EP1719383A2

EP1719383A2 - Display device having sound-generating means

Info

Publication number: EP1719383A2
Application number: EP05702903A
Authority: EP
Inventors: Martinus H. W. M. Van Delden; Daniel W. E. Schobben
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2004-02-17
Filing date: 2005-02-04
Publication date: 2006-11-08
Also published as: CN1922915A; WO2005083550A2; KR20060124703A; WO2005083550A3; JP2007526688A

Abstract

A display device has a sound-generating means and a monitor display panel with a display screen. It comprises a foot part (4) with mechanical coupling means (4b) for mechanically coupling the display panel (2) and the foot part (4). The foot part is provided with the sound-generating means (6). The sound-generating means is coupled to an acoustical coupler (7) at the bottom of the foot part and to the foot part (4) itself via one or more acoustical decouplers (8), which foot part is provided with acoustical decouplers (8) at the end (4c) opposite the end (4a) provided with the monitor coupling means (4b).

Description

Display device having a sound-generating means and a monitor display panel with a display screen

FIELD OF THE INVENTION The invention relates to a display device having a sound-generating means and a monitor display panel with a display screen.

BACKGROUND OF THE INVENTION Such devices are, for example, of the type having thin and slim (LC) display panels and are also the thin and slim (LC) display panels as such. Loudspeakers in desktop PC environments generally occupy a relatively large foot print area. Loudspeakers are therefore (more) often integrated in the monitor housing itself, in general on either side of the monitor. Integration in the monitor housing is more troublesome when using modern thin and slim LCD panel loudspeakers, i.e. very thin build-in loudspeakers are required. Although this is very well possible, there is a tendency to utilize Distributed Mode Loudspeakers (DMLs). However, the presence of large-area DMLs on either side of a thin and slim

(LC) display does not contribute to the character and the esthetics of these displays. Moreover, low frequencies as produced by (sub)-woofers cannot be generated when using DMLs, because structural modes below a frequency of 100 Hz are very hard to realize. The lower frequency range of DMLs is thus often limited at about 200 to 250 Hz. It is also to be noted that, in order to avoid acoustic shorts, very low frequencies require large surface area deflections, usually in combination with the displacement of a large volume of air enclosed in a box.

