JP6694982B2 - Acoustically transparent material - Google Patents

Description

  The present invention relates to acoustically transparent materials.

  There is a strong demand for architectural design to use simple and seamless interior materials for museums, cultural facilities, and exhibition facilities. Therefore, a reflective and hard material such as concrete or a metal material is selected for the interior of these spaces. As a result, it was far from the requirements for room acoustics that required quietness, and the reverberation was long in most cases, and the space was plagued by acoustic obstacles such as the Naruto (Flatta Eco). Also, for the ceiling of the indoor pool, etc., because it is made of a material that is resistant to water, it is often the case that a similarly hard and reflective material is used, causing a lot of reverberation and poor clarity such as announcements in the venue. There were many

  Perforated plywood (perforated veneer), which is the most popular perforated plate at the present time, is difficult to use because it absorbs only a specific frequency band due to its selective sound absorption, and more recently, it is used as an interior because the appearance of perforation is not preferred. Opportunities are decreasing. There has been a strong demand for a material for interior materials, which has a hard texture without impairing the aesthetic appearance and also has excellent acoustic transparency.

In Patent Document 1, it is possible to select a material that is originally a reflective hard material or a material that has a smooth and hard texture and to make the structure itself transparent, and also have high sound absorption characteristics (acoustic transparency) without combining with an air layer. A new sound absorbing structure that maintains
JP, 2010-059658, A

  The present invention provides a novel sound-transmitting material that can reduce the variation in sound transmission between lots in a sound-transmitting material made of SUS fiber and further realize further reduction of pop noise. With the goal.

  The present inventors have studied to modify the surface of an acoustically transparent material in order to solve the above problems. Generally, there are coatings of various materials in order to change the properties of the material surface, but the film thickness is several μm level or more, and when considering its use as an acoustically transparent material, the material that affects the transmission of sound. It will affect the void of the.

  As a result of earnest research, the inventors of the present invention, by performing a specific treatment on the surface of the SUS fiber, have an effect of reducing lot-to-lot variation of this sound transmission and an effect of further reducing pop noise while maintaining excellent acoustic characteristics. The present invention has been completed by finding out that

The present invention (I) is a sound-transmitting material in which oxidation-treated SUS fibers (b) obtained by oxidizing SUS fibers (a) are entangled with each other, and the SUS fibers (a) and Each component of the oxidation-treated SUS fiber (b) has the following relationship, which is a sound-transmitting material.
(1) Atomic concentration of Fe oxidation component on the surface of the oxidation-treated SUS fiber (b)> Atomic concentration of Fe oxidation component on the surface of the SUS fiber (a) (2) Fe component in the oxidation-treated SUS fiber (b) At which the atomic concentration of Fe is higher than the atomic concentration of the Fe oxidizing component> The depth at which the atomic concentration of the Fe component in the SUS fiber (a) is higher than the atomic concentration of the Fe oxidizing component (3) The oxidation-treated SUS fiber (b) ) Maximum atomic concentration point depth of Cr oxidation component in)> Maximum atomic concentration concentration depth of Cr oxidation component in the SUS fiber (a) The present invention (II) is the maximum atom concentration of Fe oxidation component in the oxidation-treated SUS fiber (b). The depth of the concentration point <the depth of the maximum atomic concentration of the Cr oxidation component in the oxidation-treated SUS fiber (b), which is the depth of the concentration point, in the acoustically transparent material of the invention (I).
The present invention (III) is the acoustically transparent material according to the invention (I) or (II), wherein at least some of the oxidation-treated SUS fibers (b) are sintered together.

The “surface of the SUS fiber” in the present invention has a depth of 2.0 nm from the outermost surface in consideration of contamination of the outermost surface. Here, the depth (depth) is a conversion value when the sputtering rate is set to 5.4 nm / min for SiO ₂ in each depth direction in the etching ESCA method.

  Further, the SUS fiber before the oxidation treatment in the present invention (the SUS fiber (a)) is a SUS fiber having a passivation film formed on its surface. In the claims and the specification of the present application, the relationship between the atomic concentrations of the “SUS fiber before oxidation treatment” and the “SUS fiber after oxidation treatment” is defined. At this time, the measurement of each component of the “SUS fiber before oxidation treatment” is performed on the “SUS fiber after oxidation treatment” that has been subjected to the following acid treatment. This is the surface element concentration of "the SUS fiber actually used" and "the SUS fiber which has been subjected to acid treatment after being subjected to oxidation treatment (that is, the oxide film was removed and a passive film was again formed by natural oxidation)". It is based on the knowledge that the distributions are substantially the same (at least, the above tendencies of (1) to (3) do not change).

1 cm ² of oxidized SUS fiber sheet or 1 cm ² of SUS fiber plate was immersed in 40 ml of hydrochloric acid solution having a concentration of 1 mol / L and a water temperature of 25 ° C. for 3 hours, and then placed in a beaker containing 50 ml of pure water. It was transferred and washed by immersing it in water for 10 minutes. Then, it was dried by leaving it in an environment of room temperature of 25 ° C. for 20 hours under an air atmosphere.

