PASSIVE RADIATOR WITH MASS ELEMENTS

Abstract: A passive radiator comprising a frame (1) and a radiator body (<i>3</i>) which is connected to the frame and which is movable relative to the frame along a translation axis (T). The radiator is suitable for the displacement of comparatively large air volumes. The radiator body comprises a central mass element (3a) and at least one mass element (3b, 3c, 3d) which is concentrically arranged with respect to the central mass element. The radiator further comprises connection units (<i>5a</i>, <i>5b</i>, <i>5c</i>, <i>5d</i>) for the movable interconnection of each pair of adjoining mass elements and for the movable fastening of one of the mass elements to the frame. Each of said connection units comprises at least a resilient annular connection element (5a1, 5a2; 5b1, 5b2; 5c1, 5c2; 5d1, 5d2), such that the central mass element with its adjoining connection unit forms a mass spring system, as does each concentrically arranged mass element with its adjoining connection element, while all mass spring systems thus defined have at least substantially the same resonance frequency.

Description: Passive radiator with mass elements The invention relates to a passive radiator comprising a frame and a radiator body which is connected to said frame and which is movable with respect to said frame along a translation axis. Such a radiator is known from US-A 3,669,215 and is designed for use in a bass reflex loudspeaker system. The known passive radiator comprises a basket-shaped frame and a conical body which is suspended from the frame. The suspension used consists of a deformable suspension ring which extends between a greatest circumferential rim ofthe conical body and the frame. A plate is fastened to the smallest circumferential rim ofthe conical body and is also fastened to a back part ofthe frame via three elastic wire elements. This suspension allows of limited axial displacements ofthe conical body with respect to the frame only, so that major volume displacements, i.e. displacements of major quantities of air, are only possible if the conical body has large lateral dimensions. It is an object ofthe invention to improve the passive radiator mentioned in the opening paragraph such that displacements of comparatively large air volumes are possible while the radiator has limited transverse dimensions. This object is achieved with the passive radiator according to the invention which is characterized in that the radiator body comprises a central mass element and at least one mass element concentrically positioned with respect to the central mass element, while connection units are present for the movable interconnection of every two mutually adjoining mass elements and for the movable fastening of one ofthe mass elements to the frame, each of said connection units comprising at least a resilient annular connection element, the central mass element with its adjoining connection unit forming a mass spring system, as does each conically positioned mass element with its adjoining connection elements, while all mass spring systems present and thus defined have at least substantially the same resonance frequency. The use of two or more mass elements which are interconnected by resilient connection elements leads to a construction with a multiple suspension in which each mass element present contributes to the total air displacement during use. A mass element performs individual movements with respect to an adjoining mass element along the translation axis of the radiator body during operation, which results in displacements with respect to the frame which are cumulations of individual movements. Comparatively large displacements of mass elements can be realized in this mannei, so that considerable volume displacements can be achieved with a comparatively small radiator body. To counteract parasitic resonances during use, it was found to be necessary for the mass spring systems present in the passive radiator according to the invention as defined above to have the same or practically the same resonance frequency. If this requirement is not complied with, movements of individual mass elements may get out of phase, so that serious sound distortions and/or attenuations may arise during use. Damping means may be used, if so desired, for counteracting irregularities in movements of individual mass elements. It is noted that WO-A 97/46047 (PHN 15.840) discloses a passive radiator which comprises a frame, a mass element, and a sub-frame extending between the mass element and the frame, while the mass element is movably fastened to the sub-frame by means of a first resilient suspension ring and the sub-frame is movably fastened to the frame by means of a second resilient suspension ring. The maximum stroke of the mass element is defined by the sum ofthe maximum strokes of each of said suspension rings. Although a reasonably large volume displacement is possible with this known construction, it was found that a greater maximum stroke is desirable at higher powers so as to prevent harmonic distortion in the low frequency range. An embodiment ofthe passive radiator according to the invention is characterized in that the connection units allow mainly of movements ofthe mass elements along the translation axis ofthe radiator body and counteract