JP2009282155A - Method and device for reducing ultra-low frequency sound transmission - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for reducing ultra-low frequency sound transmission, which suppresses that ultra-low frequency sound leaks from an aperture of an ultra-low frequency sound-proof house which is always open. <P>SOLUTION: In the method and the device for reducing ultra-low frequency sound transmission, which includes the ultra-low frequency sound-proof house 1 for covering an ultra-low frequency sound source 3, and a reactance type silencer 4 for ultra-low frequency, provided at the always opened aperture of the ultra-low frequency sound-proof house 1, and which reduces ultra-low frequency sound emitted from an aperture section 2 to outside, the reactance type silencer 4 for ultra-low frequency includes an entrance section 2 and an exit section 5 of predetermined perimeter lengths l<SB>1</SB>and l<SB>2</SB>, which are proportional to an apparent resistance component of acoustic impedance, and the apparent resistance component is increased by developing an acoustic boundary layer in proportion to the perimeter length l<SB>1</SB>and l<SB>2</SB>, and the ultra-low frequency is reduced by converting acoustic energy to thermal energy. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ultra-low frequency sound transmission reduction method that suppresses leakage of ultra-low frequency sound from an opening of an always-open ultra-low frequency soundproof house, an ultra-low frequency soundproof house that is always open, and a reactance type for ultra-low frequency sound. The present invention relates to an ultra-low frequency sound transmission reducing device including a silencer.

  In recent years, the perception that noise is one of the serious environmental problems has become popular. And as if this agrees, regulations such as prefectural ordinances are now becoming stricter.

  For example, when construction is carried out in a densely populated city, the noise that accompanies it will mercilessly hit the place of the residents' lives and have a profound effect. In some cases, even the residents can be affected. For this reason, when working in a densely populated area, not only construction techniques but also on-site noise countermeasures are extremely important issues.

In particular, road construction and subway construction are accompanied by excavation, and it is necessary to separate the water from the mud generated in the mud (Gravel). Vibration sieves are often used to separate the two. Yes. This vibration sieving machine is a cylindrical sieve that separates sediments and water from water. Mechanical noise, vibration, and super-low frequency sound (Super)
low frequency sound). The ultra-low frequency sound is a sound of 20 Hz or less which is the lower limit of the human audible range, and is a very low frequency sound wave that cannot be heard by the human ear.

  Since the vibration sieve machine performs dehydration by vibration using rotation of about 1000 rpm, it generates a sound of 20 Hz or less, most of which is around 16 Hz to 17 Hz due to this vibration. As a result, this ultra-low frequency sound propagates to the house and vibrates the window glass and fittings of the house to generate secondary noise, causing noise problems and physiological problems such as headache, dizziness and nausea. May cause negative effects.

  Therefore, when installing a vibration sieving machine, it is often installed inside a super low frequency soundproof house provided on the ground. The soundproof wall of this ultra low frequency soundproof house is made of reinforced concrete walls or concrete blocks, and the earth and sand generated by excavation is transported to the ground by a conveyor etc. and separated in the ultra low frequency soundproof house. Therefore, measures are taken to prevent the very low frequency sound from leaking outside.

  However, although this ultra-low frequency soundproof house is effective for noise of 1 KHz to 10 KHz, propagation of ultra-low frequency noise of 5 Hz to 20 Hz cannot be suppressed. Since it was necessary to provide an opening for transporting earth and sand, very low frequency sound leaked through this constantly open opening, which was a problem.

  Thus, it has been proposed to use a sound absorbing wall provided with a Helmholtz resonator to mute the very low frequency sound (see, for example, Patent Document 1). In addition, it has also been proposed to arrange a quarter-wave sound absorbing resonator (see, for example, Patent Document 2). Furthermore, it has also been proposed to install a plurality of vibrating screens in the soundproof house and attenuate each other with the respective ultra-low frequency sounds generated by the vibrating screens (see, for example, Patent Document 3).

  In addition to this, it is proposed that the sound insulation structure of a vehicle is analyzed as a vibration model (mass spring model) and a sound insulation wall is constructed for sound in a frequency region above the resonance frequency, although it is not an ultra-low frequency sound (for example, patents) Reference 4).

  The present applicants have already proposed an ultra-low frequency sound transmission reducing device in which a sound deadening mechanism is mounted on a soundproof house (see Patent Document 5). This soundproof house has a sound deadening mechanism in the opening through which the ultra-low frequency sound passes, connecting the base end to the opening and expanding toward the tip, and the resonance connected to the peripheral surface of the communication pipe through the slit A tube is provided. The expansion of the communication pipe affects the directivity characteristics of ultra-low-frequency sound passing through the opening due to the synergistic effect of the silencing effect of the resonant pipe functioning as a Helmholtz resonator and the expansion effect of the expanded communication pipe It can be made easy to mute by giving.

  In addition, there is no material that can mute the ultra-low frequency sound only by absorbing the sound, and one of the present applicants also has a reinforced concrete layer placed on the lower surface of the steel plate layer and an air layer on the lower surface of the reinforced concrete layer. A soundproof panel provided with a sound absorbing layer provided is proposed (Patent Document 6). However, the silencing mechanism of such a no-media type silencing structure is not yet fully understood.

JP 2003-253627 A JP-A-8-229507 JP-A-10-57725 Japanese Patent Laid-Open No. 7-13573 JP 2008-9420 A JP 2001-32400 A

  As disclosed in Patent Documents 1 to 3, soundproof walls and soundproof houses for attenuating generated ultralow frequency sounds with respect to ultralow frequency sounds have been proposed. For the purpose of use, there is a need for an opening that is always open for discharging the earth and sand separated by the vibration sieve, and it is inevitable that ultra-low frequency sound leaks from this opening.

  The technique of Patent Document 4 is an analysis of a sound insulation structure of a vehicle, and is not a technique related to an ultra-low frequency sound transmission reduction device. A vibration model (mass spring model) with an opening facing each other is presented, and it is disclosed to provide a function as a sound insulation wall for sound in a frequency region above the resonance frequency (for example, 1 KHz or more). However, this technique is intended to reduce noise generated from an engine or the like, and with this method, it is not possible to reduce very low frequency sound having an area of 20 Hz or less. Ultra-low frequency sound passes through this sound insulation wall.

  In this regard, the ultra-low frequency sound transmission reducing device of Patent Document 5 proposed by the present applicants greatly contributes to prevention of leakage of ultra-low frequency sound as compared with a conventional soundproof house. However, since the structure of the resonance tube and the like is complicated, there has been an expectation for the development of an ultra-low frequency soundproof house that can prevent leakage of ultra-low frequency sound with a simpler structure.

  In addition, in a soundproof panel having a no-media type silencing structure as in Patent Document 6, if there is an opening, ultra-low frequency sound is transmitted through this opening, and a separate measure is required for this. In this way, if there is an opening, sound insulation alone is not enough, and since the silencing principle itself of the no-media type silencing structure is not known in detail, a new ultra-low frequency is required to further reduce the ultra-low frequency sound in the future. A low frequency sound transmission reduction method and a very low frequency soundproof house are desired.

  The present invention is for solving such a problem, and an ultra-low frequency sound transmission reducing method for suppressing leakage of ultra-low frequency sound from the opening of an ultra-low frequency soundproof house that is always open, and an always open circuit. An object of the present invention is to provide an ultra-low frequency sound transmission reducing device capable of suppressing leakage of ultra-low frequency sound from an opening of an ultra-low frequency soundproof house.

The present invention covers a sound source with an ultra-low frequency soundproof house, covers the sound source with an ultra-low frequency soundproof house, and installs a reactance silencer for ultra-low frequency sound from the opening in the normally open opening of the ultra-low frequency soundproof house. An ultra-low frequency sound transmission reduction method for reducing ultra-low frequency sound radiated to the outside,
Develop an acoustic boundary layer in proportion to the wetting length of the inlet and outlet of the reactance silencer for ultra-low frequency sound, and increase the apparent resistance component of the acoustic impedance proportional to this wetting length, It is characterized by reducing the ultra-low frequency sound by converting acoustic energy into thermal energy.

  The ultra-low frequency sound transmission reducing device of the present invention includes an ultra-low frequency soundproof house that covers a sound source, and a reactance silencer for ultra-low frequency sound that is provided in an always open opening of the ultralow frequency soundproof house. An ultra-low-frequency sound transmission reducing device that reduces ultra-low-frequency sound radiated from the opening to the outside. The reactance silencer for ultra-low-frequency sound has a predetermined length proportional to the apparent resistance component of the acoustic impedance. It has an entrance part and an exit part with a wet wetting length, develops an acoustic boundary layer in proportion to the wetting length, increases the apparent resistance component, converts the acoustic energy into thermal energy, and converts it into an ultra low frequency It is characterized by reducing sound waves.

  According to the ultra-low-frequency sound transmission reduction method and the ultra-low-frequency sound transmission reduction device of the present invention, the acoustic boundary layer is formed in proportion to the wetting length of the entrance and exit of the reactance silencer for ultra-low frequency sound. This increases the frequency of acoustic boundary layer separation and reattachment, thereby increasing the apparent resistance component of the acoustic impedance. By this apparent resistance component, a part of the acoustic energy is converted into thermal energy, which is always open. Suppresses the leakage of ultra-low frequency sound from the opening of the ultra-low frequency soundproof house.

