ACCEPTABLE
SOUND LEVELS

Acceptable sound levels in different location such as kindergartens, auditoriums, libraries, cinemas ...
according to the ETB

Octave	Frequency (Hz)	Wave Length in air (m)
1	63	5.46
2	125	2.75
3	250	1.38
4	500	0.69
5	1K	0.34
6	2K	0.17
7	4K	0.085
8	8K	0.043

The A,B,C's of Noise Control - A Glossary of Noise Control Terms

 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 

Just Remember ABC. The best to control noise is using a combination of three letters or four techniques  absorb it, block it, break up its path and isolate it or better yet a composite of them.

Absorb and Dampen Absorber products like the Acousti-Foam and Acousti-Panels work to control noise through absorption.		Block Building a continuous barrier that traps or stops air movement greatly reduces airborne sound transmission. Steel Panels B 10 NR and acoustical seals reduce noise.
Break Interior and exterior walls, ceilings, floors, all allow sound to travel between and through them.  Using an acoustically resilient foam or clip in the assembly, and staggering openings such as windows and doors.		Isolate Products like our enclosures and acousti-mat  deaden noise and isolate or confine it to the area where it originated.

ABSORPTION -

A property of materials that allows a reduction in the amount of sound energy reflected. The introduction of an absorbent into the surfaces of a room will reduce the sound pressure level in that room by not reflecting all of the sound energy striking the room's surfaces. The effect of absorption merely reduces the resultant sound level in the room produced by energy that has already entered the room.

ABSORPTION COEFFICIENT -

A measure of the sound-absorbing ability of a surface. It is defined as the fraction of incident sound energy absorbed or otherwise not reflected by a surface. Unless otherwise specified, a diffuse sound field is assumed. The values at the sound-absorption coefficient usually range from about 0.01 for marble slate to almost 1.0 for long absorbing wedges often used in anechoic rooms.

ACOUSTICS -

(1) The science of sound, including the generation, transmission, and effects of sound waves, both audible and inaudible. (2) The physical qualities of a room or other enclosure (such as size, shape, amount of noise) that determine the audibility and perception of speech and music within the room.

ACOUSTIC TRAUMA -

Damage to the hearing mechanism caused by a sudden burst of intense noise, or by a blast. The term usually implies a single traumatic event.

AIRBORNE SOUND -

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

AMBIENT NOISE -

The total of all noise in the environment, other than the noise from the source of interest. This term is used interchangeably with background noise.

ANECHOIC ROOM -

A room in which the boundaries absorb nearly all the incident sound, thereby, effectively creating free field conditions.

A.N.S.I. -

The American National Standards Institute.

ARTICULATION INDEX (AI) -

A numerically calculated measure of the intelligibility of transmitted or processed speech. It takes into account the limitations of the transmission path and the background noise. The articulation index can range in magnitude between 0 and 1.0 . If the AI is less than 0.1, speech intelligibility is generally low. If it is above 0.6, speech intelligibility is generally high.

ATTENUATION -

The reduction of sound intensity by various means (e.g., air, humidity, porous materials...).

AUDIO FREQUENCY -

The frequency of oscillation of an audible sound wave. Any frequency between 20 and 20,000 Hz.

AUDIOGRAM -

A graph showing individual hearing acuity as a function of frequency.

AUDIOMETER -

An instrument for measuring individual hearing acuity.

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 frequencies 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 is also called the noise level. Sound level meters have an A-weighting network for measuring A-weighted sound level.

The A-weighted sound level LA is widely used to state acoustical design goals as a single number, but its usefulness is limited because it gives no information on spectrum content. The rating is expressed as a number followed by dBA, for example 36 dBA. A-weighted sound levels correlate well with human judgments of relative loudness, but give no information on spectral balance. Thus, they do not necessarily correlate well with the annoyance caused by the noise. Many different-sounding spectra can have the same numeric rating, but have quite different subjective qualities. A-weighted comparisons are best used with sounds that sound alike but differ in level. They should not be used to compare sounds with distinctly different spectral characteristics; that is, two sounds at the same sound level but with different spectral content are likely to be judged differently by the listener in terms of acceptability as a background sound. One of the sounds might be completely acceptable, while the other could be objectionable because its spectrum shape was rumbly, hissy, or tonal in character. A-weighted sound levels are use extensively in outdoor environmental noise standards.

BACKGROUND NOISE -

The total of all noise in a system or situation, independent of the presence of the desired signal. In acoustical measurements, strictly speaking, the term "background noise" means electrical noise in the measurement system. However, in popular usage the term "background noise" is often used to mean the noise in the environment, other than the noise from the source of interest.

BAND -

Any segment of the frequency spectrum.

BAND PASS FILTER -

A wave filter that has a single transmission band extending from a lower cutoff frequency greater than zero to a finite upper cutoff frequency.

BROADBAND NOISE -

Noise with components over a wide range of frequencies.

BROADCASTING NOISE CONTROL PRODUCTS-

Creating acoustically ideal rooms is challenging, particularly if existing spaces must be adapted. By absorbing, blocking and containing the areas of concern— flutter echo, near field reflection, room resonances, standing waves, exterior sounds—ArtUSA Industries professional solutions effectively and affordably solve acoustic control issues. The right sound is critical. That’s why ArtUSA Industries is dedicated to meeting the need of  sound engineers and producers in every corner of the globe. We solve noise problems in television, radio and film studios as well as religious recording and audio test facilities such as ABC, DISNEY, CNN, TBS and many others. ArtUSA Industries affordable, fire-resistant and easy-to-install acoustical wall panels, ceiling tiles and barrier materials are designed to help deliver the right sound. Art-Barrier products help you isolate studios and listening rooms from outside sounds. Art-Tile Ceilings are perfect for control rooms, offices and lobbies, and offer aesthetics as well as one of the industry’s highest noise reduction ratings. Art-Tile metal ceiling tiles create a sleek, modern or high-tech look at an affordable price in offices, lobbies and conference rooms— without sacrificing acoustic control. Art-Fab wall panels are gaining popularity for their combination of sleek design and outstanding acoustic control in all frequencies with components over a wide range of frequencies.

CALIBRATOR (ACOUSTICAL) -

A device which produces a known sound pressure on the microphone of a sound level measurement system, and is used to adjust the system to Standard specifications.