OBJECT AND SUMMARY OF THE INVENTION It is an object of the invention to overcome or at least reduce the previously mentioned problems in particular but not exclusively in relation to thin and slim (LC) display panels, while simultaneously allowing the generation of low-frequency sound without a substantial increase of footprint area or size occupied by the monitor display panel or the device as a whole. To this end, the display device according to the invention is characterized in that it comprises a foot part with one end provided with mechanical coupling means for mechanically coupling the display panel and the foot part, which foot part is provided with a sound-generating means which is coupled to an acoustical coupler at an end opposite the end provided with the mechanical coupling means, and the sound-generating means is coupled to the foot part via one or more acoustical decouplers, wherein the foot part is provided with said acoustical decouplers at the end opposite the end provided with the mechanical coupling means. The invention is based on the recognition that it is possible to vibrate a large rigid object, for example, a table top, by means of a much smaller exciter, such that it produces a larger sound than the sound originating from the device if sufficient acoustical coupling is ensured. Depending on the properties of the object to be excited and the acoustical coupling, the larger object may have a greater and richer sound intensity than the exciter alone, presumably because of the much larger surface area of the table when compared to the exciter. Even lower-frequency sound can thus be produced, even though the table has a much smaller excitation amplitude than the exciter itself. To achieve this, a proper acoustical coupling has to be established between the sound-generating means and the larger object. In this application, this phenomenon is also indicated by the words co-vibration and/or co-excitation. The sound-generating means in the monitor foot part is acoustically decoupled from the monitor (via the acoustical decouplers), and coupled via the acoustical coupler to an object on which the monitor foot is placed. The object of the invention is achieved by integrating a sound-generating means, e.g. one or more exciters, in the foot part of the (LCD) monitor/laptop. Clearly, this does not increase the footprint area occupied by the display panel or the device as a whole, but it does allow the generation of audible (stereo) sound, even at low frequencies. The deflections of the exciter or exciters are coupled into the table by means of an acoustical coupler, e.g. a mechanical adapter, present between the larger surface and the sound- generating means (exciter, shaker) in the foot part. The monitor foot/laptop foot part can thus provide low-frequency sound, enhanced by the object to be excited. Higher- frequency sound, both in the middle and high frequency range, can also be provided by the foot or by any other known means, such as e.g. sound-generating means integrated in or attached to the display panel. The driver is simply activated by placing the monitor-foot/laptop on the desktop, PC casing, or any other object that is large enough to hold the monitor foot. The display panel itself is in turn decoupled from the exciter so as to prevent vibration of the (LC) display panel/laptop itself. The acoustical decoupling of sound-generating means and display may be realized by providing an acoustical decoupler in between the sound-generating means and a rest of the foot part, or in between the foot part and the display panel. Using an acoustical coupler offers a very substantial increase of sound intensity at low frequencies, namely, more than 10, 15 dB, even more than 20 dB, without increasing the foot print area. Via the acoustical couplers and when placed on an object, the sound- generating means in the foot (the shaker) excites the object. This increases the sound level considerably. The acoustical decouplers prevent the vibrations generated by the sound- generating means (and/or the table itself) from being passed on to the display panel. The display panel, whether e.g. a CRT or an LCD display panel, is sensitive to vibrations which decrease the quality of the image on the display panel. The sound-generating means is preferably flexibly arranged in the foot part, such that the acoustical coupler slightly extends beyond the tangent plane of the foot itself, when the foot part is not in contact with a surface. When the foot part is positioned on a surface, the acoustical coupler contacts the surface and, due to the flexible nature of the connection between the sound-generating means and the foot part, is pushed against the surface without lifting the foot part itself. A good mechanical contact and hence a good acoustical coupling is possible. In another preferred embodiment, the acoustical coupler is retracted, in the normal position, within the outlines of the foot part, and the foot part comprises means for pushing the sound-generating means via the acoustical coupler or the acoustical coupler itself against a resting surface. Retracting the acoustical coupler within the outlines of the foot part reduces the chance of damaging the acoustical coupler and/or the sound-generating means. However, when the acoustical coupler is retracted within the outlines of the foot part, contact with a surface becomes difficult. The provision of activation means for pushing the acoustical coupler against a resting surface directly or via the sound-generating means allows a good sound reproduction. In a preferred embodiment, the device comprises means for forcing the foot part upon a supporting object. This feature has two effects, namely, the display is pressed with some force on the table, ensuring a fixed position, and a good mechanical contact is achieved, resulting in a good acoustical coupling. In one embodiment, such means are formed, for example, by one or more suction cups. A construction similar to the edge of a refrigerator door may be used. In such embodiments, non-horizontal objects with a surface that is preferably flat may be used for sound increase. Providing a suction device increases the number of positions and objects at which the device may be placed and will thus generally enhance the ease of use and contribute to the maximum available increase of sound intensity. Alternatively or in addition, in a preferred embodiment, the device is provided with a permanent magnet for forcing the foot part against a supporting object. The table top or other surface upon which one wants to affix or place the device is sometimes made of metal. Providing the device with a permanent magnet allows the sound increase to be easily obtained on a surface made of magnetizable metal, with or without using suction. Even when the surface is relatively rough, a good contact may be made. When an object upon which the device is positioned is made of magnetizable metal, provision of the permanent magnet ensures a good mechanical contact and hence a good acoustical coupling. In preferred embodiments, the device is provided with a sound-recording element and comprises a means for making a comparison between a registered sound and an emitted sound signal. The inventors have realized that, when the foot part is acoustically coupled to another object, the sound-recording means can be used to improve the quality of the sound reproduction by comparing the original signal with the recorded sound signal. This comparison can be used advantageously in several manners. In one embodiment, the recorded sound is compared with the original sound so as to redistribute the signals to the display over frequencies. Frequency redistribution of the sound may be used, for example, for:

1. Obtaining a more natural sound. The sound waves of the sound-generating means are coupled into e.g. a table top. Apart from increasing the sound intensities, this coupling may also change the sound by increasing the intensity at some frequencies to a greater extent than at other frequencies. By frequency redistribution of the intensities, this can be counteracted. It may even be used to obtain a better, more natural sound than the device itself can give;

