US3268672A - Loudspeaker - Google Patents

Description

1956 J. F. ROESEL, JR, ETAL 3,

LOUDSPEAKER Filed Dec. 3, 1962 4 Sheets-Sheet l INVENTORS l John F Roesel,Jr.,Richurd A. Whisnont and William L. Wright. BY?

a I b ATTORNEY Aug. 23, 1966 J. F. ROESEL, JR. ETAL 3,253,672

LOUDSPEAKER Filed Dec. 5. 1962 4 Sheets-Sheet 2 A g 1966 J. F. ROESEL, JR. ETAL LOUDSPEAKER 9mm, o mm mm, 2 o m my mN Sm United States Patent 3,268,672 LGUDSPEAKER John F. Roesel, .Iiu, De Land, Fla, Richard A. Whisnant, Spartanburg, S.C., and William L. Wright, Monroeviile, l a., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Dec. 3, 1962, Ser. No. 241,590 7 Claims. (Cl. 179115.5)

This invention relates to an acoustic device or transducer and more particularly to a magnetic loudspeaker for reproducing sound.

In order to reproduce relatively low frequency sound signals, having frequencies of 20 to 200 cycles, it is necessary to employ a loudspeaker which has a relatively large radiating diaphragm that is relatively stiff. Due to the fact that the diaphragm of such speakers is relatively large and relatively stiff, the reproduction by such a loudspeaker of sound having a frequency above approximately 3 to thousand cycles, is relatively inefiicient. Consequently, the reproduction of these relatively high frequencies by such a loudspeaker is not considered adequate and an additional speaker generally called a tweeter is employed. Frequently, the tweeter is a completely independent speaker having its own voice coil and its own diaphragm which is connected to the main speaker or woofer merely by an electrical connection of a crossover network. With such a crossover network the woofer reproduces the low notes whereas the tweeter reproduces the high notes. Other means have been employed, such as attaching a relatively small second cone diaphragm to the original Woofer cone diaphragm so that the smaller cone forming a part of the relatively large conical diaphragm will increase the efliciency of the reproduction of the relatively high notes.

In copending application entitled Loudspeaker, Serial No. 244,234, filed December 3, 1962, in the names of John F. Roesel, Richard A. Whisnant and William L. Wright, there is disclosed a loudspeaker having a large relatively thin radiating diaphragm the peripheral edges of which define a rectangle. The voice coil for this radiating diaphragm is rectangular in shape and has a connection to the diaphragm which defines a rectangle. The magnetic assembly provides two linear air gaps for the longitudinal sides of the rectangular voice coil. This provides the driving force for adequately reproducing relatively low notes.

Accordingly, it is an object of the present invention to provide a new and improved loudspeaker.

It is also an object to provide a new and improved loudspeaker identified as a tweeter to adequately reproduce frequencies above 4 or 5 thousand cycles.

A further object is the provision of a loudspeaker commonly known as a tweeter which is mounted on and structurally integral with a woofer.

The features of the present invention include a new and improved magnetic assembly for a loudspeaker which provides an air gap for a woofer and integral with this magnetic assembly provides a magnetic air gap for a voice coil of a tweeter.

Other objects and various features will become apparent from the reading of the following specification and examination of the accompanying drawings, in which:

FIGURE 1 illustrates a front isometric layout view of a loudspeaker embodying the invention;

FIG. 2 illustrates a partial isometric layout of the voice coil, diaphragm and magnetic assembly of the loudspeaker illustrated in FIG. 1;

FIG. 3 illustrates a rear view of the loudspeaker illustrated in FIG. 1;

FIG. 4 illustrates a crosssectional view taken along plane IVIV illustrated in FIG. 3

"ice

FIG. 5 illustrates a cross-sectional view of the loudspeaker taken along the plane V-V of FIG. 3;

FIG. 6 is an enlarged cross-sectional view of the portion of the View taken along lines VI-VI of FIG. 3;

FIG. 7 is a front view taken along lines VIIVII in FIG. 6; and

FIG. 8 illustrates the winding of the voice coil shown in FIGS. 2 through 5.

