Signal processing method, signal processing system, and speaker system

Abstract

According to the present invention, an acoustic processing system is provided with: a signal processing unit that utilizes a nonlinear model simulating a relationship in which an acoustic resistance of an acoustic port for acoustic radiation employing Helmholtz resonance depends on a volumetric flow velocity at the acoustic port, to determine an input voltage from target parameters including the volumetric flow velocity at the acoustic port; and a voltage supply unit that supplies the input voltage to a speaker device.

Description

Signal processing method, signal processing system, and speaker system

[0001] The present disclosure relates to a technique for reducing nonlinear distortion of sound emitted from a speaker device.

[0002] Reproduced sound emitted from a speaker device contains nonlinear distortion such as harmonic distortion. For example, Patent Document 1 discloses a technology for reducing nonlinear distortion of reproduced sound by using a nonlinear model that simulates a speaker unit in a speaker device.

[0003] U.S. Pat. No. 1,054,7942

[0004] A speaker device is provided with an acoustic port (e.g., a bass reflex port) for radiating sound using Helmholtz resonance. The sound reproduced by the speaker device may be accompanied by nonlinear distortion due to the acoustic port in addition to nonlinear distortion due to the speaker unit. In consideration of the above circumstances, an aspect of the present disclosure aims to reduce nonlinear distortion in the sound reproduced by the speaker device.

[0005] In order to solve the above problems, a signal processing method according to one aspect of the present disclosure uses a nonlinear model that simulates the relationship in which the acoustic resistance at an acoustic port for acoustic radiation using Helmholtz resonance depends on the volumetric flow velocity at the acoustic port, determines an input voltage from target parameters including the volumetric flow velocity at the acoustic port, and supplies the input voltage to a speaker device.

[0006] A signal processing system according to one aspect of the present disclosure includes a signal processing unit that determines an input voltage from target parameters including a volumetric flow velocity at an acoustic port using a nonlinear model that simulates the relationship in which the acoustic resistance at an acoustic port for acoustic radiation using Helmholtz resonance depends on the volumetric flow velocity at the acoustic port, and a voltage supply unit that supplies the input voltage to a speaker device.

[0007] A speaker system according to one aspect of the present disclosure comprises a speaker unit, an acoustic port for acoustic radiation utilizing Helmholtz resonance of the sound radiated from the speaker unit, and a signal processing system, wherein the signal processing system includes a signal processing unit that determines an input voltage from target parameters including the volumetric flow velocity at the acoustic port using a nonlinear model that simulates a relationship that depends on the volumetric flow velocity at the acoustic port, and a voltage supply unit that supplies the input voltage to a speaker device.

[0008] FIG. 1 is a schematic diagram of a speaker system in a first embodiment. FIG. 2 is a side view of a speaker unit. FIG. 3 is a block diagram of a signal processing system. FIG. 4 is a schematic diagram of a nonlinear model. FIG. 5 is a flowchart of a distortion reduction process. FIG. 6 is a flowchart of a second process. FIG. 7 is a part of a flowchart of a distortion reduction process in the second embodiment. FIG. 8 is a schematic diagram of a speaker system in a third embodiment. FIG. 9 is a part of a flowchart of a distortion reduction process in the second embodiment. FIG. 10 is a cross-sectional view of a speaker device in a modified example. FIG. 11 is a cross-sectional view of a speaker device in a modified example.

[0009] A: First Embodiment Fig. 1 is a schematic diagram illustrating the configuration of a speaker system 100 according to the first embodiment. The speaker system 100 of the first embodiment includes a signal processing system 10 and a speaker device 20. An audio signal X is supplied to the signal processing system 10 from a signal supply device 30. The audio signal X is a signal representing an audio waveform. For example, the audio signal X is a sample sequence representing the waveform of a sung or performed sound of a piece of music.

[0010] The signal supply device 30 is, for example, a playback device that supplies an acoustic signal X recorded on a recording medium to the signal processing system 10. Note that a communication device that supplies the acoustic signal X received from a distribution device (not shown) via a communication network to the signal processing system 10, or a sound collection device that generates the acoustic signal X by collecting ambient sounds, can also be used as the signal supply device 30. Note that the signal supply device 30 may be understood as an element of the speaker system 100.

[0011] The signal processing system 10 generates an audio signal Y by performing signal processing on the audio signal X, and supplies the audio signal Y to the speaker device 20. The speaker device 20 is a sound emitting device that radiates the sound represented by the audio signal Y.

[0012] The speaker device 20 includes a housing 40 (enclosure), a speaker unit 50, and an acoustic port 60. The housing 40 is a hollow structure that supports the speaker unit 50 and the acoustic port 60. The speaker unit 50 and the acoustic port 60 are mounted on a plate member 41 (baffle plate) located on the front side of the housing 40. The acoustic port 60 may also be mounted on the rear surface of the housing 40.

[0013] The speaker unit 50 emits sound in response to an acoustic signal Y supplied from the signal processing system 10. Fig. 2 is a cross-sectional view of the speaker unit 50. The speaker unit 50 of the first embodiment includes a frame 51, a magnet 52, a voice coil 53, a diaphragm 54, an edge 55, and a damper 56.

[0014] The frame 51 is a structure that forms the exterior of the speaker unit 50. The magnet 52 is a circular permanent magnet. The voice coil 53 is a coil that can be displaced in the axial direction within the magnetic field generated by the magnet 52. The diaphragm 54 is a truncated cone-shaped structure. The inner peripheral edge of the diaphragm 54 is fixed to the voice coil 53. The outer peripheral edge of the diaphragm 54 is connected to the frame 51 via an edge 55. The diaphragm 54 and the frame 51 are also connected via a damper 56. The edge 55 and the damper 56 are circular elastic bodies. Sound waves are radiated as the diaphragm 54 moves back and forth in the axial direction.