2. Obtaining the maximal sound intensity. A comparison of the recorded sound with the emitted sound will provide the possibility of establishing those frequencies at which the sound-increasing effect is most prominent. If the aim is to obtain a maximal sound level, most energy may be directed to these frequencies. In these embodiments, the device has a means to establish that the foot part is indeed used in the "sound coupling" mode. Some simple means for doing so would be a switch or action by which the user sets the device in this mode, or, very simply, the comparison of sound levels themselves (original vs. recorded) may be the trigger. The invention also relates to a foot part as defined in claim 10. These and other objects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figs. 1A, IB illustrate schematically known devices. Fig. 2 illustrates schematically a device according to the invention. Figs. 3 and 4 illustrate schematically embodiments of a device according to the invention. Fig. 5 illustrates a further embodiment of a device according to the invention. Fig. 6 illustrates a laptop according to the invention Fig. 7 illustrates a device having a sound-recording means. Fig. 8 illustrates the experimental set-up for measuring sound enhancement by acoustical coupling. The Figures are not drawn to scale. Generally, identical components are denoted by the same reference numerals in the Figures.

DESCRIPTION OF EMBODIMENTS Figs. 1A and IB illustrate schematically known devices. In Fig. 1A, the loudspeakers 3 are positioned on the side of the display panel 2 of device 1. The display panel is put on a foot part 4, and rests on a table 5. In Fig. IB, the loudspeakers are separate loudspeakers 3a. Problems are encountered with both types of known devices. Loudspeakers (such as loudspeakers 3a in Fig. IB) in desktop PC environments generally occupy a relatively large foot print area. Loudspeakers are therefore (more) often integrated in the monitor housing itself, in general on either side of the monitor. In modern thin and slim design LCD panel loudspeakers, integration in the monitor housing is more troublesome, i.e. very thin build-in loudspeakers are required. Although this is very well possible, there is a tendency to utilize Distributed Mode Loudspeakers (DMLs). However, the presence of large-area DMLs (such as DMLs 3 in Fig. 1 A) on either side of a thin and slim (LC) display does not contribute to the character and the esthetics of these displays. Moreover, low frequencies as produced by (sub)- woofers cannot be generated in using DMLs, because structural modes below a frequency of 100 Hz are very hard to realize. The lower frequency range of DMLs is thus often limited at about 200 to 250 Hz. It is also to be noted that, in order to avoid acoustic shorts, very low frequencies require large surface area deflections, usually in combination with the displacement of a large volume of air enclosed in a box. Figure 2 schematically illustrates a device according to the invention. The device (1) comprises a foot part (4) with one end (4a) provided with mechanical coupling means (4b) for mechanically coupling the display panel (2) and the foot part (4), which foot part is provided with a sound-generating means (6) which is coupled to an acoustical coupler (7) at an end (4c) opposite the end (4a) provided with the mechanical coupling means (4b), and the sound-generating means (6) is coupled to the foot part (4) via one or more acoustical decouplers (8), which foot part is provided with acoustical decouplers (8) at the end (4c) opposite the end (4a) provided with the mechanical coupling means (4b). In every-day language, the end 4a would most likely be called the upper or up side, end 4c the bottom side or simply the bottom. The foot part may be a pedestal upon which a monitor (LCD or other type of monitor) is put, in which case the mechanical coupling means could be clamps or swivels. The mechanical coupling means may affix the display panel and the foot part to each other, but may also, in embodiments, be reversible coupling means, i.e. they allow the display panel and the foot part to be assembled and disassembled. If the device is a laptop, the foot part may also be the bottom part of a laptop, in which case the coupling means are or comprise hinges between the bottom part and the display part of the laptop device. The acoustical decouplers are, for example, acoustical dampers, such as rubber or rubbery material, natural or synthetic material, or felt feet. The acoustical couplers transfer the sound waves generated by the sound -generating means 6 into an object upon which the device is put. The invention is based on the recognition that it is possible to vibrate a large rigid object, for example, a table top, by means of a much smaller exciter, such that it produces a larger sound than the sound originating from the device if sufficient acoustical coupling is ensured. Depending on the properties of the object to be excited and the acoustical coupling, the larger object may have a greater and richer sound intensity than the exciter alone, presumably because of the much larger surface area of the table when compared to the exciter. Even lower-frequency sound can thus be produced, even though the table has a much smaller excitation amplitude than the exciter itself. To achieve this, a positive acoustical coupling which is large enough has to be established between the sound- generating means and the larger object. In this application, this phenomenon is also indicated by the words co-vibration and/or co-excitation. The sound-generating means in the monitor foot part is acoustically decoupled from the monitor (via the acoustical decoupler), and coupled via the acoustical coupler to an object on which the monitor foot is placed. The object of the invention is achieved by integrating a sound-generating means, e.g. one or more exciters, in the foot part of the (LCD) monitor/laptop. Clearly, this does not increase the footprint area occupied by the display panel or the device as a whole, but it does allow the generation of audible (stereo) sound, even at low frequencies. The deflections of the exciter or exciters are coupled into the table by means of an acoustical coupler, e.g. a mechanical adapter, present between the larger surface and the sound- generating means (exciter) in the foot part. The monitor foot/laptop foot part can thus provide low-frequency sound, enhanced by the object to be excited. Higher-frequency sound, both in the middle and high frequency range, can also be provided by the foot, or by any other known means. The driver is simply activated by placing the monitor-foot/laptop on the desktop, PC casing, or any other object that is large enough to hold the monitor foot. The