  In the present invention, the “Fe oxidation component” refers to an iron element component that is bound to oxygen, and the “Fe component” refers to an iron element component that is not bound to oxygen. Similarly, the "Cr oxidation component" refers to a chromium element that is bonded to oxygen, and the "Cr component" refers to a chromium element that is not bonded to oxygen.

According to the present inventions (I) and (II), when producing a sound-transmitting material, by subjecting the SUS fiber to a specific treatment, the sound-transmitting properties between the sound-transmitting materials are maintained while maintaining excellent acoustic characteristics. There is an effect that variation between lots can be reduced. In addition, it was clarified that the effect of reducing pop noise was further increased in the acoustic characteristics.
According to the present invention (III), it is possible to increase the strength of the metal fiber material after sintering.

Hereinafter, the material of the acoustically transparent material according to the present invention, the manufacturing method, and the oxidation treatment method will be described first, and then the physical properties of the acoustically transparent material according to the present invention will be described. The technical scope of the present invention is not limited to the best mode described below.
1) Acoustically transparent material 1-1) Raw material 1-2) SUS fiber sheet 1-2-1) Structure of SUS fiber sheet 1-2-2) Manufacturing method of SUS fiber sheet 1-3) SUS fiber board 1- 3-1) Structure of SUS fiber board 1-3-2) Manufacturing method of SUS fiber board 1-4) Oxidation treatment method 2) Physical properties of acoustically transparent material 2-1) Atomic concentration distribution on SUS fiber surface 2-2 ) Acoustic characteristics 2-3) Reduction of variations in sound transmission 2-4) Reduction of pop noise 3) Applications of sound-transmitting materials

<< Sound-transmissive material >>
The sound-transmitting material according to the present invention is a sound-transmitting material in which oxidized SUS fibers obtained by oxidizing SUS fibers are entangled with each other, and the atomic concentration ratio of the outermost surface thereof is a specific composition. It is an acoustically transparent material having.

  The shape of the acoustically transparent material according to the present invention is not particularly limited. For example, it may have a fiber sheet shape or a plate shape. The SUS fiber board is preferably self-supporting.

<Raw material>
The raw material of the acoustically transparent material according to the present invention is stainless steel. The stainless steel is not particularly limited as long as the effects of the present invention are exhibited. The atomic concentration ratio specified in the present invention is only for Fe, Cr and oxides thereof, but the elements constituting stainless steel are not limited to these atoms. Besides, it may further contain one kind or two or more kinds of transition metal elements. For example, Mo, Ni, Al, Ti, Cu or Nb may be used.

  Further, the diameter of the fiber used for the acoustically transparent material of the present invention is not particularly limited, but, for example, 0.1 to 100 μm is preferable, 0.5 to 50 μm is more preferable, and 1 to 40 μm is further preferable. It is suitable. By setting the fiber diameter in such a range, it is possible to increase the strength of the fiber and it is easy to obtain appropriate sound permeability.

<SUS fiber sheet>
(Structure of SUS fiber sheet)
The SUS fiber sheet has a structure in which metal fibers are entangled with each other. Further, the fiber diameter of the SUS fiber constituting the SUS fiber sheet is preferably 1 μm to 50 μm, more preferably 8 μm to 20 μm, and the aspect ratio is preferably 500 to 3000, and further preferably The aspect ratio is 1000 to 2000. Such SUS fibers are suitable for entanglement of SUS fibers, and by entanglement of such SUS fibers, it is possible to obtain an SUS fiber sheet with less fluffy surface. Become. It should be noted that, as the metal fiber sheet and the manufacturing method thereof, the contents described in JP 2000-80591 A, JP 2649768 A and JP 2562761 A are also incorporated in the present specification.

(Method for producing SUS fiber sheet)
The method for producing an SUS fiber sheet according to the present invention forms a sheet containing water on a mesh when forming a sheet containing a slurry containing one or more kinds of SUS fibers by a wet papermaking method. And a fiber entanglement treatment step of intertwining the SUS fibers with each other. Here, as the fiber entanglement treatment step, for example, it is preferable to adopt a fiber entanglement treatment step of injecting a high-pressure jet water stream onto the surface of the SUS fiber sheet after paper making, specifically, a direction orthogonal to the sheet flow direction. It is possible to entangle the SUS fibers with each other over the entire sheet by arranging a plurality of nozzles on the sheet and jetting a high-pressure jet water stream from the plurality of nozzles at the same time. That is, for example, by jetting a high-pressure jet water stream in the Z-axis direction of a sheet onto a sheet composed of SUS fibers that are irregularly crossed in the plane direction by wet papermaking, the SUS fibers in the portion where the high-pressure jet water stream is jetted Are oriented in the Z-axis direction. The SUS fibers oriented in the Z-axis direction are entangled between SUS fibers irregularly oriented in the plane direction, and the fibers are three-dimensionally entangled with each other, that is, entangled to obtain physical strength. Is. Further, as the papermaking method, for example, various methods such as fourdrinier papermaking, cylinder papermaking, and inclined wire papermaking can be adopted as necessary.

