loudspeaker

Abstract

This loudspeaker avoids direct atmospheric pressure on the back of the cone, and even if the cone vibrates slightly during sound reproduction, the out-of-phase sound generated from the back of the cone does not affect it, resulting in a natural reproduced sound. [Solution] The loudspeaker connects the rear top of the frame of the speaker unit 5 to the rear metal sintered plate 6b inside the three-dimensional case 7 via bolts 26. By tightening these bolts, the circular surface of the frame of the speaker unit 5 is tightly fixed to the front metal sintered plate 6a inside the three-dimensional case 7, and the speaker box is directly or indirectly connected to the back pressure buffering mechanism of the cone paper 2.

Description

Technical Field

[0001] The present invention relates to a small-diameter loudspeaker that can reproduce low-frequency sounds with a large displacement amount well for BGM or in-vehicle use by fixing the front and rear of a speaker unit with a metal sintered plate inside a speaker case.

Background Art

[0002] An audio loudspeaker is a transducer that generates sound waves by receiving an acoustic current, and has a dynamic transducer and a radiation part such as a cone paper or dome that radiates the vibration of the vibrator as sound waves. In this type of speaker, when the cone paper of the speaker unit vibrates acoustically to generate sound waves, this mechanical vibration is transmitted from the baffle plate and the box is likely to swing. Conventionally, in order to prevent the box from swinging, a free edge is attached between the frame of the speaker unit and the cone paper, and this free edge absorbs the mechanical vibration of the cone paper. However, this free edge cannot completely absorb the mechanical vibration of the cone paper, and some vibration is transmitted to the frame of the speaker unit, causing the entire box to swing.

[0003] The inventor has found in Japanese Patent Application Laid-Open Nos. 2003-23685 and 2003-230187 that by making the baffle plate or the mount member to which the frame of the speaker unit is attached a porous sintered body, these can effectively absorb the mechanical vibration transmitted to the frame of the speaker unit. With this type of baffle plate or mount member, it becomes possible to faithfully reproduce an acoustic signal and clearly reproduce the low-frequency range.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

[0005] When the cone vibrates to produce sound, a stress opposite to that of the cone acts on the rear magnet of the speaker unit. This stress also acts on the frame, and since the cone is fixed to the frame by its free edge, this fixing point is pulled in the direction of the stress on the unit's magnet, causing the cone to also be pulled in the same direction. As a result, a combination of phases occurs between the frequencies reproduced by the cone and frequencies in the opposite direction. The cone is affected by this, and some of the reproduced frequencies are canceled out by the positive or negative phase, causing some of the sound reproduced by the input signal to disappear.

[0006] In the speakers described in Japanese Patent Publication No. 2003-23685 and Japanese Patent Publication No. 2003-230187, while the mechanical vibrations transmitted to the speaker unit frame can be absorbed by using a porous sintered body for the baffle plate or mount member, the effect of the opposite stress acting on the unit magnet part to that of the cone paper cannot be mitigated, and the phenomenon of some of the reproduced sound being lost remains unresolved. Even if these speakers are said to be capable of faithful reproduction of acoustic signals and clear reproduction of the low-frequency range, in particular, with small-diameter speakers, the cone paper area is small, making it susceptible to the effects of the opposite stress on the unit magnet part, and the reproduction of low-frequency sounds with large displacements is insufficient.

[0007] Furthermore, if atmospheric pressure is directly applied to the back of the cone, the cone will vibrate slightly during sound reproduction, causing the back pressure on the cone to change accordingly. When the back pressure on the cone changes slightly during sound reproduction, the reproduction of the acoustic signal becomes inaccurate, easily leading to sound distortion, and also resulting in insufficient faithful reproduction of low-frequency sounds. In other words, in a speaker box, if the out-of-phase sound generated from the back of the cone cannot be mitigated, a reaction stress is applied during sound generation, and the sound reproduced from the cone is canceled out by the out-of-phase sound from the back.

[0008] This invention was proposed to improve upon the aforementioned problems of conventional loudspeakers, and aims to provide a loudspeaker that can reproduce acoustic signals more faithfully and reproduce low frequencies more clearly. Another object of this invention is to provide a loudspeaker that, even with a small diameter, is hardly affected by opposing stress on the unit magnet and can adequately reproduce low-frequency sounds with large displacements. Yet another object of this invention is to provide a loudspeaker that avoids direct application of atmospheric pressure to the back of the cone paper, so that even if the cone paper vibrates slightly during sound reproduction, the out-of-phase sound generated from the back of the cone paper does not have an effect, and a natural reproduced sound can be obtained. [Means for solving the problem]

[0009] To achieve the above objective, the loudspeaker according to the present invention comprises a speaker unit consisting of a conical frame that covers the entire cone paper that radiates sound waves and has a magnet positioned in the rear top, and a speaker box comprising a three-dimensional case on which a metal sintered plate having sparse pores on its outer surface and dense pores inside is attached to the inner surface of the box. The rear top of the frame of the speaker unit is connected to the rear metal sintered plate inside the three-dimensional case via bolts, and by tightening the bolts, the circular surface of the frame of the speaker unit is tightly fixed to the front metal sintered plate inside the three-dimensional case, and the speaker box is directly or indirectly connected to the back pressure buffering mechanism of the cone paper.