[0015] 1 is a bass reflex port that uses Helmholtz resonance to enhance and radiate low-frequency sound components of the sound radiated from the speaker unit 50 to the rear side of the housing 40. That is, the speaker device 20 of the first embodiment is a bass reflex type. The acoustic port 60 is installed inside the housing 40 and connects the internal space 42 of the housing 40 to the external space. Specifically, the acoustic port 60 is a substantially cylindrical tubular body including an outer opening 61 and an inner opening 62. The outer opening 61 is an open end that communicates with the opening of the plate material 41. The inner opening 62 is an open end located inside the housing 40.

[0016] In the above configuration, the sound radiated from the speaker unit 50 to the rear side is propagated from the internal space 42 of the housing 40 to the acoustic port 60, passes through the acoustic port 60, and is radiated to the external space. As described above, the sound reproduced by the speaker device 20 includes the sound radiated from the speaker unit 50 and the sound radiated from the acoustic port 60.

[0017] Among the sounds reproduced by the speaker device 20, acoustic components, particularly in the high frequency range, are accompanied by nonlinear distortion due to the nonlinearity of each element constituting the speaker device 20. The signal processing system 10 generates an acoustic signal Y from an acoustic signal X so as to reduce the nonlinear distortion due to the nonlinearity of the speaker device 20. Specifically, the signal processing system 10 reduces the nonlinear distortion by utilizing a nonlinear model M that simulates the behavior of the speaker device 20.

[0018] Fig. 3 is a block diagram illustrating an example of the configuration of a signal processing system 10. As illustrated in Fig. 3, the signal processing system 10 includes a control device 11, a storage device 12, an input device 13, and an output device 14. The signal processing system 10 is realized by an information device such as a smartphone, a tablet terminal, or a personal computer. The signal processing system 10 may be realized as a single device, or may be realized as a plurality of devices configured separately from each other.

[0019] The control device 11 is composed of one or more processors that control each element of the signal processing system 10. For example, the control device 11 is composed of one or more types of processors such as a central processing unit (CPU), a sound processing unit (SPU), a digital signal processor (DSP), a field programmable gate array (FPGA), or an application specific integrated circuit (ASIC).

[0020] The storage device 12 is one or more memories that store programs executed by the control device 11 and various data used by the control device 11. The storage device 12 is configured with a known storage medium such as a magnetic storage medium or a semiconductor storage medium. The storage device 12 may be configured with a combination of multiple types of storage media. Furthermore, the storage device 12 may be a portable storage medium that is detachable from the signal processing system 10, or a storage medium (e.g., cloud storage) that the control device 11 can write to or read from via a communication network.

[0021] The input device 13 receives the audio signal X from the signal supply device 30. For example, an input interface such as a USB (Universal Serial Bus) terminal, an HDMI (High-Definition Multimedia Interface / registered trademark) terminal, a MIDI (Musical Instrument Digital Interface) terminal, or a phone terminal is used as the input device 13. Note that in a configuration in which an analog audio signal X is supplied from the signal supply device 30, the input device 13 is equipped with an A / D converter that converts the audio signal X from analog to digital.

[0022] The output device 14 supplies the acoustic signal Y to the speaker device 20. Specifically, the output device 14 includes a D / A converter that converts the acoustic signal Y from digital to analog, and an amplifier that amplifies the acoustic signal Y. Note that the output device 14, which is separate from the signal processing system 10, may be connected to the signal processing system 10 by wire or wirelessly. The output device 14 is an example of a "voltage supply unit."

[0023] 4 is a schematic diagram of a nonlinear model M used by the signal processing system 10 to generate the acoustic signal Y. The nonlinear model M is an equivalent circuit that simulates the speaker unit 50 and the acoustic port 60 in the speaker device 20. The nonlinear model M includes a first model M1 and a second model M2. The first model M1 is a nonlinear mathematical model that simulates the speaker unit 50, and the second model M2 is a nonlinear mathematical model that simulates the acoustic port 60.

[0024] The input voltage u of the first model M1 is the voltage supplied to the voice coil 53. That is, the signal value of the acoustic signal Y corresponds to the input voltage u. The input current i is the current flowing through the voice coil 53.

[0025] 4 , the first model M1 includes the displacement x and velocity v of the diaphragm 54 in the axial direction, the electrical resistance Re and inductance Le of the voice coil 53, and the force coefficient (electromagnetic conversion coefficient) Bl(x) of the voice coil 53. The force coefficient Bl(x) is the product of the magnetic flux density B and the winding width l of the voice coil 53, and changes nonlinearly according to the displacement x of the diaphragm 54.

[0026] The first model M1 also includes the mechanical resistance Rms, mass Mms, and compliance Cms(x) of the vibration system. The compliance Cms(x) is the reciprocal of the spring constant Kms(x) of the vibration system, as expressed by the following equation. The spring constant Kms(x) and compliance Cms(x) change nonlinearly according to the displacement x of the diaphragm 54.

[0027] The second model M2 of the nonlinear model M includes a volumetric flow velocity V, a volumetric flow velocity Vp, and an acoustic compliance Caf. The volumetric flow velocity V is the flow rate (volume flow rate) of the airflow generated in the internal space 42 of the housing 40 due to vibration of the diaphragm 54. The volumetric flow velocity Vp is the flow rate (volume flow rate) of the airflow generated in the acoustic port 60. The acoustic compliance Caf is the acoustic compliance in the internal space 42 of the housing 40.

[0028] The second model M2 also includes an acoustic resistance Rap and an acoustic mass Map at the acoustic port 60, an acoustic resistance Rrad and an acoustic mass Mrad relating to acoustic radiation from the acoustic port 60 to the external space, and a nonlinear acoustic resistance Rap2(Vp) at the acoustic port 60.

[0029] Sound behaves like a fluid inside the acoustic port 60. In addition, in the flow path from the internal space 42 to the inside of the acoustic port 60, the cross-sectional area discontinuously decreases at the boundary (near the inner opening 62) between the internal space 42 and the acoustic port 60. Therefore, a contraction effect occurs inside the acoustic port 60 near the inner opening 62.

