CN116085572A - A Pipeline Low-Frequency Noise Control Device Based on Electroacoustic Coupling - Google Patents

Abstract

The invention aims to provide a pipeline low-frequency noise control device based on electroacoustic coupling, which comprises an upstream loudspeaker, a downstream loudspeaker and a coupling circuit, wherein a main pipe section for noise control comprises an upstream air inlet pipe section, a middle silencing pipe section and a downstream outlet pipe section, the silencing pipe section is respectively provided with the upstream loudspeaker and the downstream loudspeaker, the upstream loudspeaker and the downstream loudspeaker are connected through the coupling circuit, the pipe wall of the silencing pipe section is provided with a sliding rail, the downstream loudspeaker is arranged on a movable side plate, and the side plate can do transverse translational motion along the sliding rail on the pipe wall. The invention can overcome the defect of single silencing frequency band of the traditional H-Q tube fixing structure. And by utilizing electroacoustic coupling characteristics, the sound path difference between the main pipeline and the bypass pipeline is created, the flexibility of the muffler device is improved, and the structural size is reduced.

Description

A Pipeline Low-Frequency Noise Control Device Based on Electroacoustic Coupling

This application is a divisional application titled "A Device for Controlling Low-Frequency Noise in Pipelines Based on Electroacoustic Coupling", in which the application number of the parent application is 202110046347.X, and the filing date is 2021.01.14.

technical field

The invention relates to a noise control device, in particular to a pipeline noise control device.

Background technique

Pipeline noise control methods are mainly divided into active control and passive control. The active control method mainly uses the principle of superposition of sound waves for noise control. The structure of the system is relatively complicated, and it takes a certain amount of time to achieve system stability, and the applicable working scenarios are relatively limited. Passive control methods have been developed for many years and are widely used, which can effectively eliminate medium and high frequency noise. According to the principle of noise control, if the passive control device is applied to low-frequency noise control, the anechoic frequency band will be narrow, and the size of the device is limited by the wavelength of the sound wave, usually larger.

The Herschel-Quincke (H-Q) tube is a typical low-frequency, passive control muffler device, which uses the sound path difference between the main pipeline and the bypass pipeline to make the sound waves of the sound at the intersection of the main pipeline and the bypass pipeline There is a phase difference to achieve the noise reduction effect. The published patent CN101956884A describes a semi-active device that can adjust the H-Q tube bypass line, which broadens the effective sound absorption bandwidth of the traditional H-Q tube device, so that the noise reduction device has a better sound absorption effect in the middle and low frequencies. However, this device complicates the traditional H-Q pipeline, adding controllers and other devices, which makes the volume of the muffler larger, and the sealing of the variable-length complex bypass pipeline is also a difficult problem in engineering. If the H-Q tube is used for low-frequency noise control, its low-frequency performance is limited by the length of the bypass pipeline, that is, to eliminate low-frequency noise, the length of the bypass pipeline must be very long.

Contents of the invention

The object of the present invention is to provide a pipeline low-frequency noise control device based on electro-acoustic coupling with noise reduction effect in a specific frequency band.

The purpose of the present invention is achieved like this:

The invention provides a pipeline low-frequency noise control device based on electro-acoustic coupling, which includes an upstream speaker, a downstream speaker and a coupling circuit. The acoustic tube section is provided with an upstream speaker and a downstream speaker respectively, and the upstream speaker and the downstream speaker are connected through a coupling circuit. Slide rails are provided on the tube wall of the muffler tube section, and the downstream speaker is installed on a movable side plate, which can move along the tube The slide rail on the wall makes lateral translational movement.

Preferably, the sliding side plate moves along the slide rails to adjust the distance between the upstream speaker and the downstream speaker, so that the distance between the upstream speaker and the downstream speaker matches the resonance frequency, and the distance between the upstream speaker and the downstream speaker is equal to the resonance frequency (2N-1)/2 times the corresponding wavelength, where N is a positive integer.

Preferably, the distance between the upstream loudspeaker and the downstream loudspeaker is equal to half the wavelength corresponding to the resonant frequency.

Preferably, the noise is divided into two paths after entering the main pipe section. The first path is directly transmitted to the downstream speaker through the upstream air intake pipe section and the middle muffler pipe section, and the second path reaches the surface of the upstream speaker to cause vibration of the diaphragm and generate induced electromotive force. , the downstream speaker emits sound due to the induced current, and the two sound waves converge at the downstream speaker to produce destructive interference.

Preferably, sealed back chambers are arranged outside the upstream speaker and the downstream speaker.

Preferably, both the upstream speaker and the downstream speaker are dynamic speakers.

The advantage of the present invention is that: the present invention can overcome the disadvantages of the traditional H-Q tube fixed structure and single noise reduction frequency band. Moreover, the electro-acoustic coupling feature is used to create the sound path difference between the main and side pipelines, improve the flexibility of the muffler, and reduce the structural size.

