CA1061257A - Acoustic absorber and method for absorbing sound - Google Patents
Acoustic absorber and method for absorbing soundInfo
- Publication number
- CA1061257A CA1061257A CA264,430A CA264430A CA1061257A CA 1061257 A CA1061257 A CA 1061257A CA 264430 A CA264430 A CA 264430A CA 1061257 A CA1061257 A CA 1061257A
- Authority
- CA
- Canada
- Prior art keywords
- acoustic absorber
- mils
- openings
- substrate
- acoustic
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000006098 acoustic absorber Substances 0.000 title claims abstract description 64
- 238000000034 method Methods 0.000 title claims abstract description 10
- 239000000758 substrate Substances 0.000 claims abstract description 41
- 229920000620 organic polymer Polymers 0.000 claims abstract description 22
- 238000000576 coating method Methods 0.000 claims abstract description 19
- 239000011248 coating agent Substances 0.000 claims abstract description 16
- 239000004744 fabric Substances 0.000 claims description 72
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 25
- 239000011521 glass Substances 0.000 claims description 19
- -1 polytetrafluoro-ethylene Polymers 0.000 claims description 17
- 229920001343 polytetrafluoroethylene Polymers 0.000 claims description 17
- 239000004810 polytetrafluoroethylene Substances 0.000 claims description 17
- 229940058401 polytetrafluoroethylene Drugs 0.000 claims description 17
- 239000011152 fibreglass Substances 0.000 claims description 6
- 229920002554 vinyl polymer Polymers 0.000 claims description 3
- 239000004812 Fluorinated ethylene propylene Substances 0.000 claims description 2
- 229920001774 Perfluoroether Polymers 0.000 claims description 2
- 229920009441 perflouroethylene propylene Polymers 0.000 claims description 2
- 229920000642 polymer Polymers 0.000 claims description 2
- 239000002033 PVDF binder Substances 0.000 claims 1
- 229920002981 polyvinylidene fluoride Polymers 0.000 claims 1
- 230000009102 absorption Effects 0.000 description 37
- 238000010521 absorption reaction Methods 0.000 description 37
- 238000012360 testing method Methods 0.000 description 19
- 230000001788 irregular Effects 0.000 description 13
- 238000009434 installation Methods 0.000 description 4
- 238000010276 construction Methods 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 229920002545 silicone oil Polymers 0.000 description 3
- 239000000463 material Substances 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000009941 weaving Methods 0.000 description 2
- 239000002759 woven fabric Substances 0.000 description 2
- 241000120283 Allotinus major Species 0.000 description 1
- 238000012935 Averaging Methods 0.000 description 1
- 241000271566 Aves Species 0.000 description 1
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- 229920004934 Dacron® Polymers 0.000 description 1
- 241001272567 Hominoidea Species 0.000 description 1
- 241000274177 Juniperus sabina Species 0.000 description 1
- 239000004677 Nylon Substances 0.000 description 1
- CTQNGGLPUBDAKN-UHFFFAOYSA-N O-Xylene Chemical compound CC1=CC=CC=C1C CTQNGGLPUBDAKN-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000004378 air conditioning Methods 0.000 description 1
- 229920006231 aramid fiber Polymers 0.000 description 1
- 239000010425 asbestos Substances 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- 239000008199 coating composition Substances 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- KPUWHANPEXNPJT-UHFFFAOYSA-N disiloxane Chemical class [SiH3]O[SiH3] KPUWHANPEXNPJT-UHFFFAOYSA-N 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000004927 fusion Effects 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 239000011810 insulating material Substances 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229920001778 nylon Polymers 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
- 239000011120 plywood Substances 0.000 description 1
- 229920000728 polyester Polymers 0.000 description 1
- 239000005020 polyethylene terephthalate Substances 0.000 description 1
- 229920001296 polysiloxane Polymers 0.000 description 1
- 229920000915 polyvinyl chloride Polymers 0.000 description 1
- 239000004800 polyvinyl chloride Substances 0.000 description 1
- 238000002203 pretreatment Methods 0.000 description 1
- 238000012552 review Methods 0.000 description 1
- 229910052895 riebeckite Inorganic materials 0.000 description 1
- 238000004513 sizing Methods 0.000 description 1
- ACXGJHCPFCFILV-UHFFFAOYSA-M sodium;2-(4-chloro-2-methylphenoxy)acetate;3,6-dichloro-2-methoxybenzoic acid Chemical compound [Na+].COC1=C(Cl)C=CC(Cl)=C1C(O)=O.CC1=CC(Cl)=CC=C1OCC([O-])=O ACXGJHCPFCFILV-UHFFFAOYSA-M 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000008096 xylene Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/162—Selection of materials
-
- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04B—GENERAL BUILDING CONSTRUCTIONS; WALLS, e.g. PARTITIONS; ROOFS; FLOORS; CEILINGS; INSULATION OR OTHER PROTECTION OF BUILDINGS
- E04B1/00—Constructions in general; Structures which are not restricted either to walls, e.g. partitions, or floors or ceilings or roofs
- E04B1/62—Insulation or other protection; Elements or use of specified material therefor
- E04B1/74—Heat, sound or noise insulation, absorption, or reflection; Other building methods affording favourable thermal or acoustical conditions, e.g. accumulating of heat within walls
- E04B1/82—Heat, sound or noise insulation, absorption, or reflection; Other building methods affording favourable thermal or acoustical conditions, e.g. accumulating of heat within walls specifically with respect to sound only
- E04B1/84—Sound-absorbing elements
-
- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04B—GENERAL BUILDING CONSTRUCTIONS; WALLS, e.g. PARTITIONS; ROOFS; FLOORS; CEILINGS; INSULATION OR OTHER PROTECTION OF BUILDINGS
- E04B1/00—Constructions in general; Structures which are not restricted either to walls, e.g. partitions, or floors or ceilings or roofs
- E04B1/62—Insulation or other protection; Elements or use of specified material therefor
- E04B1/74—Heat, sound or noise insulation, absorption, or reflection; Other building methods affording favourable thermal or acoustical conditions, e.g. accumulating of heat within walls
- E04B1/82—Heat, sound or noise insulation, absorption, or reflection; Other building methods affording favourable thermal or acoustical conditions, e.g. accumulating of heat within walls specifically with respect to sound only
- E04B1/84—Sound-absorbing elements
- E04B1/8409—Sound-absorbing elements sheet-shaped
-
- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04B—GENERAL BUILDING CONSTRUCTIONS; WALLS, e.g. PARTITIONS; ROOFS; FLOORS; CEILINGS; INSULATION OR OTHER PROTECTION OF BUILDINGS
- E04B1/00—Constructions in general; Structures which are not restricted either to walls, e.g. partitions, or floors or ceilings or roofs
- E04B1/62—Insulation or other protection; Elements or use of specified material therefor
- E04B1/74—Heat, sound or noise insulation, absorption, or reflection; Other building methods affording favourable thermal or acoustical conditions, e.g. accumulating of heat within walls
- E04B1/82—Heat, sound or noise insulation, absorption, or reflection; Other building methods affording favourable thermal or acoustical conditions, e.g. accumulating of heat within walls specifically with respect to sound only
- E04B1/84—Sound-absorbing elements
- E04B2001/8457—Solid slabs or blocks
- E04B2001/8461—Solid slabs or blocks layered
Landscapes
- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Engineering & Computer Science (AREA)
- Architecture (AREA)
- Structural Engineering (AREA)
- Civil Engineering (AREA)
- Electromagnetism (AREA)
- Multimedia (AREA)
- Laminated Bodies (AREA)
- Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
- Compositions Of Macromolecular Compounds (AREA)
- Soundproofing, Sound Blocking, And Sound Damping (AREA)
- Woven Fabrics (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An acoustic absorber and a method for absorbing sound utilize a substrate having a plurality of opening therethrough.
An organic polymer coating covers the substrate and partially fills the openings in the substrate to form an acoustic absorber having a porosity not greater than 60 CFM/ft2.
An acoustic absorber and a method for absorbing sound utilize a substrate having a plurality of opening therethrough.
An organic polymer coating covers the substrate and partially fills the openings in the substrate to form an acoustic absorber having a porosity not greater than 60 CFM/ft2.
Description
*
The present invention relates essentially to an acoustic absorber and a method for absorbing sound, and, more particularly, to a new and improvecl acoustic absorber which may be employed to reduce noise levels and reverberations in rooms, convention cente~s, auditoriums, enclosed stadiums, manufacturing areas and subways and to attenuate sound in longitudinal sound paths, such as ducts and corridors.
Acoustic energy, i.e., sound, may be absorbed by any medium which is capable of converting incident sound ~aves into other forms of energy and ultimately to heat. Most bullding materials possess sound-absorbing qualities, but those specifically designed to have relatively high absorption properties are conventionally known as acoustic absorbers.
In the past, porous acoustic absorbers have been utilized to absorb acoustic energy. At medium and high fre-quencies, most porous acoustic absorbers rely primarily on their .
;~ porosity for a~sorbing acoustic energy, sound waves being converted into heat by viscous friction resulting from the propagation of the sound waves through openinys~in the acoustic absorher. However, at relatively low frequencies, the porous .
` acoustic absorbers absorb acoustic energy primarily through mechanical dissipation occurring when the sound waves force the ~; - acoustic absorber into vibrating motion, the resulting flexural vibra~ion converting a fraction of the incident acoustic energy into heat, the balance of the acoustic energy being absorbed hy d , i , ", ,'.
', ' " ' ' ' ' ' ' ``
'~' , ' ' , i ~ ' , , ' ' . ' ' :: . . . .
5'~
porous absorption. Heretofore, porous acoustic absorbers have never achieved sound absorption at both high and low frequencies through the use of a flexible material.
There is provided, in accordance with the present invention, a novel acoustic absorbing structure and method which utilize an acoustic absorber having a porosity designed to absorb sound over a wide range of frequencies.
Broadly, the present invention provides, in an acoustic absorber, including a porous substrate, having a multiplicity of openings extending through the substrate, and an organic polymer applied to the substrate, the improvement wherein the organic polymer completely covers the surfaces of the substrate on both sides thereof and partially fills at least some of the openings extending through the substrate in such a manner that the acoustic absorber has a porosity not substantially greater -~
than 60 CFM/ft2, at 1/2 inch differential water pressure, and wherein the acoustic absorber is flexible~
In another aspect the present invention provides an acoustic absorber, comprising a multiplicity of individual strands of fiberglass woven together to form a porous, glass fabric substrate; and a fluorinated organic polymer coating ;~
adhering to and completely covering each individual strand and partially filling openings in the substrate, the acoustic absorber having a porosity not substantially grea~er than 60 CFM/ft2, at l/2 inch differential water pressure, a flexi-bility capable of absorbing sound waves or relatively low ~`
frequencies by mechanical dissipation caused when relatively low frequency sound waves force the acoustic absoxber into vibrating motion and numerous randomly sized and shaped o~enings capable of absorbing sound waves of relatively high frequencies ,~ ,' .
