BACKGROUND OF THE INVENTION

The present invention generally relates to the field of acousti¬ cal transducers, and more particularly, is directed to a loudspeaker assembly having a diaphragm constructed of a plurality of cone- shaped cells.

Conventional loudspeakers are formed of a moveable plate or diaphragm attached to an electric coil. The coil receivers audio sig¬ nals in the form of an electric current. The current flow through the coil causes the creation of a varying electromagnetic field in accor¬ dance with the current flow. Interaction of the electromagnetic field with a surrounding permanent magnet field causes physical displace of the diaphragm in accordance with the audio signal current flow. Dis¬ placement of the diaphragm results in a corresponding displacement of air which produces the intended sound.

In prior art speakers, high acoustic output is achieved by an increase in the surface area of the diaphragm or by the use of multi- • pie electric coils distributed along the diaphragm. However, the lack of mechanical rigidity of large surface area diaphragms limits the output power levels which can be obtained. Attempts have been made to overcome the power limitation problem by using thicker dia¬ phragms, such as those made from expanded polystyrene plates, or by fabricating the diaphragms from a honeycomb structure. Diaphragms made in this manner are not fully satisfactory as they use materials and construction methods which normally are not used for speakers. Thus, such diaphragms are higher in cost.

A number of loudspeaker diaphragms are known in the prior art. One such diaphragm is disclosed in U.S. Patent No. 4,107,479

issued in the name of Heil. This patent is directed to a loudspeaker system having a plurality of diaphragms. As shown in Figures 4 and 6 and explained at col. 9, lines 36-62, of this patent, each diaphragm is formed of four pyramidal-shaped cones 72. Drive rods 48 pass through each cone and are securely fastened in air-tight relationships to the apex of the cone. The drive rods are connected to one or more move¬ able coil assemblies which respond to electrical audio signals. The assembly is supported within a support ring 70 by a flexible surround 68 which permits movement of the diaphragms in response to move¬ ment of the drive rods. A rigid material, such as polycarbonate film, is used to form the diaphragms. A rigid aluminum foil material also may be used to construct the diaphragms.

U.S. Patent No. 4,039,044 to Heil also discloses a speaker assembly having a plurality of fixed and moveable diaphragms. The moveable diaphragms are formed of a plurality of upward and down¬ ward projecting nodes which form corresponding cones as shown in Figure 8 of the patent. Drive rods 63 and 64 (Figure 7) are attached to the apex of each cone.

Though the above described speaker assemblies known in the prior art represent an improvement over earlier speakers, they still remain deficient with respect to high power output at low cost. SUMMARY OF THE INVENTION

It is the overall object of the present invention to provide a speaker which can be used to produce high output power.

It is a specific object of the present invention to provide a high output speaker assembly having good sound reproduction qualities and is low in cost to manufacturer.

It is a further specific object of the present invention to pro¬ vide a high output speaker assembly which can be made from materi¬ als normally used in the manufacturer of speakers.

It is a still further object of the present invention to provide a high output speaker assembly which is reliable in operation while at the same time being low in cost.

The speaker diaphragm of the present invention incorporates a self-supporting structure. This structure is formed by two flat

parallel layers connected together by rods. The rods connect to each layer at the intersection of support members which are arranged in polygonal fashion so as to form squares. This structure is thus, light in weight while at the same time having high strength. The supporting members and connecting rods form tetrahedra or cones in the shape of hollow pyramids, each having a tip. Each tetrahedron is covered with a diaphragm having a certain thickness and is made of a material normally used in speaker construction.

In a further embodiment of the invention, a sheet of flexible, elastic material is stretched between upper and lower nodes, wherein the flexible sheet itself forms the connecting rods between nodes.

Thus, the diaphragm used in the speaker assembly of the present invention is constructed from materials, and according to processes, which are conventionally used in loudspeaker manufacture. The diaphragm possess a very high degree of rigidity, which makes it suitable for incorporation into large-surface-area loudspeakers equipped with a multiplicity of spaced, movable windings. The base of each of the cones rests for support on the nodes of a mesh loop in the upper plane and the tip of each rests on a node lying in the lower plane. The basic feature of the diaphragm consists in locking the angles of the connecting rods by encompassing each of the rods in the conical surface.

In the embodiment of the diaphragm which utilizes the equilib¬ rium surface imparted to a flexible elastic material stretched between the respective nodes of the mesh loops in the upper and lower planes, the areas of the diaphragm located at the intersection of the lines joining the two upper and two lower nodes, respectively, describe two lines of curvature extending in opposite directions. The two lines of curvature form a left-hand surface termed the "saddle point" or Turkish saddle," a shape which is responsible for the high level of rigidity of the diaphragm.

