Acoustic device

Abstract

To provide an acoustic device which is installed in a seat, can give sound pressure emphasized in a low frequency band to the ears of a seated listener, and can suppress the influence of low-pitched sound on a distant position.SOLUTION: In the acoustic device 10, a listening side duct 30 and a back side duct 40 are connected to an enclosure 11 in which a speaker unit 20 is housed. The listening sound pressure is applied to the ears of the listener from the openings 34 and 35 of the listener side duct 30. By reducing the difference between the duct length Lf of the listener side duct 30 and the duct length Lb of the back part-side duct 40, the effect that the sound pressure from the opening parts 34 and 35 of the listener side duct 30 and the sound pressure from the opening part 41 of the back part-side duct 40 weaken each other at a position away from the acoustic device 10 is enhanced.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an acoustic device that can provide a sound pressure that emphasizes the low frequency range to a listener seated in a seat installed in a vehicle or the like. [Background technology]

[0002] Patent Document 1 describes a speaker system for a vehicle. The speaker system shown in Fig. 3 has an enclosure housing a speaker unit installed on each of both widthwise sides of the vehicle body. The opening of the enclosure is covered by the diaphragm of the speaker unit. An acoustic tube is connected to the enclosure. The acoustic tube is composed of a first tube member, which is a pillar that constitutes the vehicle body, and a second tube member, one end of which is connected to the pillar. The second tube member opens near the floor of the vehicle body.

[0003] Paragraphs

[0056] and

[0057] of Patent Document 1 state that the sound emitted from the diaphragm of each speaker unit is emitted directly into the vehicle cabin, and that low-frequency components according to the length of the acoustic tube resonate within the acoustic tube, causing sound waves consisting mainly of low-frequency components to be emitted into the vehicle cabin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Re-tabled publication 2017 / 038443 Summary of the Invention [Problem to be solved by the invention]

[0005] In the mobile speaker system described in Patent Document 1, a Helmholtz resonator is configured with an enclosure and an acoustic tube, and therefore, near the resonant frequency of the Helmholtz resonator, the air inside the acoustic tube resonates, suppressing the amplitude of the diaphragm. Because the mobile speaker system is designed to deliver sound waves directly from the diaphragm to the listener's ear, there is a problem in that the output of sound reaching the listener's ear from the diaphragm decreases near the resonant frequency of the Helmholtz resonator. Furthermore, because the amplitude of the diaphragm decreases even in frequency bands lower than the resonant frequency of the Helmholtz resonator, it is difficult to deliver low-frequency sound waves from the diaphragm to the listener's ear with sufficient sensitivity over a wide frequency band.

[0006] Patent Document 1 describes that low-frequency components resonate within the acoustic tube, and sound waves mainly consisting of low-frequency components are radiated into the vehicle cabin. However, in the frequency band lower than the resonance frequency of the Helmholtz resonator, the sound waves radiated from the diaphragm of the speaker unit and the sound waves radiated from the opening of the acoustic tube are in opposite phase (they differ in phase by 180 degrees), and their amplitudes tend to cancel each other out, making it difficult to achieve a sufficient low-frequency acoustic effect.

[0007] Conversely, for example, when a listener sitting in the left seat of a vehicle is listening to sound waves from the diaphragm of the left speaker unit, sound waves from the right diaphragm, which is located farther away, and sound waves from the opening of the right acoustic tube cancel out in a frequency band lower than the resonant frequency of the Helmholtz resonator, making it difficult for the low-frequency sounds from the right speaker unit to reach the listener in the left seat. By utilizing this effect, it is possible to build a system in which listeners in each seat can hear individual sounds. However, as shown in Figure 3 of Patent Document 1, if the acoustic tube path is too long, it takes time for the sound waves emitted from the diaphragm to reach the opening of the acoustic tube. As a result, the sound waves emitted directly from the diaphragm and the sound waves emitted from the opening of the acoustic tube do not completely reverse in phase with each other, but rather approach each other. As a result, the sound waves from the diaphragm and the accompanying sound waves from the opening of the acoustic tube do not completely cancel out each other, creating a new problem: low-frequency sounds are more likely to reach the ears of listeners in distant positions.

[0008] The present invention is intended to solve the above-mentioned conventional problems, and aims to provide an acoustic device that enables a listener seated in a seat in a vehicle or the like to hear low-frequency sounds over a relatively wide frequency range at a sufficiently high sound pressure.

