Acoustic device

Abstract

To provide an acoustic device arranged in a seat so as to give sound pressure emphasized in a low frequency band to an ear of a sitting listener.SOLUTION: In an acoustic device 10, an enclosure 11 and a speaker unit 20 are fixed inside a seat back 2, and an opening part 12b of a duct 12 extending from the enclosure 11 is directed toward an ear E of a listener 6. A resonance frequency of a Helmholtz resonator constituted by the enclosure 11 and the duct 12 is set to be in a band higher than that of the resonance frequency of a vibration system mass including the mass of a vibration part of the speaker unit 20 and a load mass of air inside the duct 12. A listening position is set at a position to allow a straight line distance Ld from the opening part 12b of the duct 12 is shorter than a straight line distance Ls from a diaphragm of the speaker unit 20.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an acoustic device capable of providing a sound pressure with emphasis on the low frequency range to a listener seated in a seat installed in a vehicle interior or the like. [Background technology]

[0002] FIG. 3 of Patent Document 1 shows an acoustic device installed in a seat. This acoustic device includes an acoustic enclosure having an upper acoustic chamber and a lower acoustic chamber. An electroacoustic transducer, which is a speaker unit, is provided at the joint between the upper acoustic chamber and the lower acoustic chamber. One radiating surface of the electroacoustic transducer is acoustically coupled to the upper acoustic chamber, and the other radiating surface is acoustically coupled to the lower acoustic chamber. The upper chamber outlet opens near the head of a person sitting in the seat. The lower chamber outlet opens downward toward the floor, and is located significantly far from the person's head.

[0003] Paragraph

[0017] of Patent Document 1 states that the head of a seated person is significantly closer to the upper chamber outlet than to the lower chamber outlet, so that the sound heard by the seated person is much more affected by radiation from the upper chamber outlet than from the lower chamber outlet. Paragraph

[0011] also states that the pressure waves provided by the electroacoustic transducer to the upper acoustic chamber and the pressure waves provided to the lower acoustic chamber are in opposite phase, and paragraphs

[0017] and elsewhere state that at a position (50) that is relatively equidistant from the lower chamber outlet and the upper chamber outlet, the acoustic energy from the two outlets has a smaller amplitude than near the seated person's head due to destructive interference caused by the phase difference. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-82220 A Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 describes that the upper chamber outlet is located near the person's head and that acoustic energy is given to the person's head from this outlet, but does not clarify what kind of resonance action is performed by the upper acoustic chamber. A typical Helmholtz resonator having an enclosure and a duct has a resonance frequency that is inversely proportional to the duct length and proportional to the opening cross-sectional area of ​​the duct, but since the upper chamber outlet described in Patent Document 1 has a duct length of almost zero, it is easily predictable that the upper acoustic chamber will not be able to cause low-frequency resonance.

[0006] The present invention is devised to solve the above-mentioned problems of the conventional technology, and aims to provide an acoustic device that enables a person 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, while attenuating the sound pressure of the low-frequency sounds in locations away from the seat. [Means for solving the problem]

[0007] The present invention relates to an acoustic device having an enclosure, a duct communicating with an internal space of the enclosure, and a speaker unit for applying sound pressures of opposite phases to the inside and outside of the enclosure, At least the enclosure and the speaker unit are fixed to a seat, a resonant frequency Fd of a Helmholtz resonator formed by the enclosure and the duct is set in a band higher than a resonant frequency F0 of a vibration system mass including a mass of a vibration part of the speaker unit and a load mass of air in the duct; The listening position is set at a position where the linear distance Ld from the opening of the duct is closer than the linear distance Ls from the diaphragm of the speaker unit.

[0008] In the acoustic device of the present invention, the speaker unit and the enclosure are housed in a seat back or a seat cushion, It is preferable that sound pressure having an opposite phase to the sound pressure applied inside the enclosure is directed from the speaker unit to a listener seated in a seat, and that the opening of the duct opens near the ears of the listener.

[0009] The acoustic device of the present invention may be configured such that the duct is a flexible hose, at least a portion of which is housed in the seat back.

[0010] In the acoustic device of the present invention, it is preferable that the resonance frequency F0 of the vibration system mass is less than 100 Hz.

