Soundproofing Glossary of Terms

This glossary of soundproofing, sound and acoustic terms has been provided with a brief description, for the most part in non technical terms in an effort to remove some of the mystery surrounding soundproofing and acoustics. While the explanations may not be totally correct in their literal interpretations it is hoped that the plain language approach will provide a better understanding of the terminology frequently used in the field of soundproofing and acoustics...

ACOUSTICS: The science of Sound. Its production, transmission and effects. The branch of physics that treats the phenomena and laws of sounds as it effects people.

ACOUSTICAL: The properties of a material to absorb or reflect Sound (adjective) Acoustically, (Adverb).

ACOUSTICAL ANALYSIS: A review of a space to determine the level of reverberation or reflected sound in the space (in seconds) influenced by the building materials used to construct the space. Also the amount of acoustical absorption required to reduce reverberation and noise.

ACOUSTICAL CONSULTANT: A professional usually with an engineering degree who is experienced in providing advice on acoustical requirements, and noise control in a variety of situations.

ACOUSTICAL ENVIRONMENT: The acoustical characteristics of a space or room influenced by the amount of acoustical absorption, or lack of it in the space.

AIRBORNE NOISE: Noise that arrives at a point of interest by propagation through the air.

AIRBORNE SOUND: Sound that reaches the point of interest by propagation through air.

APPARENT IMPACT ISOLATION CLASS (AIIC): This is the isolation index of the apparent impact noise of a floor/ceiling assembly on site. Since ASTM E1007-14 and ASTM E336-14 came to affect, details have been provided on how to measure and present the results of acoustic tests carried out on site. All new tests carried out on site will now be preceded by the letter "A" rather than "F". Other than designating the unit of measurement for acoustic efficiency, these changes represent more accurately the reality of an onsite test, with its characteristics and weaknesses. The changes make the ASTM standards more accurate and eliminate border line cases due to the disparity in volumes and shapes of the measured rooms. Without going into the details of this new regulation, the application of these updates will allow us to obtain results that take into account indirect sound losses related to generally accepted construction methods. For current acoustic standards, for floor/ceiling assembly in multifamily buildings with more than one floor, the Canadian National Building Code (NBC) does not require a minimum Impact Noise rating but recommends a FIIC 55. Also see Impact Isolation Class & Field Impact Isolation Class

APPARENT SOUND TRANSMISSION CLASS (ASTC): In 2015 the Canadian National Building Code (NBC) introduced a new code to measure the sound transfer between multi-family dwelling units. This release of the code contains a significant change, and an improvement, in requirement for minimum soundproofing between dwelling units. The new code replaces Sound Transmission Class (STC) requirement with Apparent Sound Transmission Class (ASTC) for wall assemblies between dwelling units.

The old requirement of STC 50 is replaced with new requirement of ASTC 47. Apparent Sound Transmission Class (ASTC) is defined in ASTM specification E336. This value can be verified by field measurements, since it includes noise transmitted through flanking paths that are always present in a field situation (but not in a lab test of STC value). Even though the new number is lower than the old STC value, it is an improvement over the old requirements, since the ASTC value more accurately represents the situation to which occupants of spaces are exposed to. ASTC value can be accurately verified in the field, thus making builders more accountable for the actual performance of new buildings. Also see Sound Transmission Class (STC) & Field Sound Transmission Class (FSTC).

ARCHITECTURAL ACOUSTICS: Deals with sound in rooms and building to make them quiet – or to provide improved conditions for listening and understanding speech or music.

ARCHITECTURAL SOUNDPROOFING: The control of noise in a building space to adequately support the communications function within the space and its effect on the occupants. The qualities of the building materials used determine its character with respect to distinct hearing.

ARTICULATION CLASS: A single number rating used for comparing acoustical ceilings and acoustical screens for speech privacy purposes. AC values increase with increasing privacy and range from approximately 100-250. This classification supersedes Speech Privacy Noise Isolation Class (NIC) rating method.

ARTICULATION INDEX (AI): A measure of speech intelligibility influenced by Acoustical Environment rated from 0.01 to 1.00.The higher the number the higher the intelligibility of words and sentences understood from 0-100%.

ABSORPTION: The properties of a material composition to convert sound energy into heat thereby reducing the amount of energy that can be reflected.