[0030] Due to the contraction effect within the acoustic port 60, the acoustic resistance Rap2(Vp) at the acoustic port 60 changes depending on the volumetric flow velocity Vp within the acoustic port 60. As can be understood from the above explanation, the nonlinear model M (specifically, the second model M2) simulates the relationship in which the acoustic resistance Rap2(Vp) at the acoustic port 60 depends on the volumetric flow velocity Vp within the acoustic port 60. The acoustic resistance Rap2(Vp) can also be expressed as the component of the acoustic resistance within the acoustic port 60 that depends on the volumetric flow velocity Vp.

[0031] In the nonlinear model M described above, the following equations (1) to (3) hold.

[0032] The acoustic resistance Rap' and the acoustic mass Map' in the formula (3) are expressed by the following formula (4).

[0033] Furthermore, the volumetric flow velocity V and displacement x are defined as shown in the following equation (5): As can be seen from equation (5), the displacement x is the time integral of the volumetric flow velocity V, and corresponds to the displacement of the air inside the acoustic port 60.

[0034] By applying the formula (5), the formula (2) is transformed into the following formula (6), and the formula (3) is transformed into the following formula (7).

[0035] As can be understood from the above explanation, the nonlinear model M includes nonlinear parameters (Bl(x), Kms(x)) related to the speaker unit 50 and nonlinear parameters (Rap2(Vp)) related to the acoustic port 60. The nonlinear parameters (Rap2(Vp)) related to the acoustic port 60 are an example of "first nonlinear parameters," and the nonlinear parameters (Bl(x), Kms(x)) related to the speaker unit 50 are an example of "second nonlinear parameters."

[0036] The control device 11 uses the nonlinear model M described above to determine the input voltage u so as to reduce both the nonlinear distortion caused by the speaker unit 50 and the nonlinear distortion caused by the acoustic port 60. The nonlinear distortion caused by the speaker unit 50 is harmonic distortion that occurs in the sound radiated by the speaker unit 50 due to the nonlinearity in which the force coefficient Bl(x) and the spring constant Kms(x) depend on the displacement x of the diaphragm 54. The nonlinear distortion caused by the acoustic port 60 is harmonic distortion that occurs in the sound radiated from the acoustic port 60 due to the nonlinearity in which the acoustic resistance Rap2(Vp) depends on the volumetric flow velocity Vp.

[0037] Specifically, the control device 11 determines the input voltage u at each predetermined sampling period by calculation using the nonlinear model M. That is, the acoustic signal Y supplied from the output device 14 to the speaker device 20 is a voltage signal whose signal value is set to the input voltage u.

[0038] 5 is a flowchart of a process (hereinafter referred to as "distortion reduction process") executed by the control device 11 to determine the input voltage u. The distortion reduction process of FIG. 5 is executed at every predetermined sampling period.

[0039] The distortion reduction process includes a first process S1 and a second process S2. The first process S1 is a process for generating target parameters. The target parameters are parameters related to the nonlinear model M. Specifically, the target parameters are intermediate parameters required to reduce nonlinear distortion in the sound reproduced by the speaker device 20. In the first embodiment, the volume flow velocity Vp required for the acoustic port 60 to reduce nonlinear distortion in the reproduced sound corresponding to the acoustic signal X is exemplified as the target parameter.

[0040] In the first process S1, the control device 11 generates the total volumetric flow Vp using a target generation model F. The target generation model F is a mathematical model in which the nonlinear parameters in the nonlinear model M are linearized. The linearization is a process for ignoring the nonlinearity in the nonlinear model M.

[0041] The target generation model F of the first embodiment is a mathematical model that virtually ignores the nonlinearities of both the speaker unit 50 and the acoustic port 60 in the nonlinear model M. That is, in the target generation model F, the nonlinear parameters (Bl(x), Kms(x)) related to the speaker unit 50 and the nonlinear parameter (Rap2(Vp)) related to the acoustic port 60 of the nonlinear model M are linearized. Specifically, the target generation model F is expressed by the following formulas (8a), (9a), and (10a).

[0042] In equations (8a) and (9a), the force coefficient Bl(x), which is a nonlinear parameter of the speaker unit 50 in equations (1) and (6), is replaced with a predetermined constant Bl. Also, in equation (9a), the spring constant Kms(x), which is a nonlinear parameter of the speaker unit 50 in equation (6), is replaced with a predetermined constant Kms. In equation (10a), the acoustic resistance Rap2(Vp) (more precisely, the sum of the acoustic resistances Rap' and Rap2(Vp)), which is a nonlinear parameter of the acoustic port 60 in equation (7), is replaced with a predetermined constant Rap'.

[0043] In the first process S1, the control device 11 calculates the volume flow velocity Vp when the audio signal X is supplied to the speaker device 20, which is assumed to be a linear system, by applying the signal value of the audio signal X as an input voltage u to the formulas (8a) to (10a) of the target generation model F.

[0044] As explained above, the target parameter in the first embodiment is the volumetric flow velocity Vp in an ideal environment that is free from nonlinear distortion caused by the nonlinearity of the speaker unit 50 and the nonlinearity of the acoustic port 60. That is, in the first embodiment, the volumetric flow velocity Vp is calculated for the speaker device 20 to radiate sound corresponding to the acoustic signal X in an ideal environment in which the nonlinearity of the speaker unit 50 and the acoustic port 60 is ignored.

[0045] Note that a known method such as a general state space model may be arbitrarily employed to solve the simultaneous differential equations. For example, an analysis using a state space model is disclosed in, for example, Huang, X. Feng, S. Chen, and Y. Shen, “Analysis of total harmonic distortion of miniature loudspeakers used in mobile phones considering nonlinear acoustic damping,” The Journal of the Acoustical Society of America, vol. 149, no. 3, pp. 1579-1588, Mar. 2021, doi: 10.1121 / 10.0003644.

[0046] As can be understood from the above explanation, the control device 11 of the first embodiment functions as an element (target generation unit) that generates target parameters using a target generation model F in which the nonlinear parameters related to the speaker unit 50 and the acoustic port 60 in the nonlinear model M (signal generation model G) are linearized.

