Frequency-adjustable multifunctional pipeline acoustic end load, implementation method and application device

Abstract

The application discloses a frequency-adjustable multifunctional pipeline acoustic end load, an implementation method and an application device, relates to the field of experimental measurement of acoustic performance of a muffler, and the air pipeline acoustic end load comprises an array of electroacoustic coupling structures and at least one shunt circuit module; the array of electroacoustic coupling structures comprises at least one electroacoustic coupling structure; a shunt circuit module is connected between the positive electrode and the negative electrode of the coil of each electroacoustic coupling structure; the shunt circuit module comprises an operational amplifier, a positive electrode unit, a negative electrode unit, a first resistor and a second resistor; the negative electrode unit comprises an adjustable impedance component. The application can effectively change low-frequency impedance, further accurately measure the low-frequency performance of the muffler, control noise at low frequencies, and adjust circuit elements to absorb noise of different frequencies without changing the mechanical structure. In addition, the acoustic experimental measurement of the muffler can also be realized by using a double sound source method.

Description

Technical Field

[0001] This application relates to the field of experimental measurement of the acoustic performance of silencers, and in particular to a frequency-tunable multifunctional duct acoustic end load, its implementation method, and its application device. Background Technology

[0002] As an effective means of controlling pipeline noise, duct silencers are characterized by a wide noise control frequency range and ease of maintenance and replacement. To ensure that the silencer can fully achieve noise control at the target frequency, it is necessary to measure its acoustic performance. Commonly used acoustic measurement methods for silencers include the dual-source method and the dual-load method. Among these, the dual-load method, which involves changing different acoustic end impedances during the experiment to measure the acoustic performance of the silencer, is simpler than other methods.

[0003] Existing sound-absorbing terminals typically use sound-absorbing materials, such as porous materials and sound-absorbing wedges. Porous materials are particularly effective at absorbing sound in the mid- and high-frequency ranges. Their interiors contain numerous tiny gaps and continuous air bubbles, forming excellent sound-absorbing channels. When sound waves strike the material surface, some penetrate into the material's interior, propagating through the gaps and pores, creating viscosity and friction, gradually converting sound energy into heat energy. However, metal sound-absorbing materials and certain specially treated organic fiber materials are difficult to repair once damaged or aged, sometimes requiring replacement of the entire material or parts of the components, increasing maintenance difficulty and cost. Sound-absorbing wedges, with their gradually increasing cross-section, are designed to match the fluid's characteristic impedance, achieving near-complete absorption of incident sound waves with almost no reflection. This design gives sound-absorbing wedges a high absorption coefficient in the mid- and high-frequency ranges, with a normal incidence absorption coefficient exceeding 0.99. However, wedge structures occupy a large volume and are difficult to maintain.

[0004] However, both of the aforementioned commonly used silencing terminals have drawbacks such as difficult maintenance and insignificant low-frequency sound absorption. Therefore, the low-frequency acoustic performance data obtained from these silencing terminals is unreliable. (The low-frequency absorption coefficient of ordinary sound-absorbing materials is close to 0, and the low-frequency impedance remains almost unchanged before and after the silencing terminal is replaced. The dual-load method relies on impedance changes for measurement, making the acoustic performance data of mufflers measured with conventional sound-absorbing materials unreliable.) Furthermore, the dual-load method requires replacing the sound-absorbing material at the silencing terminal, and inconsistent installation conditions in each experiment lead to poor repeatability. Therefore, it is necessary to use a new acoustic terminal to test the low-frequency performance of the muffler. Summary of the Invention

[0005] The purpose of this application is to provide a frequency-adjustable, multifunctional duct acoustic end load, its implementation method, and application device, which can effectively change low-frequency impedance and further accurately measure the low-frequency performance of the muffler. It controls noise at low frequencies by adjusting circuit components to absorb noise at different frequencies without altering the mechanical structure.

[0006] To achieve the above objectives, this application provides the following solution:

[0007] In a first aspect, this application provides a frequency-tunable multifunctional pipe acoustic end load connected to the end of a noise reduction experimental device, comprising an electroacoustic coupling structure array and at least one shunt circuit module; the electroacoustic coupling structure array comprises at least one electroacoustic coupling structure; a shunt circuit module is connected between the positive and negative poles of the coil of each electroacoustic coupling structure.

