JP2013139709A5 - - Google Patents

Description

Sound transmission material

The present invention relates to a sound transmission material. For example, the present invention provides the sound absorbing structures exhibiting excellent sound absorbing performance (e.g., walls, windows, ceilings) of, is available as the sound absorbing structure member is a structural part of the sound absorbing structure. In particular, the present invention makes it possible to select a material that is inherently reflective hard material / smooth hard texture and to make the structure itself transparent when manufacturing a sound absorbing structure, and is high even without an air layer. available as sound absorbing structure member to maintain the sound-absorbing characteristics.

  There is a strong demand for architectural design that wants to use simple and seamless interior materials for museums, museums, cultural facilities and exhibition facilities. Therefore, a hard reflective material such as concrete or metal material is selected for the interior of these spaces. As a result, it was far from the requirements of room acoustics that required quietness, and in most cases, the reverberation was long and the space suffered from acoustic disturbances such as Naruto (Flutter Eco). In addition, the ceiling of the indoor pool is also made of water-resistant material, and in the same way, hard reflective material is often used, resulting in a space condition with a lot of sound and poor clarity such as announcements in the field. There were many.

  All of this is due to the absence of a hard sound-absorbing structural member, which has so far prevented the strong demands of architects. If it is just a sound-absorbing material with a hard texture, pumice or foam-molded metal will exhibit a certain level of sound-absorbing properties, so it cannot be used depending on the application. However, these surfaces are uneven and cannot be said to be smooth, and the sound absorption rate is medium, and it is impossible to avoid the halfway region. The building industry's demand for “a member (structure) that has a hard and smooth surface and exhibits a high sound absorption coefficient” is that it wants to realize museums and museums that have “quiet and simple interior surfaces”, or the clearness of indoor loudspeakers. Although it was a target technology that had been waiting for realization for a long time, it came out of an urgent and realistic need to provide a good indoor pool, but ideas and industrial technologies that satisfy these visual and acoustic conditions simultaneously emerged. I did not.

By the way, the conventional sound-absorbing materials, as represented by glass wool, felts, carpets, curtains, etc., are mostly “soft” and far from hard (hard) images. High-density glass wool board (example: 96kg / m ³ ) used as an anti-vibration flooring material and rock wool sound-absorbing board (product example: Mineralton / Dyroton), which is commonly used as a ceiling sound-absorbing material, have a certain degree of hardness However, it cannot be said to be “hard” in terms of strength, such as being deformed when pressed with a finger, and the sound absorption characteristic is lower than that of glass wool or the frequency range related to sound absorption is narrow.

  On the other hand, in the case of foam metal plates and sintered metal plates developed to break through this, while having both sound absorption properties and sound insulation properties and electromagnetic shielding properties, the surface is generally not smooth but uneven, although it is fine. Not suitable for museums and museum interiors. The sound absorption characteristics, when combined with an air layer, are similar to those of glass wool, but are generally lower than glass wool and higher in price. Porous stone developed for lowering the price (trade name: COUSTONE / Pumice-like material made by crushing England flintstone and solidifying with special resin, foam vermiculite / Chinese vermiculite mixed with raw stone There are also pumice stones for raising seedlings that have been sintered at 800-1500 ° C. and have absorptive and heat-retaining properties, etc., but like the metal plate, the surface is rough and brittle in strength, and the sound absorbing properties are also better than glass wool Because it is low and narrow, it is difficult to use as a sound absorbing material for indoor use.

  The perforated plywood (perforated veneer), which is currently the most popular as a perforated plate, is difficult to use because it absorbs only a specific frequency band with selective sound absorption, and more recently it is not preferred to have a perforated appearance. Opportunities are decreasing. There is also a workaround to arrange a breathable cloth on the surface, but it induces visual problems such as the pores becoming dirty and darkened by the in and out of air. In the case of MPP (Multi-perforated Panel) with a hole diameter of 1 mm or less, the aperture ratio is lower and it is positioned as a different category material from the viewpoint of sound transmission. However, “Helmholtz with glass wool filled in the back air layer” There is no characteristic that can be decisively differentiated from “type sound absorbing structure”. Here, when the hole diameter is 1 mm or less, it is said that the sound transmittance decreases due to attenuation due to air viscosity and reflection attenuation at the opening end. More specifically, as shown in FIG. 1, there is a relationship that the volume reduction in the reflection at the open end depends on fl = cl / λ, and the sound in the low frequency band is likely to be reflected without passing through a small opening. That is, it is theoretically difficult for sound in a low frequency band of 100 Hz or less to pass through a hole having a diameter of 0.5 mm or less (Non-Patent Document 1). When trying to reduce the hole diameter, it is theoretically said that the sound in the low frequency band becomes difficult to pass, and it is considered that there is a design limit.