[0010] In the loudspeaker according to the present invention, the three-dimensional case of the speaker box is a cube assembled by connecting six metal sintered plates, each having sparse pores on its outer surface and dense pores inside. For each metal sintered plate of the three-dimensional case, a through hole is engraved in the front metal sintered plate for housing the rear part of the speaker unit frame, and a through hole is provided in the upper metal sintered plate for attaching a connecting fitting to the back pressure buffering mechanism. This through hole is located behind the cone paper of the speaker unit inside the speaker box. Furthermore, it is preferable to provide a small screw hole for screwing in a bolt in the rear metal sintered plate.

[0011] In the loudspeaker according to the present invention, a support frame with a hollow horizontal U-shaped side structure is arranged as a back pressure buffering mechanism, and a speaker box is suspended from the upper horizontal part of the support frame via a connecting fitting, so that the speaker box is in communication with the hollow support frame through its upper through-hole, and the air passing through the support frame comes into contact with a plurality of metal sintered plates before being drawn in and exhausted at the exhaust port.

[0012] In the loudspeaker according to the present invention, a hollow rectangular housing is preferably arranged as another back pressure buffering mechanism, and the speaker box is connected to a flexible tube, and the flexible tube is connected to a through-hole in the side wall of the rectangular housing, so that the speaker box communicates with the hollow rectangular housing via the flexible tube, and the air passing through the rectangular housing comes into contact with a horizontally elongated metal sintered plate and is then drawn in and exhausted at the exhaust port. [Effects of the Invention]

[0013] The loudspeaker according to the present invention features a three-dimensional case with a porous metal sintered plate attached to the inner surface of the box. By tightening bolts to fix the front and rear of the speaker unit to the metal sintered plate, mechanical vibrations transmitted to the frame of the speaker unit are absorbed by the metal sintered plates at the front and rear. At the same time, the effect of opposite stress acting on the unit's magnet is mitigated, solving the phenomenon in which some of the reproduced sound disappears. The loudspeaker according to the present invention is a small-diameter speaker, and even if the area of ​​the cone is small, it is less susceptible to the effect of opposite stress on the unit's magnet. This allows for sufficient reproduction of low-frequency sounds with large displacements, enabling faithful reproduction of acoustic signals and clear reproduction of ultra-low frequencies.

[0014] In the loudspeaker according to the present invention, the speaker box is directly or indirectly connected to the back pressure damping mechanism of the cone paper, so that air behind the cone paper is drawn in and exhausted during sound reproduction, and atmospheric pressure is not directly applied to the back of the cone paper. As a result, even if the cone paper vibrates continuously within the speaker box during sound reproduction, the out-of-phase sound generated from the back of the cone paper does not have an effect, and the cone paper is not affected by out-of-phase back pressure vibrations during sound reproduction. Therefore, the reproduction of the acoustic signal becomes accurate, sound distortion does not occur, and low-frequency sounds can be reproduced faithfully. In addition, since atmospheric pressure is not directly applied to the back of the cone paper, the cone paper is less affected by sounds and vibrations outside the speaker box. [Brief explanation of the drawing]

[0015] [Figure 1] This is a front view showing the loudspeaker according to the present invention. [Figure 2] This is a side view showing the loudspeaker in Figure 1. [Figure 3] This is a lateral cross-sectional view of the speaker box, specifically a schematic cross-sectional view of the speaker box cut along line BB in Figure 1. [Figure 4] This is a schematic cross-sectional view of the support frame cut along line AA in Figure 2. [Figure 5] This is a schematic cross-sectional view of the support frame cut along line BB in Figure 1. [Figure 6] This is a schematic cross-sectional view of the support frame cut along line CC in Figure 2. [Figure 7] This is a front view showing another example of the speaker box used in the present invention, with the rectangular housing being a horizontal cross-sectional view. [Figure 8] This graph shows the speaker characteristics in the time domain for the loudspeaker of the present invention. [Figure 9] This graph shows the time-domain speaker characteristics of a conventional speaker. [Modes for carrying out the invention]

[0016] In the loudspeaker 1 according to the present invention, as shown in FIG. 3, the speaker box 8 includes a speaker unit 5 composed of a conical frame 3 that covers the entire cone paper 2 that radiates sound waves and arranges a magnet part (not shown) inside the rear top, and a three-dimensional case 7 in which a metal sintered plate 6 with sparse pores on the outer surface and dense pores inside is attached to the inner surface of the box. As illustrated in FIGS. 1 and 2, the loudspeaker 1 includes a speaker box 8. In this loudspeaker, as a backpressure buffer mechanism, a support frame 10 with a hollow U-shaped side surface is arranged, and the speaker box 8 is suspended via a connecting fitting 14 (FIG. 3) on the upper horizontal part 12 of the support frame 10.