  In the first embodiment of the present invention, a sound source is covered with an ultra-low frequency soundproof house, and a reactance silencer for ultra-low frequency sound is installed in an always open opening of the ultra-low frequency soundproof house to be radiated from the opening to the outside. An ultra-low-frequency sound transmission reduction method for reducing ultra-low-frequency sound, which develops an acoustic boundary layer in proportion to the wetting length of the entrance and exit of a reactance silencer for ultra-low frequency sound, An ultra-low-frequency sound transmission reduction method characterized by increasing an apparent resistance component proportional to the wet blot length and converting acoustic energy into thermal energy to reduce ultra-low frequency sound.

  With this configuration, an acoustic boundary layer is developed in proportion to the wetted length of the inlet and outlet of the reactance silencer for ultra-low frequency sound, thereby increasing the frequency of separation and reattachment of the acoustic boundary layer. The apparent resistance component of the acoustic impedance is increased, and a part of the acoustic energy is converted into thermal energy by this apparent resistance component, thereby suppressing the leakage of ultra-low frequency sound from the opening of the ultra-low frequency soundproof house that is always open. It becomes possible.

  A second aspect of the present invention is a configuration subordinate to the first aspect, and a cavity part in which a reactance silencer for ultra-low frequency sound expands in a direction perpendicular to the longitudinal direction between an inlet part and an outlet part. When wetting length is increased, the reactance component is decreased by increasing the vertical cavity width of the cavity, and a part of the acoustic energy is converted into thermal energy to produce ultra-low frequency sound. An ultra-low-frequency sound transmission reduction method characterized by reducing.

  With this configuration, even when the amount of loss of acoustic energy decreases due to the increase of the wetting length, the reactance component is reduced by increasing the vertical cavity width of the cavity, and a part of the acoustic energy is reduced. It is possible to suppress the leakage of ultra-low frequency sound from the opening of the ultra-low frequency soundproof house that is always open. When there are restrictions on the length in the longitudinal direction of the reactance silencer for ultra-low frequency sound and the cavity width of the cavity, a large effect can be obtained within this size.

  A third aspect of the present invention is a configuration subordinate to the first or second aspect, wherein the reactance silencer for ultra-low frequency sound is an expansion silencer, and the reactance component is reduced due to expansion, and the super An ultra-low frequency sound transmission reduction method characterized by further reducing low frequency sound.

  With this configuration, the loss amount of acoustic energy can be increased by reducing the reactance component due to expansion.

  According to a fourth aspect of the present invention, the reactance silencer for ultra low frequency sound is a resonance silencer, and the reactance component is reduced by phase interference. An ultra-low frequency sound transmission reduction method characterized by further reducing ultra-low frequency sound.

  With this configuration, the loss amount of acoustic energy can be increased by reducing the reactance component due to phase interference.

  The fifth aspect of the present invention is a configuration subordinate to any one of the first to fourth aspects, wherein the reflected wave is increased by an increase in the apparent resistance component of the acoustic impedance, and the very low frequency soundproofing is performed by the reflected wave. An ultra-low frequency sound transmission reduction method characterized by weakening standing waves in a house.

  With this configuration, it is possible to suppress the leakage of the ultra-low frequency sound from the opening of the ultra-low frequency soundproof house that is always open because the reflected wave increases due to the mismatch of the acoustic impedance and weakens the standing wave.

  A sixth aspect of the present invention includes an ultra-low frequency soundproof house that covers a sound source, and a reactance silencer for ultra-low frequency sound that is provided in an always open opening of the ultralow frequency soundproof house. Ultra-low-frequency sound transmission reducing device that reduces radiated ultra-low frequency sound. Reactance-type silencer for ultra-low frequency sound has a predetermined length of wettability proportional to the apparent resistance component of acoustic impedance. It has an inlet part and an outlet part, and develops an acoustic boundary layer in proportion to the wetting length to increase the apparent resistance component and convert the acoustic energy into thermal energy to reduce ultra-low frequency sound. Is an ultra-low frequency sound transmission reducing device.

  With this configuration, an acoustic boundary layer is developed in proportion to the wetted length of the inlet and outlet of the reactance silencer for ultra-low frequency sound, thereby increasing the frequency of separation and reattachment of the acoustic boundary layer. The apparent resistance component of the acoustic impedance is increased, and a part of the acoustic energy is converted into thermal energy by this resistance component, thereby suppressing the leakage of the ultra-low frequency sound from the opening of the ultra-low frequency soundproof house that is always open. It becomes possible.

  A seventh aspect of the present invention is a structure subordinate to the sixth aspect, in which a reactance silencer for very low frequency sound expands in a direction perpendicular to the longitudinal direction between an inlet portion and an outlet portion. And an ultra-low frequency sound transmission reducing device characterized in that the reactance component of the acoustic impedance is reduced by the cavity width in the vertical direction of the cavity to reduce the ultra-low frequency sound.

  With this configuration, even when the amount of loss of acoustic energy decreases due to the increase of the wetting length, the reactance component is reduced by increasing the vertical cavity width of the cavity, and a part of the acoustic energy is reduced. It is possible to suppress the leakage of ultra-low frequency sound from the opening of the ultra-low frequency soundproof house that is always open. When there are restrictions on the length in the longitudinal direction of the reactance silencer for ultra-low frequency sound and the cavity width of the cavity, a large effect can be obtained within this size.

  An eighth aspect of the present invention is a configuration subordinate to the seventh aspect, wherein the reactance type silencer for ultra-low frequency sound is a resonance type silencer, and an inlet portion and an outlet portion are disposed in the hollow portion. An ultra-low frequency sound transmission reducing device characterized in that it is communicated by a tubular body, and a plurality of holes are formed in the tubular body and communicated with a cavity.

With this configuration, the loss amount of acoustic energy can be increased by reducing the reactance component due to phase interference.
(Embodiment 1)
The ultra-low frequency sound transmission reducing method and the ultra-low frequency soundproof house in Embodiment 1 of the present invention will be described. The ultra-low frequency sound transmission reducing device of the first embodiment has a function of an expansion silencer. FIG. 1A is an explanatory diagram based on a basic configuration of an ultra-low frequency soundproof house and a model of the ultra-low frequency sound transmission reducing device according to Embodiment 1 of the present invention, and FIG. 1B is an ultra-low frequency diagram of FIG. FIG. 2 is a schematic view of a very low frequency soundproof house, FIG. 3 is a perspective view of an experimental soundproof house 1a, and FIG. 4 is an expansion according to Embodiment 1 of the present invention. FIG. 5 is an explanatory view of a vibration sieving machine model. FIG.

  FIG. 6 is an explanatory view showing the arrangement of the experimental soundproof house and the experimental reactance silencer in a state where the ultra-low frequency sound transmission reducing device according to the first embodiment of the present invention is not installed, and FIG. 7 shows the implementation of the present invention. FIG. 8 is an explanatory view showing the arrangement of the experimental soundproof house and the experimental reactance silencer in the state where the ultra-low frequency sound transmission reducing device in the first embodiment is installed, FIG. 8 is a measurement diagram of the background noise level in the anechoic chamber, and FIG. Is an explanatory diagram of an arrangement for measuring the sound insulation performance of the anechoic room, FIG. 10 is a diagram showing a measurement result of the sound insulation performance of the anechoic room, and FIG. 11 is an explanatory diagram of inverse square law characteristics in the anechoic room.

  Further, FIG. 12 is a sound pressure spectrum when no experimental reactance silencer is used, and FIG. 13 is a sound pressure spectrum diagram when an expansion type experimental reactance silencer is installed in an experimental soundproof house.

Fig. 14 shows the sound pressure spectrum analyzed without the experimental reactance silencer analyzed in the 1/3 octave band of 200 Hz and the spectrum diagram of the difference between the inside and outside of the SPL house, and 15 shows the expansion type analyzed in the 1/3 octave band of 200 Hz. spectrum of sound pressure spectrum and SPL Hausu out differences in the case of installing a laboratory reactance type silencer in laboratory soundproofing house at the measurement point P ₂ when 16 was installed laboratory reactance silencer expansion type of (TL), reduced volume (RSPL) illustration, FIG. 17 (TL), reduced volume (RSPL) illustration of the measurement point _{P 3} when the installed laboratory reactance silencer expansion type, FIG. 18 is (TL), reduced volume (RSPL) illustration of the measurement point P ₄ when set up laboratory reactance silencer expansion type.

  FIG. 19 is an explanatory diagram showing distance attenuation without an experimental reactance silencer, FIG. 20 is an explanatory diagram showing distance attenuation when an inflatable experimental reactance silencer is installed, and FIG. 21 is an experiment. FIG. 22 is an explanatory diagram of the sound pressure distribution inside the experimental soundproof house and the external sound pressure distribution without the reactive reactance silencer, and FIG. 22 shows the inside of the experimental soundproof house when the expansive experimental reactance silencer is installed. It is explanatory drawing of the sound pressure distribution of and the external sound pressure distribution.

  First, the silencing mechanism by the ultra-low frequency soundproof house 1 according to the first embodiment will be described with reference to the models shown in FIGS. As shown in FIGS. 1 (a) and 1 (b), the ultra-low frequency soundproof house 1 is surrounded by a high sound pressure ultra-low frequency sound source 3 such as a vibration sieve that generates ultra-low frequency sound (side surface and top surface). It covers. The wall surface is constituted by a soundproof panel having a no-media type silencing structure effective for low frequency sound (see Patent Document 6). However, the ultra-low frequency soundproof house 1 is provided with an opening 2 that is always open for transporting earth and sand. Ultra low frequency sound leaks to the outside through the opening 2.