"Architectural acoustic design <new edition> / Architectural Institute of Japan design plan pamphlet 4" P40 / Fig. 5 (Edited by Architectural Institute of Japan / Shokokusha)

An object of the present invention is to provide a novel sound transmission material. For example, when manufacturing a sound absorbing structure , the present invention enables the selection of an inherently reflective hard material / smooth hard texture material and the transparency of the structure itself, and without combining with an air layer. An object of the present invention is to provide a novel sound transmission material that maintains high sound absorption characteristics.

In the present invention (1), the difference in frequency characteristics measured according to the following measurement method 1 is within 10 dB in each 1/1 octave band, and the α ₀ change measured according to the following measurement method 2 is 0. It is an acoustic transmission material comprising an acoustic transmission type plate-like member or sheet-like member that is 10 or less.
(Measurement method 1): Frequency characteristics of sound in an audio frequency band (50 to 10000 Hz) emitted from a sound source in an anechoic chamber measured by a microphone installed at a position 1500 mm away from the sound source, and the member on the front surface of the sound source Measure the difference from the frequency characteristics when the is installed.
(Measurement method 2): 1 / each over a general reverberation design region (125 to 4000 Hz) measured according to JIS A 1405-2 “Measurement of sound absorption coefficient and impedance by an acoustic tube—Part 2: Transfer function method” Change in normal incident sound absorption coefficient (α ₀ ) in one octave band.

In the present invention (2), the plate-like member has fine holes penetrating from one surface having a hole diameter of 1 to 500 μm to the other surface, and a thickness / hole diameter ratio of 1 to 200, per unit area. The sound transmission material according to the invention (1), which is a hard plate having an aperture ratio of 3 to 50% due to the fine holes on the surface .

Here, the principle that the hard plate according to the present invention (2) has the properties defined in the present invention (1) will be described with reference to FIGS. Here, in FIG. 7, the upper side is a plan view and the lower side is a cross-sectional view. First, as shown in the left diagram of FIG. 7, when there is only one opening, the impedance changes suddenly at the opening and the viscosity of the air also acts. Like a vessel, it cannot reflect and pass through a hole (opening). Even if the number of holes is increased to several, the situation does not change. As shown in the middle diagram of FIG. 7, the sound is “blocked” (sound-insulated), and the sound-insulating property of the apparent material, that is, the transmission loss TL of the base material. (DB) is maintained. However, as shown in the right diagram of FIG. 7, the number of holes is increased while keeping the aperture ratio P constant, and when the aperture diameter becomes 1 to 500 μm, the distance between adjacent apertures decreases accordingly. The transmitted acoustic energy increases rapidly, and even if P is less than 50% (ie well below 100%), “acoustic total transmission” over a wide frequency, ie most of the acoustic energy incident on one of the materials is opposite Phenomenon that penetrates to the side. In this total acoustic transmission state, it is considered that acoustic energy as waves compete with each other, and cooperate with each other in a wave manner to transmit more than the opening area (excessive transmission with respect to the opening area). In terms of acoustophysics, this is the first material that has the ideal “locally active” nature of the material interface, which existed only as an assumption when developing the wave equation. That the material is “locally active” means that the ratio of the particle velocity component V _n perpendicular to the boundary surface to the sound velocity at the material surface, that is, the normal acoustic impedance Z _n is equal to the specific impedance Z of the material regardless of the incident angle. By nature, in this case, V _n can be calculated as V _n = p / Z. Physically, the sound is converted into a component perpendicular to the surface regardless of the direction in which the sound enters the material, that is, the property of a honeycomb structure in which many fine tubes are arranged. Since the above-mentioned “sound absorbing plate” has an infinite number of fine holes, the result is “local action”. An image of “local action” is shown in FIG.

The present invention (3) is the acoustic transmission material of the invention (2), wherein the hard plate is made of a transparent or translucent material.

