A speaker diaphragm

Abstract

 In a laminated construction of a speaker diaphragm including one or more diamond phase base layers, one or more silicon car­bide or beryllium predominant layers are combined with the diamond phase base layer as a substitute for conventional alumina or silicon nitride layers. High sound transmission speed in­herent to silicon carbide and beryllium much improves frequency characteristics in particular in the treble range.

Description

Background of the invention

[0001] The present invention relates to a speaker diaphragm, and more particularly relates to improvement in frequency charac­teristics in the treble range of a speaker diaphragm including one or more diamond phase carbon layer.

[0002] In this specification, the term "a diamond phase carbon layer" refers to a layer made of diamond or carbon having a crys­tal structure and physical properties close to those of diamond. Further, the term "a Beryllium predominant layer" refers to a layer made of Beryllium or Beryllium-base alloy.

[0003] Beryllium or Beryllium-base alloy is conventionally used for a metallic type speaker diaphragm. Beryllium has a high Young's ratio, i.e. a ratio of Young's modulus E with respect to density ρ , thanks to its light weight and high hardness. Such high Young's ratio assures good frequency performance of the speaker diaphragm in the treble range.

[0004] In recent years, production of diamond phase carbon was also rendered feasible by means of vapor phase development (vapor phase growth) under low pressure such as the micro wave plasma CVD process. Diamond phase carbon also has a remarkably high Young's ratio and, as a consequence, assures high sound transmis­sion speed in a range from 16,000 to 18,000m/sec. It is well known use of diamond phase carbon for a speaker diaphragm greatly improved its frequency characteristics, in particular in the treble range.

[0005] Despite such advantages, considerably long period is needed for production of a speaker diaphragm including a diamond phase carbon layer due to very slow development of the layer via the vapor phase development under low pressure. Such a long process period per unit production naturally results in undesirable in­crease in production cost.

[0006] In an attempt to remove such disadvantage, a speaker diaph­ragm of a laminated construction was already proposed in, for ex­ample, Japanese Patent Laid-opens Sho. 61-161897 and Sho. 61-­161898 in which a diamond phase carbon layer is combined face to face with a layer made of another material.

[0007] In one example of such a laminate type speaker diaphragm, a diamond phase carbon layer is combined with a layer made of alumina (Al₂O₃) and, in another example, a diamond phase carbon layer is combined with a layer made of silicon nitride (Si₃N₄). In production of such a speaker diaphragm, an alumina or silicon nitride layer is prepared first and a diamond phase carbon layer is subsequently formed thereon via vapor phase development such as the micro wave plasma CVD process. In practice, however, it is next to impossible to fairly develop the diamond phase carbon layer via the art of vapor phase development. Even when success­ful in development, no strong bonding between the base layer and the diamond phase carbon layer can be expected, thereby disena­bling use of this process in the real production.

[0008] As an alternative, it is thinkable to first develop, as an intermediate layer, a thin silicon carbide layer on a alumina or silicon nitride layer and, next, develop a diamond phase carbon layer thereon via vapor phase development. This process assures stronger bond between the diamond phase carbon layer and the silicon carbide intermediate layer as well as between the silicon carbide layer and the alumina or silicon nitride layer. In this case, however, formation of the silicon carbide intermediate layer increases process steps necessary for production and, con­sequently, a great deal of production cost.

[0009] In the case of a laminate type speaker diaphragm including an alumina layer, no sufficient improvement in frequency charac­teristics in the treble range is expected due to the relatively low sound transmission speed of alumina (about 10420m/sec).

Summary of the invention

[0010] It is the object of the present invention to provide a laminate type speaker diaphragm of high frequency characteristics in the treble range at low production cost.

[0011] In accordance with the first aspect of the present inven­tion, at least one silicon carbide laminate layer is combined face to face with at least one diamond phase carbon base layer.

[0012] In accordance with the second aspect of the present inven­tion, at least one Beryllium predominant layer is combined face to face with at least one diamond phase carbon base layer.

