Perforated plate-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorber

Abstract

The invention discloses a perforated plate-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorber, and relates to the technical field of low-frequency sound absorption. The composite low-frequency sound absorber comprises a sound box and an adjustable digital-analog hybrid shunt circuit, the sound box comprises a perforated plate, a front back cavity, a rear back cavity and a moving-coil loudspeaker installed in the rear back cavity. The perforated plate is located at the foremost end of the sound box; the front back cavity is a cavity formed between the moving-coil loudspeaker and the perforated plate; the sound box is connected with the adjustable digital-analog hybrid shunt circuit through the positive end and the negative end of the moving-coil loudspeaker; when sound waves reach the perforated plate, friction and vibration are generated between part of the sound waves and air in the small holes of the perforated plate and the surface of the perforated plate, and the sound waves are converted into heat energy to be dissipated; and the other part of sound waves pass through the perforated plate, reach the surface of the digital-analog hybrid shunt loudspeaker, and are converted into electric energy to be dissipated.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of low-frequency sound absorption, in particular to a perforated plate-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorption body. BACKGROUND

[0002] With the acceleration of urbanization and the increase of population density, people's requirements for the comfort and quietness of indoor and outdoor environments are getting higher and higher, and noise pollution has become a serious problem. Traditional passive sound absorption technology mainly uses porous materials and resonant sound absorption bodies, which have good sound absorption effect on high-frequency sound waves, but the sound absorption performance at low frequency is low, and a large space and material thickness are usually required to improve the sound absorption coefficient at low frequency. The shunt loudspeaker is a new type of low-frequency sound absorption body, which can change the acoustic impedance by adjusting the shunt circuit, and the sound energy is converted into electrical energy and dissipated through the shunt circuit, so that good low-frequency sound absorption effect can be achieved without relying on the thickness of the back cavity. Compared with the analog shunt loudspeaker, the digital-analog hybrid shunt loudspeaker only needs to design a few digital filter parameters to realize the equivalent shunt circuit impedance, without the need to build a negative impedance conversion circuit to offset the direct current resistance and direct current of the loudspeaker voice coil, so it has higher stability, higher precision and more convenient adjustment ability.

[0003] In the prior art, an adjustable hybrid digital-analog shunt loudspeaker is proposed, which only needs to design 2-3 digital filter parameters to realize adjustable low-frequency sound absorption. However, the low-frequency sound absorption of the hybrid digital-analog shunt loudspeaker is limited to the vicinity of the resonant frequency, and the sound absorption bandwidth is narrow, which leads to the fact that the low-frequency sound absorption performance cannot meet the actual demand. SUMMARY

[0004] Therefore, it is necessary to provide a perforated plate-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorption body in view of the above technical problems.

[0005] The application adopts the following technical scheme: The application provides a perforated plate-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorption body, which comprises: a sound box and an adjustable digital-analog hybrid shunt circuit; The sound box comprises a perforated plate, a front back cavity, a rear back cavity and a moving coil loudspeaker mounted in the rear back cavity; the perforated plate is located at the frontmost end of the sound box; the front back cavity is a cavity formed between the moving coil loudspeaker and the perforated plate; and the sound box is connected with the adjustable digital-analog hybrid shunt circuit through the positive and negative ends of the moving coil loudspeaker. When the sound wave reaches the perforated plate, part of the sound wave rubs and vibrates with the air inside the small holes of the perforated plate and the surface of the perforated plate, and is converted into heat energy and dissipated; the other part of the sound wave passes through the perforated plate to the surface of the digital-analog hybrid shunt loudspeaker and is converted into electrical energy and dissipated.

[0006] Preferably, the parameters of the perforated plate include: perforated plate thickness, hole diameter, perforation rate, front and back cavity depth.

[0007] Preferably, the circuit structure of the adjustable digital-analog hybrid shunt circuit includes: the circuit structure of the adjustable digital-analog hybrid shunt circuit under the net resistance inductance contribution and the circuit structure of the adjustable digital-analog hybrid shunt circuit under the net resistance capacitance contribution.

[0008] Preferably, the parameters of the adjustable digital-analog hybrid shunt circuit include: adjustable equivalent inductance or adjustable equivalent capacitance and adjustable equivalent resistance; Preferably, the expression of the resistance impedance of the adjustable digital-analog hybrid shunt circuit under the net resistance inductance contribution is: Z s1 = − R E ′− jcoL E ′+ R s + jcoL s ; In the formula, Z s1 is the resistance impedance of the adjustable digital-analog hybrid shunt circuit under the net resistance inductance contribution, − R E ′ is a negative resistance, used to offset the direct current resistance of the voice coil R E , negative inductance − L E ′ used to offset the inductance of the voice coil L E , j is the imaginary part, ω is the angular velocity, R s is the adjustable equivalent resistance, L s is the adjustable equivalent inductance; The expression of the resistance impedance of the adjustable digital-analog hybrid shunt circuit under the net resistance capacitance contribution is: Z s2 = −R E −jcoL E ′+R s + 1 / jcoC s ; In the formula, Z s2 is the resistance impedance of the adjustable digital-analog hybrid shunt circuit under the net resistance capacitance contribution, R san adjustable equivalent resistance, C s an adjustable equivalent capacitance.

[0009] Preferably, the parameters of the perforated plate and the parameters of the adjustable analog-digital hybrid shunt circuit are determined by an optimization algorithm with the average absorption coefficient of the composite low-frequency sound absorber in the target frequency range as the optimization target.

[0010] Preferably, the optimization process of the parameters of the perforated plate and the parameters of the adjustable analog-digital hybrid shunt circuit specifically includes: determining the optimal parameters of the perforated plate and the adjustable analog-digital hybrid shunt circuit by an optimization algorithm with the average absorption coefficient of the composite low-frequency sound absorber in the target frequency range as the optimization target; calculating the average absorption coefficient of the composite low-frequency sound absorber based on the optimal parameters; determining the optimal circuit structure of the adjustable analog-digital hybrid shunt circuit according to the average absorption coefficient of the composite low-frequency sound absorber; the parameters of the optimal circuit structure are the parameters of the adjustable analog-digital hybrid shunt circuit; and the optimal parameters of the perforated plate are the parameters of the perforated plate.

