MXPA01003198A - Loudspeakers - Google Patents

Abstract

A mid/high frequency loudspeaker drive unit comprising a stiff lightweight resonant panel form member, a housing in which the panel form member is mounted, a resilient suspension connected between the edges of the panel form member and the housing, the arrangement being such that the housing and the panel form member together define a sealed enclosure, and an electrodynamic exciter for applying bending wave energy to the panel form member to cause it to resonate to produce an acoustic output, the exciter comprising a magnet assembly rigidly fixed to the housing and defining an annular gap and a voice coil disposed in the annular gap and rigidly fixed to the panel form member near to the geometric centre thereof, the location of the voice coil in the annular gap being provided by the said resilient suspension.

Description

SPEAKERS TECHNICAL FIELD The invention relates to loudspeakers and more particularly to resonant panel loudspeakers, for example, of the kind described in International Patent Application WO 97/09842, ie so-called distributed loudspeakers BACKGROUND OF THE INVENTION In the past there has been great difficulty in providing a speaker that covers the medium and high audio frequency range in high quality. The directivity that varies enormously in this range and extension to the higher frequencies is very difficult for a single impeller. Typically, two impellers are used with the expense and complication of a crossing network between them. The crossover frequency is generally around 3kHz, which is the most sensitive to the human ear, which adds to the difficulty. The concept of the present invention is to have a medium and high frequency driver which replaces the two previously used convention drivers, which does not cross in the critical region and which has a consistent, desirably wide directivity, through its operational range. Speakers in distributed mode can be designed to operate on more than 8 octaves of the audio frequency band, although this may not always be the best solution, for example in high fidelity applications. It is contemplated that it may sometimes be appropriate to use a loudspeaker in distributed mode in association with a subwoofer for low frequencies, crossing, ie, around 100 to 200 Hz. Therefore, there is a need for a loudspeaker or at least a loudspeaker drive unit that does not necessarily operate on the 8 octaves but perhaps on 6 to 7 octaves of the audio band, which would allow a wide choice of material and various construction possibilities that would help optimize the speaker completely over its range of operation. An example of this is a high fidelity speaker / medium range drive that operates under the distributed-mode speaker principle. This can bring significant benefits to a conventional cloistered loudspeaker system by allowing the crossing point to be designed away from the critical area of 3kHz up to the 1kHz range, typically 300-500 Hz, as well as benefiting from superior radiation properties associated with a speaker in distributed mode. There is also an expanding market in multimedia and computer peripherals for compact high-performance speakers and the ever-increasing demand for better sound and more compact constructions for conventional flat-panel TVs, monitors and televisions. Therefore, there is a need for a structure that can be very compact and which can allow the addition of numerous features for performance improvement, application versatility and cost savings. The present invention provides a cost effective vehicle for such applications and allows a manufacturer to optimize its operating expenses for tooling and its production processes. The basic concept revolves around a simple construction of a driver unit or "apparatus" of the speaker which would allow an assembly of easy production and provide consistency.

DESCRIPTION OF THE INVENTION According to the invention there is provided a high / medium frequency loudspeaker driving unit comprising a member in the form of a rigid light weight resonant panel, a housing in which the panel member is installed, a elastic suspension connected between the edges of the panel member and the housing, the installation being such that the housing and the panel member together define a sealed box, and an electrodynamic vibration driver for applying wave energy flexing the member in the form of a panel to make it resonate in order to produce an acoustic output, the exciter comprising a magnetic assembly fixed rigidly to the housing and defining an annular recess and a moving voice coil placed in the annular recess and rigidly fixed to the member in panel shape close to the geometric center thereof, the location of the loudspeaker coil in the annular gap being provided by the elastic suspension. The flexural stiffness of the panel member can be in the range of 0.15Nm to 24 Nm and is preferably in the range of 2Nm to 9Nm. The vibration exciter may be attached to the panel member (hereinafter 'panel') and / or to the box by means of injection molding or by the use of adhesive. The loudspeaker mobile coil of the vibration exciter can be directly connected to a resonant panel during the injection molding of the panel. Alternatively, the moving loudspeaker coil of a driver may be attached to a preformed aperture molded into a resonant panel during assembly. Accordingly, the need for a separate loudspeaker mobile coil carrier is eliminated.