other movements. It is prevented in this embodiment that the mass elements perform disadvantageous tilting movements with respect to one another during operation, which tilting movements could lead to distortions in the sound reproduction. The annular connection elements used may be made from resilient materials which are known per se such as polyurethane or rubber and preferably each have a folded or wave structure. Shape and dimensions ofthe connection elements lie within comparatively narrow limits which are defined inter alia by the required resistance to pressure variations which occur during operation and the capacity of deforming in a flexible manner, i.e. without disadvantageous effects such as kinking or abutting, during the movement ofthe mass elements. A connection element which is too slack and/or not flexibly deformable gives rise to undesirable distortions, especially distortions ofthe second and higher order, in the sound reproduction and accordingly to unpleasant additional noises. An increase in the size of the suspension ring ofthe radiator known from US-A 3,664,215 or an increase in the size of the suspension rings ofthe radiator known from WO-A 97/46047 will not lead to satisfactory results for this reason. A greater volume displacement achieved in that manner will in fact be accompanied by an impaired sound reproduction quality. An embodiment ofthe radiator according to the invention is characterized in that at least a number ofthe connection elements comprise a further resilient annular connection element, which further connection element and the connection element mentioned earlier of such a connection unit are at a distance from one another, measured along the translation axis ofthe radiator body. This embodiment is particularly suitable if, instead of a plane or thin radiator body, a radiator body with a considerable axial dimension is used, i.e. a dimension in a direction parallel to the translation axis ofthe radiator body. The specific configuration of connection elements used in the present embodiment safeguards well-defined displacements ofthe mass elements ofthe radiator body, so that swinging movements as a result of pressure variations and/or parasitic resonances can be avoided. An embodiment ofthe radiator according to the invention is characterized in that the number of mass elements is three or four. Although a different number of mass elements is possible, it was found that a design with three or four mass elements can be well realized in practice for achieving a displacement of a comparatively large air volume. An embodiment ofthe radiator according to the invention is characterized in that the connection elements are mutually identical. This embodiment is preferable if the object is to give each mass element the same maximum axial stroke with respect to its adjoining mass element or adjoining mass elements. In a practical embodiment, the connection elements may be, for example, omega-shaped. Any further connection elements, if present, are preferably provided in mirrored positions with respect to the other connection elements so as to prevent asymmetry in the displacements and amplitudes ofthe mass elements. An embodiment ofthe radiator according to the invention is characterized in that at least a number ofthe connection elements are of mutually different sizes, said size increasing in a direction away from the central mass element. It is achieved by this measure that an annular mass element is capable of performing a relatively greater maximum displacement than a central mass element which is present, i.e. compared with its respective adjoining central or more centrally positioned mass element each time. An advantage of this configuration is that the strokes ofthe connection elements are optimally utilized without undesirable deformations ofthe connection elements occurring. An embodiment ofthe passive radiator according to the invention is characterized in that the radiator body and the connection units are together constructed as one integral unit. The mass elements and the connection elements in such a unit are preferably manufactured from one material, such as rubber. The integral unit may be constructed as a skin, in particular a thin skin, which is fastened with its circumferential edge to the frame. The number of mass elements in this embodiment may be much larger than the number of three or four mentioned elsewhere in this description. The invention further relates to a loudspeaker system comprising a housing 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 in one ofthe claims 1 to 7. The connection units and the passive radiator in the system according to the invention allow of mutual displacements ofthe mass elements defined by pressure variations in the housing, which displacements result in comparatively large air displacements, so that a comparatively large sound pressure can be achieved. In such a system the various connection units allow of strokes under the influence of pressure variations in the housing which are fully attuned to the total moving mass ofthe radiator and the tuning frequency, the so-called Helmholz resonance, ofthe system. The invention further relates to a device for providing audible, and possibly also visible information, which device according to the invention is provided with