JPH01156797A - Sound absorber - Google Patents

Abstract

PURPOSE: To obtain flat frequency characteristics in the range from the low frequency range to the intermediate and high frequency range and make the device small-sized and thin by putting three sound absorbing elements consisting of a vibrating pipe, a diaphragm, and a porous sound absorber in one enclosure. CONSTITUTION: The hollow enclosure 10 is formed of a front panel 11, a rear panel 12, and side plates 13. Then a main hole 14 is formed in the center part of the panel 11 and subordinate holes 15 are provided in its periphery. Then the vibrating pipe 1 is provided closing the main hole 14 and the diaphragm 13 is provided closing the subordinate holes 15; and an air layer 16 is formed in the enclosure 10. The porous sound absorber 6, on the other hand, is put in the pipe 1, but this sound absorber 6 passes low-frequency sound waves and never impedes the vibration of the pipe 1. Thus, the three sound absorbing elements consisting of the vibrating pipe, diaphragm, and sound absorber are put in the one enclosure to obtain the flat frequency characteristics in the range from the low frequency range to the intermediate and high frequency range and make the device small-sized and thin.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a sound absorbing device disposed in a room such as a listening room or a musical instrument performance room where acoustic characteristics need to be considered.

[Background technology] Generally, in listening rooms and musical instrument performance rooms, interior panels such as reflective panels and sound-absorbing panels are combined as appropriate.
It is designed to achieve the acoustic characteristics of the entire room. Here, the important points are control of the absolute value of the reverberation time according to the application and flattening of the frequency characteristics of the reverberation time.

The absolute value and frequency characteristics of the reverberation time in a room largely depend on the absolute value and frequency characteristics of the sound absorption coefficient of interior panels. ) and sound-absorbing panels (with an average sound absorption coefficient of 0.3
~1.0), it becomes easier to control the acoustic characteristics of the room, and it also causes the so-called color range of reverberant sound, in which the frequency characteristics of reflected sound change greatly relative to the incident sound. It is possible to create an indoor space with very good acoustic characteristics without any noise.

Normally, if it is a 20xx thick rigid plate, the frequency is 125Hz to 5kHz.
The sound absorption coefficient is 0 to 0 in the frequency band that is particularly important for architectural acoustics.
With a thickness of 0.1, it is possible to form a reflective panel with flat frequency characteristics, but with a thickness of 50 mm or less, it is not possible to form a sound absorbing panel that evenly absorbs sound waves in the above frequency range. Therefore, if the thickness exceeds 50111 mm, construction problems will occur, so it is virtually impossible to form a sound absorbing panel with a rigid plate.

On the other hand, porous sound-absorbing materials such as glass wool and rock wool are known as materials with sound-absorbing properties.
These sound absorbing materials have a problem in that they have a low sound absorption coefficient for low frequency sound waves of 1 kHz or less (particularly 500 Hz or less) when the thickness is 5011 or less.

It is also known that in order to absorb mid-range sound waves, it is possible to stretch a soft sheet and provide a 5 to 50xx air layer or porous layer on the back of the soft sheet. are low frequency sound waves below 500Hz and 1kHz.
Sound waves with high frequencies above z can hardly be absorbed.

Furthermore, if a sound-absorbing panel is formed using plywood or perforated board, it is possible to absorb low-frequency sound waves of 500 Hz or less, but since an air layer of 50 to 5001 N is required on the back side, there are construction issues. There are many problems, and the problem arises that the indoor space becomes narrow.

As described above, with a thickness of 50 zz or less, it is difficult to form a panel that evenly absorbs the sound range from bass to treble.

[Object of the Invention] The present invention has been made in view of the above-mentioned points, and its purpose is to provide a thin sound absorbing device having substantially flat sound absorption characteristics in the sound range from low to mid-high frequencies of 125 Hz to 5 kHz. It's about doing.

