Term
| designer can control acoustics through |
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Definition
| space planning, design of walls and ceilings, and selection of finishes |
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Term
| sound has three basic qualities |
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Definition
velocity-depends on the medium in which the sound is traveling and the temperature of the medium
frequency-number of cycles completed per second and is measured in Hertz. One Hertz equals one cycle per second.
*sounds that we call high notes or high-pitched sounds have higher frequencies; bass notes have lower frequencies.
power-quality of acoustic energy as measured in watts. it is this power that people perceive as loudness. |
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Term
| human ear is sensitive to vast range of sound power, from about 10-16 watts per sq. cm to 10-3 watts per sq. cm. b/c of this |
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Definition
and the fact that the sensation of hearing is proportional to the logarithm of the source intensity, the decible (dB) is used in acoustic descriptions and calculations.
decible relates actual sound intensity to the way humans experience sound. by definition, zero decible is the threshold of human hearing, and 130 dicibles is the threshold of pain. |
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Term
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Definition
*healthy young person can hear sounds in the range of about 20 to 20,000 Hz. Speech is in the range of 125 to 8000, with most in the range of 200 to 5000.
*human ear is less sensitive to low frequencies than to middle and high frequencies for sounds of equal energy.
*most common sound sources contain energy over a wide range of frequencies. measurement and analysis is often divided into eight octave frequency bands identified by their cneter frequency. |
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Term
| two basic problems in controlling noise |
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Definition
1.preventing or minimizing the transmission of sound from one space to another
2.reducing the noise within a space. |
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Term
| unwanted sound transmission from one space to another |
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Definition
| transmission of sound is primarily retarded by the mass of the partition. the stiffness, or rigidity of the partition is also important. given two partitions the same weight per sq. ft, the one with the less stiffness will perform better than the other. |
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Term
| two important concepts in noise reduction |
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Definition
1.transmission loss
2.actual noise reduction between two spaces.
transmission loss takes into account only the loss through the partition. noise reduction is dependant not only on the transmission loss, but also on the are of the partition separating the two spaces and the absorption of the surfaces in the quiet room.
noise reduction can be increased by increasing teh transmission loss of the partition, by increasing the absorption in the quiet room, by decreasing the area of the common wall between the rooms, or by some combination of all three. |
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Term
| to rate the transmission loss |
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Definition
a single-number rating is often used to rate the transmission loss of construction. this is the sound transmission class (STC).
*the higher teh STC rating, the better the barrier is in stopping sound. |
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Term
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Definition
the ideal loss through a barrier under lab conditions. partitions, floors, and other construction components built in the field are seldom constructed as well as those in the lab.
also, breatks in the barrier such as cracks, electrical outlets, doors, adn the like will significantly lessen overall noise reduction. |
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Term
| in critical situations, transmission loss and selection of barriers should be calculated |
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Definition
| using the values for various frequencies rather than the single STC average value. some materials may allow an acoustic "hole" stopping most frequencies but allowing transmission of a certain range of frequencies. |
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Term
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Definition
| can be used to specify the maximum amount of continuous background noise allowable in a space, to establish a minimum amount of noise desired to help mask sounds, and to evaluate an existing condition. |
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Term
| controlling sound transmission is only part of good acoustic design |
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Definition
proper amount of sound absorption must also be included to minimize noise within a space.
sound absorption is used to control unwanted sound reflections (noise), to improve speech privacy, adn to decrease or increase reverberation. |
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Term
| the abosorption of a material is defined by |
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Definition
the coefficient of absorption, a, which is the ratio of the sound intensity absorbed by the material to the total intensity reaching the material. the maximum absorption possible, therefore is 1, that of a free space.
generally a material with a coefficient below .2 is considered to be reflective, and one iwth a coefficient above .2 is considered soudn absorbing. |
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Term
| noise reduction coefficient (NRC) |
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Definition
| average of a material's absorption coefficients at the four frequencies of 250, 500, 1000, and 2000 Hz, rounded to the nearest multiple of .05. |
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Term
| the total absorption of a material is dependent on |
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Definition
| its coefficient of absorption and the area of the material. b/c most rooms have several materials with different areas, th total absorption in a room is the sum of the various individual absorptions. |
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Term
| rules of thumb for designing with good acoustics |
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Definition
*avoid designing rooms with hard, reflective surfaces on the walls, floor, and ceiling.
*average absorption coefficient of a room should be at least .2. an average absorption above .5 is usually not desirable, nor economically justified. lower value is suitable for large rooms, while larger values are suitable for small or noisy rooms.
*each doubling the amount of absorption in a room results in a noise reduction of only 3 dB-hardly noticeable. to make any difference, you must increase the total absorption by at least three times to change the reduction by 5 dB, which is noticeable.