Thus in summary, the present invention is directed to an electroacoustic transducer which radiates sound when activated by an electric signal fed to its terminals. The terminals include a radiating surface in the form of a movable diaphragm supported along its edges

by a stationary frame. A multiplicity of drive units are provided, each of which is formed of a circuit for generating a magnetic field and is supported by a stationary frame. Another electric circuit in the form of a winding is attached to the diaphragm and includes ter¬ minals for receiving an input signal. The diaphragm has a shape deter¬ mined by a structure incorporating two parallel flat layers. Each layer holds a succession of nodes arranged in a multiplicity of poly¬ gons. Connecting rods join the respective nodes in the two layers. Thus, the diaphragm comprises a multiplicity of adjacent hollow conically-shaped areas, the base of each cone being turned toward one of the two layers and the tip of each cone, which supports a winding, being located at a node in the other of the two layers. The connect¬ ing rods are contained within the diaphragm of each cone.

The invention will be better understood from the following description provided with reference to the attached drawings in which: BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a partial perspective view of a self-supporting structure incorporating members and connecting rods.

Figure 2 is a partial perspective view of a first embodiment of the invention, in which the multicellular diaphragm of the invention has the shape of each cell as formed by the support members and con¬ necting rods of the self-supporting structure shown in Figure 1.

Figure 3 is a partial perspective view of a second embodiment of the invention, in which the multicellular diaphragm according to the invention has the shape of the equilibrium figure of a flexible, elastic diaphragm resting for support on the connecting nodes of the support members of the self-supporting structure in Figure 1.

Figure 4 illustrates a diaphragm according to Figure 3, com¬ prising two adjacent cells eut out along the boundary lines passing through the nodes.

Figure 5 illustrates a diaphragm composed of two adjacent cells, derived from a flat section of the diaphragm shown in Figure 4 by means of a plane parallel to the planes of the nodes of the self- supporting structure.

Figure 6 represents a variant of the diaphragm in figure 5, in which the flat section created by another parallel plane retains two upper nodes on the diaphragm.

Figure 7 represents another variant of the diaphragm in Figure 5, in which the flat section, seen from another parallel plane, has a contour which is generally elliptical in shape. DESCRIPTION OF THE PREFERRED EMBODIMENT

Figure 1 gives a partial perspective view of a self-supporting structure incorporating members and connecting rods. This structure is composed of two flat, parallel layers 1 and 2, composed of support members such as 3 and 4 arranged in polygonal fashion so as to form squares such as 5, the squares in one layer being offset, parallel to the sides, by the respective values 6 and 7 equal to one half-side. The basic feature of a structure of this kind lies in the connecting rods 8 which join the respective vertices, or nodes, of the squares in each of the two layers. The sides of the squares in each layer determine the distance between two adjacent nodes, and the connecting rods, that between two respective nodes in each of the two layers. A structure of this kind is light in weight and has a high level of rigidity perpen¬ dicular to its overall plan.

Figure 2 is a partial perspective view of a first embodiment of the invention, according to which the multicellular diaphragm of the invention has the shape of each cell as determined by the supporting members and connecting rods in the self-supporting structure illus¬ trated in Figure 1.

Supporting members 10 and the connecting rods 11 describe tetrahedra in the shape of hollow pyramids having a tip 12. Each tetrahedra is covered with a diaphragm having a certain thickness and made of material which normally is used in electroacoustic trans¬ ducers. Each tip rests on the layer termed lower, and each base lies on the layer termed upper.

Figure 3 is a partial perspective view of a second embodiment of the invention, according to which the multicellular diaphragm of the invention adopts the form of the equilibrium figure of a sheet of

flexible, elastic material resting for support on the connecting nodes of the support members of the self-supporting structure in Figure 1.

As shown in Figure 3, stretching the sheet between upper and lower nodes results in upper nodes 22, 23, 24 and 25 being connected by sheet 26 to lower node 21 to form downward projecting cell 32. The remaining cells in the diaphragm are formed in a similar manner by sheet 26 connecting a set of four upper nodes to a corresponding lower node. Sheet 26 also connects sets of four lower nodes to a cor¬ responding upper node, such as upper node 33, to form upward pro¬ jecting cells.

