Acoustics Terminology

Glossary of Acoustic Terms

Acoustics is the science and art of sound. Sound containing information is termed as speech. The desirable or pleasant sound is termed music and the unwanted sound is termed as noise. Here is a glossary of acoustic terms:

Acoustics Dictionary

Acoustics Acoustics is basically a study of sound, its production, transmission, and effects.
Acoustical It is the property of a material to absorb, transmit or reflect sound.
Acoustic consultant A professional or a person who can give advice or does research about the acoustic requirement, noise problems, and vibration is basically known as an acoustic consultant.
Absorption When sound travels through one medium and hits a surface, some energy gets reflected and remaining energy gets converted into heat energy thereby reducing the total amount of sound. The sound energy converted to heat is known as absorbed sound.
Airborne noise The noise transmitted through air is known as airborne noise.
Airborne sound See Airborne noise.
Architectural Acoustics Study or review of a space or buildings to provide a good sound environment, good communication, listening, and eliminate the noise problem is called architectural acoustics.
Attenuation Reduction of sound energy as per distance traveled is called attenuation.
Ambient noise Noise generated in space from all the sources such as HVAC noise, machine noise, external noise can categorize under ambient noise.
Background noise It is the total noise which generated from all direct and reflected sound in a space which interferes with good listening and speech.
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.
Bel Unit of sound intensity
Cycle Whenever the sound is propagated through the air it moves in a different direction and a pressure wave is created. A complete oscillation of pressure above and below of atmospheric static wave is called cycle.
Decibel Unit of sound level is called decibel.
Diffusion Whenever the sound strikes a surface it will reflect or scatter in a different direction. The directions of reflected sound are changed so that listeners may have the sensation of sound coming from all directions at equal levels.
Echo Whenever the sound strikes a surface the reflected sound will produce continues repetition of the original sound which is produced. It is called echo.
Flutter echo Echo which produces due to the reflection of sound between 2 parallel walls.
Flanking noise The noise produced when sound transmitted through the holes or perimeter around the partition Is celled flanking noise.
e.g.: sound produced around ducts, ceiling plenum, pipe etc..
Frequency The number of oscillations or cycles per unit of time. Acoustical frequency is usually expressed in units of Hertz (Hz) where one Hz is equal to one cycle per second.
Hearing Range 16-20000 Hz
Speech Range 600-4800 Hz
Typical Small Table Radio Range 250-2500 Hz
Hertz The frequency of sound expressed in cycles per second. (See Cycle).
Impact sound The sound produced by the collision between two solid objects. Typical sources are footsteps, dropped objects, etc., on an interior surface (wall, floor, or ceiling) of a building.
Intensity The energy expended during sound vibration is called intensity.
Loudness The average deviation above and below the static value due to sound wave is called sound pressure. The energy expended during the sound wave vibration is called intensity and is measured in intensity units. Loudness is the physical resonance to sound pressure and intensity.
Noise The unwanted sound which interferes with communication and listening is called noise. e.g.: external noise, machine noise, traffic noise, etc.
Noise criteria (NC) (NC) is a single numerical index commonly used to define design goals for the maximum allowable noise in a given space. They primarily apply to the noise produced by a ventilation system, but they may be applied to other noise sources.
Noise reduction Noise reduction is the process of reducing the noise which developed in a space by introducing or installing the sound absorbing material.
Noise reduction coefficient(NRC) Noise reduction coefficient is the amount of sound absorbed by the material when the sound energy strikes.
Octave bands An octave band is a frequency range where the highest frequency is twice as that of the lowest frequency.

e.g. 125HZ-250HZ,500HZ-1000HZ-2000HZ,

Reflection When sound energy strikes a wall, some energy gets absorbed or converted into some other form of energy and the remaining energy bounces back. This is called a reflection. Non-porous or hard surfaces like glass, gypsum board, concrete reflect more sound than porous surfaces like a soft board, panel etc.
Resonance when a system start vibrates the adjacent system or particle starts vibrate due to the external forces or vibration gets transferred to the other system
Reverberation time The time taken for sound to decay by 60 dB or 1/1,000,000 of its original sound level after the sound source has stopped. After the sound source is switched off, the sound will continue to reflect off surfaces until the wave loses enough energy by absorption to eventually die out. Reverberation time is the basic acoustical property of a room which depends only on its dimensions and the absorptive properties of its surfaces and contents. Reverberation has an important impact on speech intelligibility.
Reverberation Sound, after it is switched off at the source, will continue to reflect off surfaces until the sound wave loses energy by absorption to eventually die out.
Sound Sound is an oscillation in pressure, stress particle displacement, particle velocity in a medium – at room temperature. (In airspeed of sound is 1125′/second or one mile in 5 seconds.) Sound produces an auditory sensation caused by the oscillation.
Sound Absorption The property possessed by materials, objects, and air to convert sound energy into heat. Sound waves reflected by a surface causes a loss of energy. That energy not reflected is called its absorption coefficient.
Sound level  A subjective measure of sound expressed in decibels as a comparison corresponding to familiar sounds experienced in a variety of situations.
Speech The act of speaking. Communication of thoughts and feelings by spoken words.
Speech Privacy The degree to which speech is unintelligible between offices. Three ratings are used, Confidential, Normal (Non-obtrusive), Minimal.
SPL: Sound Pressure Level The quantity used to describe the loudness of a sound. The sound pressure level is expressed in decibels and is measured with a sound level meter. For example, a conversation between two people inside an average-size room will produce an average “A” weighted sound pressure level of 50 to 55 lb.
Sound Transmission Class(STC) A single-number rating obtained by classifying the measured values of Sound Transmission Loss in accordance with ASTM Standard E 413, “Classification for Sound Rating Insulations”. It provides a quick indication of the performance of a partition for certain common sound insulation problems.
Sound Transmission Loss (TL) The difference between the sound power level incident on a partition and that transmitted through that partition.

TL = LW incident−LW transmitted; TL = NR + 10 log S/A

TL = Sound Transmission Loss WHERE:

LW = Sound Power Level

NR = Noise Reduction

S = Surface area of the partition

A = Acoustical absorption present in by the receiving room (in Sabines)

Soundproofing Building materials that make any structure impervious to sound or, insulates against the transmission or production of unwanted sound (noise).
Structural airborne noise The noise that arrives at a point of interest by propagation through a solid structure.
Vibration  A force which oscillates about some specified reference point. Vibration is commonly expressed in terms of frequency such as cycles per second (cps), Hertz (Hz), cycles per Minute (cpm) or (rpm) and Strokes per Minute (spm). This is the number of oscillations which occurs in that time period. The amplitude is the magnitude or distance of travel of the force.
Vibration Isolator A resilient support that tends to isolate a mechanical system from steady state excitation.
Leq/LAeq Leq/LAeq is the constant noise level that would result in the same total sound energy being produced over a given period.
L-max  Lmax is the RMS (root mean squared) maximum level of a noise source
L-min  Lmin is the RMS (root mean squared) minimum level of a noise source

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