A-Weighted Sound Level
A measure of sound pressure level designed to reflect the response of the human ear, which does not respond equally to all frequencies. The A-weighted sound level is also called the noise level measure in units of dBA Sound level meters have an A-weighting network for measuring A-weighted sound levels.
The properties of a material composition to convert sound energy into heat thereby reducing the amount of sound energy that can be reflected.
The properties of a material to absorb or reflect sound (adjective) acoustically, (adverb).
A review of a space to determine the level or reverberation or reflected sound in the space (in seconds) as influenced by the building materials used for construction of the space. Also, a study of the amount of acoustical absorption required to reduce reverberation and noise.
The acoustical characteristics of a space or room influenced by the amount of acoustical absorption, or lack of it, in the space.
Acoustics is the science of sound, including its production, transmission and effects. The acoustics of a room are those qualities that together determine its character with respect to the perception of sound.
Ambient noise encompasses all sound present in a given environment, being usually a composite of sounds from many sources near and far.
The control of noise in a building space to adequately support the communications function within the space and its effect on the occupants. The level of control required is largely dependent on the intended use of the space such as classroom, theatre, conference room or church hall. The qualities of the building materials used to determine its character with respect to distinct hearing.
Acoustical materials spaced apart can have greater absorption than the 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.
Acronym for American Society of Testing and Materials.
ASTM C423 is a standard test method for classifying the sound absorption of a material
Standard Test Method for Surface Burning Characteristics of Building Materials This test method is intended to provide only comparative measurements of surface flame spread and smoke density measurements with that of select grade red oak and fiber-cement board surfaces under the specific fire exposure conditions described herein. The results of the test are used to rate materials as follows: Class A (1): Flame Spread 0 – 25 Smoke Developed 0 – 450 Class B (2): Flame Spread 26 – 75 Smoke Developed 0 – 450 Class C (3): Flame Spread 76 – 200 Smoke Developed 0 – 450
The reduction of sound energy as a function of distance traveled.
An instrument for measuring hearing acuity.
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.
Low frequency reflections. In small rooms, acoustical panels with air space behind can better help control low frequency reflectivity.
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.
In acoustics, the cycle is the complete oscillation of pressure above and below the atmospheric static pressure.
Cycles Per Second
The number of oscillations that occur in the time frame on one second. (See Frequency). Low frequency sounds have fewer and longer oscillations.
A dimensionless unit which denotes the ratio between two quantities that are proportional to power, energy or intensity. One of these quantities is a designated reference by which all other quantities of identical units are divided. The sound pressure level in decibels is equal to 10 times the logarithm (to the base 10) of the ratio between the pressure squared divided by the reference pressure squared. The reference pressure used in acoustics is 20 micro Pascals.
Deflection is the distance an elastic body or spring moves when subjected to a static or dynamic force. Typical units are inches or mm.
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.
Reflected sound producing a distinct repetition of the original sound. Echo in mountains is distinct by reason of travel after original signal has ceased.
Classification indicating propagation of flame across a sample compared to flame propagation across concrete panels and red oak. Results are obtained through an ASTM E84 or UL723 test.
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 path above partitions; ductwork, piping, and electrical conduit penetrations through partitions; back-to-back electrical boxes within partitions, window mullions, etc.
Short echoes in 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.
Sound waves from a source outdoors where there are no obstructions.
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.
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. For example, higher frequency sound or pitch vs. low frequency.
A degree of hearing loss, temporary or permanent, due to many causes. Hearing loss can be caused by illness, disease, or exposure to excessively high noise levels. Affects 25 – 50 million people in USA of all ages. Hearing impairment as generally used means a hearing loss of mild, moderate or severe degree as opposed to “deafness” which is generally described as little or no residual hearing with or without the aid of an assisting listening device. Hearing impaired persons are particularly adversely affected by long reverberation times.
16 – 2000 Hz (Speech Intelligibility) 600 – 4800 Hz (Speech Privacy) 250 – 2500 Hz (Typical small table radio)
Frequency of sound expressed by cycles per second.
Inverse Square Law
Sound levels fall off with distance traveled. Sound level drops off 6 dB from the 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.
A listener’s auditory impression of the strength of a sound. The average deviation above and below the static value due to a 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.
The process by which the threshold of hearing of one sound is raised due to the presence of another.
Mass is 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.
Unwanted sound that is annoying or interferes with listening. Not all noise needs to be excessively loud to represent an annoyance or interference.