[0011] Preferably, calculating the average absorption coefficient of the composite low-frequency sound absorber based on the optimal parameters specifically includes: calculating the acoustic impedance ratio of the perforated plate and the electrical impedance of the adjustable analog-digital hybrid shunt circuit according to the parameters of the perforated plate and the parameters of the analog-digital hybrid shunt loudspeaker; calculating the transfer acoustic impedance ratio of the adjustable analog-digital hybrid shunt loudspeaker through the front-back cavity according to the electrical impedance of the adjustable analog-digital hybrid shunt circuit; adding the acoustic impedance ratio of the perforated plate and the transfer acoustic impedance ratio of the adjustable analog-digital hybrid shunt loudspeaker through the front-back cavity to obtain the total acoustic impedance ratio of the composite low-frequency sound absorber; extracting the real part and the imaginary part of the expression of the total acoustic impedance ratio of the composite low-frequency sound absorber to obtain the absorption coefficient of the composite low-frequency sound absorber; averaging the absorption coefficient of the composite low-frequency sound absorber in the target frequency range to obtain the average absorption coefficient of the composite low-frequency sound absorber.

[0012] Preferably, determining the optimized digital filter parameters according to the optimal circuit structure and the parameters of the adjustable analog-digital hybrid shunt circuit specifically includes: if the optimal structure of the adjustable analog-digital hybrid shunt circuit is a net resistance inductance contribution, the parameters of the digital filter function of the optimized analog-digital hybrid shunt loudspeaker are: 0, a 1. a ; wherein​T is the sampling period, R E is the negative resistance used to cancel the DC resistance of the voice coil R E is the negative inductance L E is the inductance used to cancel the voice coil L E , R s is the adjustable equivalent resistance, L s is the adjustable equivalent inductance. If the optimal structure of the adjustable digital-analog hybrid shunt circuit is a net resistance-capacitance contribution, the digital filter function of the optimized digital-analog hybrid shunt loudspeaker parameters of the digital filter function a 0, a 1, a 2 are: ; wherein, R s is the adjustable equivalent resistance, C s is the adjustable equivalent capacitance.

[0013] The above-mentioned at least one technical scheme adopted by the present application can achieve the following beneficial effects: The composite low-frequency sound absorber based on the perforated plate and the digital-analog hybrid shunt loudspeaker provided by the present application is characterized in that: sound waves first pass through the perforated plate, part of the sound waves rub against the air inside the perforated plate and the surface of the material itself and are converted into heat energy to be dissipated; the other part of the sound waves pass through the perforated plate to reach the surface of the shunt loudspeaker, drive the diaphragm of the shunt loudspeaker to vibrate and drive the coil to cut the magnetic induction lines, generate an induced electromotive force in the coil, and generate an electric current in the shunt circuit, so that the sound energy is converted into electric energy through the mechanical vibration of the diaphragm and the damping of the shunt circuit and is dissipated, thereby realizing the sound absorption function of the shunt loudspeaker. The frequencies absorbed by the above two parts are usually inconsistent, and through optimization design, the two peaks can be relatively close to each other to produce a coupling effect, thereby forming a wider sound absorption bandwidth at a lower frequency.

[0014] In summary, the present application combines the advantages of low-frequency adjustable sound absorption of digital-analog hybrid shunt loudspeaker and the advantages of mid-frequency sound absorption of perforated panel, based on the coupling effect between the two and the optimized parameters of the composite sound absorption body, it can effectively absorb low-frequency noise in sub-wavelength size, the double resonance peaks generated by the front and back cavities make the sound absorption performance in the lower frequency range significantly better than that of the traditional perforated panel type sound absorption body with the same back cavity volume, expand the sound absorption bandwidth at lower frequencies (frequency range with sound absorption coefficient greater than 0.5), improve the bandwidth / volume efficiency ratio, reduce the lower limit frequency at low frequency, and achieve better low-frequency sound absorption performance.

[0015] In addition, generally speaking, the loudspeaker product will not be directly exposed to the air, and usually has a shell for protection. Therefore, the perforated panel located in the front of the shunt loudspeaker not only plays a role in widening the sound absorption bandwidth of the shunt loudspeaker at lower frequencies, but also plays a role in protecting the shunt loudspeaker. BRIEF DESCRIPTION OF DRAWINGS

[0016] The drawings described herein are intended to provide further understanding of the present application, and form a part of the present application. The schematic embodiments of the present application and the description thereof are used to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0017] Figure 1 A structure schematic diagram of a perforated panel-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorption body provided by the present application; Figure 2 A specific structure schematic diagram of a perforated panel-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorption body provided by the present application; Figure 3 An equivalent circuit diagram of an adjustable digital-analog hybrid shunt circuit of a perforated panel-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorption body provided by the present application; Figure 4 A normal incidence sound absorption coefficient curve diagram of a perforated panel-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorption body provided by the present application; Figure 5 A normal incidence sound absorption coefficient comparison diagram of a perforated panel-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorption body provided by the present application and a perforated panel / micro-perforated panel with the same back cavity volume; Figure 6 A finite element model schematic diagram of a perforated panel-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorption body provided by the present application; Figure 7 A sound pressure velocity distribution diagram of a perforated panel-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorption body provided by the present application at two peak frequencies; Figure 8An experimental measurement device diagram of a perforated plate-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorption body provided by the present application; Figure 9 An experimental measurement and theoretical simulation result comparison diagram of normal incidence sound absorption coefficient of a perforated plate-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorption body provided by the present application. DETAILED DESCRIPTION

[0018] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described below in detail with specific embodiments of the present application and corresponding drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the specification, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0019] The technical solutions provided by the embodiments of the present application will be described in detail below with reference to the drawings.