[0008] The shunt circuit module includes an operational amplifier, a positive terminal unit, a negative terminal unit, a first resistor, and a second resistor. One end of the negative terminal unit is connected in series with the negative input terminal of the operational amplifier, and the other end of the negative terminal unit is connected in series with the positive terminal of the coil of the corresponding electroacoustic coupling structure. One end of the positive terminal unit is connected in series with the positive input terminal of the operational amplifier, and the other end of the negative terminal unit is grounded to the negative terminal of the coil of the corresponding electroacoustic coupling structure. One end of the first resistor is connected in series with the negative input terminal of the operational amplifier, and the other end of the first resistor is connected in series with the output terminal of the operational amplifier. One end of the second resistor is connected in series with the positive input terminal of the operational amplifier, and the other end of the second resistor is connected in series with the output terminal of the operational amplifier. The negative terminal unit includes an adjustable impedance component.

[0009] Optionally, the negative electrode unit includes a negative electrode inductor, a negative electrode resistor, and an adjustable impedance component connected in series; the other end of the negative electrode inductor is connected in series with the positive terminal of the coil of the corresponding electroacoustic coupling structure; the other end of the adjustable impedance component is connected in series with the negative input terminal of the operational amplifier.

[0010] The positive terminal unit includes a positive inductor and a positive resistor connected in series; the other end of the positive inductor is grounded; and the other end of the positive resistor is connected in series with the positive input terminal of the operational amplifier.

[0011] Optionally, the adjustable impedance component is a capacitor or an adjustable capacitor plate.

[0012] Optionally, when the adjustable impedance component is an adjustable capacitor plate, the capacitance value of the adjustable capacitor plate is adjusted by a switch on the target frequency adjustment toggle plate.

[0013] Alternatively, the acoustic impedance of the electroacoustic coupling structure is expressed as follows:

[0014]

[0015] Among them, Z T S represents the acoustic impedance of the electroacoustic coupling structure. D Rs is the diaphragm area of ​​the electroacoustic coupling structure, Rs is the damping of the electroacoustic coupling structure, j is the imaginary unit, M is the equivalent mass of the electroacoustic coupling structure, ω is the angular frequency, K is the equivalent stiffness of the electroacoustic coupling structure, BL is the force factor of the electroacoustic coupling structure, and Rs is the diaphragm area of ​​the electroac e and L e These are the total resistance and total inductance of the shunt circuit module, respectively, C e This refers to the capacitance value of the adjustable impedance component.

[0016] Optionally, the total resistance of the shunt circuit module is calculated based on the negative and positive resistances, and the total inductance of the shunt circuit module is calculated based on the negative and positive inductances.

[0017] Optionally, the electroacoustic coupling structure is a moving iron, electromagnetic, or moving coil loudspeaker.

[0018] Secondly, this application provides a method for implementing a frequency-tunable, multifunctional duct acoustic end load, comprising:

[0019] Adjust the capacitance and inductance values ​​of the adjustable impedance component; the capacitance and inductance values ​​of the adjustable impedance component are determined according to the target frequency.

[0020] Connect the aforementioned adjustable frequency multifunctional pipe acoustic end load to the end of the silencing experimental device and perform the first impedance end test measurement; after the first impedance end test measurement, adjust the capacitance and inductance values ​​of the adjustable impedance component and perform the second impedance end test measurement.

[0021] The low-frequency acoustic performance data of the muffler were calculated based on the sound pressure data of different impedances measured in two impedance-end experiments.

[0022] Thirdly, this application provides a dual-source measurement application device, wherein the secondary sound source in the dual-source measurement application device is the aforementioned frequency-tunable multifunctional pipe acoustic end load.

[0023] Optionally, the dual-source method for measuring the silencer further includes a horn; the horn is disposed between the secondary sound source and the air duct and is used to adjust the matching impedance between the diaphragm of the electroacoustic coupling structure and the fluid medium.

[0024] According to the specific embodiments provided in this application, the following technical effects are disclosed:

[0025] This application provides a frequency-adjustable multifunctional duct acoustic end load, its implementation method, and application device. Based on the sound transmission loss measurement method, it can effectively change the low-frequency impedance and further accurately measure the low-frequency performance of the muffler. Without changing the mechanical structure, only the circuit components are adjusted to absorb noise at different frequencies. Specifically, the circuit impedance can be adjusted by regulating the capacitance of the adjustable impedance component, thereby achieving speaker structure impedance adjustment. This facilitates the dual-load measurement method and also enables sound absorption at low frequencies (below 100Hz). Through the impedance adjustment of the circuit, low-frequency line spectrum noise can be controlled. Furthermore, this structure can adjust the circuit to implement dual-load experiments, providing strong support for the smooth conduct of experiments. Multiple impedance adjustment units (each impedance adjustment unit includes an electroacoustic coupling structure and a shunt circuit module) are arranged in an array, occupying a small volume space. Maintenance only requires replacing a single faulty component, making maintenance simple and convenient. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of an experiment on the sound transmission loss of a silencer.

