An impedance composite muffler for low-frequency and broadband noise reduction

Abstract

The present invention discloses an impedance composite muffler for low-frequency broadband noise reduction, the muffler comprising: a reactive muffler and a resistive muffler connected to each other and enclosed outside a hard cavity, wherein the reactive muffler is composed of a plurality of second-order Helmholtz resonators (THR) for reflecting the acoustic energy of noise in the frequency band below 1000 Hz; the resistive muffler is composed of a porous sound absorbing material (PSAM) for absorbing the acoustic energy of noise in the frequency band above 1000 Hz. The impedance composite muffler proposed in the present invention has strong scalability, and utilizes the complementary advantages and disadvantages of the resonant structure and the PSAM for effective combination. By adjusting the parameters of the resonant structure to set the target noise reduction frequency, low-frequency noise reduction is better achieved; and the PSAM can continuously achieve medium and high-frequency noise reduction. The combination of the two is of great help in solving low-frequency broadband noise reduction in life.

Description

Technical Field

[0001] The present invention belongs to the technical field of noise reduction of ventilation systems, and in particular relates to an impedance composite muffler for low-frequency and broadband noise reduction. Background Art

[0002] How to effectively suppress noise is a hot topic in current research, and noise reduction in ventilation systems is of paramount importance. Maintaining ventilation without disturbing noise has long been a sought-after goal. Conventional methods for reducing duct noise involve laying devices made of porous sound-absorbing material (PSAM) around the ducts. However, these devices are less effective at low frequencies, requiring a device size comparable to the sound wavelength to achieve satisfactory noise reduction. This makes these devices bulky and impractical for low-frequency noise control. Therefore, a compact, low-frequency, broadband-effective muffler is currently needed. Summary of the Invention

[0003] The purpose of the present invention is to overcome the defects of the prior art and propose an impedance composite muffler with low-frequency and broadband noise reduction.

[0004] In order to achieve the above object, the present invention proposes an impedance composite muffler for low-frequency broadband noise reduction, the muffler comprising: a reactive muffler and a resistive muffler connected to each other and wrapped outside a hard cavity, wherein:

[0005] The reactive muffler is composed of two or more second-order Helmholtz resonators and is used to reflect the sound energy of noise in the frequency band below 1000 Hz;

[0006] The resistive muffler is made of porous sound-absorbing material and is used to absorb the sound energy of noise with a frequency band higher than 1000 Hz.

[0007] As an improvement of the above-mentioned muffler, the reactive muffler includes 10 sections connected in series, with two L-shaped second-order Helmholtz resonators placed in each section, and the width of each L-shaped second-order Helmholtz resonator is w=52 mm.

[0008] As an improvement to the above-mentioned muffler, the horizontal opening of each L-shaped second-order Helmholtz resonator is connected to the hard cavity, and the resonant frequency interval between the upper and lower L-shaped second-order Helmholtz resonators is greater than 50 Hz.

[0009] As an improvement to the above-mentioned muffler, the 10 cross sections are arranged from the farthest end of the distance resistance muffler, and the resonance frequencies of the upper L-shaped second-order Helmholtz resonators on the same side are arranged in sequence from low to high, and the resonance frequencies of the lower L-shaped second-order Helmholtz resonators on the same side are arranged in sequence from low to high.

[0010] As an improvement of the above muffler, each L-shaped second-order Helmholtz resonator has the following parameters: first-order cavity height First-order cavity length l c ≤190mm; first-order neck length and the second-order neck length All ≤10mm; first-order neck radius and the second-order neck radius All ≤24mm.

[0011] As an improvement to the above-mentioned muffler, for the L-shaped second-order Helmholtz resonator, the corresponding resonance frequency is moved toward a high frequency by increasing the neck radius and / or reducing the neck length.

[0012] As an improvement to the above-mentioned muffler, for the L-type second-order Helmholtz resonator, the corresponding resonance frequency is moved to a high frequency by reducing the volume of the resonance cavity.