CHURCH NOISE CONTROL PRODUCTS -

In churches, synagogues and worship centers large or small, words and music can sound incomprehensible to the congregation if sound is not properly controlled. Poor sound quality is common in churches because of an abundance of hard surface materials. Brick, marble, stone, tile, glass, wood and sheetrock are all acoustically reflective. Sound waves bounce back and forth between parallel surfaces, creating a confusion of noise until they finally decay. Even the most strategically-placed speakers and microphones will not compensate for poor acoustics. Every room needs some absorptive materials and some reflective materials to get the right acoustic mix for the room’s intended purpose. The challenge is to find that balance. Art-Fab and Art-Sorb panels from ArtUSA Noise Control Products Inc. are designed to absorb airborne sound energy and reduce a room’s overall noise, reverberation and standing waves—creating interiors that reduce the din without sacrificing the divine. The right balance between absorption and reflection using strategically placed acoustic wall panels and baffles, create a more enjoyable worship and listening experience. ArtUSA Industries affordable acoustic and sound control solutions are the proven answers to help the message and experience   Lightweight and easy to install wall and ceiling treatments reduce reverberation and absorb sound from all directions. Traditional and or innovative solutions noise control and sound quality issues are our mission.

COCHLEA -

A spirally coiled organ located within the inner ear which contains the receptor organs essential to hear

CUTOFF FREQUENCIES -

The frequencies that mark the ends of a band, or the points at Which the characteristics of a filter change from pass to no-pass.

CYCLE -

The complete sequence of values of a periodic quantity that occurs during one period.

CYCLES PER SECOND -

A measure of frequency numerically equivalent to hertz.

CYLINDRICAL WAVE -

A wave in which the surfaces of constant phase are coaxial cylinders. A line of closely-spaced sound sources radiating into an open space produces a free sound field of cylindrical waves.

COMMUNITY AND ENVIRONMENTAL NOISE -

When neighbor businesses or residents feel there is excessive noise from industrial premises they complain. Environmental protection has become increasingly important. In addition to air and water quality, noise generation is a key environmental concern. Whether building a new facility or reducing noise at an existing site assuring that industrial noise will not be an issue is important. Analysis and design as well as the the supply and installation of the acoustical solutions should be an integral part of planning.  In existing facilities investigating and dealing with a problem at an early stage promotes the companys responsible image and can save money in the long run. Combat community and environmental noise with our innovative products.

DAMPING -

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

dBA -

Unit of sound level. The weighted sound pressure level by the use of the A metering characteristic and weighting specified in ANSI Specifications for Sound Level Meter, S1.4-1983. dBA is used as a measure of human response to sound.

DECIBEL -

A unit of sound pressure level, abbreviated dB.
- The Decibel is used to calculate changes in sound and power pressure levels.
- The Decibel is equal to ten times the logarithm to base 10 of the ratio of two quantities:
    L = 10 log (E1 / E2)
where
    E1 and E2 are the two quantities.

DIFFRACTION -

A modification which sound waves undergo in passing by the edges of solid bodies.

DIRECTIVITY INDEX -

In a given direction from a sound source, the difference in decibels between (a) the sound pressure level produced by the source in that direction, and (b) the space-average sound pressure level of that source, measured at the same distance.

DOPPLER EFFECT (DOPPLER SHIFT) -

The apparent upward shift in frequency of a sound as a noise source approaches the listener or the apparent downward shift when the noise source recedes. The classic example is the change in pitch of a railroad whistle as the locomotive approaches and passes by.

DOSIMETER -

A device worn by a worker for determining the worker's accumulated noise exposure with regard to level and time according to a pre-determined integration formula.

EAR -

What is this strange and wonderful thing we call hearing. Consider the auditory sense in comparison to vision. The threshold stimulus for vision is much less than for hearing. The dark-adapted eye needs only 0.5 attajoules (aJ) of energy falling on it to perceive light. The ear requires 100J of energy falling on the ear-drum to perceive a sound.

In the comparative dynamic ranges of seeing and hearing, however, we find a dramatically greater versatility in the ear .The dynamic range of perception is the difference, in decibels, between the Just noticeable threshold and the level of stimulus that damages the sensory organ. The dynamic range of seeing is about 9OdB an extraordinary dynamic range by any standard. The dynamic range of hearing in a young person of moderate musical tastes is 140dB, 5OdB more than for seeing; it is the visual dynamic range multiplied by 100,000. The frequency response of perception is the range of frequencies over which the sensory organ operates, usually figured in octaves. The frequency range of visible light runs from the infrared to the ultraviolet, from 460 terahertz (THz) to 750THz, about 0.7 octaves. The frequency response of audible sounds, by contrast, runs from 20 Hz to 20kHz, 10 octaves. High-order brain processing is connected to the eyes and the ears, but I argue that more cerebral processing is employed for hearing than for sight. 

Consider, analogously, the simplicity of technical equipment required to analyze stereoscopic photographs and the sophisticated technical equipment needed to analyze sonar recordings. Consider that our ears are always active and that the sounds are always being evaluated, even while we sleep. When the baby cries or a thief switches on the car engine, we awaken. They are truly miracles, these things on the sides of our heads. Let's consider their anatomy and the way they work.

The outer ear

The part of the hearing mechanism presented to the outside world is a cartilaginous flap of skin called the pinna, or auricle. It has an asymmetrical shape useful in localizing the source of sound around the head. Though we are not accustomed to looking at them closely, pinnas are just as individual as faces: No two are perfectly alike. Running through the temporal bone of the skull is the ear canal, also called the auditory canal, the auditory meatus or, plainly enough, the earhole. Terminating the Inside end of the ear canal is the eardrum or tympanum, also sometimes called the tympanic membrane. This Is a circular plate of fibers, both radial and circumferential, attached to the ear canal all the way around its own circumference. It's quite easy to rupture the eardrum, and It usually heals quickly, but each rupture can stiffen the eardrum, and enough ruptures can affect the hearing. The outer ear is inspected with an otoscope, an instrument with an internal light and a lens.

