A noise absorbing ventilation air inlet or outlet conduit

The invention relates to a ventilation air inlet or outlet for use in an outside wall and comprising means for absorbing outside noise.

It is well known to provide damping for airborne noise in conduits for ventilation purposes. A suitable length of conduit may be provided with absorbing structures on the inside ("padding"), with the intention that the flow shall be hindered as little as possible while the absorption of both high and low frequencies is high. Such conduits are very efficient due to their length, which is typically in the range 0.5-3 m, the longer the better. There is, however an application, in which it is not possible to use the required length. This relates to exhaust of air from inside a building to the outside through the wall. Traffic noise from the outside, which in a busy street may have an average of 70 db(A), will penetrate into the room with only a minimal damping when traditional "padded" conduits are used. This is primarily due to the short length, considerably less than 0.5 meter. The use of a serpentine structure, to increase the length, unfortunately would increase the area of the wall involved in the exhaust, and this is not a solution.

According to the invention, it has become possible to obtain a satisfactory damping of traffic noise even in a short conduit, in that it consists of a generally rectilinear conduit of a length corresponding to the thickness of the wall, in that it comprises a first sound absorbing structure on a part of the inside surface at the outer end of the conduit, and a second sound absorbing structure on a part of the inside surface at the inner end of the conduit.

In an advantageous embodiment at least one further sound absorbing structure is placed inside the conduit between said first and said second sound absorbing structures.

In a further advantageous embodiment said part of the inside surface of the outer end of the conduit is the downwards-facing inside surface and that said part of the inside surface of the inner end of the conduit is the upwards-facing inside surface.

In a further advantageous embodiment at least one of the sound absorbing structures has a delimiting surface placed in such a way that less than half of the free conduit area is occupied by the at least one sound absorbing structure. This means that there is a clear view through the conduit with an opening, the height of which being defined by the distances of the two delimiting surfaces from the centre line of the conduit.

While it may be advantageous to give the conduit an inclination to shield the opening from raindrops or the like and/or to give the delimiting surface an angle to the axis of the conduit, one embodiment is particular in that said delimiting surface is horizontal.

In a further advantageous embodiment there is a space of full conduit dimensions between the first and second sound absorbing structures. This has been demonstrated to increase the traffic noise absorption with respect to a construction without such a space or chamber.

In a practical manner of realizing the invention, the sound absorbing elements are fitted to an axial stick with indentations defining discrete lengths of the space.

A further practical manner of realizing the invention is particular in that the conduit has an essentially circular cross section. This will permit an angling of the free surfaces of the sound absorbing material by rotating it on the axis of the cylinder created by this cross section.

By providing the cylindrical conduit with at least one longitudinal ridge-like structure rotation of elements pushed into said conduit may be prevented, because said elements engage said at least one longitudinal ridge-like structure.

In an advantageous use of the invention said space is adjusted during installation of the conduit. This adjustment may be obtained by using a sound absorbing structure of a suitable axial extent or by pushing such a structure back and forth in the conduit until a suitable position has been reached.

A further advantageous use of a noise absorbing ventilation air inlet or outlet according to the invention is particular in that the sound absorbing elements are fitted to an axial stick with indentations, the length of the space being adjusted outside of the conduit, whereupon the assembly of stick and sound absorbing elements is pushed axially into the conduit, and the stick shortened to correspond to the thickness of the wall.

It has been realized that the sound absorbing conduit of the present invention may function with several kinds of cross section, including trapezoidal sections, however one advantageous embodiment is particular in that the conduit has an essentially circular cross section.

It is considered that one of the parameters contributing to the noise absorbing characteristics of the present invention may be that traffic noise reaches an outside wall predominantly from below, and its reflection in the conduit is reduced by the sound absorbing structure on the upper inside surface of the conduit, while its re- radiation from the ceiling inside the building is also reduced, because there is a sound absorbing structure on the lower inside surface of the part of conduit inside the building.

The invention will be further described with reference to the drawings, in which

Fig. 1 shows a side view of a conduit with sound absorbing structures according to the invention,

Fig. 2 shows the two ends of the conduit according to an embodiment of the invention,

Fig. 3 shows a side view of the same embodiment of the invention,

Fig. 4 shows a side view according to a further embodiment of the invention,

Fig. 5 shows a skeleton perspective view from the outside of the building,

Fig. 6 shows the general disposition of a ventilation inlet or outlet conduit with further sound absorbing elements between at near the ends, and

Fig. 7 show elements permitting an adjustment of the space between the sound absorbing structures.