[0028] Figure 2 This is a schematic diagram of a method for measuring the sound transmission loss of a muffler.

[0029] Figure 3 A front view of a frequency-tunable multifunctional duct acoustic end load provided in Embodiment 1 of this application;

[0030] Figure 4 This is a top view of a frequency-tunable multifunctional duct acoustic end load provided in Embodiment 1 of this application.

[0031] Figure 5 This is a schematic diagram of the dual-load method measurement principle provided in Embodiment 1 of this application.

[0032] Figure 6 This is a schematic diagram of the noise reduction principle of the electroacoustic coupling structure provided in Embodiment 1 of this application.

[0033] Figure 7 This is a schematic diagram of the basic principle of the shunt circuit module provided in Embodiment 1 of this application.

[0034] Figure 8 This is a schematic diagram of the electroacoustic coupling structure provided in Embodiment 1 of this application.

[0035] Figure 9 This is a schematic diagram of the adjustable capacitor and adjustable inductor provided in Embodiment 1 of this application.

[0036] Figure 10 This is a flowchart illustrating a method for implementing a frequency-tunable multifunctional duct acoustic end load according to Embodiment 2 of this application.

[0037] Figure 11 This is a schematic diagram showing the effect of the shunt circuit module provided in Embodiment 1 of this application on the sound absorption coefficient of the electroacoustic coupling structure.

[0038] Figure 12 This is a schematic diagram of the dual-source measurement application device provided in Embodiment 3 of this application.

[0039] Reference numerals: First microphone—1, Second microphone—2, Silencer—3, Third microphone—4, Air duct—5, Sound-generating structure—6, Electroacoustic coupling structure—7, Shunt circuit module—8, Encasing material—9, Magnetic conductor—10, Magnet—11, Coil—12, Diaphragm—13, Hoop—14, Coil support—15, Operational amplifier—16, Fourth microphone—17. Detailed Implementation

[0040] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0041] Transmission loss is defined as the ratio of the incident sound power level at the inlet of silencer 3 to the transmitted sound power level at the outlet. The experimental measurement principle of transmission loss of silencer 3 is as follows: Figure 1 As shown, the sound transmission loss needs to be obtained within the air duct 5 P i and P t To calculate the amplitude of P, we need to obtain P. t For low-frequency amplitudes, the end needs to be free of sound wave reflection, i.e., it needs to be set as a non-reflective interface. Therefore, in order to ensure the accuracy and correctness of the experimental calculations, it is necessary to ensure that the downstream of the silencer 3 meets the sound absorption capacity required by the experiment as much as possible, and it is also necessary to ensure the repeatability of the experiment before and after load adjustment.

[0042] According to national standard GB / Z 27764-2011, in such cases... Figure 2 Under the acoustic end conditions shown, two microphones, designated as microphone 1 and microphone 2, are arranged at the sound source. Microphone 3 is arranged downstream of silencer 3. The transfer function H of the microphone is obtained.12 H 13 The sound transmission loss of muffler 3 can then be calculated. If the sound absorption performance of the downstream muffler end is insufficient, it will affect the experimental results and lead to errors in the calculation of the acoustic performance of muffler 3. Therefore, a sound-absorbing end with strong sound absorption performance has a crucial impact on the correctness and effectiveness of the muffler 3 experiment. Commonly used sound-absorbing ends include porous sound-absorbing materials, perforated plates, and sound-absorbing wedges.

[0043] However, the aforementioned porous sound-absorbing materials and sound-absorbing wedges all have drawbacks such as difficult maintenance and insignificant low-frequency noise reduction effects. To address these issues, this application provides a frequency-adjustable multifunctional duct acoustic end load, which is an electroacoustic coupling impedance adjustment end, providing low-frequency reflection-free operation downstream of the duct silencer 3 test.

[0044] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] Example 1.

[0046] This embodiment provides a frequency-tunable, multifunctional duct acoustic end load, such as... Figure 5 As shown, the frequency-tunable multifunctional duct acoustic end load is connected to the end of the silencing experimental device, i.e. Figure 5 The sound-absorbing end in the middle. This silencing experimental device includes a sound source (i.e., Figure 5 The sound-generating structure includes: 6), first microphone 1, second microphone 2, silencer 3, third microphone 4, and air duct 5.