The middle ear

An open cavity within the temporal bone of the skull, between lcm cubed and 2cm cubed in volume, contains the ossilcles, which are three very small bones used to transmit the vibrations of the eardrum. The outer bone is the malleus, or hammer. Its lower end is attached to the inside of the eardrum. Also connected to it is the tensor tympanum, a very small muscle that applies tension to the eardrum through the malleus. The upper end of the malleus is connected to the incus, or anvil, the second small bone of the middle ear. The malleo-incudal joint Is held together with semi-flexible tendons, and there is an unexpected phenomenon here. When the eardrum flexes Inward, it pushes the malleus, which directly pushes the Incus. When the eardrum flexes outward, however, It pulls the malleus with it, and the upper tip of the malleus actually separates from the end of the Incus. The tendons at the Joint stretch with each flexure. Therefore, from the middle ear on, the human hearing mechanism Is asymmetrical. It responds instantly to compression waves pushing in the eardrum, but it responds with an elastic hysteresis to rarefaction waves that draw out the eardrum. A lever motion of the malleus sets the incus into rocking motion. The inner end of the incus is attached to the stapes, or stirrup, the last of these tiny bones in the middle ear. The stapes moves linearly, driven at its smaller end by the rocking of the Incus. The larger end, the foot, of the stapes completely covers an opening to the innermost part of the ear .This opening is called the oval window. A muscle called the stapedius can pull down the tip of the stapes, away from contact with the incus. This action is called the acoustic reflex, and It is stimulated by over-excursion of the ossicles, usually the result of a very loud, impulsive sound. It provides about 2OdB of vibration attenuation and requires about 175ms to take effect. The result is called a temporary loudness shift (TLS). This hollow (but busy with activity) chamber, the middle ear, Is connected to the rear of the throat by means of the Eustachian tube. This airway permits air pressures to be equalized between the two sides of the eardrum, but it can become clogged and provide a route of infection to the middle ear. The Eustachian tube is named after its discoverer, Bartolommeo Eustachio (1520~1574), an Italian physician and anatomist who worked in the days of the resurrection men, when human bodies could not legally be obtained for study.

The inner ear

The foot of the stapes covers the oval window and moves back and forth with the vibrations of the incus (and, through the incus, with the vibrations of the malleus and, through the malleus, with The cochlea contains the scala vestibuli, the scala tympani and the cochlear duct, where vibration is converted into nerve impulse the vibrations of the eardrum). The oval window is a flexible, membrane covered interruption in a bony wall between the middle ear and the inner ear. All of the structures and organs of the inner ear are suspended within the membranous labyrinth. This is a series of communicating sacs and ducts, protected from the bony osseous labyrinth (the chambers within the temporal bone) by a form of spinal fluid called the perilymph. The major organs of the Inner ear are the cochlea and the semicircular canals. These are fined with a gelatinous, serous fluid, similar to the fluid inside cells, called endolymph. Once a vibration is transmitted by the stapes through the oval window into the Inner ear, it becomes a fluid flow. When the stapes compresses the fluid within the oval window, the fluid needs a pressure release. This is provided by the round window, or fenestra rotunda.The round window, like the oval window, is a membrane covered opening in the wall between the middle and inner ear. When the stapes pushes the fluid in, the round window bulges back out into the middle ear. Immediately within the inner ear is the vestibule, a chamber into which vibrations from the cochlea and the semicircular canals emerge. At the top of the vestibule, three curved tubes are arranged at right angles to each other so that each tube curves through one perpendicular plane of three-dimensional space. The upper tube is called the superior; it curves up. The rear tube is called the posterior; it curves horizontally. The tube at the side curves around the side and Is called the lateral. These three tubes, called the semicircular canals, are used to sense the orientation of the head. For this purpose, they are filled with otolith, or ear sand. This colorfully named stuff consists of crystals of calcium carbonate, which move across sensing hair cells in the semicircular canals. This works analogously to a carpenter's bubble level, except that, instead of a bubble finding the highest point of a curved tube, the ear sands drift around the lowest parts of curved tubes. They contribute to the sense of equilibrium and balance.

The cochlea

Now we come to the cochlea, the mystery at the center of human hearing. Its interior was first described in 1851 by Alfonso Corti (1822-1876). Great advances in the understanding of cochlear mechanics and electro-physiology were made throughout his life by George Von Bekesy (1899-1972), who started as an engineer with the Hungarian telephone company but found that his auditory researches gradually took over his career. In 1961, his research in ear anatomy won him the only Nobel prize ever given In any area of acoustics. The cochlea is a helically coiled tube, which spirals about 2 times around a bony structure called the modiolus. It has three chambers running along its length. A very thin shelf of bone, called (appropriately) the bony shelf, or osseous spiral lamina, projects Into the cochlea from the modiolus, dividing it almost in half along Its length. At the tip of the bony shelf, two membranes spread apart, rather like the arms of the letter Y. One of these is quite sturdy and is called the basilar membrane; the other is much thinner and more delicate and is called Reissner's membrane, after Ernst Reissner (1824-1873). Between these membranes runs the cochlear duct. or scala media. Within the cochlear duct are the structures that convert vibrations of the fluid to nerve impulses. The channel running along the cochlea and Reissner's membrane, and connected to the oval window, is the scala vestibuli. The other major channel along the cochlea, the scala tympani, starts at the round window and runs along the basilar membrane. These canals get smaller and smaller along the length,of the cochlea, and at the apex are connected by a small opening In the basilar membrane called the helicotrema. The scala vestibuli and the scala tympani are filled with perilymph, which can flow through the helicotrema to equalize the static fluid pressures. When the stapes pushes on the oval window, fluid pressures are actually transmitted all the way up the scala vestibuli. It is within the cochlear duct that the real action takes place. This canal is much smaller than the scala vestibuli or the scala tympani and is filled with endolymph, which is much thicker than perilymph, Running along the cochlear duct, and resting on the basilar membrane, is the organ of Corti. On one side, hair cells or cilia protrude Into the cochlear duct ; on the other side are the most peripheral nerve cells, called Corti's ganglion, of the auditory nerve (or eighth cranial nerve). The hair cells In the organ of Corti actually terminate in a bundle of hairs, around 50 per cell. These are organized into a conical pattern, something like the stakes of a tepee. Electrically, the hair cells are capacitor plates. One end of the cell touches the perilymph on the other side of the basilar membrane; tile other end, with the tips of hairs, floats in the endolymph. Because the perilymph has a higher concentration of sodium ions and a lower concentration of potassium ions than does the endolymph (or, Indeed, the Interior of the hair cell), the resting hair cell has a potential of about -6OmVdc. When the bundle of hairs is deformed in one direction by waves In the cochlear fluids, its potential is changed to about -40mVdc; when deformed an equivalent amount in the other direction, it is changed to about -65mVdc. This is yet another asymmetry in the auditory pathway.These changes in the voltage of the hair cells affect the nerve cells Immediately below. It is important, however, to remember that the nerve cell Is not transmitting an analog current up to the brain. Nerve cells don't transmit continuously nuctuating signals. Rather, they electrochemically transmit impulses, or spikes; this is called nerve cell firing. It is important to remember that the electrochemical behavior of the hair cells does not correspond precisely to the velocity or the displacement of the basilar membrane, which is why purely mechanical models of cochlear behavior yield so little useful Information about hearing. The auditory nerve brings impulses to the temporal lobes of the brain, that part of the brain immediately above the middle and inner ear. You will sometimes find It said that a pure tone agitates only one very small area of the basilar membrane. This theory goes on to say that the way the brain knows what frequencies are being heard is by identifying which hair cells are in motion. That was actually believed by otophysiologists at one time, about a century ago. It's true there are resonance behaviors within the cochlea, and the resonance antinodes occur at about 0.2 octaves per millimeter. Still, virtually every sound agitates virtually every hair cell in the cochlea. Frequency discrimination is a rather higher-order brain function than anything going on in the inner ear .There are good theories about how it works, but the theories rely on psychological testing as much as study of ear mechanics or electrochemistry. The ear actually emits sound at frequencies the ear can hear properly. A damaged ear, with hair cell loss in the cochlea, will not emit sounds in the frequency ranges of hearing loss. This peculiar fact, disputed until recent years, suggests that active amplification, mechanical gain, occurs In the cochlea. The cochlear amplifier theory explains much about hearing that is otherwise inexplicable. There is no mechanism yet known by which the cochlea could amplify the vibrations transmitted to it.