[0009] Another object of the present invention is to provide an acoustic device that can easily exert the effect of attenuating low-frequency sound pressure for listeners located far from their seats, and that is suitable for listeners in each seat to listen to individual sounds. [Means for solving the problem]

[0010] The present invention provides an acoustic device having an enclosure to be installed in a seat and a speaker unit provided inside the enclosure, an internal space of the enclosure is partitioned by a diaphragm provided in the speaker unit into a listening-side space and a rear-side space, and a listening-side duct communicating with the listening-side space and a rear-side duct communicating with the rear-side space are connected to the enclosure; The listening position is set at a position where the linear distance from the opening of the listening-side duct is shorter than the linear distance from the opening of the back-side duct.

[0011] In the acoustic device of the present invention, it is preferable that the duct length from the diaphragm to the opening of the back-side duct is shorter than the duct length from the diaphragm to the opening of the listening-side duct. For example, it is preferable that the difference between the duct length of the listening-side duct and the duct length of the back-side duct be 18 cm or less.

[0012] In the acoustic device of the present invention, it is preferable that the resonance frequency of the back-side Helmholtz resonator formed by the back-side space and the back-side duct is set to a higher frequency band than the resonance frequency of the listening-side Helmholtz resonator formed by the listening-side space and the listening-side duct.

[0013] The acoustic device of the present invention is configured, for example, so that the opening area of ​​the listening-side duct is smaller than the opening area of ​​the back-side duct, and the duct length of the listening-side duct is longer than the duct length of the back-side duct.

[0014] In the acoustic device of the present invention, it is preferable that the resonant frequency of the vibration system mass, which includes the mass of the vibrating part of the speaker unit, the load mass of the air in the listening-side duct, and the load mass of the air in the back-side duct, is set to a frequency band lower than the resonant frequency of the listening-side Helmholtz resonator formed by the listening-side space and the listening-side duct. [Effects of the Invention]

[0015] In the acoustic device of the present invention, the listening position is set close to the opening of the listening-side duct, so that the sound pressure emitted from the opening of the listening-side duct is given priority to the listener. The listening-side space within the enclosure and the listening-side duct form a listening-side Helmholtz resonator, and while movement of the diaphragm of the speaker unit is suppressed near the resonant frequency of the Helmholtz resonator, air resonates within the listening-side duct, so that low-frequency sounds with sufficient sensitivity for the listener's ears to hear can be given from the opening of the listening-side duct, even in frequency bands near the resonant frequency of the Helmholtz resonator.

[0016] In a frequency band lower than the resonant frequency of the Helmholtz resonator, the air inside the listening-side duct and the diaphragm vibrate in the same phase, resulting in opposite phases between the sound pressure emitted from the opening of the listening-side duct and the sound pressure imparted from the diaphragm to the back-side space. Therefore, at a position far from the acoustic device, the sound pressure emitted from the opening of the listening-side duct and the sound imparted from the diaphragm to the back-side space cancel each other out, making it difficult for low-frequency sounds from the acoustic device to leak to positions far from the acoustic device. To generate low-frequency sounds from the listening-side duct, it is preferable to lengthen the listening-side duct to increase the load mass inside the listening-side duct, thereby substantially increasing the mass of the vibrating part of the speaker unit and lowering the resonant frequency of the vibrating part as much as possible. In this case, the sound propagation path from the diaphragm to the opening of the listening-side duct becomes longer, so the sound pressure emitted from the opening of the listening-side duct and the sound pressure applied from the diaphragm to the back-side space, which are originally opposite in phase, begin to approach each other and become in phase. Therefore, in this invention, by providing a back-side duct extending from the back-side space and lengthening the sound propagation path in the back-side duct as well, it is possible to bring the phase difference between the sound emitted from the opening of the listening-side duct and the sound emitted from the opening of the back-side duct closer to being in opposite phase, thereby maintaining the effect of preventing low-frequency sounds from leaking to positions away from the acoustic device.

