Abstract:
For a selective sound propagation pattern that has an especially high directivity, including in the bass frequency region, there is inventively provided a loudspeaker box ( 1 ) with a housing ( 2 ) and at least one loudspeaker ( 4 ) with chassis ( 6 ) which is surrounded by a housing wall ( 8 ) in such a way that in the low frequency region the rear side and front side sound of the loudspeaker ( 4 ) overlay themselves with a sound increase in a preferred direction.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention concerns a loudspeaker box having a housing and at least one loudspeaker with a chassis. 
     Loudspeakers are normally built with their chassis in a housing (i.e. a so-called enclosed loudspeaker), in order to avoid, to the greatest possible extent, an acoustical short circuit, i.e. an interaction between the sound generated by the rear side and front side of the speaker and the associated cancellation of those sounds. The sound cancellation results from the motion of the loudspeaker&#39;s membrane and the resulting combination of the two out of phase sound waves generated by the membrane&#39;s motion. The resulting sound propagation pattern of closed loudspeakers is uniform in nearly all directions, especially for low frequencies. For higher frequencies a directionality will be produced, because of the increase in reflections and propagation time effects caused by the decrease in wavelength, whereby the sound propagation will be concentrated in a particular direction. 
     The sound cancellation pattern of an open loudspeaker (i.e. a loudspeaker without a housing) is limited, in contrast, by frequency dependency whereby a good sound cancellation pattern is achieved to the greatest possible extent for low frequencies and for high frequencies a substantially poorer sound cancellation pattern is achieved. Additionally, in the region of the surface of the loudspeaker&#39;s membrane, a good sound cancellation (i.e. null points) pattern arises over a particularly large frequency band. As a result, the open loudspeaker usually demonstrates a so-called dipole-curve sound pattern in the region of the loudspeaker (also called an “eight-characteristic” curve). 
     A disadvantage of both loudspeakers—open and closed—is that a sound playback with adequately good directivity in the bass region is not assured. For high frequencies, the closed loudspeaker (the loudspeaker box) is especially suitable, since it achieves an especially good directivity. In the bass frequency region, neither the loudspeaker box nor the open loudspeaker exhibit an adequately good directivity. 
     Hence, to produce a good directivity in the bass frequency region, usually multiple loudspeakers, e.g. two loudspeakers, will be coupled together. In that case, both of the loudspeakers work in opposing phase from one another. The coupling of both loudspeakers is performed in such a way that the resulting acoustical and electrical paths are adjusted to one another so that the electrical propagation time approximately matches the acoustical propagation time. Different directivity characteristics, e.g. kidney shaped or clubbed shaped directivity characteristics, are realized depending upon the type of loudspeaker that is utilized—a closed or open loudspeaker. Alternatives that can also be used to attain directivity in the bass region are called loudspeaker arrays or loudspeaker lines. These solutions all require additional loudspeakers and therefore their construction is especially equipment intensive and expensive. 
     SUMMARY OF THE INVENTION 
     The invention is based upon the task of providing a loudspeaker box that achieves a directionality, including in the bass region, in a particularly simple way. In addition, a headrest shall be provided that realizes a good bass playback response. 
     The first stated problem is inventively solved by a loudspeaker box that has a housing and at least one loudspeaker with a chassis, that is surrounded in such a way by a housing wall so that in the low frequency region the sound on the rear side and on the front side of the loudspeakers superimpose themselves with an amplification in sound in a given direction. 
     The invention starts with the concept, that for the individualized broadcasting of sound into predetermined spatial areas, taking into consideration sound propagation, a directionality is to be achieved over a large frequency range, wherein loudspeaker feedback should be avoided. The loudspeaker construction should also be compact, so that it is also useful for small loudspeaker boxes. In place of the traditional loudspeaker arrangement comprising several loudspeakers to achieve a response in the bass region, the invention starts with a single loudspeaker that has an associated chassis and arranges those elements on the housing wall in such a way that a sound amplification arises in a given direction through the superposition of portions of the produced sound. Thereby the housing wall operates as a flat sound-wall for the loudspeaker, so that the combined effect of the rest of the housing front-side and rear-side sounds, which are of different power and phase, leads to a directivity with a sound amplification in a preferred direction and with a sound reduction in the opposite direction. In other words: a directivity in the low frequency region will also be beneficially achieved for the single loudspeaker through the arrangement of the single loudspeaker in the specially adapted housing. Consequently, the directivity of the delivered output in the low frequency region will particularly advantageously be increased. 
     The sound from the rear side and the front side effectively superimpose themselves in the shape of a pear in the area of the loudspeaker. Such a pear-shape directivity (also called a hyper kidney) is preferably employed in the near field of the loudspeakers and in the bass frequency region. Equally good is, for example, a kidney-form directivity characteristic. Through the appropriate design of the housing wall a directivity can be adjusted such that therefrom a particularly high directivity in the near field of the loudspeaker results for a specified distance. 