[0017] The loudspeaker 1 is for general audio use, BGM use, etc., and the speaker may be a woofer or a subwoofer. As long as the speaker unit 5 basically has a conical frame 3, it can be applied to various external shapes other than the shape shown in FIG. 3. Its sound wave radiation part can be the cone paper 2, or can also be applied to members called cones, domes or horns.

[0018] As shown in FIG. 3, in the speaker box 8, the three-dimensional case 7 is composed of a metal sintered plate 6, and is a cube assembled by adhesively bonding or bolting six metal sintered plates 6 to each other. This cube can be stored in a wooden outer box 18 and adhesively fixed. Since the front and rear surfaces of the three-dimensional case 7 are the baffle surfaces of the speaker unit 5, a part of the front and rear surfaces of the wooden outer box 18 may be cut out or the entire surface may be omitted so that the speaker unit 5 does not come into contact. If the speaker box 8 is to be installed in a limited narrow space such as in a vehicle, it may be miniaturized. As illustrated in FIG. 7, the speaker box 8 and a rectangular housing 16 which is a backpressure buffer mechanism may be separately configured and connected to each other via a flexible tube 17.

[0019] In the production of metal sintered plates 6 with sparse pores on the outer surface and dense pores inside, metal chips with a particle size of 6 to 50 mesh are generally used and formed into flat plates by electric heating and pressurization. During this forming process, the surface of each metal chip melts and fuses with each other, and the heat escapes into the sintered body as it cools, resulting in sparse pores on the outer surface and dense pores inside. When sound waves, which are low-frequency waves with high energy, strike the metal sintered plate 6, they are absorbed into depressions on the outer surface of the coarse pores, then compressed within the dense structure, and escape to the outside as very small amounts of heat.

[0020] The metal sintered sheet used to obtain the metal sintered plate 6 is manufactured from a single or two or more types of metal chips with a particle size of 6 to 50 mesh. These metal chips may be metal powders or cutting chips, and may be alloys having two metal components, or a mixture of multiple metal chips of different shapes and types. Examples of these metal chips include iron-based metals such as cast iron cutting chips, carbon steel billets, and stainless steel billets; aluminum-based metals such as aluminum powder and Al-Si alloy cutting chips; copper-based metals; and titanium-based metals such as titanium powder. The metal sintered sheet may also contain 25% by weight or less of glass particles, ferrite powder, cement powder, and / or thermosetting resin in the mixture of metal chips. Examples of thermosetting resins include epoxy resin, polyester resin, urethane resin, phenolic resin, and diallyl phthalate resin.

[0021] To manufacture the aforementioned metal sintered sheet, for example, a molding apparatus (not shown) having a rectangular cylindrical mold is used, and the mixed metal chips are filled into the mold. In this molding apparatus, a pair of rectangular electrode plates with the same surface area are placed facing each other on a horizontal ceramic plate, and a pair of rectangular heat-resistant side walls are placed perpendicular to them to form the mold. A wire from a low-voltage transformer is connected to the side end of one electrode plate, and a wire is also connected to the opposite side end of the other electrode plate. The metal chips are placed almost evenly into the mold, and then the press mold is lowered, and the sheet is formed into a flat plate by heating and pressurizing it with a high current of several thousand amperes. In this molding apparatus, during the sintering process, a high current of up to 8000 amperes is passed through the metal chips to heat and shape them, and the voltage is usually 20 volts. In this process, even when the heating temperature inside the mold reaches around 1000°C, applying a high current virtually eliminates volume diffusion, preventing phenomena such as spheroidization of voids, reduction or disappearance of fine voids, and instead causing partial melting and bonding at the contact points between the metal chips.

[0022] The resulting metal sintered sheet can maintain sufficient sound absorption even after molding, even if it contains small amounts of ceramics or synthetic resin in addition to metal chips. This metal sintered sheet is sufficiently porous when the additives make up about 10% by weight or less of the total amount, while vibration absorption and sound absorption decrease slightly when the additives make up 10-25% by weight. In this metal sintered sheet, the metal chip content is usually about 75% by weight or more of the total amount, and is preferably about 90% by weight or more for speaker applications that require particularly high vibration absorption and sound absorption.

