Abstract:
The present invention provides a flat speaker, in particular in the aerospace sector, with a panel for generating acoustic signals by vibration of the same, and a vibration exciter which is connected to a panel and excites this to vibrate. Here the panel has an edge stiffening. This provides the panel with the required stiffness, particularly against hand pressures, but at the same it guarantees high energy efficiency of the flat speaker.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of PCT International Application No. PCT/EP2008/055083 filed Apr. 25, 2008, which claims the benefit of U.S. Provisional Application No. 60/926,350, filed Apr. 26, 2007, and German Patent Application No. 10 2007 030 811.8, filed Jul. 3, 2007, the entire disclosures of which are herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a flat speaker, particularly in the aerospace sector, and an aircraft or space vehicle with at least one such flat speaker. 
         [0003]    Although it can be used in any sector, the present invention and its underlying concept are explained in further detail in connection with a passenger aircraft. 
         [0004]    In conventional public address systems in aircraft cabins of passenger aircraft for the broadcasting of verbal announcements, use is made of conventional electrodynamic speakers which are installed in an acoustic pipe. Because of the minimum size of the membrane required for the fundamental tone reproduction, conventional speakers have a very high directivity in the medium and high frequency sound range and therefore give rise to highly unequal sound distribution inside the cabin. This and other disadvantages can be eliminated by using flat speakers instead of conventional electrodynamic speakers. 
         [0005]    Flat speakers have a vibration exciter which is connected to a panel and excites it to vibrate. The panel is in this case advantageously designed as part of the interior lining of the aircraft cabin. Here the panel must be protected from damage by passengers, particularly by hand pressure. 
       SUMMARY OF THE INVENTION 
       [0006]    The object of this invention is therefore to provide a flat speaker with a mechanically highly loadable panel. 
         [0007]    This object is achieved by a flat speaker with the features of claim  1  and/or by a vehicle with the features of claim  14 . 
         [0008]    Accordingly a flat speaker is provided, particularly in the aerospace sector, with a panel for generating acoustic signals by vibration of the same and with a vibration exciter which is connected to the panel and excites it to vibrate. In this case the panel has edge stiffening which is designed to prevent damage to the panel by passengers, wherein the edge stiffening is designed as at least one layer which is applied to the panel and which has at least one recessed region. 
         [0009]    Furthermore, a vehicle is provided, in particular an aircraft or space vehicle, with a cabin region for passengers, pilots and/or co-pilots and at least one flat speaker according to the invention for a public address system for the passengers, pilots and/or co-pilots, the panel of the flat speaker forming a section of the cabin region itself. 
         [0010]    The underlying concept of this invention is to provide a stiffening of the panel in its edge region. This measure considerably increases the mechanical stability of the panel, thus preventing damage to the panel by passengers. At the same time the energy efficiency of the flat speaker is only slightly reduced because of the edge stiffening of the panel. Furthermore, radiation of the first panel mode is improved. 
         [0011]    Advantageous embodiments and improvements of the invention are described in the dependent claims. 
         [0012]    In this patent application a “panel” refers to an essentially plane component. 
         [0013]    Here an “edge stiffening” is understood to mean a stiffening that is also provided only in sections and is arranged in an edge region of the panel, and/or a stiffening that is also only provided in sections and is adjacent to one edge (i.e. a border) of the panel. Obviously the stiffening may also extend over the entire length and/or width of the panel in its edge region and/or adjacent to one edge of the panel. 
         [0014]    In particular, the stiffening should be designed as a component that considerably increases the flexural strength of the panel. The stiffening therefore preferably extends in the panel plane and has a cross-section which displays a high moment of superficial inertia compared to the cross-section of the panel in order to resist flexural loads introduced. Alternatively or additionally, the stiffening has a material with a high modulus of elasticity. 
         [0015]    According to a preferred development, the panel is designed as a sandwich material with at least one upper covering layer, at least one lower covering layer and a core material arranged between these covering layers. Such sandwich materials have good acoustic radiation properties. 
         [0016]    In a further preferred embodiment of the flat speaker according to the invention the edge stiffening is designed as at least one stiffening profile, in particular a U-shaped profile and/or isosceles or non-isosceles angle. Here “profile” is understood to mean a component which extends in one direction, referred to in the following as the longitudinal direction, with an essentially constant cross-section. A stiffening of this type can be produced at low cost. 