ECHO -

A wave that has been reflected or otherwise returned with sufficient magnitude and delay, so as to be detected as a wave distinct from that directly transmitted.

EDUCATIONAL NOISE CONTROL -

In classrooms, gymnasiums, indoor pools and other learning environments, poor speech intelligibility—the ability to understand what is being spoken—can adversely affect learning, achievement and enjoyment. The culprit is background noise and reverberation or echo. ArtUSA Noise Control Products, Inc. helps solve these issues in new and existing schools with cost- effective, long-lasting and easy to install enclosures, ceiling tiles, wall panels, baffles and other acoustical solutions. It is something educators know intuitively and research supports—high levels of background noise and reverberation or echo hinder learning. So, what’s the solution as class sizes continue to increase and budgets continue to shrink? ArtUSA Industries affordable acoustic and sound control solutions are the proven answers to help education and training sound better and positively influence learning.  Lightweight and easy to suspend from high, open ceilings using traditional hanging or innovative cable suspension systems baffles absorb sound from all directions to reduce reverberation in indoor pools, gymnasiums, multipurpose rooms and other large interior spaces. Baffles are offered in a variety of standard and custom colors to complement or match school colors. Fabric-wrapped wall panel absorbs up to 85% of the sound directed toward it. They are available in hundreds of fabrics to complement or match school colors in classrooms, music rooms, offices and gymnasiums. Ceiling tiles with a backer board drop into a standard grid system and help block sound traveling from adjacent rooms. Tiles without a backer board can be adhered to any wall or ceiling surface making them ideal for rooms without a grid system or those with low ceiling heights.

EQUIVALENT A-WEIGHTED SOUND LEVEL (Leq) -

The constant sound level that, in a given time period, would convey the same sound energy as the actual time-varying A-weighted sound level.

FAR FIELD -

Describes a sound source region in free space where the sound pressure level obeys the inverse-square law (the sound pressure level decreases 6 dB with each doubling of distance from the source). Also, in this region the sound particle velocity is in phase with the sound pressure. Closer to the source where these two conditions do not hold constitutes the near field region.

FILTER -

A device for separating components of a signal on the basis of their frequency. It allows components in one or more frequency bands to pass relatively unattenuated, and it attenuates components in other frequency bands.

FIRING RANGE NOISE NOISE CONTROL PRODUCTS-

The sound produced by gunfire is deafening outdoors, but when the acoustical energy it produces is confined to a small indoor space as in a firing range, it gets even louder. The noise can reach levels as much as ten times greater than those experienced in outdoor ranges. Art-Sorb panels help eliminate this indoor “range effect” by absorbing sound waves that would otherwise build up to dangerous levels causing serious discomfort and even hearing damage. Additionally, they are relatively inexpensive and easy to install. Art-Sorb panels are ideal for indoor firing ranges because they are Class 1 fire-rated and have excellent sound absorption at 500 and 1000 Herz (Hz), the most common frequencies produced by gunfire. The sound absorption coefficient of most 2" thick panels are between 0.73 and 1.05 at 500 and 1000 Hz. This means that the panels absorb between 73% and 100% of the acoustical energy at 500 Hz and 1000 Hz, depending upon the exact pattern. Panels are available in a variety of patterns and surface treatments to meet almost every firing range need. A surprisingly small amount of absorption goes a long way in most ranges. Typically, a range requires an amount of foam equal to the square footage of its ceiling. The foam is divided, however, between the ceiling and the walls for the most efficient sound absorption. This will normally reduce the amount of acoustical energy within the range by an amazing 85%. Measure the square footage of the ceiling as if you were covering it completely. Attach two-thirds of the panels ordered to the ceiling in one large block or in several bands starting directly above the firing positions and extending downrange to where the first signs of bullet damage begin to show on the ceiling. Attach the remaining one-third of foam to the walls, once again extending downrange from the firing stations to the first signs of bullet damage. Leave one to two feet clear above the floor to avoid damage to the foam panels by floor cleaning equipment. Also, avoid areas near switches and control panels to eliminate damage done by users and personnel. device for separating components of a signal on the basis of their frequency. It allows components in one or more frequency bands to pass relatively unattenuated, and it attenuates components in other frequency bands.

FREE SOUND FIELD (FREE FIELD) -

A sound field in which the effects of obstacles or boundaries on sound propagated in that field are negligible.

FREQUENCY -

The number of times per second that the sine wave of sound repeats itself, or that the sine wave of a vibrating object repeats itself. Now expressed in hertz(Hz), formerly in cycles per second (cps).

An introduction to the nature of sound with frequency, wavelength and octaves:

Sound energy is transmitted through air (or other particles) as a traveling pressure wave. In air the displacement wave amplitude may range from 10-7 mm to a few mm per second.

FREQUENCY
The frequency (cycles per second) of a sound is expressed in hertz (Hz).

f = 1/T (Hz)

The range for human hearing is from 20 to 20.000 Hz. By age 12-13.000 Hz are the limit for many people.