[0023] The obtained metal sintered sheet is cut into rectangular plates, and then one or both sides are polished to obtain individual metal sintered plates 6. A thin coating layer several millimeters thick may be provided on the surface of the sintered plate. This thin coating layer is made of synthetic resin, metal, or general-purpose ceramics, and covers all or part of the porous sintered plate. These general-purpose ceramics include concrete, glass, pottery, porcelain, tiles, roof tiles, etc.

[0024] Six metal sintered plates 6 of the same or different dimensions are bonded together or bolted to form a three-dimensional case 7. Before or after assembly, a through hole 20 is cut into the front metal sintered plate 6a for inserting the rear part of the speaker unit 5 frame. The upper metal sintered plate 6c is provided with a through hole 22 for attaching a connecting fitting 14 to the back pressure buffering mechanism, and this through hole is located behind the cone paper 2 of the speaker unit 7 inside the speaker box 8. Furthermore, the rear metal sintered plate 6b is provided with small screw holes 24 for screwing in bolts 26.

[0025] To mount the speaker unit 5 inside the three-dimensional case 7, a screw hole 28 with a diameter of 8 to 12 mm is provided in the center of the rear surface of the speaker unit. The ends of a bolt 26 are screwed into the screw holes 24 and 28, and the rear part of the frame of the speaker unit 5 is inserted into the through hole 20 of the metal sintered plate 6a. The bolt 26 can be any type of bolt, such as a double-threaded bolt, a long-threaded bolt, an eye bolt, a wing bolt, a socket head cap bolt, or a notched bolt. As the bolt 26 is tightened, the frame 3 of the speaker unit 5 is pressed against the surface of the front metal sintered plate 6a, fixing the speaker unit to the front metal sintered plate 6a. If there are multiple screw holes around the front of the frame 3, screws can be inserted into each screw hole to securely fix it to the front metal sintered plate 6a. At this time, the frame 3 of the speaker unit 5 is pulled towards the rear metal sintered plate 6b via the bolt 26.

[0026] A metal net 30, which is plastically deformed into a convex shape, is attached to the front of the speaker box 8, or metal sintered plate 6a. The metal net 30 is usually made of nickel, which has low electromagnetic wave shielding properties. The metal net 30 has a three-dimensional, rigid mesh structure as a whole, and its apparent density is 1.0 or less.

[0027] The horizontal U-shaped support frame 10 has a hollow structure as illustrated in Figures 4 to 6 and functions as a back pressure buffering mechanism for the speaker box 8. The speaker box 8 is suspended from the upper horizontal portion 12 of the support frame 10 via a connecting fitting 14. The connecting fitting 14 is a known component such as a flat bolt with a through hole and a flat nut, and when suspending the speaker box 8 from the support frame 10 with this connecting fitting, an appropriate annular buffering member (not shown) may be interposed between them.

[0028] As shown in Figures 4 to 6, the interior of the upper horizontal section 12 of the support frame 10 is an independent space, with a connecting fitting 14 positioned in its front part and the upper end of the long pipe 32 located to the rear right. On both sides of the connecting fitting 14, metal sintered plates 34 and 36 are installed in parallel, with a height equal to the interior height of the horizontal section 12. Furthermore, a metal sintered plate 38, also with a height equal to the interior height of the horizontal section 12, extends from the vicinity of the connecting fitting 14 toward the inner wall surface of the horizontal section 12 and reaches near the upper end of the pipe 32.

[0029] As shown in Figures 5 and 6, the interior of the vertical section 40 and the lower horizontal section 42 of the support frame 10 is a series of L-shaped side-connecting spaces, which are in contact with and fixed to the rear lower surface of the upper horizontal section 12. As shown in Figure 6, a long pipe 32 is arranged vertically and parallel to the right side of the vertical section 40, and a short pipe 43 is arranged vertically and parallel to the left side. The upper end of the long pipe 32 protrudes into the upper horizontal section 12, extends vertically downward from that upper end, bends at a right angle at the middle section 44 (Figure 5) to become horizontal and extends forward within the lower horizontal section 42, and its end bends at a right angle horizontally to reach an open end 46. On the other hand, the upper end 48 of the short pipe 43 extends vertically downward from near the lower surface of the upper horizontal section 12, and its lower end bends outward at a right angle to reach an open end 49.

[0030] In the vertical section 40 of the support frame 10, a sintered metal plate 50 with dimensions equal to the inner depth of the vertical section is installed vertically between pipes 32 and 43. This sintered metal plate is positioned below the upper end 48 of the short pipe 43 and above the open end 49. In the lower horizontal section 42 of the support frame 10, a sintered metal plate 52 with a height equal to its inner height is installed vertically at the horizontal center of the lower horizontal section. This sintered metal plate is positioned behind the open end 46 of the long pipe 32 and in front of the vertical section 40. Typically, the sintered metal plates 34-38, 50, and 52 have the same thickness.