[0047] 5, the control device 11 executes a second process S2 after executing a first process S1. The second process S2 uses a signal generation model G to generate an input voltage u *Specifically, the control device 11 applies the volumetric flow rate Vp (i.e., the target parameter) calculated in the first process S1 to the signal generation model G, thereby determining the input voltage u required to realize the volumetric flow rate Vp. * The signal generation model G corresponds to the nonlinear model M described above. Specifically, the signal generation model G is expressed by the following formulas (11a), (12a), and (13a). Note that the symbol "*" indicates an ideal value in a virtual environment where no nonlinear distortion occurs.

[0048]

[0049] Equation (11a) corresponds to the above-mentioned equation (7), equation (12a) corresponds to the above-mentioned equation (6), and equation (13a) corresponds to the above-mentioned equation (1). As explained above, the signal generation model G (nonlinear model M) includes the force coefficient B1(x) and the spring constant Kms(x), which are nonlinear parameters related to the speaker unit 50, and the acoustic resistance Rap2(Vp), which is a nonlinear parameter related to the acoustic port 60.

[0050] 6 is a flowchart illustrating the specific procedure of the second process S2. When the second process S2 is started, the control device 11 applies the volume flow velocity Vp calculated in the first process S1 to the equation (11a) of the signal generation model G to obtain the ideal displacement x of the diaphragm 54. * is calculated (S21).

[0051] The control device 11 detects the displacement x of the vibration plate 54. * By differentiating the ideal velocity v of the diaphragm 54, * In addition, the control device 11 applies the volume flow velocity V calculated in the first process S1 to the equation (5) to calculate the ideal displacement x for the acoustic port 60. * In the above description, the volume flow velocity Vp is used as the target parameter, but the volume flow velocity Vp and displacement xp of the acoustic port 60 are calculated. * The set of the volume flow velocity Vp and displacement xp of the acoustic port 60 may be interpreted as target parameters. * and the displacement x of the diaphragm 54 *and velocity v * As illustrated above, the target parameters are expressed as parameters including the volumetric flow velocity Vp at the acoustic port 60.

[0052] The control device 11 detects the displacement x of the vibration plate 54. * and velocity v * and the volumetric flow velocity Vp and displacement xp of the acoustic port 60 * By applying this to the equation (12a) of the signal generation model G, the ideal input current i * Then, the control device 11 calculates the displacement x of the diaphragm 54. * and velocity v * and input current i * By applying this to the equation (13a) of the signal generation model G, the input voltage u * (S25) The input voltage u * is the ideal displacement x of the acoustic port 60 * and the voltage required to achieve the volumetric flow rate Vp.

[0053] When the first process S1 and the second process S2 are executed, the control device 11 detects that the signal value is equal to the input voltage u * The output device 14 supplies the acoustic signal Y set to the input voltage u to the speaker device 20 (S3). * is supplied to the speaker device 20.

[0054] As can be understood from the above description, the control device 11 of the first embodiment uses a nonlinear model M that simulates the relationship in which the acoustic resistance Rap2(Vp) at the acoustic port 60 depends on the volumetric flow velocity Vp, and adjusts the input voltage u so that nonlinear distortion caused by the acoustic port 60 is reduced. * According to the above configuration, the nonlinear distortion caused by the acoustic port 60 in the sound reproduced by the speaker device 20 can be reduced.

[0055] Furthermore, in the first embodiment, a target generation model F obtained by linearizing the nonlinear parameters (Bl(x), Kms(x)) related to the speaker unit 50 and the nonlinear parameter (Rap2(Vp)) related to the acoustic port 60 in the nonlinear model M is used to calculate the target parameter (volumetric flow velocity Vp). Therefore, in addition to the nonlinear distortion caused by the acoustic port 60, the nonlinear distortion caused by the speaker unit 50 can also be reduced.

[0056] B: Second Embodiment A second embodiment of the present disclosure will be described. Note that, for elements in the following exemplary aspects that have the same functions as those in the first embodiment, the same reference numerals as those in the first embodiment will be used, and detailed descriptions of each will be omitted as appropriate.

[0057] In the second embodiment, the signal generation model G (nonlinear model M) applied to the second process S2 differs from that in the first embodiment. Specifically, the signal generation model G in the second embodiment is expressed by the following formulas (11b), (12b), and (13b).

[0058]

[0059] Equation (11b) of the signal generation model G is the same as equation (11a) in the first embodiment. That is, the signal generation model G in the second embodiment includes the acoustic resistance Rap2(Vp), which is a nonlinear parameter of the acoustic port 60. Furthermore, the signal generation model G in the second embodiment is a mathematical model in which the nonlinear parameters (Bl(x), Kms(x)) related to the speaker unit 50 in the signal generation model G in the first embodiment are linearized. That is, in the signal generation model G, the force coefficient Bl(x), which is a nonlinear parameter of the signal generation model G, is linearized as shown in equations (12b) and (13b). * ) is replaced with a predetermined constant B1, and the spring constant Kms(x * ) is replaced with a predetermined constant Kms.

[0060] The control device 11 performs the second process S2 of applying the target parameter (volumetric flow velocity Vp) to the signal generation model G described above to obtain the input voltage u *In the first process S1, the target parameter (volumetric flow velocity Vp) is calculated using the same target generation model F as in the first embodiment.

[0061] As explained above, in the second embodiment, the input voltage u is calculated using the signal generation model G (nonlinear model M) that simulates the relationship in which the acoustic resistance Rap2(Vp) at the acoustic port 60 depends on the volumetric flow velocity Vp. * Therefore, similarly to the first embodiment, nonlinear distortion in the sound reproduced by the speaker device 20 can be reduced.

[0062] Note that the signal generation model G in the first embodiment includes the nonlinear parameters (Bl(x), Kms(x)) of the speaker unit 50 in addition to the nonlinear parameter (Rap2(Vp)) of the acoustic port 60, and therefore can reduce the nonlinear distortion caused by the speaker unit 50 in addition to the nonlinear distortion caused by the acoustic port 60. On the other hand, the signal generation model G in the second embodiment includes only the nonlinear parameter (Rap2(Vp)) of the acoustic port 60. Therefore, in the second embodiment, it is the nonlinear distortion caused by the acoustic port 60 that is reduced from the reproduced sound of the speaker device 20.