Wavelength
The wavelength of sound is the distance between analogous points of two successive waves.

l = c / f
where
c = speed of sound (m/s)
f = frequency (Hz)

GYM AND MULTIPURPOSE NOISE CONTROL PRODUCTS -

From physical education classes, sporting events and school assemblies, to everyday cafeteria, overflow classroom space and general meeting areas, gymnasiums and multipurpose rooms are some of the most-used and most-populated areas on a school campus. With all the activities, sound levels can quickly build to boisterous levels. The large, open space, high ceilings, wood or tiled floors and painted concrete walls with school colors and themes give gyms and multipurpose rooms the flexibility to accommodate a wide range of student and community activities. However, these same traits also contribute to excessive reverberation and poor acoustics. Excessive echo, or reverberation, interferes with instruction between students and teachers, inhibits participation and enjoyment during events and reduces speech intelligibility of announcements. The hard, reflective surfaces commonly found in gyms and multipurpose rooms cause the sound waves to bounce around until they eventually decay or are absorbed. The right balance between absorption and reflection using strategically placed acoustic wall panels baffles and traps, creates a more functional and enjoyable space. ArtUSA Industries affordable acoustic and sound control solutions are the proven answers to help gyms and multipurpose rooms sound better and positively influence events and learning.  Lightweight and easy to suspend from high, open ceilings using traditional hanging or innovative cable suspension systems baffles absorb sound from all directions to reduce reverberation in indoor pools, gymnasiums, multipurpose rooms and other large interior spaces.

HAIR CELL -

Sensory cells in the cochlea which transform the mechanical energy of sound into nerve impulses.

HARMONIC -

A sinusoidal (pure-tone) component whose frequency is a whole-number multiple of the fundamental frequency of the wave. If a component has a frequency twice that of the fundamental it is called the second harmonic, etc...

HEARING -

The subjective human response to sound.

HEARING LEVEL -

A measured threshold of hearing at a specified frequency, expressed in decibels relative to a specified standard of normal hearing. The deviation in decibels of an individual's threshold from the zero reference of the audiometer.

HEARING LOSS -

A term denoting an impairment of auditory acuity. The amount of hearing impairment, in decibels, measured as a set of hearing threshold levels at specified frequencies. Types of hearing loss are:

1. Conductive Hearing Loss:
    A loss originating in the conductive mechanism of the ear

2. Sensor-neural Hearing Loss:
    A loss originating in the cochlea or the fibers of the
    auditory nerve

3. Noise induced Hearing Loss:
    A sensor-neural loss attributed to the effects of noise

HEARING THRESHOLD LEVEL (HTL) -

Amount (in decibels) by which an individual's threshold of audibility differs from a standard audiometric threshold

HERTZ (Hz) -

Unit of measurement of frequency, numerically equal to cycles per second

HVAC NOISE -

Mechanical and HVAC systems generate noise that can be transmitted into occupied spaces.   Examples of acoustical problems include: 1) breakout noise from MER walls and doors, 2) vibration transmitted from blowers, 3) drumming of duct walls, 4) regenerated noise in ducts at elbows, dampers, and diffusers, and 5) excess fan noise propagated down the ductwork.

For noise problems that become apparent after a space is occupied, the first step is to establish a criterion for the affected room. 

The second step is to meter then analyze it. The analysis reveals the severity of the noise problem and what frequencies are affected most.

The next step is to formulate options to reduce the noise based on the type of noise sources involved and their frequency spectra. These treatment options can be evaluated to select the most cost-effective solution.

Several background sound rating methods are used to rate indoor sound. They include the A-weighted sound pressure level dBA and noise criteria NC, the more recent room criteria RC and balanced noise criteria NCB, and the new RC Mark II. Each sound rating method was developed from data for specific applications; not all methods are equally suitable for rating the HVAC-related sound in the variety of applications encountered.

The degree of occupant satisfaction achieved with a given level of background sound is determined by many factors. For example, large conference rooms, auditoriums, and recording studios can tolerate only a low level of background sound. On the other hand, higher levels of background sound are acceptable and even desirable in certain situations, such as open-plan offices where a certain amount of speech and activity masking is essential. Therefore, the system sound control goal varies depending on the required use of the space.

To be unobtrusive, background sound should have the following properties:

• A balanced distribution of sound energy over a broad frequency range

• No audible or tonal characteristics such as whine, whistle, hum, or rumble

• No noticeable time varying levels from beats or other system induced aerodynamic instability

• No fluctuations in level such as throbbing or pulsing

IMPACT INSULATION CLASS (IC) -

A single-figure rating that compares the impact sound insulating capabilities of floor-ceiling assemblies to a reference contour.

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.

IMPULSIVE NOISE -

• Either a single sound pressure peak (with either a rise time less than 200 milliseconds or total duration less than 200 milliseconds) or multiple sound pressure peaks (with either rise time less than 200 milliseconds or total duration less than 200 milliseconds) spaced at least by 200 millisecond pauses,

• A sharp sound pressure peak occurring in a short interval of time.

INDUSTRIAL NOISE CONTROL PRODUCTS -

Excessive noise is one of the most common workplace hazards in industrial facilities. Prolonged exposure to noise in manufacturing, power generation, printing and other industries can result in compromised verbal communication, fatigue, lower productivity and work-related hearing loss. Manufacturing areas are not the only places where noise can be hazardous and counterproductive. Offices that share walls with factories or are subjected to outside noise from highways or airports face similar noise problems. In such environments, uncontrolled sound can interfere with the intended purpose of the space, resulting in hampered interpersonal communication, headaches and other problems. ArtUSA Noise Control Products Inc. offers many durable choices to easily and affordably create a healthier work environment. Noise control entails suppressing audible kinetic energy in two ways, and the most effective solutions may require a combination of the two: 1) Containing noise with enclosures and or barrier materials 2) Absorbing noise with panels, baffles and other acoustical absorber products. ArtUSA Noise Control Products Inc. offers flexible and rigid enclosure systems. Curtains are flexible and can either be used independently or as part of an enclosure system. Custom-configured enclosures can be made from a combination of products to produce an effective and economical method of noise reduction. Options include rooftop panels, grommets, view windows, sliding hinged and overhead doors, silencers, exhaust fans and more.

INFRASONIC -

Sounds of a frequency lower than 20 hertz.

INTENSITY -

The sound energy flow through a unit area in a unit time.

INVERSE SQUARE LAW -

A description of the acoustic wave behavior in which the mean-square pressure varies inversely with the square of the distance from the source. This behavior occurs in free field situations, where the sound pressure level decreases 6 dB with each doubling of distance from the source.

ISO -

The International Organization for Standardization.

LEVEL -

The logarithm of the ratio of a quantity to a reference quantity of the same kind. The base of the logarithm, the reference quantity, and the kind of level must be specified.