[0017] In the present invention, not only does the air in the listening-side duct act as a load mass, but the air in the back-side duct also acts as a load mass, and these load masses function to substantially increase the vibration system mass of the vibration unit including the diaphragm. This allows the resonant frequency of the vibration system mass to be set to a low frequency range, enabling low-frequency bass to be obtained from the listening-side duct. Because the air in the back-side duct acts as a load mass for the vibration unit, the resonant frequency of the vibration system mass can be set to a low frequency range without the listening-side duct being excessively thin and long. Therefore, by making the listening-side duct slightly thicker or shorter, the resonant frequency of the listening-side Helmholtz resonator can be shifted to a relatively high frequency range. As a result, the phenomenon of diaphragm amplitude suppression that occurs near the resonant frequency can be shifted to a relatively high frequency range, allowing the sound obtained from the listening duct to be set to a wide bass range. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a side view showing a state in which an acoustic device according to an embodiment of the present invention is attached to a seat in a vehicle; [Figure 2] FIG. 2 is a front perspective view of the acoustic device and seat shown in FIG. 1; [Figure 3] FIG. 3 is a longitudinal cross-sectional view of the acoustic device shown in FIG. 2 taken along line III-III; [Figure 4] 4 is a cross-sectional view of the acoustic device shown in FIG. 2 taken along line IV-IV; [Figure 5] FIG. 1 is a schematic diagram showing a simplified structure of an acoustic device according to an embodiment; [Figure 6] (A) is a diagram illustrating the acoustic behavior of an acoustic device having a general structure with an enclosure and a duct as a comparative example, and (B) is a diagram illustrating the effect of an acoustic device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] 1 to 4 show an acoustic device 10 according to an embodiment of the present invention. 1 to 4, the X1-X2 direction is the front-to-rear direction, with the X1 direction being the front, i.e., the vehicle traveling direction, and the X2 direction being the rear. The Z1-Z2 direction is the up-down direction, with the Z1 direction being upward and the Z2 direction being downward. The Y1-Y2 direction is the left-to-right direction, with the Y1 direction being the leftward direction and the Y2 direction being the rightward direction.

[0020] An acoustic device 10 is installed between a seat back 2 and a headrest 3 of an automobile seat 1. FIG. 1 shows a listener 5 seated in the seat 1. The listener 5 is the driver, and his or her head 7 is positioned in front of the headrest 3. The listening position of the acoustic device 10 is set at the position of the left and right ears E of the head 7, and openings 34, 35 of the listening-side duct are located near the listening position. As long as the openings 34, 35 are located near the listening position, the acoustic device 10 may be installed inside the seat back or inside the headrest. The seat 1 on which the acoustic device 10 is installed may be a seat in a vehicle other than an automobile, such as a train seat, or may be a seat installed in a theater or game center. Alternatively, the acoustic device 10 may be used for home use.

[0021] As shown in the cross-sectional view of FIG. 4, the acoustic device 10 has an enclosure 11, and a speaker unit 20 is housed within the enclosure 11. The speaker unit 20 has a frame 21. A front peripheral portion 21a of the frame 21 is fixed to a support portion 12 inside the enclosure 11. A magnetic circuit portion 22 is fixed to the rear of the frame 21. The magnetic circuit portion 22 is composed of a magnet and a yoke made of a magnetic material, and a magnetic gap, which is a cylindrical gap, is formed. A diaphragm 23 is supported on the frame 21. The diaphragm 23 is cone-shaped, and its front peripheral portion is supported on the frame 21 via an edge member 24, and its rear portion is supported on the frame 21 via a damper 25. The edge member 24 and the damper 25 are elastically deformable, and the elastic deformation of the edge member 24 and the damper 25 supports the diaphragm 23 so that it can vibrate freely in the front-to-rear direction (X1-X2 direction). A cylindrical bobbin 26 is fixed to the rear end of diaphragm 23. A voice coil is wound around the rear of bobbin 26 and inserted into the magnetic gap of magnetic circuit section 22. Diaphragm 23 vibrates in the front-to-rear direction due to electromagnetic forces generated by the magnetic field that crosses the voice coil in magnetic circuit section 22 and the voice current that flows through the voice coil.

[0022] The forward-facing opening of cylindrical bobbin 26 is closed with a cap member. The internal space of enclosure 11 is divided into a front listening-side space Af and a rear back-side space Ab by diaphragm 23 and the cap member. As shown in Fig. 4, a listening-side duct 30 communicating with listening-side space Af is connected to the front of enclosure 11, and a rear back-side duct 40 communicating with rear back space Ab is connected to the rear of enclosure 11.