[0020] Specifically, Figure 1 A structure schematic diagram of a perforated plate-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorption body in the present application, specifically comprising: a sound box and an adjustable digital-analog hybrid shunt circuit; The sound box comprises a perforated plate, a front-back cavity, a rear-back cavity and a moving-coil loudspeaker installed in the rear-back cavity; the perforated plate is located at the frontmost end of the sound box; the front-back cavity is a cavity formed between the moving-coil loudspeaker and the perforated plate; the sound box is connected to the adjustable digital-analog hybrid shunt circuit through the positive and negative ends of the moving-coil loudspeaker; When the sound wave reaches the perforated plate, part of the sound wave rubs and vibrates with the air inside the small holes of the perforated plate and the surface of the perforated plate, and is converted into heat energy and dissipated; another part of the sound wave passes through the perforated plate to the surface of the digital-analog hybrid shunt loudspeaker, and is converted into electric energy and dissipated.

[0021] Optionally, the parameters of the perforated plate include the thickness of the perforated plate, the diameter of the small holes, the perforation rate and the depth of the front-back cavity.

[0022] Optionally, the circuit structure of the adjustable digital-analog hybrid shunt circuit includes the circuit structure of the adjustable digital-analog hybrid shunt circuit under net resistance inductance contribution and the circuit structure of the adjustable digital-analog hybrid shunt circuit under net resistance capacitance contribution.

[0023] Optionally, the parameters of the adjustable digital-analog hybrid shunt circuit include an adjustable equivalent inductance or an adjustable equivalent capacitance and an adjustable equivalent resistance. Optionally, the expression of the resistance impedance of the adjustable digital-analog hybrid shunt circuit under net resistance inductance contribution is: Zs1 = − R E ′− jcoL E ′+ R s + jcoL s ; In the formula, Z s1 is the resistance impedance of the adjustable analog-digital hybrid shunt circuit under the net resistance inductance contribution, R E ′ is a negative resistance used to offset the DC resistance of the voice coil R E , negative inductance − L E ′ used to offset the inductance of the voice coil L E , j is the imaginary part, ω is the angular velocity, R s is the adjustable equivalent resistance, L s is the adjustable equivalent inductance; The expression of the resistance impedance of the adjustable analog-digital hybrid shunt circuit under the net resistance inductance contribution is: Z s2 = −R E −jcoL E ′+R s + 1 / jcoC s ; In the formula, Z s2 is the resistance impedance of the adjustable analog-digital hybrid shunt circuit under the net resistance inductance contribution, R s is the adjustable equivalent resistance, C s is the adjustable equivalent capacitance.

[0024] Optionally, the parameters of the perforated plate and the parameters of the adjustable analog-digital hybrid shunt circuit are determined by an optimization algorithm with the average absorption coefficient of the composite low-frequency sound absorber in the target frequency range as the optimization target.

[0025] Optionally, the optimization process of the parameters of the perforated plate and the parameters of the adjustable digital-analog hybrid shunt circuit comprises: taking the average absorption coefficient of the composite low-frequency sound absorber in a target frequency range as an optimization target, and determining the optimal parameters of the perforated plate and the adjustable digital-analog hybrid shunt circuit through an optimization algorithm; calculating the average absorption coefficient of the composite low-frequency sound absorber based on the optimal parameters; determining the optimal circuit structure of the adjustable digital-analog hybrid shunt circuit according to the average absorption coefficient of the composite low-frequency sound absorber; the parameters of the optimal circuit structure are the parameters of the adjustable digital-analog hybrid shunt circuit; and the optimal parameters of the perforated plate are the parameters of the perforated plate.

[0026] Optionally, the average absorption coefficient of the composite low-frequency sound absorber is calculated based on the optimal parameters, and the calculation specifically comprises: calculating the acoustic impedance ratio of the perforated plate and the electrical impedance of the adjustable digital-analog hybrid shunt circuit according to the parameters of the perforated plate and the parameters of the digital-analog hybrid shunt loudspeaker; calculating the transfer acoustic impedance ratio of the adjustable digital-analog hybrid shunt loudspeaker through the front-back cavity according to the electrical impedance of the adjustable digital-analog hybrid shunt circuit; adding the acoustic impedance ratio of the perforated plate and the transfer acoustic impedance ratio of the adjustable digital-analog hybrid shunt loudspeaker through the front-back cavity to obtain the total acoustic impedance ratio of the composite low-frequency sound absorber; extracting the real part and the imaginary part of the expression of the total acoustic impedance ratio of the composite low-frequency sound absorber to obtain the absorption coefficient of the composite low-frequency sound absorber; and taking the average value of the absorption coefficient of the composite low-frequency sound absorber in the target frequency range to obtain the average absorption coefficient of the composite low-frequency sound absorber.

[0027] Optionally, the parameters of the optimized digital filter are determined according to the optimal circuit structure and the parameters of the adjustable digital-analog hybrid shunt circuit, and the determination specifically comprises: If the optimal structure of the adjustable digital-analog hybrid shunt circuit is a net resistance inductance contribution, the parameters of the digital filter function of the optimized digital-analog hybrid shunt loudspeaker are: a 0、 a 1 are: ; wherein T is a sampling period, and R E is a negative resistance used to offset the direct current resistance of the voice coil R E is a negative inductance L E used to offset the inductance of the voice coil L E , R s is an adjustable equivalent resistance, L s is an adjustable equivalent inductance.

[0028] ​If the optimal structure of the adjustable digital-analog hybrid shunt circuit is net resistance-capacitance contribution, the parameters of the digital filter function of the optimized digital-analog hybrid shunt loudspeaker a 0, a 1, a 2 are: ; wherein, R s is an adjustable equivalent resistance, C s is an adjustable equivalent capacitance.

[0029] Specifically, Figure 2 A specific structure of a perforated panel-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorber in the present application is shown. The leftmost end is a perforated panel, and a digital-analog hybrid shunt loudspeaker is installed at a certain cavity distance apart. The positive and negative levels of the moving coil loudspeaker are connected by an adjustable digital-analog hybrid shunt circuit. The positive level of the moving coil loudspeaker is connected to the pin of an analog-to-digital converter (ADC) module, and then connected to a field programmable gate array (FPGA) module, a digital-to-analog converter (DAC) module, and a detection resistance R 1s feedback resistance R 1f input resistance R 1i implemented in series, and the negative terminal of the sound box is connected to the ground terminal. The digital filter parameters of the digital-analog hybrid shunt loudspeaker are set based on the FPGA module.