'7 by viscous friction caused when relatively high frequency sound waves pass through the openings, whereby acoustic energy may be absorbed over a wide range of frequencies.
In a further embodiment the present invention provides a method ~or absorbing sound waves in a structure, comprising positioning a flexible acoustic absorber including a porous substrate, having a multiplicity of openings extending through the substrate, and an organic polymer coating applied to and covering both sides of the substrate and partially filling at least some of the openings extending through the substrate in such a manner that the acoustic absorber has a porosity not substantially greater than 60 CFM/ft2, at 1/2 inch differential water pressure, the acoustic absorber being adjacent and spaced from a surface of the structure a distance sufficient to permit sound waves to pass through the acoustic absorber.
The acoustic absorber may be flexible, in which case it not only enhances sound absorption at low frequencies, but also facilitates shipping and installation, thereby reducing construction time and costs. For instance, its flexibility permits the acoustic absorber to be shipped as a roll.
The range of sound absorption may be further enhanced by providing ~he acoustic absorber with randomly sized openings, which provide a means for bracketing the ideal opening size.
Although it is desirable to maintain the porosity across the acoustic absorber relatively constant, the shape and size of ;
the openings may be varied depending on the fre~uency of the -sound waves to be absorbed. It has been found that an acoustic absorber having openings with a cross-dimension less than
The present invention relates essentially to an acoustic absorber and a method for absorbing sound, and, more particularly, to a new and improvecl acoustic absorber which may be employed to reduce noise levels and reverberations in rooms, convention cente~s, auditoriums, enclosed stadiums, manufacturing areas and subways and to attenuate sound in longitudinal sound paths, such as ducts and corridors.
Acoustic energy, i.e., sound, may be absorbed by any medium which is capable of converting incident sound ~aves into other forms of energy and ultimately to heat. Most bullding materials possess sound-absorbing qualities, but those specifically designed to have relatively high absorption properties are conventionally known as acoustic absorbers.
In the past, porous acoustic absorbers have been utilized to absorb acoustic energy. At medium and high fre-quencies, most porous acoustic absorbers rely primarily on their .
;~ porosity for a~sorbing acoustic energy, sound waves being converted into heat by viscous friction resulting from the propagation of the sound waves through openinys~in the acoustic absorher. However, at relatively low frequencies, the porous .
` acoustic absorbers absorb acoustic energy primarily through mechanical dissipation occurring when the sound waves force the ~; - acoustic absorber into vibrating motion, the resulting flexural vibra~ion converting a fraction of the incident acoustic energy into heat, the balance of the acoustic energy being absorbed hy d , i , ", ,'.
', ' " ' ' ' ' ' ' ``
'~' , ' ' , i ~ ' , , ' ' . ' ' :: . . . .
5'~
porous absorption. Heretofore, porous acoustic absorbers have never achieved sound absorption at both high and low frequencies through the use of a flexible material.
There is provided, in accordance with the present invention, a novel acoustic absorbing structure and method which utilize an acoustic absorber having a porosity designed to absorb sound over a wide range of frequencies.
Broadly, the present invention provides, in an acoustic absorber, including a porous substrate, having a multiplicity of openings extending through the substrate, and an organic polymer applied to the substrate, the improvement wherein the organic polymer completely covers the surfaces of the substrate on both sides thereof and partially fills at least some of the openings extending through the substrate in such a manner that the acoustic absorber has a porosity not substantially greater -~
than 60 CFM/ft2, at 1/2 inch differential water pressure, and wherein the acoustic absorber is flexible~
In another aspect the present invention provides an acoustic absorber, comprising a multiplicity of individual strands of fiberglass woven together to form a porous, glass fabric substrate; and a fluorinated organic polymer coating ;~
adhering to and completely covering each individual strand and partially filling openings in the substrate, the acoustic absorber having a porosity not substantially grea~er than 60 CFM/ft2, at l/2 inch differential water pressure, a flexi-bility capable of absorbing sound waves or relatively low ~`
frequencies by mechanical dissipation caused when relatively low frequency sound waves force the acoustic absoxber into vibrating motion and numerous randomly sized and shaped o~enings capable of absorbing sound waves of relatively high frequencies ,~ ,' .
'7 by viscous friction caused when relatively high frequency sound waves pass through the openings, whereby acoustic energy may be absorbed over a wide range of frequencies.
In a further embodiment the present invention provides a method ~or absorbing sound waves in a structure, comprising positioning a flexible acoustic absorber including a porous substrate, having a multiplicity of openings extending through the substrate, and an organic polymer coating applied to and covering both sides of the substrate and partially filling at least some of the openings extending through the substrate in such a manner that the acoustic absorber has a porosity not substantially greater than 60 CFM/ft2, at 1/2 inch differential water pressure, the acoustic absorber being adjacent and spaced from a surface of the structure a distance sufficient to permit sound waves to pass through the acoustic absorber.
The acoustic absorber may be flexible, in which case it not only enhances sound absorption at low frequencies, but also facilitates shipping and installation, thereby reducing construction time and costs. For instance, its flexibility permits the acoustic absorber to be shipped as a roll.
The range of sound absorption may be further enhanced by providing ~he acoustic absorber with randomly sized openings, which provide a means for bracketing the ideal opening size.
Although it is desirable to maintain the porosity across the acoustic absorber relatively constant, the shape and size of ;
the openings may be varied depending on the fre~uency of the -sound waves to be absorbed. It has been found that an acoustic absorber having openings with a cross-dimension less than
2.0 mils will ahsorb sound over a wide range of fre~uencies.
The term "cross-dimension" as used herein means the diameter of ~ - 3 -~ .,, ~,~
- ~. ~ :: ., , a round opening, the minor or major axis of an elliptical opening, the minor or major medial axis of an irregular star-shaped opening, the width or length of a rectangular opening or the base or height of a triangular opening.
The substrate can be any inorganic or organic fabric capable of withstanding the fusion temperature of the organic polymer with which it is to be coated. Suitable sub- ;
strates may be made of glass; fiberglass; asbestos; aramid fiber; nylon; long chain polyesters, such as Dacron; or wire cloth. The substrate may have a thickness of about 3 to 30 mils, a weight of about 3 to 25 oz/yd2, and openings of such a size that they may be partially filled with any suitable organic polymer ; ',~ .
,,: , .
' , '' ' . , *Trade Mark
The term "cross-dimension" as used herein means the diameter of ~ - 3 -~ .,, ~,~
- ~. ~ :: ., , a round opening, the minor or major axis of an elliptical opening, the minor or major medial axis of an irregular star-shaped opening, the width or length of a rectangular opening or the base or height of a triangular opening.
The substrate can be any inorganic or organic fabric capable of withstanding the fusion temperature of the organic polymer with which it is to be coated. Suitable sub- ;
strates may be made of glass; fiberglass; asbestos; aramid fiber; nylon; long chain polyesters, such as Dacron; or wire cloth. The substrate may have a thickness of about 3 to 30 mils, a weight of about 3 to 25 oz/yd2, and openings of such a size that they may be partially filled with any suitable organic polymer ; ',~ .
,,: , .
' , '' ' . , *Trade Mark
- 3(a) -. .
,..... .
~'~t_,`l :.
22~73~
'~. ' . ' ~ ' ~ '.
coating to form an acoustic a~sorber having a porosity not su~stantially ~reater than 60 CFM/ft2, at 1/2 inch differential water pressure. It may be woven or nQn-WOVen fabric, or may '' be of a matted or pxint-out construction. If a woven fabric is used, a plurality of strands are woven together to form openings therebetween, the strands being substantially round or flat in radial cross-section. Presently available weaving - equipment can produce a continuous piece of fabric having ~- width of about 12 feet.
' 10 Any organic polymer coating is suitable having the properties of known fabric coatings. These coatings render the'substrate impervious to water, other liquids, or dust . and dirt particles which would'adversely affect the substrate ' .
- in the absence of the coating. The coating also stabilizes the size of the openings in the acoustic absorbe'r, since the 'flexing or bendin~ o~ an uncoated substrate wouid vary the size of the openings therein, and hence the porosity of the acoustic absorber. While the composition of the coatings is not important as long as the coatiny can control the porosity of the substrate, suitable organic polymers which can be used - . - . ,.
to coat the substrate include fluorinated organic polymers and vinyl polymers. Acceptable fluorinated organic polymers include .~ .. .
polytetra~luoroethylene, perfluoroalkoxy, polyvinylidenefluoriae and fluorinated ethylenepropylene polymers; while acceptable vinyl polymers include polyvinylchloride.
- In accord;ance with known methods, the substrate may be initially treated with silicone oil, as an interior layer in the final construction, to prevent the organic polymer coating .: .
; ', " . ' ' . .
,..... .
~'~t_,`l :.
22~73~
'~. ' . ' ~ ' ~ '.
coating to form an acoustic a~sorber having a porosity not su~stantially ~reater than 60 CFM/ft2, at 1/2 inch differential water pressure. It may be woven or nQn-WOVen fabric, or may '' be of a matted or pxint-out construction. If a woven fabric is used, a plurality of strands are woven together to form openings therebetween, the strands being substantially round or flat in radial cross-section. Presently available weaving - equipment can produce a continuous piece of fabric having ~- width of about 12 feet.
' 10 Any organic polymer coating is suitable having the properties of known fabric coatings. These coatings render the'substrate impervious to water, other liquids, or dust . and dirt particles which would'adversely affect the substrate ' .
- in the absence of the coating. The coating also stabilizes the size of the openings in the acoustic absorbe'r, since the 'flexing or bendin~ o~ an uncoated substrate wouid vary the size of the openings therein, and hence the porosity of the acoustic absorber. While the composition of the coatings is not important as long as the coatiny can control the porosity of the substrate, suitable organic polymers which can be used - . - . ,.
to coat the substrate include fluorinated organic polymers and vinyl polymers. Acceptable fluorinated organic polymers include .~ .. .
polytetra~luoroethylene, perfluoroalkoxy, polyvinylidenefluoriae and fluorinated ethylenepropylene polymers; while acceptable vinyl polymers include polyvinylchloride.
- In accord;ance with known methods, the substrate may be initially treated with silicone oil, as an interior layer in the final construction, to prevent the organic polymer coating .: .
; ', " . ' ' . .
-4-~ .
.
