Abstract:
A passive radiator includes a chassis ( 11 ) and a radiator body which is connected to the chassis and which is movable with respect to the chassis along a translation axis (T*). The radiator is capable of displacing comparatively large air volumes. The radiator body includes a central mass element ( 13   a ) and at least one mass element ( 13   b ) which is arranged concentrically with respect to the central mass element. The radiator further comprises connection units for movably interconnecting each pair of adjacent mass elements and for movably connecting one of the mass elements to an element ( 11   a ) of the chassis. Each of the connection units includes two resilient annular connecting rings ( 5   a   1, 5   a   2; 5   b   1, 5   b   2 ), which have two adjacent elements which are parts of said elements secured to them. The connecting rings of at least one of the connection units bound a closed chamber ( 17   a ) containing a gaseous medium in order to counteract undesired noises. The central mass element with its adjacent connection unit as well as each concentrically arranged mass element with its adjacent connecting limb forms a mass spring system, all the mass spring systems thus defined having, at least substantially, the same resonant frequency.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a passive radiator having a chassis and a radiator body flexibly connected to the chassis and movable with respect to the chassis along a translation axis. 
     2. Description of the Related Art 
     International Patent Application No. WO-A 97/46047, corresponding to U.S. Pat. No. 5,892,184 (PHN 15.840), discloses a passive radiator which comprises a chassis, a mass element, and a sub-chassis extending between the mass element and the chassis. The mass element is movably fastened to the sub-chassis by means of a first resilient suspension ring, and the sub-chassis is movably fastened to the chassis by means of a second resilient suspension ring. The maximum axial excursion of the mass element is defined by the sum of the maximum axial excursions of each of the suspension rings. It has been found that in the case of uses requiring a comparatively high axial compliance in combination with a comparatively large axial excursion of the mass element, the suspension formed by the suspension rings may exhibit such distortions that undesired noises are produced in operation. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to improve the passive radiator of the type defined in the opening paragraph so as to counteract the generation of undesired noises. 
     This object is achieved with the passive radiator in accordance with the invention which comprises a chassis and a radiator body connected to said chassis and which is movable with respect to said chassis along a translation axis, the radiator body comprising a central mass element and at least one mass element which is arranged concentrically with respect to the central mass element, connection units being provided for movably interconnecting every two adjacent mass elements and for movably securing one of the mass elements to the element of the chassis, each of said connection units comprising two resilient annular connecting limbs, to which two connecting limbs two adjacent elements which form part of the said elements are secured, the connecting limbs of at least one of the connection units bounding a closed chamber which extends between the elements secured to said units and which is filled with a gaseous medium, the central mass element with its adjacent connection unit, as well as each concentrically arranged mass element with its adjacent connecting limb, forming a mass spring system, all the mass spring systems thus defined having at least substantially the same resonant frequency. 
     The use of two or more mass elements interconnected by resilient connecting limbs, also referred to as connecting rings, leads to a construction with a multiple suspension in which each mass element present contributes to the total air displacement during use. The connecting limbs are ring-shaped in view of their use. A mass element performs individual movements with respect to an adjacent mass element along the translation axis of the radiator body in operation, which results in displacements with respect to the chassis which are cumulations of individual movements. Comparatively large displacements of mass elements can be realized in this manner, so that considerable volume displacements can be achieved with a comparatively small radiator body. To counteract parasitic resonances and, as a consequence, the generation of undesired noises during use, the mass spring systems, present in the passive radiator according to the invention as defined above, have the same, or practically the same, resonance frequency. As a result of the use of one or more closed, i.e., impervious, chambers, translational movements of the radiator body produce pressure variations in the gaseous medium present between the connecting limbs of one or more connecting units. In the case of deflecting translational movements of the radiator body, these pressure variations are pressure rises, which have a favorable effect on the behavior of the suspension, particularly on the connecting limbs of the respective connecting unit or units. As a matter fact, these pressure rises result in pressure being exerted on the respective connecting limbs, which pressure issues from the closed chamber or chambers and prevents the connecting limbs from behaving in an unstable manner, such as flapping, fluttering or buckling, and thus producing undesired noises. This measure furthermore has the advantage that thin connecting limbs can be used, which enables a high axial compliance, i.e., a low stiffness, of the suspension formed by the connecting limbs to be achieved in the directions of translation of the radiator body. Decisive factors for the overall axial compliance of the whole arrangement are, particularly, the compliance of the medium in the closed chamber or chambers, and the resistance to deformation of the suspension. As the gaseous medium, a gas, air or another gas mixture may be used. 