[0031] In the loudspeaker 1, the speaker box 8 houses the speaker unit 5 within a three-dimensional case 7 assembled from six porous metal sintered plates 6. By tightening bolts 26, the frame 3 of the speaker unit 5 is pressed against the surface of the front metal sintered plate 6a and fixed in place, while simultaneously pulling the frame toward the rear metal sintered plate 6b. As a result, the front and rear of the speaker unit 5 can be firmly fixed to the metal sintered plates, absorbing mechanical vibrations transmitted to the speaker unit's frame 3 with the front and rear metal sintered plates 6a and 6b. This also mitigates the effect of opposing stress acting on the unit's magnet, thereby resolving the phenomenon where some of the reproduced sound disappears. Consequently, even with small-diameter speakers where the cone area 2 is small, the unit's magnet is less susceptible to the effects of opposing stress.

[0032] In the loudspeaker 1, the speaker box 8 is suspended from the upper horizontal section 12 of the support frame 10, which is a back pressure buffering mechanism for the cone paper 2, via a connecting fitting 14, and the speaker box is directly connected to the support frame 10. Inside the speaker box 8, air is drawn in and out from behind the cone paper 2 during sound reproduction, so that atmospheric pressure does not directly act on the back of the cone paper.

[0033] For example, when sound is reproduced, the vibration of the cone paper 2 pushes the air behind it out of the speaker box 8. This flowing air passes through the connecting fitting 14 and enters the upper horizontal section 12, flowing into the pipe 32 while making appropriate contact with the metal sintered plates 34, 36, and 38. The flowing air moves downward within the pipe 32 in the vertical section 40, moves perpendicularly within the pipe, and then flows out into the lower horizontal section 42 from the open end 46 of the pipe 32. Next, within the lower horizontal section 42, it moves forward while making appropriate contact with the metal sintered plate 52 and enters the vertical section 40. Here, it moves upward while making appropriate contact with the metal sintered plate 50, flows into the pipe 43 from the upper end 48 of the pipe, and then moves downward within the pipe 43 and flows out of the vertical section 40 from the open end 49. Through this outflow path, the air pushed out from the speaker box 8 comes into appropriate contact with the metal sintered plates 34, 36, 38, 50, and 52, effectively absorbing and smoothing out the pulsations contained within the air.

[0034] By installing the support frame 10, which is a back pressure damping mechanism, atmospheric pressure is no longer directly applied to the back of the cone. As a result, even if the cone vibrates continuously during sound reproduction within the speaker box, its back pressure does not change accordingly. Because the back pressure on the cone is not affected by continuous vibration during sound reproduction, the reproduction of the acoustic signal becomes more accurate, resulting in no distortion of sound, and allowing for faithful reproduction of ultra-low frequency sounds. Furthermore, since atmospheric pressure is not directly applied to the back of the cone, the cone is less affected by sounds and vibrations outside the speaker box.

[0035] The loudspeaker 1 shown in Figures 1 and 2 has a speaker box 8 suspended from a support frame 10. In this case, if the installation location of the speaker 1 is limited, the speaker box 8 may be positioned away from the support frame 10 by interposing a suitable flexible pipe (not shown). Furthermore, if the installation location is even narrower, such as inside a car or a small room, a small hollow support frame or rectangular housing may be used as a separate back pressure buffering mechanism, as illustrated in Figure 7. This rectangular housing is smaller and simpler in structure than the support frame 10.

[0036] As a modified example of the present invention, the small speaker box 8 shown in Figure 7 is connected to a flexible tube 17 via a connecting fitting 14, and the flexible tube is connected to a through-hole 52 in the side wall of a rectangular housing 16. In Figure 7, the small speaker box 8 is shown tilted on its side at a right angle from the state in Figure 1. The speaker box 8 is in communication with the rectangular housing 16 via the flexible tube 17, and the air passing through the rectangular housing comes into contact with a horizontally elongated metal sintered plate 54 before being drawn in and exhausted from the exhaust port 56.

[0037] In Figure 7, the interior of the rectangular housing 16 is divided into three sections by vertically parallel partitions 58 and 60, forming three internal chambers 62, 64, and 66 of approximately equal volume. The lower end surface of partition 58 is isolated from the inner wall of the housing 16 to form a transverse passage 68, and the upper end surface of partition 60 is isolated from the inner wall of the housing 16 to form a transverse passage 70.