[Disclosure of the Invention] (Structure) The sound absorbing device according to the present invention includes a hollow enclosure made of a rigid body, in which a main hole is bored in the center of one side, and sub-holes are bored in appropriate places around the main hole. , a vibrating membrane made of a soft sheet material that closes the secondary hole of the enclosure, and a tube made of a viscoelastic material with a cross-sectional shape that matches the main hole of the enclosure, and which vibrates with the inner peripheral surface of the enclosure. It consists of a vibrating tube that forms a sealed space with a membrane, and a porous sound-absorbing body filled in the vibrating tube.The three sound-absorbing elements, the vibrating tube, the vibrating membrane, and the porous sound-absorbing body, are combined into one enclosure. , a flat frequency response is obtained in the sound range from bass to mid-to-high frequencies due to the synergistic effect of these sound absorbing elements, and it is possible to form a thin structure.6 (Basic Principle) Used in the present invention The basic principles of operation of each sound absorbing element are explained below. First, as a sound absorption element that absorbs sound in the low frequency range below 500 Hz, as shown in Fig. 4, a sealed air layer 2 is formed around the outer periphery of a thin-walled vibration tube 1 (see Fig. 5) made of a viscoelastic material. In addition, one end of the vibrating tube 1 in the axial direction is closed. As shown in FIG. 6, the vibrating tube 1 itself has a resonant frequency with a diametrical vibration mode, and this resonant frequency fr[Hzl is expressed by the following formula, where the vibrating tube 1 has a circular cross section. , E is the Young's modulus [N/I'] of the tube wall material of the vibrating tube 1, and ρ is the ! of the vibration ItF1. The density of the wall material [kg/yr3], r is the radius of the inner circumferential surface of the vibrating tube 1 [11, ρ is the density of air [kg/x col], C is the speed of sound in air [1/Sl, t is the vibration The wall thickness of tube 1 [
11, d is the average thickness [1] of the air N2 formed around the outer periphery of the vibrating tube 1. When we conducted actual measurements to confirm this theoretical formula, we were able to obtain the results shown in the following table.

In this way, the sound absorbing element that forms the sealed air layer 2 around the outer periphery of the vibrating tube 1 has a resonant frequency fr in the radial vibration mode of the vibrating tube 1. When the sound waves carried enter the vibration tube 1, vibration v! !
The tube wall of 1 vibrates in the radial direction.

The sound wave energy is consumed as hysteresis loss in the viscoelastic material forming the pipe wall, and the sound wave is absorbed. The characteristics of this sound absorbing element are that, as shown in the table above and FIG. be. In other words, even if the thickness of the vibrating tube 1 in the axial direction is reduced, the frequency characteristics do not change.
It can absorb bass frequencies below 500Hz.

As shown in FIG. 8 or 9, the sound-absorbing element that absorbs mid-range sound from 500 Hz to 1 kHz is an air layer 4 or a porous layer 5 on the back side of a vibrating membrane 3 made of a soft sheet material.
It has a structure made of (glass wool or rock wool). The frequency characteristics of this sound-absorbing element change depending on the material and thickness of the vibrating membrane 3 or the thickness of the air layer 4 and porous layer 5. When the sound-absorbing element is configured to have an overall thickness of 5011 mm or less, the As shown in FIG. 10, it can generally be set to absorb midrange frequencies from 500 Hz to 1 kHz.

As shown in FIG. 11, high-frequency sounds above IAHz are absorbed by a sound absorber 6 made of porous material such as glass wool or rock wool cut into a disc shape. As shown in FIG. 12, this sound absorber 6 absorbs high-pitched sounds of 1 kHz or more well.

As described above, the vibration tube 1, the vibration membrane 3, and the sound absorber 6 have a frequency of 500 Hz or less and a frequency of 500 Hz-I AHz, respectively.

Since they have sound absorption characteristics in different frequency ranges, such as IAHz or higher, it is thought that by combining these, substantially flat sound absorption characteristics can be obtained from the low to high frequency range, and in the present invention, The feature is that these sound absorbing elements are rationally combined (Example 1) As shown in Fig. 1, a front panel 11 and a rear panel 12 made of rigid plates are arranged facing each other. A hollow enclosure 10 is formed by surrounding the front panel 11 and the rear panel 12 with a side plate 13. Front panel 11
A main hole 14 is formed in the center of the main hole 14, and a plurality of sub-holes 15 are formed around the main hole 14. Since the sound absorption element using the vibration tube 1 and the sound absorption element using the vibration 11513 both require air layers 2 and 4, the space inside the enclosure 10 is shared by the rain air layer 2.4. . That is, the vibrating tube 1 is installed so that the opening at one end in the axial direction matches the main hole 14, and the vibrating membrane 3
is arranged so as to close the sub-hole 15. Therefore, a sealed air layer 16 surrounded by the vibrating tube 1, the vibrating membrane 3, and the inner peripheral surface of the enclosure 10 is formed. It acts as an air layer 4 on the vibrating membrane 3.

On the other hand, the sound absorbing element made of the sound absorbing body 6 is housed within the vibration tube 1. In this case, the sound absorber 6 allows low-frequency sound waves to pass through, so even if the sound absorber 6 is present inside the vibrating tube 1, it does not impede the sound absorption ability of the vibrating tube 1. Here, in order not to impede the vibration of the vibration tube 1, the sound absorber 6
It is desirable to form a slight gap between the outer circumference of the vibrating tube 1 and the inner circumferential surface of the vibrating tube 1.