[0030] Specifically, Figure 3 An equivalent circuit diagram of an adjustable digital-analog hybrid shunt circuit of a perforated panel-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorber in the present application is shown. The adjustable digital-analog hybrid shunt circuit includes two structures: an adjustable digital-analog hybrid shunt circuit with net resistance-inductance contribution (when the switch is connected to the inductance L s branch) and an adjustable digital-analog hybrid shunt circuit with net resistance-capacitance contribution (when the switch is connected to the capacitance C s branch).

[0031] wherein, the expression of the resistance impedance of the adjustable digital-analog hybrid shunt circuit with net resistance-inductance contribution is: Z s1 = R E ′− jcoL E ′+ R s + jcoL s ;​ wherein, Z s1 is the resistance impedance of the adjustable analog-digital hybrid shunt circuit under the net resistance inductance contribution, j is the imaginary part, ω is the angular velocity, R s is the adjustable equivalent resistance, L s is the adjustable equivalent inductance, R E is equal to R E , L E is equal to L E , R E and L E are the measured direct current resistance and inductance of the moving coil loudspeaker voice coil, respectively.

[0032] wherein, the expression of the resistance impedance of the adjustable analog-digital hybrid shunt circuit under the net resistance capacitance contribution is: Z s2 = −R E −jcoL E ′+R s + 1 / jcoC s ; wherein, Z s2 is the resistance impedance of the adjustable analog-digital hybrid shunt circuit under the net resistance capacitance contribution rate, R s is the adjustable equivalent resistance, C s is the adjustable equivalent inductance.

[0033] Specifically, the resistance impedance of the adjustable analog-digital hybrid shunt circuit Z s is realized based on Figure 2 the adjustable analog-digital hybrid shunt circuit implemented in the right end. Its reciprocal adjustable analog-digital hybrid shunt circuit admittance Y s is:

[0034] wherein, u represents the voltage of the loudspeaker port, i is the output current, u outThe voltage signal output from a digital-to-analog converter (DAC) is represented by setting R 1s R 1f R 1i The ratio of voltage-current conversion can be adjusted N s The ratio is usually designed as a constant 1. The expression of the transfer function is H s The digital filter transfer function z can be obtained by transforming H z , which can be realized by an FPGA module H z

[0035] The expression of the digital filter transfer function corresponding to the adjustable digital-analog hybrid shunt circuit under the pure resistance-inductance contribution is: ; ; In the formula a 0, a 1 are the digital filter parameters to be designed, which can be realized by an FPGA module. T is the sampling period, R s is the adjustable equivalent resistance, L s is the adjustable equivalent inductance.

[0036] The expression of the digital filter transfer function corresponding to the adjustable digital-analog hybrid shunt circuit under the pure resistance-capacitance contribution is: ; ; In the formula a 0, a 1, a 2 are the digital filter parameters to be designed, which can be realized by an FPGA module. T is the sampling period, R s is the adjustable equivalent resistance, C s is the adjustable equivalent capacitance.

[0037] Therefore, the digital-analog hybrid shunt speaker only needs to design two or three digital parameters to realize the adjustable equivalent resistance impedance, and then the equivalent acoustic impedance ratio can be adjusted to realize the low-frequency adjustable sound absorption performance. ​​​​​​​

[0038] The equivalent acoustic impedance ratio of the adjustable digital-analog hybrid shunt loudspeaker is calculated according to the electrical impedance of the adjustable digital-analog hybrid shunt circuit by the electrical-acoustic analogy method Z HSL For: ; In the formula j is the imaginary unit, B is the magnetic flux density in the magnetic gap of the loudspeaker, l is the length of the voice coil conductor in the magnetic field, R as is the equivalent acoustic resistance of the loudspeaker suspension system, C as is the equivalent acoustic compliance of the loudspeaker suspension system, M as is the equivalent acoustic mass of the loudspeaker vibration system, S is the effective area of the loudspeaker diaphragm, ω is the angular frequency. C ac = V / p 0 c o 2 is the equivalent acoustic compliance of the back cavity, wherein p 0 is the air density, c 0 is the speed of sound in air, V is the back cavity volume. R E is the DC resistance of the loudspeaker voice coil ，L E is the inductance of the loudspeaker voice coil, Z s is the electrical impedance of the adjustable digital-analog hybrid shunt circuit.

[0039] Since the digital-analog hybrid shunt loudspeaker is located at the end of the front back cavity behind the perforated plate, the transfer acoustic impedance ratio through the depth of the front back cavity D 1 is Z DHSL It can be derived that: ; In the formula, Z HSL is the equivalent acoustic impedance ratio of the adjustable digital-analog hybrid shunt loudspeaker, D 1 is the depth of the front back cavity.

[0040] The acoustic impedance ratio of the perforated plate Z PP The expression of ; wherein σ represents the perforation rate, η is the air viscosity coefficient,d is a hole diameter of the perforated plate, t is a thickness of the perforated plate, K is a perforation constant, .

[0041] The total acoustic impedance ratio of the composite low-frequency sound absorption body is obtained by adding the acoustic impedance ratio of the perforated plate and the transfer acoustic impedance ratio of the adjustable number and model mixed shunt loudspeaker through the front-back cavity Z PPHSL The expression is: ; According to the total acoustic impedance ratio, the normal incidence sound absorption coefficient of the composite low-frequency sound absorption body is determined, specifically comprising: extracting the real part and the imaginary part of the total acoustic impedance ratio of the composite low-frequency sound absorption body; according to the real part and the imaginary part of the total acoustic impedance ratio of the composite low-frequency sound absorption body, the normal incidence sound absorption coefficient of the composite low-frequency sound absorption body is determined, and the formula is: ; Wherein Re( Z PPHSL ) and Im( Z PPHSL ) are the real part and the imaginary part of the total acoustic impedance ratio Z PPHSL .

