WO2002050812A1 - Systeme servant a amortir le son - Google Patents

Systeme servant a amortir le son Download PDF

Info

Publication number
WO2002050812A1
WO2002050812A1 PCT/SE2001/002794 SE0102794W WO0250812A1 WO 2002050812 A1 WO2002050812 A1 WO 2002050812A1 SE 0102794 W SE0102794 W SE 0102794W WO 0250812 A1 WO0250812 A1 WO 0250812A1
Authority
WO
WIPO (PCT)
Prior art keywords
sound
attenuation system
quarter
attenuators
sound attenuation
Prior art date
Application number
PCT/SE2001/002794
Other languages
English (en)
Inventor
Rune SVÄRD
Peter Löfgren
Tomas Nygren
Anders Daneryd
Mats ÅBOM
Claes-Göran Johansson
Mats Larsson
Original Assignee
ABB Fläkt AB
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 ABB Fläkt AB filed Critical ABB Fläkt AB
Priority to AU2002216537A priority Critical patent/AU2002216537A1/en
Publication of WO2002050812A1 publication Critical patent/WO2002050812A1/fr

Links

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
    • G10K11/172—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using resonance effects

Definitions

  • the present invention relates to a sound attenuation system comprising a fluid-carrying channel, in which sound from a sound source is transported.
  • the sound source comprises, for example, a fan, a pump, a compressor, a turbine, or a motor.
  • the invention relates to a sound attenua- tion system that comprises a plurality of reactive sound attenuators, the sound attenuation system being used, for example, in ventilation or exhaust gas plants, or plants in which sound is generated by the fluid flowing through the channel .
  • the present invention also relates to a method for attenuating sound in a fluid-carrying channel in which sound is transported.
  • the fact that the fluid becomes dense results in pressure maxima and the fact that the fluid becomes tenuous results in pressure minima.
  • a sound source is brought to 'sound in- a • channel carrying a f uid,- a -sound, field -arises , which is governed by the acoustic boundary conditions that characterize the channel.
  • the sound field is built up of particles that in certain positions move very vigorously whereas particles in other positions move very little, or are stationary. The positions where the particles are stationary, and where the relative fluid pressure is- high, are called nodes.
  • antinodes The positions where the velocity of the particles is high, and the relative fluid pressure is low, are called antinodes. For each sound frequency, a pattern arises that is dependent on the boundary conditions of the channel and on how strongly the sound at that specific frequency is generated by the sound source.
  • sound attenuators To attenuate sound progressing in a channel, it is known to utilize different types of sound attenuators. These are divided according to their physical modes of operation into three main groups: resistive, active and reactive sound attenuators .
  • the mode of operation of the resistive sound attenuators is based on the energy loss which occurs when the movement of the fluid particles is hindered because of the friction inside an absorbent material. This causes part of the sound energy to be transformed into heat that may be discharged.
  • An active obstacle in a channel that is, a channel through which sound to be attenuated progresses, is obtained by creating a sound that is in anti-phase to the sound in the channel, thus obtaining extinction of the sound.
  • the sound directed in the opposite direction is then created by a loudspeaker placed in the channel .
  • a reactive sound attenuator is a type of sound attenuator that does not really consume any energy but creates a maladjustment to the propagation of the sound.
  • Reactive sound attenuators substantially operate according to two principles and are divided into reflection sound attenuators and resonant sound attenuators.
  • Reflection sound attenuators comprise change of the cross—section area of the- channel, whereby a reflection wave propagates in a direction opposite to that of the sound propagation, resulting in a sound reduction.
  • a resonant sound attenuator may be said to introduce a frequency-dependent acoustic boundary condition that creates a re- flection wave that hinders the progressing sound.
  • a quarter- wave sound attenuator functions according to this mode of operation.
  • a quarter-wave sound attenuator usually comprises a closed tube connected to the channel and having a length corresponding to a quarter of a wavelength of the sound that is to be attenuated.