[0011] In the acoustic device of the present invention, the sound pressure obtained from the opening of the duct is It has a peak located in a frequency band lower than 100 Hz and a peak located in a frequency band higher than 100 Hz. Effect of the Invention

[0012] The resonant frequency Fd of a Helmholtz resonator, which is composed of an enclosure and a duct that communicates with the internal space of the enclosure, is calculated physically from the internal volume (V) of the enclosure, the duct's pipe length (L), and the cross-sectional area (S) {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's pipe length (L), and proportional to the cross-sectional area (S) of the duct. In the operation of a Helmholtz resonator, when the frequency of the pressure wave input into the enclosure matches the resonant frequency Fd, the air in the enclosure expands and contracts like a spring, and the air in the duct resonates in the opposite phase to the input pressure wave. When the input pressure wave becomes higher than the resonant frequency Fd, the air in the enclosure expands and contracts like a spring, but the air in the duct becomes difficult to move. When the input pressure wave becomes lower than the resonant frequency Fd, the air in the duct moves by an amount equal to the expansion and contraction of the air in the enclosure, and the air in the duct moves in the same phase as the input pressure wave.

[0013] The acoustic device of the present invention uses a bass reflex structure in which a speaker unit is attached to an enclosure, and is configured so that the vibration system mass Mms, which includes the mass of the vibration part of the speaker unit and the load mass of the air in the duct that moves with the same period as the vibration part, can resonate in a frequency band lower than the resonance frequency Fd of the Helmholtz resonator. That is, the resonance frequency F0 calculated from the spring constant of the spring support system Kms, which takes into account the damper member and edge member of the speaker unit and the elastic modulus of the air in the enclosure, and the vibration system mass Mms, is set to a frequency band lower than the resonance frequency Fd of the Helmholtz resonator. In this specification, the resonance frequency F0 at this time is called the "resonance frequency F0 of the vibration system mass Mms of the speaker system in the bass reflex structure." In the present invention, for example, the mass of the vibrating part of the speaker unit 20 is increased, the inner diameter of the duct 12 is reduced, the length of the duct is increased, and the load mass of the air inside the duct is increased, thereby designing the vibration system mass Mms to be heavy, and further designing the spring constant of the spring support system Kms of the speaker system 20 to be low, thereby adjusting the resonant frequency F0 of the vibration system mass Mms to a frequency band lower than the resonant frequency Fd of the Helmholtz resonator.

[0014] In the acoustic device of the present invention, in a bass reflex structure, the resonant frequency Fd of the Helmholtz resonator is set to a frequency band higher than the resonant frequency F0 of the vibration system mass Mms, which includes the vibrating part of the speaker unit and the load mass of the air in the duct. This makes it possible to increase the level of sound pressure radiated from the opening of the duct over a wide band from near the resonant frequency F0 to near the resonant frequency Fd, making it possible to operate the device as a so-called bandpass acoustic device.

[0015] In the acoustic device of the present invention, at least the enclosure and the speaker unit are fixed to the seat, and the listening position is set at a position where the linear distance Ld from the opening of the duct is closer than the linear distance Ls from the diaphragm of the speaker unit. Therefore, sound pressure is directly applied to the ears of the seated person from the opening of the duct, and the seated person can preferentially hear the sound with the emphasis on the low frequency range in the band from around F0 to around Fd. However, when the speaker unit operates to generate a wide band of sound pressure from around the resonant frequency F0 to around the resonant frequency Fd, the vibration part of the speaker and the air in the duct operate in phase, so that the sound pressure released from the duct to the external space and the sound pressure applied from the diaphragm of the speaker unit to the external space of the enclosure (the space opposite to the internal space of the enclosure) are in opposite phase. Therefore, at a location away from the opening of the duct, the opposite phase sound pressures interfere with each other so as to cancel each other out, and the low frequency sound from around the resonant frequency F0 to around the resonant frequency Fd can be suppressed. For example, if an acoustic device is installed on a seat inside the vehicle cabin, the sound in the above-mentioned frequency range can be emphasized and heard by the ears of the person sitting in the seat, but low-frequency sounds from around the resonant frequency F0 to around the resonant frequency Fd are less likely to leak out into the cabin away from the duct opening, and even outside the vehicle.