[0038] The inner chamber 62 houses a pipe 72, the open end of which is separated from the inner wall of the housing 16, the pipe bends at a right angle and passes through the inner chambers 64 and 66, and its rear end is tightly connected to the flexible pipe 17. The inner chamber 64 houses a horizontally elongated sintered metal plate 54 at an angle, the upper left end of which is in close contact with the wall surface of the partition wall 60, and the lower right end which is isolated from the wall surface of the partition wall 58. The inner chamber 66 houses a straight pipe 74, the open upper end of which passes through the housing 16 to become an exhaust port 56, and the open lower end which is located above the outer surface of the pipe 68 within the inner chamber 66.

[0039] For example, when sound is reproduced, the vibration of the cone paper pushes the air behind it out of the speaker box 8. This flowing air passes through the connecting fitting 14 and the flexible pipe 17 and flows into the pipe 72 through the side wall penetration hole 52 of the rectangular housing 16. The flowing air moves forward within the pipe 72, moves upward at a right angle within the pipe, and then flows out into the inner chamber 62 from the open upper end of the pipe 72. Next, it moves downward within the inner chamber 62, passes through the lateral passage 68 and enters the inner chamber 64. Within the inner chamber 64, it moves upward, comes into appropriate contact with the horizontally elongated metal sintered plate 54, passes through the gap at its lower right end, moves further upward, passes through the lateral passage 70 and enters the inner chamber 66.

[0040] In the inner chamber 66, the air moves downward, enters the pipe 74 through its lower open end, moves upward within the pipe, and flows out of the rectangular housing 16 through the exhaust port 56. Through this outflow path, the air pushed out from the speaker box 8 passes through the long flexible pipe 17 and then comes into appropriate contact with the metal sintered plate 54, effectively absorbing and smoothing out the pulsations contained within the air. [Examples]

[0041] Next, the present invention will be described based on examples, but the present invention is not limited to these examples. In the loudspeaker 1 according to the present invention shown in Figure 1, the speaker unit 5 is arranged inside a box-shaped three-dimensional case 7. The speaker unit 5 generally has a conical frame 3 that covers the entire cone paper 2, and a magnet part (not shown) is placed inside the flat top of the frame. A cylindrical voice coil is wound around this magnet part, and the annular peripheral part of the cone paper 2 is glued to the annular inner surface of the frame 3.

[0042] In the speaker box 8, a three-dimensional case 7 is constructed from 10mm thick sintered metal plates 6. The front and rear sintered metal plates 6a and 6b are 120 x 110 mm, the top and bottom sintered metal plates 6c and 6d are 110 x 85 mm, and the remaining two left and right plates are 100 x 85 mm. The six sintered metal plates 6 are assembled by bonding them together, and the resulting cube of sintered metal plates 6 is 120 x 110 x 105 mm, which is approximately equal to the internal dimensions of the wooden outer box 18. After assembling the wooden outer box 18, liquid urethane resin is injected into it, and then the cube of sintered metal plates 6 is placed inside to integrate the whole into a three-dimensional case 7. The side walls of the wooden outer box 18 do not exist for the sintered metal plate 6b.

[0043] In the three-dimensional case 7, a through hole 20 with a diameter of 80-95 mm is provided in the front metal sintered plate 6a, a small screw hole 24 with a diameter of 8.2 mm is provided in the rear metal sintered plate 6b, and a through hole 22 with a diameter of 34 mm is provided in the upper metal sintered plate 6c. The rear part of the frame of the speaker unit 5 is inserted through the through hole 20 in the front metal sintered plate 6a, while a bolt 26 is screwed into the small screw hole 24 and also into the screw hole 28 of the yoke portion of the frame 10. As the bolt 26 is tightened, the frame 3 of the speaker unit 5 is pressed against the surface of the front metal sintered plate 6a, i.e., the baffle surface, and the speaker unit is fixed to the front metal sintered plate 6a. There are multiple screw holes (not shown) around the front of the frame 3, so screws are inserted into each screw hole to securely fix the speaker unit 5 to the front metal sintered plate 6a. The front of the speaker unit 5 is fixed to the metal sintered plate 6a, and the frame 3 of the speaker unit is pulled toward the rear metal sintered plate 6b via the bolt 26.

[0044] A metal net 30, which is plastically deformed into a convex shape, is attached to the front of the speaker box 8, or metal sintered plate 6a, using dowels (not shown), and a felt cloth may be wrapped around the surface of the net. The metal net 30 is usually made of nickel, which has low electromagnetic shielding properties, and a suitable metal is used where electromagnetic shielding is required. The metal net 30 has a three-dimensional, rigid mesh structure as a whole, and its apparent density is 1.0 or less.

[0045] The speaker box 8 is suspended from the upper horizontal section 12 of the support frame 10 via a connecting fitting 14 with a through hole. The horizontal U-shaped support frame 10 has a hollow structure as illustrated in Figures 4 to 6 and functions as a back pressure damping mechanism for the speaker box 8. By suspending the speaker box 8, vibrations of the box itself are transmitted to the floor via the support frame 10, which is the back pressure damping mechanism. As a result, vibrations generated in the speaker box 8 are less likely to be transmitted to the floor surface from its installation path, and the reaction is not transmitted back to the speaker box 8, resulting in a speaker system that is less prone to howling.

