This invention relates to a loudspeaker having a cooling system, and more particularly, to a loudspeaker with a shorting ring and a heat dissipation plate thermally connected with each other for efficient heat dissipation while reducing distortion in sound by improving impedance characteristic of the loudspeaker.
Loudspeakers, or speakers, are well known in the art and are commonly used in a variety of applications, such as in home theater stereo systems, car audio systems, indoor and outdoor concert halls, and the like. A loudspeaker typically includes an acoustic transducer comprised of an electromechanical device which converts an electrical signal into acoustical energy in the form of sound waves and an enclosure for directing the sound waves produced upon application of the electrical signal.
An example of structure in the conventional loudspeaker is shown in
The diaphragm 17 is provided with an upper half roll 21 at its peripheral made of flexible material. The diaphragm 17 connects to the speaker frame 19 at the upper half roll 21 by means of, for example, an adhesive. At about the middle of the speaker frame 19, the intersection of the diaphragm 17 and the coil bobbin 25 is connected to the speaker frame 19 through a spider (inner suspension) 23 made of a flexible material. The upper half roll 21 and the spider 23 allow the flexible vertical movements of the diaphragm 17 as well as limit or damp the amplitudes (movable distance in an axial direction) of the diaphragm 17 when it is vibrated in response to the electrical input signal.
An air gap 41 and annular members including a pole piece 37, a permanent magnet 33, and an upper (top) plate 35 make up a magnetic assembly. In this example, the pole piece 37 has a back plate 38 integrally formed at its bottom. The pole piece 37 has a central opening 40 formed by a pole portion 39 for dissipating heat generated by the voice coil 27. The permanent magnet 33 is disposed between the upper plate 35 and the back plate 38 of the pole piece 37. The upper plate 35 and the pole piece 37 are constructed from a material capable of carrying magnetic flux, such as steel. Therefore, a magnetic path is created through the pole piece 37, the upper plate 35, the permanent magnet 33 and the back plate 38 through which the magnetic flux runs.
The air gap 41 is created between the pole piece 37 and the upper plate 35 in which the voice coil 27 and the coil bobbin 25 are inserted in the manner shown in
For a loudspeaker described above, heat within the loudspeaker and distortion of sound can be problematic. The voice coil is constructed of a conductive material having electrical resistance. As a consequence, when an electrical signal is supplied to the voice coil, the electric current flowing through the coil generates heat because of the interaction with the resistance. Therefore, the temperature within the loudspeaker and its enclosure will increase. A substantial portion of the electrical input power is converted into heat rather than into acoustic energy.
Such temperature rise in the voice coil creates various disadvantages. As an example of disadvantage, it has been found that significant temperature rise increases the resistance of the voice coil. This, in turn, results in a substantial portion of the input power of the loudspeaker to be converted to the heat, thereby lowering the efficiency and performance of the loudspeaker. In particular, it has been found that increased resistance of the voice coil in the loudspeaker can lead to non-linear loudness compression effects at high sound levels.
When additional power is supplied to compensate for the increased resistance, additional heat is produced, again causes an increase in the resistance of the voice coil. At some point, any additional power input will be converted mostly into heat rather than acoustic output. Further, significant temperature rise can melt bonding materials in the voice coil or overheat the voice coil, resulting in permanent structural damage to the loudspeaker.
Moreover, in the audio sound reproduction involving such a loudspeaker, it is required that the loudspeaker is capable of producing a high output power with low distortion in the sound waves. Low distortion translates to accurate reproduction of sound from the speaker. It is known in the art that a loudspeaker is more nonlinear and generates more distortion in lower frequencies which require large displacement of the diaphragm.
In order to solve this problem, it has been proposed a ring (cylinder) shaped conducting material (hereafter “shorting ring”) around a pole piece. The shorting ring stabilizes the magnetic field against changes caused by the current in the voice coil. The shoring ring acts as a short circuit winding that generates an inversely directed magnetic flux to counter the modulating effect of the voice coil on the flux in the permanent magnetic field. However, this arrangement does not, by itself, provide an efficient cooling mechanism. Thus, there is a demand for a loudspeaker that can dissipate heat efficiently while minimizing distortion of sound at the same time.