  For this reason, in the first embodiment, a very low frequency sound transmission silencer 4 is provided by attaching a very low frequency sound reactance silencer 4 to the opening 2 of the very low frequency soundproof house 1. The reactance silencer 4 for the very low frequency sound adjusts the acoustic impedance in the opening 2 to increase the reflectivity by making the acoustic impedance inconsistent with the very low frequency soundproof house 1. It converts acoustic energy into thermal energy and dissipates it. Similarly, at the exit portion 5 of the reactance silencer 4 for extremely low frequency sound, the reflectance is increased by the mismatch between the external (outside air) acoustic impedance and the internal acoustic impedance, and a part of the acoustic energy is absorbed. It is converted into thermal energy and dissipated in the reactance silencer 4 for extremely low frequency sound.

  The reactance silencer 4 for ultra-low frequency sound according to the first embodiment actively utilizes the phenomenon of separation of the acoustic boundary layer of ultra-low frequency sound. By setting the wetted length of the acoustic conduit to a predetermined length, the apparent resistance component of the acoustic impedance is increased to the expected value, and this resistance component increases the internal energy loss, and by the conventional reactance component It also functions as a muffler, and achieves exceptional muffling for extremely low frequency sound.

  Now, it will be described that the silencing mechanism of the first embodiment is basically different from the silencer using only the conventional reactance component.

  Ultra-low frequency sound of 20 Hz or less has properties that are significantly different from sound waves of a frequency targeted by a general silencer, for example, sound waves of 1 KHz or more. That is, the sound wave targeted by a general silencer is (1) the sound pressure is sufficiently smaller than the average pressure of the medium, (2) the acoustic energy does not pass through the wall surface, and (3) depends on the viscosity of the medium. The influence and energy loss are negligible.

  On the other hand, ultra-low frequency sound with a high sound pressure at 20 Hz or less has a higher sound pressure than (1) general frequency noise, and (2) sound energy is transmitted through a wall made of ordinary sound absorbing material. (3) Energy loss due to the viscosity of the medium is not negligible.

  Therefore, it is difficult to mute the ultra-low frequency sound by muffing only with the reactance component according to the conventional concept, and the ultra-low frequency sound of the ultra-low frequency sound source 3 passes through the muffler using only the conventional reactance component.

  The reactance silencer 4 for ultra-low frequency sound of the present invention is different from the conventional idea, and is a silencer having a silencing mechanism that incorporates energy loss that has been ignored in the past. In other words, the reactance silencer 4 for ultra-low frequency sound utilizes the fact that the ultra-low frequency sound with a high sound pressure p has a large particle velocity u. It is designed to encourage development. The developed acoustic boundary layer peels off unsteadily and reattaches repeatedly, increasing the energy loss of the flow.

  In a high frequency range such as 1 KHz or higher, the acceleration / deceleration period is short, so the moving speed of the particles can be ignored, and the influence of viscosity is small. On the other hand, in the ultra-low frequency sound region, when the wavelength is the representative length, the Reynolds number is small, and the influence of viscosity is large. For example, at 10 Hz, the moving distance of one cycle of particles is about 5 mm, and it is slowly accelerated and decelerated, and the acoustic boundary layer peels off unsteadily and reattaches. This will be repeated. During this time, acoustic energy is converted into thermal energy and dissipated. The frequency of peeling and reattachment is proportional to the wetted length of the acoustic boundary layer.

FIG. 1B schematically shows a model of the silencing mechanism. In the opening 2 between the ultra-low frequency soundproof house 1 and the reactance silencer 4 for ultra-low frequency sound, and the exit 5 of the reactance silencer 4 for ultra-low frequency sound, m ₁ = ρ · (l ₁ / A), and m ₂ = ρ · (l ₂ / A) where there is an air mass (inertiaance) (ρ is the density of air, l ₁ and l ₂ are the wetting lengths of the opening 2 and the outlet 5. Where A is the cross-sectional area of the acoustic conduit), the space of the reactance silencer 4 for ultra-low frequency sound has an acoustic capacitance C = V / ρc ² (V is the volume of the cavity), and the spring constant k of the vibration system K = 1 / C.

In this two-degree-of-freedom vibration system, an incident wave is incident on the opening 2 from the ultra-low frequency soundproof house 1, a reflected wave is reflected from the opening 2, and from the exit 5 of the reactance silencer 4 for ultra-low frequency sound. A transmitted wave is emitted outside, and a reflected wave is reflected inside the silencer. 1 the pressure of the incident wave as shown in (b) from very low frequency sound insulation Houses 1 to ELF sound reactance silencer 4 P _i, the pressure of the reflected waves to the ultra low frequency sound insulation Houses 1 P _r, the pressure of the transmitted wave from the ultra-low-frequency sound reactance silencer 4 external (outside) and P _t.

This vibration system is different from the conventional silencer in that an aggressive low-frequency sound reduction structure is provided between the masses m ₁ and m _{2 by} the opening 2, the exit 5, and the cavity. . The apparent resistance Δ is an apparent attenuation per unit wetting length (longitudinal direction of the silencer) when the displacements x of the masses m ₁ and m ₂ are x ₁ and x ₂ (particle velocities u ₁ and u ₂ ), respectively. It can be expressed as (Equation 1) using the coefficient r. This attenuation coefficient r depends on how often unsteady peeling and reattachment of the developed acoustic boundary layer occurs.

実施の形態１の超低周波音透過低減方法は、超低周波音の特性を利用して反射率γ（＝Ｐ_ｒ／Ｐ_ｉ）を上げるように、また、透過率θ（＝Ｐ_ｔ／Ｐ_ｉ）を下げるようにぬれぶち長さを選択するものである。すなわち期待する減衰係数ｒになるぬれぶち長さｌ_１，ｌ_２を採用する。さらに超低周波音用リアクタンス型消音器４の空洞部の容積Ｖとの関係でエネルギー損失が最大となるように調整するものである。

In the ultra-low frequency sound transmission reduction method of the first embodiment, the reflectance γ (= P _r / P _i ) is increased using the characteristics of the ultra-low frequency sound, and the transmittance θ (= P _t / spotted wetting to lower the P _i) is to choose the length. That is, the wetting spot lengths l ₁ and l ₂ with the expected attenuation coefficient r are adopted. Furthermore, it adjusts so that an energy loss may become the maximum in relation to the volume V of the cavity part of the reactance type silencer 4 for very low frequency sound.

The reactive silencer 4 for ultra-low frequency sound has a limit (allowable limit) that the length L in the sound wave traveling direction (length in the longitudinal direction in the present invention) and the volume V cannot be increased beyond the allowable amount when viewed from a practical aspect. ) In addition, muffing in the very low frequency range cannot be reduced unless the resonance frequencies k / m ₁ and k / m ₂ are small. Therefore, L is set to the allowable limit, and the damping coefficient r is increased by increasing the wetting lengths l ₁ and l ₂ .

At this time, the volume V of the cavity portion decreases in proportion to (L-l ₁ -l ₂ ) if the vertical cavity height (the cavity width in the present invention) remains unchanged. It is necessary to increase the vertical cavity height beyond the height corresponding to the volume reduction. When the wet blot lengths l ₁ and l ₂ are increased to L = l ₁ + l ₂ , the volume V decreases to 0 and the volume V itself has a practical allowable limit. There is a condition (l ₁ + l ₂ ) that maximizes the volume V on condition that both the length L and the volume V are within acceptable limits. Under these conditions, the wetting lengths l ₁ and l ₂ increase the apparent resistance component and contribute to noise reduction. At the same time, the volume V provides a noise reduction effect as an expansion silencer. In other words, there is a condition where the silencing effect is the highest within the allowable limit. The reactance silencer 4 for very low frequency sound is sized so as to satisfy this condition.

  The equation of motion of forced vibration of a two-degree-of-freedom system in the reactance silencer 4 for ultra-low frequency sound is expressed as (Equation 2) and (Equation 3). α is an impedance in consideration of the aperture ratio A / S, the air around the opening 2 being incidentally moved, and the position of the opening 2 being offset from the side of the ultra-low frequency soundproof house 1. It is a correction coefficient that corrects the effect of mismatch. As described above, A is the cross-sectional area of the acoustic conduit, and S is the side area of the ultra-low frequency soundproof house 1.

粒子の移動速度（変位の微分値）から体積速度Ｕ_１、Ｕ_２を求め、開口部２での入力インピーダンスＺ_ｉ＝Ｐ_ｉ／Ｕ_１を複素数表示すると、Ｚ_ｉ＝Ｒ_ｉ（ｍ_１，ｍ_２，Ａ，ｋ，ｒ，α，γ，θ）＋ｊＸ_ｉ（ｍ_１，ｍ_２，Ａ，ｋ，ｒ，α，γ，θ）のように記述できる。また、出口部５での放射インピーダンスＺ_ｔ＝Ｐ_ｔ／Ｕ_２も、Ｚ_ｔ＝Ｒ_ｔ（ｍ_１，ｍ_２，Ａ，ｋ，ｒ，α，γ，θ）＋ｊＸ_ｔ（ｍ_１，ｍ_２，Ａ，ｋ，ｒ，α，γ，θ）のように記述できる。ここで、パラメータｍ_１，ｍ_２，ｋはパラメータｌ_１，ｌ_２，Ａ，Ｖ，Ｌの関数である。従って、超低周波音用リアクタンス型消音器４の合成インピーダンスＺはＺ＝（Ｒ_ｉ＋Ｒ_ｔ）＋ｊ（Ｘ_ｉ＋Ｘ_ｔ）と表せる。

When volume velocities U ₁ and U ₂ are obtained from the moving speed (displacement differential value) of the particle and the input impedance Z _i = P _i / U ₁ at the opening 2 is displayed in a complex number, Z _i = R _i (m ₁ , m ₂ , A, k, r, α, γ, θ) + jX _i (m ₁ , m ₂ , A, k, r, α, γ, θ). Further, the radiation impedance Z _t = P _t / U ₂ at the outlet 5 is also Z _t = R _t (m ₁ , m ₂ , A, k, r, α, γ, θ) + jX _t (m ₁ , m ₂ , A, k, r, α, γ, θ). Here, the parameters m ₁ , m ₂ , and k are functions of the parameters l ₁ , l ₂ , A, V, and L. Therefore, the combined impedance Z of the reactance silencer 4 for ultra-low frequency sound can be expressed as Z = (R _i + R _t ) + j (X _i + X _t ).

