GB2514824A

GB2514824A - Sound attenuator with irregular array of internal ducts

Info

Publication number: GB2514824A
Application number: GB1310082.1A
Authority: GB
Inventors: Russell Wheeler
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-06-06
Filing date: 2013-06-06
Publication date: 2014-12-10
Also published as: WO2014195729A3; WO2014195729A2; GB201310082D0

Abstract

A sound attenuator 1 comprises a fluid inlet 3 and a fluid outlet 4 disposed along a main axis 10 of the attenuator. A plurality of fluid transmission ducts 6, 7, 12, 13, 14 extend between the inlet and outlet and are surrounded by sound absorbing material 9. The ducts are disposed relative to the main axis whereby the separation between at least one pair of adjacent ducts is different to the separation between one or more other pair(s) of adjacent ducts. Each duct has an axis 11 that may or may not be parallel with the main axis and each other duct. Each duct may be positioned a radial distance from the main axis whereby the radial distance between at least one duct and the main axis may be different to the other ducts. A housing 2 may contain the ducts and sound absorbing material and may be cylindrical with a circular, rectangular or square cross-section. The housing may have frusto-conical ends 3, 4 and a distal flange 5 connects the attenuator to fluid transfer apparatus such as ventilation systems. In another embodiment in cross-section the ducts are disposed symmetrically to the main axis.

Description

SOUND ATTENUATOR WITH IRREGULAR ARRAY

OF INTERNAL DUCTS

The present invention relates to sound attenuators for use in fluid transfer apparatuses, such as ventilation systems for example.

It is desirable to attenuate the sound that is transmitted through fluid transfer apparatuses, such as might be used for example in a vehicle exhaust, tunnel and car park ventilation systems, or a high velocity air terminal/discharge. It is also desirable to maintain low resistance to airflow through fluid transfer apparatuses. Generally, an increase in the sound attenuation provided by an attenuator is accompanied by an increase in the resistance to airflow of the attenuator, and a balance or compromise between these conflicting requirements is desirable.

Typically, known sound attenuators may comprise a cylindrical housing having an inner coaxial duct for the passage of fluid. Sound absorbing material may be disposed in the interstitial region around the inner duct.

The present invention provides a sound attenuator comprising a fluid inlet and a fluid outlet disposed along a main axis. A plurality of fluid transmission ducts can extend between the fluid inlet and outlet, the fluid transmission ducts each having a duct axis. The ducts can be surrounded by a sound-absorbing material.

The duets may be disposed at respective positions relative to the main axis, whereby the separation between at least two adjacent ducts is different to the separation between others of the ducts. By virtue of the invention, regions of different thickness of sound-absorbing material can be provided within the sound attenuator, thus increasing the range of frequencies that are absorbed by the attenuator and improving the effectiveness of the attenuator. Further, embodiments of the invention provide an increased "acoustic length" and thus greater sound absorption compared to previous attenuators. The duct axes can be parallel to the main axis.

Each duct axis can bc positioned at a respective radial distance from the main axis and the radial distance between at least one duct and the main axis can be different to the radial distance between the other ducts and the main axis.

Further, the radial distance between all of the ducts and the main axis can be different. Also, instead of or in addition to varying the radial distance of the duets from the main axis, an angle (0) between radial lines joining the duet axes of adjacent ducts to the main axis can be different for at least one pair of adjacent ducts than it is for other pairs of adjacent ducts.

The fluid transmission duets and the sound-absorbing material may be contained in a housing. The housing may have a circular cross-section or alternatively a rectangular or square cross-section, or indeed any other appropriate shape.

In accordance with the present invention there is also provided a fluid transfer apparatus comprising one or more sound attenuators as defined above and preferably comprising at least first and second sound attenuators. The first and second attenuators can be mounted in series along the main axis and rotationally offset with respect to each other about the axis. Advantageously, a dircct acoustic line of sight through the fluid transfcr apparatus can thereby bc reduced or eliminated, further enhancing the sound attenuation provided by the apparatus.

The present invention also provides a sound attenuator comprising a fluid inlet and a fluid outlet disposed along a main axis. A plurality of fluid transmission ducts extend between the fluid inlet and outlet. The fluid transmission ducts are surrounded by a sound-absorbing material. The duets are disposed at respective positions relative to the main axis, whereby when viewed in cross-section, the ducts are disposed symmetrically with reference to the main axis.

Advantageously, such symmetrical embodiments of the sound attenuator can be mounted in series with one another and rotationally offset with respect to each other about the main axis, and provide an accurate and simple means of adjustment of the balance between sound attenuation and airflow resistance.