[0046] The speaker characteristics of loudspeaker 1 are measured as shown in Figure 8, while those of a conventional speaker with an open baffle mounting are shown in Figure 9. The speaker characteristics in Figures 8 and 9 are measured using the pulse input method, not the conventional steady-state sweep method. The pulse input method is a time-domain measurement. By using the FFT method, the pulse input method allows for the comparison of not only the pulse response in the time domain of the speaker characteristics, but also the transfer function in the frequency domain, including phase information, provided the reference level is the same. A square wave pulse with a time width of 50 microseconds is used as the input signal.

[0047] In loudspeaker 1, the presence of the support frame 10 prevents atmospheric pressure from directly acting on the back of the cone paper 2. In speaker box 8, the support frame 10 mitigates the out-of-phase sound generated from the back of the cone paper 2, so that no reaction stress is applied when sound is generated. In other words, the sound reproduced from the cone paper 2 is not canceled out by the out-of-phase sound from its back. As a result, the sound from speaker unit 5 is not affected by the out-of-phase sound generated from the back of the cone paper 2, and a natural reproduced sound can be obtained.

[0048] As is clear from Figure 8, loudspeaker 1 shows a clear increase in ultra-low frequency sound components compared to the case in Figure 9, and an improvement in the reproduction of a wider range of sound quality and volume. In stereo playback, loudspeaker 1 is less prone to phase variations that affect the sound, the fixed position of the sound image is clearer, and the positions of instruments and singers at the time of recording are reproduced as they were. In other words, loudspeaker 1 clearly reproduces the positions of instruments and singers at the time of recording, has a wide reproduction frequency range, and produces a powerful sound that is not found in small devices, giving the feeling of enjoying music in a large space even if the installation space is limited. [Examples]

[0049] The small speaker box 8 shown in Figure 7 uses an 8cm speaker unit 5 and is connected to a flexible pipe 17 via a connecting fitting 14. The flexible pipe 17 is connected to a through-hole 52 in the side wall of a rectangular housing 16, which has the structure shown in Figure 7. The speaker box 8 is in communication with the rectangular housing 16 via the flexible pipe 17, and the air passing through the rectangular housing comes into contact with a horizontally elongated metal sintered plate 54 before being drawn in and exhausted through an exhaust port 56.

[0050] The flexible tube 17 allows the speaker box 8 and the rectangular housing 16, which acts as a back pressure damping mechanism, to be installed separately. This makes it possible to install the speaker box 8 even in places with limited installation space, such as automobiles, and enables the realization of a point source, resulting in a wide and clear reproduced sound. Furthermore, even in trucks, where installation space is even more limited than in passenger cars, it is possible to obtain clear reproduced sound that can relieve stress and provide a change of pace.

[0051] For example, in a passenger car, a speaker box 8 and a rectangular enclosure 16 are installed under the driver's and passenger's seats, respectively, and the two are connected by a flexible pipe 17. If there is no space under the seats, such as in a truck, the rectangular enclosure 16 can be installed behind the seatback. In this speaker arrangement, the direct sound emitted from the nearby speaker box 8 wraps around the seats and first reaches the listener in the front seat, followed by the direct sound that has wrapped around from the farther speaker box 8. In other words, instead of receiving a large direct sound from nearby, the listener first hears the diffracted sound that has wrapped around the seats, and then hears the sound that has reflected off the doors, ceiling, etc. On the other hand, the direct sound that travels forward through the space in front of the seats without diffraction reaches the listener as reflected sound with a time delay, and this reflected sound is then reflected multiple times within the car.

[0052] In this speaker configuration, the direct sound from speaker boxes 8,8 does not reach the listener directly; instead, diffracted sound is the first to reach the ear. After a short time, the direct sound, which has traveled forward to the front of the seat's feet, then reaches the receiving point as reflected sound. As this reflected sound repeatedly reflects within the space at the feet, each reflected sound reaches the receiving point one after another, resulting in a solid sound image in front of the seat's feet. In terms of frequency response, the ultra-low frequency sound component clearly increases, and there is a slight drop in level in the high-frequency range above 3kHz, creating a sound field that fully reproduces the ultra-low frequency range for the ear. Because the virtual sound image is localized in front of the front seats, the sound does not sound chaotic, but rather gives the impression of the reverberation of a well-tuned music hall or listening room. Since the direct sound from speaker box 8 does not reach the listener directly, the listener is freed from a feeling of sonic pressure, and a soft, fatigue-free sound field is created.

