MINIATURE FULL RANGE LOUDSPEAKER

Abstract: In a miniature loudspeaker (10) of the electromagnetic voice coil type with a stiff edge-driven concave diaphragm (16), a single suspension member (18) attached to a particular location on the voice coil form (26A) achieves high excursion performance to deliver a full audio range in a cylindrical package of minimal thickness and diameter suitable for sound systems of compact multi-media equipment including PC CRT monitors and flat displays as in lap top computers. The front end of the tubular voice coil form is attached to the perimeter of the diaphragm. The front end of the tubular voice coil form is attached to the perimeter of the diaphragm. The coaxial voice-coil-diaphragm assembly is supported by a single resilient surround suspension member with its inner edge attached around the voice coil form at a location that is offset slightly from the front end of the voice coil form.

Description: MINIATURE FULL RANGE LOUDSPEAKER PRIORITY Benefit is claimed under 35 U.S.C. § 119(e) of pending provisional application 60/093,600 filed 7/21/98. FIELD OF THE INVENTION The present invention relates to the field of loudspeakers and more particularly it relates to novel configuration of a miniature full range loudspeaker that is especially suited for use in space constrained multi-media applications. BACKGROUND OF THE INVENTION In the design of miniature loudspeakers, smaller size generally involves a tradeoff relating to low frequency response, since for a given loudness, as frequency decreases the loudspeaker, acting as a piston, is required to "pump" a larger volume of air, this displacement volume being basically the product of the diaphragm's area and the amplitude of its vibrational excursion, which is always subject to a physical limitation of the loudspeaker construction. While the loudspeaker's frequency response range can be extended to lower frequencies by applying bass reflex techniques in the enclosure design, the displacement volume still acts to set limits on the overall low frequency performance. In the category of electro-magnetic loudspeakers of the coaxial round voice-coil/cone type addressed by the present invention, as distinguished for example from horn type transducers, there are two basic types of construction: ( 1 ) the conventional dual-suspension full range type wherein the diaphragm is formed as a cone that is substantially greater in diameter than the voice coil form and where two suspension members are deployed: a "surround" suspension member at the outer edge of the cone extending to an outer basket/frame region and a "spider" at the voice coil form extending to a nearby landing formed by the basket/frame, and (2) edge-driven-diaphragm limited-frequency-range loudspeakers, wherein the diaphragm and the voice coil form are made with substantially equal diameter, the outer edge of the diaphragm being attached to the end of the voice coil form and also to a single surround suspension member which extends outwardly to an attachment landing on the frame/ asket. Such construction is conventionally utilized for "tweeters", typically utilizing a rigid dome diaphragm, and sometimes for "midrange" loudspeakers; the lacking bass frequency response is filled in by the use of a separate "woofer" unit in typically a two- or three-way speaker system. The suspension system is of key importance since it must allow a required maximum amplitude of vibration while constraining the vibrational movement essentially to a straight-line path, avoiding any contact of the voice coil or its form with surrounding magnet pole structure. The surround suspension member is required to constrain the diaphragm against any tilting, wobbling or other extraneous vibration while allowing full desired vibration and possibly even cushioning against bottoming. A generally unrecognized problem in small loudspeakers that has been addressed by the present invention involves spurious vibration of portions of the compliant surround suspension member at high audio frequencies and in directions other than the desired principal axial direction. These spurious vibrations can be transmitted to the diaphragm where it is directly attached to the surround suspension member as in conventional practice, thus degrading the high frequency performance. The present invention addresses the challenge of evolving a new loudspeaker construction that provides the full range frequency response, heretofore limited to type (1) above while realizing the volumetric advantages and benefits of the edge-driven type (2) and minimizing its drawbacks, in a manufactured product that is particularly suitable for use in conjunction with space-constrained multi-media audio systems. DISCUSSION OF RELATED KNOWN ART U.S. patent 5,181,253 to Jordan, assigned to Southern Audio Services, discloses an edge -driven dome diaphragm supported by a single surround suspension member attached at the front edge of