GB2243187A - Sound attenuator - Google Patents

Sound attenuator Download PDF

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Publication number
GB2243187A
GB2243187A GB9006468A GB9006468A GB2243187A GB 2243187 A GB2243187 A GB 2243187A GB 9006468 A GB9006468 A GB 9006468A GB 9006468 A GB9006468 A GB 9006468A GB 2243187 A GB2243187 A GB 2243187A
Authority
GB
United Kingdom
Prior art keywords
sound
plate
duct
sound attenuator
absorbent material
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.)
Granted
Application number
GB9006468A
Other versions
GB2243187B (en
GB9006468D0 (en
Inventor
Alan Cummings
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
University of Hull
Original Assignee
University of Hull
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by University of Hull filed Critical University of Hull
Priority to GB9006468A priority Critical patent/GB2243187B/en
Publication of GB9006468D0 publication Critical patent/GB9006468D0/en
Publication of GB2243187A publication Critical patent/GB2243187A/en
Application granted granted Critical
Publication of GB2243187B publication Critical patent/GB2243187B/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N1/00—Silencing apparatus characterised by method of silencing
    • F01N1/003—Silencing apparatus characterised by method of silencing by using dead chambers communicating with gas flow passages
    • F01N1/006—Silencing apparatus characterised by method of silencing by using dead chambers communicating with gas flow passages comprising at least one perforated tube extending from inlet to outlet of the silencer
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N1/00—Silencing apparatus characterised by method of silencing
    • F01N1/02—Silencing apparatus characterised by method of silencing by using resonance
    • F01N1/023—Helmholtz resonators
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N1/00—Silencing apparatus characterised by method of silencing
    • F01N1/02—Silencing apparatus characterised by method of silencing by using resonance
    • F01N1/04—Silencing apparatus characterised by method of silencing by using resonance having sound-absorbing materials in resonance chambers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N1/00—Silencing apparatus characterised by method of silencing
    • F01N1/16—Silencing apparatus characterised by method of silencing by using movable parts
    • F01N1/22—Silencing apparatus characterised by method of silencing by using movable parts the parts being resilient walls
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
    • F16L55/00—Devices or appurtenances for use in, or in connection with, pipes or pipe systems
    • F16L55/02—Energy absorbers; Noise absorbers
    • F16L55/033—Noise absorbers
    • F16L55/0336—Noise absorbers by means of sound-absorbing materials
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F13/00—Details common to, or for air-conditioning, air-humidification, ventilation or use of air currents for screening
    • F24F13/24—Means for preventing or suppressing noise
    • 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
    • G10K11/172—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using resonance effects
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2490/00—Structure, disposition or shape of gas-chambers
    • F01N2490/15—Plurality of resonance or dead chambers

Landscapes

  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Soundproofing, Sound Blocking, And Sound Damping (AREA)

Abstract

One or more sides of a duct 1 comprise a layer 17, 18 of porous sound absorbent material on a thin metal plate 15, 16 which resonates at one frequency or at different frequencies along its length by tapering (Fig. 7). The plate may define a cavity 13, 14 containing air or sound absorbent material. <IMAGE>