[0016] In order for the human ear to effectively hear low-frequency sound pressure, it is necessary to increase the sound pressure in the low-frequency range, but conversely, low-frequency sound pressure easily propagates to the surroundings, for example, through the outer panels of a vehicle. The acoustic device of the present invention can emphasize low-frequency sounds over a relatively wide frequency range to the listener's ears, while at the same time making it possible to reduce the sound pressure in the low-frequency range at locations far from the acoustic device. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a side view of a first embodiment of the invention in which an audio device is mounted in a seat back of a seat in a vehicle; [Diagram 2] 2 is an enlarged cross-sectional view of the acoustic device shown in FIG. [Diagram 3]FIG. 2 is a side view of a second embodiment of the invention in which an acoustic device is mounted in a seat cushion of a seat in a vehicle; [Figure 4] FIG. 2 is a diagram showing frequency characteristics of sound pressure heard near the opening of a duct in the first embodiment of the acoustic device of the present invention; [Diagram 5] FIG. 11 is a diagram showing frequency characteristics of sound pressure heard near the opening of a duct in the acoustic device according to the second embodiment of the present invention; [Figure 6] FIG. 11 is a diagram showing frequency characteristics of sound pressure heard near the opening of a duct in the third embodiment of the acoustic device of the present invention; [Figure 7] FIG. 11 is a diagram showing frequency characteristics of sound pressure heard near the opening of a duct in the fourth embodiment of the acoustic device of the present invention; [Figure 8] A diagram showing frequency characteristics of sound pressure heard near the opening of a duct in an acoustic device of a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In the acoustic device of the present invention, at least an enclosure and a speaker unit are fixed to a seat, and preferably these are embedded inside the seat. The enclosure and the speaker unit are fixed inside a seat back as in the first embodiment shown in FIG. 1, or fixed inside a seat cushion as in the second embodiment shown in FIG. 3. Alternatively, the enclosure and the speaker unit can be made small and fixed inside a headrest. The seat is installed inside the passenger compartment of an automobile, or installed inside a vehicle other than an automobile, such as a train. Alternatively, the seat may be one installed in a theater, a game center, or the like, or may be for home use.

[0019] 1 and 2 show an audio device 10 according to a first embodiment of the present invention. This audio device 10 is for mounting on a vehicle. In Fig. 1 and Fig. 2, the X1-X2 direction is the front-rear direction, the X1 direction is the forward direction, i.e., the traveling direction of the vehicle, and the X2 direction is the rearward direction. Y1-Y2 is the up-down direction, with the Y1 direction being upward and the Y2 direction being downward.

[0020] 1 shows a seat 1 which is a driver's seat in a vehicle, and a steering wheel 5 which is located in front of the seat 1 (in the X1 direction). The seat 1 has a seat back 2, a seat cushion 3, and a headrest 4. A listener 6 who is seated in the seat 1 is the driver, and has a torso 7 and a head 8. The head 8 is located in front of the headrest 4, and the left and right ears E of the head 8 are the listening positions.

[0021] As shown in FIG. 2, the acoustic device 10 has an enclosure 11, a duct 12, and a speaker unit 20, and constitutes a so-called bass reflex type speaker system. The enclosure 11 has a mounting hole (baffle opening) 11a that opens on a surface facing forward (X1 direction) and a connecting port 11b that opens on a surface facing upward (Y1 direction). The enclosure 11 is a sealed box with no openings formed except for the mounting hole 11a and the connecting port 11b. The speaker unit 20 is attached to the mounting hole 11a. As shown in FIG. 1, the enclosure 11 and the speaker unit 20 are fixed inside the seat back 2. One end of the duct 12 is a connecting end 12a that is connected to the connecting port 11b of the enclosure 11, and the internal space of the duct 12 and the internal space of the enclosure 11 communicate with each other. The other end of the duct 12 is an opening 12b. The opening 12b functions as a sound outlet that releases sound pressure to the outside. As shown in Fig. 1, the opening 12b of the duct 12 is located at the upper part of the seat back 2 and opens toward the ear E of the listener 6 near the ear E.