  • Resonant sound attenuators are used for absorption of preferably low frequencies.- They are efficient within a very limited frequency range only, since their resonance characteristic is very sharp. If the frequency of the sound generated by a sound source varies with time, the length of the resonant sound attenuator must be adjusted according to the changed frequency of the generated sound.
  • a quarter-wave sound attenuator to provide an attenuating effect is that its open end is suitably placed in the system so that a resonant movement is started. -This occurs in an efficient manner only when the open end is located at a point in the sound field where a pressure minimum, that is, an antinode, arises at the frequency concerned. Any change in the system, for example if a reflection attenuator is placed in a channel, results in an adjustment of the sound field in the system due to the change. It may therefore be difficult to determine a suitable position for a quarter-wave sound attenuator in a system.
  • a resonant sound attenuator has an area, Si, of substantially the same size as the inner cross-section area, S , of the channel, that is, when the ratio S ⁇ /S 2 « 1. If this open-end area, and hence S ⁇ /S 2 , is reduced, the sound-attenuating effect becomes smaller and narrower with respect to frequency. However, it is not only the available volume around a channel that limits the effect obtained.
  • the transverse dimension, that is, the diameter or width, of a quarter-wave sound attenuator should not be larger than a quarter-wavelength of the sound component, to which it is tuned, to be effective.
  • a Helmholtz resonator comprises a chamber that communicates with the channel by way of a narrow neck.
  • the fluid in the neck is influenced by disturbances in the channel.
  • a pressure from the outside displaces the fluid mass inwards in the neck, which increases the pressure in the chamber which thereby results in an outwardly-directed force on the fluid mass; at an external underpressure, the chamber volume will displace the fluid mass outwards in the neck in a corresponding manner.
  • the Helmholtz resonator In the same way as a mass suspended from a spring undergoes natural oscillations if the mass is displaced out of its position of equilibrium, the Helmholtz resonator will also have a natural frequency as a function of the dimensions of the neck ("the mass”) and the chamber ("the spring") . If the frequency of the sound wave corresponds to the natural frequency of the resonator, the fluid mass in the neck will carry out resonant oscillations, which prevents the sound from passing through. If the frequency of the sound wave deviates from the natural frequency of the resonator, no practical effect will be obtained. Helmholtz resonators are therefore effective only within a very limited frequency range .
  • a resonant sound attenuator is a membrane absorbent consisting of an elastic layer that has been fixed at a certain distance from a wall .
  • the layer is influenced by disturbances in the channel. If the frequency of the sound wave corresponds to the natural frequency of the resonant sound attenuator, the layer will carry out resonant oscillations .
  • the characteristic resistance of the layer is chosen depending on the desired attenuation.
  • the layer has a resistive effect, whereby the sound energy is transformed into heat via friction losses at the membrane's points of attachment .
  • US 5,869,792 describes a sound attenuation system intended for low frequencies, comprising arrays of Helmholtz resonators mounted within a channel on opposing sides of the channel.
  • a sound attenuation system is described comprising reactive sound attenuators in combination with resistive sound attenuators containing absorbents to attenuate sound over a wider frequency range. Sound attenuators with absorbents are most effective at medium and high frequencies but less effective at low frequencies. To attenuate low-frequency sound that is characterized by long wavelengths, large absorbent thicknesses must be used.
  • absorbent material is that this material may degrade and contaminate the fluid flowing through the channel.
  • US 4,316,522 describes a sound attenuation system, in which reactive and resistive sound attenuators are placed within a channel .
  • the use of a sound attenuator within a channel entails a flow resistance and gives rise to a pressure drop in the system.
  • Sound attenuators containing large absorbent thicknesses mean that the sound attenuators become large and give rise to a considerable pressure drop within the channel.
  • a pressure drop implies that the device that drives the fluid through the channel consumes more energy to achieve the same fluid flow through the system.
  • the sound attenuators placed within a channel must therefore be designed in such a way that the pressure drop in the system is limited.