2~
1 i ~6~5i7 from penetrating i~to the substrate. This optional pre-treatment helps maintain the flexibi:Lity of the substrate and improves the trapezoidal tear streng~h of the acoustic absorber, as well as preventing any possible changes in porosity. ~ 33~
solution of a silicone (e.g., polydiinethyl siloxane) in xylene can be applied, followed by curing at 450F for about five minutes. The application can be made by doctor knife, aostor roller, reverse roll doc~or, and any other known technique in the art of coating surfaces with liquid coating compositions. :
Besides silicone oil, the substrate can also be pre-treated with hydrocarbon oils or any other substance that keeps the sub-strate from getting wet.
If the substrate is fiberglass, it should be pre-cleaned with heat to remo~Je the sizing normally contained in glass ~abrics, and thereafter treated with silicone oil as described above. ~his will help to prevent ultraviolet deterioration of the acoustic absorber. ~
In one embodiment, the acoustic absorber includes ; -a porous, glass fabric substrate formed by weaving together a multiplicity of individual strands of fiberglass. The woven substrate is coated with an organic polymer coating in such a manner that the coating adheres to and completely covers each individual strand. The acoustic absorber has a weight of a~out 4 oz/yd2 to about 31 oz~yd2 and a thickness of about 4 mils to about 42 mils. Inasmuch as the acoustic absorber is thin and relatively light, it may be handled easily and installed with a minimum of hangers or other mountings.
~ n use, the acoustic absorber is supported adjacent '. .
.
2~
1 i ~6~5i7 from penetrating i~to the substrate. This optional pre-treatment helps maintain the flexibi:Lity of the substrate and improves the trapezoidal tear streng~h of the acoustic absorber, as well as preventing any possible changes in porosity. ~ 33~
solution of a silicone (e.g., polydiinethyl siloxane) in xylene can be applied, followed by curing at 450F for about five minutes. The application can be made by doctor knife, aostor roller, reverse roll doc~or, and any other known technique in the art of coating surfaces with liquid coating compositions. :
Besides silicone oil, the substrate can also be pre-treated with hydrocarbon oils or any other substance that keeps the sub-strate from getting wet.
If the substrate is fiberglass, it should be pre-cleaned with heat to remo~Je the sizing normally contained in glass ~abrics, and thereafter treated with silicone oil as described above. ~his will help to prevent ultraviolet deterioration of the acoustic absorber. ~
In one embodiment, the acoustic absorber includes ; -a porous, glass fabric substrate formed by weaving together a multiplicity of individual strands of fiberglass. The woven substrate is coated with an organic polymer coating in such a manner that the coating adheres to and completely covers each individual strand. The acoustic absorber has a weight of a~out 4 oz/yd2 to about 31 oz~yd2 and a thickness of about 4 mils to about 42 mils. Inasmuch as the acoustic absorber is thin and relatively light, it may be handled easily and installed with a minimum of hangers or other mountings.
~ n use, the acoustic absorber is supported adjacent '. .
-5-' . ' :' ~ ~.
and spaced from a structural surface, a distance sufficient to permit sound waves to pass through the acoustic absorber.
The acoustic absorber should be mounted at least about 1 1/2 inches from the structural surface. Optimally, the distance `
is a 1/4 wavelength, the wavelength ~ having the following relationship to frequency f, expressed in Hz:
~=c/f, :
where c is the speed of sound.
Because th~ acoustic absorber is thin, flexible, strong and relatively light, it can be installed in a number of unique ways without detracting from its sound absorbing capabilities. For instance, the acoustic absorber can be festooned, draped or hung like a banner from a ceiling or ~
similar structural surface. It is also possible to hang the , acoustic absorber horizontally below a ceiling. The fabric has such an attractive appearance and pleasant hand that it could even be pleated and hung from a curtain rod in place of a traditional curtain.
One unique method of installation, which has been quite successful in domed or enclosed stadiums, involves hanging a plurality of acoustic absorbing banners around the `
inner periphery of the stadium. In accordance with this method, each end of an acoustic absorbing banner may be attached to a corresponding rod, for example by providing -transversely extending sleeves at each end for receiving the ~
rods. One rod is attached to the stadium wall and the other ;-rod is attached to the ceiling in such a manner that the banner extends upwardly at an angle from the wall to the ceilingO
The length and width of each banner, as well as the number of banners
and spaced from a structural surface, a distance sufficient to permit sound waves to pass through the acoustic absorber.
The acoustic absorber should be mounted at least about 1 1/2 inches from the structural surface. Optimally, the distance `
is a 1/4 wavelength, the wavelength ~ having the following relationship to frequency f, expressed in Hz:
~=c/f, :
where c is the speed of sound.
Because th~ acoustic absorber is thin, flexible, strong and relatively light, it can be installed in a number of unique ways without detracting from its sound absorbing capabilities. For instance, the acoustic absorber can be festooned, draped or hung like a banner from a ceiling or ~
similar structural surface. It is also possible to hang the , acoustic absorber horizontally below a ceiling. The fabric has such an attractive appearance and pleasant hand that it could even be pleated and hung from a curtain rod in place of a traditional curtain.
One unique method of installation, which has been quite successful in domed or enclosed stadiums, involves hanging a plurality of acoustic absorbing banners around the `
inner periphery of the stadium. In accordance with this method, each end of an acoustic absorbing banner may be attached to a corresponding rod, for example by providing -transversely extending sleeves at each end for receiving the ~
rods. One rod is attached to the stadium wall and the other ;-rod is attached to the ceiling in such a manner that the banner extends upwardly at an angle from the wall to the ceilingO
The length and width of each banner, as well as the number of banners
-6-, employed, can be varied dependi.ng upon the stadium dimensions and the sound absorbing requirements. The acoustic absorbing banners are advantayeously manufactured from a translucent fabric, so that they can be hung below lighting fixtures without appreciably blocking the transmission of light.
To use the invention in dropped ceiling installations, a piece of acoustic absorbing fabric is mounted on a frame;
designed to.fit between two pairs of brackets which usually.
form a 2~ x 2' or 2' x 4' receptacle. Because it is moisture~
proof, the acoustic absorbing fabric will not rot or mildew like ~he conventional acoustic ceiling tiles normally used in dropped ceiling installations. This also permits it to be ` spray-cleaned or washed with a liquid. Inasmuch as the fabric. .
is fire.resistant, it can be used safely in industrial kitchens and other areas where flames are exposed.
The following examples further illustrate the invention. To facilitate consideration and discussion of the exam~les, it should be explained that for a particular frequency band the sound absorption coefficient of a surface is, aside from the effects of diffraction, the fraction Of randomly incident sound energy absorbed or othen~ise not reflected, measured in sabins per square foot. The noise reduction coefficient ~NRC) can be calculated by averaging the sound absorption coefficients at 250, 500, 1000 and 2000 Hz, expressed to the nearest integral multiple of .05. An Acoustical and Insulating Materials Association (AIMA) No. 7 mounting positions the face of the test specimen 16 inches above the reverberation room floor. The , sides of the mounting are enclosed with plywood so that sound can be transmitted only through the test specimen into the air space behind it.
~ , ' ~:
. . . . . : , ~2~73~
5~ .
~ ~.XAMPLE I
Plain weave glass fabric, Burlington #116, having a thickness of 3.5 mils and a weight of 3.20 oz/yd2, with a yarn warp of 450 1/2 and a yarn filling of 450 1/2, woven to a warp and fill count of 60 x 58, was coated with polytetrafluoroethylene so that the openings in the fabric were partially filIed. The . coated fabric had a porosity of about 7 to 14 CFM/ft2, at 1/2 inch di~ferential water pressure, a thickness of about 4.Q mils, :~
and a weight of about 4.0 oz/yd2.
Microscopic examination reveals that the partially ~illed openings take on different shapes and sizes. For example, there are substantially round openings having a diameter of between O.S to 1.5 mils, substantially ellipti~al .
openings having a minor axis of about 0.5 mil and a major axis of about 1.5 mils, and irregular s-tar~shapea openings having a minor medial axis of about 0.5 mil and a ma~or medial axis of about 1.5 mils.
~hen the coated fabric was tested for sound absorption ::
gualities in an AIMA No. 7 mounting, a NRC of .30 was obtained . 20 based on the ~ollowing test results:
I . . ....... , .' . SOUND ABSORPTION COEFFICIENTS () _ _ . ,:
63 Hz 125 Hz 250 Hz 500 Hz 1000 Hz 2000 }lz 4000 H2 _ . _ _ _ 01 13 26 .32 48 .J~ .
EXAI~PLE II
.
Plain weave glass fabric, Burlington #116, having a thickness of 3. 5 mils and a weight of 3. 20 02~yd~, with a yarn 22473~
'. .
~ - ~0~ 5'~ ~
warp o~ ~50 1/2 ancl a yarn ~illing o 450 1/2, woven to a warp .
and fill count of 60 x 58, was coated with polytetrafluoroethylene . so that the openlngs in the fabric werè partially filled. The coated fabric had a porosity o~ about 24 to 35 CFM/~t2, at 1/2 inch differential water pressure, a thickness of about 4.0 mils, and a ~7eight o about 4.0 oz/yd2.
Microscopic examination reveals -that the partially filled openings take on different shapes and sizesO For example, there are substantially round openings having a io diameter of between Q.5 and 3.0 mils, substantially elliptical - ~ .
openings having a minor axis of about 0.5 mil and a major axis of about 3.0 mils, and irregular star-shaped openings having . a minor medial axis of about 0.5 mil and a major medial axis of about ~.0 mils. . :
When the coated ~abric was tested for sound absorption qualities in an AI~ No. 7 mounting, a NRC of .33 waC obtained .~ based on the following test results:
_ ' SOUND ABSORPTION COEFFICIENTS (a) . ' , . 63 Hz125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz :;~
. _ ~_ ~' ~
= .18 .34 27 .41 . EXAMPLE III
. .
Plain weave glass fabric, Burlington #125, having a thickness of 5.0 mils and a wei~ht of 3.75 oz/ydZ, with a yarn warp of 450 2/2 and a.yarn filling of 450 2/2, woven to a warp and fill count of 36 x 34, was coated with polytetrafluoroethylene so that the openings in the fabric were partially filled. The . . . . ~:
, _9_ .
22~73A
36~ 7 .
coated fabric had a porosity of about 15 to ~0 CFM/ft2, at 1/2 in,ch differential water pressure,, a thickness of about 6.0 to 7.0 mils, and a weight of about 5"i5 oz/yd2.
Microscopic examination reveals that the partially filled openings take on different shapes and sizes. For example, there are substantially round openings having a diameter of about 1.0 mil, substantially elliptical openings having a minor axis of about 1.0 mil and a major axis of about 10.0 mils, irreguiar star~shaped openings having a minor medial axis of about 1.0 mil and a major medial axis of about 10.0 mils, and generally rectangular openings having a width of about 1.0 mil and a length o~ about 10.0 mils.