  When producing a slurry containing long SUS fibers, the dispersibility of the SUS fibers in water may deteriorate. Therefore, an aqueous polymer solution of polyvinylpyrrolidone, polyvinyl alcohol, CMC, etc., which has a viscous effect, may be produced. May be added in a small amount. In addition, the method for producing the SUS fiber sheet is configured to include a sintering step of sintering the obtained SUS fiber sheet at a temperature equal to or lower than the melting point of the SUS fiber in a vacuum or a non-oxidizing atmosphere after the wet papermaking step described above. Preferably. That is, if the sintering step is performed after the wet papermaking step described above, the fiber entanglement treatment is performed, and therefore, it is not necessary to add an organic binder or the like to the SUS fiber sheet, and thus decomposition gas of the organic binder or the like is sintered. It is possible to manufacture a SUS fiber sheet having a glossy surface peculiar to a metal without hindering the process. In addition, since the SUS fibers are entangled, the strength of the SUS fiber sheet after sintering can be further improved.

<SUS fiber board>
(Structure of SUS fiber board)
The SUS fiber board also has a structure in which fibers are entangled with each other. Further, in order for the SUS fiberboard to have self-sustainability, it is preferable that the Taber stiffness is 5 mN · m or more and the bending resistance is 100 mN or more. Further, as described above, in the acoustically transparent material having the self-supporting property, it is preferable that the porosity is 50% or more and the thickness is 3 mm or less, and by setting it in this range, a material having high acoustic transparency can be obtained. .. As the SUS fiber board and the manufacturing method thereof, the contents described in JP 2013-061406 A are also incorporated in the present specification.

  The Taber stiffness of the SUS fiber board of the present invention is 5 mN · m or more, preferably 8 mN · m or more, and more preferably 10 mN · m or more. The upper limit of the Taber stiffness is not particularly limited, but is 100 mN · m, for example. By having the Taber stiffness in the range, a material having self-supporting property is obtained. Taber stiffness is measured according to JIS-P8125. The Taber stiffness value can be adjusted by the hardness of the fibers used, the density of the acoustically transparent material, and the pressure during compression molding, based on the knowledge of those skilled in the art.

  The bending resistance of the SUS fiber board of the present invention is 100 mN or more, preferably 150 mN or more, and more preferably 200 mN or more. The upper limit of the bending resistance is not particularly limited, but is 2000 mN, for example. By having the Taber stiffness in the range, a material having self-supporting property is obtained. The bending resistance is a value obtained by measurement according to the Taber stiffness test of JIS-P8125. The value of the bending resistance can be adjusted by the hardness of the fibers used, the density of the acoustically transparent material, and the pressure during compression molding, based on the knowledge of those skilled in the art.

  The porosity of the SUS fiber plate of the present invention is 50% or more, preferably 60 to 90%, more preferably 70 to 90%. The upper limit of the porosity is not particularly limited, but is 95%, for example. In the material in which the fibers are entangled, by selecting a material having a porosity within the range, there is an effect that the acoustic transparency is secured while having the self-supporting property. In addition, since the porosity is not too high in the preferable range, or more preferable range, it is possible to prevent the opposite side from being seen through the acoustically transparent material even when used as a wall material or the like.

  Considering the angle dependency of the sound transmission, it is particularly preferable that the porosity of the sound transmitting material is 80 to 90%. With such a range, it is possible to exhibit high acoustic transparency that hardly depends on the incident angle of sound to the material.

The porosity is a ratio of a space where fibers do not exist to the volume of the sound transmitting material, and is calculated from the volume and weight of the sound transmitting material and the specific gravity of the fiber material.
Porosity (%) = (1-weight of acoustically transparent material / (volume of acoustically transparent material × specific gravity of fiber)) × 100
The porosity value can be adjusted based on the knowledge of those skilled in the art by the thickness and amount of the fibers used, the density of the material in which the fibers are entangled, and the pressure during compression molding.

  Here, the thickness of the SUS fiber board is preferably 3 mm or less, more preferably 50 μm to 2000 μm, further preferably 100 μm to 1500 μm, and particularly preferably 500 μm to 1000 μm. By setting the thickness of the material having the above-mentioned porosity within the above range, a material having high acoustic transparency can be obtained.

(Manufacturing method of SUS fiber board)
As a manufacturing method, a raw material containing the above-mentioned fibers can be obtained by a wet papermaking method, but in order to impart self-sustaining property, it is more preferable to manufacture by compression molding. When the sound-transmitting material of the present invention is produced by compression molding using metal fibers, first, the fibers are put together and pre-compressed to form a web. Alternatively, a binder may be impregnated between the fibers to provide a bond between the fibers. The binder is not particularly limited, for example, in addition to organic binders such as acrylic adhesives, epoxy adhesives, urethane adhesives, colloidal silica, water glass, inorganic adhesives such as sodium silicate. Can be used. Instead of impregnating with the binder, the surface of the fibers may be coated with a thermoadhesive resin in advance, and the aggregate of the metal fibers may be laminated and then heated and adhered. The impregnated amount of the binder is preferably 5 to 130 g, and more preferably ²⁰ to 70 g with respect to the sheet surface weight of 1000 g / m ² .