The panel can be co-molded with the suspension. The suspension can be. of elastic material, for example, plastics. The panel can be injection molded as a monolith or using foaming techniques. The panel can be flat or curved and can vary in thickness or cross section. The box may have built-in electrically conductive inserts to carry electrical signals efficiently from connectors on the box edge to the vibration driver. Therefore, the assembly and connectivity of the drive unit can be automated. The drive unit may be coated in other mounds and structures suitable for the application, for example, for aesthetic reasons. For example, an appropriate arrangement will make it suitable for surface installation over a high-fidelity speaker cabinet. Conversely, a suitable exterior molding will turn the appliance into a multimedia horn. In addition, the device can be installed in other structures such as television cabinets.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated diagrammatically, by way of example in the accompanying drawings, in which: Figure 1 is a perspective view, partly broken away to show hidden details, of the loudspeaker driver unit; Figure 2 is a side cross-sectional view of the loudspeaker driver unit of Figure 1, and Figure 3 is a graph representing the frequency response of the driver unit of Figures 1 and 2.

BEST MODE FOR CARRYING OUT THE INVENTION The drawings show a loudspeaker driver unit 1 intended as a medium / high frequency driver which can be used as a component in a loudspeaker system also comprising a low frequency driver, in which box the medium / high frequency and low frequency drivers can be assembled in a common cabinet, or as the single driver in a compact speaker, for example, for multimedia or computer or automobile use. The driving unit 1 comprises a generally rectangular box 2 having a plate-like body 11 surrounded by an outwardly extending fixing projection 3 formed at intervals with holes 12 in which the box can be fixed in position by means of suitable fasteners (not shown), for example, in the cabinet (not shown) of a loudspeaker. The box 2 can be made from plastics, for example, by injection molding, and is formed internally with cross reinforcement projections 13 in order to add rigidity to the box while maintaining its lightweight nature. The box 2 is formed in its base 14 with a shallow recess generally circular interior 4 having a central through hole 16, the recess being adapted to receive a circular support plate 6 on which the magnetic assembly 7 of the rigid assembly is rigidly installed. an electrodynamic vibration exciter 5 by means of a bolt 20. The exciter 5 comprises the magnetic assembly which defines an annular recess 19, and a mobile voice coil and cylindrical forming assembly 8 placed in the annular recess and axially movable therein. in response to an electrical signal applied to the speaker coil. The support plate 6 is fixed to the box in any convenient way. Accordingly, it can be fixed by fasteners or by adhesive means or it can be molded integrally with the box. Adjacent to the edge projection 3, a lightweight, rigid, generally rectangular, light weight resilient panel member 9 is elastically installed on the box 2 by means of a flexible foam suspension 10 which extends around the periphery of the panel 9. Accordingly, the box and the panel define an enclosed cavity 15. The suspension 10 can be fixed to the panel 9 and to the box 2 by means of adhesives. Panel 9 is a panel in distributed mode according to the teaching in WO 97/09842. The forming assembly 8 / moving loudspeaker of the exciter 5 is rigidly fixed to the panel 9 in a suitable conduction position close to the center as taught in WO 97/09842 to introduce the bending wave energy in the panel to make it resonant to in order to produce an acoustic output. The loudspeaker voice coil and coil former assembly 8 has an annular installation member or feet 21, for example, of plastics, fixed rigidly to its end adjacent to the panel 9 to help its fixation to the panel, which can be with the help of an adhesive. It should be noted that, unusually, the driver 5 lands to the box 2 and does not comprise a suspension between the magnetic assembly and the loudspeaker voice coil so that the centering of the loudspeaker voice coil in the annular pocket 19 of the magnetic assembly is it reaches only by the panel edge suspension 10. In this way, the moving mass of the exciter is reduced to improve its response at high frequency. The magnetic assembly can be thermally coupled to the loudspeaker voice coil to improve its power capacity and heat can be radiated from the exposed back face of the support plate 6.