It is, therefore, an object of the present invention to provide a loudspeaker having an improved cooling system while minimizing distortions of sound.
It is another object of the present invention to provide a loudspeaker having a shorting ring coupled with a heat dissipation plate, thereby stabilizing magnetic field and efficiently dissipating heat.
It is a further object of the present invention to provide a method and structure for assembling the cooling system having the shorting ring and the heat dissipation plate in the loudspeaker.
One aspect of the present invention is a loudspeaker with high heat dissipation efficiency and low sound distortion. The loudspeaker is comprised of a speaker frame, a diaphragm connected to the speaker frame in a manner capable of vibration, a voice coil which is formed on a voice coil bobbin and is connected to the diaphragm for vibrating the diaphragm, a magnetic assembly including a permanent magnet, a pole piece disposed at a central opening of the magnet assembly to form an air gap between the magnetic assembly into which the voice coil is movably positioned, a heat dissipation plate mounted on the pole piece at an inner opening thereof, a shorting ring mounted on an outer surface of the pole piece.
The heat dissipation plate and the shorting ring are made of non-magnetic and thermally conductive material. Preferably, a steel ring is mounted on the outer surface of the pole piece to narrow the air gap so that magnetic flux generated by the permanent magnet will not significantly reduced in the air gap. Alternatively, the pole piece has a magnetic flange to form the narrow air gap between the magnetic assembly. The shorting ring stabilizes the magnetic flux without regard to the position of the voice coil, thereby increasing the sound quality of the loudspeaker.
The heat dissipation plate is coupled to the shorting ring and the vibration of the diaphragm produces air flows through the inner opening of the pole piece to intake cool air and exhaust heated air between the inside and outside of the loudspeaker. The heat generated by the loudspeaker can be efficiently dissipated via the heat dissipation plate that acts as a heat sink.
Preferably, the heat dissipation plate has a gap (cut) to suppress or eliminates flows of electric current in the heat dissipation plate, thereby maintaining the low distortion effect derived from the shorting ring. Preferably, a pair of shorting rings are used in the loudspeaker, one is an upper shorting ring mounted right above the steel ring (or magnetic flange) and the other is a lower shorting ring mounted right below the steel ring (or magnetic flange). The shorting rings, the pole piece, and the heat dissipation plate are thermally coupled to one another.
Another aspect of the present invention is a method of assembling the cooling system in a loudspeaker. The method is comprised of the steps of mounting a lower shorting ring on a pole piece, mounting a steel ring made of magnetic material on the pole piece right above the lower shorting ring, inserting a heat dissipation plate in slits of the pole piece, mounting an upper shorting ring on the pole piece right above the steel ring, and mounting the pole piece at a bottom center of a frame of the loudspeaker.
In the case where the pole piece has a magnetic flange integrally formed thereon, the method is comprised of the steps of mounting a lower shorting ring on a pole piece, mounting the pole piece on a back plate; inserting a heat dissipation plate in slits of the pole piece, mounting an upper shorting ring on the pole piece right above the steel ring, and mounting the pole piece and the back plate at a bottom center of a frame of the loudspeaker.
According to the present invention, in the loudspeaker of the present invention, the cooling system can efficiently dissipate the heat through the shorting rings and the heat dissipation plate. The loudspeaker utilizing the cooling system of the present invention achieves a significant increase in the cooling efficiency while maintaining the low distortion effect based on the shorting rings. The cooling system of the present invention has a simple structure and relatively easy to assemble, thereby decreasing the overall cost and production time of the loudspeaker.
The loudspeaker of the present invention is provided with a shorting ring and a heat dissipation plate thermally connected with one another to establish a cooling system for dissipating heat generated by the loudspeaker. A shorting ring in a magnetic circuit has been proposed to improve an impedance characteristics of a loudspeaker. The cooling system of the present invention makes use of the shorting ring to improve the sound quality as well as to promote heat dissipation in combination with the heat dissipation plate. Because of the shorting ring and the heat dissipation plate, the loudspeaker of the present is able to efficiently dissipates the heat, and at the same time, to minimize distortion of the sound by compensating the impedance characteristic.