The present invention can be put into practice in various ways, but embodiments will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a cross-sectional schematic view of a sound attenuator embodying the present invention; Figure 2 is a sidc vicw of thc sound attcnuator shown in Figure 1; Figure 3 is a schematic end view of the sound attenuator shown in Figure 1; Figure 4 shows a guide plate for use in the sound attenuator shown in Figure 1; Figure 5 is a cross-sectional view of a rectangular sound attenuator in accordance with a second embodiment of the invention; Figure 6 is cross-sectional schematic view showing a superimposed pair of sound attenuators mounted in series in accordance with a further embodiment of the invention; Figure 7 is a cross-sectional schematic view of a sound attenuator in accordance with a further embodiment of the invention; Figure 8 is a cross-sectional schematic view of the sound attenuator shown in Figure 7; and Figure 9 is a cross-sectional schematic view of a further embodiment of the sound attenuator.

The sound attenuator 1 shown in Figure 1 comprises a housing 2 which has a cylindrical form and is circular in cross-section. The housing 2 has an inlet and an outlet in the form of frusto-conical end sections 3, 4 each of which includes a distal flange 5 for connection to pipes of a fluid transfer apparatus (not shown), such as a ventilation system.

Inside the main body of the housing 2 is disposed a series of fluid transmission duets 6, 7, 12, 13, 14 (not all the ducts are shown in Figure 1). Each duet comprises a tube having walls made from materials such as plastics or metals.

The attenuator has a main axis 10, and each duct has a duct axis 11. The main axis 10 runs centrally and longitudinally along the attenuator I, and the duet axes 11 run centrally and longitudinally along each duet. The duct axes 11 are parallel to the main axis 10 and parallel to one another in the embodiment shown, but in other embodiments, the duct axes 11 can be non-parallel to the main axis 10 and each other. Sound-absorbing material 9 is disposed in the space between the ducts. Preferably, the sound-absorbing material fills the spaces between the ducts. Thus, the separation of the closest points of adjacent ducts is equal to the thickness of sound-absorbing material between those points. If the ducts are parallel, the thickness of sound-absorbing material is constant along the length of the attenuator. If the ducts are non-parallel, the thickness of sound-absorbing material varies along the length of the attenuator.

The attenuator includes one or more guide plates 8, shown in Figure 4. The guide plate 8 includes a number of holes 9 which receive end portions of the ducts and hold them in place. The position of the holes 9 thus determines the arrangement of the duets. A second guide plate (not shown) is provided at the opposite end of the housing 2 to the first guide plate. The sound absorbing material 9 is provided in the interstitial spaces defined between the ducts and the guide plates and the housing 2.

As shown in Figure 2, the housing 2 comprises a tubular main body which is formed from sheet metaL Referring to Figure 3, the separation between a first pair of adjacent ducts is shown as x. At least one other pair of adjacent duets is separated by a distance not equal to x. In some instances there can be other duets which are equally spaced, or all of the ducts may be spaced differently. In one embodiment, a minimum of three ducts are provided. In another embodiment, five ducts are provided.

Thc angular scparation about the main axis 10 bctwcen a pair of ducts numbered 6 and 7 in Figure 3 is 01 and the angular separation between another pair of ducts numbered 7 and 12 isO-,. In the embodiment shown, 0, > O, and more generally the angular separation varies. Likewise, some or all ofthe other pairs of duets may have different angular separations.

The radial distance ij between one of the ducts 14 and the main axis 10 is greater than the radial distance r, between the adjacent duct 13 and the main axis. Likewise, some or all of the other ducts can have different separations from the main axis.

Figure 5 shows a sound attenuator 50 that has a rectangular cross-section. In this embodiment, nine fluid transmission ducts 51 to 59 are dispersed through the attenuator.

A pair of co-axially and serially mounted circular cross-section attenuators is shown in Figure 6. A first attenuator 60 comprises five duets 61 to 65, and a second attenuator 66 comprises a further five ducts 71 to 75, the ducts of both attenuators being arranged in an irregular array, such that there are variations in the distances between the duets. The attenuators can be connected to one another by a small connection pipe, or alternatively can be directly connected to each other by the housing end portions 3, 4. A small rotational offset of approximately 30 degrees is applied between the first and second attenuators 60, 66 such that most of the overlap between the ducts is removed.

In other words, there is virtually no line of sight acoustic transmission path through the joined pair of attenuators. The angle of offset between the two (or more) attenuators can be chosen to give differing balances of acoustic performance and resistance to airflow.

When using the rectangular form of attenuator, further units can be installed at 0 or 180 degrees to the first attenuator. When using a squarc form attenuator, further units can be installed at 0, 90, 180 or 270 degrees to the first unit.

Various types of symmetry can be incorporated in the structure of the duets.