the voice coil. U.S. patent 5,157,731 to Mitobe, assigned to Pioneer, discloses a dome radiator speaker where the voice coil diameter coincides with the dome diameter; however the dome, voice coil form, configured as a channel, and the surround suspension are formed integrally from a sheet of material. The permanent magnet is an exterior donut type. U.S. patents 4,031,337 and 3,780,232 also show edge-driven dome diaphragms. The foregoing references typify tweeters with dome diaphragms, intended to operate only in a high frequency audio range above 500 Hz, as distinguished from full range, addressed by the present invention, extending down to 100 Hz. U.S. patent 3,983,337 to Babb illustrates a 1976 attempt at a broad band miniature speaker with a reinforced cone extending well beyond the voice coil diameter; however it is of interest in discussing the theoretical limitations encountered in developing miniature full range loudspeakers. U.S. patent 4,384,174 to Susuki et al, assigned to Victor, is of interest in utilizing only a single conventional suspension member along with a novel viscous quasi-O-ring support at the periphery of the cone which extends well beyond the voice coil diameter. U.S. patent 5,739,480 to Lin discloses a speaker base for alternatively mounting different drivers. Shown is a conventional woofer construction with a first edge suspension member attached around the perimeter of the conical diaphragm and a second suspension member attached around the voice coil form, the diaphragm extending inwardly only to the region of attachment to the perimeter of the voice coil form thus leaving a large circular central opening with a diameter approximating that of the voice coil form, provided for installing an optional woofer diffuser or tweeter driver onto a driver holder base surrounded by the voice coil form. OBJECTS OF THE INVENTION It is a primary object of the present invention to provide a miniature-sized electromagnetic loudspeaker with full range audio capability. It is a further object that the loudspeaker be suited to the audio needs and requirements of multi-media computers, particularly laptop computers. It is a further object to make the loudspeaker of simple construction that can be mass-produced at low cost. It is a still further object to configure the loudspeaker with a single suspension element. SUMMARY OF THE INVENTION The above-mentioned objects have been accomplished by the present invention of a miniature loudspeaker of the voice coil electromagnetic type wherein the diaphragm is concave, as distinguished from well-known domed tweeter diaphragms, and extends only to a size equal to the diameter of the voice coil form, to which it is attached. The resulting edge-driven voice coil/diaphragm assembly is supported by a single surround suspension member attached to the tubular voice coil form in a location thereof spaced a predetermined distance along the voice coil form from its end point of attachment to the diaphragm. The magnetic system has a coaxial structure: a shallow pot acts as a pole piece, enclosing a cylindrical permanent magnet and a circular inner pole piece forming, with the edge of the pot, an annular magnetic air gap wherein the voice coil, driven by audio current, vibrates axially and in turn drives the voice coil form and the diaphragm. This vibrating voice coil/diaphragm assembly is supported via a surround suspension member that is attached peripherally to a plastic mounting ring surrounding and attached to the pot and is attached at its inside diameter to the outside of the voice coil form at a location that is spaced away from the diaphragm attachment location. The structural features including the concave edge-driven cone, the magnetic gap geometry and the special deployment of the single surround suspension member, in particular, its special attachment location on the voice coil form instead of the conventional practice of attaching it directly to the edge of the diaphragm, combine to enable unusually large amplitude of vibration thus enabling the miniature loudspeaker to perform as full audio range loudspeaker providing acoustic output at frequencies down to 100 Hz when deployed in conjunction with a bass reflex acoustic enclosure. Furthermore this special attachment location benefits high frequency performance by isolating the diaphragm from the influence of spurious high frequency vibrations of portions of the surround suspension member at directions other than the desired axial direction, particularly radial directions. The loudspeaker is intended for use with computer monitors of both the CRT type and the flat display type as used in lap top computers: it is equipped with articulated features that enable mounting in a snap-in manner to a baffle portion of an acoustic enclosure. BRIEF DESCRIPTION OF THE DRAWINGS The above and further objects, features and advantages of the present invention will be more fully understood from the