According to the above configuration, it is possible to combine the sound absorbing element using the vibrating membrane 3 and the sound absorbing element consisting of the vibrating body 6 with the same dimensions as the sound absorbing element using the vibrating tube 1, and the size can be increased. This means that sound absorption properties from low to high frequencies can be obtained. An example of the sound absorption characteristics in the case of this configuration is shown in the third example.
Shown in the figure as a solid line. In this example, enclosure 10 has 35
A sound absorbing coefficient of approximately 0.4 was obtained from low to high frequencies using a material with a thickness of 1.5 mm. Therefore, if a panel is constructed by combining these sound absorbing devices, a relatively thin sound absorbing panel can be constructed, and there will be no construction problems and the indoor space will not become narrow.

In addition, by appropriately combining this sound-absorbing panel with a reflective panel made of rigid plates, it becomes easier to control the reverberation time.
This makes it possible to create an indoor space with reverberation characteristics that suit your needs and preferences. It also becomes possible to flatten the frequency characteristics of the reverberation time.

(Example 2) In this example, a vibrating tube 1, a vibrating membrane 3, and an enclosure 1 are used.
A porous layer 17 made of glass wool, rock wool, etc. is formed in an air layer 16 surrounded by the inner peripheral surface of becomes. This configuration has the effect of improving the sound absorption coefficient for the sound absorption element using the vibration tube 1 and the sound absorption element using the vibration membrane 3, and as shown by the broken line in FIG. Compared to Example 1, the sound absorption coefficient was slightly increased.

1. Effects of the Invention] As described above, the present invention comprises a hollow enclosure made of a rigid body in which a main hole is drilled in the center of one side and sub-holes are drilled at appropriate positions around the main hole; 11
It is made of soft sheet material that closes the holes! an IJ membrane, a vibrating tube that is a tube body formed of a viscoelastic material and having a cross-sectional shape that matches the main hole of the enclosure, and which forms a sealed space together with the inner peripheral surface of the enclosure and the vibrating membrane;
It consists of a porous sound-absorbing body filled in a vibrating tube, and since it combines three sound-absorbing elements: the vibrating tube, a vibrating membrane, and a porous sound-absorbing body, the synergistic effect of these sound-absorbing elements produces low to medium tones. It has the advantage of providing flat frequency characteristics in the range up to high notes.

In addition, the air layer necessary for the vibrating tube and the air layer necessary for the vibrating membrane are shared in the space surrounded by the inner peripheral surface of the enclosure, the vibrating tube, and the vibrating membrane, and a sound absorber is placed inside the vibrating tube. Therefore, even though three sound absorbing elements are used, the sound absorbing element can be formed with a size within the size of the sound absorbing element using the vibration tube, and there is an advantage that the entire sound absorbing element can be formed in a small size.

Furthermore, since the frequency characteristics of the sound absorbing element made from a vibrating tube do not depend on the length in the axial direction, it can be formed thin, and there will be no problems with construction or the room will become narrower.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view showing Embodiment 1 of the present invention, and FIG.
The figure is a partially cutaway perspective view showing Embodiment 2 of the present invention, FIG. 3 is an operation explanatory diagram showing an example of the operating characteristics of the present invention, and FIG. 4 is a vibration tube of the present invention. FIG. 5 is a partially cutaway perspective view showing a sound absorbing element, and FIG. 5 is a perspective view showing a vibration tube used in the same.
FIG. 6 is an explanatory diagram of the operation of the vibrating tube used in the same as above, FIG. 7 is an explanatory diagram of the operation of the same as above, FIG. FIG. 10 is an explanatory diagram of the same operation as above, FIG. 11 is an illusion diagram of the sound absorber used in the present invention, and FIG. 12 is an explanatory diagram of the same operation. 1 is a vibrating tube, 3 is a vibrating membrane, 6 is a sound absorber, 10 is an enclosure, 14 is a main hole, 15 is a 1/2-inch hole, and 16 is an air layer. Agent Patent Attorney Ishi 1) Tsuyoshi 71, Vibration tube 3... Vibration membrane 6, Sound absorber 10... Enclosure 14... Main hole Figure 2 Figure 3 125 250 500 1K 2K 4 and number of circumferential lines (Hz) Figure 4 Figure 5 Figure 7 Circumferential line 1 (Hz) Figure 8 Figure 9/' Figure 10/i Number of moats (Hz) Figure 11 Figure 12 Station trench fault (Hz)

Claims (1)

[Claims] (1) A hollow enclosure made of a rigid body with a main hole drilled in the center of one side and sub-holes drilled at appropriate locations around the main hole, and a soft sheet material that closes the sub-holes of the enclosure. A vibrating membrane that is made of a viscoelastic material and has a cross-sectional shape that matches the main hole of the enclosure, and which forms a sealed space together with the inner peripheral surface of the enclosure and the vibrating membrane. A sound absorbing device comprising: a porous sound absorbing body filled with a porous sound absorbing body;