Accordingly, the acoustic power W consumed by the apparent resistance component of the reactance silencer 4 for ultra-low frequency sound is W = (R _i + R _t ) · | Pi | ² / {(R _i + R _t ) ² + (X _i + X _t ) ² }, so that when P _i has a certain frequency f, the relationship between l ₁ , l ₂ , L, A, V, r, α, γ, θ is obtained, and low The structure of the frequency reactance silencer 4 may be determined. Since the apparent attenuation coefficient r depends on l ₁ , l ₂ , A, and f, first, the size of l ₁ , l ₂ , A, and f is increased to the limit, and the volume V at this time is maximized. Increase to increase W. When the volume V increases, the reactance component (X _i + X _t ) becomes a small value.

There is also a volume V in which phase interference of sound waves in the reactance silencer 4 for ultra-low frequency sound occurs. When resonance occurs inside, the reactance component (X _i + X _t ) becomes 0 and W increases. Phase interference occurs when the cavity height in the direction perpendicular to the longitudinal direction of the reactance silencer 4 for ultra-low frequency sound is equal to ½ wavelength of the sound wave. Therefore, W can be minimized by selecting such a structure of the reactance silencer 4 for ultra-low frequency sound and arranging it so as to have a predetermined correction coefficient α. In this case, for example, as shown in FIG. 23, it is preferable to connect with a cylinder having many holes from the opening 2 to the outlet 5. Details will be described in Embodiment 2.

As described above, the theoretical analysis only shows a general tendency, and there is a difference from the actual value. Moreover, it is difficult to theoretically derive the apparent attenuation coefficient r, and it is only through experience. Accordingly, the apparent attenuation coefficient r, correction coefficient α, l ₁ , l ₂ , L, volume V, and the like are obtained experimentally and used. This method will be described later.

If these are supplemented, the correction coefficient α can be set to a small value by reducing A / S and arranging the correction coefficient α at a corner portion shifted from the center of the side surface of the ultra-low frequency soundproof house 1. For example, in the case of 10 Hz, the peeling phenomenon is performed by peeling and reattaching at least once every distance of about 5 mm by acceleration / deceleration of particles. Therefore, the relationship between the frequency, the frequency of peeling and reattachment, the wetting lengths l ₁ and l ₂ , and the attenuation coefficient r is obtained in advance by experiment. For example, the peeling is performed 50 times or more on a 240 mm wall. , Select the wetting edge lengths l ₁ and l ₂ to be reattached. An attenuation coefficient r having an effect of reducing the very low frequency sound expected at this time can be realized.

  The ultra low frequency sound generated in the ultra low frequency soundproof house 1 is reflected by the opening 2, and this reflected wave acts on the standing wave to weaken the standing wave inside the ultra low frequency soundproof house 1. In addition, the ultra-low frequency sound transmitted through the opening 2 attenuates the ultra-low frequency sound by peeling and reattaching the acoustic boundary layer, expands into the reactance silencer 4 for the ultra-low frequency sound, and further attenuates. . And when radiating from the exit part 5, the acoustic boundary layer is peeled off and reattached to attenuate the ultra-low frequency sound, and only a few transmitted waves are radiated to the outside while being reflected at the end part of the exit part 5. .

  Therefore, a specific example of the ultra-low frequency soundproof house 1 in the first embodiment will be described below. FIG. 2 shows an overview of the ultra-low frequency soundproof house 1. An example of the size of the ultra-low frequency soundproof house 1 will be described. As shown in FIG. 3, it has a box-shaped structure with a side length of 12000 mm, a depth of 8040 mm, and a height of 9960 mm. 2 is provided with an opening 2 having a lateral width d of 1992 mm and a height of e996 mm on a side surface viewed from the right side and a front surface viewed from the left side in FIG. Two ultra-low-frequency sound sources 3 (sound source and vibration sieving machine in the present invention) that generate ultra-low frequency sound of 20 Hz or less, for example, 16 Hz, are provided in the interior, and the earth and sand generated by excavation are separated from water. And the separated earth and sand are conveyed to the opening part 2 with the belt conveyor 6, and are loaded in the conveyance vehicle waiting here. A reactance-type silencer 4 for ultra-low frequency sound is connected to the opening 2, and earth and sand are conveyed to the exit 5 by the belt conveyor 6.

In the present invention, various amounts of data such as an apparent attenuation coefficient r, correction coefficients α, l ₁ , l ₂ , L, volume V, etc. are obtained for the design of the reactance silencer 4 for extremely low frequency sound. It is necessary to confirm the mute effect after designing this. A method of doing this and a similar scaled-down facility for this will be described. Of course, it is best to use a full-scale ultra-low frequency soundproofing house 1 and a full-scale ultra-low frequency sound reactance silencer 4 to prepare a similar equipment of this reduced scale. This is because it is practically difficult to obtain data with the frequency soundproof house 1 and the reactance silencer 4 for ultra-low frequency sound. In the following, the method of actually confirming the effect in the first embodiment and the similar equipment of the reduced scale will be described. However, these are the method for obtaining data necessary for the design in advance and the equipment for performing the same. It is the same.

By conducting experiments using equipment of similar sizes, data such as the apparent attenuation coefficient r, correction coefficient α, l ₁ / L, l ₂ / L, volume V, and the like are acquired and reflected in the design. In addition, before making the actual size ultra-low frequency soundproofing house 1 and the actual size ultra-low frequency sound reactance silencer 4, the effect of this design is confirmed from similar rules using similar equipment. For the huge ultra-low frequency soundproof house 1 and the actual ultra-low frequency sound reactance silencer 4, facilities similar to a reduced scale are indispensable.

  In Embodiment 1, the effect was confirmed with the experimental soundproof house 1a having a size reduced to 1/12. The effect of reducing the ultra-low frequency soundproofing is confirmed with the experimental reactance silencer 4a and the experimental soundproofing house 1a reduced to 1/12 scale, with the former being attached to the former and when not being attached. This was done by taking the difference in measurement sound. Specific numerical values described below are values actually used in a similar facility, and the measurement result is a measurement result in this similar facility.

  As shown in FIG. 3, the experimental soundproof house 1a has a side length a of 1000 mm, a depth width b of 670 mm, a height c of 830 mm, and the opening 2a has a width d of 166 mm, The height e is 83 mm. The position where the opening 2a is provided is separated from the left end of the front of the experimental soundproof house 1a (the side where the opening 2a is provided) by a distance g and from the ground surface by a distance h. The distance g is 35 mm, and the distance h is 83 mm. The experimental soundproof house 1a was prepared by preparing six acrylic plates having a thickness of 10 mm and screwing 188 locations on an iron framework having a thickness of 1 mm.

  Next, the experimental reactance silencer 4a will be described. In FIG. 4, the length L in the longitudinal direction of the experimental reactance silencer 4a is 120 mm, and the width H in the depth width b direction perpendicular to this is 490 mm. The height I in the height c direction was 490 mm. The position of the opening 2a of the experimental reactance silencer 4a connected to the opening 2a of the experimental soundproof house 1a is a distance N corresponding to the distance g of the experimental soundproof house 1a and a distance M corresponding to the distance h. Placed in position. Here, the distance N is 35 mm, and the distance M is 83 mm. Moreover, the width K of the opening 2a is 166 mm, and the height J is 83 mm. Similarly to the experimental soundproof house 1a, the experimental reactance silencer 4a was also made of an acrylic plate having a thickness of 10 mm.

Accordingly, since the acrylic plate is overlapped acoustic conduit of the experimental equipment (opening 2a) in thickness 10 mm, the wetted perimeter length _{l 1} 20 mm, the acoustic conduit wetted perimeter length of the (opening 5a) _{l 2} Although a 10 mm, wetted perimeter length _{l 1} of the opening 2 in the actual ultra low frequency sound insulation Houses 1 corresponds to 12 times the 240 mm, wetted perimeter length _{l 2} of the outlet portion 5 corresponds to 120 mm. The widths of l ₁ and l ₂ are expected to be 11 dB to 12 dB at this portion, and as a result, the acoustic boundary layer is peeled off and reattached, causing pressure loss and being dissipated as thermal energy.

  Subsequently, as the experimental ultra-low frequency sound source 3, pink noise reproduced by a CD player was amplified and used. Two vibration sieving machine models equipped with speakers as shown in FIG. 5 are arranged corresponding to the positions of FIG. 2 in the experimental soundproof house 1a, and microphones are provided at four locations inside and outside the experimental soundproof house 1a. Measurements were made. The vibration sieving machine model is made of a 25 mm thick plywood plate and has a structure as shown in FIG.

The maximum height corresponding to the position assumed to be earth and sand is 650 mm, the height of the stand assumed to be the belt conveyor 6 is 500 mm, the height of the speaker is 270 mm, and the length in the longitudinal direction (belt conveyor conveying direction) is 350 mm. The soundproof house 1a for experiment was installed in an anechoic room (Anechoic Room) and measured. The sound data collected by the microphone is A / D converted by the A / D converter and transferred to the personal computer. The frequency analyzer (Frequency) installed in the personal computer is used.
Analyzer).