LOGARITHM -

The exponent that indicates the power to which a number must be raised to produce a given number. For example, for the base 10 logarithm, used in acoustics, 2 is the logarithm of 100.

LOUDNESS -

The subjective judgment of intensity of a sound by humans. Loudness depends upon the sound pressure and frequency of the stimulus. Over much of the frequency range it takes about a threefold increase in sound pressure (a tenfold increase in acoustical energy, or, 10 dB) to produce a doubling of loudness.

LOUDNESS LEVEL -

Measured in phons it is numerically equal to the median sound pressure level (dB) of a free progressive 1000 Hz wave presented to listeners facing the source, which in a number of trials is judged by the listeners to be equally loud.

MASKING -

• The process by which the threshold of audibilty for a sound is raised by the presence of another (masking) sound.

• The amount by which the threshold of audibility of a sound is raised by the presence of another (masking) sound.

MASKING NOISE -

A noise that is intense enough to render inaudible or unintelligible another sound that is also present.

MEDIUM -

A substance carrying a sound wave.

NEAR FIELD -

The sound field very near to a source, where the sound pressure does not obey the inverse square law and the particle velocity is not in phase with the sound pressure.

NIOSH -

The National Institute for occupational Safety and Health.

NOISE -

• Unwanted sound.

• Any sound not occurring in the natural environment, such as sounds emanating from aircraft, highways, industrial, commercial and residential sources.

• An erratic, intermittent, or statistically random oscillation.

NOISE ISOLATION CLASS (NIC) -

A single number rating derived in a prescribed manner from the measured values of noise reduction between two areas or rooms. It provides an evaluation of the sound isolation between two enclosed spaces that are acoustically connected by one or more paths.

NOISE LEVEL -

For airborne sound , unless specified to the contrary, it is the A-weighted sound level.

NOISE RATING CURVE:

NOISE REDUCTION (NR) -

The numerical difference, in decibels, of the average sound pressure levels in two areas or rooms. A measurement of "noise reduction" combines the effect of the sound transmission loss performance of structures separating the two areas or rooms, plus the effect of acoustic absorption present in the receiving room.

An introduction to the Noise Rating (NR) curves developed by the International Organization for Standardization (ISO).

• The Noise Rating (NR) curves are developed by the International
  Organization for Standardization (ISO).

• Noise rating graphs are plotted of Sound Pressure Level at
  frequency to show how acceptable sound levels vary
  with frequency.

• What is acceptable varies with the room and the use of it.
  There is a different curve obtained for each type of use.

• Each such curve is obtained by an NR number.

NOISE REDUCTION COEFFICIENT (NRC) -

A measure of the acoustical absorption performance of a material, calculated by averaging its sound absorption coefficients at 250, 500, 1000 and 2000 Hz, expressed to the nearest multiple of 0.05.

NON-IMPULSIVE NOISE -

Includes: All noise not included in the definition of impulsive noise.

OCTAVE -

The interval between two sounds having a frequency ratio of two.- There are 8 octaves on the keyboard of a standard piano.

OCTAVE BAND -

A segment of the frequency spectrum separated by an octave.

OCTAVE BAND LEVEL -

The integrated sound pressure level of only those sine-wave components in a specified octave band.

OFFICE NOISE CONTROL PRODUCTS -

In today's design-oriented world, acoustical products need to do more than function. They are expected to complement, and even enhance interior spaces. That's why ArtUSA Industries is continually designing solutions with the results and look our clients are looking for. We offer a variety of impressive styles and colors. Our wall and ceiling panels are attractive and versatile, and include foam fabric-wrapped and metal panels. ArtUSA Noise Control Products, Inc. helps solve office noise issues in new and existing facilities with cost- effective, long-lasting and easy to install enclosures, ceiling tiles, wall panels, baffles, and other acoustical solutions. High levels of background noise and reverberation or echo hinder and interrupt workflow. So, what’s the solution? ArtUSA Industries affordable acoustic and sound control solutions are the proven answers to help offices sound better and work smoother.  Lightweight and easy to suspend from high, open ceilings using traditional hanging or innovative cable suspension systems baffles absorb sound from all directions to reduce reverberation in  large open office areas. Baffles are offered in a variety of standard and custom colors to complement or match school colors. Fabric-wrapped wall panel absorbs up to 85% of the sound directed toward it. They are available in hundreds of fabrics to complement new or freshen up existing color schemes. Ceiling tiles with a backer board drop into a standard grid system and help block sound traveling from adjacent rooms. Tiles without a backer board can be adhered to any wall or ceiling surface making them ideal for rooms without a grid system or those with low ceiling heights.

OSCILLATION -

The variation with time, alternately increasing and decreasing, of (a) some feature of an audible sound, such as the sound pressure; or (b) some feature of a vibrating solid object, such as the displacement of its surface.

OSHA -

The Occupational Safety and Health Administration.

PEAK SOUND PRESSURE -

The maximum absolute value of the instantaneous sound pressure in a specific time interval. Note: in the case of a periodic wave, if the time interval considered is a complete period, the peak sound pressure becomes identical with the maximum sound pressure.

PERIOD -

The duration of time it takes for a periodic wave form (like a sine wave) to repeat itself.

PERMANENT THRESHOLD SHIFT (PTS) -

A permanent decrease of the acuity of the ear at a specified frequency as compared to a previously established reference level. The amount of permanent threshold shift is customarily expressed in decibels.

PHON -

The unit of measurement for loudness level.

PINK NOISE -

Noise with constant energy per octave band width.

PITCH -

The attribute of auditory sensation that orders sounds on a scale extending from low to high. Pitch depends primarily upon the frequency of the sound stimulus, but it also depends upon the sound pressure and wave form of the stimulus.

PLANE WAVE -

A wave whose wave fronts are parallel and perpendicular to the direction in which the wave is traveling.

PRESBYCUSIS -

The decline in hearing acuity that is attributed to the aging process.

PURE TONE -

A sound for which the sound pressure is a simple sinusoidal function of the time, and characterized by its singleness of pitch.

RANDOM NOISE -

An oscillation whose instantaneous magnitude is not specified for any given instant of time. It can be described statistically by probability distribution functions giving the traction of the total time that the magnitude of the noise lies within a specified range.