[0042] In order to realize the optimal sound absorption coefficient in the low frequency range, the parameters of the composite low-frequency sound absorption body are optimized. The average sound absorption coefficient of the composite low-frequency sound absorption body in the target frequency range is taken as the optimization target, and the optimal parameters of the perforated plate and the adjustable number and model mixed shunt circuit are determined through the optimization algorithm.

[0043] Specifically, the optimal parameters of the perforated plate include: the hole diameter of the perforated plate d , the thickness of the perforated plate t , the depth of the front-back cavity D 1, the perforation rate σ ; the optimal parameters of the adjustable number and model mixed shunt circuit include: the adjustable equivalent inductance L s , the adjustable equivalent resistance R s or the adjustable equivalent capacitance C s , the adjustable equivalent resistance R s .

[0044] Wherein, R s The sound absorption coefficient of the composite sound absorption body is mainly adjusted by adjusting the acoustic resistance, and the optimal value of R s can be obtained through the optimization algorithm calculation, so as to realize the optimal low-frequency sound absorption effect.

[0045] Specifically, the target frequency range is 100 Hz-300 Hz of the lower frequency band. Using a genetic algorithm as an optimization algorithm in the embodiment, the chromosome length is set to 6, the population size is set to 500, the iteration number is set to 500, the mutation probability is set to 0.1, and the crossover probability is set to 0.7. The constraint range of the optimal parameters is represented as: t ∈[1,30]mm, d ∈[2,5]mm, σ ∈[0.01,0.1], D 1∈[10,60]mm, R s ∈[1,20]Ω, L s ∈[0.1,100]mH or C s ∈[0.1,1000] μ F.

[0046] The TS parameters of a moving coil loudspeaker measured by a Klippel RnD instrument are shown in Table 1. L E The values of R, L and C are set to 0.47 Ω, 0.47 mH and 0.47 μF respectively. R E The values of R, L and C are set to 0.47 Ω, 0.47 mH and 0.47 μF respectively. L E The values of R, L and C are set to 0.47 Ω, 0.47 mH and 0.47 μF respectively. L E The values of R, L and C are set to 0.47 Ω, 0.47 mH and 0.47 μF respectively. R E The values of R, L and C are set to 0.47 Ω, 0.47 mH and 0.47 μF respectively. R E The values of R, L and C are set to 0.47 Ω, 0.47 mH and 0.47 μF respectively, thereby offsetting the DC resistance of the loudspeaker voice coil and the inductance of the voice coil. R E The values of R, L and C are set to 0.47 Ω, 0.47 mH and 0.47 μF respectively. L E The thickness of the digital-analog hybrid shunt loudspeaker is 7.9 cm, which is slightly larger than the thickness of the loudspeaker. D 2

[0047] Table 1 TS parameters of a moving coil loudspeaker measured Based on the optimal parameters, the sound absorption coefficient of the composite low-frequency sound absorption body is calculated; and according to the sound absorption coefficient of the composite low-frequency sound absorption body, the optimal shunt circuit structure of the adjustable digital-analog hybrid shunt circuit is determined, specifically including: comparing the average sound absorption coefficients of the shunt circuit under the contribution of the net resistance inductance and the shunt circuit under the contribution of the net resistance capacitance in the target frequency range, and determining the shunt circuit with the largest average coefficient as the optimal shunt circuit.

[0048] According to the optimal parameters of the adjustable digital-analog hybrid shunt circuit corresponding to the optimal shunt circuit, the digital filter parameters of the optimized adjustable digital-analog hybrid shunt circuit are determined, including: If the optimal structure of the adjustable digital-analog hybrid shunt circuit is net resistance inductance contribution, the parameters of the digital filter function of the optimized digital-analog hybrid shunt loudspeaker are a 0, a 1, ; In the formula, T is the sampling period, R E is the negative resistance used to offset the direct current resistance of the voice coil R E is the negative inductance L E used to offset the inductance of the voice coil L E , R s is the adjustable equivalent resistance, L s is the adjustable equivalent inductance. If the optimal structure of the adjustable digital-analog hybrid shunt circuit is net resistance capacitance contribution, the parameters of the digital filter function of the optimized digital-analog hybrid shunt loudspeaker are a 0, a 1, a 2, ; In the formula, R s is the adjustable equivalent resistance, C s is the adjustable equivalent capacitance.

[0049] In this embodiment, the optimal parameters obtained by the above steps are shown in Table 2, and the optimal shunt circuit of the adjustable digital-analog hybrid shunt circuit is net resistance inductance contribution. Table 3 lists the digital filter parameters of the optimized adjustable digital-analog hybrid shunt circuit.

[0050] Table 2 Optimal parameters of the perforated plate-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorber Table 3 Optimized digital filter parameters ​​Specifically, based on the optimal parameters, the sound absorption coefficient of the composite low-frequency sound absorber is calculated, specifically including: calculating the electrical impedance of the adjustable digital-analog hybrid shunt circuit and the acoustic impedance rate of the perforated panel according to the optimal parameters of the perforated panel and the digital-analog hybrid shunt loudspeaker; calculating the transfer acoustic impedance rate of the adjustable digital-analog hybrid shunt loudspeaker through the front-back cavity according to the electrical impedance of the adjustable digital-analog hybrid shunt circuit; adding the acoustic impedance rate of the perforated panel and the transfer acoustic impedance rate of the adjustable digital-analog hybrid shunt loudspeaker through the front-back cavity to obtain the total acoustic impedance rate of the composite low-frequency sound absorber; and extracting the real part and the imaginary part of the total acoustic impedance rate to determine the normal incidence sound absorption coefficient of the composite low-frequency sound absorber.

[0051] Figure 4 The normal incidence sound absorption coefficient curve (blue solid line) of the perforated panel-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorber (PPHSL) of the embodiment determined by the above steps can be found to have a sound absorption coefficient exceeding 0.5 in a low-frequency range of 111 Hz to 352 Hz, an average absorption coefficient of 0.76, and a bandwidth of 241 Hz at a lower frequency. Two peaks appear at 152 Hz and 304 Hz, and the sound absorption coefficients are 0.91 and 0.89, respectively.