  Further, the manufacturing method of the metal fiber material is the above-described wet papermaking step or a compression step, and a sintering step in which the obtained metal fiber material is sintered at a temperature not higher than the melting point of the metal fiber in a vacuum or a non-oxidizing atmosphere. It is preferable to include. Since the metal fibers are entangled, the strength of the metal fiber material after sintering can be increased.

<Oxidation treatment method>
Regarding the SUS fiber oxidation treatment method according to the present invention, the configuration of the apparatus, the oxidation treatment step, and then the oxidation conditions will be described in order below. The oxidation method is not particularly limited as long as the same composition as the surface element concentration distribution of the SUS fiber according to the present invention is formed. Hereinafter, the heat treatment in an oxygen atmosphere will be described in detail as an example, but it is also possible to perform an oxidation treatment by, for example, dipping in a solution containing an oxidizing agent or anodizing in an electrolytic solution.

(Structure of oxidation treatment device)
The apparatus used for the oxidation treatment includes, as a configuration, a tubular heater having both ends in the longitudinal direction opened as an inlet and an outlet, a wire rod moving means for transferring SUS fiber and passing through the tubular heater, and an inlet side into the heater. It is preferable to provide an inert gas introducing means for introducing an inert gas from the above, an oxygen concentration adjusting means for adjusting the oxygen gas concentration in the heater, and a transfer speed adjusting means for adjusting the moving speed of the fiber.

(Oxidation process)
When the SUS fiber was heat-treated by using the oxidation treatment apparatus having the above-mentioned structure, and the low temperature annealing was performed in the present invention, the concentration of the oxygen gas in the oxidizing gas (air and nitrogen gas) filling the heater was made uniform. The low temperature SUS fiber will be transferred into the inside. By adjusting the three parameters of the heater temperature, the nitrogen introduction amount, and the SUS fiber transfer rate in this process, an oxide film having a desired thickness can be uniformly formed on the surface of the SUS fiber. The conditions such as the oxygen concentration may be changed during the transfer of the SUS fiber.

(Oxidation conditions)
Regarding the oxidation conditions, the heater temperature, the amount of nitrogen introduced, and the moving speed of the wire (SUS fiber) will be described below in order.

-Heater temperature The heater temperature is not particularly limited, but is preferably 300 to 700 ° C. More preferably, it is 400 ° C. to 600 ° C., and can be appropriately adjusted according to the mode of the oxide film to be formed.

-Nitrogen introduction amount The nitrogen introduction amount is not particularly limited, but it is preferable to introduce 0.10 L to 1.00 L / min. It is more preferably 0.20 to 0.80 L / min, and can be appropriately adjusted depending on the mode of the oxide film to be formed.

-Movement speed of wire rod The moving speed of the wire rod during heating is not particularly limited, but it is preferably 0.10 m to 1.00 m / min. It is more preferably 0.20 to 0.80 m / min, and can be appropriately adjusted depending on the form of the oxide film to be formed.

(Oxidation time)
The timing of performing the oxidation treatment step is not particularly limited. It may be before or after the fibers are entangled to form a sheet or plate. However, although the sintered SUS fiber is suitable for the present invention, depending on the sintering conditions, the surface element concentration distribution is affected, and therefore the conditions and the oxidation time need to be considered.

<< Physical properties of acoustically transparent materials >>
<Atomic concentration distribution on SUS fiber surface>
The surface profile in the depth direction of the SUS fiber of the present invention is characterized in that it greatly changes through the above-mentioned oxidation treatment step. Normally, the surface of stainless steel is oxidized by oxygen in the air to form an extremely thin passivation film (compound in which oxygen, hydroxyl group, and water are bonded to Cr) having a thickness of several nm. In the present invention, by performing the oxidation treatment in the above-mentioned oxygen atmosphere, it becomes possible to form an oxide film mainly composed of the Fe oxidation component on the surface side of this passivation film.

  Specifically, the atomic concentration of the Fe oxidation component on the surface of the oxidation-treated SUS fiber is higher than the atomic concentration of the Fe oxidation component on the surface of the SUS fiber, and the atomic concentration of the Fe component is higher than the atomic concentration of the Fe oxidation component. The depth is characterized by being larger than the depth at which the atomic concentration of the Fe component in the SUS fiber becomes higher than the atomic concentration of the Fe oxidation component. Furthermore, the maximum atomic concentration point depth of the Cr oxidizing component in the oxidation-treated SUS fiber is larger than the maximum atomic concentration point depth of the Cr oxidizing component in the SUS fiber.

  Further, it is preferable that the maximum atomic concentration point depth of the Fe oxidizing component in the oxidation treated SUS fiber is smaller than the maximum atomic concentration point depth of the Cr oxidizing component in the oxidation treated SUS fiber.

(Measuring method)
The analysis in the depth direction of the SUS fiber surface is performed by the etching ESCA method under the following measurement conditions while shaving a slight amount of the SUS fiber surface layer under the following sputtering conditions.