[0047] like Figure 3 and Figure 4 As shown, the frequency-tunable multifunctional duct acoustic end load provided in this application includes an array of electroacoustic coupling structures 7 and at least one shunt circuit module 8; the array of electroacoustic coupling structures 7 includes at least one electroacoustic coupling structure 7; a shunt circuit module 8 is connected between the positive and negative poles of the coil 12 of each electroacoustic coupling structure 7. The electroacoustic coupling structure 7 is a moving iron, electromagnetic, or moving coil loudspeaker, etc. The array of electroacoustic coupling structures 7 is externally covered with a wrapping material 9, which is used to fix the loudspeaker and fill the loudspeaker spacing.

[0048] The number of electroacoustic coupling structures 7 should be determined by the application of the acoustic terminal, and can be determined by the pipe diameter and the diameter of the electroacoustic coupling structure 7; the pipe diameter is the diameter of the air pipe 5 in the noise reduction experiment.

[0049] When used in an air duct with a diameter of 100mm, a loudspeaker with a diameter of 30mm is used, with a maximum of 5 loudspeakers. The number of loudspeakers depends on the duct diameter, the loudspeaker diameter, and the arrangement. Figure 3 and Figure 4 The air duct 5 has a diameter of 100mm and the speaker arrangement has a diameter of 30mm.

[0050] The following example, using a moving-coil loudspeaker, illustrates the effect of electroacoustic coupling structure 7 on noise reduction. Figure 6 As shown, when the sound pressure is disturbed, the sound wave is transmitted to the electroacoustic coupling structure 7, the diaphragm 13 of the electroacoustic coupling structure 7 vibrates, the damping of the electroacoustic coupling structure 7 loses energy, and the coil 12 of the electroacoustic coupling structure 7 generates current and the circuit resonance consumes energy.

[0051] Electromagnetic electroacoustic coupling is divided into moving-coil and moving-iron types. In the analysis method, the differences between moving-coil and moving-iron types are only reflected in the changes of various physical parameters, such as mass, stiffness, and damping. The motion model of both can be simplified as a single-degree-of-freedom vibration model. When the circuit is disconnected, the acoustic impedance of the electroacoustic coupling structure 7 can be expressed as shown in the following formula.

[0052]

[0053] Among them, Z m S represents the acoustic impedance of the electroacoustic coupling structure 7 when the shunt circuit module 8 is not connected. D Rs is the area of ​​the diaphragm 13 of the electroacoustic coupling structure 7, j is the imaginary unit, M is the equivalent mass of the electroacoustic coupling structure 7, ω = 2πf, where ω is the angular frequency, f is the frequency, and K is the equivalent stiffness of the electroacoustic coupling structure 7.

[0054] At the mechanical resonant frequency, the acoustic impedance amplitude is almost zero, resulting in the maximum sound absorption coefficient. The value of the sound absorption coefficient is related to the area and mechanical damping of the electroacoustic coupling structure 7. However, to achieve low-frequency sound absorption, for moving-coil structures with a small equivalent mass, the only way to absorb low-frequency noise is by reducing stiffness; for moving-iron structures with a larger mass, the only way is to adjust the absorption frequency by increasing stiffness. Different adjustments are required for different electroacoustic coupling structures 7. Adjusting the same structure at different frequencies also requires increasing or decreasing the stiffness of the structure, which not only increases the number of process steps but also increases time and labor costs. Therefore, this application introduces a shunt circuit module 8 to adjust the impedance of the electroacoustic coupling structure 7, which can ignore the differences between different electroacoustic coupling structures 7 and save costs.

[0055] The electroacoustic coupling structure 7 connecting the shunt circuit module 8 is as follows: Figure 8 As shown. The electroacoustic coupling structure 7 includes a magnetic conductor 10, a magnet 11, a coil 12, a diaphragm 13, a folded ring 14, and a coil support 15. One electroacoustic coupling structure 7 requires only one shunt circuit module 8 for impedance adjustment. The shunt circuit module 8 only adjusts the impedance of the electroacoustic coupling structure 7 to which it is connected.