In the above mentioned patent application entitled Loudspeaker, Serial No. 244,234, filed December 3, 1962, in the names of John F. Roesel, Richard A. Whisnant, and William L. Wright, there is disclosed a loudspeaker similar to the loudspeaker illustrated in the present application. As illustrated in the drawings, this loudspeaker includes generally a rectangular frame 50 shown in FIG. 1, and a lightweight relatively low Q diaphragm 20 which is suspended from the frame 50 by suspension means 30. Mounted on the rear of the rectangular diaphragm 20 is a rectangularly shaped voice coil assembly 4% to which the amplifier of the sound system is connected to drive the diaphragm 20. The voice coil assembly is connected to the diaphragm 20 by a connecting base member which defines the non-circular rectangular area for driving the diaphragm. Also mounted on the frame is a magnetic assembly which provides two linear parallel air gaps which are adapted to receive the two lengthwise sides of the voice coil assembly 40 to provide two linear air gaps for the voice coil necessary for vibrating the diaphragm 20, in response to audio signals being applied to the voice coil assembly 40.

The magnetic assembly to provide linear air gaps for the voice coil in the loudspeaker illustrated in the aboveidentified patent application as well as illustrated herein, includes bar type rectangula-rly shaped magnets and pole pieces which provide the linear air gaps between the pole pieces. As stated above, it is frequently desirable to employ a high frequency tweeter when utilizing a relatively large radiating diaphragm woofer. In the present invention two of the rectangularly shaped pole pieces of the magnetic assembly are extended which pole pieces are conducting opposite magnetic polarization. An aperture is provided in one of the pole pieces whereas the other pole piece has a pole piece extension which extends into the aperture of the other pole piece. A tweeter is employed having a voice coil which is positioned within the air gap defined by the extension of the two pole pieces. Further, the diaphragm of the tweeter is suspended or mounted on the pole piece having the circular aperture therein.

More specifically, the diaphragm 20 is constructed of a foamed cellular plastic which is sandwiched between two relatively thin strong layers of suitable material such as a fibrous woven Dacron. The method of producing this diaphragm is described in detail in the above-mentioned patent application. The shape of the diaphragm Ztl is shown in FIG. 1 with FIG. 4 illustrating a cross-sectional view of the length of the diaphragm and FIG. 5 illustrating a cross-sectional view of the width of the diaphragm. As shown in these figures the diaphragm Z0 is planaror relatively flat and is rectangular in shape. The diaphragm 20, rectangular in shape, has its edges tapered to a thinner portion for connection to suspension means 30. It will be seen in FIG. 1 that the tapered linear edges 21, 22, 23 and 24 of the diaphragm 20 define a rectangular edge which, as shown in FIG. 1, has rounded edges at the corners. These linear tapered edges are integral with or connected to surround suspension means 30. A cross section of the linear portions of these surround is illustrated in FIGS. 4 and 5. As illustrated in FIGURE 1, the upper tapered edge 21 of the diaphragm is integral with or connected to a linear disposed surround 32. As shown in FIG. 5, the linear edge 21 is connected to but integral with surround 32 having an outwardly extending linear roll 32b and an inwardly extending roll 32a. Likewise, the linear edge 22, as shown in FIG. 4, is integral with or connected to linear disposed surround 33 having an outwardly extending 180 roll 33b and integral therewith a linearly disposed inwardly extending roll 33a. Likewise, the lower horizontal edge 23 of diaphragm is connected to surround 34 having an outwardly extending lineardisposed roll 34b and a linearly disposed inwardly extending roll 34a. Also, the vertically disposed edge 24 of diaphragm 20, as shown in FIG. 4, is connected to surround having an outwardly extending 180 roll 35b which is integral with an inwardly extending linearly disposed 180 roll 35a. Extending outwardly from and coplanar with the tapered edge of the diaphragm 20 are coplanar fastening portions 32c, 33c, 34c and 350. As will be explained later these portions are connected to the frame 50 for mounting the diaphragm thereon.