         [0017]    According to a further preferred development of the flat speaker according to the invention, at least one of the covering layers is bent out of the plane of the panel to form the edge stiffening at its one end. In this embodiment the edge stiffening is therefore designed as part of the panel. The provision of an edge stiffening as a separate part is therefore advantageously dispensed with. The bent out end of the at least one covering layer is preferably essentially perpendicular to the plane of the panel. A moment of superficial inertia of the bent out end can therefore be maximised to resist the flexural loads introduced into the panel. 
         [0018]    In a further preferred embodiment of the flat speaker according to the invention the respective ends of the upper and lower covering layer are bent out of the plane in the same direction, overlapping each other in sections. This means that the upper and lower covering layer are either both bent upwards or downwards, for example. Such edge stiffening is simple to produce. The overlapping sections of the upper and lower covering layer are preferably glued to each other, thus producing a very stiff bond. 
         [0019]    Obviously it is equally conceivable for the upper and lower covering layer to be bent out of the plane of the panel in opposite directions. 
         [0020]    In a further preferred development of the inventive flat speaker, the core material is squeezed against at least one end and against the upper and lower covering layer and bent out of the plane of the panel to form the edge stiffening. Edge stiffening produced in this manner is also described as a “crushed-core edge”. It is characterised by high stiffness and is easy to produce. 
         [0021]    In this patent application the “upper covering layer” should preferably be turned away from the passenger in the installation position of the flat speaker, and the “lower covering layer” should be arranged facing the passenger. Preferably the upper and lower layer are both bent upwards, i.e. the lower covering layer is bent out towards the upper covering layer and the upper covering layer is bent out away from the lower covering layer. The advantage of this is that the edge stiffening thus produced is not visible to the passenger in the installation position of the flat speaker. 
         [0022]    According to a further preferred embodiment of the inventive flat speaker the edge stiffening is designed as at least one layer which is applied to the panel and which has at least one recessed, in particular rectangular region. The layer is in this case an additional layer which is applied to the upper covering layer, for example. This edge stiffening is also characterised in that it is very simple to produce. 
         [0023]    According to a further preferred embodiment of the inventive flat speaker, the panel and/or the edge stiffening has a curved shape in at least one plane. Because of this measure a further stiffening of the panel is advantageously achieved. 
         [0024]    According to a further preferred development of the inventive flat speaker, the edge stiffening is glued to the panel, in particular laminated onto it and/or laminated into it. Because the edge stiffening and the panel are typically produced from composite fibre materials, such a combination of these materials is particularly advantageous. As already mentioned, the edge stiffening forms part of the panel or can be designed as a separate component. The embodiment whereby the edge stiffening is glued to the panel only makes sense for embodiments in which the edge stiffening is designed as a separate component—and not as part of the panel itself, for example in the case where the edge stiffening is designed as a stiffening profile. 
         [0025]    In a further preferred embodiment of the inventive flat speaker the vibration exciter is connected to one of the covering layers and the edge stiffening is applied to the covering layer connected to the vibration exciter. This embodiment is particularly advantageous when the edge stiffening and the vibration exciter are applied to the upper covering layer, as the edge stiffening and the vibration exciter are not then visible to the passenger in the installation position of the flat speaker in the aircraft, for example in the acoustic pipe. 
         [0026]    In a further preferred development of the inventive flat speaker the panel has an area ranging between 400 and 800 cm 2 , preferably approximately 600 cm 2 . These values were determined experimentally as particularly advantageous in terms of the energy efficiency of the flat speaker. 
         [0027]    Further advantages in terms of high energy efficiency of the flat speaker are achieved with a panel thickness of between 4 and 8 mm. Here the thickness relates to a panel thickness in the region outside the edge stiffening. 
         [0028]    Furthermore, a panel weight ranging between 500 and 700 g/mm 2 , preferably approximately 600 g/mm 2 , have proved particularly energy efficient and at the same time sufficiently strong. 
         [0029]    In a further preferred embodiment of the inventive flat speaker the panel is rectangular in shape. This is particularly favourable from the points of good space utilisation inside the cabin and of the radiation property, mode distribution and efficiency of the flat speaker. 
         [0030]    According to a further preferred embodiment of the inventive flat speaker at least one of the covering layers comprises a composite fibre material, in particular a composite glass fibre material, and/or the core material comprises a honeycomb material, in particular of paper saturated in polyamide. These materials are particularly suitable because of their low weight and high strength, as well as their acoustic and airworthiness properties. 