When the coated fabric was tested for sound absorption qualities in an AIM~ No. 7 mounting, a NRC of .45 was obtained ~5 based,on the following test results:
. ,. .. ~ . ...
SOUND ABSORPTION COEFFICIENTS (a~
.... .. ~ . .. _ ...... _ ~ ~
63 Hz 125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz ...... _ ... _ . . .. _: .. _ :' .16 .22 .38 .44 .48 .50 , ' EXAMPLE IV
.. ... _ . . .
' Plain weave glass fahric;, Burlington #125, having a thickness of 5.0 mils and a weight'of 3.75 oz/yd2, with yarn warp of 450 2/2 and a yarn filling of 450 2/2, woven to a warp and fill count of 36 x 34, was coated with polytetrafluoroethylene so that the openings in the fabric were partially filled. The coated fabric had a porosity of about 30 to 60 CFM/ft2, at l~2 inch di~fer~ntial water pressure, a thickness of about 5.8 mils, - and a weight of about 4.9 oz/yd~.
, .
~l3~
: ' Microscopic examination reveals that the partially filled openings take on diffexent shapes and sizes. For example, there are substantially round openings having a diameter of about 1.5 m.ils, substantially elliptical openings 5 having a minor axis of about 1.5 mils and a major axis of about -10.0 mils, irregular star-shaped openings having a minor medial axis of about 1.5 mils and a major medial axis of a~out lO.0 mils,.
and generally rectangular openings having a width of about 1.5 ~ -mils and a length of about lO.0 mils~
h7hen the coated fakric was tested for sound absorption .
qualities in an AIMA No. 7 mounting, a NRC of .38 was obtained based on the following test results: --.~ . ..
~ ..
. . SOUND ABSORPTION CGEFFICIENTS (a) .
. 63 Hz ¦ 125 HZl ~5 ~ Zl 500 ~ 1000 Hz ¦ 2000 Hz ~ H~
lS -I .l7 L 39 1 .24 1 ~46 L .42 ~ .46 '.
. EXAMPLE V . ~ ;
Plain weave glass fabric, ~urlington ~128, having a thickness of 6.5 mils and a weight of 6.00 oz/yd2~ with a yarn - warp of 225 i/3 and a yarn filling of 225 l/3, woven to a warp .
and fill count of 42 x 32, was coated with polytetrafluoroethylene . so that the openings in the fabric were partially filled. The coated fabric had a porosity of about lS to l9 CFM/ft2, at l/2 inch differential water pressure, a thickness oE about 7.5 mils, and a weight of about 7.2 oz/yd2.
Microscopic examination reveals that the partially filled openings take on differ~nt sha~es and sizes~ For example, . . . . . . .
. - - , ~. .. . . .
.
~ 22473A
~ 6~
there are substantially round openinqs having a diameter of about 1.0 mils, su~stantially elliptical openings having a minor axis of about 2.0 mils and a major axis of about 5.0 .
mils, irregular star-shaped openings having a minor medial 5 axis of about 2.0 mils and a major medial axis o about 5.0 ;
mils, and generally rectangular openings having a width of about 2.0 mils and a length o~ about 5.0 mils.
- When the coated fabric was tested for sound absorption qualities in an AIMA No. ~ mounting, a NRC of .51 was obtained based on the following test resuits:
~
. . ~ .
SOUND ABSO.~PTION COEFFICIENTS (a) __ . .. . ., 63 Hz 125 Hz 250 H2 500 Hz 10~0 Hz 20D0 Hz 4000 Hz .. .. _. .'........ , :. ................. ...
.lq 16 __ 41 59 .58 .51 . --EXAMPLE VI .
Plain weave glass fabric, Burlington ~128, having a --thickness of 6.5 mils and a weight of 6.00 oz/yd2, with a yarn ~:
warp of 225 1/3 and a yarn filling of 225 1/3, woven to a warp.
and fill count of 42 x 32, was coated with polytetrafluoroethylene so that the openings in the fabric were partially filled. The coated fabric had a porosity of about 20 to 40 CFM/ft2, at 1/2 . inch differential water pressure, a thickness of about 7.5 mils, and a weight of about 7.2 oz/yd2.
Microscopic examination reveals that the partially ~`.
filled openings take o~ different sl~apes and sizes. For example, there are substantially round openings haYing a diameter of about 2.0 mils, substantially elliptical openings having a minor axis , . . . ~
"., l~ Z~
:~ of about 2.0 mils and a major axis of about 10.0 mils, irregular ~ star-shaped openings having a minor medial axis of about 2.0 mils .- and a .major medial axis of about 10.0 mils, and generally rectangular openings having a width of about 2.0 mils and a length of about 10.0 mils.
When the coated fabric was tested for sound absorption qualities in an AIMA No. 7 mounting, a NRC of .42 was obtained based on the following test results: .
.. _. . ..
- SOUND ABSORPTION CûEFFICIENTS (c~) -63 Hz ¦ 125 Hz ¦ 250 Hz ~ 500 Hz ~ 1000 Hz ¦ 2000 Ha ¦ 4000 Hz . . . . . .__ .' _ .. __ 42 33 ` -. .36 47 ,. , - . ' ' ' .: ' . EXAMPLE VII
: . Plain weave giass fabric, Burlington ~128, having a . thickness of.6.5 mils and a weight of 6.00 oz/yd2, with a yar~
; lS warp of 225 1/3 and a yarn filling of 225 /3, woven to a warp and fill count of 42 x 32, was coated-with polytetrafluoroethylene .so that the openings in the fabric were partially filled. The . coa~ed fabric had a porosity of about 60 to 80 CFM/ft2, at 1~2 inch differential water pressure, a thickness of about 7.5 mils, and a weight of abaut 7.2 oz/yd2.
Microscopic examination reveals that the partially filled openings take on different shapes and sizes. For example, there are substantially round openings having a diameter of about 2.0 mils, substantially elliptical openings having a minor axis o about 2.0 mils and a major axis of about 10.0 mils, irregular star-shaped openings having a minor medial axis of about 2.0 mils ,. : , ' ;, ~. . ' . , , - . . . .
:
and a major medial axis of about 10.0 mils, and generally rectangularopeningShaving a width of about 2.0 mils and a ' length of about 10.0 mils.
, :
When the coated fabric was tested for sound absorp-tion qualities in an AIMA No. 7 mounting, a NRC of .26 was obtained based on the following test results:
:;~ SOUND ABSORPTION COEFFICIENTS (a) 63 Hz ~ 125 Hz j 25~ ~ = z C D 1 2000 Hz 000 21 ~ 23 1 .21 1 .28 1 2 ~ .28 1 24 ;
EXAMPLE VIII
- Plain weave glass fabric, Burlington #1528, having a "
thickness of 6.5 mils and a weight of 5.95 oz/yd2, with a yarn warp of 150 1/2 and a yarn filling of 150 1/2, woven to a warp and fill count of 42 x 32, was coated with polytetrafluoro-ethylene so that the openings in the fabric were partially .:;
filled. The coated fabric had a porosity of about 8 to 11 ` 2 CFM/ft , at 1/2 inch differential water pressure, a thickness of about 7.5 mils, and a weight of about 7.2 oz/yd2.
Microscopic examination reveals that the partially filled openings take on different shapes and sizes. For example, there are substantially round openings having a diameter of ;~ ~
about 0.5 mil, substantially elliptical openings having a !'' minor axis of about 0.5 mil and a major axis of about 3.0 mils, irregular star-shaped openings having a minor medial axis of , about 0.5 mil and a major medial axis of about 3.0 mils, and ` generally rectangular openings having a width of about 0.5 mil and a length of about 3.0 mils.
~
~,;,''' .~" ' .
"; ~.
~ 3 . ~ .
When the coated fabric was tested for sound absorption qualities in an AIMA No. 7 mounting, a NRC of .45 was obtained based on the foilowing test results: ~
.
. . .
- SOUND ABSORPTION COEFFICIENTS (a) : . __ _ _ ._ ~. ._ .
563 ~Iz125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz . . _ _ :~
68 26 .42 33 . 50 1 53 .SS
:- , . '' ' - EXAMPLE IX
Plain weave glass fabric, Burlington #1142, having a `:
thickness of 10.0 mils and a weight of B.25 oz/yd2, with a yarn ; io warp.of 37 1/0 and a yarn filling of 37 1/0, woven to a warp and fill coun-t of 32 x 21, was coated with polytetrafluoroethylene so that the openings in the ~abric were partially filled. The coated .
fabric had a porosity of about 15 to 20 CFM/ft2, at 1/2 inch differential water pressure, a thickness of about 10.5 mils, and a weight of about 9.5 oz~yd2.
Microscopic examination reveals that the partially illed openings take on different shapes and sizes. For example, there are substantially round openings having a diameter of about 2.0 mils, substantially elliptical openings having a minor axis of about 2.0 mils and a major axis of about 15.0 mils, irregular star-shaped openings having a minor meaial axis of about 2.0 mils and a major medial axis of about 15.0 mils, and generally rectangular openings having a width of about 2.0 mils and a length of about 15.0 mils~
When the coated fabric was tested for sound absorption qualities in an AIMA No. 7 mounting, a NRC of .66 was obtained bas~d on the following test resul.ts: . :
.
;~ ,- . .. . ..
; - . , . . : . .::
.: ' ~" . ' . : : ' . ,- . . , .
~ 1 22473A
~06~'7 ; ~ .
SOUND ABSO~?~PTION COEFFICI~NTS (a) ,-: _ . 63 Hz 125 Hz 250 Hæ S00 Hz1000 Hz~000 Hz 4000 Hz , ~ ' . :~
` .60 .~9 .54 . .70 .72 .75 .' . . .
- . EXAMPI,E X
. . . . .
5 . Plain weave qlass fabric, Burlington #141, having a thickness of 11.0 mils and a weight of 8.80 oz/yd2, with a yarn warp of 225 3t2 and a yarn filling of ~25 3/2, woven to a warp and fill count of 32 x 21, was coated with polytetrafluoroethylene so - that the openings in the fabric were partially fllled. The co.ated fabric had a porosity of about 20 to 40 CFM/ft2, at 1/2 inch . . differential water pressure, a thickness of about 12.5 mils, and a weight of about ll.S oz/yd~.
Microscopic examination reveals that the partially filled openings take on different shapes and sizes~ For example, ~ 15 there are substantially round openings having a diameter of about 2.0 mils, substanti-ally elliptical openings having a minor axi~
of àbout 2.0 mils and a major axis of about 15.0 mils, irregular star-shaped openings having a minor medial axis of about 2.0 `.