RELIGOUS FACILITY NOISE CONTROL PRODUCTS -

In churches, synagogues and worship centers large or small, words and music can sound incomprehensible to the congregation if sound is not properly controlled. Poor sound quality is common in churches because of an abundance of hard surface materials. Brick, marble, stone, tile, glass, wood and sheetrock are all acoustically reflective. Sound waves bounce back and forth between parallel surfaces, creating a confusion of noise until they finally decay. Even the most strategically-placed speakers and microphones will not compensate for poor acoustics. Every room needs some absorptive materials and some reflective materials to get the right acoustic mix for the room’s intended purpose. The challenge is to find that balance. Art-Fab and Art-Sorb panels from ArtUSA Noise Control Products Inc. are designed to absorb airborne sound energy and reduce a room’s overall noise, reverberation and standing waves—creating interiors that reduce the din without sacrificing the divine. The right balance between absorption and reflection using strategically placed acoustic wall panels and baffles, create a more enjoyable worship and listening experience. ArtUSA Industries affordable acoustic and sound control solutions are the proven answers to help the message and experience   Lightweight and easy to install wall and ceiling treatments reduce reverberation and absorb sound from all directions. Traditional and or innovative solutions noise control and sound quality issues are our mission.

REFLECTION -

The return of a sound wave from a surface.

REFRACTION -

The bending of a sound wave from its original path, either because it is passing from one medium to another or by changes in the physical properties of the medium, e.g., a temperature or wind gradient in the air.

RESONANCE -

The relatively large amplitude of vibration produced when the frequency of some source of sound or vibration "matches" the natural frequency of vibration of some object, component, or system.

RESONATOR -

A device that resounds or vibrates in sympathy with a source of sound or vibration.

REVERBERANT FIELD -

The region in a room where the reflected sound dominates, as opposed to the region close to the noise source where the direct sound dominates.

REVERBERATION -

The persistence of sound in an enclosed space, as a result of multiple reflections, after the sound source has stopped.

REVERBERATION ROOM -

A room having a long reverberation time, especially designed to make the sound field inside it as diffuse (homogeneous) as possible.

REVERBERATION TIME (RT) -

The reverberation time of a room is the time taken for the sound pressure level to decrease 60 dB from its steady-state value when the source of sound energy is suddenly interrupted. It is a measure of the persistence of an impulsive sound in a room as well as of the amount of acoustical absorption present inside the room. Rooms with long reverberation times are called live rooms.

RMS SOUND PRESSURE -

The square root of the time averaged square of the sound pressure.

ROOM SOUND PROPAGATION ( Indoor ) -

The sound in a room will propagate to the receiver by direct sound and reverberant sound.

For a continuing source in a room, the sound level is the sum of direct and reverberant sound and is given by:
L_p = L_w + log (D / (4 p r²) + 4 / R) (dB)

where

D = directivity coefficient
R = room constant (m²)
r = distance from source (m)

Room constant:

R = S a_m / (1-a^m) (m²)

where

S = total surface of the room (m2)
a = absorption coefficient
a_m = mean apsorption coefficient for the room

Absorption coefficient:

a = Ia / Ii

where

I_a = sound intensity absorbed I_i = incident sound intensity

The rooms total absorption, m² Sabine:

A_m = S S a (m² Sabine)

The mean apsorption coefficient for the room a_m = A_m / S

The sound level as a sum of direct and reverberant sound for a source in a room

For a continuing source in a room, the sound level is the sum of direct and reverberant sound and is given by:

L_p = L_w + log (D / (4 p r²) + 4 / R)      (dB)

where

D = directivity coefficient R = room constant (m² Sabine) r = distance from source (m)

Directivity coefficient:

The figure can be used to estimate the directivity coefficient D.

The figure permits calculation of theoretical sound pressure levels L_p, from both direct and reverberant sound, at a given distance (r) from a source inside room of sound power level L_w. R is the room constant.

ROOM SOUND PROPAGATION ( Outdoor ) -

When the distance from the the power source doubles, the sound pressure level decrease with 6 dB. This relationship is also known as the inverse square law.

L_p = L_w
where

r = distance from source (m)
K' = constant

When source radiates hemispherically with the source near ground K' = - 8.
When source radiates spherically K' = - 11.

Other factors affecting the radiation of sound might be direction of the source, barriers and atmospheric conditions.
The eq. can be modifyed as:

L_p = L_w - 20 log r + K' + DI - A_a - A_b

where

DI = directivity index
A_a = attenuation due to atmospheric conditions
A_b = attenuation due to barriers

ROOT-MEAN-SQUARE (RMS) -

1. The root-mean-square value of a time-varying quantity is obtained by squaring the function at each instant, obtaining the average of the squared values over the interval of interest, and then taking the square root of this average. For a sine wave, if you multiply the RMS value by the square root of 2, or about l.41, you get the peak value of the wave. The RMS value, also called the effective value of the sound pressure, is the best measure of ordinary continuous sound, but the peak value is necessary for assessment of impulsive noises.

2. A term describing the mathematical process of determining an 'average' value of a complex signal.

SABIN -

A measure of the sound absorption of a surface; it is the equivalent of one square foot of a perfectly absorptive surface.

SCHOOL AND TRAINING ROOM NOISE -

A work group of the Acoustical Society of America (ASA) in conjunction with the American National Standards Institute (ANSI) recommends that classroom noise not exceed 35 decibels. Many American class- rooms today can be as loud as 50 decibels, For satisfactory communication, speech should be 15 decibels above background noise. The group also recommends that reverberation time not exceed O.6 seconds. Depending on its source, noise can be controlled by containing it, absorbing it,or both. Walls and ceilings treated with acoustic panels. They will absorb excess reverberation within a room. Noise from outside a classroom, whether from traffic or hallway conversation, can be contained with barriers installed within walls or above drop ceilings to block noise out. An ArtUSA Industries professional can help to identify your noise problem and offer the right solution.  

SHIELDING -

The attenuation of a sound, achieved by placing barriers between a sound source and the receiver.

SONE -

The unit of measurement for loudness. One sone is the loudness of a sound whose loudness level is 40 phons. Loudness is proportional to the sound's loudness rating, e.g., two sones are twice as loud as one sone.

SOCIOCUSIS -

Loss of hearing caused by noise exposures that are part of the social environment, exclusive of occupational-noise exposure, physiological changes with age, and disease.

SOUND -

1. An oscillation in pressure, stress, particle displacement, particle velocity, etc., in an elastic or partially elastic medium, or the superposition of such propagated alterations.

2. An auditory sensation evoked by the oscillation described above. Not all sound waves can evoke an auditory sensation: e.g. ultrasound.

SOUND INTENSITY -

power per unit area, vary substantially with distance from source, and also diminish as a result of intervening obstacles and barriers, air absorption, wind and other factors.