Mounted on the rear surface of the diaphragm 20, is, as shown in the drawings, a voice coil assembly which is secured by glue or some other suitable means to the rear planar surface. The voice coil assembly 40 includes, as shown in FIG. 2, a channel coil support 41 for supporting a voice coil 42. The support 41 has two rectangularly shaped horizontally disposed parallel supporting members 41a and 41b which are connected to a rectangular base 410. The edges of 41a and 41b are integral with the rectangular base 410 and perpendicular thereto. Further, a supporting strip 41d, shown in FIGS. 4 and 5, is constructed midway between the ends of supporting members 41a and 41b to prevent vibration of the supporting members 41a and 41b. The members 41a, 41b, 41c and 41d are constructed of some suitable relatively light metal such as aluminum and are relatively thin so that the voice coil can be placed into a relatively thin air gap. The windings of the rectangular voice coil 42 are wound around the outer surfaces of the supporting members 41a and 41b.

The rectangular voice coil 42 includes parallel longitudinal voice coil sections 43 and 44 with parallel voice coil end sections 45 and 46. Sections 43 and 44 are bonded by some suitable adhesive or glue for attachment to support member 41a and 4112, respectively. Voice coil sections 43 and 44 extend beyond the ends of support members 41a and 41b, respectively, so that voice coil sections 45 and 46 are positioned outwardly from the ends of support members 41a and 41b. The voice coil 42 is centered lengthwise on the coil support 41. The voice coil 42 is comprised of one or more layers of electrically conductive wire which are coated with some suitable electrical insulating material. The wire is wound in a helical fashion in a rectangular pattern, such as illustrated in FIG. 8. If two layers are used the wire is wound back over the first layer of wire in a helical fashion in a rectangular pattern and both the voice coil leads 48 are on the same end of the voice coil. The voice coil, after it is wound is encapsulated with an adhesive or bonding material to make the voice coil 42 rigid and prevent movement of wires in the voice coil. The rectangular driving base member 410 is secured to the rear surface of the diaphragm 20 by some suitable adhesive. In the embodiment illustrated in FIG. 4, the base 410 of the voice coil 40 is secured to diaphragm 20 midway between and parallel to the top and bottom of the diaphragm 20 and is horizontally disposed.

The driving base member 41c of the voice coil 42, being non-circular or rectangular and forming a relatively large planar connection with diaphragm 20, provides a uniform non-critical drive to the diaphragm 20 when actuated by signals applied to the voice coil 42. Being rectangular in shape, the supporting member 41 is adaptable to be made relatively large to thereby provide a heat sink of relatively large heat dissipating area for the voice coil. For this reason, the voice coil assembly has relatively high power handling capabilities. In addition, such a construction enables the driving surface, i.e. the driving base memher 410, to be relatively large and to provide a relatively large driving surface over the effective rectangular radiating area of the planar dia-phram 20. As such, the voice coil assembly 40 together with the magnetic structure 60, to be described later, result in excellent means for driving a relatively large radiating diaphragm 20 which consequently has relatively good coupling to the air and hence requires no special enclosure or baffle. This results in excellent low frequency reproduction by the loudspeaker.

It has been discovered that the optimum distance between the sides of the support 41 and suspension means 30 should be approximately 4 to 5 inches, however, depending on the rigidity of diaphragm 20, adequate performance can be provided if this distance is between two and eight inches. The thickness of the diaphragm 20, for optimum performance was found to be in the neighborhood of one-fourth of an inch. However, the thickness of the cellular plastic planar diaphragm 20 could be between an eighth of an inch and one inch and still provide suitable performance.

As shown in FIGS. 1, 3, 4 and 5, there is provided a frame assembly 50 which can be made of metal or some suitable other material. The rectangular frame member 50 consists of two horizontally disposed L- members 51 and 53 and two vertically disposed L- members 52 and 54. These L-members are secured at their ends to provide a rectangular picture frame to which is mounted the edges of the suspension means 30 in a rectangular pattern. The supporting L- members 51, 52, 53 and 54 have vertically disposed outer flanges 51a, 52a, 53a and 54a, respectively.

