A SILENCING VENTILATING DEVICE, IN PARTICULAR FOR A VENTILATING PASSAGE IN A WALL OR PARTITION

Abstract: A silencing ventilating device, in particular for a ventilating passage in a wall or partition, and comprising a tubular casing (11) and at least one tubular inner pipe (12) having at least one opening in its wall constituting a communication between a continuous ventilating passage (15) and an enclosed space (14) formed by transverse baffles (17) extending from the inner pipe (12) and/or the casing (11). The total area of passage of the opening(s), depending on the volume of the enclosed space, is tuned, in the manner of a Helmholtz resonator to a given frequency to be damped. Said enclosed space (14), consequently, may have a circular or an annular cross section. A plurality of enclosed spaces may be provided by employing at least two inner pipes and/or by installing further transverse baffles.

Description: The invention relates to a silencing ventilating device for a ventilating passage in a wall or partition, and comprising a tubular casing and at least one body situated inside said tubular casing leaving open at least one continuous ventilating passage inside said tubular casing, said body having at least one enclosed space and at least one opening in its wall constituting a communication between an enclosed space and an adjacent continuous ventilating passage, said enclosed space being tuned in the manner of a Helmholtz resonator to a given frequency to be damped. Such silencing ventilating devices are known from US-A-2 299 112. The body inside the tubular casing is composed of bars or plates forming a plurality of parallel, straight and elongated chambers or enclosed spaces of constant cross section debouching in a continuous ventilating passage. Said chambers or enclosed spaces are tuned in the manner of a Helmholtz resonator to a given frequency to be damped. Such a silencing ventilating device deadens noises or sounds of a relatively small definite frequency range and is used e.g. to repress motor or blower noises in ventilating ducts of an air conditioning system. In case noises with a large range of frequencies, e.g.. streetnoises, have to be repressed or deadened the silencing effect of said known device isn't satisfactory, as only a part of the noises is repressed or deadened, whereas the other part is transmitted nearly uninfluenced. Moreover, e.g. from the brochure Gebr. Trox GmbH "Silencers, silencing coulisses, sound; absorbing elements, series M.X.Z.", 1979, page No. 5-SD2, pages 1, 2, 16, 17, silencing ventilating devices are known based on the silencing effect of sound absorbing material filling up the enclosed space. For that reason, said material, at the location of the partition between the enclosed space and the continuous ventilating passage, is surrounded by a maximally porous envelope, e.g. a wall with a multiplicity of perforations therein or a glass fabric. In many cases, the damping to be obtained with these is insufficient in especially the lower frequency ranges. It is an object of the present invention to improve a silencing ventilating device of the type described in the first paragraph in such a manner that it has substantially enhanced silencing properties over a wide range of frequencies. This is achieved by a device according to claim 1. These features amplify the frequency range with only a slight weakening of the silencing effect. By combining the Helmholtz resonator and the sound absorbing material a more effective silencing effect is obtained than is possible with silencing ventilating devices of the prior art. In cases where damping is desired in more than one frequency range, it is possible with a silencing ventilating device in which the inner pipe is shut off at its ends by transverse end baffles and each of said enclosed spaces has a different volume. In a silencing ventilating device wherein enclosed spaces are created by means of transverse baffles between the casing and the inner pipe, the same effect can be obtained when each of said enclosed spaces has a different volume. By combining several of the proposed features, the number of frequency ranges in which optimum damping according to the present invention can be obtained, can be increased still further when, in a silencing ventilating device in which at least two inner pipes of different diameter are provided and the innermost inner pipe is shut off at its ends by transverse end baffles, and further transverse end baffles are provided between the casing and the adjacent inner pipe, according to a further embodiment of the present invention, there is provided in a number of enclosed spaces of different volume. In this manner, it is possible to arrange Helmholtz resonators having different frequency ranges within the innermost inner pipe and between the casing and the outermost inner pipe. Highly important for obtaining the desired silencing effect is that the total area of passage to an enclosed space is given the desired size. This can be realized in a comparatively simple but highly accurate manner when, according to still a further embodiment of the present invention an opening in the wall is formed by a saw cut. Depending on the required area of passage, one or a plurality of saw cuts of accurately determined length and width, and hence having a total area of passage that can be determined exactly, can be provided within an inner pipe otherwise having a closed cylindrical circumferential surface. Some embodiments of the silencing ventilating device according to the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a longitudinal section of an embodiment having a seal between the inner pipe and the casing; and Fig. 2 is a longitudinal section of an embodiment having a sealed innermost inner pipe and a seal between the casing and an adjacent inner pipe. The silencing ventilating device shown in Fig. 1 comprises a casing 11 and an inner pipe 12. At the ends, there are provided between casing 11 and inner pipe 12 annular transverse baffles 13, thereby creating between the casing and the pipe a compartment 14 that is enclosed with respect to the surroundings. The internal passage of the inner pipe forms the free ventilating duct 15. Inner pipe 12 has holes in its wall in the form of saw cuts 16, forming an open connection between duct 15 and the compartment 14. The latter is divided into two enclosed spaces 14a, 14b by an annular transverse baffle 17, with the lengths and widths of the saw cuts 16 being chosen for each enclosed space in such a manner that two Helmholtz resonators are produced, each tuned to a different damping frequency range. In order to amplify this range, sound-absorbing material is provided in at least one of the enclosed spaces 14a, 14b. Fig. 2 shows a silencing ventilating device composed of a casing 21 and two inner pipes, the innermost being designated by reference numeral 22 and the outermost by 23. By means of transverse baffles 24 provided at the ends of inner pipe 22, there is created a compartment 25 which is subdivided into two enclosed spaces 25a, 25b by a further transverse baffle 26. Between casing 21 and inner pipe 23 there are disposed at the ends annular transverse baffles 27, thereby forming a compartment 28 which is subdivided into three enclosed spaces 28a, 28b, 28c by further annular transverse baffles 29, 30. Transverse baffles 24 and 27 leave the annular space between the two inner pipes 22, 23 clear, thereby creating a free ventilating passage 31. The latter is in open communication with the enclosed spaces 25a, 25b, 28a, 28b and 28c by means of saw cuts 32 in inner pipe 22 and saw cuts 33 in inner pipe 23. The lengths and widths of the various saw cuts 32, 33, in relation to the enclosed spaces to which they provide access, are chosen in such a manner that each enclosed space forms a Helmholtz resonator tuned to a different frequency. Here too, one or a plurality of enclosed spaces is at least partly filled with sound-absorbing material. Modifications are possible within the scope of the claims, for instance, the perforations may have any other form than that of a saw cut, which is preferred. The only important feature is that the total area thereof is tuned, in the manner of a Helmholtz resonator, to the volume of the enclosed space to which access is provided from a ventilating passage. Besides, starting from the embodiment shown in Fig. 2, the number of enclosed spaces can be increased by providing one or a plurality of pairs of additional inner pipes. Moreover, it is naturally possible, depending on the desired damping pattern, e.g. in the embodiment shown in Fig. 2, to provide one of the enclosed spaces with a known, porous circumferential wall. Furthermore, the design of the silencing ventilating device at the two ends has not been described herein. These may be provided in a known manner with mounting means, seepage covers, insect grids and shut off means. Although a circular cross section is preferred, any other form, in particular a square or rectangular form is also possible. Although the casing and inner pipe are shown herein as single-piece elements, it is also possible to compose these of sections, e.g. having the size of one enclosed space.