[0022] The position of the ears E of an adult of a normal build seated on the seat 1 when the head 8 is in contact with the headrest 4 is the listening position of the acoustic device 10. Two ducts 12 are connected to the enclosure 11, and the openings 12b of the two ducts 12 are open to positions close to the left and right ears E of the listener 6. Alternatively, two sets of acoustic devices 10 each having one duct 12 connected to the enclosure 11 equipped with the speaker unit 20 may be provided, and each acoustic device 10 may be provided inside the seat back 2, and the openings 12b of the ducts 12 of each acoustic device 10 may be open to positions close to the left and right ears E. At least a part of the duct 12 is provided inside the seat back 2, but in order to facilitate the arrangement and routing of the duct 12 inside the seat back 2, it is preferable that the duct 12 is formed of a flexible hose. The cross section of the duct 12 is circular, elliptical, rectangular, or the like, and the cross-sectional area is constant over the entire length of the duct.

[0023] FIG. 2 shows the center line Os of the speaker unit 20. The speaker unit 20 has a frame 21 fixed to the mounting hole 11a of the enclosure 11 with the center line Os tilted slightly clockwise with respect to the front-rear direction (X1-X2 direction). The frame 21 has a magnetic circuit section 22 fixed to one side along the center line Os, and a cone-shaped diaphragm 23 provided on the other side along the center line Os. A bobbin extends from the center of the diaphragm 23 to the left side of the figure along the center line Os, a voice coil is wound around the bobbin, and the voice coil is located within the magnetic gap of the magnetic circuit section 22. A hole formed at the connection between the diaphragm 23 and the bobbin is covered with a cap member on the right side of the figure. The diaphragm 23, the bobbin, the voice coil, the cap member, and the like constitute the vibration section of the speaker unit 20. The outer periphery of the diaphragm is supported by the frame 21 by an edge member, and the bobbin is supported by the frame by a damper member. The edge member and the damper member function as part of a spring support system that supports the vibrating part so that it can vibrate freely along the center line Os. A part of the mass of this spring support system is added to the mass of the vibrating part.

[0024] In the speaker unit 20, the vibration part including the diaphragm 23 is vibrated linearly along the center line Os within the frame 21 by electromagnetic force excited by the voice current given to the voice coil and the transverse magnetic flux given to the voice coil from the magnetic circuit part 22. The vibration of the diaphragm 23 gives an internal sound pressure (internal pressure wave) Pi toward the internal space of the enclosure 11, and an external sound pressure (external pressure wave) Po toward the external space of the enclosure 11. The internal sound pressure Pi and the external sound pressure Po have air density periods that differ by 180 degrees, and are in opposite phase to each other. As shown in FIG. 1, the position of the ear E when the listener 6 sits and places his / her head 8 against the headrest 4 is the listening position, and the linear distance Ld from the listening position to the center of the opening of the opening 12b of the duct 12 is shorter than the linear distance Ls from the listening position to the center of gravity of the diaphragm 23 of the speaker unit 20. The linear distance Ls is preferably at least twice, and more preferably at least three times, the linear distance Ld. The linear distance Ld is about 100 mm to 200 mm, for example, 150 mm.

[0025] Next, the operation of the audio device 10 will be described. In the acoustic device 10 shown in Fig. 1 and Fig. 2, a Helmholtz resonator is configured by an enclosure 11 and a duct 12. Without taking into consideration the operation of the speaker unit 20, the Helmholtz resonator has a predetermined resonance frequency Fd. The resonance frequency Fd is physically calculated from the internal volume (V) of the enclosure and the duct path length (L) and cross-sectional area (S) of the duct, and is found by the formula Fd = (C / 2·π)√(S / V·L); (C is the speed of sound). The resonance frequency Fd is inversely proportional to the internal volume (V) of the enclosure and the duct path length (L), and proportional to the cross-sectional area (S) of the duct.

[0026] When the speaker unit 20 operates, the internal sound pressure Pi generated by the operation of the diaphragm 23 becomes an input pressure wave to the Helmholtz resonator. When the frequency of the input pressure wave is equal to or close to the resonance frequency Fd, the air in the duct 12 resonates, and the sound pressure radiated from the opening 12b of the duct 12 increases. At this time, the vibration of the internal sound pressure Pi given by the diaphragm 23 and the vibration of the air in the duct 12 are in opposite phases to each other, and the sound pressure radiated to the outside from the opening 12b of the duct 12 and the external sound pressure Po radiated from the speaker unit 20 to the outside of the enclosure 11 are in phase. In a band where the frequency of the internal sound pressure Pi is higher than the resonance frequency Fd, the sound pressure radiated from the opening 12b of the duct 12 decreases as the frequency of the internal sound pressure Pi increases. This is because when the frequency of the input pressure wave to the Helmholtz resonator is in a frequency band higher than the resonant frequency Fd, even if the air inside the enclosure 11 expands and contracts, the air in the duct 12 finds it difficult to follow, and the air in the duct 12 becomes difficult to move.