  • the object of the present invention is to provide a sound attenuation system and a method therefor that efficiently attenuate the sound in a channel over a wide frequency range without giving rise to a pressure drop in the system.
  • a sound attenuation system is provided with a plurality of quarter-wave sound attenuators that are arranged in at least one array.
  • the optimum theoretical length of a quarter-wave sound attenuator is a quarter of a wavelength.
  • the optimum length of a quarter-wave sound attenuator in fact is shorter than the length predicted by theory.
  • the cut-off frequency implies that, below the cut-off frequency, only plane waves exist that are attenuated rapidly with the distance along the channel, and above the cut-off frequency both plane waves and higher modes exist that propagate along the channel.
  • the cut-off frequency of a channel depends on the transverse dimension of the chan- nel and the velocity of the sound.
  • the length L 0 of the quarter-wave attenuator is adapted to be smaller than c/4f 0 .
  • the frequency to which the quarter-wave sound attenuators are tuned is greater than c/4L 0 .
  • the length of a quarter-wave sound attenuator would be up to 35 % shorter than the length L 0 .
  • the word 'quarter-wave sound attenuator' shall mean quarter-wave sound attenuators with a length corresponding to a quarter-wavelength of a sound component to be attenuated, or less .
  • the quarter-wave sound attenuators have an opening transverse dimension d and a length L, where the ratio d/L is less than 1. In another embodiment, the ratio d/L is less than 2/3. In yet another embodiment, the ratio d/L is less than 1/2. These values correspond to a maximum transverse dimension of the quarter-wave sound attenuators and to a quarter, a sixth and an eighth of a wavelength, respectively, of a component, that is to be attenuated, of the sound generated by the sound source.
  • the quarter-wave sound attenuators in an array are tuned to either the same frequency or to different frequencies. In another embodiment, each array is tuned to attenuate different tones in the sound.
  • the resonance characteristic of a quarter-wave sound attenua- tor is checked, for example, by arranging the openings of the quarter-wave sound attenuators with a thin resistive layer either across the openings or on the side walls of the quarter-wave sound attenuator at the openings .
  • the at least one array has a total area Si of all the quarter-wave sound attenuator openings included in the array.
  • Si corresponds to at least 50 % of the cross- section area, S 2 , of the channel, that is, S ⁇ /S 2 is equal to 0.5.
  • the ratio S ⁇ /S 2 is at least 0.8, preferably at least 0.9 and most preferably 1.0 or greater.
  • the quarter-wave sound attenuators are arranged either around the periphery of the channel or within the channel .
  • the quarter-wave sound attenuators are arranged, for example, perpendicular to the channel and have, for example, even sides with a uniform, rectangular, round, oval or hexagonal cross section.
  • the cross section of the channel is in the form of a polygon or comprises straight sides
  • at least two arrays of quarter-wave sound attenuators are placed on at least two adjacent or opposing sides of the channel.
  • the arrays are arranged either opposite to or adjacent to each other in the channel.
  • the quarter-wave sound attenuators are arranged around the whole periphery of the channel .
  • the said at least one array has an ex- tension in the direction of the channel corresponding to at least one-half of a wavelength of the frequency of a component of the sound generated by the sound source.
  • ex- tension in the direction of the channel corresponding to at least one-half of a wavelength of the frequency of a component of the sound generated by the sound source.
  • a reflection sound attenuator is arranged in the channel .
  • the reactive sound attenuators are adapted to have either a common movable end wall or individual movable end walls where the frequency of the sound generated by a sound source varies with time.
  • the end walls are arranged to be movable for adjusting the length of the chambers defined by the end wall.
  • the end walls are adjusted, for example, by means of a mechanical or servomechanical control system.
  • the end wall is mounted on slide rails, or slidably arranged against a sliding surface coated with a low-friction lining, or a roller table to reduce the friction between fixed and movable parts .
  • Figure 1 shows a sound attenuation system, according to an embodiment of the invention, comprising two arrays of quarter-wave sound attenuators placed on opposing sides of a rectangular channel,