[0063] As explained above, the first embodiment is more effective than the second embodiment in terms of reducing nonlinear distortion caused by the speaker unit 50. On the other hand, in the second embodiment, the number of nonlinear parameters in the signal generation model G is reduced, so that the acoustic signal Y (input voltage u * ) is generated, the processing load required is reduced.

[0064] C: Third Embodiment In the third embodiment, the target generation model F applied to the first process S1 differs from that in the first embodiment. Specifically, the target generation model F in the third embodiment is expressed by the following equations (8b), (9b), and (10b). In the first process S1, the control device 11 calculates the target parameters (specifically, the volumetric flow velocity Vp of the acoustic port 60) using the target generation model F, exemplified below.

[0065]

[0066] Equations (8b) and (9b) of the target generation model F are similar to equations (8a) and (9a) in the first embodiment. That is, in the target generation model F of the third embodiment, the nonlinear parameters (Bl(x), Kms(x)) related to the speaker unit 50 in the nonlinear model M are linearized. Specifically, in the target generation model F, the force coefficient Bl(x) of the speaker unit 50 is replaced with the constant Bl, and the spring constant Kms(x) of the speaker unit 50 is replaced with the constant Kms.

[0067] On the other hand, as can be seen from equation (10b), in the target generation model F of the third embodiment, the nonlinear parameter (Rap2(Vp)) related to the acoustic port 60 in the nonlinear model M is maintained nonlinear. As can be seen from the above explanation, the target generation model F of the third embodiment includes the nonlinear parameter (Rap2(Vp)) related to the acoustic port 60.

[0068] The signal generation model G applied to the second process S2 in the third embodiment is the same as that in the first embodiment. That is, the signal generation model G in the third embodiment includes nonlinear parameters (Bl(x), Kms(x)) related to the speaker unit 50 and a nonlinear parameter (Rap2(Vp)) related to the acoustic port 60. As in the first embodiment, the control device 11 applies the target parameters (specifically, the volumetric flow velocity Vp) calculated in the first process S1 to the signal generation model G in the second process S2, thereby calculating the input voltage u * Calculate the following.

[0069] As explained above, in the third embodiment, the input voltage u is calculated using the signal generation model G (nonlinear model M) that simulates the relationship in which the acoustic resistance Rap2(Vp) at the acoustic port 60 depends on the volumetric flow velocity Vp. * Therefore, similarly to the first embodiment, nonlinear distortion in the sound reproduced by the speaker device 20 can be reduced.

[0070] The target generation model F of the third embodiment includes the nonlinear parameter (Rap2(Vp)) of the acoustic port 60 in the nonlinear model M, while the nonlinear parameters (Bl(x), Kms(x)) related to the speaker unit 50 in the nonlinear model M are linearized. Therefore, in the third embodiment, nonlinear distortion caused by the speaker unit 50 can be reduced from the reproduced sound of the speaker device 20.

[0071] In the target generation model F, in a configuration in which the nonlinear parameter (acoustic resistance Rap2(Vp)) of the acoustic port 60 is linearized (for example, in the first embodiment), the displacement x * The displacement x of the diaphragm 54 may be overestimated. * As a result of overestimating the value of x, it may occur that nonlinear distortion such as harmonic distortion in the reproduced sound is not sufficiently reduced. In the third embodiment, since the target generation model F includes the nonlinear parameters of the acoustic port, the displacement x of the diaphragm 54 in the distortion reduction process is * Therefore, there is an advantage that nonlinear distortion caused by the speaker unit 50 can be reduced with high precision in the reproduced sound of the speaker device 20.

[0072] D: Fourth Embodiment In the fourth embodiment, the signal generation model G (nonlinear model M) applied to the second process S2 differs from that in the first embodiment. Specifically, the signal generation model G in the fourth embodiment is expressed by the following formulas (11c) to (13c).

[0073]

[0074] Equations (12c) and (13c) of the signal generation model G are similar to equations (12a) and (13a) in the first embodiment. In equation (11c) of the signal generation model G in the third embodiment, the acoustic compliance Caf, which was set to a constant in the first embodiment, is changed to a nonlinear parameter (acoustic compliance Caf(x)) that changes nonlinearly in accordance with the displacement x of the diaphragm 54. The acoustic compliance Caf(x) is the acoustic compliance in the internal space 42 of the housing 40. Note that the acoustic compliance Caf(x) is an example of a "third nonlinear parameter."

[0075] The control device 11 performs the second process S2 of applying the target parameter (volumetric flow velocity Vp) to the signal generation model G described above to obtain the input voltage u * In the first process S1, the target parameter (volumetric flow velocity Vp) is calculated using a target generation model F similar to that of the third embodiment, which is expressed by equations (8b) to (10b). That is, the target generation model F of the fourth embodiment includes the nonlinear parameter (Rap2(Vp)) of the acoustic port 60, and the nonlinear parameters (Bl(x), Kms(x)) of the speaker unit 50 and the nonlinear parameter (Caf(x)) related to the acoustic compliance in the internal space 42 are linearized.

[0076] As explained above, in the fourth embodiment, the input voltage u is generated by using the signal generation model G (nonlinear model M) that simulates the relationship in which the acoustic resistance Rap2(Vp) at the acoustic port 60 depends on the volumetric flow velocity Vp. * Therefore, similarly to the first embodiment, nonlinear distortion in the sound reproduced by the speaker device 20 can be reduced.

[0077] Furthermore, in the fourth embodiment, the signal generation model G includes the acoustic compliance Caf(x), which is a nonlinear parameter related to the internal space 42 of the housing 40, and the acoustic compliance Caf(x) is linearized in the target generation model F. Therefore, according to the fourth embodiment, in addition to being able to reduce nonlinear distortion caused by the speaker unit 50 as in the third embodiment, it is also possible to reduce nonlinear distortion caused by the acoustic compliance Caf(x) from the reproduced sound.