     An embodiment of the passive radiator in accordance with the invention is characterized in that the connection units allow mainly movements of the mass elements along the translation axis of the radiator body, and counteract other movements. In this embodiment, it is prevented that the mass elements perform undesired tilting movements with respect to one another during operation, which tilting movements could lead to distortions in the sound reproduction. The annular connecting limbs used may be made from resilient materials which are known per se, such as, polyurethane or rubber, and preferably have a folded or corrugated structure. 
     An embodiment of the radiator in accordance with the invention is characterized in that a sealed chamber extends at least between the connecting limbs of the connection unit which adjoins the central mass element. 
     The embodiment of the radiator described above is preferably characterized in that the central mass element has a projection which extends to a location between the connecting limbs of the connection unit which adjoins the central mass element. The use of this characteristic feature results in a reduction of the closed chamber, which leads to greater pressure variations when the radiator body moves. An advantage of this that very thin connecting limbs can be used, preferably membranous limbs. Preferably, the projection is annular. 
     An embodiment of the radiator in accordance with the invention is characterized in that the sealed chamber contains a damping means for damping movements of the gaseous medium. The use of this characteristic feature enables the mechanical Q factor of the mass-spring systems to be reduced, as a result of which, any mutual resonances are damped out very effectively. 
     In the embodiment described above, the damping means preferably comprises an annular body of a porous material, for example, a cellular material, such as, a polyurethane foam. Such a material has a structure of small open cells. In operation, i.e., while the radiator body performs a translation, a gaseous medium present in the closed chamber flows through the cellular structure. This flow presents a mechanical resistance to translational movements of the radiator body with respect to its environment. 
     A practical embodiment of the radiator in accordance with the invention is characterized in that the annular body of a porous material forms part of the central mass element of the radiator body. The annular body may then be a part secured to the central mass element. The central mass element may be provided with a tuning mass, for which purpose a recess or cavity may be provided. 
     An embodiment of the radiator in accordance with the invention is characterized in that the number of mass elements is two, three or four. Although it is possible to use more mass elements, it has been found that a construction using two, three or four mass elements is satisfactory and can well be realized in practice in order to obtain a reliable radiator which is free from undesired noises and has a large excursion. 
     An embodiment of the radiator in accordance with the invention is characterized in that the shapes of the connecting limbs are identical to one another. This embodiment is to be preferred if it is an object to give each mass element the same maximum axial excursion with respect to its adjacent mass element or adjacent mass elements. In a practical embodiment, the connecting limbs may be, for example, omega-shaped. Any further connecting limbs are preferably arranged mirror-inverted positions with respect to each other for reasons of symmetry, so as to prevent asymmetry in the excursions and amplitudes of the mass elements. 
     An embodiment of the radiator according to the invention is characterized in that at least a number of the connecting limbs are of mutually different sizes, said sizes increasing in a direction away from the central mass element. By this measure, it is achieved that in relative terms, i.e., relative to its adjacent centrally disposed or more centrally disposed mass element, an annular mass element can perform a greater maximum relative displacement. An advantage of this configuration is that the connection units are utilized in an optimum manner without the deflections causing any undesired deformations of the connecting limbs. 
     The invention further relates to a loudspeaker system comprising an enclosure or cabinet which accommodates an electrodynamic loudspeaker and a passive radiator. The loudspeaker may be of any type which is known per se. The passive radiator present in the loudspeaker system according to the invention is constructed as defined above. The connection units of the passive radiator in the system according to the invention, allow well-defined mutual displacements of the mass elements under the influence of pressure variations in the enclosure, these displacements resulting in comparatively large air displacements, thereby enabling a comparatively high sound pressure to be achieved. Under the influence of pressure variations in the enclosure, the various connection units in such a system allow excursions which are fully adapted to the total moving mass of the radiator and the tuning frequency, the so-called Helmholtz resonance, of the system. For the above-mentioned reason, the resonant frequency of the mass spring systems that have been provided is preferably equal to the Helmholtz frequency of the enclosure including the loudspeaker and passive radiator, in the case that the system in accordance with the invention has 2 mass elements. 