The effect and structure of the shorting ring is described, for example, in U.S. Pat. No. 5,815,587 and Japanese Patent Laid-Open Publication No. 11-168797. One of the main effect of the shorting ring is that the magnetic field is stabilized against changes caused by the current in the voice coil. Another main effect is that the current of the voice coil is coupled to an impedance which is largely independent of the position of the voice coil in the vertical (axial) direction of the air gap. Thus, the shorting ring promotes to achieve low distortion in a wide frequency range of the audible sounds.
With reference to the perspective view of
More specifically, the cooling system of
The steel ring 135 has a magnetic property which can interact with a voice coil 58 (
The upper shorting ring 131 and the lower shorting ring 133 sandwich the steel ring 135 on the surface of the pole piece 125, to efficiently reduce the sound distortion. Preferably, the steel ring 135 has a thickness slightly larger than that of the shorting rings 131 and 133 so that the surface of the steel ring 135 is projected from the surface of the shorting rings 131 and 133. The shorting rings 131 and 133 should be as close as possible to the gap edge to maximize the heat transfer without causing interference with the voice coil travel tolerance in the air gap. Thus, the steel ring 135 forms the air gap of the magnetic circuit where the voice coil moves up/down in the air gap (
When inserted in the slits 127, a surface 112 of the side edge of the heat dissipation plate 111 is flush with the outer surface of the pole piece 125 so that the surface 112 contacts with the inner surfaces of the shorting rings 131 and 133. The heat dissipation plate 111 also thermally ties the upper and lower shorting rings 131 and 133 as well as directly absorbs the radiated heat from the voice coil. As noted above, the voice coil of the loudspeaker generates heat so that the air gap is heated which raises the temperature of the shorting rings 131 and 133. Since the heat dissipation plate 111 physically contacts with the shorting rings 131 and 133, the heat of the shorting rings 131 and 135 is conducted to the heat dissipation plate 111.
The heat of the heat dissipation plate 111 is conducted to the back plate 123 which itself works as a heat sink since it has a large surface area and thermal capacity and is mounted on a frame of the loudspeaker. Thus, a part of the heat from the voice coil is dissipated to the outside through the back plate 123. Another part of the heat from the voice coil conducted to the heat dissipation plate 111 is also transmitted to the outside through the air via an opening 92 at the bottom of the pole piece 125 (
More specifically, with respect to the heat dissipation through the air, when the loudspeaker is operated, there arises movements of air due to the vibrations of the diaphragm by the reciprocal movements of the voice coil. Thus, the vibration promotes the heated air to exhaust from the opening 92 while intaking the cool air from the outside to the inside of the loudspeaker. This air circulation cools the heat dissipation plate 111, the pole piece 125, the steel ring 135, and the shorting rings 131 and 135, the air gap, and accordingly, the voice coil.
In the assembly process, the heat dissipation plate 111 is press fit to the slits 127 shown in
With reference to
Since the pole piece 125 is integrally formed with the back plate 123, after or before the heat dissipation plate 111 is mounted, the lower shorting ring 133 is mounted first from the top of the pole piece 125 and assembled at the lower half of the pole piece 125. Then, the steel ring 135 is mounted from the top of the pole piece 125 and assembled at the middle portion of the pole piece 125. Finally, the upper shorting ring 131 is assembled at the upper portion of the pole piece 125. Because of the sizes of the components are so designed as noted above, the heat dissipation plate 111 is tightly attached to the pole piece 125, and the end surface 112 of the side edge of the heat dissipation plate 111 contacts with the inner surfaces of the shorting rings 131, 133 and the steel ring 135. In other words, all of the components in the cooling system are connected with one another for the efficient thermal conduction.
More specifically, in
The magnetic flange 235 is to form a narrow air gap without using the steel ring 135 shown in
Unlike the heat dissipation plate 111 of
Referring now to
The loudspeaker of
The diaphragm 54 is provided with an upper half roll 55 at its peripheral made of flexible material such as an urethane foam, butyl rubber and the like. The diaphragm 54 is connected to the speaker frame 52 at the upper half roll 55 by means of, for example, an adhesive. The speaker frame 52 has a plurality of radially and downwardly extending frame members 57 and is integrally constructed of a stiff antivibrational material, such as aluminum.