[0078] E: Fifth Embodiment Figure 7 is a flowchart of the distortion reduction process in the fifth embodiment. After calculating the ideal volume flow velocity Vp of the acoustic port 60 for the acoustic signal X in the first process S1, the control device 11 limits the volume flow velocity Vp to a predetermined range (hereinafter referred to as the "limit range") (Sa). The limit range is the range from a minimum value Vmin to a maximum value Vmax. The minimum value Vmin and the maximum value Vmax are set experimentally or statistically so as to suppress high-frequency noise components that cannot be reduced by the distortion reduction process of the first embodiment.

[0079] Specifically, if the volumetric flow rate Vp calculated by the first process S1 is below the minimum value Vmin, the control device 11 sets the volumetric flow rate Vp to the minimum value Vmin. On the other hand, if the volumetric flow rate Vp is above the maximum value Vmax, the control device 11 sets the volumetric flow rate Vp to the maximum value Vmax. The second process S2, which applies the limited volumetric flow rate Vp, is the same as in the above-mentioned embodiments.

[0080] The fifth embodiment also achieves the same effects as the first embodiment. Moreover, in the fifth embodiment, the volume flow velocity Vp applied to the nonlinear model M is limited within a limited range, so that the energy of nonlinear distortion in the reproduced sound of the speaker device 20, which is difficult to sufficiently reduce by the nonlinear model M, can be suppressed.

[0081] F: Sixth Embodiment Fig. 8 is a schematic diagram of a speaker system 100 according to a sixth embodiment. As illustrated in Fig. 8, the speaker system 100 of the sixth embodiment is configured by adding a sensor 70 to the first embodiment.

[0082] The sensor 70 is a flow velocity sensor that measures the volumetric flow velocity Vp inside the acoustic port 60. For example, a flow meter such as an LDV (Laser Doppler Velocimeter) that optically detects the flow of air inside the acoustic port 60 is used as the sensor 70.

[0083] 9 is a flowchart of the distortion reduction process in the sixth embodiment. When the distortion reduction process is started, the control device 11 (signal processing unit) acquires a measurement value from the sensor 70 (Sb). The control device 11 performs a second process S2 in which the measurement value from the sensor 70 is applied as a volumetric flow velocity Vp of the nonlinear model M, thereby reducing the input voltage u * Specifically, the nonlinear acoustic resistance Rap2(Vp) at the acoustic port 60 is set in accordance with the measurement value by the sensor 70.

[0084] The specific steps (S21 to S25) of the second process S2 are the same as those in the first embodiment. Therefore, the sixth embodiment also achieves the same effects as those in the first embodiment. In particular, in the sixth embodiment, the result of the volume flow velocity Vp detected by the sensor 70 inside the acoustic port 60 is converted into the input voltage u * That is, the actual sound wave behavior at the acoustic port 60 is determined by the input voltage u * Therefore, the input voltage u * In comparison with a configuration in which all values ​​used to determine the value are determined by calculation, the nonlinear distortion caused by the acoustic port 60 can be reduced with high precision.

[0085] G: Modifications Specific modifications that can be added to the above-mentioned embodiments are exemplified below. Two or more embodiments arbitrarily selected from the following examples may be combined as appropriate within the scope of not mutually contradicting each other.

[0086] (1) In the fifth embodiment, nonlinear distortion is suppressed by limiting the volumetric flow velocity Vp to a limited range. However, the configuration and processing for suppressing the energy of nonlinear distortion that is difficult to sufficiently reduce using the nonlinear model M are not limited to the above examples. For example, nonlinear distortion may be reduced by signal processing on the audio signal X. Specifically, the control device 11 performs signal processing on the audio signal X to suppress audio components in the high-frequency range, where nonlinear distortion is difficult to sufficiently reduce using the nonlinear model M. The signal processing is, for example, equalization processing that adjusts the intensity of each band of the audio signal X. The control device 11 determines the input voltage u by calculations (Sa1 to Sa5) of the nonlinear model M to which the signal-processed audio signal X is applied.

[0087] (2) In the sixth embodiment, a flow meter that measures a volumetric flow rate is used as the sensor 70, but the form of the sensor 70 is not limited to this example. For example, a pressure sensor (e.g., a MEMS sensor) that uses a detection element such as a piezoelectric element or capacitance may be used as the sensor 70 inside the acoustic port 60. The control device 11 calculates the volumetric flow rate Vp from the pressure measured by the sensor 70 and determines the input voltage u by a calculation that applies the volumetric flow rate Vp.

[0088] Furthermore, although the sixth embodiment illustrates the sensor 70 installed inside the acoustic port 60, it is not essential that the sensor 70 be installed inside the acoustic port 60. For example, the sensor 70 may be installed near the acoustic port 60. For example, the sensor 70 that collects radiated sound may be installed near the outer opening 61 of the acoustic port 60. For example, an external microphone that detects ambient sound pressure, such as a dynamic microphone or a condenser microphone, is used as the sensor 70. The control device 11 calculates the volumetric flow velocity Vp from the sound pressure detected by the sensor 70, and determines the input voltage u by a calculation that applies the volumetric flow velocity Vp.

[0089] As can be understood from the above description, the sensor 70 is collectively expressed as an element that detects acoustic characteristics inside or near the acoustic port 60. The acoustic characteristics include the volumetric flow rate exemplified in the sixth embodiment, as well as the pressure or sound pressure exemplified in this modification.

[0090] (3) In the above-described embodiments, the speaker device 20 is a bass reflex type having a bass reflex port as the acoustic port 60, but the type (enclosure type) of the speaker device 20 is not limited to the above examples.

[0091] For example, as illustrated in Fig. 10, the above-described embodiments are similarly applied to a Kelton-type speaker device 20 in which sound emitted forward from a speaker unit 50 is emitted through an acoustic port 60. Furthermore, as illustrated in Fig. 11, the above-described embodiments are similarly applied to a bandpass-type speaker device 20 having an acoustic port 60 through which sound emitted forward from a speaker unit 50 passes and an acoustic port 60 through which sound emitted rearward passes.