display panel itself is in turn decoupled from the exciter so as to prevent vibration of the (LC) display panel/laptop itself. The acoustical decoupling of sound-generating means and display may be realized by providing an acoustical decoupler in between the sound-generating means and a rest of the foot part, or in between the foot part and the display panel. Using an acoustical coupler offers a very substantial increase of sound intensity at low frequencies, namely more than 10, 15 dB, even more than 20 dB, without increasing the foot print area. The sound increase can easily be measured by placing the device on a table, measuring the sound intensity and then doing the same when the device is in air (or positioned on, for example, a thick felt pad), thus eliminating acoustical coupling between the foot part and the table. The accompanying Figures illustrate several preferred embodiments. The sound-generating means is preferably flexibly arranged in the foot part, such that the acoustical coupler slightly extends beyond the tangent plane of the foot itself, when the foot part is not in contact with a surface. When the foot part is positioned on a surface, the acoustical coupler contacts the surface and, due to the flexible nature of the connection between the sound-generating means and the foot part, is pushed against the surface, without lifting the foot part itself. A good mechanical contact and hence a good acoustical coupling is possible. An example of this embodiment is schematically illustrated in Fig. 3, in which the dotted line indicates the tangent plane of the foot. In another preferred embodiment, schematically indicated by way of example in Fig. 4, the acoustical coupler is retracted, in the normal position, within the outlines of the foot part, and the foot part comprises means for pushing the sound -generating means via the acoustical coupler or the acoustical coupler itself against a resting surface. Retracting the acoustical coupler within the outlines of the foot part reduces the chance of damaging the acoustical coupler and/or the sound-generating means. However, when the acoustical coupler is retracted within the outlines of the foot part, contact with a surface becomes difficult. The provision of activation means for pushing (schematically indicated in Fig. 4 by the force F) the acoustical coupler against a resting surface directly or via the sound-generating means allows a good sound reproduction. Such means may be simple mechanical means, such as a wedge that may be pushed inwards to push the exciter and acoustical coupler against the table top, a lever which is switched, or electromechanical means such as coil-activated magnets which exert forces. In a preferred embodiment, the device has means for forcing the foot part upon a supporting object. This feature has two effects, namely, the display is pressed with some force on the table, ensuring a fixed position, which helps in establishing a good mechanical contact via couplers 7, resulting in a good acoustical coupling. In one embodiment, such means are formed, for example, by one or more suction cups. A construction similar to the edge of a refrigerator door may be used. In such embodiments, non-horizontal objects with a surface that is preferably flat may be used for sound increase. Providing a suction device increases the number of positions and objects at which the device may be placed and will thus generally enhance the ease of use and contribute to the maximum available increase of sound intensity. In Fig. 5, this is schematically indicated by the grey parts 8a. Figure 6 illustrates a laptop according to the invention. The mechanical coupling means for coupling the display panel and the foot part, which comprises the key board of a laptop, is formed by hinges with which the user may open or close the laptop. In preferred embodiments, the device is provided with a sound-recording element and comprises a means for making a comparison between a registered sound and an emitted sound signal. The inventors have realized that, when the foot part is acoustically coupled to another object, the sound-recording means can be used to improve the quality of the sound reproduction by comparing the original signal with the recorded sound signal. This comparison can be used advantageously in several manners. In one embodiment, the recorded sound is compared with the original sound so as to redistribute the signals to the display over frequencies. Frequency redistribution of the sound may be used, for example, for: • Obtaining a more natural sound. The sound waves of the sound-generating means are coupled into e.g. a table top. Apart from increasing the sound intensities, this coupling may also change the sound by increasing the intensity at some frequencies to a greater extent than at other frequencies. By frequency redistribution of the intensities, this can be counteracted. It may even be used to obtain a better, more natural sound than the device itself can give; • Obtaining the maximal sound intensity. A comparison of the recorded sound with the emitted sound will provide the possibility of establishing those frequencies at which the sound-increasing effect is most prominent. If the aim is to obtain a maximal sound level, most energy may be directed to these frequencies. In these embodiments, the device preferably has a means to establish that the foot part is indeed used in the "sound coupling" mode. Some simple means for doing so would be a switch or action by which the user sets the device in this mode, or, very simply, the comparison of sound levels themselves (original vs. recorded) may be the trigger. Fig. 7 illustrates an example of a device in accordance with the described preferred embodiment. The vibrating element may change the frequency distribution of the sound, because certain frequencies are more amplified than others. Fig. 7 illustrates a device comprising a sound-recording means 71, which records the sound generated. This sound is compared in comparator C with the original sound (slightly delayed in time, to account for the time difference). The measured difference of intensity and e.g. frequency distribution of intensity is fed back to amplifier A to change the signal to the sound-generating means in such a way that, of course within measuring accuracy, the recorded sound eventually corresponds to the original signal or comes at least closer to the original signal. This comparison can be used advantageously in several manners. In one embodiment, the recorded sound is compared with the original sound so as to redistribute the signals to the display over frequencies. Frequency redistribution of the sound (equalization) may be used, for example, for: - Obtaining a more natural sound. Apart from increasing the sound