     Preferably the chassis is arranged as a symmetrical, mirror image of the housing. This symmetrical arrangement of the chassis in the cross-section or longitudinal section of the housing results in both sides—front and a rear sides—each having an approximately equal volume of air. Therefore the air resistance or stiffness exerted upon the movement of the speaker&#39;s membrane is approximately equal in both directions of movement. Moreover the approximately equal volumes of air on both sides cause an especially equalized base frequency response. 
     The housing is suitably constructed in the form of a cylinder. Such a tube shaped housing with a circular cross-section makes particularly possible a simple symmetrical arrangement of the chassis. Additionally, a housing in the form of a rectangular box is also preferably suitable for the construction of the loudspeaker box. The cross section of the rectangular box is, for example, a rectangle or a square. Furthermore, a housing may be built with an elongated cross section or longitudinal section, preferably an oval chassis. 
     A sound opening is preferably provided in the housing for at least both the front side and rear side sound. An equal number of sound openings on both sides is preferred. Furthermore the shape of the sound openings is appropriately selected for particularly good directivity. Advisably at least one of the sound openings is located in the area of the sound cone of the rear side and front side sounds. 
     In order to obtain sound directing acoustic dampening, at least one of the sound openings is provided with dampening material. For example, the sound opening on the rear of the chassis is provided with dampening material. A selective sound reduction will be produced on one side through this covering of the rear side sound opening. For example, one side of the frequency response will be lowered in broadband, for example, attenuated 1 to 8 dB. A pear shaped sound propagation pattern is obtained through this single sided selective sound dampening. Fibrous material is an example of material that may serve as a dampening material. The sound reduction can be adjustable or variable by installing different acoustical dampening material or variable quantities or thickness of the dampening material, so that an especially good directivity is achieved at a given distance from the loudspeaker box. 
     This is suitable for the use in a vehicle, in particular in a headrest, in part through the especially compact design and the especially compact construction of the loudspeaker box. Depending on the type and extent of the sound-filled area—the area of the seat associated with the headrest, for example —and also depending upon the desired intensity of the sound of this area, at least one loudspeaker box is integrated into the headrest. Beyond that additional loudspeaker boxes can be provided, particularly in the seat or seat back. The stability of the loudspeaker box also contributes to the mechanical stability of the headrest, particularly when it is part of the frame of the headrest. The mechanical stability of the headrest is provided by an appropriate frame construction and the housing of the loudspeaker box is also so constructed, for instance, out of a soft synthetic material. The opposite case is a loudspeaker box housing that is preferably built out of hard synthetic material or aluminum, where the housing itself contributes to the stability of the headrest. This hard housing section will be appropriately padded, for example, with foam. 
     The advantage obtained through the invention particularly lies in a housing comprising a housing wall surrounding the loudspeaker chassis and wherein the structure of the sounds from the front side and the rear side of the loudspeaker affect each other, especially at low frequencies, and wherein the sound of one side is specifically so lowered, so that the two sound parts, which each have different power and phase, lead to a superposition with a directivity that has a sound increase or amplification in a preferred direction and a sound reduction or attenuation in the opposite direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will be further explained by the use of figures. The figures illustrate: 
     FIG. 1 Cross-sectional schematic of a loudspeaker box. 
     FIG. 2 Schematic of the loudspeaker box according to FIG. 1 in profile. 
     FIG. 3 Schematic of a loudspeaker box implemented as a square box. 
     FIG.  4 . Diagram of the directivity of the loudspeakers in the near field (FIG. 4 a ) and in far field (FIG. 4 b ). 
     FIG.  5 . Profile schematic of a headrest with an integrated loudspeaker 
     FIG.  6 . Schematic of the front view of a headrest with an integrated loudspeaker box. 
     FIG.  7 . Schematic of a headrest with an integrated loudspeaker box as a tubular frame. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Similar parts are labeled with the same reference number in all figures. 
     FIG. 1 illustrates a loudspeaker  1  with a housing  2  and a loudspeaker  4  with a chassis  6 . The chassis  6  is surrounded by a housing wall  8 . 
     The housing  2  is formed as a hollow cylinder. The chassis  6  with the housing wall  8  is preferably arranged symmetrically as a mirror image in the housing  2 , i.e. the chassis  6  is in a substantially symmetrical arrangement with respect to the housing&#39;s  2  lengthwise direction. Because of this, both sides of the loudspeaker  4 , to the greatest possible extent, face an equal volume of air L. As an alternative to the symmetrical arrangement of the chassis  6 , an arrangement that is partially offset within the housing  6  is also possible. In this arrangement, an essentially equal volume of air L is achieved on both sides of the chassis  6  by arranging a compensation volume V on the side of the larger air volume L, e.g. plastic sealing cord or other plastic elements. By having an approximately equal volume of air on both sides—front side and back side—an approximately equal frequency response is made possible. 
     The housing wall  8  is built as a flat sound wall. Both the front side and the rear side of the housing  2  have at least one sound opening  10   a  and  10   b , respectively. In this arrangement, the sound openings  10   a  and  10   b  are arranged on a line that lies on opposite sides of the housing  2  and are each in the area of the sound cones of the rear side and front side sounds, respectively. The sound opening that lies at the rear side of loudspeaker  4  is supplied with dampening material  12 . The attenuation material  12  serves to selectively reduce the sound emerging in the direction of the associated sound opening  10   a , so that in the forward direction of sound opening  10   b , a sound amplification selectively occurs and an especially high directivity is achieved though an elevated discharge power in the preferred direction that is illustrated with arrow R. 