the loudspeaker system according to the invention. It is noted about the claims that various combinations of characteristics as defined in the dependent claims are possible. The invention will now be explained in more detail by way of example with reference to the drawing, in which Fig. 1 diagrammatically and in longitudinal section shows a first embodiment of the passive radiator according to the invention, Fig. 2 diagrammatically and in longitudinal section shows a second embodiment ofthe radiator according to the invention, Fig. 3 diagrammatically and in longitudinal section shows a third embodiment ofthe radiator, Fig. 4 diagrammatically and in longitudinal section shows an embodiment of the loudspeaker system according to the invention, and Fig. 5 is a diagrammatic front elevation of an embodiment ofthe device according to the invention. The passive radiator according to the invention shown in Fig. 1 is suitable for use in a bass reflex loudspeaker system. The radiator comprises a frame 1 , a radiator body 3 which is movable relative to the frame 1 along a translation axis T, and connection means for flexibly connecting the radiator body 3 to the frame 1. The frame 1 in this example is cylindrical. The radiator body 3 in this example comprises a central mass element 3a and three mass elements 3b, 3c and 3d which are concentrically arranged around the mass element 3a. The central mass element 3 a in this example is constructed as a cylinder with two closed, convex end faces. The other mass elements 3b, 3c and 3d in this example are also cylinders, but they have open end faces. The cylinders may be provided with closed cylinder walls or with more or less open cylinder walls. Said connection means in this example comprise four connection units 5a, 5b, 5c and 5d. The three connection units 5a, 5_b and 5c serve for connecting the two respective adjoining mass elements 3a and 3b; 3b and 3c; and 3c and 3d so as to be mutually movable each time. The connection unit 5_d serves for movably connecting the mass element 3d to the frame 1. In this example, each ofthe connection units 5a, 5b, 5c and 5d are formed from two annular connection elements 5al, 5a2; 5bl, 5b2; 5cl, 5c2; and 5dl, 5d2, respectively. These connection elements in this example have an omega-shaped cross-section and are manufactured from rubber. The annular connection elements are connected at their edges to the mass elements 3a, 3b, 3c and 3d and to the frame 1, as applicable, by means which are known per se, such as glue, and on account of their shapes and material properties have a behavior such that mainly movements ofthe mass elements 3a, 3b, 3c and 3d along the translation axis T are admitted during use, while undesirable tilting movements ofthe mass elements are counteracted. In this example, the connection elements are mutually identical, while a symmetrical suspension arrangement is obtained in that the wave crests of two mutually opposed connection elements 5al and 5a2; 5b 1 and 5b2; 5c 1 and 5c2; and 5dl and 5d2 face away from each other. Four mutually independent mass spring systems are present in the passive radiator according to the invention as shown in Fig. 1. These mass spring systems are formed by the mass element 3a with its adjoining connection unit 5a (or its adjoining connection elements 5al and 5a2); the mass element 3b with its adjoining connection elements 5al, 5a2 and 5bl, 5b2; the mass element 3c with its adjoining connection elements 5bl, 5b2 and 5cl, 5c2; and the mass element 3d with its adjoining connection elements 5cl, 5c2 and 5dl, 5d2. One ofthe characteristic features ofthe embodiment shown is that these mass spring systems all have the same or substantially the same resonance frequency so as to ensure that the mass elements 3a, 3b, 3c and 3d always move in phase during operation. A reliable operation ofthe passive radiator is safeguarded by this measure, with the maximum displacement ofthe central mass element 3a from its idle position, which is the position shown in Fig. 1, being the sum of the maximum displacements allowed by the individual connection units 5a, 5_b, 5c and 5d. It will be obvious that the maximum displacement of the mass element 3b is the sum ofthe maximum strokes of the individual connection units 5_b, 5c and 5d; the maximum displacement ofthe mass element 3 c is the sum ofthe maximum strokes ofthe connection units 5c, and 5d; and the maximum displacement ofthe mass element 3d corresponds to the maximum stroke ofthe connection unit 5d. Large air displacements are rendered possible by the comparatively great maximum displacement ofthe radiator body 3 obtained here. The passive radiator according to the invention shown in Fig. 2 has an annular frame 1 1 and a radiator body Y3 which comprises a number of mass elements. The radiator body 13 is displaceable relative to the frame 11 along a translation axis T . In this example, the radiator body 3 has a cylindrical central mass element 13a and two cylindrical mass elements 13b and 13c. The mass elements 13a, 13b and 13c all lie in one and the same zone and are arranged mutually coaxially, with the translation axis T as the common axis. The mass elements 13a, 13b and 13c are mechanically interconnected two-by-two by means of pairs of resilient annular connection elements 5al, 5a2 and 5b 1, 5b2, respectively. The