Acoustic device and sound masking system

Abstract

To provide an acoustic device for effectively inhibiting a large difference between a directly under sound pressure level and a sound pressure level at another position from being generated even when being exposed and arranged in an above-floor space, and a sound masking system in which a characteristic of the acoustic device is used.SOLUTION: An acoustic device 1 comprises a speaker 2 for generating masking sound and a cover member 3 that covers the speaker 2 and is configured to be capable of being arranged on a ceiling portion T of an indoor space S in a state of being exposed to the space S. The cover member 3 has a form for discharging the sound from the speaker 2 to the outer surroundings and comprises a bottom wall 31 having at least a sound-absorbing function on an undersurface. The cover member 3 may comprise a top wall 33 in addition to the bottom wall 31.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an acoustic device and a sound masking system using the acoustic device. [Background technology]

[0002] In office buildings, it is common for floors to be divided into multiple areas. In such cases, there is a need to prevent conversations and other sounds from being heard and transmitted between adjacent areas, and various sound masking systems have been developed to meet this need.

[0003] A common type of sound masking system is one that places an acoustic device that outputs masking sound in the space above the ceiling formed between the ceiling panel facing the floor and the ceiling surface of the building (see, for example, Non-Patent Document 1).

[0004] Another possible method is to place the acoustic equipment exposed in the space above the floor, but if the acoustic equipment is placed exposed above the floor instead of in the attic, it is likely that a large difference will occur between the sound pressure level directly below the acoustic equipment and the sound pressure level in other locations, and it is expected that the sound intensity will easily vary in different areas on the floor.

[0005] Although it is possible to adjust the intensity of the sound by changing the hanging height of the sound device or by placing reflecting walls in appropriate locations, there is a need for sound devices that allow such adjustments at the time of installation to be completed as easily as possible.

[0006] The above explanation has focused on the acoustic equipment used in sound masking systems, but similar issues have also been pointed out for acoustic equipment used for regular background music. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] "Sound Masking System", Kokuyo General Catalog 2008 Furniture Edition, Kokuyo Co., Ltd., December 2007, p. 223 Summary of the Invention [Problem to be solved by the invention]

[0008] The main object of the inventions of claims 1 to 7 is to provide an acoustic device that can effectively prevent large differences in sound pressure levels between directly below and other positions even when the device is placed exposed in an above-floor space.

[0009] Furthermore, the main object of the inventions of claims 8 to 10 is to provide a sound masking system that can suppress unevenness in the sound pressure level of the masking sound at various locations in the above-floor space by using the acoustic devices of claims 1 to 7 as the sound source of the sound masking sound. [Means for solving the problem]

[0010] The acoustic device of the invention described in claim 1 comprises a speaker that generates sound and a cover member that covers the speaker, and is capable of being placed on the ceiling of an indoor space while being exposed to the air. The cover member is shaped so that sound from the speaker can be emitted to the surrounding area, and has a bottom wall on the underside that has at least sound-absorbing properties.

[0011] The acoustic device of the invention described in claim 2 is the device described in claim 1, wherein the cover member is approximately circular in plan view and has at least the bottom wall and a peripheral wall continuous with the outer peripheral edge of the bottom wall, and the speaker is arranged facing upward at approximately the center of the cover member.

[0012] The acoustic device according to the invention of claim 3 is the device of claim 2, wherein the cover member has a top wall on the top surface thereof that has a function of inverting sound.

[0013] The acoustic device according to the invention of claim 4 is the device of claim 3, wherein the bottom wall and the top wall are mainly made of sound-absorbing material.

[0014] The acoustic device according to the invention of claim 5 is the device of claim 4, wherein the sound absorber is a sound-absorbing felt board.

[0015] The acoustic device according to the invention of claim 6 is the device of claim 2, wherein the peripheral wall is mainly made of cloth fabric.

[0016] The acoustic device according to the invention of claim 7 is the device of claim 1, in which the cover member is suspended and supported below the ceiling surface via a suspension tool.

[0017] The sound masking system of the invention described in claim 8 comprises a plurality of acoustic devices described in claim 1, 2, 3, 4, 5, 6 or 7 arranged at intervals in the horizontal direction, and is configured to emit masking sound from the acoustic devices.

[0018] The sound masking system of the invention described in claim 9 is the system described in claim 8, which is configured so that the difference between the sound pressure directly below a specific sound device on the floor and the sound pressure at positions equidistant from two adjacent sound devices is within 2 dB.