. mils and a major medial axis of abou~ 15.0 mils, and generally xectangular openings having a width of about 2.0 mils and a length of about 15.0 milsO
: When the coated fabxic was tested for sound absorption `.
qualities in an ~IMA No. 7 mounting, a NRC of .66 was obtained based on the following test results: :;
', ~16-., , ' ` ~ .
22~73A
:' ' ~' ~' ', '. .
' ` ' ~0~2~t7.. . .
. . ... __ ..
.~ . SOUNr) ABSORPTION COEFFICII~NTS (a) .~ 63 Hz ¦ 125 Hz ¦ 250 Hz ¦ 500 ~Iz ¦ 1000 ~Iz ¦ 2000 ~Iz ¦ 4000 Hz _ . ~. .. ._ 83- ~4 1 73 ,53 .70 66 65 ~:~
EXAMPLE XI
~.
Plain weave glass fabric, Burlington ~141, having a.
thickness of 11.0 mils and a weight of 8.80 oz/yd2, with a yarn arp of 225 3/2 and a yarn filling of 225 3/2, woven to a warp and fill count of 32 x 21, was coated with polytetrafluoroethylene .~ so that ~he openings in the ~abric were partially fillQd. The coated fabric had a porosity of about 40 to 60 CFM/ft2, at 1/2 inch diffe1ential water pressure, a thickness of about 12.5 mils~
and a weight of about 10.8 oz/yd2.
Microscopic examination reveals that the partially filled openings take on different shapes and sizes. For example, :.
there are substantially round openings having a diameter of about 2.0 mils, substantially elliptical openings having a minor axis of about 2.0 mils and a major axis of about 20~0 mils, irregular star-shaped openings having a minor medial axis of about.2.0 mils and a major medial axis of about 20.0 mils, and generally rectan-`20 gul~r openings having a width of about 2.0 mils and a length of about 20.0 mils. ;
When the coated fabric was tested for sound absorption :
gualities in an AIMA No. 7 mounting, a NRC of ,52 was obtained .:~
based on the follow:ing.test results: -~
..
.
' , ' ' , '~
. . .
g ~ ~ .
~
~16'~ t7 :
. SOUND ~SORPTION CO~FFICXENTS (a) _ _ __ . ~
. 63 Hz 125 Hz 250 Hz 500 ~Iz 1000 Hz 2000 ~Iz ~000 Hz .
.35 .38 .73 .~2 .48 ~6 .4~
' FXAMPLE XII
Plain weave glass fabric, Burlington ~141, having a thickness of 11.0 mils and a weight of 8.80 oz/yd2, with a yarn warp of 225 3/2 and a yarn filling of 225 3/2, wo~en to a warp and fill count of 32 x 21, was coated with polytetrafluoroethylene . so that the o~enings in the fabric were partially filled. The L0 coated fabric had a porosity of about 80 to 110 CFM~ft2, at 1/2 - inch differential water pressure, a thickness of about 12.5 mils, .and a weight of about 10.0 oz/yd2.
.
Microscopic.examination reveals that the partially illed openings take on different shapes and sizes. For example, 15 there are substantially round openings having a ~iameter o . ,~
about 2.0 mils, substantially elliptical openings having a minor axis of about 2.0 mils and a major axis of about 20.0 mils, irregular star-shaped openings having a minor medial axis.of ... : -about.2.0 mils and a major medial axis of about 20.0 mils, and ~enerally rectangular openings having a width of ~bout 2.0 mils and a length of about 20.0 milsL
When the coated fabric was tested for sound absorption ~ualities in an AIM~ No. 7 mounting, a NRC of ~27 was obtained based on the fo1lowing test results:
. ' .
. , ' : ' -lB~ - :
2 24 7 3~
~L~36~Z~7 ' . ' . . .
SOUND ~BSORPTION COEFFICI13NTS ~) 63 Hz ¦ 125 Hz ¦ 250 Hz 1500 Hz ¦ 1000 Hz ¦ 2000 Hz ¦ 4000 H~
10 1 .23 1 .36 1.26 1 .18 ~ .26 1 .28 ' EXAMPLE XIII
Eight harness satin weave glass fabric, Burlington.
: ~183, having a thickness of 6 . 0 mils and a w~ight of 16.75 oæ/yd2, with a yarn warp of 225 3/2 and a yarn filling of 225 3/2, woven ~o a warp and fill count of 54 x 48, was coated with ; polytetrafluoroethylene so that the openings in the fabric were partially filleda The coated fabric had a .porosity of .. . . . . .
about 15 CFM/ft2, at 1/2 inch differential water pressure~
substantially round open1ngs having a diameter o~ about ; 2,0 ~o 5.0 mils, a thickness of about 25.0 mils, and a . weight of about 20. 5 oz/yd2.
When the coated fabric was tested for sound absorption . qualities in an AIMA No. 7 mounting, a~ NRC of .54 was obtained .based on the following test results: .
, - . .
. SOI~ND ABSORPTION COEFFICIENTS (a) - .
.
.63 }Iz ~25 N~250 Hz ¦ 500 Hz ¦ 1000 Hz ¦ 2000 Hæ ¦ 4000 Hz ' 20 .73 5851 1 .54 1 .51 1 .61 1 .~4 ,''. . . .
E~A~IPLE XIV
Eight harness satin weave glass ~abric, Burlington ~183, havi.ng a thickness of 6Ømils and a weight of 16.75 ~z/yd2, - .
.. ~. -, : .
2~so3 :
with a yarn warp of 225 3/2 and a yarn filling of 225 3/2,woven to a warp and fill count of 54 x 48, was coated with polytetrafluoroethylene so that the openings in the fabric were partially filled. The coated fabric had a porosity of about 30 CFM/ft , at l/2~inch aifferential water pressure, substantially round openings having a diamet~r of about 2.0 to 5.0 mils, a thickness of about 25.0 mils, and a weight of about 20.0 oz/yd .
When the coated fabric was tested for sound absorption qualities in an AIMA No. 7 mounting, a NRC of .59 was obtained based on the following test results:
SOUND ABSORPTION COEFFICIENTS (~) .. _ . _l l 63 Hz 125 Hz 250 Hz500 Hz 1000 Hz 2000 Hz 4000 Hz --._ _ . _ ._ . . : .
_.40 .41 58 58_ 55 .65 59 EXAMPLE XV `~ ;
Eight harness satin weave glass fabric, Burlington, #1584, having a thickness of 25.5 mils and a weight of 25.15 oz/yd2, with a yarn warp of 150 4/2 and a yarn filling of 150 4/2~ woven to a warp and fill count of 42 x 35, was coated with polytetrafluoroethylene so that openings in the fabric were partially filled. The coated fabric had a porosity of about 30-40 CFM/ft2, at 1/2 inch differential water pressure, substantially triangular openings having a base of about 0.5 mil and a height of about 1.0 mil, a thickness of about 42.0 mils, and a weight of about 30.5 oz/yd2.
When the coated fabric was tested for sound absorp-tion qualities in an AIMA No. 7 mounting, a NRC of .44 was obtained ~;
based on the following test results:
,' ~, '.
,~ . 2;~ 131~
.' ' O ' ~ .
5'~
." ' ' ' ~
. . . . . . _ . SOUND l~BSORPTION CO~FFICIE:NTS (c~) :' . ...
63 Hz 125 Hz250 Hz 500 Hz1000 Hz2000 Hz 4000 Hz 71 5044 .52 ~0 .41 44 ., .
EXAMPLE XVI
S Eight harness satin weave fabric, Burlington #1584, having a thickness of 25.5 mils and a ~eight of 25.15 oz/yd', with a yarn warp of 150 4/2 and a yarn filling o~ 150 4/2, woven to a warp and fill count of 42 x 35, was coated with polytet~afluoroethylene so that the openings in the ~abric ~:
10 were partially filled. The coated fabric had a porosity of . ~:
about 40 to 50 CFM/ft2, at 1/2 inch differential water pressure, ``
substantially triangular openings haviny a base of a~out 1.0 - mil and a height o~ about 3.0 mils~ a thickness of about 42.0 mils, and a weight of about 31.0 oz/yd2. .
When the coated ~abric was tested for sound absorption qualities in an AI~ No. 7 mounting, a NRC of .59 was obtained ~- based on the following test results.
.
_._ _ . .. _ _ . . . . .. . :, .
SOllND ABSORPTION COEFFICIENTS (a) . .. . _.. _ . . ' 63 Hz 125 Hz250 Hz 500 Hz1000 Hz2000 Hz4000 Hz .
. 94- --- ~ 62 55 65 ~ 53 57 .
r . . EX~PLE XVII
Plain weave glass fabric, Burlington ~1142, having a ~hickness of 10.0 mils and a wei~ht of 8.25 ozjyd2, with a yarn ~.
~21--~.
'5~
warp of 37 1/0 and a yarn filling of 37 1/0, woven to a warp and fill count of 32 x 21, was coated with polytetrafluoro-ethylene so that the openings in the fabric were partially filled. The coated fabric had a porosity of less than 10 CFM/ft , at 1/2 inch differential water pressure, a thickness of about 12.0 mils, and a weight of about 11.0 oz/yd2.
Microscopic examination reveals that the partially filled openings take on different shapes and sizes. For example, there a~e substantially round openings having a diameter of between 1.0 to 3.0 mils substantially elliptical openings having a minor axis of about 1.0 mil and a major axis of about 6.0 mils, and irregular star-shaped openings having a minor medial axis of about 1.0 mil and a major , . .
medial axis of about 6.0 mils.
When the coated fabric was tested for sound absorp- ;
tion qualities in an AIMA No. 7 mounting, a NRC of .67 ob-tained based on the following test results~
..... . '"
SOUND ABSORPTION COEFFICIENTS (~) . I l .. _ _ ._ 63 Hz ¦ 125 Hz ¦ 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz t ~ - ~~ ~-.56 1 .63 53 83 .67 17 _ .
~ review of the preceding examples indicates that better sound absorption qualities, i.e., NRC valves between '~
.30 and .66, are obtained when the porosity of the acoustic absorbers is about 60 CFM/ft2 or less. If the porosity in- ;
creases substantially above 60 CFM/ft , i.e., Examples VII
and XII, th~ sound absorption qualities of the acoustic absorbers diminish.
It will be understood that the described embodiments are merely exemplary and that persons skilled in the art may ..
-22- ~
make many variations and modifications without departing from the spirlt and s~ope o~ the invention. For example, the sound absorbing properties of the acoustic absorber may be controlled by varying the thickness and weight of the acoustic absorber, as well as its porosity and weave characteristics. The acoustic absorber o~ the present invention may also be used for attenuat-ing sound in longltudinal sound paths (e.g., air conditioning ;
ducts, corridors, and exhaust pipes) by being spacedly positioned therein so that sound waves are attenuated as they propagate down the sound paths. All such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims~
,. , . " ,. '~ " . '.
