A structure and design method for improving the noise reduction performance of a single-channel active control system in a staggered window

Abstract

The present invention discloses a structure and a design method for improving the noise reduction performance of a single-channel active control system in a staggered window. The structure is composed of a layer of perforated plates and a layer of folded duct structure. Due to the rigid reflection of the inner wall of the staggered window ventilation path, the single-channel active control system cannot reduce noise at certain frequencies. The structure can effectively improve the noise reduction of these frequencies and has little impact on other frequencies. The total thickness of the structure is only about 1 / 40 of the wavelength of the corresponding frequency.

Description

1. Technical Field

[0001] The present invention relates to the field of noise control. A structure for improving the noise reduction performance of a single-channel active control system in a staggered window is proposed. The structure is composed of a layer of perforated plates and a layer of folded pipes, and can effectively improve the noise reduction effect of the single-channel active control system at a frequency that cannot be reduced due to the rigid reflection of the inner wall of the staggered window. 2. Background Technology

[0002] Soundproof windows can effectively reduce the noise transmitted into the room, but closing the windows affects the natural ventilation of the room. If staggered glass is used to form ventilation channels, the resonance effect generated by the channels can be used to reduce the noise transmitted from the outside to the room. On this basis, the use of single-layer or multi-layer micro-perforated plates and micro-perforated films can further improve the noise reduction (CN101793122A, CN103075088A), but the noise reduction of staggered windows at low frequencies is small.

[0003] Installing an active noise control system in a soundproof window can improve its noise reduction effect at low frequencies, but a single-channel active control system cannot reduce noise at certain frequencies (CN102364002A, H. Huang, X. Qiu, J. Kang, Active noise attenuation in ventilation windows, Journal of the Acoustical Society of America, 130, 176-188, 2011). Using multiple secondary sources to form a directional sound source or a combined sound source can significantly improve the noise reduction of the active control system, but the multi-channel system is complex and costly (CN101389158A, CN104918173A).

[0004] A sound absorption structure composed of a perforated plate and a solenoid can achieve a sound absorption coefficient of more than 0.8 at 387Hz-429Hz. The use of coiled solenoids of different sizes for mixed distribution can expand the sound absorption bandwidth, achieving a sound absorption coefficient of more than 0.8 in the frequency band of 633Hz-849Hz (CN107195292A). A similar sound absorption screen composed of a screen plate, a perforated plate and a quarter-wavelength resonant tube can achieve a sound absorption coefficient of more than 0.9 near the design frequency (CN104732967A). The thickness of this sound absorption structure is only about one percent of the wavelength of the design frequency, but there is no example of a similar structure being applied to active noise reduction.

[0005] The present invention proposes to use a perforated plate + folded pipe structure to improve the noise reduction effect of a single-channel active control system in a staggered window, and provides a design method thereof. Introducing a perforated plate + folded pipe structure designed for frequencies that cannot be noise-reduced at one end of the pipe near the inlet can eliminate the valley point of the secondary channel transfer function, thereby achieving effective noise reduction for these frequencies. The structure is simple, low in cost, small in space, easy to install and stable in operation. III. Summary of the invention

[0006] 1. Purpose of the invention: To introduce a structure consisting of perforated plates and folded pipes into an ordinary staggered window, thereby improving the noise reduction amount of a single-channel active control system at certain frequencies and thus improving the overall noise reduction performance.

[0007] 2. Technical solution: To achieve the above-mentioned purpose of the invention, the schematic diagram of the perforated plate + folded duct structure unit installed at one end of the staggered window ventilation path of the present invention is shown in the attached Figure 1 The structure consists of multiple units. See the attached diagram for the staggered windows installed with the structure. Figure 2 The present invention is implemented according to the following steps:

[0008] (1) Install a single-channel active control system on the staggered window ventilation path, examine its noise reduction effect, and find the frequency f with the minimum noise reduction. Figure 3 The distance between the right wall and f is L. If f is close to c 0 / 4L is an odd multiple, then the reason why the noise reduction at this frequency is not high is the valley point of the secondary channel transfer function caused by the rigid reflection of the right wall. If the transfer function from the secondary source to the center of the outlet appears at f, this conclusion can be further confirmed.