The outer planar edges of the suspension means 30 are clamped between these outer flanges 51a, 52a, 53a and 54a and a rectangular clamping plate 55. The rectangular clamp member or frame 55 includes an upper horizontally disposed plate member 55a, a lower horizontally disposed member 55c and two vertically disposed clamping sections 55b and 55d. The ends of these clamping sections are integral or secured thereto to form the rectangular clamping assembly 55. Suitable screws which pass through holes in the clamping assembly 55 into the vertically disposed flanges 51a, 52a, 53a and 54a of the L-members 51 through 54 clamp the outer planar fastening portions 320, 33c, 34c and 350 of the suspension means 30. More specifically, the outer relatively thin portion 320, as shown in FIG. 5, is secured between clamping member 55a and flange 51a. The fastening portion 330 of suspension means 30 is clamped between clamping member 5517 and vertically disposed flange 52a. Portion 34c is clamped between clamping member 550 and vertically disposed flange 53a. as shown in FIG. 4, is clamped between vertical flange 54a and clamping strip 55d. Suitable clamping material, such as rubber or felt, can be employed between these fastening or terminal portions and frame 55 as well as between these portions and flanges 51a, 52a, 53a and 54a. Screws 56 are applied through the fastening strips 55a, 55b, 55c and 55d, through portions 32c, 33c, 34c and 350 and the vertically disposed flanges. Screws 56 are tightened sufliciently to provide secure mounting of the terminal strips 320, 33c, 34c and 35c.

A magnetic assembly 60 is secured to the side flange 52b and 54b of the L- channels 52 and 54, respectively, by L- members 72 and 71. The magnetic assembly 60 provides two horizontally disposed air gaps 69 and for the voice coil assembly 40, as illustrated in FIG. 2. These two air gaps are adapted to receive voice coil section 43 and 44 of the voice coil 42.

More specifically, the magnetic assembly 60, shown in FIGS. 1 and 2, comprises a rectangular rear pole member 61. The term pole member hereinafter is meant to mean a non-magnetized member which conducts a magnetic field but in itself is not a permanent magnet. Secured to the rear pole member 61 are two rectangular magnets 63 and 64 which are equally spaced on opposite sides of the center of the rear pole member 61. These rectangularly shaped magnets are the type on which one side is Likewise, terminal strip 350,

magnetized north and the other side south. As shown in FIG. 1,.the magnetic member 63 has a rear portion 63a which is polarized north with the front half portion 63b polarized south. Likewise, the magnetic member 64 has a rear half portion 64a polarized north and the front half portion 64b polarized south. It will be understood that portions 63a and 64a may be either north or south, however, they must both be magnetized the same. Likewise, the portions 63b and 64b must be polarized in the same direction, but in the opposite direction to portions 63a and 64a. The portions 63a and 64a are secured by some suitable adhesive to and longtiudinally of the rear pole member 61. The outer surface of portions 63b and 6412 are secured to outer pole members 67 and 68, respectively, for conducting the appropriate magnetic field therethrough. As shown in the drawing, the rectangularly shaped front pole member 68 is rectangular and has the same shape and dimensions as the magnet 64 with the edges thereof being coplanar with the edges of the magnet 64. Pole member 67 has three edges coplanar with the edges of magnet 63, but has one end extending outwardly therefrom.

Secured to the upper edge of the rear pole member 61 is a rectangularly shaped horizontally disposed top pole member 65. This pole member is placed, as shown in FIG. 5, perpendicular to the rear pole member 61 and provides a magnetic linear air gap 69 between pole member 65 and pole members 67 and 68. This linear air gap is adapted to receive a voice coil section 43, shown in FIG. 2. The spacing between the ends of members 64 and 68 and members 63 and 67 is sufficiently wide to receive the supporting strip 41d of the voice coil assembly 46. A rectangular horizontally disposed lower pole member 66 is secured to the lower edges of rear pole member 61 and has the same shape and size as the upper pole member 65. As shown in the drawing, the pole member 66 is positioned on rear pole member 61 and perpendicular thereto to provide a surface spaced from and parallel to the lower edge surface of front pole members 67 and 68. This forms lower air gap 76 which is sufficiently wide to receive the lower voice coil section 44 of voice coil 42. The distance between the parallel air gaps 69 and 76 is of course, determined by the distance between the parallel members 41a and 41b. For optimum performance it has been found that this distance is approximately 1.5 inches. By providing a sufficient distance between members 61a and 41b the placement of the base member 41c on the rear surface of diaphragm 28 is not critical and at the same time provides adequate support for aligning the voice coil with the air gaps 69 and '70 during the operation thereof. More specifically, by having the driving force from the voice coil assembly 40 being distributed or applied to the rear surface of diaphragm 26 over a relatively large rectangular area, defined by the area of base 410, structural stability of the voice coil is achieved with a relatively uniform force being applied through this area so that the exact placement of the voice coil on the diaphragm is not critical. With the rear diaphragm surface of diaphragm 26 being substantially planar it is possible to have such a relatively large driving area.