Description

DESCRIPTION A SOUND ATTENUATOR The present invention relates to a sound attenuator and, more especially, to a sound attenuator for attenuating low frequency ductborne sound.
Conventional dissipative sound attenuators for use in air moving ducts comprise layers of a fibrous sound absorbing material, such as mineral wool or glass fibre, between which is defined an air flow passage. The absorbent layers are contained within a sheet metal outer casing. This type of sound attenuator has been found to be effective at mid to high frequencies, in the region of 500 to 2000 Hz, but is very inefficient at low frequencies, in the region of 50 to 200 Hz. Since the sound to be attenuated in an air moving duct is usually produced by a fan it has most of its energy at low frequencies and as a consequence the outlet noise from a conventional sound attenuator consists almost exclusively disturbing if it is transmitted to occupied building spaces.
It is an object of the present invention to provide a sound attenuator for effectively attenuating low frequency sound, and more especially for attenuating low frequency ductborne sound.
According to the present invention there is provided a sound attenuator comprising a layer of porous sound absorbent material positioned adjacent to a plate which exhibits a resonance effect within the range of frequency to be attenuated.
In use, the plate, which may or may not be of metal, exhibits a resonance effect at the frequency or frequencies to be attenuated whereby it vibrates in a direction transverse to the direction of sound propagation, in sympathy with the sound waves. The effect of this is to cause air within the pores of the sound absorbent material positioned adjacent to the plate to vibrate in a direction normal to the plate. The viscous drag forces on the air in the pores - which are largely responsible for the acoustic energy losses - are brought to bear in a particularly efficient manner on the sound to be attenuated, thereby enhancing the performance of the attenuator. At the lowest resonant frequency of the plate significant increases in attenuation over a frequency range of one octave can be achieved.
Advantageously, a cavity is provided behind the #Thoto This may be air filled or filled with a further A air filled zr pA layer of porous sound absorbent material.
In a preferred embodiment of the present invention the sound attenuator comprises a plurality of plates each tuned to a different resonant frequency. This allows the frequency range in which sound attenuation occurs to be broadened.
In another preferred embodiment of the present invention the sound attenuator comprises a tapered plate - that is to say the sides of the plate taper inwardly along the length of the plate. The effect of tapering the plate is to give a range of resonant frequency over the length of the plate, thereby broadening the range of frequencies at which sound attenuation occurs.
The resonant frequency of the sound attenuator according to the present invention is dependent upon a number of design parameters. These design parameters include the material of the plate, the thickness and width of the plate (at any given point along its length), and the thickness of the cavity (if any) behind the plate. As a consequence the range of frequencies at which sound attenuation occurs can be varied in a particularly versatile way.
Since the sound attenuator according to the present invention provides much improved sound attenuation, particularly at low frequencies, over conventional sound attenuators, the overall length of the sound attenuator required to achieve a given acoustic performance is much less than that of a conventional sound attenuator. This could also reduce the overall cost of the sound attenuator.
According to a further aspect of the present invention there is provided a duct in combination with a sound attenuator comprising a layer of porous sound absorbent material behind which is a plate which exhibits a resonance effect within the range of frequencies to be attenuated such that it vibrates in a direction transverse to the direction of propagation of sound waves in the duct.
Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a schematic perspective view of a duct incorporating a sound attenuator according to a first embodiment of the present invention; Fig. 2 shows a cross-section through the duct of Fig. 1; Fig. 3 shows a schematic perspective view of a duct incorporating a sound attenuator according to a second embodiment of the present invention; Fig. 4 shows a cross-section through the duct of Fig. 3; Fig. 5 shows a schematic perspective view of a duct incorporating a sound attenuator according to a third embodiment of the present invention Fig. 6 shows a cross-section through the duct of Fig. 5;; Fig. 7 shows a schematic perspective view of a duct incorporating a sound attenuator according to a fourth embodiment of the present invention, and Fig. 8 shows a cross-section through the duct of Fig. 7.
Referring to Figs. 1 and 2 of the accompanying drawings there is shown a rectangular duct which is defined by walls 1, 2, 3 and 4. One of these four walls, 4, is comprised of a thin flexible plate and is capable of vibrating or resonating in sympathy with the sound waves in the duct as shown by the upper and lower dotted lines 5 and 6. A layer of porous sound absorbent material 7 is provided within the duct and covers the flexible plate 4.
In use sound waves in the duct of the same frequency as the resonant frequency of the flexible plate 4 cause it to vibrate in a direction transverse to the direction of propagation of the sound waves in the duct. This, in turn, causes air contained within the pores of the sound absorbent material 7 to vibrate strongly at the same frequency and in a direction normal to the flexible plate 4. The viscous drag forces on the air in the pores absorb acoustic energy from the air in the duct and thereby attenuate sound waves at the resonant frequency of the flexible plate 4.
Referring now to Figs. 3 and 4 of the accompanying drawings there is shown an identical arrangement to that of Figs. 1 and 2, except that in this embodiment of the present invention a thin, flexible plate 8 is positioned in the duct itself such as to bisect the duct into an airway 9 and a cavity 10. A layer of porous sound absorbent material 11 covers the side of the flexible plate 8 defining the airway 9. The thickness of the cavity 10 determines the resonant frequency of the plate 8, otherwise, the operation of this embodiment of the present invention is identical to that of Figs. 1 and 2.
Referring now to Figs. 5 and 6 of the accompanying drawings there is shown a duct defined by walls 1, 2, 3 and 4. The inner space of the duct is divided into an airway 12 and two cavities 13 and 14 by thin flexible plates 15 and 16. A layer 17 and 18 of porous sound absorbent material covers each flexible plate 15 and 16 on the side thereof defining the airway 12 and each flexible plate is positioned at a respective distance from the immediately adjacent facing wall 2 and 4, of the duct. As the cavities 15 and 14 are of different thickness each flexible plate 15 and 16 is tuned to a different resonant frequency. Thus the range of frequencies at which attenuation occurs is broadened.
Referring finally to Figs. 7 and 8 of the accompanying drawings there is shown an arrangement similar to that of Figs. 3 and 4. In this respect the inner space of the duct is bisected by a thin flexible plate 19 into an airway 20 and a cavity 21, and the flexible plate 19 is covered on the airway side by a layer of porous sound absorbent material 22. However, in this embodiment of the present invention the flexible plate 19 is tapered along its length. The tapering of the flexible plate 19 gives rise to a range of different resonant frequencies over the length of the flexible plate 19, thereby broadening the range of frequencies at which attenuation occurs.
In order to further improve the sound attenuation properties of the embodiment of the sound attenuator according to the present invention described with reference to Figs. 3 and 4, 5 and 6, and 7 and 8 a second layer of porous sound absorbent material may be placed within the cavity behind each plate.