[0052] Figure 4 The middle red dashed line represents the normal incidence sound absorption coefficient of the digital-analog hybrid shunt loudspeaker (HSL) alone, which can be found to have a resonance sound absorption characteristic, and the parameters used are all the optimized related parameters in Table 2-3, and the resonance sound absorption frequency is 191 Hz. Figure 4 The middle black dash-dot line represents the normal incidence sound absorption coefficient of the perforated panel (PP) alone, which can be found to have a resonance sound absorption characteristic, and the resonance sound absorption frequency is 245 Hz. It can be seen that based on the coupling effect of the digital-analog hybrid shunt loudspeaker and the perforated panel, the proposed composite low-frequency sound absorber effectively expands the sound absorption bandwidth at a lower frequency and achieves excellent low-frequency sound absorption performance.

[0053] Figure 5 The normal incidence sound absorption coefficient of the perforated panel-digital-analog hybrid shunt loudspeaker (PPHSL) composite low-frequency sound absorber provided by the present application is compared with the sound absorption coefficients of the perforated panel (PP) and the micro-perforated panel (MPP) with the same back cavity volume (the back cavity thickness is D = D 1+ D 2) are shown in the following table. Figure 5 The blue solid line in the middle represents the normal incidence sound absorption coefficient of the composite low-frequency sound absorber, the red dashed line represents the sound absorption coefficient of the perforated panel sound absorber, and the black dash-dot line represents the sound absorption coefficient of the micro-perforated panel sound absorber.

[0054] Table 4 Parameters of the perforated panel (PP) and the micro-perforated panel (MPP) Table 4 Parameters of the perforated panel (PP) and the micro-perforated panel (MPP) By Figure 5 It can be seen that the composite low-frequency sound absorption body (PPHSL) has an absorption coefficient of more than 0.5 in the low-frequency range of 111 Hz to 352 Hz, an average absorption coefficient of 0.76, and a bandwidth of 241 Hz at a lower frequency. The traditional perforated plate sound absorption body (PP) has a resonance sound absorption characteristic, an absorption coefficient of more than 0.5 in the low-frequency range of 141 Hz to 177 Hz, an average absorption coefficient of 0.57, and a sound absorption bandwidth of 36 Hz. The traditional micro-perforated plate sound absorption body (MPP) has a resonance sound absorption characteristic, an absorption coefficient of more than 0.5 in the low-frequency range of 122 Hz to 239 Hz, an average absorption coefficient of 0.76, and a sound absorption bandwidth of 117 Hz.

[0055] Figure 5 It can be seen from the comparison that, compared with the traditional perforated plate sound absorption body, the composite low-frequency sound absorption body has better low-frequency sound absorption performance: it expands the sound absorption bandwidth at a lower frequency, improves the bandwidth / volume efficiency ratio, and reduces the lower limit frequency at a lower frequency. The thickness of the composite low-frequency sound absorption body is only about 1 / 22 of the maximum wavelength of the half absorption coefficient, and good low-frequency sound absorption performance can be achieved in a subwavelength size.

[0056] Supplementary analysis 1: numerical simulation analysis and sound absorption mechanism analysis of the low-frequency sound absorption performance of the perforated plate-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorption body by the finite element (FEM) numerical simulation method.

[0057] Figure 6 A finite element model of a perforated plate-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorption body provided by the present application is shown in the figure. The finite element model of the perforated plate-digital-analog hybrid shunt loudspeaker combination structure is constructed based on COMSOL Multiphysics v5.3 software, as shown in Figure 4 The plane wave is incident from the end of the impedance tube (x z = 1.3 m), and the incident sound pressure is set to 1 Pa. The boundary at the front end of the impedance tube (x z = 0 is set to an impedance boundary. x b The boundary at the front end of the impedance tube (x y a = 0.176 m, 0 z D The boundary at the front end of the impedance tube (x x b , 0 y a ​​​​​The impedance boundary of the perforated plate is set at (point 1). The TS parameters of the loudspeaker are shown in Table 1, and the parameters of the perforated plate and shunt circuit are shown in Table 2. The grid cell size is set to a free tetrahedral grid, using an extremely fine grid size for subdivision.

[0058] The formula for solving the sound absorption coefficient using the finite element method (FEM) is as follows: ; Based on the above settings, the low-frequency sound absorption performance of the perforated plate-digital hybrid splitter loudspeaker composite low-frequency sound absorber under optimized parameter configuration was analyzed using theoretical analysis and finite element simulation.

[0059] Figure 9 A comparison chart of experimental measurement and theoretical simulation results of the normal incident sound absorption coefficient of a perforated plate-digital hybrid shunt loudspeaker composite low-frequency sound absorber provided by the present invention. Figure 9 The green dotted line in the figure represents the low-frequency absorption coefficient of the composite low-frequency sound absorber calculated by the finite element numerical simulation method. It can be found that the absorption coefficient exceeds 0.5 in the low-frequency range of 113 Hz to 356 Hz, the average absorption coefficient is 0.75, and the bandwidth is 243 Hz. Figure 9 The blue dashed line in the diagram represents the theoretical solution, which is... Figure 4 The solid blue line in the graph depicts the normal incident absorption coefficient of the composite low-frequency sound absorber. It can be observed that the absorption coefficient exceeds 0.5 in the low-frequency range of 111 Hz to 352 Hz, with an average absorption coefficient of 0.76 and a bandwidth of 241 Hz. Comparison between the finite element simulation results and the theoretical results shows that the results are basically consistent, verifying the effectiveness of the theoretical model of the composite low-frequency sound absorber.

[0060] Figure 7 The sound pressure and velocity distribution diagrams at two peak frequencies of a perforated plate-digital hybrid shunt loudspeaker composite low-frequency sound absorber provided by this invention further illustrate the sound absorption mechanism. Figure 7 (a) and Figure 7 Figure (b) shows the sound pressure and velocity distribution of the perforated plate-digital hybrid shunt loudspeaker composite low-frequency absorber at 154 Hz and 310 Hz, respectively. Figure 9 The green dotted lines represent the two peak frequencies of the low-frequency absorption coefficient of the composite low-frequency sound absorber calculated by the finite element numerical simulation method. The background color represents the sound pressure level, and the size and direction of the arrows represent the speed and direction of sound.