As shown in FIGS. 1, 2 and 6, the pole piece or magnetic conductor 61 extends beyond the end of magnet 63 as does the pole piece or magnetic conductor 67. As shown in FIG. 6, a circular or cylindrical recess '73 is located at the outer side of pole piece 67 at one end thereof. The other side of pole piece 67 has a reduced thickness area 75'. Extending through this end of pole piece 67 is a circular aperture 74. Mounted, by a screw or other means, on the extended end of pole piece 61 is a cylindrically shaped pole piece 76 which extends transverse to pole piece 61 in a position to extend into and coaxial with circular aperture 74 of pole piece 67. The pole piece 76 is positioned within the circular aperture 74 and is concentric therewith. Since pole pieces 61 and 67 are magnetically conducting polarization of opposite magnetic polarity the cylindrically shaped pole piece 76 cooperates with the circular aperture 74 to provide a circular magnetic air gap 78. Pole piece 76 has a conically shaped recess 77 at one end thereof. In addition, port apertures 79 are provided through pole piece 67 in recess "73. This reduces back loading on the diaphragm of a tweeter 80.

The tweeter 86 is mounted on pole piece 67 and comprises a conventional diaphragm having a frustoconical portion 81 which is integral with or secured to a central dome portion 82 having a single circular surround connecting the dome portion 82 and the frustoconical diaphragm 81. Mounted on the diaphragm 81 is a cylindrical voice coil support 83 having a conventional cylindrically disposed voice coil winding 84 mounted thereon. A cylindrical diaphragm support 86- is secured to pole piece 67 within the cylindrically disposed recess 73 and at the periphery thereof. The outer edges of the frustoconical diaphragm 81 are rigidly secured by some adhesive to the outer portion of the cylindrical diaphragm support 86.

The tweeter is dimensioned such that the voice coil 84, cylindrical in shape, is positioned within the magnetic air gap 78 so as to provide the necessary magnetic air gap for driving the diaphragm of the tweeter, as shown in FIG. 6.

Thus, it is seen that the magnetic assembly 60, in the present invention, is utilized not only to drive the larger radiating diaphragm 20 to provide reproduction of relatively low notes, but the same magnetic assembly is utilized to provide a circular or cylindrical disposed air gap for a tweeter and provide a support for the tweeter. A suitable crossover network can be provided between the voice coil leads 48 of voice coil assembly 40 and leads of the voice coil 84 of the tweeter. The construction of such a crossover network is well known to those in the art and will not be described in detail.

In order to provide effective radiations of the relatively high frequencies reproduced by the tweeter 80, apertures 28 are provided in the diaphragm 20 opposite the tweeter, as shown in FIG. 6 and FIG. 1. As illustrated in FIG. 6, these apertures are placed in a circular recess 27 formed on the back surface of the diaphragm 20. The pic shaped apertures 28 are separated by diametrically disposed reenforcing ribs 29. Hence, by employing these apertures the high frequencies radiating from the tweeter 80 will seem to be emanating directly from the larger radiating diaphragm 20. In addition to the magnetic pole pieces of the magnetic assembly 66 being additionally utilized to provide a cylindrically shaped air gap for the tweeter the magnetic assembly is being utilized to support the tweeter.