[Measurement condition]
Analyzer: Quantera SXM (manufactured by ULVAC-PHI)
X-ray light source: Monochromatic AlKα
X-ray output, X-ray irradiation diameter: 25.0 W, φ100 μm
Measurement area: Point 100 μm ²
Photoelectron uptake angle: 45 deg
Narrow Scan: 140 eV; 0.125 eV / Step

[Sputtering conditions]
Accelerating voltage / current: 2.0kV
Sputter rate: 5.4 nm / min (SiO ₂ conversion)

<Acoustic characteristics>
(Acoustic transparency)
The acoustically transparent material according to the present invention has a difference in frequency characteristics (hereinafter referred to as “insertion loss”) measured according to the following measurement method 1 within 5 dB in each 1/1 octave band having a center frequency of 63 Hz to 8 kHz. It is preferable to have a property of (preferably within 2 dB). The acoustically transparent material is preferably 6 dB or less (preferably 3 dB or less) in each 1/3 octave band having a center frequency of 31.5 Hz to 16 kHz. When a continuous sine wave sweep is used, it shall be based on the case of evaluation in the 1/3 octave band.

  Various methods are conceivable as the evaluation method regarding the sound transmittance. More specifically, in the anechoic room or the highly sound absorbing room, the former is a direct sound area (the area where the direct sound is sufficiently larger than the indirect sound (reflected sound / reverberant sound)) compared to the latter. , The level difference of the response of the microphone to the speaker when the sample is placed at a right angle to the reference line (the line connecting the microphone and the speaker) and when the sample is not placed (dB ) Is evaluated as the insertion loss Δ (dB). By the way, the signal emitted from the speaker may be any of sine wave, pink noise, and quake (FM sound), and the duration may be continuous or short tone. Furthermore, the filter for band limiting is the sound source. It may be a side sound, a sound receiving side, a short sound, or a continuous frequency sweep sound. At the same time, the position of the sample may be immediately before the speaker, immediately before the microphone, or in the middle of the two, and as long as the measurement system is regarded as a linear system, the results are almost the same. Incidentally, although it is specified here that the sample is evaluated at a right angle to the reference line, the sample can be installed at an angle to the reference line and the angle dependence can be evaluated if necessary. In the case where the measurement method 1 causes a difference in the results, in the sound transmission in the specification, the result obtained by the following method is prioritized.

  Measurement method 1: The simplest method for measuring the insertion loss is to use an axis that connects a speaker and a microphone (hereinafter referred to as a "speaker-microphone axis") in an anechoic room or a highly sound absorbing room equivalent thereto. , A continuous sine wave sweep sound between 20 Hz and 20 kHz (with respect to background noise) with an angle θ = 0 ° formed by the normal direction of the acoustically transparent material (the state in FIG. 7 is assumed to be angle θ = 0). Sound of 20 dB or more at S / N ratio) is radiated, and after being received by a microphone or a sound level meter installed at a position apart from this speaker by several tens of cm to several m (preferably about 30 cm to 5 m), The difference between the frequency response characteristics when recorded on a level recorder, etc. and the frequency response characteristics when the member is installed immediately before the speaker or microphone, or in the middle of both, is defined as the insertion loss Δ (dB). ..

<Variation reduction effect on surface element concentration distribution and sound transmission>
The sound-transmitting material of the present invention has the effect of reducing variations in sound transmission by having a specific surface element concentration distribution on its surface. Here, in general, in a sound transmitting material that allows sound to pass, the ease of passing sound depends on the voids of the material, the surface state of the material, and the specific gravity. That is, when the voids are small, the surface of the material is soft, or the specific gravity is small, the sound tends to be difficult to pass through. This is because when the sound hits such a material, it is reflected and absorbed by the material, which impedes the transmission of the sound.

  The cause of this effect is not clear, but it can be estimated as follows. The stainless fiber board, which has been found as an all-transparent plate, has a structure in which stainless steel is fiberized and aggregated. As is generally known, stainless steel (SUS) is an alloy steel containing Cr for the purpose of suppressing the generation of rust which is a weak point of iron. By containing Cr, a passivation film of about several nm is formed on the SUS surface, and this passivation film prevents rust of iron. On the other hand, this thin Cr passivation film is softer and has a smaller specific gravity than iron oxide formed on the iron surface. It is presumed that this softness and small specific gravity may have caused variations in sound transmission.

  In response to this problem, this treatment can form iron oxide on the Cr passivation film, increasing the hardness of the surface and increasing the specific gravity while maintaining the rust resistance of iron. It is a thing. It is presumed that as a result, the absorption and vibration of sound, which is a factor that inhibits sound transmission, was reduced, and variation could be reduced.

  That is, the present invention makes it possible to reduce variations in sound transmission by increasing the hardness of the stainless fiber surface or increasing the specific gravity of the surface without deteriorating the sound transmission.

  The evaluation for reducing the variation in sound transmission is performed by the following method.

(Evaluation methods)
For the acoustically transparent material to be evaluated (for example, n = 10), the above-described insertion loss Δ (dB) is measured, and the coefficient of variation is calculated from the average value and standard deviation thereof and evaluated.