.
.
- .
.. ' ..,' . . ,.~ r . ~
. . ~ , ' ;
'." " ' ~ ~
~3--, -, . :
To use the invention in dropped ceiling installations, a piece of acoustic absorbing fabric is mounted on a frame;
designed to.fit between two pairs of brackets which usually.
form a 2~ x 2' or 2' x 4' receptacle. Because it is moisture~
proof, the acoustic absorbing fabric will not rot or mildew like ~he conventional acoustic ceiling tiles normally used in dropped ceiling installations. This also permits it to be ` spray-cleaned or washed with a liquid. Inasmuch as the fabric. .
is fire.resistant, it can be used safely in industrial kitchens and other areas where flames are exposed.
The following examples further illustrate the invention. To facilitate consideration and discussion of the exam~les, it should be explained that for a particular frequency band the sound absorption coefficient of a surface is, aside from the effects of diffraction, the fraction Of randomly incident sound energy absorbed or othen~ise not reflected, measured in sabins per square foot. The noise reduction coefficient ~NRC) can be calculated by averaging the sound absorption coefficients at 250, 500, 1000 and 2000 Hz, expressed to the nearest integral multiple of .05. An Acoustical and Insulating Materials Association (AIMA) No. 7 mounting positions the face of the test specimen 16 inches above the reverberation room floor. The , sides of the mounting are enclosed with plywood so that sound can be transmitted only through the test specimen into the air space behind it.
~ , ' ~:
. . . . . : , ~2~73~
5~ .
~ ~.XAMPLE I
Plain weave glass fabric, Burlington #116, having a thickness of 3.5 mils and a weight of 3.20 oz/yd2, with a yarn warp of 450 1/2 and a yarn filling of 450 1/2, woven to a warp and fill count of 60 x 58, was coated with polytetrafluoroethylene so that the openings in the fabric were partially filIed. The . coated fabric had a porosity of about 7 to 14 CFM/ft2, at 1/2 inch di~ferential water pressure, a thickness of about 4.Q mils, :~
and a weight of about 4.0 oz/yd2.
Microscopic examination reveals that the partially ~illed openings take on different shapes and sizes. For example, there are substantially round openings having a diameter of between O.S to 1.5 mils, substantially ellipti~al .
openings having a minor axis of about 0.5 mil and a major axis of about 1.5 mils, and irregular s-tar~shapea openings having a minor medial axis of about 0.5 mil and a ma~or medial axis of about 1.5 mils.
~hen the coated fabric was tested for sound absorption ::
gualities in an AIMA No. 7 mounting, a NRC of .30 was obtained . 20 based on the ~ollowing test results:
I . . ....... , .' . SOUND ABSORPTION COEFFICIENTS () _ _ . ,:
63 Hz 125 Hz 250 Hz 500 Hz 1000 Hz 2000 }lz 4000 H2 _ . _ _ _ 01 13 26 .32 48 .J~ .
EXAI~PLE II
.
Plain weave glass fabric, Burlington #116, having a thickness of 3. 5 mils and a weight of 3. 20 02~yd~, with a yarn 22473~
'. .
~ - ~0~ 5'~ ~
warp o~ ~50 1/2 ancl a yarn ~illing o 450 1/2, woven to a warp .
and fill count of 60 x 58, was coated with polytetrafluoroethylene . so that the openlngs in the fabric werè partially filled. The coated fabric had a porosity o~ about 24 to 35 CFM/~t2, at 1/2 inch differential water pressure, a thickness of about 4.0 mils, and a ~7eight o about 4.0 oz/yd2.
Microscopic examination reveals -that the partially filled openings take on different shapes and sizesO For example, there are substantially round openings having a io diameter of between Q.5 and 3.0 mils, substantially elliptical - ~ .
openings having a minor axis of about 0.5 mil and a major axis of about 3.0 mils, and irregular star-shaped openings having . a minor medial axis of about 0.5 mil and a major medial axis of about ~.0 mils. . :
When the coated ~abric was tested for sound absorption qualities in an AI~ No. 7 mounting, a NRC of .33 waC obtained .~ based on the following test results:
_ ' SOUND ABSORPTION COEFFICIENTS (a) . ' , . 63 Hz125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz :;~
. _ ~_ ~' ~
= .18 .34 27 .41 . EXAMPLE III
. .
Plain weave glass fabric, Burlington #125, having a thickness of 5.0 mils and a wei~ht of 3.75 oz/ydZ, with a yarn warp of 450 2/2 and a.yarn filling of 450 2/2, woven to a warp and fill count of 36 x 34, was coated with polytetrafluoroethylene so that the openings in the fabric were partially filled. The . . . . ~:
, _9_ .
22~73A
36~ 7 .
coated fabric had a porosity of about 15 to ~0 CFM/ft2, at 1/2 in,ch differential water pressure,, a thickness of about 6.0 to 7.0 mils, and a weight of about 5"i5 oz/yd2.
Microscopic examination reveals that the partially filled openings take on different shapes and sizes. For example, there are substantially round openings having a diameter of about 1.0 mil, substantially elliptical openings having a minor axis of about 1.0 mil and a major axis of about 10.0 mils, irreguiar star~shaped openings having a minor medial axis of about 1.0 mil and a major medial axis of about 10.0 mils, and generally rectangular openings having a width of about 1.0 mil and a length o~ about 10.0 mils.
When the coated fabric was tested for sound absorption qualities in an AIM~ No. 7 mounting, a NRC of .45 was obtained ~5 based,on the following test results:
. ,. .. ~ . ...
SOUND ABSORPTION COEFFICIENTS (a~
.... .. ~ . .. _ ...... _ ~ ~
63 Hz 125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz ...... _ ... _ . . .. _: .. _ :' .16 .22 .38 .44 .48 .50 , ' EXAMPLE IV
.. ... _ . . .
' Plain weave glass fahric;, Burlington #125, having a thickness of 5.0 mils and a weight'of 3.75 oz/yd2, with yarn warp of 450 2/2 and a yarn filling of 450 2/2, woven to a warp and fill count of 36 x 34, was coated with polytetrafluoroethylene so that the openings in the fabric were partially filled. The coated fabric had a porosity of about 30 to 60 CFM/ft2, at l~2 inch di~fer~ntial water pressure, a thickness of about 5.8 mils, - and a weight of about 4.9 oz/yd~.
, .
~l3~
: ' Microscopic examination reveals that the partially filled openings take on diffexent shapes and sizes. For example, there are substantially round openings having a diameter of about 1.5 m.ils, substantially elliptical openings 5 having a minor axis of about 1.5 mils and a major axis of about -10.0 mils, irregular star-shaped openings having a minor medial axis of about 1.5 mils and a major medial axis of a~out lO.0 mils,.
and generally rectangular openings having a width of about 1.5 ~ -mils and a length of about lO.0 mils~
h7hen the coated fakric was tested for sound absorption .
qualities in an AIMA No. 7 mounting, a NRC of .38 was obtained based on the following test results: --.~ . ..
~ ..
. . SOUND ABSORPTION CGEFFICIENTS (a) .
. 63 Hz ¦ 125 HZl ~5 ~ Zl 500 ~ 1000 Hz ¦ 2000 Hz ~ H~
lS -I .l7 L 39 1 .24 1 ~46 L .42 ~ .46 '.
. EXAMPLE V . ~ ;
Plain weave glass fabric, ~urlington ~128, having a thickness of 6.5 mils and a weight of 6.00 oz/yd2~ with a yarn - warp of 225 i/3 and a yarn filling of 225 l/3, woven to a warp .
and fill count of 42 x 32, was coated with polytetrafluoroethylene . so that the openings in the fabric were partially filled. The coated fabric had a porosity of about lS to l9 CFM/ft2, at l/2 inch differential water pressure, a thickness oE about 7.5 mils, and a weight of about 7.2 oz/yd2.
Microscopic examination reveals that the partially filled openings take on differ~nt sha~es and sizes~ For example, . . . . . . .
. - - , ~. .. . . .
.
~ 22473A
~ 6~
there are substantially round openinqs having a diameter of about 1.0 mils, su~stantially elliptical openings having a minor axis of about 2.0 mils and a major axis of about 5.0 .
mils, irregular star-shaped openings having a minor medial 5 axis of about 2.0 mils and a major medial axis o about 5.0 ;
mils, and generally rectangular openings having a width of about 2.0 mils and a length o~ about 5.0 mils.
- When the coated fabric was tested for sound absorption qualities in an AIMA No. ~ mounting, a NRC of .51 was obtained based on the following test resuits:
~
. . ~ .
SOUND ABSO.~PTION COEFFICIENTS (a) __ . .. . ., 63 Hz 125 Hz 250 H2 500 Hz 10~0 Hz 20D0 Hz 4000 Hz .. .. _. .'........ , :. ................. ...
.lq 16 __ 41 59 .58 .51 . --EXAMPLE VI .
Plain weave glass fabric, Burlington ~128, having a --thickness of 6.5 mils and a weight of 6.00 oz/yd2, with a yarn ~:
warp of 225 1/3 and a yarn filling of 225 1/3, woven to a warp.
and fill count of 42 x 32, was coated with polytetrafluoroethylene so that the openings in the fabric were partially filled. The coated fabric had a porosity of about 20 to 40 CFM/ft2, at 1/2 . inch differential water pressure, a thickness of about 7.5 mils, and a weight of about 7.2 oz/yd2.
Microscopic examination reveals that the partially ~`.
filled openings take o~ different sl~apes and sizes. For example, there are substantially round openings haYing a diameter of about 2.0 mils, substantially elliptical openings having a minor axis , . . . ~
"., l~ Z~
:~ of about 2.0 mils and a major axis of about 10.0 mils, irregular ~ star-shaped openings having a minor medial axis of about 2.0 mils .- and a .major medial axis of about 10.0 mils, and generally rectangular openings having a width of about 2.0 mils and a length of about 10.0 mils.
When the coated fabric was tested for sound absorption qualities in an AIMA No. 7 mounting, a NRC of .42 was obtained based on the following test results: .
.. _. . ..