  • Figure 2 shows a sound attenuation system, according to an embodiment of the invention, comprising two arrays of quarter-wave attenuators and one reflection sound attenuator,
  • Figure 3 shows a sound attenuation system, according to an embodiment of the invention, comprising two arrays of quarter-wave sound attenuators arranged on adjacent sides of a channel and with a thin resistive layer over the openings of the quarter-wave sound attenuators,
  • Figure 4 shows a sound attenuation system, according to an embodiment of the invention, comprising a configuration of adjustable quarter-wave sound attenuators provided with a common movable end wall, and
  • Figure 5 shows a sound attenuation system, according to an embodiment of the invention, comprising reactive sound attenuators arranged within a channel .
  • Figure 1 shows a sound attenuation system comprising a fluid- carrying channel with four sides 10, 11, 12, 13.
  • Two arrays 14, 15 of quarter-wave sound attenuators are arranged around the periphery of the channel on two opposing sides 11, 13.
  • the total opening area Si that is, the sum of the openings 16 of all of the quarter-wave sound attenuators included in the arrays, corresponds to at least 50 % of the cross-section area S 2 of the channel.
  • the extension of the arrays in the direction 17 of the channel corresponds to at least one-half of a wavelength of an undesired component of the sound travelling through the channel.
  • This configuration avoids the sensitive location that is required with a quarter-wave sound attenuator that has to be located at a point in the sound field where a pressure minimum arises in the sound component, that is, at an antinode, to provide an attenuating effect.
  • the reactive sound attenuators are formed from, or coated with, a material that is chemically resis- tant, for example a metal or a polymeric material.
  • a quarter-wave sound attenuator is provided with at least one hole to discharge accumulated moisture. The size of said at least one hole must be sufficiently small to have a minimal effect on the sound- attenuating capacity of the quarter-wave sound attenuator.
  • Figure 2 shows two arrays of quarter-wave sound attenuators 20, 21 arranged on two opposing sides of a rectangular channel 22.
  • a reflection sound attenuator 23 is arranged in the channel.
  • Figure 3 shows two arrays of quarter-wave sound attenuators 30 arranged on two adjacent sides of a channel 31.
  • the openings of the quarter-wave sound attenuators are provided with a thin resistive layer 32.
  • a thin resistive layer 32 achieves considerably better attenuation of both plane waves and higher modes.
  • This configuration of a sound attenuation system extends the attenuation to the intermediate- frequency range without giving rise to a pressure drop in the system and results in a wider resonance characteristic of the quarter-wave sound attenuators.
  • An additional advantage is that the use of absorbent material is avoided.
  • Figure 4 shows two arrays 40, 41 placed on opposing sides of a rectangular channel 43.
  • the quarter-wave sound attenuators of the arrays are provided with a common movable end wall 44 that comprises individual blocks 45 moving within a lattice 46, the fixed sides walls of which, together with the movable end wall 44, define chambers.
  • the individual blocks 45 have either the same dimensions, or each block has different dimensions depending on whether all the quarter-wave sound attenuators included in the array are tuned to the same fre- quency or to different frequencies.
  • the movable end wall 44 is mounted on slide rails to reduce the friction between fixed parts 46 and movable parts 44 in the system.
  • the movable end wall slides against a roller table.
  • the fixed parts 46 and/or the movable parts 44 are coated with a low- friction lining to reduce the friction between the adjacent fixed and movable parts of the sound attenuation system.
  • the reactive sound attenuators are adapted to have individually movable end walls .
  • Figure 5 shows four arrays of quarter-wave sound attenuators 50 arranged within a channel 51.
  • the total opening area of the openings 52 of all of the individual quarter-wave sound attenuators included in the array corresponds to at least 50% of the cross-section area, S 2 , of the channel.
  • the openings of the quarter-wave sound attenuators are provided with a thin resistive layer 53.
  • the thin resistive layer is arranged, for example, to cover the openings or arranged within the quarter-wave sound attenuators. This configuration pro- vides for more compact sound attenuators which are effective for attenuation of intermediate and high frequencies.