  Moreover, although the ultra-low frequency sound generated from an actual vibration sieve is about 16 Hz, the experimental soundproof house 1a and the experimental reactance silencer 4a are 1/12 of the actual size. The frequency used was 192 Hz in proportion.

  FIG. 6 and FIG. 7 show the mounting state of the experimental soundproof house 1a and the experimental reactance silencer 4a, and the arrangement of speakers and microphones. The measurement point P1 is a position 50 mm from the inner wall surface of the experimental soundproof house 1a, the measurement point P2 is a position 83 mm from the outlet side surface of the experimental reactance silencer 4a, and the measurement point P3 is a position 166 mm from the outlet side surface. Point P4 is a position of 415 mm from the side surface on the outlet side.

  The microphone used was a 1/2 inch type condenser microphone for measurement (manufactured by Ono Sokki, MI-1233). The microphone sensitivity is -28.45 dB, the frequency response is a sound field shape, and the frequency range is 20 Hz to 20000 Hz. A microphone preamplifier (MI-3110, manufactured by Ono Sokki Co., Ltd.) was used as a microphone amplifier, and a pistonphone (Lion, NC-72) that generates a sound pressure level of 114 dB-250 Hz was used for calibration. These amplified signals were displayed on a display by FFT (Fast Fourier Transform). The sampling frequency of the experiment was 2 kHz (c characteristic), the number of sample points was 4096, and the number of averaging was 50 times.

  Then, in order to correctly evaluate the attenuation of sound waves, an experimental soundproof house 1a and an experimental reactance silencer 4a were installed in an anechoic chamber and measured. For this reason, three characteristics of the anechoic chamber, (1) background noise level, (2) sound insulation performance, and (3) inverse square law characteristic (sound pressure level distance attenuation level) were measured. The arrangements of FIGS. 6 and 7 were measured in an anechoic chamber.

  The background noise (1) of the anechoic room is all noises other than the IEC when attention is paid to one noise among noises synthesized from a plurality of noise sources. According to the standard, it should be at least 10 dB lower than the generated sound pressure level of the object to be measured. The measurement was performed with a 1/1 octave band with all peripheral devices stopped. The measurement results are as shown in FIG. NC is an NC curve.

  The sound insulation performance of the characteristic (2) of the anechoic chamber was measured in an arrangement as shown in FIG. The measurement results are as shown in FIG. 10, and the room sound pressure level with a center frequency of 100 Hz to 4 KHz is plotted on the sound insulation grade reference curve diagram. From this, the sound insulation performance of the anechoic room is also satisfied with the level of D-40.

Further, the inverse square law characteristic of the characteristic (3) was measured. The interval between the measurement points in the anechoic room is 0.2 m from 2 m to 0.5 m from the speaker placed on the wall, and 0.5 m from 2 m to 3.5 m. The inverse square law characteristics, and the distance from the sound source to r, the intensity of sound is inversely proportional to ^{r 2,} the sound pressure level relative to the _{r 0} is attenuated by _{20 · log 10 (r / r} 0) It is a characteristic. The measurement frequencies are 125 Hz, 250 Hz, 500 Hz, 1 KHz, 2 KHz, 4 KHz. When the distance r is doubled, it attenuates by 6 dB, and this indicates the free sound field. According to the measurement result, FIG. 11 shows that the anechoic chamber is a free sound field up to about 1.5 m. ing.

Now, since the experimental reactance silencer 4a (actual silencer 4 for ultra-low frequency sound in actual size) of the first embodiment also functions as an expansion silencer, the expansion silencer will be described. The expansion-type silencer is a silencer that utilizes a change in cross section, and is reflected and reduced at a location where the cross section has changed. Expands from the cross-sectional area _{S 1} in the cross-sectional area _{S 2,} further if reduced cross-sectional area _{S 3} from the cross-sectional area _{S 2,} sound waves incident from the _{S 1} part in the enlarged cross sectional _{(S 1} → _{S 2)} reflected back to the S ₁ side, the rest of the sound wave travels into the cavity of S _2. Thereafter, part of the reflected light is further reflected at the reduced cross section (S ₂ → S ₃ ) and returned to the inside of the cavity or the S ₁ side, and the remaining sound wave passes through the silencer. The transmission loss (TL) of this silencer is obtained by (Equation 4).

ここで、ｃは音速、ｌは空洞の長さ、ｆは周波数である。実験用リアクタンス型消音器４ａではｌ＝０．１ｍ、Ｓ_１＝０．０８３×０．１６６ｍ２、Ｓ２＝０．４７×０．４７ｍ２、（Ｓ_２／Ｓ_１＝１６）であり、（数４）によればｆ＝１９２ＨｚのときＴＬ＝４．４ｄＢ程度の減衰が期待できる。この膨張型消音器としての透過損失（ＴＬ）と容積との関係を示した図が図３１（ａ）である。

Here, c is the speed of sound, l is the length of the cavity, and f is the frequency. In the experimental reactance silencer 4a, l = 0.1 m, S ₁ = 0.083 × 0.166 m 2, S2 = 0.47 × 0.47 m 2, (S ₂ / S ₁ = 16), ), When f = 192 Hz, attenuation of about TL = 4.4 dB can be expected. FIG. 31A shows a relationship between the transmission loss (TL) and the volume as the expansion silencer.

Subsequently, the experimental soundproofing house 1a equipped with the experimental reactance silencer 4a in the first embodiment (ultra-low frequency soundproofing house 1 equipped with the reactance silencer 4 for ultralow frequency sound in actual size) It will be explained that the frequency sound is reduced. The sound pressure of pink noise was measured under the arrangement shown in FIG. 7 and the following conditions (1) and (2). (1) “A state where nothing is installed in the opening 2a of the experimental soundproof house 1a”, (2) “A state where the expansion-type experimental reactance silencer 4a is installed in the opening 2a of the experimental soundproof house 1a” It is. Figure 7 measurement points _P 1 shown _{in, P 2, P 3, P} 4 are each experimental soundproofing Hausu in 1a _(P 1), laboratory soundproofing Hausu 1a opening 83mm from the outlet _{(P 2), 166mm (P} 3) 415 mm (P ₄ ). At the same time as (1) and (2), the sound pressure of pink noise was measured in (3) “in a state where the resonance type experimental reactance silencer 4a is installed in the opening 2a of the experimental soundproof house 1a”. However, this result will be described in the second embodiment.

And the sound pressure spectrum of the _{P 1} and _P 2, _{P 1} and _P 3, _{P 1} and _{P 4} each point at that time, SPL at _{P 1} and _P 2, _{P 1} and _P 3, _{P 1} and _{P 4} (Sound Pressure level) Spectrum diagrams of the difference between inside and outside the house are shown in FIGS. FIG. 12 is a sound pressure spectrum when the experimental reactance silencer 4a is not provided, and FIG. 13 is a sound pressure spectrum diagram when the expansion type experimental reactance silencer 4a according to the first embodiment is installed. These sound pressure spectra can be obtained by FFT analysis of pink noise measured with four microphones. 12 and 13, the transmission loss (transmission loss when the experimental reactance silencer 4a is not installed) is shown.
loss, TL) and transmission loss (TL) when the experimental reactance silencer 4a is installed. The difference between the inside and outside of the SPL house is the silencing effect of the entire experimental ultra-low frequency sound transmission reducing apparatus including the experimental reactance silencer 4a and the experimental soundproof house 1a.

  Next, the SPL house internal / external difference due to the 1/3 octave band and the volume reduction by the experimental reactance silencer 4a of the first embodiment were also measured.

(1) “In a state where nothing is installed in the opening 2a of the experimental soundproof house 1a”, (2) “In a state where the experimental reactance silencer 4a is installed in the opening 2a of the experimental soundproof house 1a” The pink noise measured inside and outside (measurement points P ₁ , P ₂ , P ₃ , P ₄ ) was analyzed by 1/3 octave at center frequencies of 160 Hz, 200 Hz, 250 Hz, and 315 Hz. FIGS. 14 and 15 show the sound pressure spectrum analyzed at 200 Hz closest to 192 Hz and the SPL house internal / external difference spectrum at P ₁ and P ₂ , P ₁ and P ₃ , and P ₁ and P ₄ . Although a 1/3 octave analysis was performed at the center frequencies of 160 Hz, 250 Hz, and 315 Hz, the same tendency was generally exhibited, so duplication was avoided and not shown here. This difference between the inside and outside of the SPL house is the soundproofing effect of the entire experimental ultra-low frequency sound transmission reducing device. If a difference is further taken between the state in which the experimental reactance silencer 4a is installed and the state in which the experimental reactance silencer 4a is not installed, this becomes the attenuation effect by the experimental reactance silencer 4a.

FIGS. 16, 17 and 18 show the difference between the SPL inside and outside the house (TL) and the volume reduction (RSPL) by the experimental reactance silencer 4a. 16 at the measurement point P ₂ at the time of set up laboratory reactance silencer 4a of the inflatable type in the first embodiment (TL), reduced volume (RSPL), FIG. 17 is a laboratory reactance silencer 4a at the measuring point _{P 3} when installing the (TL), reduced volume (RSPL), FIG. 18 at the measurement point _{P 4} when set up laboratory reactance silencer 4a (TL), reduced volume (RSPL) It is.