following description taken with the accompanying drawings in which: FIG. 1 is a front view of a loudspeaker of the present invention. FIG. 2 is a side view of the loudspeaker of FIG. 1. FIG. 3 is a central cross-section of the loudspeaker of FIG. 2. FIG. 4 is a rear view of the loudspeaker of FIGs. 1 and 2. FIG. 5 is an enlarged view of the circled portion of FIG. 3. FIG. 6 is an enlarged three-dimensional view of the loudspeaker of FIGs. 1, 2 and 4, viewed from a rear region. DETAILED DESCRIPTION FIG. 1 depicts in a front view, a miniature full range loudspeaker 10 of the present invention, having a mounting ring 12 defining a circular perimeter from which a pair of hookup wires 14 are shown extending outwardly. The circular diaphragm 16 is supported by a surround suspension member 18 attached peripherally to mounting ring 12. FIG. 2, a side view of the loudspeaker of FIG. 1, shows the loudspeaker 10 with surround suspension member 18 extending upwardly from mounting ring 12. A formed coaxial metal pot 20 extends downwardly, engaged by mounting ring 12 which is formed to have a polar array of buttress blocks 12A extending downwardly and bearing against the wall of pot 20. Mounting ring 12, typically molded from plastic, is configured with clusters of articulated fastening members by which the loudspeaker 10 can be snap-in mounted to an associated baffle. FIG. 3, a central cross-section from the same viewpoint as FIG. 2, shows pot 20 constituting a lower pole piece of a cylindrical permanent magnet 22, fitted at its opposite upper pole with a disc-shaped pole piece 24 that extends to face the inner side of the upper rim of pot 20, thus forming the loudspeaker's annular magnetic air gap. A voice coil form 26A, wound with a voice coil deployed in the magnetic air gap, extends upwardly to where it joins the perimeter of diaphragm 16, seen to have a concave shape. The voice coil/diaphragm assembly is supported in place by a surround suspension member 18. NOTE: in FIGs. 2, 3 and 5 loudspeaker 10 is shown facing upwardly; it should be understood that this upward direction is actually the forward direction of loudspeaker 10, and similarly the downward direction as shown is actually the rearward direction of loudspeaker 10. FIG. 4, a rear view of loudspeaker 10, shows mounting ring 12 configured with six buttress blocks 12A arrayed around pot 20. Two hookup wires 14 extend outwardly. Mounting ring 12 is also configured with four mounting clusters 12B by which the loudspeaker 10 can be mounted in a snap-in manner to a baffle. FIG. 5, an enlarged yiew of the circled region of FIG. 3, shows voice coil 26B in the magnetic air gap between upper pole piece 24 and the inner rim of pot 20 that forms the opposite pole piece. The upper edge of voice coil form 26A is adhesively attached to the lower side of a flat narrow flange formed around the edge of concave diaphragm 16. The inner edge of resilient surround suspension member 18, which may include a short flange as shown, is adhesively attached to voice coil form 26A at a location somewhat below its upper end, while its outer edge is attached via the outer flange onto an annular flat forward-facing suspension-attachment surface on the forward side of the mounting ring 12, shown at the upper region of a buttress block 12 A. The structure provides for an usually long excursion range for the voice coil/diaphragm assembly which includes voice coil 26B, voice coil form 26 A, diaphragm 16 and surround suspension member 18, thus enhancing the low frequency capabilities of the loudspeaker 10 so that it can operate as a full range unit. The cross-sectional shape of surround suspension member 18 shows the arched portion extending upwardly to a front plane of loudspeaker 10 as defined by the perimeter of diaphragm 16. FIG. 6 is an enlarged three-dimensional view of loudspeaker 10 as seen from a rear location, showing mounting ring 12, with buttress blocks 12A arrayed around pot 20, from which the two hookup wires 14 are shown extending outwardly. These are connected through integrated flat conductors 28 to the voice coil, eliminating a conventional two-terminal board and mounting rivet. There are a total of six buttress blocks 12A (refer to FIG. 4) arranged in a polar array around pot 10, each fitting closely against the wall of pot 20, where optionally they may be fastened adhesively or otherwise. At four locations mounting ring 12 is configured with a mounting cluster 12B, including a flag-shaped lock tab 12C and a rotation stop post 12D, which serves to provide snap-in attachment to a baffle of an acoustic enclosure, typically a bass-reflex system. The baffle is configured with a circular opening dimensioned to clear surround suspension member 18 so that loudspeaker 10 can be rear-mounted onto the baffle; four cantilevered arms on the baffle engage mounting clusters 12B. Mounting ring 12 is formed to provide a stepped mounting strip 12E between each pair of