[0061] Depend on Figure 7 It can be seen that: in f= 154 Hz, the sound velocity gradually decreases from left to right in the impedance tube, and the sound pressure reaches the maximum value on the surface of the impedance boundary of the hybrid digital-analog shunt loudspeaker, which indicates that at this frequency, most of the sound energy is converted into electrical energy dissipated by the hybrid digital-analog shunt loudspeaker, and the hybrid digital-analog shunt loudspeaker plays a major role in the absorption of sound waves. f = 310 Hz, the sound velocity reaches the maximum value at the perforated panel, and rapidly decreases after passing through the perforated panel; the sound pressure reaches the maximum value on the surface of the perforated panel, and rapidly decreases after passing through the perforated panel, which indicates that at this frequency, most of the sound energy is converted into heat energy dissipated by the perforated panel, and the perforated panel plays a major role in the absorption of sound waves.

[0062] Supplementary analysis 2: The low-frequency sound absorption performance of the perforated panel-hybrid digital-analog shunt loudspeaker composite low-frequency sound absorption body is verified by experimental testing.

[0063] Figure 8 The experimental measurement device diagram of the hybrid digital-analog shunt loudspeaker combination structure in the impedance tube. In order to verify the theoretical model, an impedance tube with a length of 1.3 m and an inner diameter of 0.176 m is built, which can effectively measure the normal incidence sound absorption coefficient in the frequency range of about 50 Hz ~ 977 Hz. The leftmost end of the impedance tube is connected to the sound source, and the right end of the tube is connected to the perforated panel-hybrid digital-analog shunt loudspeaker composite low-frequency sound absorption body. In the experiment, an Ikhwa AHAI1031 type dynamic signal acquisition analyzer is used, and the sound absorption coefficient is measured based on the transfer function method according to the ISO 10534-2 standard. Two microphones are respectively located at a distance of x 1= 0.58 m and x 2= 0.78 m from the sound source.

[0064] The perforated panel in the experiment is manufactured by 3D printing technology, and its parameters are shown in Table 2. The Thiele-Small parameters of the selected moving coil loudspeaker unit are measured by Klippel RnD instrument, as shown in Table 1, and the back cavity depth of the loudspeaker unit is 7.9 cm, which is slightly larger than the thickness of the loudspeaker. The voltage-current conversion circuit includes an OP07 type operational amplifier, two input resistors ( R 1i = 10 Ω), two feedback resistors ( R 1f = 20 Ω) and two detection resistors ( R 1s = 10 Ω). The ADC, DAC and FPGA modules are realized by using a NI MyRIO embedded device. The positive and negative poles of the loudspeaker unit are respectively connected to a pin of the ADC module input terminal and the ground wire, and the output terminal of the DAC module is connected to the uout The digital filter parameters of the optimized design shown in Table 3 are based on the FPGA field programmable gate array settings, wherein the sampling period T is set to 0.02 s.

[0065] Figure 9 A comparison chart of experimental measurement and theoretical simulation results of the normal incidence absorption coefficient of the perforated plate-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorber provided by the present application. Figure 9 The red solid line in the figure is the experimental measurement result of the normal incidence absorption coefficient of the composite low-frequency sound absorber, and the results show that in the low-frequency range of 105 Hz to 413 Hz, the average absorption coefficient is 0.7, and the bandwidth is 308 Hz; there are two sound absorption peaks at 143 Hz and 336 Hz, and the sound absorption coefficient is about 0.8 and 0.89. Experiments have proved that the proposed composite low-frequency sound absorber exhibits excellent low-frequency sound absorption performance.

[0066] The green dotted line represents the simulation results based on the finite element method (FEM), and it can be found that the absorption coefficient exceeds 0.5 in the low-frequency range of 113 Hz to 356 Hz, the average absorption coefficient is 0.75, and the bandwidth is 243 Hz. The blue dashed line represents the theoretical solution, and it can be found that the absorption coefficient exceeds 0.5 in the low-frequency range of 111 Hz to 352 Hz, the average absorption coefficient is 0.76, and the bandwidth is 241 Hz. By comparing the experimental results with the theoretical simulation results, it can be found that the experimental results are basically consistent with the theoretical simulation results, which verifies the effectiveness of the theoretical model of the composite low-frequency sound absorber. Some deviations are mainly caused by measurement errors of TS parameters and manufacturing process errors of perforated plates based on 3D printing technology.

[0067] The present embodiment proposes a perforated plate-digital-analog hybrid shunt loudspeaker composite low-frequency sound absorber. First, a theoretical model is established; then the parameters of the composite structure are optimized using a genetic algorithm to achieve the best sound absorption performance at low frequencies; then numerical simulation analysis is performed based on the finite element method and the sound absorption mechanism is analyzed; finally, the theoretical model is verified by experimental testing. The experimental results show that the composite structure has an absorption coefficient of 0.5 or more in the range of 105 Hz to 413 Hz, a bandwidth of 308 Hz, and an average absorption coefficient of 0.7. The research shows that by utilizing the coupling effect between the perforated plate and the digital-analog hybrid shunt loudspeaker and optimizing the parameters through a genetic algorithm, the proposed composite low-frequency sound absorber can expand the bandwidth at low frequencies, effectively absorb low-frequency noise at sub-wavelength size, and outperform traditional perforated plate sound absorbers in terms of low-frequency sound absorption performance: improve the bandwidth / volume efficiency ratio and reduce the lower limit frequency at low frequencies.

[0068] The technical features of the above embodiments can be combined in any manner, and the optimization algorithm is not limited to the genetic algorithm. For the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but as long as the combinations of the technical features do not contradict each other, they should be considered as falling within the scope of the present application.