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Pipe Accessories (AREA)
  • Exhaust Silencers (AREA)
  • Soundproofing, Sound Blocking, And Sound Damping (AREA)

Abstract

Système servant à amortir le son et comprenant un conduit (31) dans lequel s'écoule un liquide et qui transporte le son provenant d'une source de son, ainsi qu'une pluralité d'atténuateurs de son de quart d'onde disposés en au moins un ensemble (30).
PCT/SE2001/002794 2000-12-14 2001-12-14 Systeme servant a amortir le son WO2002050812A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2002216537A AU2002216537A1 (en) 2000-12-14 2001-12-14 Sound-damping system

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE0004623-5 2000-12-14
SE0004623A SE0004623D0 (sv) 2000-12-14 2000-12-14 Ljuddämpningssystem

Publications (1)

Publication Number Publication Date
WO2002050812A1 true WO2002050812A1 (fr) 2002-06-27

Family

ID=20282224

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE2001/002794 WO2002050812A1 (fr) 2000-12-14 2001-12-14 Systeme servant a amortir le son

Country Status (3)

Country Link
AU (1) AU2002216537A1 (fr)
SE (1) SE0004623D0 (fr)
WO (1) WO2002050812A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005108696A1 (fr) * 2004-05-07 2005-11-17 Silenceair International Pty Limited Dispositif de ventilation et systeme d'ossature associe
WO2009111275A1 (fr) * 2008-03-03 2009-09-11 3M Innovative Properties Company Processus de gestion des fréquences acoustiques audibles dans les systèmes de circulation de gaz

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2283322A1 (fr) * 1974-08-30 1976-03-26 Gen Electric Panneau d'insonorisation pour canal d'ejection
US4316522A (en) * 1979-11-07 1982-02-23 Industrial Acoustics Company, Inc. Acoustic filter silencer
US4645032A (en) * 1985-09-05 1987-02-24 The Garrett Corporation Compact muffler apparatus and associated methods
US5276291A (en) * 1992-07-10 1994-01-04 Norris Thomas R Acoustic muffler for high volume fluid flow utilizing Heimholtz resonators with low flow resistance path
US5869792A (en) * 1995-12-04 1999-02-09 Vibron Limited Reactive acoustic silencer

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2283322A1 (fr) * 1974-08-30 1976-03-26 Gen Electric Panneau d'insonorisation pour canal d'ejection
US4316522A (en) * 1979-11-07 1982-02-23 Industrial Acoustics Company, Inc. Acoustic filter silencer
US4645032A (en) * 1985-09-05 1987-02-24 The Garrett Corporation Compact muffler apparatus and associated methods
US5276291A (en) * 1992-07-10 1994-01-04 Norris Thomas R Acoustic muffler for high volume fluid flow utilizing Heimholtz resonators with low flow resistance path
US5869792A (en) * 1995-12-04 1999-02-09 Vibron Limited Reactive acoustic silencer

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005108696A1 (fr) * 2004-05-07 2005-11-17 Silenceair International Pty Limited Dispositif de ventilation et systeme d'ossature associe
US8641494B2 (en) 2004-05-07 2014-02-04 Silenceair International Pty Limited Ventilation device and frame system
WO2009111275A1 (fr) * 2008-03-03 2009-09-11 3M Innovative Properties Company Processus de gestion des fréquences acoustiques audibles dans les systèmes de circulation de gaz
WO2009111276A1 (fr) * 2008-03-03 2009-09-11 3M Innovative Properties Company Processus de gestion des fréquences acoustiques audibles dans les systèmes de circulation de gaz

Also Published As

Publication number Publication date
AU2002216537A1 (en) 2002-07-01
SE0004623D0 (sv) 2000-12-14

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