[0053] When speaker boxes 8,8 are installed under the seats, the direct sound from both speaker boxes is slightly lower in pitch for people inside the car. However, the reflected sound creates a virtual sound image in front, making the primary reflections sound as if they were direct sound, creating a pseudo-space that makes the small space seem much larger. Therefore, even inside the car, a sound image spreads as if the music is coming from the windshield, creating an immersive acoustic space with temporal acoustic characteristics similar to a concert hall while driving, allowing for relaxed and attentive driving.

[0054] Using a DVD player or similar device, sound can be played from speaker boxes 8,8 installed under the seats, while a movie can be projected onto the car's windshield using a projector (not shown). When watching a movie with this speaker system, the actors' voices, the direction of movement of people and objects, and sounds from the image can be heard from their source on the windshield, allowing for an immersive movie-watching experience with music and film, much like watching a movie in a theater. This creates a small, intimate movie theater within the car, providing a private theater experience for a small group of people.

[0055] Existing car speakers are generally installed in the front and rear doors, facing inward. These doors have numerous small holes to allow rainwater to pass through and be discharged to the outside, so the doors themselves are relatively poorly sealed, and sound tends to leak out from them. Also, if car speakers are placed on the dashboard or below the rear window, the vibrations from the speakers enter the engine compartment and hood, and the amplified sound escapes through the surface seams and body, so if the volume is increased, the sound will leak out into the surroundings. As a result, even if the car itself is relatively well-sealed, if you play music at a high volume like in a movie theater, the sound will leak outside the car and disturb the neighbors.

[0056] This speaker system takes advantage of the relatively high level of airtightness of the car itself, and by changing the sound generation location inside the car, it reduces sound leakage to the outside. Because this speaker system mounts the speakers under the seats, even if sound fills the car interior, the sound vibrations are not transmitted to the car body that is exposed to the outside, maintaining the car's sound-sealing properties. As a result, when enjoying a home theater inside the car in a garage or similar location, noise will not leak to the surrounding area. [Explanation of symbols]

[0057] 1. Loudspeaker 2 Cone paper 3 Conical frame 5 speaker units 6. Metal sintered plate 8 speaker boxes 10 Support frame 26 volts

Claims

1. A loudspeaker comprising a speaker unit consisting of a conical frame that covers the entire cone paper that radiates sound waves and has a magnet positioned inside the rear top, and a three-dimensional case having a metal sintered plate attached to the inner surface of the box, which has sparse pores on the outer surface and dense pores inside, formed by fusing metal chips together by heating and pressurizing with a high current of several thousand amperes, the rear top of the speaker unit frame is connected to the rear metal sintered plate inside the three-dimensional case via bolts, and by tightening the bolts, the circular surface of the speaker unit frame is tightly fixed to the front metal sintered plate inside the three-dimensional case, and the speaker box is directly or indirectly connected to a back pressure buffering mechanism in which a metal sintered plate is installed inside, and a loudspeaker that clearly reproduces ultra-low frequencies as flowing air comes into contact with the metal sintered plate as it bends and moves through multiple inner chambers within the back pressure buffering mechanism.

2. The speaker box's three-dimensional case is a cube assembled by connecting six metal sintered plates, each having sparse pores on its outer surface and dense pores inside, and each metal sintered plate of the three-dimensional case has a through hole carved into the front metal sintered plate for housing the rear part of the speaker unit frame, and a through hole provided in the upper metal sintered plate for attaching a connecting fitting to the back pressure buffering mechanism, the through hole being located behind the cone paper of the speaker unit inside the speaker box, and furthermore, a small screw hole for screwing in a bolt is provided in the rear metal sintered plate, as described in claim 1.

3. The loudspeaker according to claim 1, wherein a hollow horizontal U-shaped support frame is arranged as a back pressure buffering mechanism, and a speaker box is suspended from the upper horizontal part of the support frame via a connecting fitting, so that the speaker box communicates with the hollow support frame through an upper through hole, and the air passing through the support frame comes into contact with a plurality of metal sintered plates before being drawn in and out at the exhaust port.

4. The speaker box comprises a speaker unit consisting of a conical frame that covers the entire cone paper that radiates sound waves and has a magnet positioned inside the rear top, and a three-dimensional case made of a metal sintered plate with sparse pores on the outer surface and dense pores inside attached to the inner surface of the box, and a hollow rectangular housing is separately arranged as a back pressure buffering mechanism, and the speaker box is connected to a flexible tube, and the flexible tube is connected to a through-hole in the side wall of the rectangular housing, so that the speaker box is in communication with the hollow rectangular housing via the flexible tube, and the air passing through the rectangular housing comes into contact with the horizontally elongated metal sintered plate and is then drawn in and out at the exhaust port.

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