Claims: A silencing ventilating device for a ventilating passage in a wall or partition, and comprising a tubular casing (11; 21) and at least one body situated inside said tubular casing leaving open at least one continuous ventilating passage (15; 31) inside said tubular casing, said body having at least one enclosed space (14; 25, 28) and at least one opening (16; 32, 33) in its wall constituting a communication between an enclosed space and an adjacent continuous ventilating passage, said enclosed space being tuned in the manner of a Helmholtz resonator to a given frequency to be damped, characterized in that said body is formed of a tubular inner pipe (12; 22, 23) and transverse baffles (13, 17; 24, 26, 27, 29, 30) extending from the inner pipe or the tubular casing for forming an enclosed space, a plurality of enclosed spaces being present, at least one of said enclosed spaces being at least partly filled with sound absorbing material. A silencing ventilating device as claimed in claim 1, characterized in that the inner pipe (22) is shut off at its ends by transverse end baffles (24) and in that each of said enclosed spaces (25a, 25b) has a different volume. A silencing ventilating device as claimed in claim 1, characterized in that transverse end baffles (13; 27) are placed between the casing (11; 21) and the inner pipe (12; 23) and in that each of said enclosed spaces (14a, 14b; 28a, 28b, 28c) has a different volume. A silencing ventilating device as claimed in claim 1, characterized in that at least two inner pipes (22, 23) of different diameter are provided and the innermost inner pipe (22) is shut off at its ends by transverse end baffles (24), there being also provided transverse end baffles (27) between the casing (21) and the adjacent inner pipe (23), and in that the enclosed spaces (25a, 25b, 28a, 28b, 28c) are of different volume. A silencing ventilating device as claimed in any one of the preceding claims, characterized in that an opening in the wall is formed by a saw cut (6; 16; 32, 33).

Inventors: ZWAAN, ADRIANUS JACOBUS
Applicants: ZWAAN, ADRIANUS JACOBUS
Application year: 1987
Main classification: F24F13
IPC codes: F01N1, F24F13, G10K11