Noise Criteria (NC)
Noise criteria curves used to evaluate existing listening conditions at ear level by measuring sound levels at the loudest locations in a room. NC criteria can be referred to equivalent dBA levels.
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.
The Noise Reduction Coefficient (commonly abbreviated NRC) is a scalar representation of the amount of sound energy absorbed upon striking a particular surface. An NRC of 0 indicates perfect reflection. An NRC of 1 indicates perfect absorption. Higher Numbers = Higher Performance. Type A Mount: Sound absorption test for materials mounted direct to a flat surface like a wall or ceiling. Type E400 Mount: Sound absorption test for materials installed into a T-Bard suspended ceiling grid.
A pitch interval of 2 to 1. The tone whose frequency is twice that of the given tone.
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, 250, 500, 1000, 2000, and 4000 Hz.
The amount of sound wave energy (sound) that is reflected off a surface. Hard non-porous surfaces reflect more sound that soft porous surfaces. Some sound reflection can enhance the quality of the signal of speech and music.
The emphasis of sound at a particular frequency.
Resonant Frequency is a frequency at which resonance exists.
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.
The reverberation time of a room is the time it takes for sound to decay by 60 dB once the source of sound has stopped. 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.
A unit of sound absorption based on 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 125 – 4000 Hz. The number of sabins developed by other acoustical materials are determined by the amount of material used and its absorption coefficients.
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 (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.
A thin layer of material between 2 layers of absorptive material, such as foil, lead, steel, etc. that prevents sound wave from passing through absorptive material.
Signal To Noise Ratio
The sound level at the listeners ear of a speaker above the background noise level. The inverse square law impacts the S/N ratio.
Smoke Developed Index
Classification that relates to a comparison of smoke development of a particular material compared to concrete panels and red oak. Results are obtained through an ASTM E84 or UL723 test.
Sound is an oscillation in pressure, stress particle displacement, particle velocity in a medium. Sound produces an auditory sensation caused by the oscillation.
The ability of a material to convert sound energy, thereby reducing the amount of sound energy that can be reflected back.
A material that when placed around a source of noise inhibits the transmission of that noise beyond the barrier. Blocking sound requires materials that are dense and heavy. Often, a series of materials are used to create multi-layered assemblies to prevent the transmission of sound and create a soundproof barrier.
A subjective measure of sound expressed in decibels as a comparison corresponding to familiar sounds experienced in a variety of situations.
Sound Level Meter
A device that converts sound pressure variations in air into corresponding electronic signals. The signals are filtered to excluded signals outside frequencies desired.
The sound pressure is 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 of 10 of the ratio of the sound pressure to the reference pressure. The reference pressure shall be explicitly stated and is defined by standard.
Sound Transmission Loss
Describes the accumulated decrease in intensity of a waveform or sound energy as a wave propagates outwards from a source or through a structure.
The description of a sound waves components of frequency and amplitude.
The ability of a listener to hear and correctly interpret verbal messages. In a classroom with high ceilings and hard parallel surfaces such as glass and tile, speech intelligibility is a particular problem. Sound bounces off walls, ceilings and floors, distorting the teacher’s instructions and interfering with students’ ability to comprehend. Centers between 250 and 4000k.
The degree to which speech is unintelligible between offices. Three ratings are used: Confidential, Normal (Non-Obtrusive) and Minimal.
Sound Transmission Class: Quantifies the performance of a material or partition to attenuate airborne sound. This roughly reflects the decibel reduction of a building material or partition. Higher Numbers = Higher Performance.
Time Weighted Average (TWA)
The yardstick used by the Occupational Safety and Health Administration (OSHA) to measure noise levels in the workplace. It is equal to a constant sound level lasting eight hours that would cause the same hearing damage as the variable noises that a worker is actually exposed to. (This hearing loss, of course, occurs over long-term exposures.) Same as LOSHA.
Measurement for screws and bolts indicating the amount of threads per an inch.
Sounds of a frequency higher than 20,000 Hz. The frequency region containing these frequencies is called the ultrasonic region.
Vibration is 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.
A resilient support that tends to isolate a mechanical system from steady state excitation.
The cubic space of a room bounded by walls, floors, and ceilings determined by the Volume=Length x Width x Height of space. Volume influences reverberation time.
Sound that passes through air produces a wavelike motion of compression and refraction. Wavelength is the distance between two identical positions in the cycle or wave. Similar to ripples or waves produces by dropping a stone in water. Length of sound wave varies with frequency. Low frequency equals longer wavelengths.