In the view this expansion type laboratory reactance silencer 4a of the first embodiment, the center frequency 200Hz in _{P 2} 16 _dB, and left approximately 20dB higher damping effect in P 3, _{P 4.} Although it is attenuated even at center frequencies of 250 Hz and 315 Hz, the sound pressure is increased at 160 Hz.

Incidentally, examined the effect of attenuation due to distance and measurement point _{P 2,} P 3, _{P 4} moves away. According to this, distance attenuation is as shown in FIG. 19 without the experimental reactance silencer 4a, and as shown in FIG. 20 when the expansion type experimental reactance silencer 4a of the first embodiment is installed. became. Since the attenuation rate is almost the same between the case without the experimental reactance silencer 4a and the case with the experimental reactance silencer 4a, the presence or absence of the experimental reactance silencer 4a affects the distance attenuation. It is judged not to give.

Furthermore, numerical analysis was performed in order to see the effect as a silencer when the expansive experimental reactance silencer 4a of the first embodiment was installed. As an analysis method, a scalar potential at a point x in the medium at time t is p (x, t) within a range of discretization error using acoustic finite elements and boundary elements, and a wave of p (x, t) The Hernholtz equation (Formula 5), which is a complex representation of the equation, was solved. Here, p ^to (x) is a complex representation of p (x, t), k = ω / c. ω is the angular frequency (= 2πf), and c is the speed of sound. FIG. 21 shows the sound pressure distribution when the experimental reactance silencer 4a is not installed, and FIG. 21 shows the sound pressure distribution when the expansion type experimental reactance silencer 4a is installed.

ここで周波数ｆは１９２Ｈｚであり、図２１の左側は実験用防音ハウス１ａ内部の音圧分布、右側は外界（外気）である。図２２の左側も実験用防音ハウス１ａ内部の音圧分布、右側は外界を示し、この中間に設置されているのが膨張型の実験用リアクタンス型消音器４ａである。単位はＰａである。Ｌ０は図示した最小の音圧レベル０（０〜０．０４３Ｐａ）を示し、Ｌ１０は最大の音圧レベル１０（０．８２１Ｐａ以上）を示している。等高線で囲まれた領域は同じ音圧レベルのゾーンを示す。

Here, the frequency f is 192 Hz, the left side of FIG. 21 is the sound pressure distribution inside the experimental soundproof house 1a, and the right side is the outside (outside air). The left side of FIG. 22 also shows the sound pressure distribution inside the experimental soundproof house 1a, the right side shows the outside world, and the expansive experimental reactance silencer 4a is installed in the middle. The unit is Pa. L0 indicates the illustrated minimum sound pressure level 0 (0 to 0.043 Pa), and L10 indicates the maximum sound pressure level 10 (0.821 Pa or higher). A region surrounded by contour lines indicates a zone having the same sound pressure level.

  According to this calculation result, the sound pressure is reduced by about 4 dB to 5 dB when the outlet portion 5a is compared when the experimental reactance silencer 4a is not installed and when the expansion type experimental reactance silencer 4a is installed. I understand. It has dropped from L4 (sound pressure level 4) to L3 (sound pressure level 3). It can be seen that the effects of the expansion silencer 4 dB to 5 dB can be expected as the effect of the experimental reactance silencer 4 a.

  From the above, when the expansion type reactance silencer 4 for ultra-low frequency sound is installed in the ultra-low frequency soundproof house 1, as shown in FIGS. 16, 17, and 18, the frequency to be controlled is around 16 Hz (experimental reactance type). In the silencer 4a, which corresponds to around 200 Hz), it is possible to attenuate the very low frequency sound by about 16 dB. This shows almost the same tendency at frequencies of 20 Hz and 26 Hz (corresponding to center frequencies of 250 Hz and 315 Hz).

  The ultra-low frequency sound transmission reducing device (ultra-low frequency soundproof house and ultra-low frequency sound reactance silencer) according to the first embodiment has a wall surface for ultra-low frequency sound of 20 Hz or less that normally passes through the soundproof house. Accelerate the development of the acoustic boundary layer due to viscosity, and unsteadyly peel and reattach the developed acoustic boundary layer to increase the energy loss of the flow. That is, it is possible to slowly accelerate and decelerate over time, repeatedly peel off and reattach the acoustic boundary layer, and convert part of the acoustic energy into thermal energy.

  Also, the longitudinal length of the reactance silencer for ultra-low frequency sound is set to an allowable limit, and the wet width is increased while compensating for the longitudinal width of the cavity that decreases with this increase. The acoustic energy can be reduced by expansion to a predetermined cavity height in the vertical direction. At the same time, the reflectance γ increases, and this reflected wave acts on the standing wave formed in the ultra-low frequency soundproof house, so that the standing wave can be weakened. When there is a restriction on the length in the longitudinal direction of the reactance silencer for ultra-low frequency sound or the cavity height of the cavity, a great effect can be obtained.

(Embodiment 2)
Next, the ultra-low frequency sound transmission reduction method and the ultra-low frequency soundproof house in Embodiment 2 will be described. The ultra-low frequency sound transmission reducing device according to the second embodiment has a function of a resonance type silencer.

FIG. 23 is a perspective view of a resonant experimental reactance silencer according to Embodiment 2 of the present invention, and FIG. 24 is a sound pressure spectrum when the resonant experimental reactance silencer is installed in the experimental soundproof house 1a. FIG. FIG. 25 is a spectrum diagram of the sound pressure spectrum and the difference between the inside and outside of the SPL house when a resonant experimental reactance silencer analyzed at 200 Hz is installed in the experimental soundproof house 1a, and FIG. 26 is a resonant experimental reactance silencer. vessels of the measurement point P ₂ when installed (TL), reduced volume (RSPL) illustration, FIG. 27 at the measuring point P ₃ when the installed laboratory reactance type silencer resonance (TL) , reduced volume (RSPL) illustration, FIG 28 is a (TL), reduced volume (RSPL) illustration of the measurement point _{P 4} when set up laboratory reactance silencer resonance type.

  FIG. 29 is an explanatory diagram showing distance attenuation when a resonance type experimental reactance silencer is installed, and FIG. 30 is a sound pressure inside the experimental soundproof house 1a when an expansion type experimental reactance silencer is installed. It is explanatory drawing of distribution and sound pressure distribution of the external world.

  The ultra-low frequency soundproof house 1 and the resonance-type reactance silencer 4 for the ultra-low frequency sound of the second embodiment are the same as the ultra-low frequency soundproof house 1 and the inflatable ultra-low frequency sound reactance of the first embodiment. Since the basic silencer 4 and the basic structure and numerical values are common, the same reference numerals indicate the same configuration and numerical values, and detailed description thereof is omitted. 1 to 22 are also referred to in the second embodiment as necessary. The experimental soundproof house 1a and the experimental reactance silencer 4a have a scale that is 1/12 of the ultralow frequency soundproof house 1 and the ultralow frequency sound reactance silencer 4.

  23A, the length L (see FIG. 1A) of the experimental soundproof house 1a is 120 mm, the depth width H is 490 mm, and the height I is 490 mm. The opening 2a of the experimental reactance silencer 4a connected to the opening 2a of the experimental soundproof house 1a is arranged at a distance N and a distance M. Here, the distance N is 35 mm, the distance M is 83 mm, the width K of the opening 2a is 166 mm, and the height J is 83 mm. The experimental reactance silencer 4a is also made of an acrylic plate having a thickness of 10 mm, similar to the experimental soundproof house 1a.

Accordingly, since acrylic plates having a thickness of 10 mm are stacked, l ₁ (see FIG. 1A) is 20 mm, and l ₂ (see FIG. 1A) is 10 mm. Then, the width _{l 1} of the opening 2 in the absolute size of the ultra-low frequency sound insulation Houses 1 is 12 times the 240 mm, a width _{l 2} of the opening 5 is 120 mm. And in Embodiment 2, since it connects with the cylinder 7 (cylindrical body in this invention) in which many holes 8 were formed from the opening part 2a (opening part 2) to the exit part 5a (exit part 5). The length L is the wetting length of the second embodiment. The wet wetting length increases or decreases depending on the number of holes 8, the opening area, and the like.

  Since the experimental reactance silencer 4a of the second embodiment also functions as a resonance silencer, this resonance silencer will be described. In order to function as a resonance silencer, a half-wavelength branched cavity is required. The wavelength of the similar equipment is 340/192 = 1.77 m obtained by dividing the speed of sound (room temperature) by the frequency, and the half wavelength is 890 mm. This varies slightly with temperature. On the other hand, since the cavity height J in the vertical direction of the cavity is 490 mm and becomes 980 mm when the sound wave reciprocates, the cavity height in the vertical direction of the actual cavity is subtracted from the height J83 mm of the opening 2. 897 mm. This is approximately ½ wavelength required for the occurrence of phase interference.

  In the example shown in FIG. 23A, the structure of the resonance silencer is a cylinder having a cross-sectional area A in which N holes 8 are opened from the opening 2a (opening 2) to the outlet 5a (exit 5). 7 is connected. The inside of the cylinder 7 communicates with the inside of the cavity through N holes 8.

When the air in the hole 8 has a mass m _h and the air confined in the cavity becomes a spring having a spring constant k = ρc ² / V, the sound near the resonance frequency is intensely incident on the cavity. Vibrate. During this vibration, the air mass in the hole 8 rubs violently with the inside of the hole 8 and the acoustic energy is converted into heat energy and absorbed. The sound is absorbed mainly only in the vicinity of this resonance frequency. The resonance occurs when the vertical height of the reactance silencer 4 for ultra-low frequency sound is equal to ½ wavelength of the sound wave. The transmission loss of this Helmholtz resonator is expressed by (Equation 6).

