GB2236541A

GB2236541A - Speaker diaphragm

Info

Publication number: GB2236541A
Application number: GB9019476A
Authority: GB
Inventors: Koichi Miyata; Kazuo Kumagai; Koji Kobashi
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 1989-09-08
Filing date: 1990-09-06
Publication date: 1991-04-10
Anticipated expiration: 2010-09-06
Also published as: GB2236541B; JPH0396200A; GB9019476D0

Abstract

A speaker diaphragm comprises a titanium diaphragm, an intermediate coating layer, and a diamond film formed thereon, said intermediate coating layer consisting of a single layer or multiple layers each made of one member selected from Mo, Si, W, Ta, Si3N4, and Al2O3. The speaker diaphragm exhibits improved frequency characteristics in the high-frequency range. In the situation where there is a first layer of Mo, W or Ta and a second layer of Si, Si3 N4 or Al2O3, the first layer provides a better adhesion to the titanium diaphragm and the second layer facilitates the deposition of diamond film. The diamond film may be formed by chemical vapour deposition.

Description

SPEAKER DIAPHRAGM BACKGROUND OF THE INVENTION 1. Field of the Invention: The present invention relates to a speaker diaphragm coated by a diamond film, which exhibits outstanding high-frequency characteristics.

2. Description of the Prior Art: To improve the high-frequency characteristics of tweeters, a tweeter diaphragm has recently been developed, which is made up of a titanium diaphragm (refexred to as titanium diaphragm hereafter) and a diamond-like carbon (DLC) film coated thereon by plasma chemical vapor deposition (CVD). It is described in "New Diamond", vol. 3, No. 1, pp. 20-25 (1987).

Although the DLC film-coated speaker diaphragms mentioned above have better acoustic characteristics than uncoated diaphragms, it is expected that titanium speaker diaphragms coated with diamond films have acoustic properties for superior to the DLC film-coated speaker diaphragms because of the faster sound velocity in diamond films the DLC films, as is generally known.

However, difficulties are encountered in the CVD deposition of.dimond films on titanium, because hydrogen used in the diamond deposition process reacts with titanium, preventing the diamond film formation and deteriorating titanium by occlusion.

SUMMARY OF THE INVENTION The present invention solved the above-mentioned problems by forming an intermediate coating layer between the titanium and diamond, and achieved the formation of a diamond film on the titanium diaphragm. As a result, the present invention provided a speaker diaphragm having outstanding high-frequency characteristics.

The gist of the present invention resides in a speaker diaphragm which comprises a titanium diaphragm, an intermediate coating layer, and a diamond film formed thereon, said intermediate coating layer consisting of a single layer or multiple layers each made of one member selected from Mo, Si, W, Ta, Si3N4, and Al203.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. Fig. 1 is a schematic diagram showing the Electron- Assisted Chemical Vapor Deposition (EACVD) apparatus used in the invention.

Fig. 2 is the frequency characteristics of the speaker diaphragm pertaining to the present invention and two conventional speaker diaphragms.

Fig. 3 is Scanning Elective Microscopy (SEM) photograph of the diamond film formed on the speaker diaphragm according to the invention.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, an intermediate coating layer is first formed on the titanium diaphragm so as to form a diamond film thereon, while preventing hydrogen, which is used to deposit the diamond film, from reacting with the titanium material. This intermediate coating layer is required to strongly adhere to titanium and to permit a diamond film to be formed thereon. These requirements are met by selecting the intermediate coating material from Mo, Si, W, Ta, Si3N4, and A1203. The intermediate coating layer prevents the titanium diaphragm from deteriorating and permits a diamond film to be formed thereon.

In the above-mentioned materials, Mo, W, and Ta have a good adhesion to titanium, but the formation of diamond is slow in the CVD process. By contrast, Si, Si3N4, and A1203 have a poorer adhesion to titanium, but a diamond film is formed rapidly on these materials. Therefore, an improved result is obtained by employing an intermediate coating layer of dual structure: the first layer adjacent to the titanium diaphragm is made of any of Mo, W, and Ta, and the second layer is made of any of Si, Si3N4, and A1203.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The examples of the invention will be described with reference to the accompanying drawings.

Example 1 The speaker diaphragm pertaining to the present invention is produced by the procedure explained below: The titanium diaphragm was 25 pm thick and has a dome shape. First, a 1 pm thick intermediate coating layer of Mo was deposited by electron-beam vapor deposition on the convex surface of the titanium diaphragm. The intermediate coating layer was buff-polished for 30 minutes with a diamond paste (having a particle diameter of 1/4 m) so that the intermediate coating layer generates high nucleation density is diamond.