The voice coil leads 85 of tweeter 80 are preferably glued to the frustoconical diaphragm 81 extending outwardly through the connection between cylindrical support 36 and diaphragm 81. The tweeter connections 85 extend through a tubular shield 87 and thence through holes 88 on a supporting bar 89. This supporting bar 89, as shown in FIG. 3, is mounted on the rear pole piece 61 to provide a convenient access to the lead 85.

As stated above, the preferred construction and method of fabricating the diaphragm 20 is as illustrated in the above-identified patent application.

Secured to the ends of the rear pole piece 61 are two L- members 71 and 72 for mounting the magnetic structure 66 on the frame 56. Suitable holes in the rear flange of the L- members 71 and 72 are provided which are secured to the vertically disposed L- members 52 and 54. The magnetic assembly is positioned on frame member 52 and 54 so that the voice coil sections 43 and 44 are centrally disposed within the horizontally disposed air gaps 69 and 70. Additionally, the end voice coil sections 45 and 46 are equally spaced from ends of pole piece 67 and pole piece 68, respectively. The assembly 60 is positioned over assembly 40 so that sections 43 and 44 extend into air gaps 69 and 70 a distance such that they are centered, depthwise, on front pole pieces 67 and 68, as shown in FIG. 5. This distance between the ends of the voice coil and the ends of the magnet structure is a comprise between tolerance requirements and keeping the portion of the voice coil that extends beyond the magnet structure to a minimum since it does not contribute to the performance of the voice coil. More specifically, this portion of the coil acts as a simple mass, which will effect the frequency response of the unit.

As set forth in the above-mentioned patent application, the diaphragm should be relatively lightweight, of a material that has a relatively low Q, yet with an optimum amount of stiffness. It has been found that a satisfactory material, which meets these requirements of constructing a relatively flat or planar diaphragm 20, is foam polystyrene. Other similar materials are polyurethane, prefoamed cellulose, polyethylene, acetate, epoxy foams, etc.

The preferred construction and method for manufacturing diaphragm 20 is set forth in the above-mentioned patent application.

Although my invention has been described in considerable detail, such description is intended as being illustrative rather than limiting, since the invention may be variously embodied.

We claim as our invention:

1. A loudspeaker for reproducing audible signals comprising a diaphragm, a first voice coil for driving said diaphragm in response to current being applied thereto, said first voice coil having a linear portion, a magnetic assembly for providing a first voice coil air gap for said first voice coil, including a first magnetic member having a first polarity and a second magnetic member having a different polarity, said first and said second magnetic members being positioned on opposite sides of said first voice coil providing a first linear air gap for receiving said linear portion of said first voice coil, a second voice coil, a third magnetic member magnetically connected to said first magnetic member, a fourth magnetic member magnetically connected to said second magnetic member, said third magnetic member having an aperture therein, said fourth magnetic member and positioned within said aperture so as to provide a second air gap for said second voice coil.

2. A loudspeaker for reproducing audible signals comprising a first diaphragm, a first voice coil for driving said first diaphragm in response to current being applied thereto, said voice coil having a linear portion, a magnetic assembly providing a linear air gap for receiving said linear portion of said first voice coil and including a first magnetic member having a first polarity and a second magnetic member having a different polarity, said first and said second magnetic members being positioned on opposite sides of said first voice coil to form said linear air gap, a third magnetic member magnetically connected to said first magnetic member, a fourth magnetic member being magnetically connected to said second magnetic member, a second circular diaphragm having a second circular voice coil mounted thereon, said third magnetic member having a circular aperture therein, said fourth magnetic member being cylindrical in shape and positioned within said circular aperture to form a circular air gap therebetween, said second circular voice coil being positioned within said circular air gap, and means for mounting the peripheral edges of said circular diaphragm on said third magnetic member.

3. A loudspeaker for reproducing audible signals comprising a first diaphragm having first and second surfaces which are substantially planar and disposed substantially parallel to each other, a first voice coil for driving said first diaphragm in response to current being applied thereto, said first voice coil having a linear portion, a magnetic assembly providing a linear voice coil air gap for receiving said linear portion of said first voice coil, and including a first magnetic member having a first polarity and a second magnetic member having a different polarity, a third magnetic member magnetically connected to said first magnetic member, a fourth magnetic member being magnetically connected to said second magnetic member, said third magnetic member having a circular aperture therein, said fourth magnetic member being cylindrical in shape and positioned within said circular aperture, a second circular diaphragm having a circular voice coil mounted thereon, means for mounting the peripheral edges of said circular diaphragm on said third magnetic member with said circular voice coil being positioned within said circular air gap, and an aperture in said first diaphragm opposite said second circular diaphragm.

