This application claims priority under 35 U.S.C. ยง 119 to Japanese Patent Application No. 2004-171575 filed Jun. 9, 2004, the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to loudspeakers for use in personal computers, PDAs, cellular phones and other miniature devices and, more particularly, to dynamic exciters incorporated into loudspeakers.
2. Description of the Related Arts
Loudspeakers suitable for use in such miniature devices include a dynamic exciter, as disclosed, for example, in Japanese Patent Application Publication No. 2003-143690.
The dynamic exciter 500 comprises a cylindrical frame member 502, an electromagnetic coil 503 secured to the upper end wall of the cylindrical frame member 502, a permanent magnet 504 having polarized upper and lower ends, a disc-like inner yoke 505 secured to the polarized upper end of the magnet 504, and a cylindrical outer yoke 506 with the bottom wall thereof secured to the polarized lower end of the magnet 504. The inner yoke 505 and the outer yoke 506 are both formed from a metal of high permeability. The inner yoke 505, the magnet 504 and the outer yoke 506 constitute a magnetic circuit assembly 508. An annular magnetic gap is formed between the inner yoke 505 and the outer yoke 506 of the magnet circuit assembly 508.
An annular suspension member or annular leaf spring 507 is provided between the frame member 502 and the outer yoke 506 so that the frame member 502 elastically supports the magnetic circuit assembly 508. The electromagnetic coil 503 extends into the annular magnetic gap formed between the inner yoke 505 and the outer yoke 506.
In
In the dynamic exciter 500, when an electric current is applied to the electromagnetic coil 503, electromagnetic force is generated between the electromagnetic coil 503 and the magnetic circuit assembly 508, so that the diaphragm 601 is exited and generates a sound output.
The dynamic exciter 500 is compact and suitable for use in a loudspeaker for miniature devices such as personal computers, PDAs, and cellular phones.
However, the dynamic exciter 500 suffers from the following problems:
As noted from the above, the dynamic exciter 500 has a single mechanical resonance system consisting of a mass and a spring, i.e., a mass of the magnetic circuit assembly 508 including the magnet 504 and the yokes 505 and 506, and a spring of the suspension member 507 elastically supporting the mass or the magnetic circuit assembly 508.
The characteristic curve T1 apparently deviates from the desired characteristic curve T0. Namely, the characteristic curve T1 has a steep peak in the low-frequency range and shows low sound pressure levels in the high-frequency range. The steep peak in the curve T1 generally corresponds to the resonance frequency of the above-described single mechanical resonance system in the dynamic exciter 500.
Although it is desired to regulate the dynamic exciter to lessen such a deviate of the characteristic curve T1 from the characteristic curve T0, it is difficult or substantially impossible for the exciter having only a single mechanical resonance system to effect such a modulation.
An object of the present invention is to provide a dynamic exciter and a loudspeaker with a dynamic exciter, the dynamic exciter having frequency characteristics in which the amplitude of vibrations or sound pressure level is generally kept constant in a wide frequency range including a low frequency range and a high frequency range.
According to the present invention, a dynamic exciter includes a frame member adapted to be attached to a diaphragm of a loudspeaker; a permanent magnet having an axis and polarized opposite ends in a direction of the axis, an electromagnetic coil positioned across the magnetic circuit; a first suspension member supportingly connecting the permanent magnet to the frame member; and a second suspension member supportingly connecting the electromagnetic coil to the frame member. Namely, the dynamic exciter is characterized in that it includes two resonance systems, i.e., one comprising the first suspension member and the permanent magnet and the other comprising the second suspension member and the electromagnetic coil.
Specifically, the dynamic exciter may comprise a yoke connected to the permanent magnet so that the yoke and permanent magnet constitute a magnet circuit assembly through which the magnetic circuit generated by the permanent magnet extends. The first suspension member supportingly connects the magnetic circuit assembly to the frame member.
The yoke may comprise a disc-like inner yoke secured to one of the polarized opposite ends of the permanent magnet, and a cylindrical outer yoke having an end wall secured to the other of the polarized opposite ends of the permanent magnet. The cylindrical outer yoke extends in the direction of the axis of the magnet and surrounds the permanent magnet and the disc-like inner yoke to form the magnetic gap in an annular shape between the disc-like inner yoke and the cylindrical outer yoke. The first suspension member is connected between the cylindrical outer yoke and the frame member. The electromagnetic coil extends in the direction of the axis into the magnetic gap.