Locally placed selective small masses 17, for example, in the range from about 2 to 12 grams are attached to the panel to optimally tune the coupled resonances such that the overall response is adjusted appropriately. This technique has the specific advantage. of extending the low frequency range of the assembly. An aperture 18 through the panel 9 coaxial with the loudspeaker voice coil extends the response at high frequency. A little acoustic absorbent material (not shown) may be useful in the cavity 15 to reduce the magnitude of higher order standing waves in the cavity, and may further refine the frequency response. A drive unit as described above can have the following specifications: Panel size = 210x148.5mm (standard size A5) Core = 3mm polycarbonate honeycomb type, 3.5mm cell diameter Linings = 100% glass reinforced polycarbonate liners μm (liner orientation 0 ° / 90 °) 50% by weight glass Flexural rigidity = 5.6Nm Surface density, μ = 0.7kg / m2 Zm = 16Ns / m Diameter of the loudspeaker coil = 26mm The coil is places in a position in standard distributed mode. (4/9, 3/7 = ratio) Large ferrite ring magnet to improve BL and power handling. "As described above, there is no suspension between the magnet and the loudspeaker and the panel remains in place. position by the foam suspension around the edge.The panel can be aligned and positioned accurately using the hole in the panel inside the loudspeaker voice coil to assist the alignment of the loudspeaker voice coil in the annular gap. Possibly locating pins in the box near the edges of the panel to prevent lateral movement of the panel The frequency response of this panel is shown in Figure 3. Smaller versions of the drive unit are planned with high quality piezoexcitators which can extend the response to the ultrasonic range which could be useful in conjunction with new audio formats with a sound bandwidth of 50kHz or 100kHz; It is beyond the reach of conventional piston technology.

INDUSTRIAL APPLICABILITY The invention thus provides an innovative loudspeaker drive unit for medium and high frequencies which solves significant problems in known installations both concerns of frequency crossing and dispersion problems.

Claims (9)

1. CLAIMS Having described the invention as an antecedent, the content of the following claims is claimed as property: 1. A loudspeaker driving unit comprising a member in the form of a rigid light weight panel, a member of the structure in which the member is installed in the form of a panel, an elastic suspension connected between the edges of the panel-shaped member and the structure member, and an electrodynamic exciter for applying ben wave energy to the panel-shaped member to produce an acoustic output, the exciter comprising a magnetic assembly fixed rigidly to the structure member and defining an annular recess and a moving loudspeaker coil placed in the annular recess and fixed rigidly to the panel-shaped member, characterized in that the location of the loudspeaker voice coil in the annular recess is provided by the elastic suspension, the driving unit is a medium frequency / alt drive unit Thus, the structure member is a housing which, together with the panel member defines a sealed box, the panel-shaped member is adapted to resonate in order to produce an acoustic output and in which the loudspeaker coil it is fixed to the member in the form of a panel near its geometric center. A loudspeaker drive unit accor to claim 1, characterized in that the box comprises a plate type body surrounded by a fixing projection. A loudspeaker driver unit accor to claim 2, characterized in that the plate type body comprises a through opening and wherein the magnetic assembly of the vibration exciter is rigidly installed on the plate type body by which a part of its Surface closes the through opening in the body. A speaker driver unit accor to claim 3, characterized in that it comprises a recess in the plate-like body, and wherein the magnetic assembly comprises a support plate installed in the recess in the duck-like body, forming the recess with the through opening. 5. A speaker driver unit accor to any of the prece claims, characterized in that the elastic suspension is made of foamed material. A speaker driver unit accor to any of the prece claims, characterized in that the panel-shaped member comprises a core of honeycomb material sandwiched between the liner layers and has a flexural stiffness in the range of 0.15 to 24. Nm. 7. A speaker driver unit accor to claim 6, characterized in that the flexural stiffness is in the range 2 to 9Nm. A speaker driver unit accor to any of the prece claims, characterized in that it comprises an opening through the panel-shaped member and coaxial with and smaller than the diameter of the mobile speaker coil. 9. A loudspeaker voice coil accor to any of the prece claims, characterized in that it comprises at least one discrete mass installed in the member in the form of a panel and placed to dampen the low frequency response thereof.