Description of drawings

Figure 1 is a schematic diagram of the intersection and superposition of two sound waves at the downstream speaker;

Fig. 2 is a structural representation of the present invention;

Figure 3 shows the transmission loss of the device when the distance between the two loudspeakers is 1m.

Detailed ways

The present invention is described in more detail below in conjunction with accompanying drawing example:

Referring to Figures 1-3, an electro-acoustic coupling based pipeline low-frequency noise control device of the present invention includes a main pipe section, an upstream speaker 3, a back cavity 2, a coupling circuit 4, a downstream speaker 5, a back cavity 6, a side plate 7 and a limiter Block 9, the main pipe section includes the upstream intake pipe section 1 , the middle muffler pipe section and the downstream outlet pipe section 8 .

After the incident sound wave enters the muffler pipe section from the inlet pipe section 1 of the main pipe section, it is transmitted from the outlet pipe section 8, and the amplitude of the incident sound wave is reduced. There is an upstream loudspeaker 3 arranged on the side of the main pipe near the intake pipe section 1, and a closed back cavity 2 is arranged on the back of the upstream loudspeaker 3, and the upstream loudspeaker 3 is connected to the downstream loudspeaker 5 through a coupling circuit 4. There is a slide rail on the pipe wall of the muffler pipe section, and the downstream speaker 5 is installed on a movable side plate 7, and the side plate can move laterally along the slide rail of the pipe wall, and there is a closed back cavity on the back of the downstream speaker 5 6. The limit block 9 is arranged on the pipe wall of the outlet pipe section 8 , and the limit block is used to limit the end of the side plate 7 close to the outlet pipe section 8 . Both the upstream loudspeaker 3 and the downstream loudspeaker 5 are dynamic loudspeakers. The upstream and downstream speakers can be replaced, and the most suitable speaker can be selected for different noise source characteristics, that is, the peak frequency of the noise source corresponds to the resonance frequency of the selected speaker. The muffler is a passive muffler, and the system has no external energy input. Two or more moving coil loudspeakers are placed in sequence along the transmission direction of the noise in the duct. The speaker groups are connected through coupling circuits. The position parameters of the loudspeaker group and the coupling circuit parameters are adjustable, so as to realize the coverage of noise in different frequency bands.

The two speakers are connected through a coupling circuit, and the two speakers form an equivalent bypass pipe section connected in parallel with the main pipe section, and the intake pipe section 1 and the outlet pipe section 8 are respectively located at both ends of the main pipe section. After the noise enters the main pipe section, it is divided into two paths, and one path reaches the surface of the upstream speaker 3, causing the diaphragm to vibrate, generating an induced electromotive force, and then forming an induced current in the two coupled speaker circuits, and the downstream speaker 5 produces sound due to the induced current. , and the other path is directly transmitted to the downstream speaker 5 through the main pipe section. The two paths of sound waves finally converge at the downstream speaker 5 . Since the transmission phases of the two paths of sound waves are different, destructive interference will occur, and the noise propagating downstream after the final convergence is reduced (as shown in FIG. 1 ). At the same time, the downstream loudspeaker 5 is installed on a side plate 7 that can slide along the slide rail. Therefore, the position of the downstream loudspeaker 5 is adjustable, which provides another measure for adjusting the sound path difference between the main pipe section and the equivalent bypass pipe section.

A sealed back cavity is arranged outside the speaker group to prevent the speaker from leaking sound to the external environment.

According to the knowledge of acoustics, when two columns of sound waves with the same wavelength and the same amplitude meet, the sound waves will superimpose each other. The peaks and troughs of the sound waves will exactly meet and cancel each other out, resulting in the effect of noise reduction, which is also the mechanism followed by active noise control. In the present invention, the crest or trough of the sound wave that is introduced from the intake pipe section 1 and travels to the upstream speaker 3 will excite the vibration of the speaker diaphragm, and an induced electromotive force will be generated inside the speaker to make the downstream speaker 5 connected to it emit sound. Due to the rapid transmission of the circuit, the speaker system is equivalent to transmitting the sound wave at the upstream speaker 3 to the downstream immediately, with almost no time delay. In this way, based on the sound wave superposition principle, when the distance L between the two speakers is exactly equal to (2N-1)/2 times the wavelength (N=1, 2, 3...), the effect of noise reduction is just achieved. According to the theory of sound wave superposition, when the distance L between two speakers is equal to (4N-3, 4N-1)/4 times the wavelength, they all have a certain noise reduction effect, but when the distance is exactly equal to (2N-1)/2 times the wavelength , the noise reduction effect is the best. The design of the present invention can make the distance L between the two speakers change with the position of the side plate (as shown in Figure 2), that is, the position of the downstream speaker 5 can be moved to the corresponding position with the side plate, thereby obtaining the best Noise reduction effect.

The noise reduction effect calculation method of the present invention is as follows.