また、共鳴周波数ｆｒは次式で表される。

The resonance frequency fr is expressed by the following equation.

ここで、ｃは音速、Ｇは孔８の空気の導伝率（conductivity）、Ｖは空洞部の容積、Ａは音響管路である筒７の断面積である。共鳴型消音器の孔８が円形の場合は（数８）で表される。Ｎは孔の個数、Ａ’は円形の孔８の断面積、ｄは円形の孔８の直径、ｈは円形の孔８の深さ（板の厚さ）である。そして、（数８）の中の０．８ｄは管端補正（end
correction）であって、これは孔８内の空気が一つの塊として振動するとき、孔８の入口、出口における周囲の空気が付随的に動くことを考慮して補正するものである。この共鳴型消音器としての透過損失（ＴＬ）と容積との関係を示した図が図３１（ｂ）である。

Here, c is the speed of sound, G is the conductivity of the air in the hole 8, V is the volume of the cavity, and A is the cross-sectional area of the cylinder 7 that is the acoustic conduit. When the hole 8 of the resonance silencer is circular, it is expressed by (Equation 8). N is the number of holes, A ′ is the cross-sectional area of the circular hole 8, d is the diameter of the circular hole 8, and h is the depth (thickness of the plate) of the circular hole 8. And 0.8d in (Equation 8) is the tube end correction (end
This is a correction that takes into account that the surrounding air at the inlet and outlet of the hole 8 moves incidentally when the air in the hole 8 vibrates as one lump. FIG. 31B shows a relationship between the transmission loss (TL) and the volume as the resonance type silencer.

In the experimental reactance silencer 4a of the second embodiment, N = 24, V = 0.0207122 m ³ , A = 0.083 × 0.166 m ² , d = 0.016 m, h = 0.01 m, According to (Equation 6), it is predicted that TL = 11 dB can be attenuated. Thus, the experimental reactance silencer 4a of the second embodiment also functions as a resonance silencer.

In the second embodiment, the very low frequency sound is attenuated by the same silencing mechanism as described in the first embodiment. An opening 2 between the ultra-low frequency sound insulation Houses 1 and very low frequency sound reactance type silencer 4, to the outlet portion 5 of the external (outside air) and very low frequency sound reactance type silencer 4, respectively m ₁ = Ρ · (l ₁ / A), m ₂ = ρ · (l ₂ / A), and the cavity of the first embodiment is a cavity between m ₁ and m ₂ , and the acoustic capacitance C = V / ρc ² and the spring constant k = 1 / C. The apparent attenuation coefficient r is not l ₁ , l ₂ , but the length L of the reactance silencer 4 for ultra-low frequency sound (the length of the cylinder 7) is the wet blot length, and is proportional to the wet blot length. It has a size.

  Assuming these facts, in the reactance silencer 4 for ultra-low frequency sound of the second embodiment, the (Equation 1), (Equation 2), and (Equation 3) are set to have an apparent attenuation coefficient r and spring constant k. It is basically established. The acoustic boundary layer is peeled off and reattached by the viscosity of the long surface of the cylinder 7 to positively cause energy loss. That is, in addition to the function of the resonance muffler, the sound wave attenuation action by the acoustic boundary layer is superimposed and added.

When viewed practically, the reactance silencer 4 for ultra-low frequency sound has a limitation that the length L in the sound wave traveling direction (length in the longitudinal direction in the present invention) and the volume V cannot be increased beyond an allowable amount. In addition, muffing in the very low frequency range cannot be reduced unless the resonance frequencies k / m ₁ and k / m ₂ are small. Therefore, L is set to the allowable limit, that is, the wet lip length is set to the allowable limit. However, this wetting length varies depending on the number of holes 8, the opening area, the plate thickness, and the like.

  Therefore, the volume V is within the allowable limits, and the vertical cavity height is configured to be ½ wavelength of the sound wave, thereby causing at least resonance of the sound wave. Under these conditions, the number of holes 8, the opening area, By increasing / decreasing the plate thickness and the like, the conditions for obtaining the highest silencing effect as a resonance silencer are obtained by (Equation 6), (Equation 7), and (Equation 8). The size of the reactance silencer 4 for ultra-low frequency sound may be adjusted so as to satisfy this condition.

  When the cylinder 7 having a large number of holes 8 is provided as described above, sound reduction due to resonance in the reactance silencer for ultra-low frequency sound, phase interference of sound waves, and the length from the opening 2 to the outlet 5 The acoustic boundary layer can be peeled off and reattached using the entire length L, and this phenomenon can also be used at the outlet 5, so that a great sound reduction effect can be obtained. In addition, the reflected wave at the opening 2 can be increased, and the standing wave inside the ultra-low frequency soundproof house 1 can be weakened. FIG. 31B shows a relationship between the transmission loss (TL) and the volume as the resonance type silencer.

Next, a description will be given of the results of experiments using similar equipment on a reduced scale that ultra-low frequency sound can be reduced by the ultra-low frequency soundproof house 1 and the reactance silencer 4 for ultra-low frequency sound according to the second embodiment. The sound pressure of pink noise was measured under the arrangement shown in FIG. 7 and the following conditions (1) and (3). (1) “A state in which nothing is installed in the opening of the experimental soundproof house 1a”, (3) “A state in which the resonance type experimental reactance silencer 4a is installed in the opening of the experimental soundproof house 1a”. . Figure 7 measurement points _P 1 shown _{in, P 2, P 3, P} 4 are each experimental soundproofing Hausu in 1a _(P 1), laboratory soundproofing Hausu 1a opening 83mm from the outlet _{(P 2), 166mm (P} 3) 415 mm (P ₄ ). At the same time as (1) and (3), the sound pressure of pink noise was measured in (2) “in a state in which an expansion type experimental reactance silencer 4a was installed in the opening of the experimental soundproof house 1a”. These are as described in the first embodiment. Therefore, (1) is common to the first and second embodiments.

And the sound pressure spectrum of the _{P 1} and _P 2, _{P 1} and _P 3, _{P 1} and _{P 4} each point at that time, SPL at _{P 1} and _P 2, _{P 1} and _P 3, _{P 1} and _{P 4} (Sound FIG. 24 shows a spectrum diagram of the difference in pressure level inside and outside the house. FIG. 24 is a spectrum diagram of the sound pressure spectrum and the difference between the inside and outside of the SPL house when the resonance type experimental reactance silencer 4a analyzed by pink noise is installed in the experimental soundproof house 1a. From FIG. 24, transmission loss (transmission loss when the experimental reactance silencer 4a is not installed).
loss, TL) and transmission loss (TL) when the experimental reactance silencer 4a of the second embodiment is installed. The difference between the inside and outside of the SPL house is the soundproofing effect of the entire experimental ultra-low frequency sound transmission reducing device including the experimental reactance silencer 4a.

  Next, the difference between the inside and outside of the SPL house by the 1/3 octave band and the sound reduction by the experimental reactance silencer 4a of the second embodiment will be described.

(1) “A state in which nothing is installed in the opening of the experimental soundproof house 1a”, (3) “A state in which the resonant experimental reactance silencer 4a is installed in the opening of the experimental soundproof house 1a” The pink noise measured inside and outside the house (measurement points P ₁ , P ₂ , P ₃ , P ₄ ) was analyzed by 1/3 octave at center frequencies of 160 Hz, 200 Hz, 250 Hz, and 315 Hz.

The sound pressure spectrum analyzed in the 200 Hz 1/3 octave band closest to 192 Hz and the spectrum of the SPL house internal and external differences at P ₁ and P ₂ , P ₁ and P ₃ , and P ₁ and P ₄ are shown in FIG. Although an analysis of a 1/3 octave band at a center frequency of 160 Hz, 250 Hz, and 315 Hz was also obtained, since the same tendency is generally exhibited, duplication is avoided and is not illustrated here. The difference between the inside and outside of the SPL house is the sound reduction effect of the entire experimental ultra-low frequency sound transmission reducing device including the experimental reactance silencer 4a. If the difference is further taken between the state where the experimental reactance silencer 4a is installed and the state where the experimental reactance silencer 4a is not installed, this becomes the sound reduction effect by the experimental reactance silencer 4a.

26, 27, and 28 show the difference between the SPL inside and outside the house (TL) and the volume reduction (RSPL) by the experimental reactance silencer 4a. As can be seen, in the resonance type experimental reactance silencer 4a of the second embodiment, the attenuation effect of about 12 dB is obtained at all of P ₂ , P ₃ , and P ₄ at the center frequency of 200 Hz, and the center frequency is 250 Hz. Even at 315 Hz, an attenuation effect is obtained. However, although the sound pressure increased slightly at P ₂ at a center frequency of 160 Hz, it attenuated by 2 dB at P ₃ and P ₄ .

Also in the experimental reactance silencer 4a of the second embodiment, the influence of distance attenuation due to the distance from the measurement points P ₂ , P ₃ , and P ₄ was examined. The distance attenuation is as shown in FIG. Also in this case, it is determined that the presence or absence of the experimental reactance silencer 4a does not affect the distance attenuation.

  Numerical analysis was performed to see the effect as a silencer when the resonant-type experimental reactance silencer 4a of the second embodiment was installed. FIG. 30 shows the sound pressure distribution. The frequency f is 192 Hz. Similarly to FIG. 22, the left side of FIG. 30 shows the sound pressure distribution inside the experimental soundproof house 1a, the right side shows the outside world, and the resonance type is used in the middle for this experiment. This is a reactance silencer 4a. The unit is Pa. L0 indicates the illustrated minimum sound pressure level 0 (0 to 0.043 Pa), and L10 indicates the maximum sound pressure level 10 (0.821 Pa or higher). A region surrounded by contour lines indicates a zone having the same sound pressure level.