     The invention further relates to an apparatus for presenting audible and, at option, visible information, the apparatus in accordance with the invention including the loudspeaker system in accordance with the invention. Such an apparatus is, for example, an audio-video or multi-media apparatus. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail by way of example with reference to the drawings, in which: 
     FIG. 1 is a diagrammatic longitudinal sectional view which shows a first embodiment of the passive radiator in accordance with the invention; 
     FIG. 2 is a diagrammatic longitudinal sectional view which shows a second embodiment of the passive radiator, in accordance with the invention, in a rest condition; 
     FIG. 3 is a diagrammatic longitudinal sectional view which shows the second embodiment of the passive radiator, in accordance with the invention, in an operating condition; 
     FIG. 4 is a diagrammatic longitudinal sectional view which shows a third embodiment of the passive radiator in accordance with the invention; 
     FIG. 5 is a diagrammatic longitudinal sectional view which shows a fourth embodiment of the passive radiator in accordance with the invention; 
     FIG. 6 is a diagrammatic longitudinal sectional view which shows a fifth embodiment of the passive radiator in accordance with the invention; 
     FIG. 7 is a diagrammatic longitudinal sectional view which shows an embodiment of the loudspeaker system in accordance with the invention; and 
     FIG. 8 is a diagrammatic front view which shows an embodiment of the apparatus in accordance with the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The passive radiator, in accordance with the invention shown in FIG. 1, is suitable for use in a bass reflex loudspeaker system. The radiator comprises a chassis  1 , a radiator body  3  movable relative to the chassis  1  along a translation axis T, and connection means for flexibly connecting the radiator body  3  to an element la of the chassis  1 . In the present example, the element  1   a  is cylindrical. The radiator body  3  in the present example comprises a central mass element  3   a  and three mass elements  3   b ,  3   c  and  3   d  which are arranged concentrically with respect to the central mass element  3   a . The central mass element  3   a  in the present example is constructed as a cylinder having an imperforate cylindrical wall closed with two convex end faces. The other mass elements  3   b ,  3   c  and  3   d  in the present example are also cylinders but have open end faces. The cylinders may be have imperforate cylindrical walls or more or less open cylindrical walls. In the present example said connection means comprise four connection units  5   a ,  5   b ,  5   c  and  5   d . The three connection units  5   a ,  5   b  and  5   c  serve for connecting the two respective adjacent mass elements  3   a / 3   b ,  3   b / 3   c , and  3   c / 3   d , so as to be movable relative to one another. The connection unit  5   d  serves for movably connecting the mass element  3   d  to the element  1   a  of the chassis  1 . In the present example, each of the connection units  5   a ,  5   b ,  5   c  and  5   d  is formed by two annular connecting limbs  5   a   1 / 5   a   2 ,  5   b   1 / 5   b   2 ,  5   c   1 / 5   c   2 , and  5   d   1 / 5   d   2 , respectively. In the present example, these connecting limbs are of omega-shaped cross-section and are made of rubber. At their edges the annular connecting limbs are connected to the mass elements  3   a ,  3   b ,  3   c  and  3   d  and to the element  1   a  of the chassis  1 , as applicable, by fixing means which are known per se, such as, an adhesive, and, on account of their shapes and material properties. The annular connecting limbs have a behavior such that during use, mainly movements of the mass elements  3   a ,  3   b ,  3   c  and  3   d  along the translation axis T are admitted, while undesirable tilting movements of the mass elements are counteracted. In the present example, the connecting limbs are identical to one another, wave crests of two facing connecting limbs  5   a   1 / 5   a   2 ,  5   b   1 / 5   b   2 ,  5   c   1 / 5   c   2 , and  5   d   1 / 5   d   2  being remote from each other so as to obtain a symmetrical suspension arrangement. 