In Fig. 1 is shown a schematic representation of a conduit 1, with two sound absorbing structures 2 and 3 near the respective ends of the conduit. At the outside of the wall the sound absorbing structure 2 is disposed so that it faces downwards, and at the inside wall the sound absorbing structure 3 faces upwards.

In Fig. 2 is shown the views from outside and inside respectively, and the sound absorbing structures 2 and 3 are shown in a circular conduit.

In Fig. 3 is shown a schematic representation of a different embodiment of the invention, in that there is shown a horizontal distance h between the delimiting planes 4 and 5 of the sound absorbing structures.

In Fig. 4 is shown a schematic representation of yet a different embodiment of the invention, in that there is a space 1 inside the conduit between the two sound absorbing structures 2 and 3. This space 1 may be varied by varying the horizontal distance between the inside ends of the respective sound absorbing structures. Either one or both of the structures may be shifted axially, or the axial extent of one or both of the sound absorbing structures is adjusted during installation.

In Fig. 5 is shown a perspective sketch of a conduit 1 with sound absorbing structures 2 and 3, from the outside.The horizontal distance h between the delimiting planes 4 and 5 is shown.

In Fig. 6 is shown the general disposition of the two end sound absorbing structures 2 and 3 inside the otherwise smooth conduit 1 , with further sound absorbing structures A placed in between. Again, here there is a possibility to adjust the spaces or chambers between the structures, and the heights of the structures may also be adjusted as described in conjunction with the description of Fig. 3.

In Fig. 7 several features are shown. First of all, the essentially cylindrical conduit 1 has ridges R formed as shown at a), which is uncomplicated if the conduit is obtained by extrusion in a polymer material. The ridges R are engaged by grippers G that hold the sound absorbing structures 2 and 3 as shown at b). The grippers G are mounted on the stick S that has indentations or waists W that permit a snap fit of the grippers G at pre-defined axial distances. In use, the conduit 1 is placed in a hole through the wall (not shown), the two sound absorbing structures 2 and 3 are fitted in the desired relationship and with the distance between them defining the chamber 1 decided by snapping onto the stick S. The whole stick is pushed into the conduit 1, whereby the ridges R engage the grippers G to prevent relative rotation, and the outermost sound absorbing structure is placed essentially flush with the mouth of the conduit 1. It will be understood that the view in b) is from the outside. Finally, the stick is cut off, and covers, rain guards, and (on the inside) a diffusor are fitted to the surrounding wall.

It should be noted that many of the advantages of the present invention may also be obtained with a conduit of other than circular cross section.

Summing up, the invention relates to an air inlet or outlet in an outside wall. This type of conduit permits traffic noise to enter the room it is connected to. Traditional noise-damping conduits are not suitable for prevention of this. According to the invention at least two plugs of sound material displaying a cross section that fills part of the conduit are applied at least at each of the outside and the inside ends of the conduit. A further improvement in performance may be obtained by suitably choosing the orientation of the at least two plugs of sound absorbing material, so that it is opposite near the outwards-facing opening and the inwards- facing openings of the conduit.

The invention has been described in some detail above, but this is not limiting per se, as the skilled person will be able to devise additional mechanical solutions that perform in an equivalent manner, thereby obtaining similar advantageous results.

The foregoing description of the specific embodiments will so fully reveal the general nature of the present invention that others skilled in the art can, by applying current knowledge, readily modify or adapt for various applications such specific embodiments without undue experimentation and without departing from the generic concept, and therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. The means, materials, and steps for carrying out various disclosed functions may take a variety of forms without departing from the invention.

Thus, the expressions "means to ... " and "means for ...", or any method step language, as may be found in the specification above and/or in the claims below, followed by a functional statement, are intended to define and cover whatever structural, physical, chemical, or electrical element or structure, or whatever method step, which may now or in the future exist which carries out the recited functions, whether or not precisely equivalent to the embodiment or embodiments disclosed in the specification above, i.e., other means or steps for carrying out the same function can be used; and it is intended that such expressions be given their broadest interpretation.