Specifically, the frame member may be cylindrical and extended in the direction of the axis of the magnet, outside the cylindrical outer yoke. At least one of the first and second suspension members may be an annular leaf spring member disposed inside the frame member, the annular leaf spring member extending transversely relative the axis of the magnet. The annular leaf spring member may have a plurality of slits which extend radially inwardly from a radially outer portion thereof and are circumferentially arranged. The annular leaf spring member may be formed to have concentric corrugations.
When the dynamic exciter is installed in a casing of a loudspeaker, which has an opening closed by a diaphragm, the dynamic exciter is attached to the diaphragm through the frame member. It is preferable for the magnetic circuit assembly is engaged with or connected to a yieldable member mounted on a wall of the casing of the loudspeaker which wall is positioned opposite to the opening so as to properly limit the vibration of the magnetic circuit assembly. The yieldable member may be made of a spongy material.
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings.
With reference to FIGS. 1 to 4B, a dynamic exciter 100 according to an embodiment of the present invention has a frame member 102, an electromagnetic coil 103, and a permanent magnet 104 having polarized vertical opposite ends. The frame member 102, the electromagnetic coil 103 and the magnet 104 are concentrically arranged about a vertical center axis of the magnet 104. A disc-like inner yoke 105 is secured to the upper end of the magnet 104 and a cylindrical outer yoke 106 is secured to the lower end of the magnet 104. The inner yoke 105 and the outer yoke 106 are both formed from a metal of high permeability and cooperate with the magnet 104 to constitute a magnetic circuit assembly 109 through which a magnetic circuit generated by the magnet 104 extends. A first annular suspension member or annular leaf spring 107 is provided between the outer yoke 106 and the frame member 102 so as to supportingly connect the magnetic circuit assembly 109 to the frame member 102. A second annular suspension member or annular leaf spring 108 is provided between the electromagnetic coil 103 and the frame member 102 so as to supportingly connect the electromagnetic coil 103 to the frame member 102. The electromagnetic coil 103 extends vertically through an annular magnetic gap formed between the inner yoke 105 and the outer yoke 106 of the magnetic circuit assembly 9.
In the illustrated embodiment, the first and second suspension members 107 and 108 are formed from a resin sheet material, a cloth impregnated with resin, a metal sheet material, or a combination of these materials and, as shown in
The dynamic exciter 100 is adapted to be secured through the frame member 102 to a diaphragm 201 of a loudspeaker as will be described later.
In the dynamic exciter 100 described above, there are formed two mechanical resonance systems each consisting of a mass and a spring, i.e., a first mechanical resonance system having the first suspension member 107 as a spring and the magnetic circuit assembly 109 as a mass, and a second mechanical resonance system having the second suspension member 108 as a spring and the electromagnetic coil 103 as a mass. The first and second mechanical resonance systems respectively have predetermined natural frequencies which are different from each other.
An operation of the dynamic exciter 100 will be hereinbelow explained.
When an electric current flows through the electromagnetic coil 103, an electromagnetic force is generated between the electromagnetic coil 103 and the magnetic circuit assembly 109 so as to vibrate the electromagnetic coil 103 and the magnetic circuit assembly 109. The vibrations of the electromagnetic coil 103 and the magnetic circuit assembly 109 are transmitted through the first and second suspension members 107 and 108 to the frame member 102. Accordingly, the diaphragm 201 of a loudspeaker provided on the frame member 102 is vibrated to generate an acoustic signal.
Namely, according to the illustrated embodiment, the dynamic exciter 100 excites the diaphragm 201 of the loudspeaker through the two mechanical resonance systems thereof, i.e., the first mechanical resonance system having the first suspension member 107 and the magnetic circuit assembly 109, and the second mechanical resonance system having the second suspension member 108 and the electromagnetic coil 103.
In general, the magnetic circuit assembly 109 has a large mass because of its material, whereas the electromagnetic coil 103 has a small mass. Therefore, the first mechanical resonance system including the magnetic circuit assembly 109 has a natural frequency in a lower-frequency range, while the second mechanical resonance system including the electromagnetic coil 103 has a natural frequency in a higher-frequency range. The first and second mechanical resonance systems cooperate with each other to allow the frequency characteristic curve of the dynamic exciter to be generally flat over a wide frequency range including the low-frequency range and the high-frequency range. Advantageously, the frequency characteristics of the first and second mechanical resonance systems can be adjusted independently of each other so as to improve the frequency characteristics of the dynamic exciter 100.
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Although the present invention has been described in terms of specific embodiments, it is anticipated that alternations and modifications thereof will no doubt become apparent to those skilled in the art. It is therefore intended that the following claims be interpreted as covering all such alternations and modifications as fall within the true sprit and scope of the invention.
Number | Date | Country | Kind |
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JP2004-171575 | Jun 2004 | JP | national |