*although absorptive materials can be placed anywhere, ceiling treatment for sound absorption is more effective in large rooms, while wall treatment is more effective in small rooms. |
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Term
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Definition
| prolongation of sound as it repeatedly bounces off hard surfaces. affects teh intelligibility of speech and the quality of music. reverberation can be controlled by modifying the amount of absorptive or reflective finishes in a space. |
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Term
| three primary ways sound can be controlled withing a space |
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Definition
1. reducing the level of loundness of the sound source
2. modifying the absorption in the space
3. introducing nonintrusive background sound to mask the unwanted sound |
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Term
| reducing level of sound source is not always possible |
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Definition
however, if the sound source is from noise outside or an adjacent room, the transmissin loss of the enclosing walls can be improved.
modifying the absorption of the space can achieve some noise reduction, but there are practical limits to adding absorptive materials.
in most cases, introducing nonintrusive background sound is desirable b/c it can mask unwanted noise. may come from a steady hum of HVAC, business machines, traffic, conversation, or from other sources. |
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Term
| white sound, random noise, acoustic perfume |
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Definition
| speakers are placed in the ceiling of a space and connected to a sound generator, which produces a continuous, unnoticeable sound at particular levels across the frequency spectrum. |
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Term
| the control of sound transmission through a barrier |
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Definition
| is primarily dependent on the barrier's mass and to a lesser extent on its stiffness. walls and floors are generally rated with their STC value; higher STC rating, better the barrier |
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Term
| several methods used to build a sound-resistant partition |
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Definition
1. simply adding mass to the wall. done by using a heavy material for the partition, such as masonry, or by using more than one layer of gyp. partitons with a higher STC, generally have a double layer of gyp on one or both sides of the stud.
2. place insulation within the stud cavity.
3. resilient channels can be used as furring strips on one side of the partition. only one leg of the channel touches the stud so teh wallboard floats and dampens sound striking it rather than transmitting it to the stud. |
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Term
| in addition to construction |
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Definition
| gaps in teh barrier must be sealed. edges at the floor, ceiling, and intersecting walls must be caulked. penetrations of the barrier should be avoided, but if necessary, they should be sealed as well. *electrical outlets should not be placed back-to-back but should be staggered in separate stud spaces and caulked. *pipes, ducts, adn similar penetrations provide a path for both airborne sounds and mechanical vibration and should not be rigidly connected to the barrier. |
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Term
| construction with a lower STC rating than the barrier itself |
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Definition
| should be avoided or given special treatment b/c it will decrease the overall rating of the barrier. |
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Term
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Definition
perimeter should be completely sealed at the jab and head and with a threshold or automatic door bottom at the sill.
auto door bottom is a piece of hardware that drops a seal from the door to the floor or threshold as the door closes. door itself should be as heavy as possible, preferably solid-wood core.
interior glass lights should be designed with laminated glass.
flanking paths for sound to travel, including ducts, plenums, and hallways should be eliminated or treated appropriately. |
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Term
| speech privacy in areas divided by full-height partitions is usually achieved |
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Definition
| by sound loss throught the partitions and, to a lesser extent, by the proper use of sound-absorbing surfaces. |
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Term
| five important factors in designing for speech privacy in an open area |
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Definition
(all must be present to acheive optimum environment)
1. ceiling must be highly absorptive. ideal-create clear sky condition so that sounds are not reflected from their source to other parts of the space.
2.area must include space dividers that reduce the transmission of sound from one space to the adjacent spaces. dividers should have a combo of absorptive surfaces to minimize sound reflections placed over a solid liner called a septum.
3. other surfaces, such as floor, furniture, windows, adn light fixtures, must be designed or arranged to minimize sound reflections.
4. if possible, activities should be distanced to take advantage of the normal attenuation of sound with distance.
5. area should have a properly designed background masking system. if right amount of sound-absorbing surfaces is provided, masking system will absorb all sounds in the space, not just unwanted sounds. |
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Term
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Definition
| sound resulting from direct contact of an object with a sound barrier, can occur on any surface, but generally occurs on a floor and ceiling assembly. quantified by impact insulation class (IIC) number, single-number rating of a floor/ceiling's impact sound performance. higher the IIC rating, the better the floor performs in reducing impact sounds in the test frequency range. can most easily be increased by adding carpet. also be improved by providing a resiliently suspended ceiling below, floating a finished floor on resilient pads over the structural floor, or by providing sound-absorbing material (insulation) in the air space between the floor and finished ceiling below. |
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Term
| to help minimize acoustical problems |
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Definition
1. plan similar use areas next to each other.
2. use buffer spaces such as closets and hallways to separate noise-producing spaces whenever possible.
3. stagger doorways in halls and other areas to avoid providing a straight-line path for noise.
4. try to locate furniture and other potential noise-producing objects away from the wall that is separating spaces.
5. minimize area of the common wall between two rooms where a reduction in sound transmission is desired.
6. avoid room shapes that reflect or focus sound. barrel-vaulted hallways and circular rooms |
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Term
| three methods used for all ceilings |
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Definition
1. NRC-noise reduction coefficient-single-number rating of the average sound absorption of a material over a limited frequency range. can range from 0 (no sound absorption), to 1.0 (total absorption)
2. speech range absorption (SRA) single number rating, which more closely represents the frequencies of speech and may be a better rating to use in evaluting adn selecting ceiling tiles.
3. ceiling attenuation class (CAC)-single number measure of transmission loss through ceiling tiles between two closed rooms where there is no wall or other barrier above the suspended ceiling. CAC can be improved by using composite tiles that have a gypsum wallboard backing. |
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Term
| two methods used to measure speech privacy |
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Definition
1. articulation class (AC)-single number summation of how effective a ceiling is in absorbing sound reaching it from over low partitions. uses nine-foot high ceiling and standard 60" partitions
2. articulation index (AI)-measures the performance of all the elements of a particular configuration working together including ceiling absorption, space dividers, furniture, light fixtures, partitions, background masking systems (white noise), adn HVAC system sound. predicts the intelligibility of speech for a group of talkers and listeners.
confidential speech privacy exists when speech cannot be understood and occurs when the AI is below about .05.
normal speech provacy means concentrataed effort is required to understand intruding speech and exists when the AI is between .05 and .20. Unacceptable privacy exists when the AI is above .30. |
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