Brief description of the drawings

[0013] 

Figs.1 to 3 are side sectional fragmentary views of dif­ferent embodiments of the speaker diaphragm in accordance with the present invention.

Fig.4 is a side sectional view of the entire configuration of one example of the speaker diaphragm in accordance with the present invention.

Figs.5 and 6 are simplified side views of equipments used for production of the speaker diaphragm shown in Fig.4,

Fig.7 is a graph for showing the frequency characteristics of the speaker diaphragm in accordance with the present inven­tion,

Fig.8 is a spectrum diagram of Raman spectroscopy used for definition of the diamond phase carbon used for the present in­vention, and

Fig.9 is a graph for showing the frequency characteristic of the speaker diaphragm in accordance with the present inven­tion.

Description of the preferred embodiments

[0014] The diamond phase carbon layer used for the present inven­tion is further defined in detail as follows. Raman spectroscopy for diffraction analysis is generally used for this definition. A spectrum such as shown in Fig.8 is obtained by measurement based on Raman spectroscopy. The diamond phase carbon layer usable for the present invention exhibits a sharp peak at a wave number of 1333 ± 10cm⁻² which is characteristic of diamond. Dif­fraction analysis is also used for the definition. In the case of measurement based on diffraction such as X-ray diffraction or electron diffraction, the diamond phase carbon layer usable for the present invention develops 2 or more diffracted stripes re­lated to plane distances (spacing of lattice planes) such as shown in Table 1.

Table 1

[0015] Plane distance (°A)
2.06 ± 0.05
1.26 ± 0.05
1.08 ± 0.03
1.03 ± 0.03
0.89 ± 0.02
0.82 ± 0.02

[0016] In the case of the embodiment shown in Fig. 1, a laminated combination 3A is made up of a silicon carbide layer 1 and a diamond phase carbon layer 2 superimposed to each other. In the case of the embodiment shown in Fig.2, a laminated combination 3B is made up of a silicon carbide layer 1 and two diamond phase carbon layers 2 sandwiching the silicon carbide layer 1. In the case of the embodiment shown in Fig.3, a laminated combination 3C is made up of two silicon carbide layers 1 and three diamond phase carbon layers 2 superimposed in an alternate fashion. In this case, the surfaces of the laminated combination 3C are oc­cupied by the diamond phase carbon layers 2. These surfaces may be occupied by the silicon carbide layers 1 too. From the view­point of acoustic characteristics, however, presence of the diamond phase carbon layers 2 on the surfaces of the laminated combination is more advantageous. From this point of view, the laminated combination should preferably include odds number of layers. Whereas from the viewpoint of productivity, the laminated combination should preferably include as few layers as possible. When both views are taken into consideration, the three layer lamination may be most advantageous.

[0017] The thickness of the silicon carbide layer should preferably be in a range from 5 to 40 µ m and that of the diamond phase carbon layer in a range from 2 to 30 µ m. Further, the ratio be­tween the total thickness of the silicon carbide layer(s) and the diamond phase carbon layer(s) should preferably be in a range from 1/5 to 10.

[0018] One example of the entire configuration of the speaker diaphragm in accordance with the present invention is shown in Fig.4 in which the laminated combination 3B of Fig.2 is employed.

[0019] In production of the speaker diaphragm of this embodiment, a silicon carbide layer is first developed on a proper substrate by means of, for example, hot CVD process and, thereafter, the sub­strate is removed. Next, a diamond phase carbon layer is formed on the silicon carbide layer by means of vapor phase development such as micro wave plasma CVD process.

[0020] Development of the silicon carbide layer via hot CVD process is preferably carried out at a temperature of about 1200°C under presence of a mixed gas containing 5 parts by volume of C₃H₈. 1 part of SiCl₄ and 50 parts of H₂. Development of the diamond phase carbon layer via micro wave plasma CVD process is preferably carried out at a temperature of about 850°C using a mixed gas containing 1 part by volume of CH₄ and 100 parts of H₂.

