JPH0238555Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an improvement of a so-called flat-plate speaker in which a voice coil is formed on the surface of a diaphragm.

To explain this type of speaker with reference to FIG. 1, 1 is a magnet, 2 is a front plate, and 3 is a magnet.
is a pole piece, 4 is a back plate, and a plane diaphragm 6 is arranged in a magnetic gap 5 formed between the front plate 2 and the pole piece 2.

The diagnostic plate 6 is generally obtained by disposing a printed coil 6b formed in a helical shape by etching or the like as a conductive means on at least one side of a plastic film 6a, and by passing an audio current through the printed coil 6b. The driving force causes the plastic film 6a to vibrate and radiate sound waves into the atmosphere.

In such a speaker, the planar diaphragm 6 is disposed within the magnetic gap 5, so the magnetic gap 5 must necessarily be made large in order to obtain the necessary vibration area.

As a result of the fact that the spacing between the magnetic air gaps is significantly increased compared to a general cone-shaped or dome-shaped speaker that uses a voice coil, the magnetic flux density of the magnetic air gap 5 becomes extremely large when using a magnet similar to the conventional one. Therefore, sufficient conversion efficiency cannot be obtained.

To solve this problem, a magnet with a large energy product or a material with high magnetic permeability is used, but this increases the cost and is not preferred.

This invention relates to the structure of a planar drive speaker that increases efficiency by concentrating the magnetic flux in the magnetic air gap near the printed coil using a magnetic fluid.

Figure 2 is a cross-sectional view of the magnetic gap part of the flat speaker of this invention.
pole, the bottom surface is the N pole), 2 is the front plate,
3 is a pole piece, 5 is a magnetic gap, 6 is a plane diaphragm, 6a is a plastic film, and 6b is a printed coil.

With the above configuration, an S pole is formed on the end face of the front plate 2, and an N pole is formed on the end face of the pole piece.

A non-magnetic spacer 7 is inserted into the magnetic gap so as to be flush with the upper surface of the front plate 2 forming the magnetic gap 5.

The planar diaphragm 6 is placed above the spacer 7 and the front plate 2 with a distance D corresponding to the required maximum amplitude, and then a magnetic fluid 8 is placed in the gap formed between the planar diaphragm 6 and the spacer 7.
flows in and is held by the magnetic attraction of the air gap.

Normally, the magnetic lines of force within the magnetic gap 5 have a spindle shape with the maximum width at the central axis, and the magnetic flux density is minimum at the central axis, and the larger the width of the magnetic gap 5, the larger the bulge of the magnetic lines of force. The magnetic flux density becomes even smaller.

However, in this invention, the lines of magnetic force in the magnetic gap 5, which would normally bulge out, are concentrated in the magnetic fluid 8 on the top surface of the spacer, and the printed coil portion essentially has a high magnetic flux density, increasing the electroacoustic conversion efficiency. Can be done. Furthermore, since the magnetic fluid is in close contact with the printed coil 6b, heat conduction is good, and the voice coil temperature rise can be kept low even at large inputs. It is possible to obtain an electrodynamic planar drive speaker with a very large maximum acoustic output, which has been difficult to achieve with planar drive speakers, and it can be used in large speaker systems, so it has a wide range of applications.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional planar drive type speaker.
FIG. 2 is a sectional view of the magnetic circuit portion of the electrodynamic planar drive speaker of the present invention. 5 is a magnetic gap, 6 is a plane diaphragm, 7 is a spacer, and 8 is a magnetic fluid.

Claims (1)

[Scope of utility model registration request] In a planar drive speaker having a planar diaphragm 6 equipped with a conductive means in the magnetic gap 5, a spacer 7 made of a non-magnetic material is installed in the magnetic gap 5 so as to form the same surface as the upper surface of the plate 2, and A planar drive speaker characterized in that a magnetic fluid 8 is inserted into the gap between the diaphragm 7 and the planar diaphragm 6.