[0023] FIG. 4 shows a vibration center line O extending in the vibration direction of the diaphragm 23. When viewed in the plan cross-sectional view of FIG. 4, the listening-side duct 30 is composed of a left duct 31 occupying the left half (Y1 side) of the listening-side duct 30 with the vibration center line O as the boundary, and a right duct 32 occupying the right half (Y2 side). The left duct 31 and the right duct 32 are symmetrical in the left-right direction (Y1-Y2 direction) with respect to the vibration center line O. A forward sound pressure SPf is applied to the listening-side space Af by the vibration of the diaphragm 23 and is input to both the left duct 31 and the right duct 32. The left duct 31 has a front duct 31a extending leftward (Y1 direction) and a side duct 31b extending rearward (X2 direction). The right duct 32 also has a front duct 32a extending rightward (Y2 direction) and a side duct 32b extending rearward (X2 direction).

[0024] As shown in FIG. 3, the front pipe 32a and the side pipe 32b of the right duct 32 are stacked in two layers in the vertical direction (Z1-Z2 direction), and the maze-shaped pipe section in the upper layer is connected to the maze-shaped pipe section in the lower layer via multiple communication sections 32c. The pipe section of the front pipe 32a and the pipe section of the side pipe 32b are also connected via multiple communication sections 32c. The pipe section has a rectangular internal cross section at every point, and the internal cross-sectional shape is a uniform shape with a long side H1 and a short side W1. As shown in FIG. 3, in the right duct 32, an extension pipe 33b is connected to the top of the two upper and lower side pipes 32b, and the end of the extension pipe 33b forms an opening 35. As shown in FIG. 2, the opening 35 opens forward (in the X1 direction). In the left duct 31 as well, the two-tiered pipe sections of the front pipe line 31a and the side pipe line 31b are connected via communication sections 31c at multiple locations, and the pipe section of the front pipe line 31a and the pipe section of the side pipe line 31b are also connected via communication sections 31c at multiple locations. The pipe sections that make up the left duct 31 also have a rectangular internal cross section. In the left duct 31 as well, an extension pipe line continues to the top of the two-tiered side pipe lines 31b, and as shown in Figure 2, the end of the extension pipe line forms an opening 34 that opens forward (in the X1 direction).

[0025] In the left duct 31, the forward sound pressure SPf input from the listening-side space Af to the forward duct 31a passes through a single duct path made up of tubular sections with a uniform rectangular cross section and is emitted forward (in the X1 direction) from the opening 35. In the right duct 32, the forward sound pressure SPf input from the listening-side space Af to the forward duct 32a passes through a single duct path made up of tubular sections with a uniform rectangular cross section and is emitted forward (in the X1 direction) from the opening 35.

[0026] As shown in FIG. 4, the back-side duct 40 communicates with the back-side space Ab within the enclosure 11. As shown in FIG. 1, the back-side duct 40 extends downward along the rear surface of the seat back 2, with an opening 41 of the back-side duct 40 facing downward (in the Z2 direction). As shown in FIG. 4, the internal cross-sectional shape of the back-side duct 40 is rectangular, with a long side H2 and a short side W2. The cross-sectional area of ​​the back-side duct 40 is uniform over its entire length.

[0027] 1, acoustic device 10 is set so that the listening position is the position of ear E when listener 5 of a standard-sized adult is seated in seat 1 with head 7 in contact with headrest 4. The positions of openings 34, 35 and 41 are determined so that linear distance L1 from openings 34, 35 of listening-side duct 30 to the listening position (position of ear E) is sufficiently shorter than linear distance L2 from opening 41 of back-side duct 40 to the listening position. To enable the listener to preferentially listen to the sound emitted from listening-side ducts 34, 35, linear distance L1 is preferably equal to or less than one-half of linear distance L2, and more preferably equal to or less than one-third of linear distance L2.

[0028] Next, the operation of the acoustic device 10 will be described. 5 is a schematic diagram showing a simplified structure of acoustic device 10 to explain the operation of acoustic device 10 according to an embodiment of the present invention. In acoustic device 10, listening-side space Af within enclosure 11 and listening-side duct 30 form listening-side Helmholtz resonator Hf, and rear-side space Ab within enclosure 11 and rear-side duct 40 form rear-side Helmholtz resonator Hb.