Connecting sheet 26 between upper and lower nodes creates a first family of curved lines 34 and a second family of curved lines 28. Lines 34 connect, for example, upper nodes 24 and 33 and form the boundary between downward cells 31 and 32. Line 28 connect, for example, lower nodes 21 and 29 which also form the boundary between adjacent upward projecting cells. Lines 34 and 28 intersect at point 30 to form a "saddle point" which provides a high level of rigidity to the corresponding surfaces.

The use of the diaphragm illustrated in Figure 3 in connection with an electric coil assembly is shown in Figure 4. In this construc¬ tion, a coil assembly is attached to each of the lower nodes.

The loudspeakers constituting the object of this invention com¬ prise radiant diaphragms incorporating a large surface area and which have none of these disadvantages.

In the embodiment shown in Figure 3, use is made solely of the respective nodes lying in the two layers, e.g., 21 for one of the layers and 22 for the other, and the shape of the transducer diaphragm is delimited by the application of a sheet of flexible, elastic material stretched between the nodes of the two layers. This material may, for example, be rubber or a plastic material possessing comparable elasticity and pliability.

After producing a mold for a surface of this kind, it becomes possible to form diaphragms for electroacoustic transducers which possess the properties of a very rigid self-supporting surf aee, without entailing the need for supporting members and connecting rods.

The function of the connecting rods is performed by the dia¬ phragm itself, i.e., whatever the relative values of the- distances between adjacent nodes, for example 23, and 24, and between two nodes 21 and 22 selected in each upper and lower layer, the curved surface of the diaphragm always contains at least one straight line such as 25, which thus performs the function of a connecting rod incorporated into the diaphragm itself.

The distance-setting function between nodes such as 23 and 24 in the upper layer is performed by the pliable elastic sheet 26 stretched between the upper and lower nodes. This shape is a left- hand surface incorporating two families of reciprocal lines of curva¬ ture, including first a family of lines such as 34 which connect two upper nodes such as 24 and 33 and form the boundary between two cells such as 31 and 32, and second, a family of lines such as 28, which connect two lower nodes such as 21 and 29, both families of lines, with their opposing curvatures, intersecting at point 30.

The left-hand surface formed at this point, known in mathe¬ matical geometry as a "saddle point" or Turkish saddle," confers a high level of rigidity on the corresponding surfaces. This special shape performs the function assumed by the supporting members of the self-supporting structure in Figure 2, and permits their elimina¬ tion in the diaphragm according to the invention.

Figure 4 represents a diaphragm according to Figure 3, com¬ prising only two adjacent cells cut out along the boundary lines pass¬ ing through the nodes. The construction of a loudspeaker using this diaphragm embodies the attachment of a movable winding 41 to each lower node, this node being subjected to a magnetic field generated by a magnet 42 mounted coaxially. A peripheral strip on the outer edge of the movable diaphragm 43 is made of a pliable material 44 which constitutes means for suspending the diaphragm from the stationary rame 45 in order to allow the diaphragm to be displaced vertically 46 (the peripheral strip and the frame are represented only partially for reasons of clarity).

Figure 5 represents a membrane comprised of two adjoining cells derived from a flat section of the diaphragm in Figure 4 by

means of a plane parallel to the planes of the nodes of the self-sup¬ porting structure. This embodiment is particularly advantageous in comparison with the embodiment in Figure 4 since it allows a simpler incorporation of the peripheral pliable suspension strip 51 and the stationary frame 52. The entire assembly is thus easily used in con¬ ventional speaker systems.

Figure 6 represents another embodiment of the diaphragm in Figure 5 in which a flat section is formed by another plane parallel to the planes of the nodes in the self-supporting structure. This plane allows two upper nodes 63 and 64 on the diaphragm, thereby increas¬ ing the radiating surface-area and imparting to the outer contour 65 of the diaphragm the general shape of a curvilinear diamond.

Figure 7 represents still another embodiment of the diaphragm in Figure 5, in which a flat section is formed by means of another plane parallel to the planes of the nodes of the self-supporting struc¬ ture. This additional plane allows a diaphragm contour which has a consistently convex curvature and a generally elliptical shape.

It must be noted that, in the above described embodiments, the diaphragm always incorporates in its shape rectilinear areas which perform the function of the connecting rods of the self-supporting surface from which it is derived and to which it owes its advantageous properties.

While the invention has been illustrated and described in detail in the drawings and foregoing description it will be recognized that- changes and modi ications can and will occur to those skilled in the art. It is therefore intended by the appending claims, to cover any such changes and modi ications as fall within the true spirit and scope of the invention.