[0009] (2) Divide the cross-sectional area of ​​the ventilation path evenly into several small units of equal area, with a side length of a x and a y , when dividing, ensure a x and a y The difference is not big, the thickness t of the perforated plate is generally taken as 0.2-2mm;

[0010] (3) Based on

[0011]

[0012] Determine the aperture d of the perforated plate, where α max Generally, it is around 0.5.

[0013]

[0014]

[0015] Where η is the viscosity coefficient of air 1.81×10-5 Pa·s, ρ 0 、c 0 The air density is 1.21kg / m 3 The speed of sound in air is 343m / s, ω=2πf is the angular frequency, and the perforation ratio is

[0016]

[0017] S=a x ×a y The area of ​​each small unit;

[0018] (4) Select an appropriate equivalent length l of the folded pipe, which should be slightly smaller than c 0 / 4f value;

[0019] (5) Determine the appropriate folding pipe width w so that y h +y c =0, where

[0020]

[0021]

[0022] Where S' = w × h is the cross-sectional area of ​​the folded pipe;

[0023] (6) According to the d and w determined in steps (3) and (5),

[0024]

[0025] Calculate the theoretical sound absorption coefficient, the center frequency of the sound absorption coefficient should be f;

[0026] (7) Fold the pipeline according to the determined parameters. If a x ×a y The unit area of ​​cannot accommodate the folded pipe with an equivalent length of , so a can be appropriately increased. x 、a y Then repeat steps (2)-(7) with the small hole of the perforated plate at the center of the starting end of the folded pipe, see attached Figure 1 ;

[0027] (8) Establish a three-dimensional acoustic finite element model of the ventilation path and the design structure to simulate the sound absorption coefficient and active noise reduction effect. If there is a problem, repeat (2)-(8) until the introduction of the design structure can effectively improve the noise reduction at f;

[0028] 3. The beneficial effects of the present invention are: a perforated plate + folded pipe structure is proposed and applied to active control, which can effectively improve the noise reduction effect of the single-channel active control system in the staggered window. The structure is simple, environmentally friendly and easy to install. IV. Description of the drawings

[0029] Figure 1 It is a schematic diagram of a single perforated plate + folded pipe structural unit according to the present invention.

[0030] Figure 2 It is a schematic diagram of the staggered window installed with the perforated plate + folded pipe structure described in the present invention.

[0031] Figure 3 Schematic diagram of staggered window sizes and single-channel active control system in a specific embodiment.

[0032] Figure 4 It is the sound pressure level of the evaluation point before and after active noise reduction when the perforated plate + folded pipe structure is not introduced in the specific embodiment.

[0033] Figure 5 It is the sound pressure level produced at the evaluation point by a secondary source of constant source strength in a specific embodiment.

[0034] Figure 6 is the sound absorption coefficient of the perforated plate + folded pipe structure in the specific embodiment.

[0035] Figure 7 It is a comparison of the noise reduction effect before and after the perforated plate + folded pipe are introduced in the specific embodiment. V. Specific implementation methods

[0036] The following uses numerical simulation results as an example to illustrate the specific implementation and effects of the invention. Figure 3 The three-dimensional acoustic finite element model of the staggered window shown in the figure, where L x =1.5m, L y =0.25m, L z =0.32m, L=1.0m, and the spaces outside the entrance and exit are both semi-infinite spaces, that is, it is assumed that the staggered window is installed on an infinite rigid wall with a thickness of 0.25m. In the simulation, it is assumed that the secondary source is a point sound source, the primary source is a point sound source outside the entrance at a distance of 0.5m from its center, and the error microphone is located at a top corner inside the staggered window near the exit, see the attached Figure 3 The secondary source strength required for active control is obtained by minimizing the square of the sound pressure at the error point. The sound pressure level of the evaluation point 0.1m from the center outside the outlet before active noise reduction is recorded as SPL without , the sound pressure level at this point after active noise reduction is SPL with , then the noise reduction at this point is NR = SPL without- SPL with , use NR to evaluate the noise reduction effect of the system.