[0027] When the frequency of the internal sound pressure Pi input to the enclosure 11 falls in a band lower than the resonance frequency Fd of the Helmholtz resonator, the spring function of the air inside the enclosure 11 decreases, and the change in the air pressure inside the enclosure 11 is transmitted directly to the inside of the duct 12, causing the air inside the duct 12 to vibrate in phase with the diaphragm 23 of the speaker unit 20. When the sound pressure radiated from the opening 12b of the duct 12 vibrates in phase with the internal sound pressure Pi, the external sound pressure Po radiated from the speaker unit 20 toward the outside of the enclosure 11 and the sound pressure radiated from the opening 12b of the duct 12 have opposite phases. In a conventional bass reflex speaker system using a Helmholtz resonator, the listening position is located away from both the opening 12b of the duct 12 and the speaker unit 20, so the sound pressure from the opening 12b and the external sound pressure Po, which are in opposite phase to each other, interfere with each other in a counter-offering manner, and the audible sound pressure attenuates more as the operating frequency of the diaphragm 23 of the speaker unit 20 becomes lower.

[0028] 1, if the listening position is set at a position where the linear distance Ld from the opening 12b of the duct 12 is closer than the linear distance Ls from the speaker unit 20, the listener 6 can directly hear the sound pressure from the opening 12b without being significantly affected by the interference of the external sound pressure Po emitted from the speaker unit 20, even when the speaker unit 20 operates at a frequency lower than the resonance frequency Fd. Therefore, the acoustic device 10 of the embodiment sets the resonance frequency F0 of the vibration system mass Mms of the speaker system in the bass reflex structure to a band lower than the resonance frequency Fd of the Helmholtz resonator, and increases the amplitude of the air in the duct 12 in the band where the diaphragm 23 of the speaker unit 20 and the air in the duct 12 vibrate in phase, thereby amplifying the sound pressure acting on the ear E from the opening 12b of the duct 12.

[0029] 4 to 7 show frequency characteristics of sound pressure obtained from the opening 12b of the duct 12 in each embodiment of the present invention. As shown in each figure, when the resonance frequency F0 of the speaker system in the bass reflex structure is set to a band lower than the resonance frequency Fd of the Helmholtz resonator, it becomes possible to amplify the sound pressure acting on the ear E from the opening 12b of the duct 12 in the band from the vicinity of the resonance frequency F0 to the vicinity of the resonance frequency Fd. When the resonance frequency F0 of the vibration system mass Mms is set to a low frequency range below 100 Hz, it becomes possible for the listener 6 to hear a reproduced sound with an emphasis on the low frequency range at his / her ear E. In addition, when the resonance frequency F0 of the vibration system mass Mms is set to a band below 100 Hz and the resonance frequency Fd of the Helmholtz resonator is set to a band higher than 100 Hz, the sound pressure applied from the opening 12b of the duct 12 to the ear E has a peak located near the resonance frequency F0 in a frequency band lower than 100 Hz and a peak located near the resonance frequency Fd in a frequency band higher than 100 Hz, and functions as a bandpass acoustic device in which the frequency band from near the resonance frequency F0 to near the resonance frequency Fd is emphasized. As shown in each embodiment, when the linear distance Ld from the opening 12b of the duct 12 to the ear E is 150 mm, the sound pressure difference in the band from the peak near the resonance frequency F0 to the peak near the resonance frequency Fd is 10 dB or less, and the sound pressure decreases as the frequency becomes lower than the peak near the resonance frequency F0, and the sound pressure decreases as the frequency becomes higher than the peak near the resonance frequency Fd.