intensities, the co- vibrating object (e.g. the table top) may also change the sound by increasing the intensity at some frequencies to a greater extent than at other frequencies. By frequency redistribution of the intensities, this can be counteracted. It may even be used to obtain a better, more natural sound than the device itself can give. For example, the device as such may have only a very limited sound-reproducing capability below 1 kHz. Experiments have shown that a substantial sound increase is obtained across the frequency spectrum. This offers the possibility of a louder sound at all frequencies, but one could also selectively increase the sound at lower frequencies so as to obtain a more natural sound. The overall sound increase would then be less than maximal, but the sound would be more natural. A natural sound is in fact easier to distinguish, even at the same overall sound intensity. The feedback loop then acts as an equalizer. The sound intensity of the device in air drops sharply at lower frequencies when the device is used in air. The device according to the invention boosts the sound intensity at lower frequencies, and a comparison of the incoming signal and the signal recorded by the microphone allows equalization of the sound intensities (at least with a range of frequencies). Fig. 8 schematically indicates the manner in which the sound increase is measurable. The device is positioned on a table 81 in the proper orientation, with its foot part on the table and the acoustical coupling means touching the table, and with suction action if the device has a suction cup. In a preferred embodiment, the shaker acts as a power efficient resonator and produces mostly one frequency (e.g. 30 to 200 Hz, preferably e.g. 50 to 100 Hz). In other embodiments, two or more squeeters (i.e. tweeters that can also produce midrange frequencies) are integrated in the foot or the rim of the display. In another embodiment, the sound-generating means in the foot produces a wider frequency range (e.g. 70 to 800 Hz). The higher sound frequencies (above the working frequency (frequencies) of the foot) may be reproduced in preferred embodiments by a number of very small tweeters (e.g. two tweeters having a diameter of e.g. 10 mm) which can be integrated seamlessly in the rim of the monitor so as to provide a clear sound with a good stereo width. Such display devices are examples of preferred embodiments in which the sound-generating means in the foot part are arranged to generate sound at a first frequency or frequencies, or frequency range, and the display part has sound-generating means for generating sound in a second frequency range, wherein the first frequency range is below the second frequency range. The sound level at 1 m distance is measured at a working frequency of the shaker in the foot. The foot is removed and placed on a woolen cloth or suspended in air. The sound level is again measured, using of course the same signal. If the sound level increase is more than 6 dB for one or more of the working frequencies of the sound-generating means (shaker) in the foot, preferably for all frequencies, the device is within the scope of the claim. If not, it is beyond the scope of the claim. The increase is preferably at least 10, more preferably at least 15 dB, most preferably at least 20 dB. The table has a wooden (plywood) table top of 90*180 cm with a thickness of 18 mm. This corresponds more or less to a standard table top in offices. In the standard test, a table having a plywood table top of 18 mm and a size of 90*180 cm is used. However, this is merely for the purpose of establishing a bench mark. Experiments have shown that very similar results are obtained e.g. when a table of 14 mm plywood and size 160*80 cm or a steel table top and size 100*200 mm is used. The standard of the plywood table with the specified measures is used to establish a frame of reference; the values for other types of table tops are roughly similar. It is noted that, within the concept of the invention, the device is made in such a way that a table vibrates when the foot part is positioned on a table or other vibrating object. To some extent, such effects always occur. However, each loudspeaker box is normally made to minimize such an effect as much as possible, in other words, co-excitation is counteracted or minimized as much as possible. In conventional designs, the loudspeakers do not make contact or hardly make contact with the table because they are usually suspended in an enclosure which in fact comprises or functions as a very good vibration damper. In contrast, the effect of co-excitation is an integral part in the present invention. The measurement described above, which can easily be performed by any person skilled in the art, clearly distinguishes devices according to the invention from those beyond its scope. It is to be noted with reference to the claims that various characteristic features defined in the set of claims may occur in combination. In summary, the invention may be described as follows. A display device has a sound-generating means and a monitor display panel with a display screen. It comprises a foot part (4) with mechanical coupling means (4b) for mechanically coupling the display panel (2) and the foot part (4). The foot part is provided with the sound -generating means (6). The sound-generating means is coupled to an acoustical coupler (7) at the bottom of the foot part and to the foot part (4) itself via one or more acoustical decouplers (8), and the foot part is provided with acoustical decouplers (8) at the end (4c) opposite the end (4a) provided with the monitor coupling means (4b). Via the acoustical couplers, the sound -generating means in the foot (the shaker), when placed on a table, excites the table. This increases the sound level considerably. The acoustical decouplers prevent the vibrations generated by the sound- generating means (and the table itself) from being passed on to the display panel. The display panel, whether e.g. a CRT or an LCD display panel, is sensitive to vibrations which decrease the quality of the image on the display panel. It will be evident that many variations are possible within the scope of the invention. It will be appreciated by persons skilled in the art that the invention is not limited by what has been particularly shown and described hereinbefore. The invention resides in each and every novel characteristic feature and each and every combination of characteristic features. Reference numerals in the claims do not limit their protective scope. Use of the verb "comprise" and its conjugations does not exclude the presence of elements other than those stated in the claims. Use of the article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims

