Apparatus for reducing sound nuisance and for diluting undesirable substances

The invention relates to an apparatus for reducing sound nuisance, wherein the apparatus is placed between a sound source (2) and a location (3) where the sound is not wanted. The invention also relates to an apparatus for dissi- pating fog and to an apparatus for diluting undesirable substances .

Apparatuses as mentioned in the preamble are known. For example, along motorways where they come close to residential areas, acoustic baffles are often provided between the sound source and the appartments to be protected against the sound nuisance. These acoustic baffles are comprised of concrete or metal walls, which are usually positioned on an embankment. These baffles are positioned along a motorway, between the road and, for example, a residential area there- behind. Their purpose is to absorb or reflect the sound. In many cases these baffles have to be higher than the residential area that needs to be protected against the sound.

The drawback of these baffles is that they require strong and costly constructions. In addition, they obstruct the view and generally have a negative effect on the scenery. Although there are also transparent acoustic baffles, these baffles are expensive and will become dirty or besmirched with graffiti and the like. Moreover, the existing acoustic baffles are less effective against sound nuisance to homes near airports caused by, for example, aircraft landing or taking off.

The German patent application DE 10049884 describes an apparatus for the protection against environmental disturbance and pollution, in particular against sound generated by a sound source. The sound source is at least partly surrounded by an air mat or air wall using compressed air or other compressed gasses. A drawback attached to this is however the high energy consumption and the costs associated with this.

It is an object of the present invention to provide an apparatus for the dissipation of sound as mentioned in the preamble, whose installation is relatively simple and which does not, or to a much lesser extent, obstruct the view and which is considerably more effective compared with apparatuses according to the prior art. It is also an object of the invention to provide an apparatus for reducing the sound nuisance for homes located near runways for aircraft taking off or landing. These objectives are achieved by an apparatus according to claim 1.

By means of the generated air curtain the sound is deflected away from the location where the sound is not wanted. In order for the deflection of the sound providing sufficient sound reduction, the angle of the air curtain (5) in relation to the horizontal plane should be between 45° and 90°, preferably approximately 90°. If the angle is approximately 90°, the deflection of sound away from the location where it is not wanted will, under most conditions, be opti- mal. The protection thus provided against sound nuisance is substantially determined by outlet openings for air. Compared to the existing acoustic baffles, these are easy to install. As the sound is dissipated by an air current that as such is not visible, it forms no visual obstacle whatsoever and therefore does not detract from the scenery. Moreover, this generated air current may provide protection between houses and flying aircraft, which is not possible with solid baffles.

Such an air curtain makes it possible to screen an entire area from the sound. It is also possible to choose a pattern in which the thickness of the air current increases or decreases. A thicker air current is able to deflect more sound, which is of importance with strong sound sources.

The apparatus according to the invention is provided with a sound sensor, which is connected with a control of the apparatus. This allows the apparatus to be controlled such that it is only activated when sound nuisance actually occurs. For example, during the night the noise load along motorways will not be present continuously. Since at those

times or at other quiet moments only an occasional car passes, the sound nuisance will also occur only occasionally. It is then possible to control the apparatus such that the sensor measures the noise load continuously and passes this on to the control. The control compares this noise load with a predetermined threshold. When the measured noise load exceeds the predetermined threshold, the apparatus according to the invention is activated. By using several apparatuses according to the invention placed in succession, and each being provided with a sensor, a sound-damping curtain of air current according to the invention is able to move with the traffic or a stream of traffic. In this way the apparatus is only in action when sound nuisance actually occurs. An apparatus according to the invention is not only used advanta- geously when damping noise caused by a road, but an apparatus according to the invention is also effective for reducing sound nuisance caused by aircraft.

In an embodiment of the invention, the apparatus also comprises second means for the generation of a second air curtain, wherein these second means are positioned in or in the vicinity of the first air curtain. In this way the first air curtain can be extended, for example, to obtain a greater height, but the direction of the second air curtain may also be oriented at an angle to the direction of the first air curtain, making it possible to encapsulate a sound source or to screen a house or a residential area from the noise of aircraft landing or taking off.

In an embodiment preferred from a constructional viewpoint, the means for generating an air curtain comprise a compressor connected with at least one compartment, wherein each compartment at the connection with the compressor is provided with a controllable valve, and wherein each compartment comprises at least one outlet opening for the generation of the air curtain. By way of the compartments, wherein the supply of air to each compartment is controlled separately by means of the valve relating to the compartment, the apparatus is divided into sections. This allows portions of the air curtain to be switched on and off as required. For example, in the

case of a moving sound source, such as an aircraft talcing off or landing, or a car, the air curtain can be controlled to move with the sound source. The sound sensors then provide the input for the control of the compartments. In this case, there will be at least two sound sensors. Depending on requirements there may also be more sensors, for example, one for each compartment. It is then not necessary to switch on the complete air curtain when an unacceptable sound level occurs somewhere at the apparatus. By using an apparatus comprising a compressor for the generation of air pressure, and outlet openings for locally generating the air stream, a flexible and widely applicable apparatus is obtained. This allows the compressor with the accompanying energy supply to be placed at the position most favourable for the purpose. This is not necessarily the most favourable position for the generation of the air curtain and thus the position for the outlet openings.

The flexibility of such an apparatus is further increased if the outlet openings are closable by means of a controllable valve. This provides a simple manner for adapting for example the air curtain's height or the velocity of air flow, and thereby the sound-damping effect, to the situation. For example, the valves may partly be controlled subject to the signal emitted, by one or several of the sensors connected with the apparatus, for example, sound sensors.