  According to this calculation result, when comparing the opening and exit of the case where the experimental reactance silencer 4a is not installed and the case where the resonant experimental reactance silencer 4a is installed, L4 (sound pressure level 4) to L3 (sound pressure level 4) The sound pressure level is reduced to 3), and the region becomes smaller by one step as the expansion type L4 region becomes the L3 region. As can be seen from FIGS. 26, 27, and 28, the sound pressure is reduced by about 12 dB around 200 Hz. It can be seen that the expansion is attenuated as a whole from the expansion-type experimental reactance silencer 4a.

  As described above, when the resonance type ultra-low frequency sound transmission reducing device of the second embodiment is installed in an ultra-low frequency soundproof house, the frequency to be controlled is around 16 Hz (corresponding to around 200 Hz in the experimental reactance silencer 4a). ), A very low frequency sound is attenuated by about 12 dB by installing a resonance type ultra low frequency sound transmission reducing device. This shows almost the same tendency at frequencies of 20 Hz and 26 Hz (corresponding to the central frequencies of 250 Hz and 315 Hz).

  The ultra-low frequency sound transmission reducing device (ultra-low frequency soundproof house and ultra-low frequency sound reactance silencer) according to the second embodiment is normally 20 Hz or less that passes through the soundproof house due to its long wetness and resonance structure. It promotes the development of the acoustic boundary layer due to the viscosity between the ultra-low frequency sound and the wall surface, and the developed acoustic boundary layer is detached unsteadyly and reattached to increase the pressure loss of the flow. That is, it slowly accelerates and decelerates, repeatedly peels off and reattaches the acoustic boundary layer, and converts part of the acoustic energy into thermal energy.

  Then, the height of the cavity in the vertical direction of the cavity is resonated as a half wavelength of the sound wave, and the length of the wet spot that decreases at the opening to the cylinder is compensated by this resonance, so that the sound reduction effect can be enhanced as a whole. At this time, the reflectance γ increases, and this reflected wave acts on the standing wave formed in the ultra-low frequency soundproof house, so that the standing wave can be weakened. When there is a restriction on the length in the longitudinal direction of the reactance silencer for ultra-low frequency sound or the cavity height of the cavity, a great effect can be obtained.

  The present invention can be applied to an ultra-low frequency soundproof house that is always open and covers a sound source such as a vibration sieve machine.

(A) Explanatory drawing by the model of the basic composition of the ultra-low frequency soundproof house and its ultra-low frequency sound transmission reduction device in Embodiment 1 of the present invention, (b) (a) of the ultra-low frequency sound transmission reduction device of FIG. Schematic diagram showing the vibration model Overview of ultra-low frequency soundproof house Perspective view of experimental soundproof house 1a 1 is a perspective view of an inflatable experimental reactance silencer according to Embodiment 1 of the present invention. FIG. Illustration of vibration sieve machine model Explanatory drawing which shows arrangement | positioning of the experimental soundproof house 1a in the state which does not install the very low frequency sound transmission reduction device in Embodiment 1 of this invention, and an experimental reactance type silencer Explanatory drawing which shows arrangement | positioning of the experimental soundproof house 1a of the state which installed the very low frequency sound transmission reduction device in Embodiment 1 of this invention, and a reactance type silencer for experiment Measurement diagram of background noise level in anechoic room Illustration of an arrangement for measuring the sound insulation performance of an anechoic room The figure which shows the measurement result of the sound insulation performance of the anechoic room Illustration of inverse square law characteristics in an anechoic room Sound pressure spectrum without experimental reactance silencer Sound pressure spectrum diagram when an inflatable experimental reactance silencer is installed in the experimental soundproof house 1a. Sound pressure spectrum analyzed with 200 Hz 1/3 octave band without a reactive reactance silencer and spectrum diagram of SPL house inside / outside difference Spectral diagram of sound pressure spectrum and difference between inside and outside of SPL house when expansion type experimental reactance silencer analyzed in 1/3 octave band of 200 Hz is installed in experimental soundproof house 1a (TL), reduced volume (RSPL) illustration of the measurement point P ₂ when the installing expandable laboratory reactance type silencer (TL), reduced volume (RSPL) illustration of the measurement point P ₃ when established the expandable laboratory reactance type silencer Explanatory diagram of (TL) and sound reduction (RSPL) at measurement point P ₄ when an expansion type experimental reactance silencer is installed Explanatory drawing which shows distance attenuation in case of no reactance type silencer for experiment Explanatory drawing showing distance attenuation when an inflatable experimental reactance silencer is installed Explanatory drawing of the sound pressure distribution inside the experimental soundproof house 1a and the sound pressure distribution in the outside world without the experimental reactance silencer Explanatory drawing of the sound pressure distribution inside the experimental soundproof house 1a and the external sound pressure distribution when the expansive experimental reactance silencer is installed The perspective view of the resonance-type experimental reactance silencer in Embodiment 2 of this invention Sound pressure spectrum diagram when a resonance type reactance type silencer is installed in the experimental soundproof house 1a. Spectral diagram of sound pressure spectrum and difference between inside and outside of SPL house when resonance type experimental reactance silencer analyzed at 200 Hz is installed in experimental soundproof house 1a (TL), reduced volume (RSPL) illustration of the measurement point P ₂ when installed resonance type laboratory reactance type silencer (TL), reduced volume (RSPL) illustration of the measurement point P ₃ when installed resonance type laboratory reactance type silencer (TL), reduced volume (RSPL) illustration of the measurement point P ₄ when installed resonance type laboratory reactance type silencer Explanatory drawing showing distance attenuation when a resonant type reactance-type silencer is installed Explanatory drawing of the sound pressure distribution inside the experimental soundproof house 1a and the external sound pressure distribution when the expansive experimental reactance silencer is installed

Explanation of symbols

1 ELF soundproofing Haus 2 opening 3 infrasound source 4 ELF sound reactance silencer 5 outlet 6 the belt conveyor 7 cylinder 8 holes m _{1, m 2} weight k of air, _{k t} spring constant C Acoustic Capacitances l ₁ , l ₂ Wetting lip length A Cross-sectional area of acoustic conduit S Side area of ultra-low frequency soundproof house S ₁ , S ₂ , S ₃ cross-sectional area V, V _t Cavity volume P ₁ , P ₂ , P ₃ and P ₄ measurement points α Correction coefficient r Attenuation coefficient γ Reflectivity θ Transmittance

Claims (8)

Cover the sound source with an ultra-low frequency soundproof house, and install a reactance silencer for the ultra-low frequency sound in the normally open opening of the ultra-low frequency soundproof house to reduce the ultra-low frequency sound emitted from the opening to the outside. An ultra-low frequency sound transmission reduction method,
The acoustic boundary layer is developed in proportion to the wet and dry lengths of the reactance silencer for the ultra-low frequency sound, and the apparent resistance component in proportion to the wet length is increased. An ultra-low-frequency sound transmission reduction method characterized by converting ultra-low frequency sound by converting acoustic energy into thermal energy. The reactance silencer for ultra-low frequency sound has a cavity that expands in a direction perpendicular to the longitudinal direction between the inlet and the outlet.
When the wetting length is increased, the reactance component is decreased by increasing the vertical cavity width of the cavity, and a part of the acoustic energy is converted into thermal energy to reduce the ultra-low frequency sound. The ultra-low frequency sound transmission reduction method according to claim 1.   3. The ultra-low frequency sound according to claim 1, wherein the ultra-low frequency sound reactance type silencer is an expansion type silencer, and the ultra low frequency sound is further reduced by reducing a reactance component due to expansion. Transmission reduction method.   3. The ultra low frequency sound according to claim 1, wherein the reactance silencer for the ultra low frequency sound is a resonance silencer, and the ultra low frequency sound is further reduced by reducing a reactance component due to phase interference. Wave sound transmission reduction method.   5. The method of reducing transmission of ultra-low frequency sound according to claim 1, wherein a standing wave in the ultra-low frequency soundproof house is weakened by increasing an apparent resistance component of the acoustic impedance. . Ultra-low frequency sound radiated from the opening to the outside, comprising an ultra-low frequency soundproof house covering the sound source, and a reactance silencer for ultra-low frequency sound provided in an opening that is always open of the ultra-low frequency soundproof house An ultra-low frequency sound transmission reducing device that reduces noise,
The ultra-low frequency sound reactance silencer includes an inlet portion and an outlet portion having a predetermined wetted length proportional to an apparent resistance component of acoustic impedance, and an acoustic proportional to the wetted length. An ultra-low-frequency sound transmission reducing device that develops a boundary layer to increase the apparent resistance component and converts acoustic energy into thermal energy to reduce ultra-low frequency sound.   The reactance silencer for ultra-low frequency sound has a cavity portion that expands in a direction perpendicular to the longitudinal direction between the inlet portion and the outlet portion, and reactance of acoustic impedance with a cavity width in the vertical direction of the cavity portion 7. The ultra-low frequency sound transmission reducing device according to claim 6, wherein the ultra-low frequency sound is reduced by reducing components.   The reactance type silencer for ultra-low frequency sound is a resonance type silencer, wherein the inlet and the outlet are communicated with each other through the hollow portion, and the tubular body has a plurality of holes. The ultra-low frequency sound transmission reducing device according to claim 7, wherein the device is formed and communicated with the hollow portion.

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