[0092] As can be understood from the above examples, the acoustic port 60 in this disclosure is comprehensively expressed as a port for acoustic radiation that utilizes Helmholtz resonance of the sound radiated from the speaker unit 50, and it is not important in this disclosure as to in which direction the sound radiated from the speaker unit 50 passes through the port.

[0093] (4) In the sixth embodiment, the measurement value by the sensor 70 is used as the volumetric flow velocity Vp to be applied to the distortion reduction process, but the method of using the measurement value by the sensor 70 is not limited to the above example. For example, a configuration is also conceivable in which the relationship between the volumetric flow velocity Vp and the acoustic resistance Rap2(Vp) is identified in advance using the measurement value by the sensor 70.

[0094] (5) The method for determining the input voltage u using the nonlinear model M is not limited to the methods exemplified in the above embodiments. Any known technique may be used to calculate the input voltage u using the nonlinear model M.

[0095] (6) In the above-described embodiments, the speaker system 100 in which the signal processing system 10 and the speaker device 20 are configured as separate entities has been exemplified, but the above-described embodiments are also applicable to a speaker system 100 (active speaker) in which the signal processing system 10 is installed inside a housing 40. Furthermore, the speaker system 100 may be realized as a stationary system, or may be realized as a portable information device such as a smartphone, a tablet terminal, or a personal computer.

[0096] (7) As described above, the functions of the signal processing system 10 illustrated above are realized through cooperation between one or more processors constituting the control device 11 and a program stored in the storage device 12. The program according to the present disclosure may be provided in a form stored on a computer-readable recording medium and installed on a computer. The recording medium may be, for example, a non-transitory recording medium, such as an optical recording medium (optical disk) such as a CD-ROM, but may also include any known type of recording medium, such as a semiconductor recording medium or a magnetic recording medium. Note that a non-transitory recording medium includes any recording medium other than a transient, propagating signal, and does not exclude volatile recording media. Furthermore, in a configuration in which a distribution device distributes a program via a communication network, the storage medium that stores the program in the distribution device corresponds to the non-transitory recording medium described above.

[0097] (8) The term "nth" (n is a natural number) in this application is used only as a formal and convenient label to distinguish each element in the description and does not have any substantive meaning. Therefore, there is no room for restrictive interpretation of the position or order of each element based on the term "nth."

[0098] H: Supplementary Note From the above-described exemplary embodiments, the following configurations can be understood, for example.

[0099] A speaker system according to one aspect (aspect 1) of the present disclosure uses a nonlinear model that simulates the relationship in which acoustic resistance at an acoustic port for sound radiation utilizing Helmholtz resonance depends on a volumetric flow velocity at the acoustic port to determine an input voltage from target parameters including the volumetric flow velocity at the acoustic port, and supplies the input voltage to a speaker device. In the above aspect, the input voltage to the speaker device is determined using the nonlinear model that simulates the relationship in which acoustic resistance at the acoustic port depends on the volumetric flow velocity. Therefore, nonlinear distortion in the sound reproduced by the speaker device can be reduced.

[0100] In a specific example (Aspect 2) of Aspect 1, the nonlinear model includes a first nonlinear parameter that represents the dependence of the volumetric flow velocity on the acoustic resistance, and further, the target parameter is generated using a target generation model in which the first nonlinear parameter in the nonlinear model is linearized. In the above aspect, the target parameter is generated using the target generation model in which the first nonlinear parameter is linearized, and an input voltage is determined from the target parameter. Therefore, nonlinear distortion caused by the acoustic port can be reduced in the reproduced sound of the speaker device.

[0101] The nonlinear model simulates a linear or nonlinear relationship in which the displacement (and even velocity or acceleration) of the diaphragm in a speaker unit depends on multiple characteristics, such as electromagnetic force, mechanical resistance, or elastic force, acting on each element of the speaker unit.

[0102] In a specific example (Aspect 3) of Aspect 2, the nonlinear model further includes a second nonlinear parameter related to a speaker unit of the speaker device, and the target generation model is a model in which the first nonlinear parameter and the second nonlinear parameter in the nonlinear model are linearized. In the above aspect, target parameters are generated using a target generation model in which both the first nonlinear parameter and the second nonlinear parameter are linearized, and an input voltage is determined from the target parameters. Therefore, in addition to nonlinear distortion caused by the acoustic port, nonlinear distortion caused by the speaker unit can also be reduced.

[0103] In a specific example (Aspect 4) of Aspect 1, the nonlinear model includes a first nonlinear parameter representing the dependence of the volumetric flow velocity on the acoustic resistance and a second nonlinear parameter related to a speaker unit of the speaker device, and further includes the first nonlinear parameter in the nonlinear model, and generates the target parameters using a target generation model in which the second nonlinear parameter is linearized. In the above aspect, the target parameters are generated using a target generation model in which the first nonlinear parameter is linearized, and the second nonlinear parameter is linearized, and an input voltage is determined from the target parameters using the nonlinear model. Therefore, nonlinear distortion caused by the speaker unit can be reduced in the sound reproduced by the speaker device.

[0104] In a specific example (Aspect 5) of Aspect 1, the nonlinear model includes a first nonlinear parameter representing the dependence of the volumetric flow velocity on the acoustic resistance, a second nonlinear parameter related to a speaker unit of the speaker device, and a third nonlinear parameter related to acoustic compliance in the internal space of the speaker device, and the target parameters are generated using a target generation model that includes the first nonlinear parameter in the nonlinear model and in which the second nonlinear parameter and the third nonlinear parameter are linearized. In the above aspect, the target parameters are generated using a target generation model that includes the first nonlinear parameter and in which the second nonlinear parameter and the third nonlinear parameter are linearized, and an input voltage is determined from the target parameters using the nonlinear model. Therefore, nonlinear distortion caused by the speaker unit and acoustic compliance can be reduced in the sound reproduced by the speaker device.