[0019] The sound masking system of the invention described in claim 10 is the system described in claim 8, wherein each of the acoustic devices has built-in sound source data and an amplifier circuit for reproducing masking sound, and is configured so that the output level of the masking sound emitted from each of the acoustic devices can be individually adjusted. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide an acoustic device that can effectively suppress large differences in sound pressure levels between directly below it and other locations even when it is placed exposed in an above-floor space, and a sound masking system that makes use of the characteristics of that acoustic device. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic front view of a sound masking system according to an embodiment of the present invention; [Figure 2] FIG. 2 is an enlarged cross-sectional view of the vicinity of the acoustic device in the embodiment. [Figure 3] FIG. [Figure 4] FIG. [Figure 5] FIG. [Figure 6] FIG. [Figure 7] FIG. 7 is a cross-sectional view taken along line AA in FIG. [Figure 8] FIG. 2 is an explanatory diagram of a circuit for driving a speaker of the audio device. [Figure 9] FIG. 2 is a perspective view of a housing that constitutes a cover member of the acoustic device. [Figure 10] Front view of the same housing [Figure 11] FIG. 11 is a cross-sectional view taken along line BB in FIG. [Figure 12] FIG. 4 is an exploded perspective view showing the bottom wall and the top wall of the cover member. [Figure 13] FIG. 2 is an explanatory diagram for explaining the sound pressure characteristics of the acoustic device. [Figure 14] (a) is an enlarged cross-sectional view of the vicinity of an acoustic device showing another embodiment of the present invention, (2) is an enlarged cross-sectional view of the vicinity of an acoustic device showing yet another embodiment of the present invention, and (3) is an explanatory diagram of the parts used in the same embodiment. [Figure 15] FIG. 10 is a perspective view of a housing showing still another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] An embodiment of the present invention will be described below with reference to FIGS.

[0023] As shown in Figures 1 to 13, the sound masking system Z of this embodiment is composed of multiple acoustic devices 1, which will be described later, arranged horizontally at intervals U, and each acoustic device 1 emits a masking sound.

[0024] The acoustic device 1 includes a speaker 2 that generates at least a sound masking sound, and a cover member 3 that covers the speaker 2, and is disposed on the ceiling portion T of the indoor space S while being exposed to the space. In this embodiment, the speaker 2 is configured to be able to emit both the sound masking sound and background music sound, but it is of course possible to stop the background music sound and emit only the sound masking sound.

[0025] Specifically, the ceiling portion T in this embodiment is configured such that a ceiling board X is disposed via a girder W below an architectural ceiling V, such as a deck plate, as shown in Fig. 2, and the aforementioned space S is formed between the ceiling board X and the floor surface Y. Then, as shown in Figs. 1 to 7, an acoustic device 1 is suspended from the ceiling board X via a suspension mechanism 4.

[0026] As shown in Fig. 7, the speaker 2 is a conventional type and is disposed facing upward on the top surface of the speaker box 21. Inside the speaker box 21, as shown schematically in Fig. 8, a basic circuit board 20A is mounted, which includes: a USB memory 22a storing sound source data for sound masking sound, a USB memory 22b storing sound source data for background music sound, audio decoders 23a and 23b converting the digital audio data stored in the USB memories 22a and 22b into analog audio data, electronic volumes 24a and 24b individually adjusting the volume levels of the audio signals output from the audio decoders 23a and 23b, and a power amplifier 25 amplifying the audio signals that have passed through the electronic volumes 24a and 24b and supplying them to the speakers. 21a is a plate-shaped sound-absorbing material interposed between the basic circuit board 20A and the speaker 2.

[0027] The basic circuit board 20A is also provided with a volume control means 20B equipped with a CPU 26 and a remote control signal receiver 27. The volume control means 20B is used to separately adjust the volume for sound masking and the volume for background music. A memory attached to the CPU 26 stores a program for outputting control signals to the electronic volumes 24a and 24b when a volume command signal is received from a remote control 28 via the remote control signal receiver 27, so that the output of the speaker 2 corresponds to the volume command signal. These programs and circuit configurations are conventional, and therefore detailed description is omitted. Reference numeral 29 denotes a status memory that sequentially stores status information. The remote control signal receiver 27 is located at the center of the underside of the speaker box 21 and faces the space S above the floor Y through an opening 31b in a bottom wall 31 (described later).