[0056] The basic principle of shunt circuit module 8 is as follows: Figure 7 As shown, the shunt circuit module 8 includes an operational amplifier 16, a positive terminal unit, a negative terminal unit, a first resistor R1, and a second resistor R2. One end of the negative terminal unit is connected in series with the negative input terminal of the operational amplifier 16, and the other end of the negative terminal unit is connected in series with the positive terminal of the coil 12 of the corresponding electroacoustic coupling structure 7. One end of the positive terminal unit is connected in series with the positive input terminal of the operational amplifier 16, and the other end of the negative terminal unit is grounded to the negative terminal of the coil 12 of the corresponding electroacoustic coupling structure 7. One end of the first resistor R1 is connected in series with the negative input terminal of the operational amplifier 16, and the other end of the first resistor R1 is connected in series with the output terminal of the operational amplifier 16. One end of the second resistor R2 is connected in series with the positive input terminal of the operational amplifier 16, and the other end of the second resistor R2 is connected in series with the output terminal of the operational amplifier 16.

[0057] The negative electrode unit includes a negative electrode inductor L connected in series. e1 Negative resistance R e1 and adjustable impedance component C e1 Negative inductance L e1 The other end is connected in series with the positive terminal of the coil 12 of the corresponding electroacoustic coupling structure 7; adjustable impedance component C e1 The other end is connected in series with the negative input terminal of operational amplifier 16. The positive unit includes a positive inductor L connected in series. e2 and positive resistance R e2 Positive inductor L e2 The other end is grounded; positive resistor R e2 The other end is connected in series with the positive input terminal of operational amplifier 16.

[0058] In the shunt circuit module 8, the negative input terminal of operational amplifier 16 is connected in series with the negative inductor L. e1 Negative resistance R e1 and adjustable impedance component C e1 Negative inductor L e1 Negative resistance R e1 For the inductance and resistance of coil 12 in the electroacoustic coupling structure 7, C e1 This is an additional capacitor. An additional positive inductor L is connected in series at the positive input of operational amplifier 16. e2 and positive resistance R e2 Since operational amplifier 16 can change the phase of the impedance between the positive input terminal and ground, the positive inductor L can be... e2 and positive resistance R e2 The equivalent negative impedance reduces the resistance and inductance of the electroacoustic coupling structure 7 and the coil 12.

[0059] The change in impedance between the positive input terminal and ground of operational amplifier 16 is related to the first resistor R1 and the second resistor R2 in shunt circuit module 8. The relationship between them is as follows:

[0060]

[0061] Among them, Z 变换后 Z 变换前 These are the changed and original impedances between the positive input terminal and ground of operational amplifier 16, respectively.

[0062] The adjustable impedance component is a capacitor or an adjustable capacitor plate. The capacitance value of the capacitor or adjustable capacitor plate is determined by the target frequency. Adjustable capacitors and adjustable inductors are examples of such components. Figure 9 As shown. The peak frequency of the sound absorption coefficient can be changed by adjusting the circuit components. No disassembly or reassembly is required; the low-frequency impedance transformation process can be completed simply by adjusting the circuit components.

[0063] Add adjustable capacitor C e1 and adjustable inductor L e2 The combined effect of these two factors adjusts the circuit's resonant frequency, thereby regulating the frequency corresponding to the peak sound absorption coefficient at that end. When the adjustable impedance component is an adjustable capacitor plate, the capacitance value of the adjustable capacitor plate is adjusted by a switch on the target frequency adjustment toggle panel. Replacing the adjustable capacitor plate with an adjustable capacitor plate... Figure 7 The capacitor C in e1 The final output capacitance value of the adjustable capacitor plate can be adjusted by moving the switch on the toggle panel according to different target frequencies. The total capacitance of the adjustable capacitor plate is the sum of the small capacitors that are turned on. Different needs can be met by simply adjusting the capacitance value of the adjustable capacitor plate, avoiding the design and installation work of traditional acoustic terminals and reducing the non-repeatability caused by assembly.

[0064] Example 2.

[0065] In one exemplary embodiment, such as Figure 10 As shown, a method for implementing a multifunctional duct acoustic end load based on the above-mentioned adjustable frequency is provided, including the following steps.

[0066] Step S1: Adjust the capacitance and inductance values ​​of the adjustable impedance component; the capacitance and inductance values ​​of the adjustable impedance component are determined according to the target frequency. The capacitance and inductance values ​​can be arbitrarily combined to meet noise control at the target frequency.

[0067] Step S2: Connect the adjustable multi-functional duct acoustic terminal load to the end of the anechoic experimental device and perform the first impedance terminal test measurement. After the first impedance terminal test measurement, adjust the capacitance and inductance values ​​of the adjustable impedance component and perform the second impedance terminal test measurement. After the first impedance terminal test measurement, adjusting the capacitance and inductance values ​​of the adjustable impedance component can easily change the low-frequency impedance of the terminal, allowing for the second test measurement.