In the present invention (4), the metal fibers are entangled with each other, which is obtained by papermaking a slurry in which the sheet-like member contains one or more metal fibers by a wet papermaking method. It is a sound transmission material of the said invention (1) which is a metal fiber sheet.

The present invention (5) is a fluorofiber paper in which the sheet-like member is composed of short fiber-like fluorine fibers oriented in an irregular direction, and the fibers of the fibers are bonded by heat fusion. It is an acoustic transmission material of invention (1).

A mode in which the sound transmitting material is used as a sound absorbing structure member will be described. The aspect (1) is a sound absorbing structure having the sound transmitting material according to any one of the inventions (1) to (5) and a sound absorbing material and / or an air layer behind the sound transmitting material .

The present embodiment (2) has an air layer behind the sound transmission member and the sound transmission material of the invention (3), a sound absorbing structure is a lighting acoustical ceiling or lighting sound absorption window.

According to the present invention, there is an effect of having extremely high sound permeability with respect to a wide sound range. Furthermore, the effect when the sound transmission material according to the present invention is used as a sound absorbing structure member will be described.
First, according to the present invention (1) and (6), when producing a sound absorbing structure, a sound transmitting material comprising a plate-like member or a sheet-like member within a predetermined range for a predetermined parameter is used for the sound absorbing structure. If it is used as a member, it can provide a sound-absorbing structure with high sound-absorbing characteristics, so it is free to meet the needs of inherently reflective hard materials, smooth hard texture materials, and transparent sound-absorbing structures. There is an effect that a special property can be added to the sound absorbing structure. Furthermore, according to the present invention (1), if the sound transmitting material is employed, it is possible to obtain a sound absorbing structure that maintains high sound absorbing characteristics without being combined with an air layer. There exists an effect that a sound-absorbing structure with the property can be provided.

  According to the present invention (2), in addition to the above effects, a hard plate that hardly sees the opening of the hole even when approaching several tens of centimeters is used. There is an effect that it is possible to select a material that is inherently reflective hard material and smooth hard material. Contrary to the conventional sense that sound transmission becomes difficult with increasing wavelength by making the hole diameter sufficiently small within a certain range of aperture ratio, it becomes easy to transmit sound, and finally all sound in all bands. The fact that it exhibits transparency is unexpected for those skilled in the art.

  According to the present invention (3), in addition to the above effects, since the hard plate is made of a transparent or translucent material (for example, an acrylic plate), the hole diameter is visually very small, and each one is not recognized as an opening. However, only a slight cloudy feeling is added, and an acoustic absorption plate having a “hard and smooth surface” that is close to “nothing” both acoustically and visually can be provided.

According to this invention (4), in addition to the said effect, since it is comprised so that a metal fiber sheet may be employ | adopted as an acoustic transmission material which is a member for sound-absorbing structures, the sound-absorbing structure with a waterproof effect can be provided. There is an effect that can be done.

According to the present invention (5), in addition to the above-described effect, the sound-absorbing structure having a waterproof effect is provided since the fluororesin fiber paper is adopted as the sound transmitting material that is a member for the sound- absorbing structure. There is an effect that can be.

  According to the present invention (7), in addition to the above effects, the sound absorbing structure is constructed by a combination of a transparent or translucent material and an air layer. The sound absorbing ceiling can be configured, or a sound absorbing ceiling with high clarity can be secured by providing a “sound absorbing ceiling resistant to water and moisture” in an indoor pool or the like.

Hereinafter, first, the sound transmission material according to the present invention will be described, and then the sound absorption structure when the sound transmission material is used as a member for the sound absorption structure will be described. The technical scope of the present invention is not limited to the best mode described below.

Sound transmission material according to the acoustically transparent member present invention, the difference of the frequency characteristics measured in accordance with the measuring method 1 below is within 10dB at each 1/1 octave band, and was measured according to the measuring method 2 below α _It consists of a sound transmission type plate-like member or sheet-like member whose ₀ change is 0.10 or less.
Measurement method 1: Frequency characteristics of an audio frequency band (50 to 10000 Hz) emitted from a sound source in an anechoic chamber measured by a microphone installed at a position 1500 mm away from the sound source, and the member placed on the front of the sound source Measure the difference from the frequency characteristics.
Measurement method 2: Each 1/1 octave over a general reverberation design region (125 to 4000 Hz) measured according to JIS A 1405-2 “Measurement of sound absorption coefficient and impedance by acoustic tube—Part 2: Transfer function method” The amount of change in normal incident sound absorption coefficient (α ₀ ) in the band.