[0021] Next, production of the speaker diaphragm such as shown in Fig.4 will be explained in detail. For this production, equip­ments such as shown in Figs.5 and 6 are preferably used. In the first place, a dome-shaped carbon substrate 5 is set in position within a quartz tube 7 of a hot CVD equipment 6 as shown in Fig.5 and the interior of the quartz tube 7 is evacuated down to a vacuum degree of 10⁻⁵ torr. Then the carbon substrate 5 is heated to a temperature of 1200°C by means of a heater 9. Under this temperature condition, mixed gas containing SiCl₄, C₃H₈ and H₂ is introduced into the quartz tube 7 via a gas conduit 10 un­til the internal pressure becomes equal to the atmospheric pres­sure, thereby developing a silicon carbide layer of 20 µ m on the carbon substrate 5. The mixed gas contains 30cc/min of SiCl₄, 20cc/min of C₃H₈ and 500cc/min of H₂.

[0022] Next, the carbon substrate 5 carrying the silicon carbide layer is taken out of the quartz tube 7 and heated at 800°C for removal of the carbon substrate 5 via burning.

[0023] Micro wave plasma CVD process is carried out in a CVD equip­ment 12 shown in Fig. 6. A dome-shaped silicon carbide layer 11 is set in position within a quartz tube 13 of the CVD equipment 12 and subjected to radiation of micro wave of 2.45 GHz by means of a micro wave conduit 14 and a resonator 15 to raise the tem­perature of the silicon carbide layer 11 up to 850°C. Under this temperature condition, mixed gas containing 5cc/min of CH₄ and 500cc/min of H₂ is introduced into the quartz tube 13 via a gas conduit 16 until the inner pressure becomes equal to 100 torr, thereby developing a diamond phase carbon layer of 10 µ m on one face of the silicon carbide layer 11. Next, the silicon carbide layer is again placed up side down in the quartz tube 13 for development of a like diamond phase carbon layer on the other face.

[0024] Thus, a speaker diaphragm including a silicon carbide layer sandwiched with two diamond phase carbon layers is obtained, which is then subjected to measurement of its frequency charac­ teristics. The result of the measurement is shown in Fig.7, in which the result of a like measurement using a speaker diaphragm made up of a silicon carbide layer of 40 µ m only is also shown for comparison purposes. This graphic representation well en­dorses the excellent frequency characteristic of the speaker diaphragm in accordance with the present invention. When the sample is also subjected to Raman spectroscopy, presence of a clear peak at a wave number of 1333 ± 10cm⁻¹ is confirmed. That is, a diamond phase carbon layer is correctly present on the silicon carbide layer.

[0025] In accordance with this embodiment of the present invention, a diamond phase carbon layer is developed on the face of a silicon carbide layer. Thanks to a strong affinity between silicon carbide and diamond phase carbon, both layers are bonded to each other very firmly without need for presence of any inter­mediate layer, thereby much simplifying the production process. High sound transmission speed of the silicon carbide layer assure high sound transmission characteristics of the speaker diaphragm itself. More specifically, in the case of a laminate type speaker diaphragm made up of a silicon carbide layer of 20µ m thickness sandwiched by two diamond phase carbon layers of each 10µ m, its sound transmission speed is about 13,600m/sec. In the case of a speaker diaphragm made up of an alumina layer of 20µ m thickness sandwiched by two diamond phase carbon layers of 10 µ m with presence of intermediate silicon carbide layers of 0.5µ m, the resultant sound transmission speed is about 13,100m/sec. In the case of a speaker diaphragm made up of a silicon nitride layer of 20µ m thickness sandwiched by two diamond phase carbon layers of each 10µ m with presence of intermediate silicon car­bide layers of 0.5µ m, the resultant sound transmission speed is about 13,500m/min. Such high sound transmission speed much im­proves frequency characteristic of the speaker diaphragm in par­ticular in the treble range.

[0026] In the various embodiments described in the foregoing paragraphs, the silicon carbide layer or layers may be replaced by a Beryllium predominant layer or layers. In this case, the thickness of the Beryllium layer should preferably be in a range from 5 to 60µ m, that of the diamond phase carbon layer in a range from 5 to 50µ m and the total thickness of the speaker diaphragm should preferably be in a range from 20 to 80µ m.

