Abstract:
A speaker diaphragm of the present invention is prepared in a manner such that a boron layer is formed on one face of a dome-shaped metal foil by means of a physical vapor deposition method such as ion-plating, cathode sputtering, vacuum evaporation or the like, when necessary the metal foil is thinned by etching, and then, if necessary, another boron layer is formed on the other face of the metal foil. Alternatively, a metal layer is formed on the surface of the boron layer. The resultant speaker diaphragm is light in weight and high in modulus and also has appropriate internal mechanical resistance against vibration, thereby providing a speaker of high efficiency and satisfactory characteristics.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of our earlier application Ser. No. 781,002 filed Mar. 24, 1977, and now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a speaker diaphragm using a metal foil such as titanium, aluminium or the like as a substrate thereof, which diaphragm is especially suitable for a tweeter, and a method of making the same. 
     Hitherto, a product of natural fiber such as pulp, form-forming (blown) high polymer resin, high polymer resin film, metal foil or the like have been used as a materials for speaker diaphragms. However, these are not necessarily satisfactory as diaphragm materials for the following reasons: Diaphragms using a natural fiber product have disadvantages that they are inefficient because of their small specific modulus and are readily influenced by humidity or temperature; although they have an advantage that no adverse sharp resonation occurs during operation because they have appropriate internal mechanical resistance, i.e., attenuation caused by friction among the fibers. Diaphragms using metal foils have the disadvantage that a sharp resonation occurs therein because of their low internal mechanical resistance and a strain appears because of their non-linear motion when amplitude of vibration is great; although they are good in efficiency because they have a relatively high specific modulus and not influenced by humidity or temperature. 
     It is generally known that for a suitable diaphragm, materials having a high specific modulus, light weight and appropriate internal mechanical resistance are suitable. It has been difficult to provide diaphragms satisfying the abovementioned incompatible characteristics by using existing materials only for the diaphragms. 
     Although titanium and aluminium, which are generally employed as a metal materials for speaker diaphragms, are mechanically strong and have relatively high specific modulus, that is the ratio of Young&#39;s Modulus to the density (e.g. 2.3-2.7×10 11  (cm/sec) 2 ), yet, in order to obtain a good efficient speaker, diaphragm materials of a much higher specific modulus are required. 
     SUMMARY OF THE DISCLOSURE 
     The present invention discloses a speaker diaphragm light in weight, having a high specific modulus and an appropriate internal mechanical resistance, by forming at least one boron layer on the face(s) of a metal foil made of titanium, aluminium or the like, and to provide a method of making such a speaker diaphragm comprising the layer of boron, which is frangile compared with metals and difficult to machine though having a hardness next to diamond and excellent in specific modulus. 
    
    
     BRIEF DESCRIPTION EXPLANATION OF THE DRAWINGS 
     FIGS. 1A-1C, 2A-2D, 3A-3D, and 4A-4D are cross-sectional views showing the manufacturing steps of a first, a second, a third, and a fourth embodiment, respectively, of the speaker diaphragm of the present invention. 
     FIG. 5 is a cross-sectional view of another embodiment of the speaker diaphragm of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the present invention, a metal foil such as aluminium, titanium, copper or the like shaped, for example in a dome or hemisphere, is employed as the substrate of a diaphragm, and boron is applied on the surface of the substrate by a physical vapor deposition method (e.g. ion-plating, cathode sputtering, vacuum evaporation or the like). One characteristic of the present invention is that, such a composite diaphragm is then etched by chemical etching using various kinds of etching solutions or an ion etching method, to thin the metal foil, thereby achieving higher specific modulus (E/ρ) as well as lighter weight (where ρ indicates density and E indicates Young&#39;s modulus). Since the boron has such low density of 2.3-2.47 g/cm 3  and such high specific modulus of 16.3×10 11  (cm/sec) 2 , the resultant composite diaphragm consisting principally of the boron layer performs well and exhibits satisfactory characteristics. 
     Preferred examples of the present invention are elucidated hereinafter referring to the accompanying drawings. 
     Example 1 
     First, as shown in FIG. 1A, a metal foil 1 of about 10 μm in thickness such as aluminium, titanium, copper or the like is formed into a dome-shape. Then, as shown in FIG. 1B, on a surface of said metal foil 1, a boron layer 2 of at least 10 microns in thickness is formed by means of a physical vapor deposition method such as ion-plating, cathode sputtering, vacuum evaportaion or the like method. Finally, the metal foil 1 is etched by chemical etching using etching various solutions (e.g. containing 10% of NaOH for aluminium foil, 10% of HF for titanium foil and HNO 3  for copper foil) or by cathode sputter etching, to be thinned to a predetermined amount of approximately 1-3 microns in thickness. In this manner a diaphragm for speakers as shown in FIG. 1C can be produced. 
     Example 2 
     A composite diaphragm shown in FIG. 2C is manufactured using the same processes as in Example 1 (FIGS. 1A-1C). Then, on the rear face of metal foil 1 of said composite diaphragm, another boron layer 3 of at least 10 microns in thickness is further formed as shown in FIG. 2D to obtain a diaphragm for speakers. 
     According to the itching process as described in the above-mentioned Examples 1 and 2 (FIGS. 1 and 2), the metal foil 1 can be satisfactorily thinned to an extent of 1 to 3 microns in thickness, thereby reducing weight of the diaphragm and improving efficiency. 
     Example 3 
     A metal foil 1 is first formed into a dome-shape as shown in FIG. 3A, and then thinned, as shown in FIG. 3B, to approxiamtely 5-6 microns in thickness by a chemical (non-electrolysis) etching method. Finally, as shown in FIG. 3C a boron layer 2 is formed of at least 10 microns in thickness on the surface of the metal foil 1 to obtain a speaker diaphragm. Alternatively, another boron layer 3 can be formed on the rear face of the metal foil 1 in addition to the front surface, to obtain a speaker diaphragm. 
     According to the process shown in FIG. 3, though there is a problem that the metal foil 1 can not be made sufficiently thin because of the etching made without any support by the boron layer, there is an advantage in that the boron layers 2 and 3 are strongly combined with the metal foil 1 because the whole face(s) of metal foil 1 is (are) roughened by the etching. 
     Table 1 shows densities as well as specific moduli of the speaker diaphragms of the abovementioned examples of the present invention, and of the prior art. The specific moduli of the diaphragms of the examples of the present invention are calculated considering each composite diaphragm as a single-layered body. 
     