     The form, amount and thickness of the dampening material  12  that is arranged in the sound opening  10   a  is selected so that a defined sound lowering and resulting directivity is adjusted into the preferred direction. Preferably a fibrous material will be used as the dampening material. The dampening material  12  achieves an attenuation of about 1 to 8 dB over a particularly wide band frequency range. 
     FIG. 2 shows a side view of the loudspeaker box  1  of FIG. 1, whereby the housing wall  8  that surrounds the chassis  6  extends over the entire length of the housing  2 . The housing wall  8  will be introduced in the housing  2 , for example and not in the manner illustrated, with the respective ends of the housing  2  closed and attached respectively thereto. A plurality of sound openings  10   a  and  10   b  in housing  2  are intended for both the rear side and also the front side, respectively, of the housing wall  8 . The rear side openings  10   a  are provided with dampening material  12 . The symmetrical construction of the chassis  6  in the housing  2  can not be only in the longitudinal, but can also be, alternatively, in the cross direction. 
     FIG. 3 illustrates an alternative form of the loudspeaker box  1 , wherein the housing  2  is in the form of a square box. The chassis  6  with the surrounding housing wall  8  and the loudspeaker  4  is arranged symmetrically with regards to the surface that is diagonally placed across the square cross section of the housing  2 . The housing  2  is provided with rear and front side sound openings  10   a  and  10   b , respectively. The rear side oriented sound openings are provided with dampening material  12 . Because the arrangement of the loudspeaker  4  reduces the rear side air volume L, the front side of housing  2  has a compensation volume V. 
     In the operation of the loudspeaker box  1  of FIGS. 1 through 3, the rear side sound of the loudspeaker  4  is specifically lowered by the dampening material  12  that is mounted in the sound opening  10   a , whereby the two different power and phase sound parts in the forward direction cause a sound increase in the direction of the sound opening  10   b . Thereby the loudspeaker box  1  causes a sound propagation pattern in the form of a pear, an example of which is shown in FIG. 4 a  for the near field (for approximately 15 cm distance from loudspeaker  4 ) and is shown in FIG. 4 b  for the far field (for approximately 60 cm distance from loudspeaker  4 ). The thin line in FIG. 4 a  and FIG. 4 b  respectively characterize the shape of the sound propagation pattern for a high frequency of approximately 600 Hz. The thick line  16  respectively describes the shape of the sound propagation pattern for a low frequency of approximately 150 Hz. The distance of the sound opening  10   a  and  10   b  of the both sides is about 5 cm according to the utilized measuring object. The rear side attenuation for a frequency of approximately 150 Hz is approximately 10 to 25 dB. 
     As FIGS. 4 a  and  4   b  illustrate, a so called hyper-kidney is shown, especially in the near field of the loudspeaker  4  of the respective loudspeaker box  1 . Accordingly, an especially high directivity to one side is ensured for both high and low frequency, whereby use of the loudspeaker box  1  in a vehicle (not shown), especially in a headrest  14  as is shown in FIG. 5, makes possible an especially well aimed and sufficiently good sound coverage for the seating position associated with the headrest  14 . The headrest  14  is installed by means of at least one post  15  onto a seat (not shown), especially onto its backrest. 
     Preferably, the loudspeaker box  1  will be integrated into the padding of the vehicle&#39;s headrest  14 . 
     In FIG. 6 a headrest  14  with an integrated loudspeaker box  1  is illustrated, which includes two loudspeakers  4  that are located close to each other. The loudspeaker  4  arranged inside the loudspeaker box  1  is shown in shadow in this drawing. The headrest  14  is shown in lengthwise section, so that several rear and front side sound openings  10   a  and  10   b , respectively, are visible. The loudspeaker box  1  is in the upper part of the headrest  14  and is at least partially surrounded by a foam cushion  16 . 
     Through the especially compact design of the loudspeaker box  1  and also through the type of materials used in the housing  2 , for example plastic, the loudspeaker box  1  provides a particular mechanical stability of the head rest  14  if it is integral into a solid part of the headrest  14  or if it, as is shown in FIG. 7, is an integral part of the frame  18 . Therein the loudspeaker box  1  is surrounded by a tube frame and contains at least one loudspeaker  4  on the inside. Alternatives can also integrate several loudspeaker boxes  1  of different types or a loudspeaker box  1  with a plurality of loudspeakers into the frame  18  of the headrest  14 . For example,  2  loudspeaker boxes  1  can be integrated into the headrest  14  such that a stereo playback is possible. A further alternative design for the loudspeaker box  1  is constructed such that the loudspeaker  4  with chassis  6  is incorporated into the hollow area of the frame  18  of the head rest  14 , that provides the supporting and protective function of the headrest  14 , so that the frame  18  is itself built out of the housing  2  for the loudspeaker box  1 . The frame  18  therefore fulfills a double function—housing  2  of the loudspeaker box  1  and also providing for mechanical stability of the headrest  14 .