4. A loudspeaker for producing sound signals comprising a first diaphragm, a first voice coil for driving said first diaphragm and having a rectangular configuration with first and second side portions, a magnetic assembly for providing first and second linear voice coil air gaps for said first and second side portions and including a first U-shaped magnetic member of a first polarity and having two leg portions, a second magnetic member of a different polarity and disposed between said leg portions to form said first and second linear voice coil air gaps, said first and second side portions disposed respectively within said first and second linear voice coil air gaps, a third magnetic member magnetically connected to said second magnetic member and having a circular aperture therein, a fourth magnetic member being magnetically connected to said first magnetic member and being cylindrical in shape, said fourth magnetic member being positioned within said aperture to form a circular voice coil air gap, a second diaphragm having a circular voice coil disposed within said circular voice coil air gap.

5. A loudspeaker as claimed in claim 4, wherein said first diaphragm has substantially planar first and second surfaces which are disposed substantially parallel to each other, said first voice coil mounted upon said first diaphragm for driving said first diaphragm.

6. A loudspeaker as claimed in claim 5, wherein said second diaphragm is of a conical configuration for producing high frequencies.

7. A loudspeaker for reproducing base and high frequencies comprising a first diaphragm for radiating said base frequencies having relatively fiat first and second surfaces which are disposed substantially parallel to each other, a first voice coil for driving said first diaphragm and having a linear portion, a magnetic assembly for providing a linear voice coil air gap for said linear portion of said first voice coil and including a first magnetic member of a first polarity, a second magnetic member of a different polarity, a third magnetic member magnetically connected to said first magnetic member, a fourth magnetic member magnetically connected to said second magnetic member, said third magnetic member having an aperture therein, said fourth magnetic member being of a cylindrical configuration and disposed within said aperture to form a circular voice coil air gap, at second conically shaped diaphragm for radiating said high frequencies having a second circular voice coil, said second circular voice coil being disposed within said circular voice coil air gap.

References Cited by the Examiner UNITED STATES PATENTS 5/1958 Manley et a1 l79ll5.5 9/1959 Harris 340-8

Claims (1)

1. A LOUDSPEAKER FOR REPRODUCING AUDIBLE SIGNALS COMPRISING A DIAPHRAGM, A FIRST VOICE COIL FOR DRIVING SAID DIAPHRAGM IN RESPONSE TO CURRENT BEING APPLIED THERETO, SAID FIRST VOICE COIL HAVING A LINEAR PORTION, A MAGNETIC ASSEMBLY FOR PROVIDING A FIRST VOICE COIL AIR GAP FOR SAID FIRST VOICE COIL, INCLUDING A FIRST MAGNETIC MEMBER HAVING A FIRST POLARITY OF AND A SECOND MAGNETIC MEMBER HAVING DIFFERENT POLARITY, SAID FIRST AND SAID SECOND MAGNETIC MEMBERS BEING POSITIONED ON OPPOSITE SIDES OF SAID FIRST VOICE COIL PROVIDING A FIRST LINEAR AIR GAP FOR RECEIVING SAID LINEAR PORTION OF SAID FIRST VOICE COIL, A SECOND VOICE COIL, A THIRD MAGNETIC MEMBER MAGNETICALLY CONNECTED TO SAID FIRST MAGNETIC MEMBER, A FOURTH MAGNETIC MEMBER MAGNETICALLY CONNECTED TO SAID SECOND MAGNETIC MEMBER, SAID THIRD MAGNETIC MEMBER HAVING AN APERTURE THEREIN, SAID FOURTH MAGNETIC MEMBER AND POSITIONED WITHIN SAID APERTURE SO AS TO PROVIDE A SECOND AIR GAP FOR SAID SECOND VOICE COIL.

Images