[0030] The sound pressure acting on the ear E from the opening 12b of the duct 12 is high between a peak near the resonance frequency F0 and a peak near the resonance frequency Fd, but the sound pressure from the opening 12b and the outward sound pressure Po from the speaker unit 20 are in opposite phase. Therefore, at a location away from both the opening 12b and the speaker unit 20, the opposite phase sound pressures interfere and cancel each other out, and the audible sound pressure drops significantly. Therefore, low-frequency sounds are less likely to be transmitted to a location away from the seat 1 where the listener 6 is seated. In particular, the low-frequency sound pressure from the peak near the resonance frequency F0 to the peak near the resonance frequency Fd is likely to propagate to the surroundings. For example, when the seat 1 is inside the cabin of a car, low-frequency sounds are likely to propagate to the outside of the car body, but as described above, the opposite phase sound pressures interfere and cancel each other out, making it easier to prevent sound leakage to the outside of the car body.

[0031] In the acoustic device 10, a relatively low-frequency sound pressure is emphasized and given to the ears of the listener 6 from the opening 12b of the duct 12, but it is also possible to generate mid-frequency sound pressure with the acoustic device 10. It is also possible to generate mainly low-frequency sound pressure with the acoustic device 10, and further provide another speaker unit in the seat 1 or around the listener 6 that emits mid- to high-frequency sounds.

[0032] Fig. 3 shows an acoustic device 110 according to a second embodiment of the present invention. Like the acoustic device 10 shown in Fig. 2, this acoustic device 110 has a Helmholtz resonator consisting of an enclosure 11 and a duct 12 connected to the enclosure 11, and a speaker unit 20 is fixed to the enclosure 11. The enclosure 11 and the speaker unit 20 are fixed inside the seat cushion 3. The duct 12 is made up of a flexible hose, and a part of it passes through the inside of the seat cushion 3 and the inside of the seat back 2. An opening 12b of the duct 12 is located at the top of the seat back 2 and opens at a position close to the ear E of the listener 6. In the acoustic device 110 of the second embodiment, the speaker unit 20 is provided inside the seat cushion 3, so that the linear distance Ls from the center of gravity of the diaphragm 23 of the speaker unit 20 to the ear E at the listening position can be secured to be long, and the linear distance Ls can be set to be four or more times, or even five or more times, the linear distance Ld from the opening 12b of the duct 12 to the ear E. By increasing the difference between the linear distances Ls and Ld, it becomes possible to hear the sound emitted from the opening 12b of the duct 12 without significant interference from the external sound pressure Po of the speaker system.

[0033] In the acoustic device 10 of the first embodiment shown in Fig. 1, the outward sound pressure Po from the speaker unit 20 is directed toward the torso of the listener 6, and in the acoustic device 110 of the second embodiment shown in Fig. 3, the outward sound pressure Po from the speaker unit 20 is directed toward the buttocks of the listener 6. In the acoustic devices 10 and 110, the resonance frequency F0 of the vibration system mass Mms is set to a band below 100 Hz, so that the bass is emphasized and given from the opening 12b of the duct 12 toward the ear E, and the outward sound pressure Po with the same period as this bass is given to the body of the listener 6 as vibration, so that the listener 6 can feel the bass with his whole body. EXAMPLES

[0034] Figures 4 to 7 show examples of the acoustic devices 10, 110 of the present invention, and Figure 8 shows a comparative example. Each of the examples and the comparative example is a simulation result showing the frequency characteristics of sound pressure when a 1 W sine wave is input to the voice coil of the speaker unit 20, and the sound pressure is assumed to be measured at a position 150 mm away from the opening 12b of the duct 12 under the condition that the outward sound pressure Po from the speaker unit 20 is ignored. The horizontal axis is a logarithmic axis showing frequency (Hz), and the vertical axis shows sound pressure level (dB).