The mechanical impedance of a dynamic speaker can be expressed as: Z _m = δ+jωM+K/jω+A ² /jωC _a

是虚数，ρ₀、c₀为空气的密度和空气中的声速。K为扬声器机械部分的等效刚度，M为扬声器机械部分的等效质量，δ为扬声器机械部分的等效阻尼。Where C _a =V/ρ ₀ c ₀ ² is the equivalent acoustic reactance added by the sealed cavity on the back of the speaker, V is the volume of the back cavity, A is the effective vibration area of the speaker diaphragm surface, ω is the angular frequency,

is an imaginary number, ρ ₀ and c ₀ are the density of air and the speed of sound in air. K is the equivalent stiffness of the mechanical part of the speaker, M is the equivalent mass of the mechanical part of the speaker, and δ is the equivalent damping of the mechanical part of the speaker.

So the resonant frequency of the loudspeaker can be expressed as:

When two loudspeakers are connected to form a closed loop, the electrical impedance in the loop will produce an equivalent mechanical impedance ΔZ=(Bl) ² /2(R _e +jωL _e ).

Where Re is the DC resistance of the speaker, Le is the inductance of the voice coil, and Bl is the product of the magnetic induction of the magnetic field gap and the effective line length of the voice coil in the magnetic field (unit: T*m).

The resulting equivalent impedance acts on the equivalent damping and equivalent mass of the loudspeaker system, causing the resonance frequency of the loudspeaker to shift to:

The Thiele/Small parameters of the mechanical impedance characteristic of the dynamic speaker used are: damping δ=1.67Ns/m, mass M=6.5g, stiffness K=1000N/m. Therefore, according to the theoretical formula, the resonant frequency of a single loudspeaker in the connected system is f _L =170 Hz. At the resonant frequency, the sound wave transmitted to the surface of the speaker diaphragm is more likely to excite the vibration of the diaphragm, thereby completing the transmission of sound energy, so the noise reduction effect at the resonant frequency range is also the best.

In view of the characteristics of the selected speakers in the present invention, slide the downstream side plate to adjust the distance between the two speakers, so that the distance between the two speakers matches the resonance frequency, that is, the distance is equal to the half-wavelength corresponding to the resonance frequency. Taking this position as an example, the present invention will be described in detail.

Cooperating with the inherent characteristics of the speaker selected in the present invention, the downstream side plate installed with the downstream speaker 5 is displaced to the position L=c ₀ /(2f _L ), so that the noise reduction device can obtain the best noise reduction effect at this frequency.

According to the control principle, the noise control of the pipeline can be obtained as follows:

The effective noise reduction effect is evaluated by the noise reduction amount greater than 5 decibels dB. From the calculation results, the effective noise reduction frequency band shown in Figure 3 is basically consistent with the theoretically predicted noise reduction frequency band.

From the above analysis, it can be seen that the noise reduction device has a good sound absorption effect in the low frequency band.

Claims (6)

1. A pipeline low-frequency noise control device based on electro-acoustic coupling, characterized in that it includes an upstream loudspeaker, a downstream loudspeaker and a coupling circuit, and the main pipe section for noise control includes an upstream air intake pipe section, a middle muffler pipe section and a downstream outlet The pipe section and the anechoic pipe section are respectively provided with an upstream speaker and a downstream speaker, and the upstream speaker and the downstream speaker are connected through a coupling circuit. Make lateral translational movement along the slide rail on the pipe wall. 2. A pipeline low-frequency noise control device based on electro-acoustic coupling according to claim 1, wherein the sliding side plate moves along the slide rail to adjust the distance between the upstream speaker and the downstream speaker, so that the upstream speaker and the downstream speaker The distance between the loudspeakers matches the resonance frequency, and the distance between the upstream loudspeaker and the downstream loudspeaker is equal to (2N-1)/2 times the wavelength corresponding to the resonance frequency, where N is a positive integer. 3. A device for controlling low-frequency noise in pipelines based on electro-acoustic coupling according to claim 2, wherein the distance between the upstream speaker and the downstream speaker is equal to the half-wavelength corresponding to the resonance frequency. 4. A pipeline low-frequency noise control device based on electro-acoustic coupling according to claim 2, characterized in that: the noise is divided into two paths after entering the main pipe section, the first path directly passes through the upstream intake pipe section, the middle part of the noise The sound tube section is transmitted to the downstream speaker, and the second channel reaches the surface of the upstream speaker to cause vibration of the diaphragm and generate an induced electromotive force. The downstream speaker emits sound due to the induced current, and the two channels of sound waves converge at the downstream speaker, resulting in destructive interference. 5. The device for controlling low-frequency noise in pipelines based on electro-acoustic coupling according to any one of claims 1-4, wherein a sealed back cavity is arranged outside the upstream speaker and the downstream speaker. 6 . The electro-acoustic coupling-based pipeline low-frequency noise control device according to any one of claims 1-4, characterized in that: both the upstream speaker and the downstream speaker are moving coil speakers.

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