At about the middle of the speaker frame 52, the intersection of the diaphragm 54 and the coil bobbin 56 is connected to the speaker frame 52 through a spider (inner suspension) 61 made of a flexible material such as cotton with phenolic resin and the like. The upper half roll 55 and the spider 61 allow the flexible vertical movements of the diaphragm 54 as well as limit the amplitudes (movable distance in an axial direction) of the diaphragm 54 when it is vibrated in response to the electrical input signal.
The loudspeaker also comprises a magnetic assembly (magnetic circuit) including an air gap 72, an upper plate 66, a permanent magnet 62, and the pole piece 125. The cooling system is formed with the pole piece 125, the upper and lower shorting rings 131, 133, the steel ring 135, and the heat dissipation plate 111. The back plate 123 is provided at the inner bottom of the speaker frame 52. The pole piece 125, the permanent magnet 62 and the upper plate 66 are positioned axially inward from the speaker frame 52. The pole piece 125 (back plate 123) has a central opening (air passage) 92 in the axial direction.
The permanent magnet 62 is disposed between the upper plate 66 and the back plate 123. The upper plate 66, the pole piece 125, and the back plate 123 are made of magnetic material capable of carrying magnetic flux, such as steel. Therefore, a magnetic circuit is created through the pole piece 125, the steel ring 135, the air gap 72, the upper plate 66, the permanent magnet 62, and the back plate 123 through which the magnetic flux generated by the permanent magnet 62 runs.
The voice coil 58 and the coil bobbin 56 are inserted in the air gap 72 created between the steel ring 135 and the upper plate 66 in the manner shown in
The upper shorting ring 131 and lower shorting ring 133 are provided to stabilize the magnetic field against changes caused by the current in the voice coil 58. The heat generated by the voice coil 58 is transmitted to the upper shorting ring 131, steel ring 135, and lower shorting ring 133. The heat is further conducted to the pole piece 125 and the heat dissipation plate 111. The heat transferred to the heat dissipation plate 111 is dissipated through the opening 92 to the outside by the movements of the air caused by the vibration of the diaphragm 54. Conversely, the cool air from the outside through the opening 92 cools down the heat dissipation plate 111, the pole piece 125, shorting rings 131, 133, steel ring 135, and the voice coil 58.
The structure of the loudspeaker shown in
The pole piece 225 has the magnetic flange 235 for creating the narrow air gap of the magnetic path. The shorting rings 131 and 133 are mounted on the pole piece 225 which is attached to the back plate 223. As seen from
The structure of the loudspeaker shown in
Then, preferably, the semicircular members 231a and 231b are soldered to form the upper shorting ring 231, and the semicircular members 233a and 233b are soldered to form the lower shorting ring 233. The pole piece 425 is provided with insertion cuttings (slits) 427. Similar to the foregoing examples, the heat dissipation plate 411 is inserted in the slits 427 on the pole piece 425. The end surfaces of the side edges of the heat dissipation plate 411 contact the inner surfaces of the upper shorting ring 231 and the lower shorting ring 233, thereby allowing the heat generated by the voice coil 58 is transmitted to the shorting rings 231, 233 and to the heat dissipation plate 411. The heat from the heat dissipation plate 411 is dissipated to the outside through an opening 392 (
A heat dissipation plate 511 is inserted in slits on the pole piece 525 in a manner to contact with the inner surface of the shorting ring 531. Thus, the heat generated by the voice coil in the loudspeaker is transmitted to the shorting ring 531 and to the heat dissipation plate 511. The heat from the heat dissipation plate 511 is dissipated to the outside through an opening 492 of the pole piece 525. The cool air from the outside is introduced through the opening 492 to cool the heat dissipation plate 511, the pole piece 525, the shorting ring 531, and the voice coil.
As described in the foregoing, in the loudspeaker of the present invention, the cooling system can efficiently dissipate the heat through the shorting rings and the heat dissipation plate. The loudspeaker utilizing the cooling system of the present invention achieves a significant increase in the cooling efficiency while maintaining the low distortion effect based on the shorting rings. The cooling system of the present invention has a simple structure and relatively easy to assemble, thereby decreasing the overall cost and production time of the loudspeaker.
Although only a preferred embodiment is specifically illustrated and described herein, it will be appreciated that many modifications and variations of the present invention are possible in light of the above teachings and within the purview of the appended claims without departing the spirit and intended scope of the invention.