[0068] Step S3: Calculate the low-frequency acoustic performance data of the muffler based on the sound pressure data measured at different impedances in two impedance-end experiments. After obtaining the sound pressure data at different impedances from the two impedance-end experiments, the low-frequency acoustic performance data of the muffler can be obtained.

[0069] The purpose of acoustic termination is to change the acoustic impedance in the low-frequency range. Since the absorption coefficient of ordinary sound-absorbing materials is close to zero, the low-frequency impedance remains almost unchanged before and after replacing the acoustic termination. Therefore, the acoustic performance data of the muffler measured at low frequencies is unreliable. Therefore, the method proposed in this application can effectively change the low-frequency impedance, and further, can accurately measure the low-frequency performance of the muffler.

[0070] After being excited by the sound source, the sound wave is transmitted along the air duct 5 to the first microphone 1, the second microphone 2, and the silencer 3. Due to the inconsistency between the impedance of the silencer 3 and the air impedance, reflected sound waves propagate upstream. The sound wave continues to propagate along the air duct 5, passing through the third microphone 4, until it reaches the duct acoustic end load with adjustable impedance provided in this application. Since the phase of the received sound wave is different due to the different positions of each microphone, the acoustic performance of the silencer 3 can be interpreted after obtaining the transfer function between each microphone.

[0071] When the sound wave is transmitted to the adjustable impedance pipe acoustic end load provided in this application, the diaphragm 13 of the electroacoustic coupling structure 7 and the coil 12 generate relative motion, inducing a current in the coil 12. Since the coil 12 is connected in series with the shunt circuit module 8, the adjustment function of the shunt circuit module 8 is activated, and the circuit impedance changes as follows:

[0072] In operational amplifier 16, the first resistor R1 and the second resistor R2 serve as adjustment mechanisms, defining the impedance adjustment range ( Figure 7 The electrical impedance of the area (shown by the dashed box) is set to the form shown in the following formula.

[0073] Z = -R1R2·(R e2 +jωL e2 (3).

[0074] Where Z is the impedance of the impedance adjustment region.

[0075] The first resistor R1 and the second resistor R2 are used to calculate the circuit impedance. Positive inductor L... e2 An external inductor is added to compensate for the negative inductance L of coil 12. e1 .

[0076] When the first resistor R1 and the second resistor R2 are equal:

[0077] Z = -(R) e2 +jωL e2 (4).

[0078] The total impedance Z of the shunt circuit module 8 e for:

[0079] Z e =(R e1 -R e2 )+j[ω(L e1 -L e2 )-1ωC e1 (5).

[0080] The acoustic impedance of the electroacoustic coupling structure 7 after the addition of the shunt circuit module 8 is expressed as shown in the following formula.

[0081]

[0082] Among them, Z T S represents the acoustic impedance of the electroacoustic coupling structure 7. D Rs is the area of ​​the diaphragm 13 of the electroacoustic coupling structure 7, Rs is the damping of the electroacoustic coupling structure 7, BL is the force factor of the electroacoustic coupling structure 7, and Rs is the damping of the electroacoustic coupling structure 7. e and L e These are the total resistance and total inductance of shunt circuit module 8, respectively. e1 This refers to the capacitance value of the adjustable impedance component.

[0083] The total resistance of shunt circuit module 8 is calculated based on the negative and positive resistances, and the total inductance of shunt circuit module 8 is calculated based on the negative and positive inductances, i.e., R. e =R e1 -R e2 L e =L e1 -L e2 .

[0084] When a target frequency is used, the real part of the structure's impedance is equal to the characteristic impedance of the fluid, and the imaginary part of the structure is 0. At this time, the sound absorption coefficient of the structure at the current target frequency is 1, which can achieve sound absorption at that target frequency.

[0085] When the electroacoustic coupling structure 7 array connected to the shunt circuit module 8 successfully absorbs sound, no reflected sound waves will be generated between the muffler 3 and the frequency-adjustable multifunctional pipe acoustic end load in the air duct 5, thus ensuring the accuracy and correctness of the experimental results.

[0086] Based on the above, it can be shown that the frequency-tunable multifunctional duct acoustic end load of this application has a sound absorption effect on the target frequency.

[0087] The shunt circuit module 8 has a certain adjustment effect on the acoustic impedance of the structure, which can adjust the peak value of the sound absorption coefficient to the required frequency. For different application scenarios, sound absorption at different frequencies is required. Conventional sound-absorbing materials and sound-absorbing wedges need to be redesigned and manufactured. However, this application only needs to change the size of the capacitor in the impedance shunt circuit module 8 to select a suitable target frequency. It is easy to realize experimental measurement of the dual-load method, reduce the disassembly and assembly of the structure, and improve the repeatability of the experiment.