AREA EFFECT: Acoustical materials spaced apart can have greater absorption than same amount of material butted together. The increase in efficiency is due to absorption by soft exposed edges and also to diffraction of sound energy around panel perimeters.

ATTENUATION: The reduction of sound energy as a function of distance traveled.

"A" WEIGHTING: An electronic filtering system in a sound meter that allows meter to largely ignore lower frequency sounds in a similar fashion to the way our ears do.

AMBIENT NOISE/SOUND: Noise level in a space from all sources such as HVAC or extraneous sounds from outside the space. Masking sound or low-level background music can contribute to ambient level of sound or noise.

BACKGROUND NOISE: The sum total of all noise generated from all direct and reflected sound sources in a space that can represent an interface to good listening and speech intelligibility. (Hearing impaired persons are especially victimized by background noise).

BAFFLE: A free hanging acoustical sound absorbing unit. Normally suspended vertically in a variety of patterns to introduce absorption into a space to reduce reverberation and noise levels.

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: A measurement of sound intensity named in honor of Alexander Graham Bell. First used to relate intensity to a level corresponding to hearing sensation.

BOOMINESS: Low frequency reflections. In small rooms acoustical panels with air space behind can better help control low frequency reflectivity.

CEILING ATTENUATION CLASS (CAC): This indicates a ceiling’s ability to prevent airborne sound from traveling between adjacent rooms when the dividing wall does not connect with the structural ceiling. CAC can be applicable between adjacent rooms and between rooms and a corridor. Higher values provide more insulation. CAC is measured in decibels according to the ASTM E1414 standard. This a very common measurement for suspended ceiling tiles and typically the ceiling tile will also have an NRC (Noise Reduction Coefficient) as well.

CLOUD: In acoustical industry terms, an acoustical panel suspended in a horizontal position from ceiling/roof structure. Similar to a baffle but in a horizontal position.

COCKTAIL PARTY EFFECT: Sound in a noisy crowded room generated mostly by conversation. Levels rise and fall as people compete with one another to be heard. Perception of speech can be nearly impossible in high levels of noise.

DAMPING: The dissipation of vibratory energy in solid media and structures with time or distance. It is analogous to the absorption of sound in air.

DECIBEL (dB): Sound level in decibels as a logarithmic ratio. Sound intensity described in decibels.

DEFLECTION: The distance an elastic body or spring moves when subjected to a static or dynamic force. Typical units are inches or mm.

DIFFUSION: The scattering or random reflection of a sound wave from a surface. The directions of reflected sound is changed so that listeners may have sensation of sound coming from all directions at equal levels.

ECHO: Reflected sound producing a distinct repetition of the original sound. Echo in mountains is distinct by reason of distance of travel after original signal has ceased. Also know as reverberation.

ECHO FLUTTER: Short echoes in a small reverberative spaces that produce a clicking, ringing or hissing sound after the original sound signal has ceased. Flutter echoes may be present in long narrow spaces with parallel walls.

EQUAL LOUDNESS CONTOURS: Curves represented in graph form as a function of sound level and frequency which listeners perceive as being equally loud. High frequency sounds above 2000 Hz are more annoying. Human hearing is less sensitive to low frequency sound.

FIELD IMPACT ISOLATION CLASS (FIIC): This is a unit of measurement that determines the degree of isolation of the impact noise of a floor/ceiling assembly on site rather than in a laboratory. The higher the FIIC, the better the acoustic insulation. A FIIC test is carried out on site, in real buildings. It can be argued that this rating is more representative of reality than a IIC laboratory test. Also see Impact Isolation Class (IIC).

FIELD SOUND TRANSMISSION CLASS (FSTC): A sound transmission rating obtained under “real-life” conditions. The general method to obtain this rating is almost the same as the method used in laboratory conditions. Procedures, however, have been added to take into account the differences between field conditions and laboratory conditions (e.g. flanking paths, absorption, modal distribution, etc.) Also see Sound Transmission Class (STC).

FLANKING: The transmission of sound around the 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.

FREE FIELD: Sound waves from a source outdoors where there are no obstructions.

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.

FREQUENCY ANALYSIS: An analysis of sound to determine the character of the sound by determining the amount of sounds at various frequencies that make up the overall sound spectrum. i.e.: Higher Frequency Sound or Pitch vs. Low Frequency.

HERTZ (Hz): Frequency of sound expressed by cycles per second.