[0028] The cover member 3 is shaped to be able to emit sound from the speaker 2 to the surrounding area, and is provided with a bottom wall 31 on the underside that has at least a sound-absorbing function. More specifically, as shown in Figures 3 to 7, the cover member 3 of this embodiment is generally circular in plan view and includes the bottom wall 31, a peripheral wall 32 that is continuous with the outer periphery of the bottom wall 31, and a top wall 33 that is continuous with the upper edge of the peripheral wall 32, and the speaker 2 is disposed in a generally central position within the cover member 3, facing upward.

[0029] Specifically, the cover member 3 includes a housing 35, a sound-absorbing felt board 31a covering the bottom surface of the housing 35, a breathable cloth 32a covering the periphery of the housing 35, and a sound-absorbing felt board 33a covering the top surface of the housing 35. As shown in FIGS. 9 to 11 , the housing 35 is made of wood, for example, and includes a circular lower ring plate 35a, a middle ring plate 35b arranged above the lower ring plate 35a with its axis aligned, an upper ring plate 35c arranged above the middle ring plate 35b with its axis aligned, and a plurality of vertical frame plates 35d connecting the lower, middle, and upper ring plates 35a, 35b, and 35c. The vertical frame plates 35d are arranged radially in a plan view at intervals in the circumferential direction, and gaps 35e are formed between the vertical frame plates 35d to allow air and sound to pass through.

[0030] 4, 5, 7, 12, etc., the bottom wall 31 of the cover member 3 is mainly composed of a sound-absorbing felt board 31a, which serves as a sound absorber, supported by a ring plate 35a below the housing 35. A cloth fabric (not shown) may be attached to the underside of the sound-absorbing felt board 31a. The bottom wall 31 can also be modified by stacking multiple sound-absorbing felt boards 31a.

[0031] As shown in FIGS. 5 and 7, the peripheral wall 32 of the cover member 3 is made up of vertical frames 35d of the housing 35 and a cloth fabric 32a stretched on the outside of these vertical frames 35d.

[0032] As shown in Figures 3, 5, 12, etc., the top wall 33 of the cover member 3 is mainly composed of a sound-absorbing felt board 33a, which serves as a sound absorber, supported by a ring plate 35c on the top of the housing 35. A cloth or similar material may be attached to the top surface of this sound-absorbing felt board 33a. Furthermore, as shown in Figure 12, the sound-absorbing felt board 33 may be structured so that it can be divided into two parts along an imaginary line. Furthermore, this top wall 33 can be modified by stacking multiple sound-absorbing felt boards 33a.

[0033] 4 and 7, an opening 31b is formed in the center of the bottom wall 31, i.e., in the center of the sound-absorbing felt board 31a, and the speaker box 21 that holds the speaker 2 is mounted on the upper surface of the bottom wall 31. The remote control signal receiver 27, which is provided in the center of the lower surface of the speaker box 21, faces the space S through the opening 31b in the bottom wall 31.

[0034] Additionally, the peripheral edge of sound-absorbing felt board 33a, which is a sound absorber, is attached to the underside of ring plate 35c on top of housing 35, and a reinforcing frame member 33b for attaching hanging mechanism 4 is attached to the bottom of sound-absorbing felt board 33a. Reinforcing frame member 33b is made of metal, for example, with a downward-facing channel-like cross section, and both ends are fastened to ring plate 35c on top of housing 35. In this embodiment, reinforcing frame member 33b is in the form of a single horizontal bar, but it may also be radial in plan view, for example.

[0035] The suspension mechanism 4 includes a duct rail 41, which is provided on the underside of the ceiling panel X and has structural support and power distribution functions, and a suspension device 42 for supporting the cover member 3 of the audio device 1 on the duct rail 41. The suspension device 42 is a string-like device with an upper mounting portion 42a at its upper end supported on the duct rail 41 so that its mounting position can be changed, and a lower mounting portion 42b at its lower end attached to the reinforcing frame member 33b of the cover member 3. The suspension mechanism 4 is well known as a mechanism for suspending and supporting lighting fixtures and the like from a ceiling, and a detailed description thereof will be omitted. The power cord 43 for supplying power to the speaker box 21 may be partially exposed outside the suspension device 42 as in the illustrated example, or the entire cord may be inserted inside the suspension device 42.