- SOUND ABSORPTION CûEFFICIENTS (c~) -63 Hz ¦ 125 Hz ¦ 250 Hz ~ 500 Hz ~ 1000 Hz ¦ 2000 Ha ¦ 4000 Hz . . . . . .__ .' _ .. __ 42 33 ` -. .36 47 ,. , - . ' ' ' .: ' . EXAMPLE VII
: . Plain weave giass fabric, Burlington ~128, having a . thickness of.6.5 mils and a weight of 6.00 oz/yd2, with a yar~
; lS warp of 225 1/3 and a yarn filling of 225 /3, woven to a warp and fill count of 42 x 32, was coated-with polytetrafluoroethylene .so that the openings in the fabric were partially filled. The . coa~ed fabric had a porosity of about 60 to 80 CFM/ft2, at 1~2 inch differential water pressure, a thickness of about 7.5 mils, and a weight of abaut 7.2 oz/yd2.
Microscopic examination reveals that the partially filled openings take on different shapes and sizes. For example, there are substantially round openings having a diameter of about 2.0 mils, substantially elliptical openings having a minor axis o about 2.0 mils and a major axis of about 10.0 mils, irregular star-shaped openings having a minor medial axis of about 2.0 mils ,. : , ' ;, ~. . ' . , , - . . . .
:
and a major medial axis of about 10.0 mils, and generally rectangularopeningShaving a width of about 2.0 mils and a ' length of about 10.0 mils.
, :
When the coated fabric was tested for sound absorp-tion qualities in an AIMA No. 7 mounting, a NRC of .26 was obtained based on the following test results:
:;~ SOUND ABSORPTION COEFFICIENTS (a) 63 Hz ~ 125 Hz j 25~ ~ = z C D 1 2000 Hz 000 21 ~ 23 1 .21 1 .28 1 2 ~ .28 1 24 ;
EXAMPLE VIII
- Plain weave glass fabric, Burlington #1528, having a "
thickness of 6.5 mils and a weight of 5.95 oz/yd2, with a yarn warp of 150 1/2 and a yarn filling of 150 1/2, woven to a warp and fill count of 42 x 32, was coated with polytetrafluoro-ethylene so that the openings in the fabric were partially .:;
filled. The coated fabric had a porosity of about 8 to 11 ` 2 CFM/ft , at 1/2 inch differential water pressure, a thickness of about 7.5 mils, and a weight of about 7.2 oz/yd2.
Microscopic examination reveals that the partially filled openings take on different shapes and sizes. For example, there are substantially round openings having a diameter of ;~ ~
about 0.5 mil, substantially elliptical openings having a !'' minor axis of about 0.5 mil and a major axis of about 3.0 mils, irregular star-shaped openings having a minor medial axis of , about 0.5 mil and a major medial axis of about 3.0 mils, and ` generally rectangular openings having a width of about 0.5 mil and a length of about 3.0 mils.
~
~,;,''' .~" ' .
"; ~.
~ 3 . ~ .
When the coated fabric was tested for sound absorption qualities in an AIMA No. 7 mounting, a NRC of .45 was obtained based on the foilowing test results: ~
.
. . .
- SOUND ABSORPTION COEFFICIENTS (a) : . __ _ _ ._ ~. ._ .
563 ~Iz125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz . . _ _ :~
68 26 .42 33 . 50 1 53 .SS
:- , . '' ' - EXAMPLE IX
Plain weave glass fabric, Burlington #1142, having a `:
thickness of 10.0 mils and a weight of B.25 oz/yd2, with a yarn ; io warp.of 37 1/0 and a yarn filling of 37 1/0, woven to a warp and fill coun-t of 32 x 21, was coated with polytetrafluoroethylene so that the openings in the ~abric were partially filled. The coated .
fabric had a porosity of about 15 to 20 CFM/ft2, at 1/2 inch differential water pressure, a thickness of about 10.5 mils, and a weight of about 9.5 oz~yd2.
Microscopic examination reveals that the partially illed openings take on different shapes and sizes. For example, there are substantially round openings having a diameter of about 2.0 mils, substantially elliptical openings having a minor axis of about 2.0 mils and a major axis of about 15.0 mils, irregular star-shaped openings having a minor meaial axis of about 2.0 mils and a major medial axis of about 15.0 mils, and generally rectangular openings having a width of about 2.0 mils and a length of about 15.0 mils~
When the coated fabric was tested for sound absorption qualities in an AIMA No. 7 mounting, a NRC of .66 was obtained bas~d on the following test resul.ts: . :
.
;~ ,- . .. . ..
; - . , . . : . .::
.: ' ~" . ' . : : ' . ,- . . , .
~ 1 22473A
~06~'7 ; ~ .
SOUND ABSO~?~PTION COEFFICI~NTS (a) ,-: _ . 63 Hz 125 Hz 250 Hæ S00 Hz1000 Hz~000 Hz 4000 Hz , ~ ' . :~
` .60 .~9 .54 . .70 .72 .75 .' . . .
- . EXAMPI,E X
. . . . .
5 . Plain weave qlass fabric, Burlington #141, having a thickness of 11.0 mils and a weight of 8.80 oz/yd2, with a yarn warp of 225 3t2 and a yarn filling of ~25 3/2, woven to a warp and fill count of 32 x 21, was coated with polytetrafluoroethylene so - that the openings in the fabric were partially fllled. The co.ated fabric had a porosity of about 20 to 40 CFM/ft2, at 1/2 inch . . differential water pressure, a thickness of about 12.5 mils, and a weight of about ll.S oz/yd~.
Microscopic examination reveals that the partially filled openings take on different shapes and sizes~ For example, ~ 15 there are substantially round openings having a diameter of about 2.0 mils, substanti-ally elliptical openings having a minor axi~
of àbout 2.0 mils and a major axis of about 15.0 mils, irregular star-shaped openings having a minor medial axis of about 2.0 `.
. mils and a major medial axis of abou~ 15.0 mils, and generally xectangular openings having a width of about 2.0 mils and a length of about 15.0 milsO
: When the coated fabxic was tested for sound absorption `.
qualities in an ~IMA No. 7 mounting, a NRC of .66 was obtained based on the following test results: :;
', ~16-., , ' ` ~ .
22~73A
:' ' ~' ~' ', '. .
' ` ' ~0~2~t7.. . .
. . ... __ ..
.~ . SOUNr) ABSORPTION COEFFICII~NTS (a) .~ 63 Hz ¦ 125 Hz ¦ 250 Hz ¦ 500 ~Iz ¦ 1000 ~Iz ¦ 2000 ~Iz ¦ 4000 Hz _ . ~. .. ._ 83- ~4 1 73 ,53 .70 66 65 ~:~
EXAMPLE XI
~.
Plain weave glass fabric, Burlington ~141, having a.
thickness of 11.0 mils and a weight of 8.80 oz/yd2, with a yarn arp of 225 3/2 and a yarn filling of 225 3/2, woven to a warp and fill count of 32 x 21, was coated with polytetrafluoroethylene .~ so that ~he openings in the ~abric were partially fillQd. The coated fabric had a porosity of about 40 to 60 CFM/ft2, at 1/2 inch diffe1ential water pressure, a thickness of about 12.5 mils~
and a weight of about 10.8 oz/yd2.
Microscopic examination reveals that the partially filled openings take on different shapes and sizes. For example, :.
there are substantially round openings having a diameter of about 2.0 mils, substantially elliptical openings having a minor axis of about 2.0 mils and a major axis of about 20~0 mils, irregular star-shaped openings having a minor medial axis of about.2.0 mils and a major medial axis of about 20.0 mils, and generally rectan-`20 gul~r openings having a width of about 2.0 mils and a length of about 20.0 mils. ;
When the coated fabric was tested for sound absorption :
gualities in an AIMA No. 7 mounting, a NRC of ,52 was obtained .:~
based on the follow:ing.test results: -~
..
.
' , ' ' , '~
. . .
g ~ ~ .
~
~16'~ t7 :
. SOUND ~SORPTION CO~FFICXENTS (a) _ _ __ . ~
. 63 Hz 125 Hz 250 Hz 500 ~Iz 1000 Hz 2000 ~Iz ~000 Hz .
.35 .38 .73 .~2 .48 ~6 .4~
' FXAMPLE XII
Plain weave glass fabric, Burlington ~141, having a thickness of 11.0 mils and a weight of 8.80 oz/yd2, with a yarn warp of 225 3/2 and a yarn filling of 225 3/2, wo~en to a warp and fill count of 32 x 21, was coated with polytetrafluoroethylene . so that the o~enings in the fabric were partially filled. The L0 coated fabric had a porosity of about 80 to 110 CFM~ft2, at 1/2 - inch differential water pressure, a thickness of about 12.5 mils, .and a weight of about 10.0 oz/yd2.
.
Microscopic.examination reveals that the partially illed openings take on different shapes and sizes. For example, 15 there are substantially round openings having a ~iameter o . ,~
about 2.0 mils, substantially elliptical openings having a minor axis of about 2.0 mils and a major axis of about 20.0 mils, irregular star-shaped openings having a minor medial axis.of ... : -about.2.0 mils and a major medial axis of about 20.0 mils, and ~enerally rectangular openings having a width of ~bout 2.0 mils and a length of about 20.0 milsL
When the coated fabric was tested for sound absorption ~ualities in an AIM~ No. 7 mounting, a NRC of ~27 was obtained based on the fo1lowing test results:
. ' .
. , ' : ' -lB~ - :
2 24 7 3~
~L~36~Z~7 ' . ' . . .
SOUND ~BSORPTION COEFFICI13NTS ~) 63 Hz ¦ 125 Hz ¦ 250 Hz 1500 Hz ¦ 1000 Hz ¦ 2000 Hz ¦ 4000 H~
10 1 .23 1 .36 1.26 1 .18 ~ .26 1 .28 ' EXAMPLE XIII
Eight harness satin weave glass fabric, Burlington.
: ~183, having a thickness of 6 . 0 mils and a w~ight of 16.75 oæ/yd2, with a yarn warp of 225 3/2 and a yarn filling of 225 3/2, woven ~o a warp and fill count of 54 x 48, was coated with ; polytetrafluoroethylene so that the openings in the fabric were partially filleda The coated fabric had a .porosity of .. . . . . .
about 15 CFM/ft2, at 1/2 inch differential water pressure~
substantially round open1ngs having a diameter o~ about ; 2,0 ~o 5.0 mils, a thickness of about 25.0 mils, and a . weight of about 20. 5 oz/yd2.
When the coated fabric was tested for sound absorption . qualities in an AIMA No. 7 mounting, a~ NRC of .54 was obtained .based on the following test results: .
, - . .
. SOI~ND ABSORPTION COEFFICIENTS (a) - .
.
.63 }Iz ~25 N~250 Hz ¦ 500 Hz ¦ 1000 Hz ¦ 2000 Hæ ¦ 4000 Hz ' 20 .73 5851 1 .54 1 .51 1 .61 1 .~4 ,''. . . .