Subsequently, a diamond film was deposited on the intermediate coating layer of Mo (which has been formed on the titanium diaphragm 1) useing an EACVD apparatus as shown in Fig.

1. This procedure was performed in the following manner. The titanium diaphragm 1 was set on the substrate holder 3 in the vacuum chamber 2. The vacuum chamber 2 was evacuated to 10 2 Torr by a vacuum pump (not shown). Into the vacuum chamber 2 was introduced a mixed gas of hydrogen and methane (1 vol%) at a flow rate of 100 ml/min through the gas inlet pipe 4. With the main valve 5 in the exhaust pipe closed, the pressure in the vacuum chamber 2 was adjusted to 30 Torr by means of a flow control valve 6. An electric current was supplied to the filament 8 (for heating up to 2,0000C) from the filament power source 7, and simultaneously a 90V positive electric potential was applied to the substrate holder 3 from the bias power source 9.The substrate was kept at 8000C by adjusting the output of the filament power source 7 in response to the temperature of the substrate holder 3 measured by the thermocouple 10.

The synthesis of diamond film was carried out for 3 hours under the above-mentioned conditions. A I pm thick diamond film was formed on the intermediate coating layer of Mo. This diamond film exhibited faceted surfaces of diamond as shown in Fig. 3 by SEM. The titanium diaphragm substrate showed no sign of deterioration.

The diamond film-coated speaker diaphragm was assembled to form an ordinary tweeter and tested for the acoustic characteristics. The results are shown in Fig. 2. It is found that the diamond film-coated diaphragm in this example has a higher resonance frequency than the conventional titanium and DLC-coated diaphragms.

Example 2 A titanium diaphragm was coated with a diamond film in the same manner as in Example 1 except that the 1 pm thick intermediate coating layer was formed by A1203 instead of Mo.

The resulting speaker diaphragm exhibited better frequency characteristics because A1203 transmits sound faster than Mo.

Example 3 A titanium diaphragm was coated with a diamond film including an intermediate coating layer of dual structure: the first layer was a 1 um thick Mo film and the second layer a 1 pm thick Si film. Formed on the intermediate coating layer was a 1 pm thick diamond film in the same manner as in Example 1. The formation of the diamond film on the Si layer was faster than that on the Mo layer. The obtained speaker diaphragm exhibited improved high-frequency characteristics than the incoated diaphragm.

Meanwhile, the intermediate coating layer, which was made of Mo and A1203 in Example 1 and Example 2, respectively, may L J also be made of any of Si, W, Ta, and Si3N4, and the resulting speaker diaphragms will exhibit improved frequency characteristics in the high-frequency range. In the case of the intermediate coating layer of dual structure, which consisted of an go layer and an Si layer in Example 3, the first layer adjacent to the titanium diaphragm substrate may be.made of any of Mo, W, and Ta, and the second layer may be made of any of Si3N4, A1203, and SiO. Thus the first layer provides a better adhesion to the titanium diaphragm and the second layer ~ facilitates the deposifion of diamond film.

Although the above-mentioned examples were carried out by means of EACVD for diamond depositionj it is also possible to use any of the known processes of diamond deposition such as microwave plasma CVD, radio frequency plasma CVD and DC plasma CVD.

As mentioned above, the present invention provides a speaker diaphragm which comprises a titanium diaphragm, an intermediate coating layer, and a diamond film formed thereon, said intermediate coating layer consisting of a single layer or multiple layers each made of one member selected from Mo, Si, W, Ta, Si3N4, and A1203. The intermediate coating layer prevents the reaction of hydrogen, used the diamond deposition process, with the titanium diaphragm and hence prevents the deterioration of he titanium diaphragm, while a diamond film is formed thereon r by the vapor phase synthesisvprocess. In addition, the by the ya intermediate coating layer facilitates the deposition of a diamond film thereon. The deposited diamond film contributes to the improvement of the acoustic characteristics of the speaker diaphragm in the high-frequency range.

Claims

WHAT IS CLAIMED IS:

1. A speaker diaphragm which comprises a titanium diaphragm, an intermediate coating layer, and a diamond film formed thereon, said intermediate coating layer consisting of a single layer or multiple layers each made of one member selected from Mo, Si, W, Ta, Si3N4, and Awl203.