noise is a desirable signal used in acoustical measurements. Pink noise is random noise whose spectrum falls at 3 dB per octave: it is useful for use with sound analyzers with constant percentage bandwidths. Unwanted, bothersome, or distracting sound.

Noise reduction (NR): The difference in sound pressure level between any two points along the path of sound propagation. As an example, noise reduction is the term used to describe the difference in sound pressure levels between the inside and outside of an enclosure.

Noise reduction coefficient (NRC): The arithmetic average, to the nearest multiple of .05, of the sound absorption coefficients in the 1/3 octave bands centered at 250Hz, 500Hz, 1000Hz, and 2000Hz.

Normal incidence sound absorption: Of a surface, at a specified frequency, the fraction of the perpendicularly incident sound power absorbed or otherwise not reflected.

Normalized noise isolation class (NNIC): A single-number rating calculated in accordance with Classification E 413 using measured values of normalized noise reduction.

Normalized noise reduction (NNR): Between two rooms, in a specified frequency band, the value that the noise reduction in a given field test would have if the reverberation time in the receiving room were .5 s.

[O]

[P]

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

Post echo: A position of an echo send control after the main channel fader.

[Q]

[R]

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.

Reverberant sound field: The sound in an enclosed or partially enclosed space that has been reflected repeatedly or continuously from the boundaries.

Reverberation: The persistence of sound in an enclosed or partially enclosed space after the source of sound has stopped; by extension, in some contexts, the sound that so persists.

Reverberation room: A room so designed that the reverberant sound field closely approximates a diffuse sound field, both in the steady state when the sound source is on, and during the decay after the source of sound has stopped.

Reverberation time: The tailing off of a sound in an enclosure because of multiple reflections from the boundaries.

Room mode: The normal modes of vibration of an enclosed space.

[S]

Soft room: Room with highly sound absorptive surfaces.

Sound: Sound is vibrational disturbance, exciting hearing mechanisms, transmitted in a predictable manner determined by the medium through which it propagates. To be audible the disturbance must fall within the frequency range 20Hz to 20,000Hz.

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.

Sound absorption coefficient: Of a surface, in a specified frequency band, the measure of the absorptive property of a material as approximated by the method of Test Method C423. Ideally, the fraction of the randomly incident sound power absorbed or otherwise not reflected.

Sound attenuation: The reduction of the intensity of sound as it travels from the source to a receiving location. Sound absorption is often involved as, for instance, in a lined duct. Spherical spreading and scattering are other attenuation mechanisms.

Sound Barrier: A material that when placed around a source of noise inhibits the transmission of that noise beyond the barrier. Also, anything physical or an environment that interferes with communication or listening. For example, a poor acoustical environment can be a barrier to good listening and especially so for persons with a hearing impairment.

Sound insulation: The capacity of a structure to prevent sound from reaching a receiving location. Sound energy is not necessarily absorbed; impedance mismatch, or reflection back toward the source, is often the principal mechanism.

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

Sound level: Of airborne sound, a sound pressure level obtained using a signal to which a standard frequency-weighting has been applied.

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. Live orchestral music reaches brief peaks in the 105 dB range and live rock easily goes over 120 dB.

Sound transmission class (STC): A single-number rating, calculated in accordance with Classification E 413 using values of sound transmission loss. It provides an estimate of the performance of a partition in certain common sound insulation problems. A single number rating that indicates the sound transmission loss of a partition or ceiling system between adjacent closed rooms, abbreviated STC.

Sound waves: Sound waves can be thought of like the waves in water. Frequency determines the length of the waves; amplitude or volume determines the height of the waves. At 20Hz, the wavelength is 56 feet long! These long waves give bass its penetrating ability, (why you can hear car boomers blocks away).

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.

Source room: In architectural acoustical measurements, the room that contains the noise source or sources.

Speech intelligibility: A measure of sound clarity that indicates the ease of understanding speech. It is a complex function of psychoacoustics, signal-to-noise ratio of the sound source, and direct-to-reverberant energy within the listening environment.

Standing wave: A resonance condition in an enclosed space in which sound waves traveling in one direction interact with those traveling in the opposite direction, resulting in a stable condition.

Structureborne noise: Generation and propagation of time-dependent motions and forces in solid materials which result in unwanted radiated sound.

Subwoofer: A speaker designed exclusively for low-frequency reproduction. A true subwoofer should be able to at least reach into the bottom octave (20-40Hz). There are many "subwoofers" on the market that would be more accurately termed "woofers".

[T]

Treble: The higher frequencies of the audible spectrum.

[U]

Unidirectional: A pick-up pattern which is more sensitive to sound arriving from one direction than from any other.

[V]

Vibration isolation: A reduction, attained by the use of a resilient coupling, in the capacity of a system to vibrate in response to mechanical excitation.

Vibration isolator: A resilient support that tends to isolate a mechanical system from steady state excitation.

[W]

Wave length: The length of one cycle (in feet, inches, etc.), the distance measured in the direction of progression of a wave, from any given point characterized by the same phase.

Wave velocity: The time it takes for one point of the waveform to travel a certain distance.

Waveform: The physical or mathematical nature of a soundwave. Normally refers to the common graphic representation of a soundwave, with level on the x-axis, and time on the y-axis.

Wet: Having reverberation or ambience.

[X]

[Y]

[Z]

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