[0029] Before describing the acoustic effects of the acoustic device 10 according to the embodiment of the present invention, the acoustic effects of an acoustic device as a comparative example will be described with reference to FIG. 6(A). The comparative example is an acoustic device that does not have rear-side duct 40 and that assumes that rear sound pressure is applied directly from diaphragm 23 to the external space behind (in the X2 direction), i.e., that does not have rear-side Helmholtz resonator Hb and that only listening-side Helmholtz resonator Hf is configured. The solid line in Figure 6(A) shows the frequency characteristics of the rear sound pressure applied from diaphragm 23 to the external space behind in the comparative example, and the dashed line shows the frequency characteristics of the listening-side sound pressure observed at openings 34, 35 of listening-side duct 30. The acoustic device is used as a subwoofer, and the frequency band used is a low-frequency range of approximately 150 Hz or less, mainly a frequency band lower than the resonant frequency Fd of listening-side Helmholtz resonator Hf. In the frequency band lower than the resonant frequency Fd of the listening-side Helmholtz resonator Hf, the diaphragm 23 and the air inside the listening-side duct 30 move in the same phase, so the listening-side sound pressure observed at the openings 34, 35 of the listening-side duct 30 and the rear sound pressure applied from the diaphragm 23 to the external space behind it are out of phase with each other by 180 degrees.

[0030] The acoustic device assumed in the comparative example, like acoustic device 10 of the embodiment of the present invention, has openings 34, 35 of listening-side duct 30 located near ear E of listener 5 seated in seat 1, and the output portion of the back sound pressure applied from diaphragm 23 to the external space behind it is located away from ear E of listener 5. As a result, listener 5 is not significantly affected by the out-of-phase sound pressure emitted from diaphragm 23 to the external space behind it, and can preferentially hear the sound emitted from listening-side duct 30. On the other hand, at a position far from the acoustic device, the listening-side sound pressure emitted from openings 34, 35 of listening-side duct 30 and the back sound pressure applied from diaphragm 23 to the external space behind it reach the listener, causing interference between the listening-side sound pressure and the back sound pressure, which are out of phase with each other. As a result, bass sounds in a frequency band lower than the resonance frequency Fd of listening-side Helmholtz resonator Hf are weakened at a position far from the acoustic device. Therefore, it is suitable for use as a system in which different sound sources are listened to at individual seats.

[0031] Increasing the air load in the listening-side duct 30 effectively increases the mass of the vibration system, including the diaphragm 23, and lowers the resonant frequency of the vibration unit. Increasing the air load in the listening-side duct 30 requires narrowing or lengthening the listening-side duct 30. However, making the listening-side duct 30 too narrow increases the likelihood of air noise being generated within the duct. Therefore, increasing the length of the listening-side duct 30 effectively lowers the resonant frequency of the vibration unit. However, increasing the length of the duct increases the time it takes for the listening sound pressure emitted forward by the vibration of the diaphragm 23 to reach the openings 34 and 35 of the listening duct 30. As a result, the listening sound pressure coming from the openings 34, 35 and the out-of-phase rear sound pressure coming rearward from the diaphragm 23 become closer in phase, and the interference between the listening sound pressure and the rear sound pressure at positions away from the acoustic device 10 becomes weaker, making it easier for low-frequency sounds in a frequency band lower than the resonance frequency Fd of the listening-side Helmholtz resonator Hf to reach positions away from the acoustic device 10. When listeners in individual seats listen to individual sound sources, the low-frequency sounds from the distant speaker systems become harsh on the ears.

[0032] The acoustic device 10 according to the embodiment of the present invention can solve the problems related to the characteristics of the acoustic device described in the comparative example. Acoustic device 10 is provided with a back-side duct 40 that communicates with back-side space Ab within enclosure 11, and back sound pressure applied from diaphragm 23 to back-side space Ab passes through back-side duct 40 and is discharged from opening 41 to the external space behind seat 1. Because it takes time for the back sound pressure generated from diaphragm 23 to reach opening 41 of back-side duct 40, it is possible to make the phase difference between the listening sound pressure emitted from openings 34, 35 of listening-side duct 30 and the back sound pressure emitted from opening 41 of back-side duct 40 antiphase, i.e., approaching 180 degrees. Therefore, at positions far from the acoustic device 10, the listening sound pressure and the back sound pressure tend to cancel each other out in a frequency band lower than the resonance frequency Fd of the listening-side Helmholtz resonator Hf, and when listeners in individual seats listen to individual sound sources, it becomes possible to prevent the phenomenon of low sounds from a distant speaker system becoming harsh on the ears.