adjacent blocks 12A to further facilitate snap-in mounting. When loudspeaker 10 is mounted against the rear of the baffle, the outer flange of surround suspension member 18 serves as a gasket, eliminating the need to provide a separate gasket as required in conventional mounting practice. A plurality of apertures are provided around the wall of pot 20 between buttresses 12A to allow acoustic venting so that the sound pressure from the rear of diaphragm 16 can communicate to the interior of the enclosure system, typically bass reflex. The invention could also be practiced with variations from the preferred embodiment described above without departing from the spirit of the invention. The permanent magnet could be made in the form of a donut with a cylindrical central core associated with disc pole piece 24, while the other pole piece would be formed simply as a cylindrical collar; this would suffer from magnetic field leakage which in the above embodiment is contained by the pot 18 and which could be detrimental to utilizing the loudspeaker in computer service and/or could require the expense of additional magnetic shielding. Permanent magnet 22 may be of any known magnet material commonly utilized in loudspeakers; the pole pieces (pot 18 and disc 16) are typically of magnetically soft iron or steel but may be made from other material suited to their magnetic function as pole pieces. Diaphragm 16 may be made from any suitable material that provides rigidity and light weight: metal such as titanium or aluminum, or non-metal such as plastic or impregnated/reinforced paper. The concave shape of diaphragm 16 serves to reduce the height of the loudspeaker so as to provide a low profile package overall. Functionally the invention could be practiced in less preferred form with diaphragm 16 made in a convex shape; alternatively it could be made flat but that may make it more difficult to obtain the desired rigidity with a thin lightweight sheet of material. As an alternative to the "butt" joining of the diaphragm 16 to the top end of the voice coil form 26A shown in FIG. 5, there is an option of forming diaphragm 16 so as to provide a annular downward-facing channel that would flank the upper edge of voice coil form 26A, to facilitate locating and fastening operations. A preferred embodiment of the loudspeaker 10 has overall dimensions 31 mm diameter by 14 mm depth. The diaphragm 16 is made concave to a maximum depth of 2.6 mm. The outside of the voice coil form 16A and the concave portion of the diaphragm are 19 mm in diameter. Referring again to FIG. 5, the voice coil form 26 A is made to extend upwardly 4.3 mm beyond the voice coil 26B. The location designated for attachment of surround suspension member 18 along voice coil form 26A is chosen to be 1.6 mm from the end so as to make the forward extent of the surround suspension member 18 flush with the front plane of the loudspeaker 10, i.e. the perimeter of the diaphragm 16. Proper selection of material of surround suspension member 18 and its fastening location along the free region of voice coil form 26 A act to cushion and isolate the diaphragm 16 and to ensure that the voice coil 26B is constrained coaxially in the magnetic gap while it vibrates longitudinally, so that its travel is kept in a straight line free of wobble or other extraneous movement. A key dimension relating to low frequency loudness capability is the clearance allowed for excursion of the voice coil/diaphragm assembly: this is made to be 2.55 mm at two potential bottoming locations: between the lower extremity of the voice coil form 26A and the floor of pot 20, and between the lower extremity of diaphragm 16 and upper pole piece 24. Thus a maximum symmetrical excursion range of 5.1 mm peak-to-peak is provided. As a size efficiency factor, the excursion can be compared to the total thickness of the loudspeaker. For a hypothetical cylindrical loudspeaker of given diameter with a cone of equal diameter and a peak-to-peak excursion equal to the loudspeaker thickness, this factor would be 100%; that is, the volume of displaced air would equal the volume of the loudspeaker itself. In the embodiment of the present invention described above this factor is 5.1mm/ 12mm i.e. 42.5%o, compared to typically less than 10% for conventional loudspeakers. The voice coil 26B is made 2.9 mm in length; the working magnetic air gap spacing is 1.47 mm. The pot 20 is made 1.75 mm thick, permanent magnet is made 3.77 mm thick, and upper pole piece 24 is made 1.4 mm thick. The surround suspension member 18 is configured and arranged to provide a degree of constraint to the maximum excursions of the voice coil/diaphragm assembly in both the upward limit which is not constrained otherwise, and in the lower limit, where it acts to cushion against bottoming. Regarding the arched shape of surround suspension member 18, it is believed that the arched shape shown with the arc subtending an angle of 180 