The intencity from a source pasing a spherical surface around the source can be expressed as:

I = W / A = W / 4 p r²      (W/m²)

In a progressing leveled wave, intensity can be expressed as:

I = W / A = p² / r c      (W/m²)

where

I = intensity of sound      (W/m²)
W = power      (W)
A = area      (m²)
r = radius in the spherical surface      (m)
p = root mean square pressure      (N/m²)
r = density      (kg/m³)
c = velocity of sound      (m/s)

Sound intensity expressed in dB:

L_I = 10 log (I / I0) (dB)

where

I₀ = reference intensity (W/m²)

The normal reference level is 10^-12 W/m².

SOUND LEVEL -

The weighted sound pressure level obtained by the use of a sound level meter and frequency weighting network, such as A, B, or C as specified in ANSI specifications for sound level meters (ANSI Sl.4-1971, or the latest approved revision). If the frequency weighting employed is not indicated, the A-weighting is implied.

SOUND LEVEL METER -

An instrument comprised of a microphone, amplifier, output meter, and frequency-weighting networks which is used for the measurement of noise and sound levels.

SOUND POWER -

The total sound energy radiated by a source per unit time. The unit of measurement is the watt.

Sound Power Level -

Sound power level are connected to the sound source and independent of distance. Sound power are indicated in decibel.

L_w = 10 log (W / W₀)

where

W₀ = reference power      (W)

The normal reference level is 10^-12 W which is the lowest sound persons of excellent hearing can discern. Note that older american litterature may contain sound power level data referenced to 10^-13 W.

SOUND PRESSURE -

The instantaneous difference between the actual pressure produced by a sound wave and the average or barometric pressure at a given point in space.

SOUND PRESSURE LEVEL (SPL) -

20 times the logarithm, to the base 10, of the ratio of the pressure of the sound measured to the reference pressure, which is 20 micronewtons per square meter. In equation form, sound pressure level in units of decibels is expressed as SPL (dB) = 20 log p/pr.

Since sound measuring instruments respond to sound pressure the "decibel" is generally associated with sound pressure level.

Sound pressure level quantify in decibels the intensity of given sound sources. Sound pressure level vary substantially with distance from source, and also diminish as a result of intervening obstacles and barriers, air absorption, wind and other factors.

Since I = p² / r c then:

L_p = 10 log (p² / p²0) = 20 log (p / p₀)

where

p = root mean square pressure      (N/m²)

The usual reference level p_o is 20x10^-6 N/m².

• Note that the noise from fans, machines etc. in general are
  documented in sound power level.

• If the sound pressure doubles,the sound pressure level
  increases with 6 dB.

• The lowest sound level that people of excellent hearing can
   discern has an acoustic sound power about 10^-12 W, 0 dB

• The loudest sound generally encountered is that of a jet
   aircraft with a sound power of 105 W, 170 dB

SOUND TRANSMISSION CLASS (STC) -

The preferred single figure rating system designed to give an estimate of the sound insulation properties of a structure or a rank ordering of a series of structures.

SOUND TRANSMISSION LOSS (STL) -

A measure of sound insulation provided by a structural configuration. Expressed in decibels, it is 10 times the logarithm to the base 10 of the reciprocal of the sound transmission coefficient of the configuration.

SPECTRUM -

The description of a sound wave's resolution into its components of frequency and amplitude.

SPEECH-INTERFERENCE LEVEL (SIL) -

A calculated quantity providing a guide to the interference of a noise with the reception of speech. The speech-interference level is the arithmetic average of the octave band levels of the interfering noise in the most important part of the speech frequency range. The levels in octave bands centered at 500, 1000, and 2000 Hz are commonly averaged to determine the speech-interference level.

SPEED (VELOCITY) OF SOUND IN AIR -

344 m/sec (l128 ft/sec) at 70 degrees F in air at sea level.

SPHERICAL DIVERGENCE -

The condition of propagation of spherical waves that relates to the regular decrease in intensity of a spherical sound wave at progressively greater distances from the source. Under this condition the sound pressure level decreases 6 decibels with each doubling of distance from the source.

SPHERICAL WAVE -

A sound wave in which the surfaces of constant phase are concentric spheres. A small (point) source radiating into an open space produces a free sound field of spherical waves.

STEADY-STATE SOUNDS -

Sounds whose average characteristics remain relatively constant in time. A practical example of a steady-state sound source is an air conditioning unit.

STUDIO NOISE -

Designing an acoustically ideal sound stage, studio, control room or listening room is a challenge under any conditions. In the real world, where such rooms must fit into an existing building, the acoustical challenges are even greater. Three problems face the designer or acoustic engineer. Sound isolation Outside noise getting in. Automobile traffic, airplanes, footsteps, and conversation in hallways or adjacent rooms make it difficult to record quiet, clear musical passages and voices without sacrificing dynamic range. Noise and Vibration Control Building noise. Heat, ventilating and air-conditioning machinery generates sounds that range from a low-frequency rumble to a high-frequency hiss. Equipment noise. Cooling fans in PCs and studio equipment are another common source of unwanted sounds. With today's digital electronic recording equipment, subliminally audible vibration and noise are likely to be recorded along with the artist's performance. Room Acoustics Slap and flutter echo High-frequency sound information can lose clarity due to reflective delays caused by parallel hard surfaces in a live recording or listening environment. Near-field reflections. When hard surfaces are located close to the recording or listening position, reflected sound waves can have unpredictable effects on audio clarity imaging and frequency response. Room resonance.  Room walls and floors often act as resonators or sounding boards at long wavelengths, causing amplification of bass fundamental frequencies and harmonics. Standing waves. When a sound's wavelength coincides with the length of a room boundary the wave "stands." This leads to boosting of certain frequencies and cancellation of others, especially at low frequencies where holes and spikes in frequency response are likely to occur.    

"Live end/dead end" acoustics are created in control room settings by using sound-absorbing panels to treat the wall behind the speakers and a portion of the two adjacent walls, but leaving the listener area untreated or "live': Studio acoustics are enhanced by treating three non-parallel surfaces, i.e. .two adjacent walls and the ceiling or floor. Unlike conventional materials such as acoustical tile, sponge rubber, cork or carpet, Our panels are engineered to absorb sound evenly over a broad frequency spectrum. Their engineered surface patterns dissipate and trap high-frequency sound energy while offering more absorptive area that conventional flat materials.

.

TEMPORARY THRESHOLD SHIFT (TTS) -

A temporary impairment of hearing acuity as indicated by a change in the threshold of audibility.

Disclaimer