  Here, examples of the plate-like member or sheet-like member having the above properties include a hard plate having a predetermined structure, a metal fiber sheet, and a fluorine fiber paper. Hereinafter, these will be described in order.

≪Hard plate with specified structure≫
The hard plate having the predetermined structure has fine holes penetrating from one surface having a hole diameter of 1 to 500 μm to the other surface, and has a thickness / hole diameter ratio of 1 to 200, It is a hard plate having an aperture ratio of 3 to 50% due to fine holes. Each requirement will be described in detail below.

(material)
The material used as the hard plate is not particularly limited, and plastic plates such as acrylic, polycarbonate (PC), polyethylene (PE), and allyl-styrene copolymer (ABS), glass plates, iron, aluminum, lead, etc. Examples thereof include a metal plate. Here, for example, when the sound transmitting material is used as a member of a daylighting sound absorbing ceiling or a daylighting sound absorbing window, the hard plate is preferably made of a transparent or translucent material.

(Structure-thickness)
The thickness of the hard plate is not particularly limited as long as the relationship between the thickness of the hard plate and the hole diameter of the fine holes is satisfied, but is preferably 0.1 to 100 mm, more preferably 1 to 60 mm. If the thickness is less than 0.1 mm, a problem in strength is likely to occur. If the thickness exceeds 100 mm, it is difficult to open a long through-hole having a diameter of 0.5 mm or less on the plate surface.

(Structure-hole diameter)
The diameter of the micropores provided in the hard plate is 1 to 500 μm, preferably 50 to 500 μm, more preferably 100 to 300 μm. Even if the major axis is less than 1 μm, there is no particular problem, but the difficulty in manufacturing technology increases and the cost becomes high. When the long diameter exceeds 500 μm, it becomes easy to visually recognize the opening when approaching the hard plate, not only aesthetic defects are likely to occur, but also when a breathable cloth or the like is disposed on the surface of the sound transmitting material, This part is likely to cause visual problems such as dirt and darkening due to air coming and going.

(Structure-thickness / hole diameter ratio)
The ratio of the thickness / hole diameter of the hard plate is 1 to 200, preferably 1 to 50, more preferably 1 to 20, and still more preferably 1 to 5.

(Aperture ratio)
The aperture ratio of the holes provided in the hard plate is a value obtained by dividing the sum of the aperture areas of the holes existing per unit area by the unit area in terms of 100 fractions. The opening ratio is preferably 3 to 50%, more preferably 5 to 30%. If the aperture ratio exceeds 50%, there is no theoretical problem. If the hole is perfectly circular, it can theoretically be opened up to 78.5%, but if it exceeds 50%, the aperture is maintained in a state where the strength is maintained. Difficult to do. Even if the aperture ratio is less than 3%, there may be no problem depending on the application, but it is difficult for sound in a low frequency band of 300 Hz or less to pass through.

(Production method)
The method for producing a hard plate according to the present invention is not particularly limited, and examples thereof include a method of making a hole in a hard plate by a mechanical drill, a laser beam, an electric heater or the like or an etching method.

≪Metal fiber sheet≫
The metal fiber sheet is a metal fiber sheet in which the metal fibers are entangled with each other, which is obtained by papermaking a slurry containing one or more metal fibers by a wet papermaking method. Each requirement will be described in detail below. In addition, as the said metal fiber sheet and its manufacturing method, the content of description of Unexamined-Japanese-Patent No. 2000-80591, patent 2649768, and patent 2562761 shall also be integrated in this specification.

(material)
One or more metal fibers are one or more combinations selected from fibers made of metal materials such as stainless steel, aluminum, brass, copper, titanium, nickel, gold, platinum and lead. It is.

(Construction)
The metal fiber sheet has a structure in which metal fibers are entangled with each other. The metal fiber constituting the metal fiber preferably has a fiber diameter of 1 μm to 50 μm, preferably 8 μm to 20 μm, and an aspect ratio of 500 to 3000, and more preferably an aspect ratio of 1000 to 2000. belongs to. Such a metal fiber is suitable for entanglement of metal fibers, and by entanglement of such metal fibers, it is possible to form a metal fiber sheet with less standing if the surface is flaky. Become.