CLAIMS:

1. A display device having a sound-generating means and a monitor display panel with a display screen, wherein the display device comprises a foot part (4) with one end (4a) provided with mechanical coupling means (4b) for mechanically coupling the display panel (2) and the foot part (4), which foot part is provided with a sound -generating means (6), which is coupled to an acoustical coupler (7) at an end (4c) opposite the end (4a) provided with the mechanical coupling means (4b), and the sound-generating means is coupled to the foot part (4) via one or more acoustical decouplers (8), wherein the foot part is provided with said acoustical decouplers (8) at the end (4c) opposite the end (4a) provided with the mechanical coupling means (4b).

2. A display device as claimed in claim 1, wherein the sound-generating means (6) is flexibly arranged in the foot part (4), wherein the acoustical coupler (7) slightly extends beyond the tangent plane of the foot itself, when the foot part is not in contact with a surface.

3. A display device as claimed in claim 1, wherein, in the normal position, the acoustical coupler is retracted within the outlines of the foot part, and the foot part comprises means for pushing the sound-generating means via the acoustical coupler or the acoustical coupler itself against a resting surface.

4. A display device as claimed in claim 1, wherein the device comprises means for forcing the foot part upon a supporting object.

5. A display device as claimed in claim 4, wherein the forcing means are formed by suction cups.

6. A display device as claimed in claim 4, wherein the forcing means comprises permanent magnets.

7. A display device as claimed in claim 1, wherein the device is provided with a sound-recording element and comprises a means for making a comparison between a registered sound and an emitted sound signal.

8. A display device as claimed in claim 1, wherein the sound -generating means in the foot part are arranged to generate sound at a first frequency or frequencies, or frequency range, and the display part has sound-generating means for generating sound in a second frequency range, wherein the first frequency range is below the second frequency range.

9. A display device as claimed in claim 8, wherein the first frequency or frequency range is below 800 Hz.

10. A foot part presenting all the features of the foot part disclosed in any one of the preceding claims and being thus constructed and evidently intended for use in the display device as claimed in any one of the preceding claims.