E~A~IPLE XIV
Eight harness satin weave glass ~abric, Burlington ~183, havi.ng a thickness of 6Ømils and a weight of 16.75 ~z/yd2, - .
.. ~. -, : .
2~so3 :
with a yarn warp of 225 3/2 and a yarn filling of 225 3/2,woven to a warp and fill count of 54 x 48, was coated with polytetrafluoroethylene so that the openings in the fabric were partially filled. The coated fabric had a porosity of about 30 CFM/ft , at l/2~inch aifferential water pressure, substantially round openings having a diamet~r of about 2.0 to 5.0 mils, a thickness of about 25.0 mils, and a weight of about 20.0 oz/yd .
When the coated fabric was tested for sound absorption qualities in an AIMA No. 7 mounting, a NRC of .59 was obtained based on the following test results:
SOUND ABSORPTION COEFFICIENTS (~) .. _ . _l l 63 Hz 125 Hz 250 Hz500 Hz 1000 Hz 2000 Hz 4000 Hz --._ _ . _ ._ . . : .
_.40 .41 58 58_ 55 .65 59 EXAMPLE XV `~ ;
Eight harness satin weave glass fabric, Burlington, #1584, having a thickness of 25.5 mils and a weight of 25.15 oz/yd2, with a yarn warp of 150 4/2 and a yarn filling of 150 4/2~ woven to a warp and fill count of 42 x 35, was coated with polytetrafluoroethylene so that openings in the fabric were partially filled. The coated fabric had a porosity of about 30-40 CFM/ft2, at 1/2 inch differential water pressure, substantially triangular openings having a base of about 0.5 mil and a height of about 1.0 mil, a thickness of about 42.0 mils, and a weight of about 30.5 oz/yd2.
When the coated fabric was tested for sound absorp-tion qualities in an AIMA No. 7 mounting, a NRC of .44 was obtained ~;
based on the following test results:
,' ~, '.
,~ . 2;~ 131~
.' ' O ' ~ .
5'~
." ' ' ' ~
. . . . . . _ . SOUND l~BSORPTION CO~FFICIE:NTS (c~) :' . ...
63 Hz 125 Hz250 Hz 500 Hz1000 Hz2000 Hz 4000 Hz 71 5044 .52 ~0 .41 44 ., .
EXAMPLE XVI
S Eight harness satin weave fabric, Burlington #1584, having a thickness of 25.5 mils and a ~eight of 25.15 oz/yd', with a yarn warp of 150 4/2 and a yarn filling o~ 150 4/2, woven to a warp and fill count of 42 x 35, was coated with polytet~afluoroethylene so that the openings in the ~abric ~:
10 were partially filled. The coated fabric had a porosity of . ~:
about 40 to 50 CFM/ft2, at 1/2 inch differential water pressure, ``
substantially triangular openings haviny a base of a~out 1.0 - mil and a height o~ about 3.0 mils~ a thickness of about 42.0 mils, and a weight of about 31.0 oz/yd2. .
When the coated ~abric was tested for sound absorption qualities in an AI~ No. 7 mounting, a NRC of .59 was obtained ~- based on the following test results.
.
_._ _ . .. _ _ . . . . .. . :, .
SOllND ABSORPTION COEFFICIENTS (a) . .. . _.. _ . . ' 63 Hz 125 Hz250 Hz 500 Hz1000 Hz2000 Hz4000 Hz .
. 94- --- ~ 62 55 65 ~ 53 57 .
r . . EX~PLE XVII
Plain weave glass fabric, Burlington ~1142, having a ~hickness of 10.0 mils and a wei~ht of 8.25 ozjyd2, with a yarn ~.
~21--~.
'5~
warp of 37 1/0 and a yarn filling of 37 1/0, woven to a warp and fill count of 32 x 21, was coated with polytetrafluoro-ethylene so that the openings in the fabric were partially filled. The coated fabric had a porosity of less than 10 CFM/ft , at 1/2 inch differential water pressure, a thickness of about 12.0 mils, and a weight of about 11.0 oz/yd2.
Microscopic examination reveals that the partially filled openings take on different shapes and sizes. For example, there a~e substantially round openings having a diameter of between 1.0 to 3.0 mils substantially elliptical openings having a minor axis of about 1.0 mil and a major axis of about 6.0 mils, and irregular star-shaped openings having a minor medial axis of about 1.0 mil and a major , . .
medial axis of about 6.0 mils.
When the coated fabric was tested for sound absorp- ;
tion qualities in an AIMA No. 7 mounting, a NRC of .67 ob-tained based on the following test results~
..... . '"
SOUND ABSORPTION COEFFICIENTS (~) . I l .. _ _ ._ 63 Hz ¦ 125 Hz ¦ 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz t ~ - ~~ ~-.56 1 .63 53 83 .67 17 _ .
~ review of the preceding examples indicates that better sound absorption qualities, i.e., NRC valves between '~
.30 and .66, are obtained when the porosity of the acoustic absorbers is about 60 CFM/ft2 or less. If the porosity in- ;
creases substantially above 60 CFM/ft , i.e., Examples VII
and XII, th~ sound absorption qualities of the acoustic absorbers diminish.
It will be understood that the described embodiments are merely exemplary and that persons skilled in the art may ..
-22- ~
make many variations and modifications without departing from the spirlt and s~ope o~ the invention. For example, the sound absorbing properties of the acoustic absorber may be controlled by varying the thickness and weight of the acoustic absorber, as well as its porosity and weave characteristics. The acoustic absorber o~ the present invention may also be used for attenuat-ing sound in longltudinal sound paths (e.g., air conditioning ;
ducts, corridors, and exhaust pipes) by being spacedly positioned therein so that sound waves are attenuated as they propagate down the sound paths. All such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims~
,. , . " ,. '~ " . '.
.
.
- .
.. ' ..,' . . ,.~ r . ~
. . ~ , ' ;
'." " ' ~ ~
~3--, -, . :
Claims (11)
1. In an acoustic absorber, including a porous substrate, having a multiplicity of openings extending through the substrate, and an organic polymer applied to the substrate, the improvement wherein the organic polymer completely covers the surfaces of the substrate on both sides thereof and partially fills at least some of the openings extending through the substrate in such a manner that the acoustic absorber has a porosity not substantially greater than 60 CFM/ft2, at 1/2 inch differential water pressure; and wherein the acoustic absorber is flexible.
2. An acoustic absorber according to Claim 1, wherein the substrate is a woven fiberglass fabric.
3. An acoustic absorber according to Claim 1, wherein a majority of the openings have a cross-dimension substantially less than 2 mils.
4. An acoustic absorber according to Claim 1, 2 or 3, wherein the acoustic absorber has a weight not substantially less than 4 oz/yd2 and not substantially greater than 31 oz/yd2.
5. An acoustic absorber according to Claim 1, 2 or 3, wherein the acoustic absorber has a thickness not substantially less than 4 mils and not substantially greater than 42 mils.
6. An acoustic absorber according to Claim 1, 2 or 3, wherein the openings in the acoustic absorber are randomly sized.
7. An acoustic absorber according to Claim 1, 2 or 3, wherein the organic polymer coating is a fluorinated organic polymer.
8. An acoustic absorber according to Claim 1, 2 or 3, wherein the organic polymer coating is a fluorinated organic polymer selected from the group consisting of polytetrafluoro-ethylene, fluorinated ethylene-propylene polymers, perfluoroalkoxy and polyvinylidene-fluoride.
9. An acoustic absorber according to Claim 1, 2 or 3, wherein the organic polymer coating is a vinyl polymer.
10. An acoustic absorber, comprising a multiplicity of individual strands of fiberglass woven together to form a porous, glass fabric substrate; and a fluorinated organic polymer coating adhering to and completely covering each individual strand and partially filling openings in the substrate, the acoustic absorber having a porosity not substantially greater than 60 CFM/ft2, at 1/2 inch differential water pressure, a flexibility capable of absorbing sound waves of relatively low frequencies by mechanical dissipation caused when relatively low frequency sound waves force the acoustic absorber into vibrating motion and numerous randomly sized and shaped openings capable of absorbing sound waves of relatively high frequencies by viscous friction caused when relatively high frequency sound waves pass through the openings, whereby acoustic energy may be absorbed over a wide range of frequencies.
11. A method for absorbing sound waves in a structure, comprising positioning a flexible acoustic absorber including a porous substrate, having a multiplicity of openings extending through the substrate, and an organic polymer coating applied to and covering both sides of the substrate and partially filling at least some of the openings extending through the substrate in such a manner that the acoustic absorber has a porosity not substantially greater than 60 CFM/ft2, at 1/2 inch differential water pressure, the acoustic absorber being adjacent and spaced from a surface of the structure a distance sufficient to permit sound waves to pass through the acoustic absorber.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US62779975A | 1975-10-31 | 1975-10-31 | |
| US72735176A | 1976-09-28 | 1976-09-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1061257A true CA1061257A (en) | 1979-08-28 |
Family
ID=27090533
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA264,430A Expired CA1061257A (en) | 1975-10-31 | 1976-10-29 | Acoustic absorber and method for absorbing sound |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA1061257A (en) |
| DE (1) | DE2649802C2 (en) |
| GB (1) | GB1552922A (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2560253A1 (en) * | 1984-02-28 | 1985-08-30 | Holder Philippe | Acoustic and thermal insulation element in particular for a construction panel. |
| US4832147A (en) * | 1987-06-19 | 1989-05-23 | E. I. Dupont De Nemours And Company | Sound reduction membrane |
| DE4126884B4 (en) * | 1991-08-14 | 2004-09-30 | Perstorp Häussling GmbH | Soundproofing molded part and process for its production |
| US7566475B2 (en) | 2004-11-09 | 2009-07-28 | International Automotive Components Group North America, Inc. | Acoustic insulator with controlled airflow resistance and method of making same |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1031961B (en) * | 1956-09-03 | 1958-06-12 | Gen Aniline & Film Corp | Laminates made from fibrous glass materials |
| DE1118543B (en) * | 1960-08-25 | 1961-11-30 | Telefunken Patent | Damping material for mechanical or acoustic vibrations or shocks |
| GB1242864A (en) * | 1968-05-15 | 1971-08-18 | Dunlop Holdings Ltd | Acoustical elements |
| FR2147352A5 (en) * | 1971-07-23 | 1973-03-09 | Saint Gobain |
-
1976
- 1976-10-28 GB GB4495976A patent/GB1552922A/en not_active Expired
- 1976-10-29 CA CA264,430A patent/CA1061257A/en not_active Expired
- 1976-10-29 DE DE19762649802 patent/DE2649802C2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE2649802C2 (en) | 1986-08-21 |
| GB1552922A (en) | 1979-09-19 |
| DE2649802A1 (en) | 1977-05-05 |
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