(Production method)
The method for producing a metal fiber sheet according to the present invention forms a sheet containing moisture on the net when forming a slurry containing one or more metal fibers by wet papermaking. And a fiber entanglement process step for entanglement of the metal fibers. Here, as the fiber entanglement treatment step, for example, it is preferable to employ a fiber entanglement treatment step of injecting a high-pressure jet water flow onto the metal fiber sheet surface after papermaking, specifically, a direction orthogonal to the sheet flow direction. By arranging a plurality of nozzles at the same time and simultaneously injecting a high-pressure jet water stream from the plurality of nozzles, the metal fibers can be entangled over the entire sheet. That is, for example, by jetting a high-pressure jet water stream in the Z-axis direction of the sheet onto a sheet composed of metal fibers irregularly intersecting the plane direction by wet papermaking, the metal fiber of the portion where the high-pressure jet water stream was jetted Are oriented in the Z-axis direction. This metal fiber oriented in the Z-axis direction is entangled between metal fibers irregularly oriented in the plane direction, and each fiber is entangled three-dimensionally, that is, the physical strength can be obtained by entanglement It is. In addition, as a papermaking method, various methods such as long net papermaking, circular net papermaking, and inclined wire papermaking can be employed as necessary. In addition, when producing a slurry containing long-fiber metal fibers, the dispersibility of the metal fibers in water may be deteriorated, so a polymer aqueous solution such as polyvinylpyrrolidone, polyvinyl alcohol, or CMC having a viscosity forming action. May be added in a small amount. Further, the method for producing a metal fiber sheet includes a sintering step in which the obtained metal fiber sheet is sintered at a temperature below the melting point of the metal fiber in a vacuum or in a non-oxidizing atmosphere after the wet papermaking step described above. It is preferred that That is, if the sintering process is performed after the wet papermaking process described above, the fiber entanglement process is performed, so there is no need to add an organic binder or the like to the metal fiber sheet, so the decomposition gas such as the organic binder is sintered. It becomes possible to produce a metal fiber sheet having a glossy surface peculiar to a metal without any obstacle in the process. Moreover, since the metal fibers are entangled, the strength of the sintered metal fiber sheet can be further improved.

≪Fluorine fiber paper≫
The said fluorine fiber paper is paper which is comprised by the short fiber-like fluorine fiber orientated in the irregular direction, and the fibers of this fiber are couple | bonded by heat sealing | fusion. In addition, the description content of Unexamined-Japanese-Patent No. 63-165598 shall also be integrated in this specification as the said fluorine fiber paper and its manufacturing method. Hereinafter, each element will be described in detail.

(material)
The fluorofiber according to the present invention is manufactured from thermoplastic fluororesin, and its main component is PTFE, TFE, PFE, FEP, ETFE, PVDF, PCTFE, PVF, but made from fluororesin If it is, it will not be limited to these, Furthermore, these and other resin can also be mixed and used. Here, the fluorofiber is preferably a single fiber having a fiber length of 1 to 20 mm and a fiber diameter of 2 to 30 μm in order to obtain a paper-like material by a wet papermaking method. Is preferred.

(Production method)
The fluorine fiber paper according to the present invention is a fluorine fiber mixed paper obtained by mixing and drying a fluorine fiber and a substance having a self-adhesive function by a wet papermaking method, and heat-pressing the fluorine fiber mixed paper at or above the softening point of the fluorine fiber. After the fibers are heat-sealed, the substance having a self-adhesive function can be dissolved and removed with a solvent and re-dried if necessary. Here, as a substance having a self-adhesive function, natural pulp made of plant fibers such as wood, cotton, hemp, and straw, which are usually used for papermaking, PVA, polyester, aromatic polyamide, acrylic, and polyolefin-based thermoplastics Synthetic pulp and synthetic fiber made of synthetic polymer, and paper-making paper strength enhancer made of natural polymer and synthetic polymer can be used, but it has a self-adhesive function and is mixed with fluorine fiber in water. It is not limited to these as long as it can be dispersed.

Sound transmission material according to the physical properties present invention sound transmission material, (less difference 10dB in the frequency characteristics, alpha ₀ change 0.10) aforementioned parameters characteristic added to the sound absorbing structure using the sound transmission material When constructed, it has the property of maintaining high sound absorption characteristics without being combined with an air layer.