For example, when viewed in cross-section, the duets may be symmetrical with respect to reflection about a plane passing though the main axis or may be symmetrical with respect to rotation between 0 and 180 degrees about the main axis. When multiple such attenuators are combined in series, the symmetrical configuration of ducts advantageously allows specific alignments of the ducts to be achieved. In the example shown in Figure 7, the sound attenuator 76 has five ducts 77, 78, 79, 80, 81, including four ducts 77, 78, 79, 80 equidistantly distributed around the periphery of the attenuator and a central duct 81 located coaxially with the main axis. The ducts are symmetrical with respect to rotation of 90 degrees about the main axis 10.

Figure 9 shows an attenuator that is symmetrical with respect to rotation about the main axis of 180 degrees. A first pair of adjacent ducts 91, 92 is positioned towards an opposite side of the attenuator to a second pair of adjacent ducts 93, 94. In operation, two such attenuators can be mounted co-axially and serially, and if their ducts are aligned (ie zero rotational offset), a minimum sound attenuation and minimum airflow resistance is provided. The two attenuators can alternatively be rotationally offset by 90 degrees, giving the lowest level of alignment between the ducts and the highest level of sound attenuation and resistance to airflow. Any angle of offset between 0 and 90 degrees can be chosen to provide a suitable balance.

In use, a fluid such as air flows into the sound attenuator I through the inlet 3 and arrives at the guide plate 8. The guide plate directs the flow of air into the ducts and as the air travels through the ducts, some of its acoustic energy is transmitted through the ducts into the sound-absorbing material 9. The air then passes through the second guide plate and out of the outlet 4 with a reduced noise-level. Where, multiple attenuators arc mounted in series, the reduction in noise-level is corrcspondingly improved.

Claims

SC I AIMS1. A sound attenuator comprising a fluid inlet and a fluid outlet disposed along a main axis, and a plurality of fluid transmission ducts extending between the fluid inlet and outlet, the fluid transmission ducts being surrounded by a sound-absorbing material, and the duets being disposed at respective positions relative to the main axis, whereby the separation between at least one pair of adjacent ducts is different to the separation between one or more other pairs of adjacent duets.
2. A sound attcnuator according to claim 1, whcrcin thc ducts cach have a duct axis and the duct axes are parallel to the main axis.
3. A sound attenuator according to claim I or 2, wherein each duct is positioned at a respective radial distance from the main axis and the radial distance between at least one duct and the main axis is different to the radial distance between the other ducts and the main axis.
4. A sound attenuator according to claim 3, wherein the radial distance bctwccn cach duct and thc main axis is different.
5. A sound attenuator according to any of claims I to 4, wherein an angle () between radial lines joining the duct axes of adjacent ducts to the main axis is different for at least one pair of adjacent ducts than it is for one or more other adjacent pairs of ducts.
6. A sound attenuator according to any of claims 1 to 5, further comprising a housing containing the fluid transmission ducts and the sound-absorbing material.
7. A sound attenuator according to claim 6, wherein the housing has a circular cross-section.
8. A sound attenuator according to claim 6, wherein the housing has a rectangular or square cross-section.
9. A sound attenuator according to any of claims 6 to 8, wherein the housing comprises a frusto-conical end section, including a distal flange for engagement with a pipe.
10. A sound attenuator according to any of claims 6 to 9, further including at least one guide plate for determining the positions of the fluid transmission ducts.
11. A sound attenuator according to any of the preceding claims, comprising three or more fluid transmission ducts.
12. A sound attenuator according to any of the preceding claims, comprising five or more fluid transmission ducts.
13. A sound attenuator according to any of the preceding claims, wherein the fluid transmission ducts arc symmetrical with respect to rotation about the main axis by an angle of 90 or 180 dcgrccs
14. A sound attenuator according to any of the preceding claims, wherein the fluid transmission ducts are symmetrical with respect to reflection in a plane containing the main axis.
15. A sound attenuator comprising a fluid inlet and a fluid outlet disposed along a main axis, and a plurality of fluid transmission ducts extending between the fluid inlet and outlet, the fluid transmission ducts being surrounded by a sound-absorbing material, and the ducts being disposed at respective positions relative to the main axis, whereby when viewed in cross-section, the ducts are disposed symmetrically with reference to the main axis.
16. A sound attenuator according to claim 15, wherein the fluid transmission ducts are symmetrical with respect to rotation about the main axis by an angie of between 0 and 180 degrees.
17. A sound attenuator according to claim 15 or 16, wherein the fluid transmission ducts are symmetrical with respect to reflection in a plane containing the main axis.
18. A fluid transfer apparatus comprising one or more sound attenuators according to any of the preccding claims.
19. A fluid transfer apparatus according to claim 18, comprising first and second sound attenuators.
20. A fluid transfer apparatus according to claim 19, wherein the first and second attenuators are mounted in series along the main axis and rotationally offset with respect to each other about the axis.