<Pop noise reduction effect>
Noise due to pop sound (pop noise) is noise in the low frequency range captured by the microphone. Separated from voiced sound, it is generated by the microphone unit sensing the impact wind (movement of air) from the nearest wind source. This impact wind is different from fan wind such as natural wind, indoor air conditioning, or a fan in that it is the wind from the latest wind source. The effect of reducing the pop sound has been recognized even in the conventional sound-transmitting material that is not subjected to the oxidation treatment. However, the acoustically transparent material of the present invention has the effect of further reducing this pop noise.

  The pop noise can be measured by, for example, a pop noise measuring device described below.

(Pop noise measuring method and noise measuring device)
Hereinafter, a pop noise measuring method and a noise measuring device which can be used in the present invention will be described with reference to the drawings. Further, in the following description, the right side in FIGS. 4 and 5 may be referred to as the X side, and the left side may be referred to as the −X side.

  That is, in order to reproduce the impact wind and stably measure the pop noise, it is required that there is no sound accompanied by air movement and that the air movement is rapid. Therefore, the impact wind generation device must have sufficient responsiveness and controllability with respect to the drive source, and must not generate noise such as the drive sound of the device or noise caused by the impact wind that interferes with noise measurement. Desired.

  For plosive sounds such as p, t, and k that generate pop noise, the process of exhaling, that is, the expulsion formed during the process of formation of closure → sustaining → opening, and the process of inhaling a lot There is a break. Among them, it is the former, that is, the external disturbance corresponding to unvoiced plosive sounds such as p, t, and k, that mainly causes pop noise in the microphone, and is particularly remarkable in the directional singing microphone and the condenser microphone.

  Fig. 6 shows the frequency spectrum of the initial part (plosive sound "p" accompanied by shock wind) and the subsequent vowel part "u" when a voiced sound "pu" is emitted 50 mm in front of the condenser microphone (FFT maximum value every 10 ms). ) Is shown. The spectrum indicated by reference numeral (u) in FIG. 6 corresponds to a vowel formant having a plurality of peaks. On the other hand, the spectrum marked with (p) corresponds to the maximum slope of the consonant “p” and is a noise that is attenuated at a constant rate around 10 to 15 dB / Oct, that is, pop noise. The silent shock wind generator needs to generate the spectrum of this part accurately and with good reproducibility.

  FIG. 4 is a block diagram showing a noise measuring device. The noise measuring device 2 includes a control device 3 for controlling the silent shock wind generator, a DC coupling sound card 4, a DC power amplifier 5, a silent shock wind generator 6, and a sound pickup device 7.

  The control device 3 emits an electric signal for driving the silent shock wind generation device 6 and processes a signal for each frequency sent from the sound collection device 7 via the DC coupling sound card 4. It is a device. Usually, a general PC can be used as a substitute.

  The DC coupling sound card 4 is a device for converting an electric signal sent from the control device 3 into an analog signal (sine wave or the like) for driving the silent shock wind generator 6 and sending it to the DC power amplifier 5. Is.

  The DC power amplifier 5 is a device for amplifying an analog signal sent from the DC coupled sound card 4. As a result, it is possible to generate sufficient impact wind for the reproduction of pop noise from the silent impact wind generation device 6.

  FIG. 5 is a diagram for explaining the details of the silent impact wind generation device 6. The left side is a side view, and the right side is a view seen from the opening end side of the silent shock wind generation device 6. The silent shock wind generator 6 has sufficient responsiveness and controllability with respect to the drive source, and does not generate noise such as abnormal noise due to the drive sound of the device or the shock wind when measuring the noise. In order to satisfy the above, the configuration shown in FIG.

  As shown in FIG. 5, on the opening surface of the high-compliance roll-edge speaker 61 that can be driven with a sufficient amplitude, a substantially conical tube formed so that the tube diameter is continuously reduced so that abnormal noise does not occur. A trapezoidal first speed-up adapter 621 (first speed increasing unit) and a second speed-up adapter 622 (second speed increasing unit) are provided. As a result, the silent shock wind generated from the high-compliance roll edge speaker 61 is accelerated by the first speed-up adapter 621 and the second speed-up adapter 622 and is emitted to the X side. As the high compliance roll edge speaker 61, JA0801 manufactured by Yamaha Corporation is used.

  The material of the first and second speed-up adapters may be any material as long as it does not generate abnormal noise, and examples thereof include hard materials such as metal and plastic. Further, if necessary, a pipe 623 which is a straight pipe portion for rectification can be provided. Further, a mechanical impedance adjusting member 624 may be provided on the open end side of the pipe 623 in order to reduce the generation of abnormal noise. The total length of the pipe 623 and the mechanical impedance adjusting member 624 is 30 mm. The speaker box 8 and the glass wool 9 as the sound absorbing material are installed for the purpose of reducing the backflow of the airflow generated in the back to the sound collecting device 7 side. If the presence of the phenomenon is not recognized, it is not necessary to provide the speaker box 8. Absent. With such a configuration, a silent shock wind excluding the sound portion from the burst sound having a bundle diameter of about 50 mm and a wind speed of several m to several tens m / sec is generated at a position 100 mm away from the opening end of the silent shock wind generator 6. be able to. As the sound pickup device 7, TYPE4152N manufactured by Accor Co., Ltd. is used.

  Hereinafter, the operation of the noise measuring device of the present invention having the above configuration and the noise measuring method will be described in more detail.