Sound-absorbing structure The sound-absorbing structure according to the present invention includes the above-described sound-transmitting material and a sound- absorbing material and / or an air layer behind the sound-transmitting material . Here, it does not specifically limit as a sound-absorbing material, What is used widely, such as glass wool, can be used. Various adjustments and control are possible by selecting the base material, adjusting the back air layer, selecting the back sound absorbing material, and the like, and many forms are conceivable depending on the application. For example, it can be widely used not only for buildings and structures but also for applications that require noise countermeasures, acoustic countermeasures, and acoustic adjustments, such as transportation equipment such as automobiles, trains, and aircraft.

Here, when a hard material is used as the sound transmitting material , it is possible to construct a sound absorbing structure having a “sound absorbing surface having a hard surface” as shown in FIG. Further, when a transparent or translucent hard material is selected as the sound transmitting material and an air layer is formed behind the hard material (that is, no sound absorbing material is provided), as shown in FIG. It becomes possible to construct a sound-absorbing structure having a “hard sound-transmitting material ”. Table 1 shows configuration examples and application examples of the embodiment shown in FIGS. 9 and 10. In the table, the sound absorbing structure member is a sound transmitting material.

Examples 1 and 2 and Comparative Examples 1 and 2 {acoustic transmission material (hard material)}
(Production example)
Thickness 10 mm, a transparent acrylic plate of 100mm square, CO ₂ laser device, by using an electric drill, an NC lathe appropriate, to prepare the Comparative Examples 1 and 2 of the acoustic transmitting material shown in Table 2. And the sound-transmitting material of Example 1 was produced by making an aluminum plate having a thickness of 2 mm and 100 mm square using an electric drill.

(Sound absorption characteristics confirmation test)
The sound absorption characteristics of each of the produced sound transmission materials of Examples and Comparative Examples were confirmed. The confirmation method was based on transmission frequency characteristics and normal incidence sound absorption coefficient.

As for the transmission frequency characteristics, as shown in FIG. 2, the sound transmitting material 2 of each example and each comparative example is installed on the front surface of a sound generating device of about 2250 cm ³ to which a speaker 1 having an effective diameter of 10 cm is attached. The transmission frequency characteristic measured by the microphone 3 installed at a position 1500 mm from the front surface was measured, and the change was confirmed. For the speaker 1, a sine wave sweep without applying frequency modulation from approximately 100 Hz to 10 kHz was used as a signal. The measurement results are shown in FIGS. FIG. 3 shows the measurement results when the sound transmission material of Example 1 is installed and when no sample is installed (control), and FIG. 4 shows the transmission frequency characteristics when the sound transmission material of Comparative Examples 1 and 2 is installed. It is a measurement result. As is apparent, each measured value in FIG. 4 is a result of the fact that most of the sound input to the speaker could not pass through the sound absorbing plate of each comparative example, unlike the control waveform. On the other hand, in the case of the sound absorbing structure of the first embodiment, as is clear from FIG. 3, most of the sound is transmitted in the entire measured sound range {in FIG. 3, the control (solid line) and the embodiment. 1 (dotted line) substantially overlaps}.

The normal incident sound absorption coefficient (α ₀ ) was measured according to JIS A1405-2 by using the apparatus shown in FIG. The inner diameter of the acoustic tube was 44.8 mm, a 96 Kg / m ³ glass wool sound absorbing material was used as the sound absorbing material, and a 1/2 inch condenser microphone was used as the microphone 1 and the microphone 2 with an interval of 7 cm. The result is shown in FIG. FIG. 6 shows the measurement results of the normal incident sound absorption coefficient when the control (no sample) and the sound transmission material of Example 1 are used. The characteristics are the same as those for the glass wool sound absorbing material behind. In particular, from 1 kHz to 2 kHz, the sound absorption rate is higher than that of the sound absorbing material alone, which is considered to be a synergistic effect of the sample and the sound absorbing material on the sound wave.

Example 2 (metal fiber sheet)
(Production example)
A metal fiber sheet according to Example 2 was produced in the same manner as in Example 1 of Patent 2562761, except that the film thickness was as shown in Table 3.

