JPS6311822Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a magnetic circuit for an internal magnetic type speaker using a rectangular yoke.

Conventionally, alnico magnets have been used as magnets in magnetic circuits for internal magnet type speakers, but it has been proposed to develop an optimal magnetic circuit using conventional alnico magnets.
65430, but Co is the main component of alnico magnets.
Since it is difficult to obtain ferrite magnets recently, it has been applied to ferrite magnets. However, due to the difference in magnetic properties between alnico magnets and ferrite magnets, if the same characteristics were to be obtained, ferrite magnets had to be larger than alnico magnets, and even the yoke had to be larger. .

The present invention solves the above-mentioned problems and at the same time provides a magnetic circuit in which the optimum shape of the magnetic circuit is determined when a ferrite magnet is used as the magnet of the magnetic circuit for an internal magnetic type speaker.

The first embodiment of the present invention will be explained with reference to the drawings.
Figure a is a top view of the magnetic circuit for an internal magnet type speaker according to the present invention, and figure b is a longitudinal cross-sectional view of figure a, in which 1 is a yoke with both ends open in one direction, and a through hole 2 is provided in the upper part. A prismatic ferrite magnet is attached to the inner bottom surface of the yoke 1, and 4 is a conical or pyramidal center pole attached to the magnet. It goes without saying that there is a voice coil (not shown) supported in the gap between the center pole 4 and the yoke hole 2 so as to be movable up and down. In FIG. 1, ty is the thickness of the yoke, hy and hm are the height of the yoke and the height of the ferrite magnet, respectively, and wy and w ^m are the width of the yoke and the dimensions of the ferrite magnet, respectively. Magnetic permeability in ferrite magnets is 1.05-1.10
Therefore, the internal leakage of magnetic flux from the magnet to the yoke is smaller than that of alnico magnets, and the main problem of internal leakage is from the center pole to the yoke. There is only residual magnetic flux density (Bg). Therefore, in order to obtain a predetermined Bg, the cross-sectional area of the magnet must be increased. Due to the above, it is necessary to use a magnet having a cross-sectional area that is equal to the inner volume of the yoke.

FIG. 2 shows the results of examining the important ratio of magnet height hm to yoke height hy using a magnetic circuit constructed from these components. The setting conditions at this time are ty = 4 (unit: m/m) for a square yoke.
wy48, w□m□35, φp, φ14, tg=0.75, and by changing the ratio of these, Bg has the maximum value when hy/hm is 2.4 to 2.6, as shown in Figure 2. It has been found. From the above results, if the magnet height relative to the yoke height is between 2.4 and 2.6, the residual magnetic flux density can be utilized with the best characteristics.

As is clear from the above examples, by using a square ferrite magnet, the conventional square yoke can be used as is without any modification, and magnetic leakage can be greatly reduced. be. In addition, the air gap magnetic flux density can be obtained with characteristics equivalent to those of the conventional method, and its industrial effects are great.

[Brief explanation of the drawing]

FIG. 1a is a top view of the magnetic circuit for an internal magnet type speaker of the present invention, b is a longitudinal sectional view of a, and FIG. 2 is an explanatory diagram of the air gap magnetic flux density.

Claims (1)

[Scope of utility model registration request] In a magnetic circuit for an internally magnetic speaker, which has a square yoke with a height and width and is open at both ends in one direction, has a through hole at the top, and a permanent magnet with the largest internal capacity is attached to the bottom of the inner periphery of the yoke. , the yoke height
1. A magnetic circuit for an internal magnetic speaker, characterized in that the ratio of hy to a permanent magnet hm is 2.4 to 2.6<hy/hm<, and a prismatic ferrite magnet is used as the permanent magnet.