[0013] As an improvement of the above-mentioned muffler, the flow resistivity σ of the porous sound-absorbing material is 15374 Pa·s / m 2 , porosity φ is 0.9942, tortuosity factor α ∞ is 1.04, and the viscosity characteristic length Λ is 9.2×10 -5 μm, and the thermal characteristic length Λ is 1.97×10 -4 μm.

[0014] Compared with the prior art, the advantages of the present invention are:

[0015] The impedance composite silencer proposed in the present invention has strong scalability. It uses the complementary advantages and disadvantages of the resonant structure and PSAM to form an effective combination. The target noise reduction frequency can be set by adjusting the parameters of the resonant structure to better achieve low-frequency noise reduction. PSAM can continuously achieve medium and high-frequency noise reduction. The combination of the two can greatly help solve the problem of low-frequency broadband noise reduction in life. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the impedance composite muffler model of the present invention;

[0017] Figure 2 It is the arrangement diagram of each unit of the reactive muffler;

[0018] Figure 3 This is the experimental result diagram of impedance composite muffler;

[0019] Figure 4 This is the calculation result diagram of the muffler broadband performance. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0021] Example

[0022] The embodiment of the present invention provides an impedance composite muffler that can achieve low-frequency broadband noise reduction. Figure 1 As shown, part of the right side is l PSAM The resistive silencer composed of PSAM is used to absorb the sound energy of noise with a frequency band higher than 1000Hz; the other part is the left l THRS The reactive silencer is composed of multiple second-order Helmholtz resonators (THR) and is used to reflect the sound energy of noise below 1000Hz. The reactive silencer consists of 10 sections, with two THR units placed in each section, for a total of 20. The right part pointed by the arrow is a structural diagram of two THR units placed in the same section. Including the upper THR and the lower THR, the width of each THR unit is fixed at w = 52mm. By adjusting other parameters to set the resonant frequency of each unit, it is finally combined into a broadband and effective reactive silencer. The remaining parameters are l c ≤190mm; in, represents the first-order cavity height, l c represents the length of the first-order cavity, and They represent the first-order neck length and the second-order neck length respectively. and They represent the first-order neck radius and the second-order neck radius respectively.

[0023] The acoustic parameters of the PSAM are shown in Table 1. Calculating the noise reduction performance of the PSAM reveals that it has excellent noise reduction effects for frequencies above 1000 Hz, while its efficiency drops sharply for frequencies below 1000 Hz.

[0024] Table 1: Five acoustic parameters of PSAM

[0025]

[0026] The present invention designs the resonant frequencies of 20 L-shaped second-order Helmholtz resonators. The frequency of each resonator is first controlled by adjusting the neck parameters. When the neck parameters are insufficient to adjust the frequency, the frequency of each resonator is further controlled by adjusting the volume of the resonant cavity. For example, when the resonant frequency of an L-shaped second-order Helmholtz resonator needs to be adjusted to a higher frequency, increasing the neck radius or decreasing the neck length can both shift the resonant frequency toward a higher frequency. When increasing the neck radius or decreasing the neck length is insufficient to adjust the resonant frequency to a higher frequency, reducing the volume of the resonant cavity can also achieve this goal.

[0027] In order to avoid the influence of mutual coupling between units, the present invention requires that the 20 THR units be arranged in a certain order. The resonance frequencies of two adjacent units on the same side need to be relatively small, so the THR units on the same side are arranged in order from low to high resonance frequencies; while the resonance frequencies of two THR units on the same cross section need to be relatively large, and the final arrangement order is as follows: Figure 2 As shown in the figure, the numbers 1 to 20 indicate the order of the units from low to high resonant frequency. We also produced a sample of the reactive muffler for experimental testing. The experimental test data show that the designed reactive muffler can achieve a transmission loss of more than 20dB in the frequency band of 248-1000Hz.

[0028] The resistive silencer composed of PSAM and the reactive silencer composed of THR are effectively combined to form an impedance composite silencer, which can achieve excellent noise reduction effect in the low frequency band while ensuring that the noise reduction performance in the high frequency band will not decrease.