     The passive radiator in accordance with the invention, as shown in FIG. 1, has four mass spring systems which are independent of one another. These mass spring systems are formed by the mass element  3   a  with its adjacent connection unit  5   a  formed by the adjacent connecting limbs  5   a   1  and  5   a   2 ; the mass element  3   b  with its adjacent connecting limbs  5   a   1 / 5   a   2  and  5   b   1 / 5   b   2 ; the mass element  3   c  with its adjacent connecting limbs  5   b   1 / 5   b   2  and  5   c   1 / 5   c   2 ; and the mass element  3   d  with its adjacent connecting limbs  5   c   1 / 5   c   2  and  5   d   1 / 5   d   2 . One of the characteristic features of the embodiment shown is that the mass spring systems all have the same, or substantially the same, resonant frequency so as to ensure that the mass elements  3   a ,  3   b ,  3   c  and  3   d  always move in phase during operation. The embodiment of the passive radiator in accordance with the invention as shown in FIG. 1 has four concentric continuous chambers  7   a ,  7   b ,  7   c  and  7   d  which are coaxial with the translation axis T and which are, respectively, bounded by the central mass element  3   a , the connecting limbs  5   a   1 ,  4   a   2  and the mass element  3   b ; the mass element  3   b , the connecting limbs  5   b   1 ,  5   b   2  and the mass element  3   c ; the mass element  3   c , the connecting limbs  5   c   1 ,  5   c   2  and the mass element  3   d ; the mass element  3   d , the connecting limbs  5   d ,  5   d   2  and the element  1   a  of the chassis  1 . Of the chambers  7   a ,  7   b ,  7   c  and  7   d , the chamber  7   a  is closed, or sealed, and filled with air of which the pressure in the position shown, i.e., the rest position, of the radiator corresponds to the atmospheric pressure. The pressure may alternatively be slightly higher than the atmospheric pressure. The measures that have been taken ensure a reliable operation of the passive radiator, the maximum displacement of the central mass element  3   a  from its rest position being the sum of the maximum excursions allowed by the individual connection units  5   a ,  5   b ,  5   c  and  5   d . It will be obvious that the maximum displacement of the mass element  3   b  is the sum of the maximum excursions of the individual connection units  5   b ,  5   c  and  5   d ; the maximum displacement of the mass element  3   c  is the sum of the maximum excursions of the connection units  5   c , and  5   d ; and the maximum displacement of the mass element  3   d  corresponds to the maximum excursion of the connection unit  5   d . Large air displacements are possible as a result of the comparatively large maximum displacement of the radiator body  3  obtained here. 
     The easy-to-realize and, consequently, practical passive radiator according to the invention shown in FIG. 2 has a chassis  11  and a radiator body  13  which comprises two mass elements. The radiator body  13  is movable relative to the chassis  11  along a translation axis T*. The radiator body  13  has a cylindrical central mass element  13   a  which is circumferentially closed and a cylindrical mass element  13   b  which is circumferentially closed. The chassis  11  has a cylindrical element  11   a . The elements  11   a ,  13   a  and  13   b  all lie in one zone and are arranged coaxially with one another, the central axis of the central mass element  13   a  being coincident with the translation axis T*. The mass elements  13   a  and  13   b  are mechanically interconnected by means of a pair of resilient annular connecting limbs  15   a   1  and  15   a   2 . The mass element  13   b  is also mechanically connected to the element  11   a  of the chassis  11  by means of a pair of resilient annular connecting limbs  15   b   1 ,  15   b   2 . The configuration of mass elements  13   a  and  13   b  and connecting limbs  15   a   1 ,  15   a   2  and  15   b   1 ,  15   b   2  as used in this embodiment implies that there are two mass spring systems. These mass spring systems are formed by the mass element  13   a  and the pair of connecting limbs  15   a   1 ,  15   a   2 ; by the mass element  13   b  and the connecting limbs  15   a   1 ,  15   a   2  and  15   b   1 ,  15   b   2 . These mass spring systems have the same resonant frequency (natural frequency). The connecting limbs  15   a   1 ,  15   a   2  and  15   b   1  are made of rubber or another air-tight material and are all flexible and compliant in directions parallel to the translation axis T* and offer sufficient resistance to lateral deformations. In the present embodiment, the space bounded by the central mass element  13   a , the mass element  13   b , both made of, for example, a hard plastic, and the connecting limbs  15   a   1  and  15   a   2  connected to the elements  13   a  and  13   b  takes the form of a sealed chamber  17   a , in which a volume of air is present. If desired, the space bounded by the mass element  13   b , the element  11   a  and the connecting limbs  15   b   1  and  15   b   2  connected to these two elements may also take the form of a sealed chamber  17   b , in which case the element should be circumferentially closed. 