IMPACT ISOLATION CLASS (IIC): The methods to measure the degree of impact noise isolation provided by a floor/ceiling assembly, in laboratory conditions, are described in the ASTM E 492 or ISO 140/6 standards. For field measurements refer to ASTM E 1007 or ISO 140/7. The impacts for these measurements are produced by the “Standard Tapping Machine”, an electrically operated mechanism consisting of five 0.5 kg hammers which fall regularly and freely onto floor surface from 40 mm height at a rate of 10 impacts/second. The sound pressure levels generated in the room directly below the floor/ceiling assembly undergoing testing are then measured, for each of the 16 third-octave-bands between 100 Hz and 3150 Hz. The IIC rating of the tested floor/ceiling assemblers determined by sliding the classification curve on the graph representing the normalized sound pressure levels, until the following conditions described in the ASTM E 989 (ISO 717/2) standards, are met:

  • The sum of the deviations above the normalizing curve should not exceed 32 dB.
  • The maximum deviation above the normalizing curve should not exceed 8 dB (see previous note on the classification of the isolation of airborne noise according to the ISO standard).

When the IIC contour is positioned in such a way that these two requirements are satisfied the Impact Isolation Class (IIC) can be obtained by reading the normalized impact sound pressure level at the intersection of the IIC contour frequencies of 500 Hz and by subtracting this value from the number 110.

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.

INVERSE SQUARE LAW: Sound levels fall off with distance traveled. Sound level drops off 6 dB from source point for every doubling of distance.

LIVE END/DEAD END: An acoustical treatment plan for rooms in which one end is highly absorbent and the other end is reflective and diffusive.

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.

MASKING: The process by which the threshold of hearing of one sound is raised due to the presence of another.

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.

NOISE: Unwanted sound that is annoying or interferes with listening. Not all noise needs to be excessively loud to represent an annoyance or interference.

NOISE ISOLATION CLASS (NIC): A single number rating of the degree of speech privacy achieved through the use of an acoustical ceiling and sound absorbing screens in an open office. NIC has been replaced by the Articulation Class (AC) rating method.

NORMALIZED NOISE ISOLATION CLASS (NNIC): The Normalized Noise Isolation Class (NNIC) rating is obtained by applying the ASTM E 413 classifiction standards to the Normalized Noise Reduction (NNR) values measured on a partition.

NORMALIZED NOISE REDUCTION (NNR): Noise Reduction normalized as a function of a 0.5 second reverberation time in the receiving room. Where:

  • NNR = NR + 10 log (RT/0.5)
  • NNR = Normalized Noise Reduction
  • NR = Noise Reduction
  • RT = Reverberation Time in the Receiving Room

NOISE REDUCTION (NR): The amount of noise that is reduced through the introduction of sound absorbing materials. The level (in decibels) of sound reduced on a logarithmic basis.

NOISE REDUCTION COEFFICIENT (NRC): The NRC of an acoustical material is the arithmetic average to the nearest multiple of 0.05 of its absorption coefficients at 4 one third octave bands with center frequencies of 250, 500, 1000, 2000 Hertz. An NRC of 0.00 indicates perfect reflection; an NRC of 1.00 indicates perfect absorption.

OCTAVE BANDS: Sounds that contain energy over a wide range of frequencies are divided into sections called bands. A common standard division is in 10 octave bands identified by their center frequencies 31.5, 63, 125, 250, 500, 1000, 2000, 4000 Hz.

PHON: Loudness contours. A subjective impression of equal loudness by listeners as a function of frequency and sound level (dB). An increase in low frequency sound will be perceived as being much louder than an equivalent high frequency increase.

PITCH: The perceived auditory sensation of sounds expressed in terms of high or low frequency stimulus of the sound.

REFLECTION: The amount of sound wave energy (sound) that is reflected off a surface. Hard non-porous surfaces reflect more sound than soft-porous surfaces. Some sound reflection can enhance quality of signal of speech and music.

RESONANCE: The emphasis of sound at a particular frequency.

RESONANT FREQUENCY: A frequency at which resonance exists.

REVERBERATION: The time taken for sound to decay 60 dB to 1/1,000,000 of its original sound level after the sound source has stopped. Sound after it has ended 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 TIME: Sound after it is ended at the source will continue to reflect off surfaces until the sound wave loses energy by absorption to eventually die out.