[0033] To achieve the effect of mutually attenuating interference between the listening sound pressure emitted from the openings 34 and 35 of the listening-side duct 30 and the rear sound pressure emitted from the opening 41 of the rear-side duct 40 when listening from a distance from the acoustic device 10, it is preferable that the phase difference between the listening sound pressure and the rear sound pressure does not deviate by more than 30 degrees from the ideal 180-degree offset for cancellation. To achieve this, it is preferable that the difference (Lf - Lb) between the duct length Lf of each of the left duct 31 and right duct 32 of the listening-side duct 30 and the duct length Lb of the rear-side duct 40 be less than 1 / 12 of the wavelength used. If the upper frequency limit of the bass to be reproduced as a subwoofer is set to 150 Hz, it is preferable that the difference (Lf - Lb) be 18 cm or less. If the upper frequency limit of the bass to be reproduced is set to 120 Hz, it is preferable that the difference (Lf - Lb) be 23 cm or less. Furthermore, if the difference in duct lengths is 28 cm or less, the effect of mutual weakening due to interference between the listening sound pressure emitted from the openings 34, 35 of the listening-side duct 30 and the rear sound pressure emitted from the opening 41 of the rear-side duct 40 can be enhanced in the band where the frequency of the reproduced low-pitched sounds is 100 Hz or less.

[0034] As shown in the schematic diagram of Fig. 5, acoustic device 10 of the embodiment is provided with rear-side duct 40, so when diaphragm 23 vibrates, not only the air in listening-side duct 30 but also the air in back-side duct 40 acts as a load mass. By providing listening-side duct 30, the mass of the vibration system including diaphragm 23 increases, so it is possible to shift the resonance frequency F0 of the vibration system mass including diaphragm 23 to an even lower band, as indicated by arrow (i), compared to the acoustic characteristics of the comparative example in Fig. 6(A).

[0035] In the acoustic device 10, the air in the rear-side duct 40 is added to the vibration system mass, so it is possible to lower the resonant frequency of the vibration system mass without extremely increasing the duct length of the listening-side duct 30. Because it is no longer necessary to extremely increase the duct length of the listening-side duct 30, it is possible to shift the resonant frequency Fd of the listening-side Helmholtz resonator Hf to a higher frequency range than in the comparative example in FIG. 6(A), as indicated by arrow (ii). Incidentally, the resonant frequency Fd of the Helmholtz resonator without taking into account the operation of the vibrating part of the speaker unit 20 is physically calculated using the internal volume (V) of the enclosure, the duct's duct length (L), and the cross-sectional area (S), and is found by the formula Fd = (C / 2·π)√(S / V·L); (C is the speed of sound). The resonant frequency Fd is inversely proportional to the internal volume (V) of the enclosure and the duct length (L), and proportional to the cross-sectional area (S) of the duct.

[0036] 6(A), near the resonance frequency Fd of the listening-side Helmholtz resonator Hf, the amplitude of the diaphragm is suppressed and the sound pressure from the diaphragm is reduced by the internal pressure of the enclosure caused by the resonance of the air inside the listening-side duct 30. However, as shown by the dashed line, because the air inside the listening-side duct 30 is resonating, a relatively large sound pressure can be generated from the openings 34, 35 of the listening-side duct 30 in a frequency band that includes the resonance frequency F0 of the vibrating part and the resonance frequency Fd of the listening-side Helmholtz resonator Hf. In acoustic device 10 according to an embodiment of the present invention, the load mass of the air in back-side duct 40 can shift the resonant frequency F0 of the vibrating unit, including diaphragm 23, to a lower frequency band as shown by arrow (i) in Fig. 6(A), and since the load mass of the vibrating unit can be increased without making listening-side duct 30 extremely long, the resonant frequency Fd of listening-side Helmholtz resonator Hf can be shifted to a higher frequency band as shown by arrow (ii) in Fig. 6(A). Therefore, as shown by arrow (iii) in Fig. 6(A), it becomes possible to provide audible sound pressure over a wide frequency band from openings 34, 35 of listening-side duct 30 to ear E of listener 5.