[0037] The sound pressure level of the evaluation point before and after active noise reduction obtained by simulation is attached. Figure 4 It can be seen that the noise reduction at 435Hz is the smallest, which is a negative value, and 435Hz is close to c0 / odd multiples of 4L; examine the secondary channel transfer function, attached Figure 5 The sound pressure level generated by the secondary source with constant source strength at the evaluation point. It can be seen that the sound pressure at 435Hz is the smallest when the structure is not installed. Therefore, it is confirmed that the reason why this frequency cannot be noise-reduced is the valley point of the secondary channel transfer function caused by the rigid reflection of the right wall of the staggered window. A perforated plate + folded pipe structure is designed for this frequency. In order to expand the working bandwidth, four different sound absorption units are designed for four different frequencies near 435Hz, 410 Hz, 430Hz, 450Hz and 470Hz, and the side length of each unit is a. x =80mm, a y =62.5mm, the cross section of the ventilation path includes 4×4 sound absorption units, which are divided into 4 groups, 4 in each group, and the parameters are shown in Table 1. The sound absorption coefficient of the structure varies with frequency as shown in the attached Figure 6 , its effective sound absorption frequency band is 400Hz-480Hz.

[0038] Table 1 Design parameters of perforated plate + folded pipe structure

[0039]

[0040] After the introduction of this structure, the noise reduction effect of the single-channel active control system was examined again. The comparison between the noise reduction effect of the single-channel active control system and the noise reduction effect before the introduction of the structure is shown in the attached figure. Figure 7 Attached Figure 7 After the structure is introduced, the noise at 435Hz can also be effectively reduced. The noise reduction at this frequency is increased from -6.0dB before the structure is introduced to 7.5dB. The reason is that the structure improves the radiation capacity of the secondary source at 435Hz. See the attached Figure 5 Due to the significant improvement in the noise reduction at 435Hz, the total sound pressure level noise reduction between 100Hz-500Hz also increased from 21.2dB to 26.2dB, that is, the structure effectively improved the overall noise reduction effect of the single-channel active control system in the staggered window. The total thickness of the structure is about 2cm, which is only 1 / 40 of the design frequency wavelength.

[0041] The present invention provides a structure and a design method for improving the noise reduction of a single-channel active control system in a staggered window. The structure is composed of a layer of perforated plates and a layer of folded pipe structure. The structure is designed for the frequency at which the single-channel active control system cannot reduce noise, and the noise reduction near the frequency can be effectively improved, thereby improving the overall noise reduction effect. The structure is simple, environmentally friendly, easy to install, small in space, low in cost, and stable in operation.

Claims

1. A design method for improving the active noise reduction performance of a single-channel active control system in a staggered window, characterized in that The following steps are involved: (1) Investigate the noise reduction effect of the single-channel active control system in the staggered window and find the frequency f that cannot be reduced; Investigate the acoustic transfer function from the secondary source to the center of the staggered window outlet. If f corresponds to the valley point of the transfer function, it is confirmed that the frequency is related to the rigid reflection of the inner wall of the staggered window, and the structure is designed according to the frequency; (2) Divide the cross-sectional area of ​​the staggered window ventilation path into several small units, each with a side length of a. x and a y ; (3) Take the perforated plate thickness t between 0.2 and 2 mm, according to Determine the aperture d of the perforated plate, where η is the viscosity coefficient of air 1.81×10 -5 Pa·s, ρ0, c0 are air densities of 1.21 kg / m 3 and the speed of sound in air is 343m / s, ω=2πf is the angular frequency, S=a x ×a y is the area of ​​each sound absorbing unit; (4) Determine the folded pipe width w so that y h +y c =0, where Where, is the equivalent length of the folded pipe, S'=w×h is the cross-sectional area of ​​the folded pipe; (5) According to the d and w determined in steps (3) and (4), Calculate the theoretical sound absorption coefficient; (6) Fold the pipeline according to the determined parameters. If a x ×a y The unit area of ​​​​the equivalent length of l cannot accommodate the folded pipe, so a can be increased x 、a y , then repeat steps (2)-(6), with the small hole of the perforated plate being at the center of the starting end of the folded pipe; (7) Establish a three-dimensional acoustic finite element model of the ventilation path and design structure to simulate the sound absorption coefficient and active noise reduction effect. If there is a problem, repeat (2)-(7) until the introduction of the design structure can effectively improve the noise reduction at f.

Images