[0088] Figure 11 The graph shows the sound absorption coefficient of the electroacoustic coupling structure 7 applied to the air duct, specifically the influence curve of the shunt circuit module 8 on the sound absorption coefficient of the electroacoustic coupling structure 7. The horizontal axis, f, represents frequency, and the vertical axis, α, represents the sound absorption coefficient. Because air has a relatively small characteristic medium, the structural impedance is close to the characteristic impedance of air, resulting in limited impedance regulation of the shunt circuit module 8 on the electroacoustic coupling structure 7. By adjusting the circuit components, the circuit resonant frequency can be adjusted to any desired frequency. Therefore, the electroacoustic coupling structure 7 is more advantageous for low-frequency sound absorption at the end than traditional sound-absorbing materials. The array of electroacoustic coupling structures 7 can achieve impedance regulation of low-frequency noise, thereby obtaining accurate low-frequency transmission loss of the silencer 3.

[0089] Based on the method of measuring the transmission loss of silencers, this application proposes a frequency-tunable multifunctional duct acoustic end load based on an electroacoustic coupling structure; the circuit impedance can be adjusted by adjusting the capacitor, thereby realizing the impedance adjustment of the speaker structure and conveniently realizing the dual-load measurement method; the impedance adjustment end (i.e., the frequency-tunable multifunctional duct acoustic end load provided in this application) can also achieve sound absorption at low frequencies (below 100Hz), which is a low frequency that is difficult to achieve with current sound-absorbing materials and sound-absorbing wedges.

[0090] The electroacoustic coupling structure 7 allows for noise absorption at different frequencies by adjusting only the circuit components without altering the mechanical structure. It employs an array of multiple impedance adjustment units (electroacoustic coupling structure 7 and shunt circuit module 8), resulting in a small footprint. Maintenance is simple and convenient, requiring only the replacement of a single faulty component. The electroacoustic coupling structure 7 is available in electromagnetic and piezoelectric versions. The electromagnetic version achieves sound absorption at lower frequencies, while the piezoelectric version is commonly used for ultra-high frequency electroacoustic transduction, with a minimum frequency of around 250Hz, making it difficult to control low-frequency noise in the pipeline.

[0091] Example 3.

[0092] This embodiment provides a dual-source measurement application device, wherein the secondary sound source in the dual-source measurement application device is the frequency-tunable multifunctional duct acoustic end load described in Embodiment 1. The dual-source measurement application device includes: a secondary sound source, a main sound source, a first microphone, a second microphone, a silencer, a third microphone, a fourth microphone, and an air duct; the silencer is located in the middle of the air duct, the first and second microphones are disposed on one side of the silencer, and the third and fourth microphones are disposed on the other side of the silencer.

[0093] The dual-source method for measuring silencers may further include a horn; the horn is positioned between the secondary sound source and the air duct and is used to adjust the matching impedance between the diaphragm of the electroacoustic coupling structure and the fluid medium.

[0094] The tunable multi-functional duct acoustic end load can be used as a secondary sound source to meet the requirements of the dual-source method for measuring the acoustic performance of silencers, such as... Figure 12 As shown, adding a horn between the secondary sound source and the duct improves the impedance matching between the loudspeaker diaphragm and the fluid medium, further adjusting the directivity of the loudspeaker assembly and improving energy conversion efficiency. Traditional muffler acoustic performance measurement includes the dual-source method. The measurement principle involves installing microphones upstream and downstream of the muffler; specifically, a first microphone 1 and a second microphone 2 are installed upstream, and a third microphone 4 and a fourth microphone 17 are installed downstream. These are used to measure sound pressure data. By measuring the sound pressure data under two conditions—with only the upstream sound source and only the downstream sound source activated—the acoustic performance of the muffler can be obtained after analysis. This method is applicable to any reflection environment, more closely resembling the measurement environment in actual engineering practice, and avoids the dependence of the dual-load method on the downstream non-reflective boundary.

[0095] This application employs a horn structure to connect the loudspeaker assembly and the air duct 5, achieving a gradual transition from high sound pressure inside the air duct 5 to low sound pressure on the diaphragm surface. This enables impedance matching between the loudspeaker and the gas inside the air duct 5, improving efficiency. Furthermore, during the dual-source measurement process, this part acts as a secondary sound source radiating sound pressure into the duct. The horn structure can further increase the radiation impedance, improve the efficiency of electroacoustic coupling, and control the directivity of the loudspeaker, accurately directing it into the air duct 5 to form a plane wave, rather than radiating to the duct wall and forming a reverberation field. This effectively supports the acoustic measurements of the silencer.