                       TABLE 1______________________________________ComponentsThickness of      Thickness ofMetal Foil Boron Layers Densities                            Specific Moduli(microns)  (microns)    (g/cm.sup.3)                            (cm/sec).sup.2______________________________________Prior ArtAluminium  0            2.8       2.6 × 10.sup.11Titanium   0            4.5       2.4 × 10.sup.11Present InventionAluminium (3)      10, on one face                   2.49     13.5 × 10.sup.11Aluminium (3)      20, on one face                   2.45     14.2 × 10.sup.11Titanium (3)      10, on one face                   2.88     11.9 × 10.sup.11Titanium (3)      20, on one face                   2.67     13.1 × 10.sup.11Copper (3) 10, on one face                   3.92      8.3 × 10.sup.11Copper (3) 20, on one face                   3.26      9.8 × 10.sup.11Aluminium (3)      20, on both faces                   2.42     14.7 × 10.sup.11Titanium (3)      20, on both faces                   2.64     13.9 × 10.sup.11Copper (3) 20, on both faces                   3.21     10.2 × 10.sup.11Aluminium (3)      40, on both faces                   2.39     15.1 × 10.sup.11Titanium (3)      40, on both faces                   2.51     14.2 × 10.sup.11Copper (3) 40, on both faces                   2.82     10.9 × 10.sup.11______________________________________ 
    
     Example 4 
     A metal foil 4 is first formed into a dome-shape as shown in FIG. 4A. The thickness of the foil is selected to be 20 microns in case of aluminium foil and 10 microns in case of titanium or copper foil. Next, a boron layer 5 is applied as shown in FIG. 4B having a thickness of 10 microns on the rear face of said metal foil 4 by means of a physical vapor deposition method. Then, said metal foil 4 is thinned to the thickness of 1-3 microns by chemical- or ion-etching as shown in FIG. 4C. Subsequently, a metal layer 6 of approximately 1-3 microns in thickness is formed by a physical vapor deposition method on the rear face of said boron layer 5, as shown by FIG. 4D, to obtain a speaker diaphragm. 
     Table 2 shows densities and specific moduli of the speaker diaphragms for various thicknesses of the boron layer 5 and for various kinds and thickness of metals constituting the diaphragm. 
     
                                           TABLE 2__________________________________________________________________________ComponentsThickness of       Kinds and Thickness                     Densities                          Specific ModuliBoron Layer (microns)       of Metal Layers (microns)                     (g/cm.sup.3)                          (cm/sec).sup.2__________________________________________________________________________10          Aluminium, on both faces: 1                     2.49 12.1  × 10.sup.1110          Titanium, on both faces: 1                     2.78 11.2  × 10.sup.1110          Copper, on both faces: 1                     3.50  9.08 × 10.sup.1110          Aluminium, on one face: 1                     2.6  10.7  × 10.sup.11       Titanium, on the other       face: 110          Titanium, on one face: 1                     3.14 10.5  × 10.sup.11       Copper, on the other       face: 110          Copper, on one face: 1                     3.0   9.03 × 10.sup.11       Aluminium, on the other       face: 110          Aluminium, on one face: 1                     3.84 10.5  × 10.sup.11       Tungsten, on the other       face: 110          Titanium, on one face: 1                     4.02 11.3  × 10.sup.11       Tungsten, on the other       face: 110          Copper, on one face: 1                     4.38  9.34 × 10.sup.11       Tungsten, on the other       face: 120          Aluminium, on both faces: 1                     2.44 12.0  × 10.sup.1120          Titanium, on both faces: 1                     2.59 11.7  × 10.sup.1120          Copper, on both faces: 1                     2.98 10.2  × 10.sup.11__________________________________________________________________________ Remark: ##STR1## 
    
     Nickel or silicon can be also employed for the metals of the foil 4 and th metal layer 6 in each embodiment of the abovementioned Table 2. 
     The diaphragm of the embodiment of FIG. 4 is constructed in a manner such the boron layer 5 is sandwiched between the metal foil 4 and the metal layer 6. Accordingly, water-resistivity of the diaphragm is improved and peeling off of the boron layer 5 from the metal foil 4 is prevented. 
     In order to prevent deterioration of the characteristics of the speaker diaphragms with the lapse of time, it is desirable to coat the surface of each speaker diaphragm of the abovementioned Examples with a resin (e.g. epoxy, urethane or the like resin) exhibiting good water-resistivity and adhesiveness, to a thickness of approximately 2-3 microns by means of any known method, e.g. spraying. One example of a speaker diaphragm coated with the resin layer is shown in FIG. 5, wherein numeral 7 designates the bottom, top and side resin layer applied on the whole face of the diaphragm of the type shown in FIG. 3. 
     As elucidated in the foregoing description, the present invention can provide a speaker diaphragm light in weight as well as having a high specific modulus.