Claims (7)

1. A sound attenuator comprising a layer of porous #sound absorbent material positioned adjacent to a plate which exhibits a resonance effect at the frequency, or throughout the range of frequencies to be attenuated.
2. A sound attenuator according to claim 1, wherein the plate is comprised of metal.
3. A sound attenuator according to claim 1 or 2, wherein a cavity is provided behind the plate; which cavity is either air filled or filled with a further layer of porous sound absorbent material.
4. A sound attentuator according to claim 1, 2 or 3, comprising a plurality of plates each tuned to a different resonant frequency.
5. A sound attenuator according to claim 1, 2 or 3 wherein the sides of the said plate taper inwardly along the length of the plate.
6. A sound attenuator according to any preceeding claim in combination with an air moving duct wherein the or each plate forms a side of the duct and the porous sound absorbent material covers the side of the plate defining the duct airway.
7. A sound attenuator substantially as hereinbefore described with reference to the accompanying drawings.
GB9006468A 1990-03-22 1990-03-22 A sound attenuator Expired - Fee Related GB2243187B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB9006468A GB2243187B (en) 1990-03-22 1990-03-22 A sound attenuator

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB9006468A GB2243187B (en) 1990-03-22 1990-03-22 A sound attenuator

Publications (3)

Publication Number Publication Date
GB9006468D0 GB9006468D0 (en) 1990-05-23
GB2243187A true GB2243187A (en) 1991-10-23
GB2243187B GB2243187B (en) 1994-05-25

Family

ID=10673085

Family Applications (1)

Application Number Title Priority Date Filing Date
GB9006468A Expired - Fee Related GB2243187B (en) 1990-03-22 1990-03-22 A sound attenuator

Country Status (1)

Country Link
GB (1) GB2243187B (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0724110A1 (en) * 1995-01-24 1996-07-31 FILTERWERK MANN &amp; HUMMEL GMBH Noise damping pipe
US8272475B2 (en) 2008-04-30 2012-09-25 Metso Paper, Inc. Sound attenuator for low frequencies, method for manufacturing sound attenuator for low frequencies and system for attenuating low frequencies for example in air-conditioning ducts of paper mills

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB495755A (en) * 1937-03-16 1938-11-16 Abram Rupert Neelands Silencing equipment for air, heating, ventilating, and exhaust ducts, tunnels or the like, and sound treatment for rooms
GB496093A (en) * 1938-05-21 1938-11-24 Francois Cementation Co Ltd Improvements in apparatus for suppressing or reducing the propagation of sound in air
GB590540A (en) * 1943-06-08 1947-07-21 Arthur John King Improvements in sound-absorbent structures
GB614404A (en) * 1945-08-27 1948-12-15 Cementation Co Ltd Improvements in or relating to means for reducing the sound effect of the passage of air or other gases through conduits
GB2121475A (en) * 1982-05-12 1983-12-21 Messerschmitt Boelkow Blohm Element having resonators for silencing gaseous flow
GB2121911A (en) * 1982-05-12 1984-01-04 Messerschmitt Boelkow Blohm A sound-damping element having resonators
GB2170861A (en) * 1985-02-08 1986-08-13 Colchester Woods Air duct silencer splitter

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB495755A (en) * 1937-03-16 1938-11-16 Abram Rupert Neelands Silencing equipment for air, heating, ventilating, and exhaust ducts, tunnels or the like, and sound treatment for rooms
GB496093A (en) * 1938-05-21 1938-11-24 Francois Cementation Co Ltd Improvements in apparatus for suppressing or reducing the propagation of sound in air
GB590540A (en) * 1943-06-08 1947-07-21 Arthur John King Improvements in sound-absorbent structures
GB614404A (en) * 1945-08-27 1948-12-15 Cementation Co Ltd Improvements in or relating to means for reducing the sound effect of the passage of air or other gases through conduits
GB2121475A (en) * 1982-05-12 1983-12-21 Messerschmitt Boelkow Blohm Element having resonators for silencing gaseous flow
GB2121911A (en) * 1982-05-12 1984-01-04 Messerschmitt Boelkow Blohm A sound-damping element having resonators
GB2170861A (en) * 1985-02-08 1986-08-13 Colchester Woods Air duct silencer splitter

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0724110A1 (en) * 1995-01-24 1996-07-31 FILTERWERK MANN &amp; HUMMEL GMBH Noise damping pipe
US5722358A (en) * 1995-01-24 1998-03-03 Filterwerk Mann & Hummel Gmbh Tube with variable inside diameter
US8272475B2 (en) 2008-04-30 2012-09-25 Metso Paper, Inc. Sound attenuator for low frequencies, method for manufacturing sound attenuator for low frequencies and system for attenuating low frequencies for example in air-conditioning ducts of paper mills

Also Published As

Publication number Publication date
GB2243187B (en) 1994-05-25
GB9006468D0 (en) 1990-05-23

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Legal Events

Date Code Title Description
PCNP Patent ceased through non-payment of renewal fee

Effective date: 20030322