  First, the drive signal of the silent shock wind generator 6 was determined from the following viewpoints. A sine wave signal to a cosine wave signal (1), (2) and (3) as shown in FIG. 7 is applied to the silent shock wind generator 6 via the DC power amplifier 5. In FIG. 7, in the range where the signal duration is 25 msec from the sine wave rising portion close to the pronunciation condition, which is denoted by reference numeral (2) (the sine wave in the range surrounded by the two-dot broken line in FIG. 7). Measure the noise.

  Next, the operation of the noise measuring device and the noise measuring method will be described. A signal for driving the silent shock wind generator 6 is applied from the control device 3 to the DC power amplifier 5 via the DC coupling sound card 4. With this drive signal, the speaker cone of the high-compliance roll edge speaker 61 of the silent shock wind generator 6 gradually moves to the −X side in the left side view of FIG. 5, and then returns to the X side at once, thereby generating the silent shock wind. Radiate. The emitted silent shock wind is accelerated by the first speed-up adapter 621 and the second speed-up adapter 622 and is emitted to the X side. The silent shock wind emitted to the X side reaches the sound collection device 7. The pop noise detected by the sound pickup device 7 is converted into an electric signal, returned to the silent shock wind generator control device 3, and recorded as pop noise for each frequency. In this way, it is possible to investigate the influence of pop noise of the sound collecting device to be measured.

  Here, by installing the sound-transmitting material of the present invention between the silent shock wind generator 6 and the sound collecting device 7, it is possible to measure the pop noise reduction effect of the sound-transmitting material of the present invention. it can.

(Principle of pop noise reduction)
The reason why the acoustically transparent material of the present invention greatly reduces pop noise is not clear, but the following principle is presumed.

  First, the effect of reducing the pop noise will be described in detail. The sound-transmitting material of the present invention not only exhibits effective wind noise elimination performance against so-called steady wind such as natural wind or air-conditioning draft blown at a constant pressure, but in particular, it is a rapid movement of air molecule lumps. It also functions as a shield against "impact wind". On the other hand, it has a characteristic of exhibiting almost complete transparency to "sound" which is a movement of atmospheric pressure change (the medium itself vibrates but does not move). It is considered that pop noise can be reduced by having these characteristics together. This characteristic is common to conventional products.

  Further, since the sound transmitting material of the present invention is subjected to the oxidation treatment, the hardness of the SUS fiber surface can be increased and the specific gravity can be increased as described above. It is presumed that the property imparted by this oxidation treatment can increase the function as a shield against the "impact wind".

<< Applications of acoustically transparent materials >>
The acoustically transparent material of the present invention is generally used for walls of cultural facilities and houses, ceilings of museums and galleries and indoor pools, windshields for microphones, movie screens and the like.

(Manufacture of SUS fiberboard)
SUS fibers (stainless steel AISI316L, fiber diameter 30 μm) were superposed so as to be uniform to form a cotton-like web. This web was weighed so as to have a basis weight of 950 g / m ² and compressed between flat plates to have a thickness of 800 μm. This compressed, plate-shaped material was placed in a sintering furnace, heated to 1100 ° C. in a vacuum atmosphere, and sintered to obtain a SUS fiber board 1.

(Manufacture of SUS fiber sheet)
A SUS fiber sheet 1 was manufactured by the same method as in Example 1 of Patent 2562761 except that the thickness of the SUS fiber (stainless steel AISI316L, fiber diameter 30 μm) was 50 μm.

(Oxidation process)
The SUS fiber board 1 and the SUS fiber sheet 1 were each subjected to an oxidation treatment under the conditions shown in Table 1. Oxidation-treated SUS fiber boards and sheets of Comparative Examples 1-2 and Examples 1-7 were obtained.

(Surface atomic concentration distribution measurement)
For Comparative Example 1 and Examples 1 to 6, the surface element concentration distribution in the depth direction was measured by the etching ESCA method according to the above-described conditions. The measurement targets were Fe component, Fe oxidation component, Cr component, Cr oxidation component, oxygen atom and Ni. The measurement results of Comparative Example 1 are shown in FIG. 1, and the measurement results of Examples 1 to 6 are shown in FIGS. 2A to 2F, respectively. In Comparative Example 1, the measurement results of the SUS fiber board 1 before the oxidation treatment are described, but the measurement results of the SUS fiber board after the oxidation treatment subjected to the above-mentioned acid treatment are also substantially the same. Further, also for the SUS fiber sheet, similar results were obtained in the unoxidized surface treatment, the acid treatment, and the surface element concentration distribution after the oxidation treatment.