[0029] Experimental testing

[0030] In view of the above calculation results, the present invention further produced a sample of the silencer for experimental testing. The 3D printed sample is divided into two parts, one part is an expansion cavity, and a PSAM is placed on the inner wall of the cavity to absorb the sound energy of noise above 1000Hz; the other part is a resistive silencer, which is used to reflect the sound energy of noise below 1000Hz. The two parts are tightly connected and assembled in a square impedance tube. Two microphones are installed on both ends of the sample for data collection, and the double load method is used to test the transmission loss of the silencer. The experimental results show that when the sound wave is incident from either end of the two ports of the silencer, the difference in noise reduction performance is very small and can be almost ignored. The experimental measurement data is as follows Figure 3 As shown in the figure, it can be seen that starting from 244Hz, the transmission loss of the muffler is higher than 20dB. In the low frequency band within 1000Hz, most of them are higher than 30dB, and the maximum transmission loss exceeds 60dB. The proposed impedance composite muffler shows excellent noise reduction performance.

[0031] Since the cut-off frequency of the square impedance tube is 1600Hz, and in fact the impedance composite muffler can still maintain efficient noise reduction performance in the high frequency band above 1600Hz, the noise reduction performance of the muffler in the frequency band above 1600Hz is further calculated. The calculation results are as follows: Figure 4 As shown in the figure, it can be seen that the muffler still maintains efficient noise reduction performance in the frequency band above 1600 Hz, which fully demonstrates that the proposed muffler can have excellent noise reduction effect in a wide frequency range.

[0032] These results demonstrate that the proposed impedance composite muffler can achieve excellent noise reduction across a wide frequency range, ensuring ventilation without disturbing noise. The above design example is provided solely to illustrate the design steps and implementation results. In specific applications, designs can be tailored to target different frequency bands and bandwidths based on actual application scenarios.

[0033] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and are intended to be encompassed by the claims of the present invention.

Claims

1. An impedance composite muffler for low-frequency broadband noise reduction, characterized in that: The muffler includes: a reactive muffler and a resistive muffler which are wrapped around a hard cavity and connected to each other, wherein: The reactive muffler is composed of two or more second-order Helmholtz resonators and is used to reflect the sound energy of noise in the frequency band below 1000 Hz; The resistive muffler is composed of porous sound-absorbing material and is used to absorb the sound energy of noise with a frequency band higher than 1000 Hz; The reactive muffler comprises 10 sections connected in series, each section being provided with two L-shaped second-order Helmholtz resonators, each having a width of w=52 mm; The horizontal opening of each L-shaped second-order Helmholtz resonator is connected to the hard cavity, and the resonant frequency interval between the upper and lower L-shaped second-order Helmholtz resonators is greater than 50 Hz; The 10 sections are arranged from the farthest end of the distance resistance muffler, and the resonance frequencies of the upper L-shaped second-order Helmholtz resonators on the same side are arranged in sequence from low to high, and the resonance frequencies of the lower L-shaped second-order Helmholtz resonators on the same side are arranged in sequence from low to high.

2. The low-frequency, broadband noise reduction impedance composite muffler according to claim 1, characterized in that: Each L-type second-order Helmholtz resonator parameter is the first-order cavity height First-order cavity length l c ≤190mm; first-order neck length and the second-order neck length All ≤10mm; first-order neck radius and the second-order neck radius All ≤24mm.

3. The impedance composite muffler for low-frequency, broadband noise reduction according to claim 2, characterized in that: For an L-type second-order Helmholtz resonator, the corresponding resonance frequency is shifted to a higher frequency by increasing the neck radius and / or decreasing the neck length.

4. The impedance composite muffler for low-frequency, broadband noise reduction according to claim 2, characterized in that: For an L-type second-order Helmholtz resonator, by reducing the volume of the resonant cavity, the corresponding resonant frequency is moved to a high frequency.

5. The impedance composite muffler for low-frequency, broadband noise reduction according to claim 1, characterized in that: The flow resistivity σ of the porous sound-absorbing material is 15374 Pa·s / m 2 , porosity φ is 0.9942, tortuosity factor α ∞ is 1.04, and the viscosity characteristic length Λ is 9.2×10 -5 μm, Thermal characteristic length Λ , 1.97×10 -4 μm.

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