[0036] With an acoustic device 1 configured as described above, sound emitted upward from the speaker 2 is deflected downward by the presence of the top wall 31 of the cover member 3, passes through the peripheral wall 32, and is emitted to the surrounding area. Furthermore, sound reflected near the center of the top wall 33 travels approximately directly downward, but the presence of the bottom wall 31 of the cover member 3, which has sound-absorbing properties, near the area directly below alleviates the phenomenon in which the sound pressure level at position P0 directly below the acoustic device 1 becomes extremely high compared to the sound pressure levels at other surrounding positions. Therefore, even if the acoustic device 1 is placed on the ceiling portion T of an indoor space S while exposed to the space S, uneven sound pressure levels in the space S can be effectively prevented.

[0037] In this embodiment, the cover member 3 is generally circular in plan view, and the speaker 2 is disposed in the approximate center thereof facing upward, so that sound can be emitted evenly in a 360-degree range. This makes it possible to deliver sound with approximately uniform sound pressure throughout the entire space S.

[0038] Furthermore, because sound absorbing materials with sound absorbing properties are used not only on the bottom wall 31 but also on the top wall 33, it is possible to further reduce the sound pressure level of sound that is reversed near the center of the top wall 33 and directed directly downward. This makes it possible to effectively prevent the sound pressure level at the position P0 directly below the acoustic device 1 from becoming too high.

[0039] 13 shows an example of measurement of how the sound pressure level on the floor surface Y is distributed when only the diameter of the cover member 3 is changed for the acoustic device 1 shown in the above-mentioned Figures 2 to 12. Figure 13 is a sound pressure characteristics table showing the results of measuring the sound pressure level on the floor surface Y using two types of devices (referred to as "Example 1" and "Example 2") with different dimensions for the bottom wall 31 and the top wall 33.

[0040] Specifically, Example 1 uses a wooden housing 35, and the diameter of the sound-absorbing felt boards 31a, 33a on the bottom wall 31 and top wall 33 is set to 480 mm, which is shown by the dashed line Q in the sound pressure characteristics table. On the other hand, Example 2 uses a wooden housing 35 having the same height dimensions, and the diameter of the sound-absorbing felt boards 31a, 33a on the bottom wall 31 and top wall 33 is set to 550 mm, which is shown by the solid line R in the sound pressure characteristics table.

[0041] The measurements were carried out in an environment where the height from floor Y to ceiling panel X was set to 2850 mm, and the height from floor Y to the bottom wall 31 of the acoustic device 1 was set to 2410 mm. Sound pressure levels were measured at 0.5 m intervals between a position P0 directly below the acoustic device 1 on floor Y and a furthest position P3.5, 3.5 m horizontally away from this position P0.

[0042] 13, the results show that for Example 1 (dashed line Q), the sound pressure level at the position directly below P0 was 57 dB, and the sound pressure level at the farthest position P3.5 was 49.6 dB, resulting in a sound pressure difference of 7.4. On the other hand, for Example 2 (solid line), the sound pressure level at the position directly below P0 was 53.3 dB, and the sound pressure level at the farthest position P3.5 was 49.4 dB, resulting in a sound pressure difference of 3.9 dB. It can be seen that the sound pressure difference is not extremely large in either Example 1 or 2, but in particular, for Example 2, the sound pressure difference is small at 3.9 dB, indicating that the sound pressure level within the space S is equalized.

[0043] Furthermore, by repeating similar tests while changing the dimensions of the acoustic device 1, it was found that the sound pressure difference did not change much even if the diameter of the sound-absorbing felt boards 31a, 33a of the cover member 3 was increased beyond 550 mm, but that the sound pressure difference increased as the diameter was decreased. Therefore, from these results, it was confirmed that in the above-mentioned measurement environment simulating a standard office space S, the lower limit of the diameter of the sound-absorbing felt boards 31a, 33a is about 550 mm, and that if the diameter is made larger than that lower limit, it can be expected that the sound pressure level within the space S will be equalized.

[0044] Furthermore, because this acoustic device 1 has not only bottom wall 31 with sound absorption capabilities but also top wall 33 with sound inversion capabilities, the ability to reflect sound emitted from speaker 2 downward and release it into the surroundings can be determined in advance at the design stage. This makes it easier to adjust the sound pressure level during construction than when sound emitted upward from speaker 2 is reflected off ceiling panel X of space S, for example.