[0035] <Example 1> 4 shows the frequency characteristics in Example 1. The parameters in Example 1 are as follows. Capacity of enclosure 11: 150cc Duct 12 length: 50cm Inner diameter of duct 12 (inner diameter): 2 cm Effective vibration diameter of diaphragm 23: 6.2 cm Resonant frequency of Helmholtz resonator Fd: 110Hz Resonant frequency of the vibration system mass F0: 48Hz

[0036] <Example 2> 5 shows the frequency characteristics in Example 2. The parameters in Example 2 are as follows. Capacity of enclosure 11: 300cc Duct 12 length: 50cm Inner diameter of duct 12 (inner diameter): 3 cm Effective vibration diameter of diaphragm 23: 6.2 cm Resonant frequency of Helmholtz resonator Fd: 107Hz Resonant frequency of the vibration system mass F0: 68Hz

[0037] <Example 3> 6 shows the frequency characteristics in Example 3. The parameters in Example 3 are as follows. Capacity of enclosure 11: 300cc Duct 12 length: 50cm Inner diameter of duct 12 (inner diameter): 3 cm Effective vibration diameter of diaphragm 23: 8 cm Resonant frequency of Helmholtz resonator Fd: 112Hz Resonant frequency of the vibration system mass F0: 48Hz

[0038] <Example 4> 7 shows the frequency characteristics in Example 4. The parameters in Example 4 are as follows. Capacity of enclosure 11: 200cc Duct 12 length: 30cm Inner diameter of duct 12 (inner diameter): 3 cm Effective vibration diameter of diaphragm 23: 8 cm Resonant frequency of Helmholtz resonator Fd: 118Hz Resonant frequency of the vibration system mass F0: 70Hz

[0039] <Comparative Example> Fig. 8 shows the frequency characteristics of a comparative example. The comparative example is a simulation result showing the frequency characteristics of the sound pressure level near the opening of the duct in a general bass reflex speaker system. The resonance frequency Fd of the Helmholtz resonator is set to about 70 Hz, and the resonance frequency F0 of the vibration system mass is set to a frequency band higher than the resonance frequency Fd.

[0040] As shown in the comparative example of Fig. 8, in a conventional bass reflex speaker system, the resonance frequency Fd of the Helmholtz resonator is set to a frequency band lower than the resonance frequency F0 of the speaker system, thereby increasing the sound pressure near the resonance frequency Fd. However, the sound pressure is increased only in a narrow band near the resonance frequency Fd. In contrast, in the first to fourth embodiments, the sound pressure acting on the ear E from the opening 12b of the duct 12 can be increased in a wide band from the resonance frequency F0 of the vibration system mass of the speaker system to the resonance frequency Fd of the Helmholtz resonator, and the bass sound in a wide band can be heard with emphasis.

[0041] According to the embodiment shown in Figures 4 to 7, in order to increase the load mass of the air in the duct 12 and set the resonant frequency F0 of the vibration system mass of the speaker system to a band lower than the resonant frequency Fd of the Helmholtz resonator, it is preferable to make the length of the duct 12 8 times or more, and more preferably 10 times or more, the inner diameter (inner diameter) of the duct 12. [Explanation of symbols]

[0042] 1 sheet 2 Seat back 3 Seat cushion 4 Headrest 10,110 Sound equipment 11 Enclosure 12 Duct 12b opening 20 Speaker unit 22 Magnetic circuit section 23 Vibration plate E ear (listening position)

Claims

1. An acoustic device having an enclosure, a duct communicating with an internal space of the enclosure, and a speaker unit for applying sound pressures of opposite phases to the inside and outside of the enclosure, At least the enclosure and the speaker unit are fixed to a seat, a resonant frequency Fd of a Helmholtz resonator formed by the enclosure and the duct is set to a frequency band higher than a resonant frequency F0 of a vibration system mass including a mass of a vibration part of the speaker unit and a load mass of air in the duct; An acoustic device, wherein a listening position is set at a position where a linear distance Ld from the opening of the duct is closer than a linear distance Ls from the diaphragm of the speaker unit.

2. the speaker unit and the enclosure are housed in a seat back or a seat cushion, 2. The acoustic device of claim 1, wherein a sound pressure having an opposite phase to the sound pressure applied inside the enclosure is directed from the speaker unit to a listener seated in a seat, and the opening of the duct opens near the ears of the listener.

3. 3. The acoustic device according to claim 2, wherein the duct is a flexible hose, at least a portion of which is housed in the seat back.

4. 4. An acoustic device according to claim 1, wherein the resonance frequency F0 of the vibration system mass is less than 100 Hz.

5. The sound pressure obtained from the opening of the duct is 5. The acoustic device according to claim 4, further comprising a peak located in a frequency band lower than 100 Hz and a peak located in a frequency band higher than 100 Hz.

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