SABIN: A unit of sound absorption based of one square foot of material. Baffles are frequently described as providing X number of sabins of absorption based on the size of the panel tested, through the standard range of frequencies 125-4000 Hz. The number of sabins developed by other acoustical materials are determined by the amount of material used and its absorption coefficients.

SABINE FORMULA: A formula developed by Wallace Clement Sabine that allows designers to plan reverberation time in a room in advance of construction and occupancy. Defined and improved empirically the Sabine Formula is T=0.049(V/A) where T = reverberation time or time required (for sound to decay 60 dB after source has stopped) in seconds. V = Volume of room in cubic feet. A = Total square footage of absorption in sabins.

SEPTUM: A thin layer of material between 2 layers of absorptive material. i.e.: foil, lead, steel, etc. that prevents sound wave from piercing through absorptive material.

SIGNAL TO NOISE RATIO: Is the sound level at the listeners ear of a speaker above the background noise level. The inverse square law impacts on the S/N ratio. Signal to Noise Ratios are important in classrooms and should be in range of 15 to 20 dB.

SOUND: Sound is an oscillation in pressure, stress particle displacement, particle velocity in a medium – in room temperature. (In air speed 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 ABSORPTION COEFFICIENT: The fraction of energy striking a material or object that is not reflected. For instance if a material reflects 70% of the sound energy incident upon its surface, then its Sound Absorption Coefficient would be 0.30.

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 LEVEL: A subjective measure of sound expressed in decibels as a comparison corresponding to familiar sounds experienced in a variety of situations.

SOUND PRESSURE: The total instantaneous pressure at a point in space, in the presence of a sound wave, minus the static pressure at that point.

SOUND PRESSURE LEVEL: The sound pressure level, in decibels, of a sound is 20 times the logarithm to the base 10 of the ratio of the sound pressure to the reference pressure. The reference pressure shall be explicitly stated and is defined by standards.

SOUNDPROOFING: Building materials that helps structures control sound/vibration or, insulates against the transmission or production of unwanted sound (noise).

SOUND LEVEL METER: A device that converts sound pressure variations in air into corresponding electronic signals. The signals are filtered to exclude signals outside frequencies desired.

SPEECH PRIVACY: The degree to which speech is unintelligible between offices. Three ratings are used, Confidential, Normal (Non obtrusive), Minimal.

SOUND PRESSURE LEVEL (SPL): 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 converstaion 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.

To determine the Sound Transmission Class (STC) in conformance to the ASTM E 413 (lSO 71 7/1) one must slide the STC contour along its Y-axis of the graph on which the transmission loss curve is plotted until the following conditions are met:

  • The sum of the deviation below the STC contour does not exceed 32 dB.
  • No deviation below the STC contour exceeds 8 dB.

When the STC contour is positioned in such a way that these two requirements are satisfied the sound transmission class can be obtained by reading the transmission loss value at the intersection of the STC contour at the frequency of 500 Hz. This value corresponds to the STC of the partition.

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 OR
  • 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 Sabins)

The standards for measuring Sound Transmission Loss are:
Laboratory Measurements: ASTM E 90 ISO 140/1, /2, /3
Field Measurements: ASTM E 336 ISO 140/4, /5

The Sound Transmission Loss (TL) of a partition can be obtained in laboratory conditions by following the guidelines given below, in conformance to the ASTM E 90 standard.

  1. For each one-third-octave-band, measure the noise reduction (NR) provided by the partition.
  2. Measure the quantity of acoustical absorption in the receiving room (where the sound power levels are transmitted).
  3. Transform the values of noise reduction to sound transmission loss, using the correction 10*log (S/A).

SPECTRUM: The description of a sound wave’s components of frequency and amplitude.

STRUCTURE BORNE NOISE: Noise that arrives at a point of interest by propagation through a solid structure.

ULTRASOUNDS: Sounds of a frequency higher than 20,000 Hz. The frequency region containing these frequencies is called the ultrasonic region.

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.

WAVELENGTH: Sound that passes through air it produces a wavelike motion of compression and Parefaction. Wavelength is the distance between two identical positions in the cycle or wave. Similar to ripples or waves produced by dropping two stones in water. Length of sound wave varies with frequency. Low frequency equals longer wavelengths.

If there are any sound, soundproofing or acoustical terms you felt I missed here feel free to email me [email protected].

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