mass element 13c is also mechanically connected to the frame 11 by means of a pair of resilient annular connection elements 5c 1, 5c2. The configuration of mass elements 13a, 13b and 13c and connection elements 5al, 5a2; 5bl, 5b2; and 5cl, 5c2 as used in this embodiment implies that there are three mass spring systems. These mass spring systems are formed by the mass element 13a and the pair of connection elements 5al, 5a2; by the mass element 13b and the connection elements 5al, 5a2 and 5bl, 5b2; and by the mass element 13c and the connection elements 5bl, 5b2 and 5cl, 5c2; respectively. All these mass spring systems have the same resonance (or natural) frequency. The connection elements used 5al, 5a2; 5b 1, 5b2; 5c 1, 5c2 are all flexible and yielding in directions parallel to the translation axis T and offer sufficient resistance to lateral deformations. The connection elements differ in size in this embodiment, the object of this being to render possible mutually differing displacements ofthe mass elements 13a, 13b and 13c in axial directions, i.e. in directions parallel to the translation axis T . In this example, the pair of connection elements 5al, 5a2 allows ofthe smallest axial displacement, and the pair of connection elements 5c 1, 5c2 allows ofthe greatest axial displacement. The maximum absolute displacement ofthe individual mass elements 13a, 13b and 13c, in other words the maximum displacement relative to the frame 11, obviously rises in the order 13c, 13b, 13a, the central mass element 13a thus having the greatest maximum absolute displacement or amplitude. The passive radiator according to the invention shown in Fig. 3 has a frame 21 and a foil 22 which is fastened to the frame 21 and which can yield along a translation axis T ** . The foil 22, for example made of rubber, has been provided with a concentric structure, for example by means of variations in thickness or density, such that it comprises a central mass element 23a and a large number of annular mass elements 23x and annular connection elements 25y which in mutual conjunction constitute mass spring systems with the same resonance frequency each time. The foil 22 accordingly is a unit in which a radiator body with mass elements and connection elements for the flexible connection ofthe radiator body to the frame and for the mutual flexible connection ofthe mass elements has been integrally accommodated. Suitable structures for this may be determined by means of computer calculations and/or simulations. The loudspeaker system according to the invention shown in Fig. 4, a bass reflex system, comprises a housing or resonance box 100 in which a passive radiator according to the invention, in this example the embodiment shown in Fig. 1 and indicated with reference numeral 103, and an electrodynamic loudspeaker 102 are present. The loudspeaker 102 drives the radiator 103 during operation, the loudspeaker and radiator in that case together ensuring the sound production in the low-frequency range ofthe sound spectrum. The system is accordingly a sub- woofer device. The housing 100 of the system is provided with a first opening 104 through which the frame 1 of the passive radiator 103 is passed, and with a second opening 106 through which a frame 101 ofthe loudspeaker 102 is passed. The frame 1 and the frame 101 are fastened to the edge portions 100a and 100b ofthe housing surrounding the openings 104 and 106, respectively. For a further description ofthe passive radiator, the reader is referred to the passages in the present document relating to Fig. 1 , while it should be noted that the resonance frequency ofthe mass spring systems present is equal to the Helmholz resonance ofthe system. The loudspeaker 102 used in the system shown comprises a sub-frame 101a, a membrane 105, and an electromagnetic actuator 107. The sub-frame 101a, which is conical in this example, extends between the frame 101 and the conical membrane 105. A dust cover 117 is present in the membrane 105 in this example. The sub-frame 101a has a closed enveloping surface, opposite which reverberation openings may be present in the frame 101. The membrane 105 has a front part 105a with an opening 109 and a rear part 105b with a tubular central element 111. A first actuator part 107a, in the form of a coil in this example, ofthe actuator 107 is present on the element 111. The coil 107a is electrically connected via electrical conductors 108 to connection contacts 110 fastened to the frame 101. The actuator 107 further comprises a second actuator part 107b, which is provided with an annular magnet 107bl, a yoke part 107b2, and a yoke part 107b3 fastened to a frame part 101b of the frame 101 in this example. An air gap 107c, in which the coil 107a extends, is present between the yoke parts 107b2 and 107b3. When the actuator is energized, the coil 107a, and thus the membrane 105, will perform an axial displacement along a membrane axis 105c in either of the axial directions indicated with a double arrow X. The membrane 105 is suspended in the sub-frame 101a, and the sub-frame 101a is suspended in the frame 101 in the loudspeaker 102. The loudspeaker 102 is for this purpose provided with a first flexible connection element 113, which connects the front part 105a of the membrane 105 to the sub-frame 101a, and with a second