[0045] Furthermore, if the top wall 33 is also made primarily of sound-absorbing material in addition to the bottom plate 31, as in this embodiment, the sound pressure level of the sound directed substantially directly downward from the top wall 33 can be reduced, and the problem of the sound pressure level directly below the acoustic device 1 becoming extremely high can be more effectively prevented. Moreover, if sound-absorbing felt boards 31a, 33a are used as the sound absorbers for the bottom wall 31 and the top wall 33, the bottom wall 31 and the top wall 33 can be given appropriate rigidity and can also be made lighter.

[0046] Furthermore, since the peripheral wall 32 of the cover member 3 is mainly made of cloth fabric 32a, not only can it look good, but it can also effectively reduce noise in the high frequency range.

[0047] Furthermore, in this embodiment, the cover member 3 is suspended below the underside (ceiling surface) of the ceiling board X via the suspension device 42, so the installation height of the acoustic device 1 can be easily adjusted. Moreover, because the suspension device 42 is supported by a duct rail 41 fixed to the underside of the ceiling board X, the installation position of the acoustic device 1 can also be adjusted appropriately in the horizontal direction. This makes it easy to install the acoustic device 1 in the optimal position without requiring much effort.

[0048] In this embodiment, a sound masking system Z is formed by placing multiple acoustic devices 1 as described above on the ceiling T of space S. Each acoustic device 1 has the performance as described above, namely, the ability to prevent the sound pressure level directly below the acoustic device 1 from becoming too high. Therefore, when a sound masking sound is generated from each acoustic device 1, the sound masking sound can be diffused throughout space S located above floor Y without causing large sound pressure variations.

[0049] Each acoustic device 1 can change the difference in sound pressure between the position directly below it on the floor surface Y and the position equidistant from two adjacent acoustic devices 1 by adjusting the size, separation distance, or material of the bottom wall 31 and top wall 33 of the cover member 3. When using these acoustic devices 1 in a sound masking system, it is desirable to set the sound pressure difference to within approximately 2 dB. In other words, such a setting makes it possible to provide high-quality sound masking sound with little sound unevenness anywhere in the space above the floor surface.

[0050] Furthermore, in this sound masking system Z, the volume of the sound masking sound emitted from each acoustic device 1 can be adjusted individually, so when there are partitions, furniture, etc. that obstruct the diffusion of sound, it is possible to correct the sound pressure level of each part of the sound masking sound by individually adjusting the volume of each acoustic device 1. That is, as described above, each acoustic device 1 is equipped with sound source data (data in the sound masking USB memory 22a) and an amplifier (power amplifier 25) for reproducing the sound masking sound, and is configured so that the volume of the sound masking sound emitted from each acoustic device 1 can be individually adjusted using a remote control 28 or the like.

[0051] Therefore, it is possible to provide sound masking sound with less uneven sound pressure using fewer acoustic devices 1 than in conventional sound masking systems that simultaneously change the volume of multiple acoustic devices 1. In other words, conventional sound masking systems tend to place many acoustic devices closely together to prevent local drops in sound pressure level due to the presence of furniture, partitions, etc., but with the sound masking system Z, local changes in sound pressure level can be corrected by adjusting the volume of each individual acoustic device 1, making it possible to achieve masking performance that is comparable to that of conventional systems using fewer acoustic devices 1.

[0052] It should be noted that the present invention is not limited to the above-described embodiment, and the following embodiments are also included.

[0053] For example, the cover member of the invention according to claim 1 may be any type that is configured to allow sound from the speaker to be emitted to the surroundings, such as a cover member that does not have a peripheral wall or a top wall and has only a bottom wall below the speaker, or a cover member that does not have a top wall and is primarily configured with a bottom wall and peripheral walls. In other words, the cover member may have at least a bottom wall that covers the underside of the speaker. Either type of cover member may be attached directly to the ceiling surface, or may be suspended via a suspension device.