     The embodiment shown in FIG. 2 is shown in its rest position. FIG. 3 shows a part of this embodiment but now the radiator body  13  has performed a movement along the translation axis T* out of the rest position under the influence of external pressure variations, the central mass element  13   a  having an excursion A with respect to mass element  13   b . The shape of the connecting limbs  15   a   1  and  15   a   2  in the rest position of the radiator is shown in broken lines in FIG.  3 . In the operating position of the radiator, the volume of the sealed chamber  17   a , as is also illustrated in FIG. 3, is smaller than in the rest position. This means that there has been a rise in air pressure during the movement of the mass element  13   a  with respect to the mass element  13   b . As stated hereinbefore, such a rise in pressure has a favorable effect on the behavior of the connecting limbs  15   a   1  and  15   a   2 , particularly as regards the maintenance of their bent shapes. As a result of the measures taken, the connecting limbs  15   a   1  and  15   a   2  can be surprisingly thin. In the present example, the thickness is 0.3 mm. 
     In the following description of further embodiments, the same reference numerals as used in the description of the embodiment shown in FIG. 2 will be used for like parts in the various embodiments. 
     In the embodiment of the radiator in accordance with the invention shown in FIG. 4 the central mass element  13   a , which in the present embodiment is made of a hard plastic, has a radially projecting annular projection  13   a   1  which surrounds the mass element  13   a  concentrically. The annular projection  13   a   1 , which is integral with the mass element  13   a  and has inherently imperforate walls, extends into the air-filled sealed chamber  17   a . The presence of the projection  13   a   1  provides a substantial reduction of the volume of the chamber  17   a , as a result of which comparatively large pressure variations can occur during axial excursions of the mass element  13   a  with respect to the mass element  13   b . With the mass element  13   b  in the sealed chamber  17   a , the projection  13   a  defines a narrow passage  19 , which has a damping effect on the air streams produced in the chamber  17   a  during movements of the radiator body  13  with respect to the chassis  1 . The annular projection  13   a   1  preferably has trapezoidal longitudinal section which decreases in a radially outward direction. 
     The embodiment shown in FIG. 5 has a central mass element  13   a  to which an annular body  13   a   2  of a porous material, in the present example a polyurethane foam, is secured. The annular body  13   a   2  is disposed in the sealed chamber  17   a  and, in operation, it has a damping effect on air streams generated in the chamber  17   a . In a longitudinal sectional view, the porous body  13   a   2  is tooth-shaped and has a top facing the adjacent mass element  13   b . Preferably, a narrow annular gap  21  is formed between the body  13   a  and the mass element  13   b.    
     FIG. 6 shows an embodiment of the passive radiator in accordance with the invention having two sealed chambers  17   a  and  17   b . The central mass element  13   a  has a central base  13   a   3  and an annular body  13   a   2  which extends into the sealed chamber  17   a , the base  13   a   3  and the body  13   a   2  forming an integral body having imperforate walls. In a central area the mass element  13   a  has a cavity for receiving a tuning mass  23 . In the present example, the element  11   a  of the chassis  11  has an annular inward projection  11   a   1  in order to reduce the volume of the chamber  17   b . A passage  25  is situated between the projection  11   a   1  and the facing mass element  13   b.    