(Sound absorption characteristics confirmation test)
The transmission frequency characteristics and normal incidence sound absorption coefficient were measured by the same method as in the example. The results are shown in FIGS. 11 and 12, respectively. First, FIG. 11 is a diagram illustrating transmission frequency characteristics of the sound transmission material of the second embodiment. Here, in the figure, (1) is the control, and (2) is the sound transmission material of Example 2. In FIG. 11, the control (1) and the second embodiment (2) are substantially overlapped. As described above, in the case of the sound transmitting material of Example 2, most of the sound is transmitted in the entire measured sound range, as is apparent from FIG. Next, the left side of FIG. 12 is the normal incident sound absorption coefficient of the sound transmission material of the second embodiment. Here, in the figure, (1) is the control (no sheet), and (6) is the sound transmission material of Example 2. Thus, it was confirmed that the change in the sound absorption coefficient at each frequency was small as compared with the case without the sheet.

Example 3 (Fluorine fiber sheet)
(Production example)
A fluorine fiber sheet (fluororesin fiber sheet) according to Example 3 was produced in the same manner as in Example 1 of JP-A-63-165598 except that the film thicknesses shown in Table 3 were used.

(Sound absorption characteristics confirmation test)
The transmission frequency characteristics and normal incidence sound absorption coefficient were measured by the same method as in the example. The results are shown in FIGS. 11 and 12, respectively. First, FIG. 11 is a diagram showing transmission frequency characteristics of the sound transmission material of Example 3. Here, in the figure, (1) is the control, and (3) is the sound transmission material of Example 3. In FIG. 11, the control (1) and Example 3 (3) are substantially overlapped. Thus, in the case of the sound transmission material of Example 3, as is clear from FIG. 11, most of the sound is transmitted in the entire sound range measured. Next, the left side of FIG. 12 shows the normal incident sound absorption coefficient of the sound transmission material of Example 3. Here, in the figure, (1) is the control (no sheet), and (7) is the sound transmitting material of Example 3. Thus, it was confirmed that the change in the sound absorption coefficient at each frequency was small as compared with the case without the sheet.

Example 5 (Sound absorption characteristics confirmation test with and without air layer)
The normal incident sound absorption coefficient was measured using various porous sheets and glass wool sound absorbing materials as samples. Here, as the various porous sheets, in addition to the metal fiber sheet of Example 2 and the fluorine fiber sheet of Example 3, various general-purpose porous sheets were tested for comparison.

≪Measurement method≫
(Normal incidence sound absorption coefficient and sheet position)
When a sheet was placed and a glass wool of 32 kg / m ^{3 with} a thickness of 5 cm was placed 2 cm behind the sheet, and when the end of the apparatus was shortened by 2 cm and the sheet and the sound absorbing material were brought into close contact with each other. A 1/2 inch condenser microphone (B & K4133) was installed at 7 cm intervals, and the sound absorption coefficient was measured from these two transfer functions. As a sound source, 1Oct. Band noise with a center frequency of 250, 500, lk, and 2 kHz was input from a noise generator (NODE7030). The speed of sound was calculated from room temperature. The frequency that can be measured is 300Hz to 2kHz. The microphone output was amplified by a preamplifier, and then taken into a personal computer for about 20 seconds by an A / D converter. The sampling frequency was 2048 Hz up to a center frequency of 500 Hz, 4096 Hz at 1 kHz, and 8192 Hz at 2 kHz.

The calculation procedure of the sound absorption coefficient α is as follows: After obtaining the 512-point FFT (Hanning window) of microphones 1 and 2 and the autocorrelation (microphone 1) and cross-correlation, the transfer function H is calculated from the average of 20 times. _Ask for _twelve . α can be calculated as shown in Equation (1).

Formula 1

(Characteristics of the sheet)
Table 3 shows the respective characteristics of the sheet. The air permeability (the time it takes for a certain amount of air to pass through a certain area of paper under a certain pressure) is s (seconds) / 100 ml. For each sample, an O-shaped ring having the same size as the inner diameter of the apparatus was prepared, and a sheet was attached to the ring for use.