[0037] As shown in the schematic diagram of Figure 5, in the acoustic device 10 of this embodiment, the resonant frequency of the listening-side Helmholtz resonator Hf is calculated using the internal volume Vf of the listening-side space Af and the line lengths of the two ducts, namely the line length Lf of the left duct 31 and the line length Lf of the right duct 32, as parameters, and the resonant frequency of the back-side Helmholtz resonator Hb is calculated using the internal volume Vb of the back-side space Ab and the line length Lb of the back-side duct 40 as parameters. In the acoustic device 10 of the present invention, it is preferable to set the resonant frequency of the back-side Helmholtz resonator Hb to a frequency band higher than the resonant frequency of the listening-side Helmholtz resonator Hf, for example, by making the duct length Lb of the back-side duct 40 shorter than the duct length Lf of the listening-side duct 30 and / or by making the internal cross-sectional area of ​​the back-side duct 40 larger than the internal cross-sectional area of ​​the listening-side duct 30.

[0038] 6(B) shows the frequency characteristics of the sound pressure obtained from diaphragm 23 when focusing only on rear-side Helmholtz resonator Hb, assuming that listening-side Helmholtz resonator Hf is not present. As shown in FIG. 6(B), the movement of diaphragm 23 is suppressed near the resonance frequency Fdb of rear-side Helmholtz resonator Hb due to the resonance of vibrations in rear-side duct 40. By setting the resonance frequency Fdb of rear-side Helmholtz resonator Hb to a frequency band higher than the resonance frequency of listening-side Helmholtz resonator Hf, the region where the movement of diaphragm 23 is suppressed can be shifted to a higher frequency band, preventing the phenomenon of the movement of diaphragm 23 being restricted due to rear-side Helmholtz resonator Hb within the frequency band used as a subwoofer. [Explanation of symbols]

[0039] 1 seat 3 Headrest 5 Listeners 10 Sound equipment 11 Enclosure 20 Speaker unit 22 Magnetic circuit section 23 Diaphragm 30 Listening side duct 31 Left duct 32 Right duct 34,35 Opening 40 Back duct 41 Opening E ear (listening position) Af Listening space Ab dorsal space Fd Resonance frequency of the vibrating part Fd,Fdb Resonant frequencies of the Helmholtz resonator Hf Helmholtz resonator on the listening side Hb Dorsal Helmholtz Resonator L1, L2 O Vibration center line

Claims

1. An acoustic device having an enclosure to be installed in a seat and a speaker unit provided inside the enclosure, an internal space of the enclosure is partitioned by a diaphragm provided in the speaker unit into a listening-side space and a rear-side space, and a listening-side duct communicating with the listening-side space and a rear-side duct communicating with the rear-side space are connected to the enclosure; An acoustic device characterized in that the listening position is set at a position where the linear distance from the opening of the listening-side duct is shorter than the linear distance from the opening of the back-side duct.

2. 2. The acoustic device according to claim 1, wherein the length of the duct path from the diaphragm to the opening of the back-side duct is shorter than the length of the duct path from the diaphragm to the opening of the listening-side duct.

3. 3. The acoustic device according to claim 2, wherein the difference between the duct length of the listening-side duct and the duct length of the back-side duct is 18 cm or less.

4. 2. The acoustic device according to claim 1, wherein the resonant frequency of the rear-side Helmholtz resonator formed by the rear-side space and the rear-side duct is set to a higher frequency band than the resonant frequency of the listening-side Helmholtz resonator formed by the listening-side space and the listening-side duct.

5. 5. The acoustic device according to claim 4, wherein the opening area of ​​the listening-side duct is smaller than the opening area of ​​the back-side duct, and the duct length of the listening-side duct is longer than the duct length of the back-side duct.

6. 6. The acoustic device according to claim 4, wherein the resonant frequency of a vibration system mass including the mass of the vibrating part of the speaker unit, the load mass of the air in the listening-side duct, and the load mass of the air in the back-side duct is set to a frequency band lower than the resonant frequency of the listening-side Helmholtz resonator formed by the listening-side space and the listening-side duct.

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