flexible connection element 115 which connects the sub-frame 101a at the level ofthe front part 105a to the frame 101. The connection elements 113 and 115 in this example are constructed as annular elements with omega-shaped cross-sections. The connection elements 113 and 115, for example made from polyurethane, may be fastened to the membrane 105 and the sub-frame 101a, and the sub- frame 101a and the frame 101, respectively, by means of glue connections. Preferably, the first connection element 113 and the second connection element 115, which extend coaxially relative to one another, are constructed as one flexible element. A flexible centering element 119 is furthermore present in the loudspeaker 102. in this example in the form of a centering disc with a concentric wave pattern made from a suitable material, such as a textile fabric, which connects the sub-frame 101a to the back part 105b, in particular to the central element 111 thereof. The centering element 119 and the connection elements 113 and 115 are bearing means which are comparatively slack and yielding in axial directions along arrow X, but are comparatively stiff in other directions, so that the membrane 105 with the coil 107a, including the sub-frame 101a, are capable of performing well-defined axial displacements with respect to the frame 101. Obviously a different loudspeaker from the loudspeaker shown may be used, such as a loudspeaker element with a single suspended vibration system. The device according to the invention shown in Fig. 5 is a flat-panel multimedia TV set. The device is provided with a cabinet 201 in which a picture screen 203 and two loudspeaker systems according to the invention are present. The cabinet 201 has an on/off- switching unit 207 at its front side. The loudspeaker systems in this example correspond to the loudspeaker system as shown in Fig. 4 and have the reference numeral 205 in Fig. 5. Each loudspeaker system 205 accordingly has a housing 100 with a loudspeaker 102 and a passive radiator 103 according to the invention. Instead of the device shown, the device according to the invention may alternatively be a conventional TN set, a monitor, or a piece of audio equipment. Furthermore, the radiator used in the device may be constructed as shown in Figs. 2 or 3 or in some other manner which lies within the scope ofthe invention, and a loudspeaker different from the loudspeaker shown in Fig. 4 may be used. Furthermore, the invention is not limited to the embodiments ofthe radiator shown in Figs. 1 and 2. Instead of three or four mass elements, two or more than four mass elements may thus be used, and sinusoidal or alternatively shaped suitable connection elements may be used instead of omega-shaped connection elements.

Claims: CLAIMS: 1. A passive radiator comprising a frame and a radiator body which is connected to said frame and which is movable with respect to said frame along a translation axis, characterized in that the radiator body comprises a central mass element and at least one mass element concentrically positioned with respect to the central mass element, while connection units are present for the movable interconnection of every two mutually adjoining mass elements and for the movable fastening of one ofthe mass elements to the frame, each of said connection units comprising at least a resilient annular connection element, the central mass element with its adjoining connection unit forming a mass spring system, as does each conically positioned mass element with its adjoining connection elements, while all mass spring systems present and thus defined have at least substantially the same resonance frequency. 2. A passive radiator as claimed in claim 1, characterized in that the connection units allow mainly of movements ofthe mass elements along the translation axis ofthe radiator body and counteract other movements. 3. A passive radiator as claimed in claim 2, characterized in that at least a number ofthe connection units comprises a further resilient annular connection element, which further connection element and the connection element mentioned earlier of such a connection unit are at a distance from one another, measured along the translation axis ofthe radiator body. 4. A passive radiator as claimed in claim 1, characterized in that the number of mass elements is three or four. 5. A passive radiator as claimed in claim 1 or 3, characterized in that the connection elements are mutually identical. 6. A passive radiator as claimed in claim 1 or 3, characterized in that at least a number ofthe connection elements are of mutually different sizes, said sizes increasing in a direction away from the central mass element. 7. A passive radiator as claimed in claim 1, characterized in that the radiator body and the connection units are together constructed as one integral unit. 8. A loudspeaker system comprising a housing which accommodates an electrodynamic loudspeaker and the passive radiator as claimed in any one ofthe claims 1 to 7. 9. A device for providing audible, and possibly visible information, provided with the loudspeaker system as claimed in claim 8.

Inventors: D HOOGH GUIDO O M, D'HOOGH, GUIDO, O., M.
Applicants: KONINKL PHILIPS ELECTRONICS NV, KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 2000
Main classification: H01R
IPC codes: H04R1