Claims

1. A hybrid perforated plate-digital analog hybrid shunt loudspeaker composite low frequency absorber, characterized in that, The application relates to a sound box and an adjustable digital-analog hybrid shunt circuit. The sound box comprises a perforated plate, a front back cavity, a rear back cavity and a moving-coil loudspeaker installed in the rear back cavity; the perforated plate is located at the front end of the sound box; the front back cavity is a cavity formed between the moving-coil loudspeaker and the perforated plate; the sound box is connected with the adjustable digital-analog hybrid shunt circuit through the positive and negative ends of the moving-coil loudspeaker. When sound waves reach the perforated plate, part of the sound waves rubs and vibrates with the air inside the small holes of the perforated plate and the surface of the perforated plate, and is converted into heat energy and dissipated; the other part of the sound waves passes through the perforated plate to reach the surface of the digital-analog hybrid shunt loudspeaker, and is converted into electric energy and dissipated. The parameters of the perforated plate include the thickness of the perforated plate, the diameter of the small holes, the perforation rate and the depth of the front back cavity.

2. A hybrid perforated plate-digital model shunt loudspeaker composite low frequency absorber according to claim 1, wherein, The circuit structure of the adjustable digital-analog hybrid shunt circuit includes the circuit structure of the adjustable digital-analog hybrid shunt circuit under the contribution of net resistance inductance and the circuit structure of the adjustable digital-analog hybrid shunt circuit under the contribution of net resistance capacitance.

3. A hybrid perforated plate-digital model shunt loudspeaker composite low frequency absorber according to claim 1, wherein, The parameters of the adjustable digital-analog hybrid shunt circuit include adjustable equivalent inductance or adjustable equivalent capacitance and adjustable equivalent resistance.

4. A perforated plate-digital hybrid shunt loudspeaker composite low frequency absorber according to claim 3, wherein, The expression of the resistance impedance of the adjustable digital-analog hybrid shunt circuit under the contribution of net resistance inductance is:

5. A hybrid perforated plate-digital model shunt loudspeaker composite low frequency absorber according to claim 3, wherein, j omega L Z s1 = − R E ′− j omega L E ′+ R s + omega s ； wherein Z s1 R is the resistance impedance of the adjustable digital-analog hybrid shunt circuit under the net resistance-inductance contribution, R E R' is the negative resistance used to cancel the DC resistance of the voice coil R E L' is the negative inductance L E L' is the negative inductance used to cancel the inductance of the voice coil L E , j is the imaginary part, The expression of the resistance impedance of the adjustable digital-analog hybrid shunt circuit under the contribution of net resistance capacitance is: is the angular velocity, R s R is the adjustable equivalent resistance, L s L is the adjustable equivalent inductance; ' - j omega L Z s2 = −R E + 1 / j omega C E ′+R s The parameters of the perforated plate and the parameters of the adjustable digital-analog hybrid shunt circuit are determined by optimization algorithms based on the average sound absorption coefficient of the composite low-frequency sound absorption body in a target frequency range as an optimization target. s ； wherein Z s2 R is the resistance impedance of the adjustable analog-digital hybrid shunt circuit under the net resistance capacitance contribution rate, R s R is the adjustable equivalent resistance, C s C is the adjustable equivalent capacitance.

6. A hybrid perforated plate-digital model shunt loudspeaker composite low frequency absorber according to claim 2 or 4, characterized in that, The optimization process of the parameters of the perforated plate and the parameters of the adjustable digital-analog hybrid shunt circuit specifically includes:

7. A perforated plate-digital hybrid shunt loudspeaker composite low frequency absorber according to claim 1, wherein, determining the optimal parameters of the perforated plate and the adjustable digital-analog hybrid shunt circuit through optimization algorithms based on the average sound absorption coefficient of the composite low-frequency sound absorption body in a target frequency range as an optimization target; calculating the average sound absorption coefficient of the composite low-frequency sound absorption body based on the optimal parameters; determining the optimal circuit structure of the adjustable digital-analog hybrid shunt circuit according to the average sound absorption coefficient of the composite low-frequency sound absorption body; the parameters of the optimal circuit structure are the parameters of the adjustable digital-analog hybrid shunt circuit; and the optimal parameters of the perforated plate are the parameters of the perforated plate. The calculation of the average sound absorption coefficient of the composite low-frequency sound absorption body based on the optimal parameters specifically includes:

8. A perforated plate-digital hybrid shunt loudspeaker composite low frequency absorber according to claim 7, characterized in that, calculating the acoustic impedance rate of the perforated plate and the resistance impedance of the adjustable digital-analog hybrid shunt circuit according to the parameters of the perforated plate and the parameters of the digital-analog hybrid shunt loudspeaker; calculating the transfer acoustic impedance rate of the adjustable digital-analog hybrid shunt loudspeaker through the front back cavity according to the resistance impedance of the adjustable digital-analog hybrid shunt circuit; adding the acoustic impedance rate of the perforated plate and the transfer acoustic impedance rate of the adjustable digital-analog hybrid shunt loudspeaker through the front back cavity to obtain the total acoustic impedance rate of the composite low-frequency sound absorption body; extracting the real part and the imaginary part of the expression of the total acoustic impedance rate of the composite low-frequency sound absorption body to obtain the sound absorption coefficient of the composite low-frequency sound absorption body; averaging the sound absorption coefficient of the composite low-frequency sound absorption body in a target frequency range to obtain the average sound absorption coefficient of the composite low-frequency sound absorption body. ​ 9. A perforated plate-digital hybrid shunt loudspeaker composite low frequency absorber according to claim 7, characterized in that , According to the optimal circuit structure and parameters of the adjustable digital-analog hybrid shunt circuit, the optimized digital filter parameters are determined, specifically including: If the optimal structure of the adjustable digital-analog hybrid shunt circuit is net resistance inductance contribution, the parameter of the digital filter function of the optimized digital-analog hybrid shunt speaker 0、 a 1, a 1 is: ； wherein T is the sampling period, R E is a negative resistance to cancel the DC resistance of the voice coil R E is a negative inductance L E is a negative inductance to cancel the inductance of the voice coil L E , R s is an adjustable equivalent resistance, L s is an adjustable equivalent inductance; If the optimal structure of the adjustable mixed-signal shunt circuit is based on the net resistance and capacitance contribution, then the optimized digital filter function of the mixed-signal shunt speaker... parameters a 0、 a 1. a 2 is: ； wherein, R s is an adjustable equivalent resistance, C s is an adjustable equivalent capacitance.

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