         [0031]    A cell width of the honeycomb material of between 2 and 4 mm is preferred, and in particular preference approximately 3.2 mm. The cell width is measured between two opposing walls of a cell of the honeycomb material. This embodiment has also proved in experiments both as energy efficient and sufficiently strong. 
         [0032]    In a further preferred embodiment of the inventive flat speaker the edge stiffening comprises a composite fibre material and/or a metal and/or a plastic. The edge stiffening may therefore be of any design. A composite carbon fibre material may, in particular, also be considered as a composite fibre material. 
         [0033]    According to a further preferred embodiment of the inventive vehicle the section of the cabin region is designed as an interior lining, preferably in a ceiling or wall region of the cabin region, as part of a passenger acoustic pipe and/or as part of a seat. 
         [0034]    The invention is explained in further detail in the following on the basis of exemplary embodiments with reference to the attached figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    In the figures: 
           [0036]      FIG. 1  shows in a perspective view a flat speaker according to an embodiment of the present invention; 
           [0037]      FIG. 2  shows a section A-A from  FIG. 1 ; 
           [0038]      FIG. 3  shows a section B-B from  FIG. 1 ; 
           [0039]      FIG. 4  shows section B-B from  FIG. 1  according to a further embodiment of the present invention; 
           [0040]      FIG. 5  shows section B-B from  FIG. 1  according to yet a further exemplary embodiment of the present invention; 
           [0041]      FIG. 6  shows in an elevation a flat speaker according to yet a further exemplary embodiment of the present invention; and 
           [0042]      FIG. 7  shows a section C-C from  FIG. 6 . 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0043]    In the figures the same reference symbols denote the same components or components with similar functions unless otherwise indicated. 
         [0044]      FIG. 1  shows, in a perspective view, a flat speaker  1  according to an exemplary embodiment of this invention. 
         [0045]    Flat speaker  1  has a preferably essentially rectangular panel  2  and a vibration exciter  3  arranged on it approximately centrally and connected to the panel. Vibration exciter  3  consists in this case of a magnet and a vibration coil, but here it only represented diagrammatically for the sake of clarity. 
         [0046]    Preferably panel  2  is fastened by means of support elements  4 ,  5 ,  6 ,  7  in an acoustic pipe  8  of an aircraft above passengers  9 , only roughly indicated. 
         [0047]    In the position of installation of flat speaker  1  shown, the x-axis points in the longitudinal direction of the aircraft towards the nose, the y-direction points in the transverse direction of the aircraft, from right to left, and the z-direction points in the vertical direction of the aircraft. 
         [0048]    Panel  2  extends superficially essentially in the x-y-plane and bends with a radius R, as shown in  FIG. 2 , in the y-z plane. 
         [0049]    Panel  2  has edge stiffenings (provided, for example, with reference numbers  11 ,  12 ,  13 ,  14 ,  15 ) in order to resist forces, hand pressures, for example, introduced in particular in the z-direction. 
         [0050]    An upward curving edge of upper covering layer  17  is defined with edge stiffening  15 . This therefore also stiffens panel  2  since it also makes a not inconsiderable contribution to the moment of superficial inertia of panel  2  about the y-axis. 
         [0051]      FIG. 2  shows a section A-A from  FIG. 1 . 
         [0052]    Panel  2  has a sandwich material  16 . Sandwich material  16  is composed of a lower covering layer  17 , a lower covering layer  17 , a lower covering layer  18  and a honeycomb material  19  arranged between them. Here the honeycombs of honeycomb material  19  extend essentially perpendicularly to panel plane x-y. Upper covering layer  17  and lower covering layer  18  are preferably produced from a composite glass fibre material and honeycomb material  19  is produced from a paper. Lower covering layer  18  faces towards the interior of the cabin, i.e. the passengers  9 , in the installation position of flat speaker  1 . 
         [0053]    Upper covering layer  17  is preferably connected directly to vibration exciter  3 . 
         [0054]    Edge stiffenings  13 ,  14  are obtained in the exemplary embodiment according to  FIG. 2  by applying the “crushed-core” technique to the ends of sandwich material  16 . In this case the honeycomb material end  22  is first squeezed together with ends  23 ,  24  of upper and lower covering layers  17 ;  18  respectively, thereby compressing the intermediate honeycomb material end  22 , and is then bent upwards, i.e. in the z-direction. The result is the condition shown in  FIG. 2 . Edge stiffening  14  is located on one end of panel  2  opposing edge stiffening  13  of panel  2 , and is also produced according to the “crushed-core” technique. 