     The loudspeaker system in accordance with the invention shown in FIG. 7, i.e., a bass reflex system, comprises an enclosure or acoustic box  100  which accommodates the passive radiator in accordance with the invention, in the present example, a radiator in accordance with the embodiment shown in FIG.  2  and bearing the reference numeral  103 , and an electrodynamic loudspeaker  102 . The loudspeaker  102  drives the radiator  103  during operation, the loudspeaker and the radiator in this example together providing the sound production in the low-frequency range of the sound spectrum. The system is, consequently, a sub-woofer device. The enclosure  100  of the system has a first opening  104  through which the chassis  11  of the passive radiator  103  extends, and a second opening  106  through which a chassis  101  of the loudspeaker  102  extends. The chassis  11  and the chassis  101  are secured to the edge portions  100   a  and  100   b  of the enclosure which surround the openings  104  and  106 , respectively. 
     For a more detailed description of the passive radiator  103 , reference is made to the passages in the present document which relate to the radiator shown in FIG. 2, and it is to be noted that the resonant frequency of the mass spring systems provided in the radiator  103  is equal to the Helmholtz resonance of the system. 
     The loudspeaker  102  used in the system shown comprises a conical diaphragm  105  and an electromagnetic actuator  107 . In the present example, a dust cap  117  is present in the diaphragm  105 . The diaphragm  105  has a front part  105   a  with an opening  109  and a rear part  105   b  with a tubular central element  111 . The element  111  carries a first actuator part  107   a  of the actuator  107 , which part takes the form of a coil in the present example. The coil  107   a  is electrically connected to terminals  110  disposed on the chassis  101  via electrical conductors  108 . The actuator  107  further comprises a second actuator part  107   b , which in the present example includes an annular magnet  107   b   1 , a yoke part  107   b   2 , and a yoke part  107   b   3  secured to a chassis part  101   b  of the chassis  101 . An air gap  107   c , in which the coil  107   a  extends, is formed between the yoke parts  107   b   2  and  107   b   3 . When the actuator is energized, the coil  107   a , and thus the diaphragm  105 , will perform an axial excursion along a diaphragm axis  105   c  in either of the axial directions indicated by a double arrow X. 
     The loudspeaker  102  has been provided with a flexible connecting limb  115 , which connects the front part  105   a  of the diaphragm  105  to the chassis  101 . In the present example, the flexible connecting limb  115  is constructed as an annular element of omega-shaped cross-section. The connecting limb  115 , which is made, for example, of polyurethane, may be connected to the diaphragm  105  and the chassis  101  by means of an adhesive joint. 
     In the present example, the loudspeaker  102  further includes a flexible centering element  119  in the form of a centering disc having a concentric corrugation pattern and made of a suitable material, such as, a textile fabric, which connects the chassis  101  to the back part  105   b , in particular to the central element  111  thereof. The centering element  119  and the connecting limbs  113  and  115  are suspension means which are comparatively slack and flexible in axial directions indicated by the arrow X but which are comparatively stiff in other directions, as a result of which, the diaphragm  105  with the coil  107   a  is capable of performing well-defined axial excursions with respect to the chassis  101 . Obviously, another loudspeaker than the loudspeaker shown may be used, such as, a loudspeaker element with a multiply suspended vibration system. 
     The apparatus in accordance with the invention shown in FIG. 8 is a flat-panel multimedia TV set. The apparatus has a cabinet  201  which accommodates a display screen  203  and two loudspeaker systems in accordance with the invention. The cabinet  201  has an on/off-switch unit  207  at its front side. The loudspeaker systems in the present example correspond to the loudspeaker system as shown in FIG.  7  and bear the reference numeral  205  in FIG.  8 . Each loudspeaker system  205  consequently has an enclosure  100  with a loudspeaker  102  and a passive radiator  103  in accordance with the invention. Instead of the apparatus shown, the apparatus in accordance with the invention may alternatively be a conventional TV set, a monitor, or a piece of audio equipment. Furthermore, the radiator used in the apparatus may be constructed as shown in FIGS. 1,  3 ,  4 ,  5  or  6  or in some other manner within the scope of the invention, and a loudspeaker different from the loudspeaker shown in FIG. 7 may be used. Furthermore, the invention is not limited to the embodiments of the passive radiator shown in the Figures. For example, instead of two, three or four mass elements, more than four mass elements may be used, and instead of omega-shaped connecting limbs sinusoidal or differently shaped suitable connecting limbs may be used.