It is also possible to improve the reliability of the apparatus by providing a buffer space between the compressor and the compartments.

This creates a buffer for an amount of compressed air, so that there is always sufficient compressed air available when several compartments are opened simultaneously. It is then not always necessary for the compressor to be of such dimensions as to be able at any moment to supply all of the outlet openings with air of the maximum pressure. This may mean considerable savings for the compressor. Therefore an apparatus of this kind also optimises the efficiency. In an apparatus according to the invention, composed of several compartments, not all the compartments will at all times demand an equal supply of compressed air. Compressed air is

now supplied, according to requirement, from the buffer space to the compartments by suitably controlling the relevant valves. In this way a much more constant air pressure can be maintained. In addition, the compressor will be switched on and off less frequently, which also benefits a reliable operation.

In another embodiment, the apparatus according to the invention serves for diluting undesirable substances. If at one side of the apparatus according to the invention a source is located that emits undesirable substances, for example substances causing stench or irritations, and the air curtain of the apparatus is generated, the air curtain will carry these undesirable substances upward to a particular height. From the point at that height these substances will disperse in the air, with the result that the concentration on or near the ground at the other side of the generated air curtain will be considerably lower than without the air curtain. A good example of such an emission of undesirable substances is, for example, the emission caused by cattle in a field. By using an apparatus according to the invention it is possible to reduce the concentrations of these emissions in a neighbouring residential area to below the maximally allowable level. The apparatus according to the invention may be applied in a similar manner at a production plant emitting harmful substances.

In a favourable embodiment, the apparatus according to the invention is provided with a sensor for detecting the undesirable substances. The apparatus is then only activated when the concentration of the undesirable substance (s) ex— ceeds a certain value.

In another application, the apparatus can be used to dissipate fog. In some seasons fog, in particular ground fog may occur. An apparatus according to the invention is then able to mix aerial strata, causing the fog near the ground to dissolve. In an automatic embodiment, the apparatus is for this purpose provided with a fog sensor.

The invention will now be further elucidated by describing some exemplary embodiments of the invention and by way of the appended drawing, in which:

Figure 1 schematically shows an example of an embodiment and application of an apparatus according to the invention;

Figure 2 schematically shows a construction detail of the apparatus of Figure 1;

Figure 3 schematically shows another application of an apparatus according to the invention; and Figure 4 schematically shows an example of a third application of an apparatus according to the inven- tion.

Figure 1 schematically shows an example of an embodiment of the apparatus 1 according to the invention, in the application where the sound source is formed by traffic 2 on a road. The apparatus 1 is positioned between the sound source 2 and a residential area 3. The apparatus 1 serves to prevent sound nuisance from the sound source in residential area 3. A sensor 4 measures the amount of noise produced, and is connected with the apparatus 1 for the dissipation of sound. If the measured sound exceeds a predetermined value, the apparatus 1 generates an air curtain 5, in this example approximately from the ground straight upward, whereby the sound is deflected in the direction of the air stream 5 and thus away from the residential area 3.

Figure 2 schematically shows a construction detail of the apparatus 1. The air stream forming the air curtain 5c, is created by compressed air streaming from the outlet openings 6 provided in the compartments 7. The compressed air is supplied to the compartment 7 from the buffer reservoir 8. The compressed air is generated by a compressor, not shown, and stored in buffer reservoir 8. The outlet openings 6 can be shut off by controllable valves (not shown) which valves are controlled via the signal from the sensor 4. If the sensor 4 measures an elevated sound level, more outlet openings 6 are opened, so that the air stream 5 formed becomes thicker as well as longer, thereby achieving an adequate reduction of the sound level in the residential area 3. In this way the profile of the air curtain is controlled. If the sound source is a vehicle moving over the road, the above-described profile may, divided into sections by means of the valves that

control the air supply to the compartments, move with the vehicle along the air curtain. This facilitates a very economical use of the compressed air.

Figure 3 schematically shows another application of an apparatus 1 according to the invention. In Figure 3 the sound source 2 is an aircraft. The apparatus 1 serves to prevent the sound from the sound source 2 from causing a sound nuisance in the residential area 3. To this end the apparatus 1 is in this example composed of 6 embodiments Ia, Ib, Ic, Id, Ie, and If, in accordance with the invention. The apparatuses Ia - If are elevated and each one produces a respective air curtain 5a - 5f, which air curtains are directed in a perpendicular orientation in relation to one another, and each is directed upward at an angle of 45°. In this way the sound from the aircraft 2 is, as it were, heaved over the residential area 3.

Figure 4 finally schematically shows an example of a third application of an apparatus 1 according to the invention. Here an apparatus 1 is positioned between a residential area 3 and a field with cattle. This field with cattle causes emissions of undesirable substances, generally indicated with reference numeral 12. Said emissions bring a certain concentration of these substances into the air. It is not permitted for the concentration of these substances to exceed a certain value in the residential area 3. If this value is exceeded, apparatus 1 is activated by means of the emission-sensitive sensor of the apparatus, which generates an upwardly directed air stream, by which the emission substances are carried upward. As a result of these emission substances being car- ried upward, they will dissipate whereby the concentration of the substances in the residential area 3 will be reduced. It will .be obvious that the present invention in its application is not limited by the examples given here for the purpose of elucidation. The protective scope of the invention is deter- mined by the appended claims.