[0027] A sample of this embodiment of the speaker diaphragm in ac­cordance with the present invention was prepared using the equip­ments shown in Figs.5 and 6 for evaluation of its frequency characteristics. In this case, a dome-shaped thin copper layer was used for the substrate and preparation of the sample was carried out basically in a manner same as the sample of the foregoing embodiment. The copper substrate was subjected to deposition of Beryllium and aluminum by means of electron beam method for development of a Be-Al alloy layer of 20µ m thickness on one face of the copper substrate. The Be-Al alloy contained 2wt% of Al and Be in balance. The copper substrate was removed by treatment with a HNO₃ solution. Then the alloy layer is sub­jected to radiation of micro wave of 2.45GHz in a CVD equipment to heat it up to 850°C. Under this temperature, mixed gas con­taining 5cc/min of CH₄ and 500cc/min of H₄ was introduced into the equipment until the inner pressure becomes to 100 torr to develop a diamond phase carbon layer of 10µ m thickness. Like diamond phase carbon layer was developed on the other face of the alloy layer in a same manner.

[0028] The sample so prepared was subjected to measurement of sound transmission speed and internal loss (1/Q) for evaluation of its frequency characteristics. A conventional sample I made up of a Be-Al alloy layer of 40µ m only and a conventional sample II made of a diamond phase carbon layer of 40µ m thickness only were prepared for comparison purposes. The results of the measure­ments are given in Table 2.

Table 2

Sample	Sound transmission speed (m/sec)	Relative inverse internal loss (Q)
Conventional sample I	12,200	1
Conventional sample II	16,500	0.8
Present invention	14,000	0.36

[0029] It is clear from these data that this embodiment of the present invention also assures high degree of sound transmission speed with considerably increased internal loss.

[0030] The result of the measurement of frequency characteristics is shown in Fig.9, which also endorses clear advantage of the present invention. Raman spectroscopy also showed a peak at a wave number of 1333 ± 10cm⁻¹.

Claims

1. A speaker diaphragm comprising
at least one diamond phase carbon layer, and
at least one silicon carbide laminate layer combined face to face with said diamond phase carbon layer.

2. A speaker diaphragm as claimed in claim 1 in which
three or more in total of said diamond phase carbon and silicon carbide layers are superimposed in an alternate fashion.

3. A speaker diaphragm as claimed in claim 2 in which
odds number of layers are combined.

4. A speaker diaphragm as claimed in claim 3 in which
said diamond phase carbon layers appear on both faces of said speaker diaphragm.

5. A speaker diaphragm as claimed in claim 1 in which
the thickness of said silicon carbide layer is in a range from 5 to 40µ m.

6. A speaker diaphragm as claimed in claim 1 or 5 in which
the thickness of said diamond phase carbon layer is in a range from 2 to 30µ m.

7. A speaker diaphragm as claimed in one of claims 1, 5 and 6 in which
the ratio between the total thickness of said silicon car­bide layers and that of said diamond phase carbon layers is in a range from 1/5 to 10.

8. A speaker diaphragm comprising
at least one diamond phase carbon layer, and
at least one Beryllium predominant layer combined face to face with said diamond phase carbon layer.

9. A speaker diaphragm as claimed in claim 8
in which
three or more in total of said diamond phase carbon and Beryllium predominant layers are superimposed in an alternate fashion.

10. A speaker diaphragm as claimed in claim 9 in which
odds number of layers are combined.

11. A speaker diaphragm as claimed in claim 10 in which said diamond phase carbon layers appear on both faces of said speaker diaphragm.

12. A speaker diaphragm as claimed in claim 8 in which
the thickness of said Beryllium predominant layer is in a range from 5 to 60µ m.

13. A speaker diaphragm as claimed in claim 1 or 12 in which
the thickness of said diamond phase carbon layer is in a range from 5 to 50µ m.

14. A speaker diaphragm as claimed in one of claims 1, 12 and 13 in which
the total thickness of said speaker diaphragm is in a range from 20 to 80µ m.

Drawing