(Sound permeability confirmation test)
-Measuring method Based on the measuring method 1 described in the present specification, the sound transmittance was evaluated. Regarding the transmission frequency characteristics, there are various methods such as using continuous sine wave sweep, FM short tone, steady state pink noise, and FM seismic noise. Here, as shown in FIG. 3, a speaker a with an effective diameter of 10 cm is used. A continuous sine wave sweep sound was emitted from the attached sounding device of about 2250 cm ³ , and the acoustically transparent material b of each Example and each comparative example was installed on the front surface thereof, and installed at a position of about 1500 mm from the front surface of the speaker a. The effective value of the sound pressure response measured by the microphone c was recorded as a transmission frequency characteristic on a level recorder or the like. In that state, the change with or without the acoustically transparent material b was measured and confirmed as an insertion loss Δ (dB). For the sound source emitted from the speaker a, a continuous sine wave sweep without frequency modulation was used as a signal from 20 Hz to 20 kHz. The sound used here has an S / N ratio of 20 dB or more with respect to background noise. The insertion loss was calculated by the following formula.
Insertion loss Δ (dB) = microphone frequency response without sample (dB) -frequency response with sample placed (dB)

  Here, the sound transmission is such that the insertion loss Δ (dB) is within 2 dB in each 1/1 octave band of the center frequency of 63 Hz to 8 kHz, or each 1/3 octave band of the center frequency of 31.5 Hz to 16 kHz. In the case of 3 dB or less, it was judged as “good”, within 5 dB and within 6 dB, respectively, “slightly inferior”, over 5 dB, and over 6 dB, inferior. Since a continuous sine wave sweep was used, the evaluation was made in the above-mentioned 1/1 and 1/3 octave bands.

(Variation test of sound transmission between lots)
The insertion loss Δ (dB) was measured and the coefficient of variation was calculated for each of 10 samples of Examples 1 to 7 and Comparative Examples 1 to 2 by the above-described test method. When the calculated coefficient of variation of the acoustic permeability of the acoustically transparent material is 0.5 or less, it is indicated by ⊚, when it is 1 or less, by ◯, and when it is 1 or more, by x.

(Reduction of pop noise)
According to the method described above, pop noise was measured for each of 10 of Examples 1 to 7 and Comparative Examples 1 and 2. When the average value of the pop noise attenuation was less than 40 dB, it was evaluated as ×, when 40 dB or more was evaluated as ◯, and when 43 dB or more was evaluated as ⊚.

(Autonomy)
By holding the end of the 5 cm square sample and lifting the opposite end, it was evaluated as "independent" when it did not bend, and evaluated as "absent" when it bent.

  The above results are shown in Table 2. Reduction in lot-to-lot variation and pop noise in Examples 1 to 7 is ⊚, Comparative Examples 1 and 2 are each ◯, and the Examples exhibit more stable sound transmission performance than the Comparative Examples, At the same time, it is shown that pop noise can be reduced.

5 is a result of measuring the surface element distribution of the unoxidized SUS fiber of Comparative Example 1 by the etching ESCA method. 3 is a result of measuring the surface element distribution of the oxidation-treated SUS fiber plate of Example 1 by an etching ESCA method. 3 is a result of measuring the surface element distribution of the oxidation-treated SUS fiber plate of Example 2 by an etching ESCA method. 5 is a result of measuring the surface element distribution of the oxidation-treated SUS fiber plate of Example 3 by the etching ESCA method. 8 is a result of measuring the surface element distribution of the oxidation-treated SUS fiber plate of Example 4 by the etching ESCA method. 8 is a result of measuring the surface element distribution of the oxidation-treated SUS fiber plate of Example 5 by the etching ESCA method. 9 is a result of measuring the surface element distribution of the oxidation-treated SUS fiber plate of Example 6 by the etching ESCA method. It is a layout of the device for acoustic effect measurement. It is a block diagram which shows a pop noise measuring apparatus. It is a figure which shows a silent shock wind generation device with which a pop noise measuring device is equipped. Relative sound pressure when the reference sound pressure in the initial part (plosive sound "p" accompanied by shock wind) and the following vowel part "u" when the voiced sound "pu" is emitted, and time (Left) and graph showing the relationship between the relative sound pressure level with respect to the reference sound pressure (0 dB-SPL) in the initial part (“p”) and the subsequent vowel (“u”), and the frequency. (Right). A graph showing the relationship between the relative voltage with respect to the maximum allowable voltage and time, which is the data when a waveform examination was performed to reproduce the situation close to the time when an actual burst sound was generated in the silent shock wind generator. Is.

a speaker b sample c microphone 1 ... acoustically transparent material 2 ... noise measuring device 3 ... silent shock wind generator control device 4 ... DC coupled sound card 5 ... ... DC power amplifier 6 ... Silent shock wind generator 7 ... Sound pickup device 8 ... Speaker box 9 ... Glass wool 61 ... High compliance roll edge Speaker 62 ... Impact wind speed-up adapter 101 ... Wind shield 621 ... First speed-up adapter 622 ... Second speed-up adapter 623 ... Pipe 624 ... Mechanical impedance adjusting member

Claims (2)

A sound transmissive material in which SUS fibers are entangled with each other,
The atomic concentration of the Fe oxidation component on the outermost surface of the SUS fiber by the etching ESCA method is 15 Atom% or more and 40 Atom% or less,
The acoustically transparent material, wherein the atomic concentration of the Cr oxidation component on the outermost surface of the SUS fiber by etching ESCA method is 10 Atom% or less . At least part of the previous SL S US fibers are sintered, sound transmission material according to claim 1 Symbol mounting, characterized in that.

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