[0096] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0097] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A frequency-tunable, multifunctional duct acoustic end load, connected to the end of a noise reduction experimental device, characterized in that, The frequency-tunable multifunctional duct acoustic end load includes an electroacoustic coupling structure array and at least one shunt circuit module; the electroacoustic coupling structure array includes at least one electroacoustic coupling structure; a shunt circuit module is connected between the positive and negative terminals of the coil of each electroacoustic coupling structure. The shunt circuit module includes an operational amplifier, a positive terminal unit, a negative terminal unit, a first resistor, and a second resistor. One end of the negative terminal unit is connected in series with the negative input terminal of the operational amplifier, and the other end of the negative terminal unit is connected in series with the positive terminal of the coil of the corresponding electroacoustic coupling structure. One end of the positive terminal unit is connected in series with the positive input terminal of the operational amplifier, and the other end of the positive terminal unit is grounded to the negative terminal of the coil of the corresponding electroacoustic coupling structure. One end of the first resistor is connected in series with the negative input terminal of the operational amplifier, and the other end of the first resistor is connected in series with the output terminal of the operational amplifier. One end of the second resistor is connected in series with the positive input terminal of the operational amplifier, and the other end of the second resistor is connected in series with the output terminal of the operational amplifier. The negative electrode unit includes a negative electrode inductor, a negative electrode resistor, and an adjustable impedance component connected in series; the other end of the negative electrode inductor is connected in series with the positive terminal of the coil of the corresponding electroacoustic coupling structure; the other end of the adjustable impedance component is connected in series with the negative input terminal of the operational amplifier; the adjustable impedance component is a capacitor or an adjustable capacitor plate. The positive terminal unit includes a positive inductor and a positive resistor connected in series; the other end of the positive inductor is grounded; the other end of the positive resistor is connected in series with the positive input terminal of the operational amplifier. The acoustic impedance of the electroacoustic coupling structure is expressed as follows: ； in, The acoustic impedance represents the electroacoustic coupling structure. The diaphragm area of ​​the electroacoustic coupling structure. Damping for the electroacoustic coupling structure, The imaginary unit, The equivalent mass of the electroacoustic coupling structure. It is the angular frequency. The equivalent stiffness of the electroacoustic coupling structure. For the force factor of the electroacoustic coupling structure, and These are the total resistance and total inductance of the shunt circuit module, respectively. This refers to the capacitance value of the adjustable impedance component.

2. The frequency-tunable multifunctional duct acoustic end load according to claim 1, characterized in that, When the adjustable impedance component is an adjustable capacitor plate, the capacitance value of the adjustable capacitor plate is adjusted by the switch on the target frequency adjustment toggle plate.

3. The frequency-tunable multifunctional duct acoustic end load according to claim 1, characterized in that, The total resistance of the shunt circuit module is calculated based on the negative and positive resistances, and the total inductance of the shunt circuit module is calculated based on the negative and positive inductances.

4. The frequency-tunable multifunctional duct acoustic end load according to claim 1, characterized in that, The electroacoustic coupling structure is a moving iron, electromagnetic, or moving coil loudspeaker.

5. A method for implementing a frequency-tunable multifunctional duct acoustic end load according to any one of claims 1-4, characterized in that, The implementation method includes: Adjust the capacitance and inductance values ​​of the adjustable impedance component; the capacitance and inductance values ​​of the adjustable impedance component are determined according to the target frequency. The frequency-adjustable multifunctional duct acoustic end load according to any one of claims 1-4 is connected to the end of the silencing experimental device for the first impedance end test measurement; after the first impedance end test measurement, the capacitance and inductance values ​​of the adjustable impedance component are adjusted, and the second impedance end test measurement is performed; the low-frequency acoustic performance data are calculated based on the sound pressure data of different impedances from the two impedance end test measurements.

6. A dual-source measurement application device, characterized in that, The secondary sound source in the dual-source method measurement application device is the frequency-tunable multifunctional duct acoustic end load as described in any one of claims 1-4.

7. The dual-source measurement application device according to claim 6, characterized in that, The dual-source measurement application device also includes a horn; the horn is placed between the secondary sound source and the air duct and is used to adjust the matching impedance between the diaphragm of the electroacoustic coupling structure and the fluid medium.

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