[0054] Other embodiments using a suspension mechanism with a suspension tool include those shown in Figures 14(a) and 14(b). The acoustic device 1 shown in Figure 14(a) is attached via a suspension mechanism 4 to a skeleton-type ceiling portion T where the architectural ceiling V is exposed. In this case, a duct rail 41 of the suspension mechanism 4 is attached to the architectural ceiling V via a mounting member 44. Here, parts that are the same as or correspond to those in the above-mentioned embodiment are given the same reference numerals and will not be described again. Meanwhile, the acoustic device 1 shown in Figure 14(b) is suspended from a ceiling panel X via a suspension mechanism 4 that has a hook ceiling 45 instead of a duct rail 41. The hook ceiling 45 is a typical type used when suspending a lighting device from a ceiling, and has a pair of hook holes 45a on its underside, as shown in Figure 14(c). Then, by inserting a pair of terminals (not shown) protruding from the upper mounting portion 42a of the suspension device 42 into the hook holes 45a and rotating it horizontally, the mechanical and electrical connections between the hook ceiling 45 and the suspension device 42 are simultaneously made. In Figure 14(b), the hook ceiling 45 is fastened to the underside of the ceiling board X, but in the case of a skeleton ceiling, the hook ceiling 45 may be attached to the architectural ceiling V via a mounting member (not shown).

[0055] Furthermore, in the above-described embodiment, the housing of the cover member is made of wood, but the housing may be made of synthetic resin as shown in Fig. 15. That is, this housing 135 is formed by integrally molding a lower ring plate 135a, a vertical frame 135d continuous with the outer periphery of this lower ring plate 135a, and an upper ring plate 135c continuous with the upper end of this vertical frame 135d from synthetic resin.

[0056] Furthermore, the speakers do not necessarily have to be facing exactly straight up, but may be positioned at an angle.The number of speakers arranged inside one cover member is also not limited to one, but multiple speakers may be arranged.

[0057] Furthermore, the sound masking sound source and the background music sound source are not limited to those in the illustrated embodiment, and various modifications are possible without departing from the spirit of the present invention. For example, in the embodiment shown in FIG. 8, a sound masking sound is generated using a USB memory 22a for the sound masking sound source and an audio decoder 23a. However, the USB memory 22a may be eliminated, and a DSP (digital signal processor) may be provided in place of the audio decoder 23a to generate a similar sound masking sound. That is, a sound source signal may be generated from a programmed DSP, and sound may be emitted from the speaker 2. In this case, the background music sound source may be a USB memory, as in the above embodiment. Of course, an SD card or the like may be used instead of a USB memory.

[0058] In addition, various modifications are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0059] S…Space T…Ceiling part X: Ceiling board Y…Floor surface Z...Sound masking system 1…Sound equipment 2. Speaker 3...Cover member 31...Bottom wall 31a...Sound-absorbing felt board 32...peripheral wall 32a...Cloth fabric 33...Ceiling wall 33a...Sound-absorbing felt board 35…Case 4...Hanging mechanism 41...Duct rail 42...Hanging device 135…Case

Claims

1. An acoustic device that includes a speaker that generates sound and a cover member that covers the speaker, and that can be placed on the ceiling of an indoor space in an exposed state, The cover member is configured to allow sound from the speaker to be emitted to the surroundings, and has a bottom wall on the underside that has at least a sound-absorbing function.

2. The acoustic device of claim 1, wherein the cover member has a generally circular shape in a plan view and includes at least the bottom wall and a peripheral wall continuous with the outer peripheral edge of the bottom wall, and the speaker is arranged facing upward at approximately the center of the cover member.

3. 3. The acoustic device according to claim 2, wherein the cover member has a top wall on its upper surface that has a function of inverting sound.

4. 4. The acoustic device according to claim 3, wherein the bottom wall and the top wall are mainly made of sound absorbing material.

5. 5. The acoustic device according to claim 4, wherein the sound absorbing body is a sound absorbing felt board.

6. 3. The acoustic device according to claim 2, wherein the peripheral wall is mainly made of cloth material.

7. 2. The acoustic device according to claim 1, wherein the cover member is suspended below a ceiling surface via a suspension device.

8. 8. A sound masking system comprising a plurality of acoustic devices according to claim 1, 2, 3, 4, 5, 6 or 7 arranged at intervals in the horizontal direction, and emitting a sound masking sound from said acoustic devices.

9. 9. The sound masking system of claim 8, wherein the difference between the sound pressure directly below a specific acoustic device on the floor and the sound pressure at positions equidistant from two adjacent acoustic devices is set to be within 2 dB.

10. Each of the acoustic devices has built-in sound source data and an amplifier for reproducing a sound masking sound, 9. The sound masking system according to claim 8, wherein the output level of the sound masking sound emitted from each of the acoustic devices can be adjusted individually.

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