         [0055]      FIG. 3  shows a section B-B from  FIG. 1 . Section B-B is represented in abbreviated form for the sake of clarity. 
         [0056]    Edge reinforcements  11  and  12  formed together on ends of the panel opposing each other in the y-direction are produced similarly and the principle underlying this will be explained in the following on the basis of edge stiffening  11 . 
         [0057]    An end  25  of upper covering layer  17  projecting from honeycomb material  19  is bent upwards (i.e. in the z-direction). One end  26  of lower covering layer  18 , projecting from honeycomb material  19 , is then bent upwards (i.e. in the z-direction), so that end  26  is arranged with a section  27  overlapping end  25 . End  26  is preferably glued fixedly to honeycomb core  19  and end  25  of upper covering layer  17  in the position shown in  FIG. 3 . Projection U of section  27  is in this case preferably approximately 3-10 mm. 
         [0058]    It would be equally conceivable to bend end  25  downwards (i.e. against the z-direction), and bend end  26  of lower covering layer  18  upwards (i.e. in the z-direction), and then to glue them. 
         [0059]      FIG. 4  shows section B-B from  FIG. 1  according to a further exemplary embodiment of the invention. 
         [0060]    Edge stiffenings  11  and  12  are constructed as separate components according to the exemplary embodiment according to  FIG. 4 . Edge stiffenings  11 ,  12  are constructed as L-shaped stiffening profiles extending in the y-direction and are glued to its one leg  31  on upper covering layer  17  (shown by way of example for edge stiffening  11 ), in particular also laminated onto it or laminated into it, the other leg  32  extending perpendicularly (i.e. in the z-direction) to the x-y-plane of panel  2 . 
         [0061]    Stiffening profiles may, for example, consist of plastic or also of metal. However, they are preferably produced from a composite fibre material. 
         [0062]      FIG. 5  shows section B-B from  FIG. 1  according to yet a further exemplary embodiment of the invention. Here edge stiffenings  11 ,  12  are designed on the basis of the exemplary embodiment according to  FIG. 2 , similarly to edge stiffenings  13 ,  14 , and are therefore not explained any further at this point. 
         [0063]      FIG. 6  shows, in an elevation, a flat speaker  1  according to a further exemplary embodiment of this invention. 
         [0064]    Panel  2  has an edge stiffening  33 . Edge stiffening  33  is designed as an essentially rectangular strip adjacent to edges (designated by reference numbers  34 ,  35  by way of example) of panel  2 . Here edge stiffening  33  has a preferably essentially rectangular recess  36 . 
         [0065]    As can be seen in  FIG. 7 , which shows a section C-C in  FIG. 6 , edge stiffening  33  is constructed of several layers  37 ,  38  and  39 , for example a composite carbon material. 
         [0066]    According to the exemplary embodiments according to  FIGS. 1 to 6  panels  2  preferably have an area of approximately 600 cm 2 , a thickness DS (see  FIG. 2 ) of approximately 6 mm and a weight of approximately 600 g/m 2 . The cell width of honeycomb material  19  is preferably 3.2 mm. 
         [0067]    Although this invention has here been described on the basis of preferred exemplary embodiments, it is not restricted to them but can be modified by any means. 
         [0068]    The different embodiments of edge stiffenings described here may, for example, be combined in any manner. For example, one end of the panel may be designed according to the “crushed-core” technique and another end may have an edge stiffening in the form of a stiffening profile. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  Flat speaker 
           2  Panel 
           3  Vibration exciter 
           4  Supporting element 
           5  Supporting element 
           6  Supporting element 
           7  Supporting element 
           8  Passenger acoustic pipe 
           9  Passengers 
           11  Edge stiffening 
           12  Edge stiffening 
           13  Edge stiffening 
           14  Edge stiffening 
           15  Edge stiffening 
           16  Sandwich material 
           17  Upper covering layer 
           18  Lower covering layer 
           19  Honeycomb material 
           22  Honeycomb material end 
           23  End 
           24  End 
           25  End 
           26  End 
           27  Section 
           31  Leg 
           32  Leg 
           33  Edge stiffening 
           34  Edge 
           35  Edge 
           36  Recess 
           37  Layer 
           38  Layer 
           39  Layer 
         x Spatial direction 
         y Spatial direction 
         z Spatial direction 
         R Radius 
         D Thickness 
         U Projection