degrees or slightly less is optimal, however the invention could be practiced, with at least partial equivalence, utilizing known alternate configurations of surround suspension member 18, e.g. a series of concentric corrugations. The detailed configuration of the mounting ring 12 and particular method of attachment to a baffle and associated housing are not of critical importance to the acoustic function of the invention; there variations that could enable the basic practice of the invention at some tradeoff of convenience, e.g. conventional mounting with screw hardware instead of snap-in mounting. Also snap-in mounting could be accomplished with alternative configurations and/or with a different number of attachment clusters other than four. The snap-in fastening system can be implemented with metal spring or resilient plastic locking members. The invention could be practiced utilizing a twist-lock mounting arrangement, involving rotation of the speaker basket, incorporated in conjunction with or as an alternative to snap-in mounting. This invention may be embodied and practiced in other specific forms without departing from the spirit and essential character-istics thereof. The present embodiments therefore are considered in all respects as illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description. All variations, substitutions, and changes that come within the meaning and range of equivalency of the claims therefore are intended to be embraced therein.

Claims: What is claimed is: 1. A miniature full-range loudspeaker, comprising: a circular diaphragm having predetermined diameter at a perimeter thereof; a tubular voice coil form, having an outside diameter closely approaching that of the said diaphragm, a forward end and a rearward end, the forward end being attached co-axially to said diaphragm in a peripheral region thereof; a voice coil, wound on a rear region of said voice coil form, extending forward toward a mid region thereof thus leaving a free space on said voice coil form between said voice coil and said diaphragm; a magnet assembly made and arranged to define an annular gap with magnetic flux traversing said voice coil in a known enabling manner for loudspeakers; a cylindrical sidewall of said loudspeaker surrounding said magnet assembly and said voice coil; an annular mounting ring, surrounding the sidewall and attached thereto at a forward region thereof, configured to provide an annular flat forward-facing suspension-attachment surface disposed in a plane that is perpendicular to a central axis of said loudspeaker and that is located between the forward end of said voice coil and the forward end of said voice coil form; and an annular surround suspension member of resilient material, surrounding said voice coil form, having an outer flange attached at a rear side thereof onto the suspension-attachment surface of said mounting ring and an inner edge that is edge-attached to the free space on said voice coil form between said voice coil and said diaphragm. 2. The miniature full-range loudspeaker as defined in claim 1 characterized by said surround suspension member having a radial cross- sectional shape configured generally as an arc extending forwardly between the outer flange and an inner flange narrower than the outer flange, extending to the inner edge of said surround suspension member. 3. The miniature full-range loudspeaker as defined in claim 2 wherein the arc subtends an angle not exceeding 180 degrees. 4. The miniature full-range loudspeaker as defined in claim 3 wherein said diaphragm is configured to have a concave shape such that the perimeter of said diaphragm defines a most forward region thereof. 5. The miniature full-range loudspeaker as defined in claim 4 wherein: the outer flange of said suspension member is configured with a rear attachment surface made and arranged to interface the suspension-attachment surface of said mounting ring; and the inner edge of said surround suspension member is located substantially in a common plane with the outer flange thereof. 6. The miniature full-range loudspeaker as defined in claim 5 wherein: the inner edge of said surround suspension member is edge-attached to the free space on said voice coil form at a location that is offset rearwardly from the perimeter of said diaphragm such that a most forward front surface point of said surround suspension member and the perimeter of said diaphragm are both caused to be located substantially in a front plane of said loudspeaker. 7. The miniature full-range loudspeaker as defined in claim 5 wherein: said surround suspension member is made to have a predetermined thickness in a region thereof between a forwardmost surface point thereof and the rear attachment surface of the outer flange.

Inventors: WILLIAMSON CLAYTON C, WILLIAMSON, CLAYTON, C.
Applicants: JBL INC, JBL INCORPORATED
Application year: 1999
Main classification: H04R25
IPC codes: H04R1, H04R7, H04R9