(Measurement result)
The measurement result of the normal incident sound absorption coefficient is shown in FIG. 12 including only the sound absorbing material (no sample). FIG. 12 (left) shows the result of providing a gap of 2 cm between the sheet and the sound absorbing material having a thickness of 5 cm, and FIG. 12 (right) shows the result of not providing the gap between the sheet and the sound absorbing material. Is shown. In addition, (a) shows the results in the case of no sheet and samples 1, 2, 8 and 3, and (b) shows in the case of no sheet and samples 4, 5, 7 (fluorine fiber sheet of Example 3), 6 ( The result of the metal fiber sheet of Example 2 is shown. As a result, in the result of “with 2 cm gap” in FIG. 12 (left), first, it is understood that the sound absorption coefficient of the printing paper having no aperture is considerably lowered in both the low frequency range and the high frequency range as compared with the case without the sheet. . On the other hand, the samples 1 to 5 have a somewhat different sound absorption rate at each frequency compared to the case without the sheet, but compared to the sample 8 (printing paper), the sound absorption rate does not change greatly and tends to be close to “total sound transmission”. Indicates. In addition, regarding the samples 6 and 7 according to this example, the change in the sound absorption coefficient at each frequency was small as compared with the case without the sheet, and it was confirmed that the sound absorption was “total sound transmission”. On the other hand, in the result of “no gap” shown in FIG. 12 (right), the samples 1 to 5 and 8 tended to have a lower sound absorption rate than that without the sheet. However, Samples 6 and 7 according to the present example showed almost the same sound absorption coefficient as that without the sheet, and it was confirmed that it was “total sound transmission” that was outstanding as compared with the other samples. Glass wool sound-absorbing material deviates from the air impedance at low frequencies. In addition, it is expected that the appearance of the glass wool surface will be different when the sheet is brought into direct contact, but in Samples 6 and 7, the lower the air permeability than the other sheets is “total sound transmission”. Seem. As described above, it was confirmed that the sheets according to the samples 6 and 7 according to the present example were “total sound transmission” regardless of the presence or absence of voids.

Volume reduction due to reflection at open end (ASHRAE) Schematic diagram of sound permeability (transmission frequency characteristics) measurement method Measurement result of transmission frequency characteristics of Example 1 and blank Measurement results of transmission frequency characteristics of Comparative Examples 1 and 2 Schematic diagram of normal incidence sound absorption measurement device Measurement result of normal incidence sound absorption coefficient of Example 1 Principle of the present invention Principle diagram of the present invention (image of “local action”) Figure showing an example of a sound-absorbing material with a hard surface Figure showing an example of a sound-absorbing material with a transparent and hard surface Example 2, Example 3 and blank transmission frequency characteristic measurement results Measurement results of normal incidence sound absorption coefficient of Examples 2 and 3 (+ confirmation of presence / absence of air gap and sound absorption effect)

1 Speaker 2 Sample 3 Microphone

Claims (5)

Sound transmission type in which the difference in frequency characteristics measured according to the following measurement method 1 is within 10 dB in each 1/1 octave band, and the α ₀ change measured according to the following measurement method 2 is 0.10 or less. An acoustic transmission material comprising a plate-like member or a sheet-like member.
(Measurement method 1): Frequency characteristics of sound in an audio frequency band (50 to 10000 Hz) emitted from a sound source in an anechoic chamber measured by a microphone installed at a position 1500 mm away from the sound source, and the member on the front surface of the sound source Measure the difference from the frequency characteristics when the is installed.
(Measurement method 2): 1 / each over a general reverberation design region (125 to 4000 Hz), measured according to JIS A 1405-2 “Measurement of sound absorption coefficient and impedance by an acoustic tube—Part 2: Transfer function method” Change in normal incident sound absorption coefficient (α ₀ ) in one octave band. The plate-like member has micropores penetrating from one surface having a pore diameter of 1 to 500 μm to the other surface, the thickness / pore diameter ratio is 1 to 200, and the micropores on the surface per unit area The sound transmission material according to claim 1, which is a hard plate having an aperture ratio of 3 to 50%. The sound transmission material according to claim 2, wherein the hard plate is made of a transparent or translucent material . The sheet-like member is a metal fiber sheet obtained by papermaking a slurry containing one or more metal fibers by a wet papermaking method, wherein the metal fibers are entangled with each other. Item 1. The sound transmitting material according to Item 1. The sound transmission material according to claim 1, wherein the sheet-like member is a fluorine fiber paper which is constituted by short fiber-like fluorine fibers oriented in an irregular direction, and the fibers of the fibers are bonded by heat fusion. .