[0105] In a specific example (Aspect 6) of any one of Aspects 1 to 5, the volumetric flow rate is further limited to a predetermined range. According to the above aspect, by limiting the volumetric flow rate applied to the nonlinear model to a predetermined range, it is possible to suppress noise caused by the acoustic port in the reproduced sound of the speaker device, which is difficult to suppress with a nonlinear model.

[0106] In a specific example (Aspect 7) of any of Aspects 1 to 6, a detection result from a sensor that detects acoustic characteristics inside or near the acoustic port is further acquired, and the input voltage is determined by a calculation that applies the detection result. According to the above aspect, the result of detecting the acoustic characteristics by the sensor inside or near the acoustic port is applied to the determination of the input voltage by the signal processing unit. In other words, the behavior of the actual sound wave at the acoustic port is taken into account when the input voltage is determined by the signal processing unit. Therefore, nonlinear distortion can be reduced with high precision compared to an aspect in which all numerical values ​​used to determine the input voltage are determined by calculation.

[0107] The "acoustic characteristics" are variables applied to the nonlinear model. Specifically, characteristics such as flow velocity (volumetric flow velocity) or pressure inside the acoustic port are detected by a sensor as the acoustic characteristics.

[0108] The "vicinity of the acoustic port" refers to, for example, the space on the input side of the acoustic port (i.e., inside the housing of the speaker device) or the space on the output side of the acoustic port (i.e., outside the housing of the speaker device).

[0109] "Calculation applying detection results" includes both: (1) a form in which a nonlinear function in a nonlinear model (e.g., the relationship between volumetric flow velocity and acoustic resistance) is identified using the detection results from a sensor; and (2) a form in which the numerical values ​​of variables in a nonlinear model are controlled (e.g., real-time feedback control) according to the detection results from a sensor.

[0110] A signal processing system according to one aspect of the present disclosure includes a signal processing unit that determines an input voltage from target parameters including a volumetric flow rate at an acoustic port using a nonlinear model that simulates the relationship in which the acoustic resistance at an acoustic port for acoustic radiation using Helmholtz resonance depends on the volumetric flow rate at the acoustic port, and a voltage supply unit that supplies the input voltage to a speaker device. In the above aspect, the input voltage to the speaker device is determined using the nonlinear model that simulates the relationship in which the acoustic resistance at the acoustic port depends on the volumetric flow rate. Therefore, nonlinear distortion in the sound reproduced by the speaker device can be reduced. Note that the above-described aspects (Aspects 2 to 6) of the signal processing method according to the present disclosure are also applicable to the signal processing system according to the present disclosure.

[0111] A speaker system according to one aspect of the present disclosure includes a speaker unit, an acoustic port for radiating sound from the speaker unit using Helmholtz resonance, and a signal processing system. The signal processing system includes a signal processing unit that determines an input voltage from target parameters including a volumetric flow velocity at the acoustic port using a nonlinear model that simulates a relationship that depends on the volumetric flow velocity at the acoustic port, and a voltage supply unit that supplies the input voltage to the speaker device. In the above aspect, the input voltage to the speaker device is determined using a nonlinear model that simulates a relationship that depends on the volumetric flow velocity of the acoustic resistance at the acoustic port. Therefore, nonlinear distortion can be reduced in the sound reproduced by the speaker device.

[0112] 100...speaker system, 10...signal processing system, 11...control device, 12...memory device, 13...input device, 14...output device, 20...speaker device, 30...signal supply device, 40...housing, 41...plate material, 50...speaker unit, 51...frame, 52...magnet, 53...voice coil, 54...diaphragm, 55...edge, 56...damper, 60...acoustic port, 70...sensor.

Claims

1. A signal processing method implemented by a computer system, which uses a nonlinear model that simulates the relationship in which the acoustic resistance at an acoustic port for acoustic radiation using Helmholtz resonance depends on the volumetric flow velocity at the acoustic port, determines an input voltage from target parameters including a volumetric flow velocity at the acoustic port, and supplies the input voltage to a speaker device.

2. The signal processing method of claim 1, wherein the nonlinear model includes a first nonlinear parameter representing the dependence of the volumetric flow velocity on the acoustic resistance, and further comprising: generating the target parameter using a target generation model in which the first nonlinear parameter in the nonlinear model is linearized.

3. The signal processing method of claim 2, wherein the nonlinear model further includes a second nonlinear parameter related to a speaker unit of the speaker device, and the target generation model is a model in which the first nonlinear parameter and the second nonlinear parameter in the nonlinear model are linearized.

4. The signal processing method of claim 1, wherein the nonlinear model includes a first nonlinear parameter representing the dependence of the volumetric flow velocity on the acoustic resistance and a second nonlinear parameter relating to a speaker unit of the speaker device, and further, the target parameters are generated using a target generation model that includes the first nonlinear parameter in the nonlinear model and in which the second nonlinear parameter has been linearized.

5. The signal processing method of claim 1, wherein the nonlinear model includes a first nonlinear parameter representing the dependence of the volumetric flow velocity on the acoustic resistance, a second nonlinear parameter relating to a speaker unit of the speaker device, and a third nonlinear parameter relating to acoustic compliance in the internal space of the speaker device, and further, the target parameters are generated using a target generation model including the first nonlinear parameter in the nonlinear model and in which the second nonlinear parameter and the third nonlinear parameter are linearized.

6. The signal processing method of claim 1, further comprising limiting said volumetric flow rate to a predetermined range.

7. The signal processing method according to claim 1, further comprising obtaining a detection result from a sensor that detects acoustic characteristics inside or near said acoustic port, and determining said input voltage by a calculation that applies said detection result.

8. A signal processing system comprising: a signal processing unit that determines an input voltage from target parameters including a volumetric flow velocity at an acoustic port by utilizing a nonlinear model that simulates the relationship in which an acoustic resistance at an acoustic port for acoustic radiation utilizing Helmholtz resonance depends on a volumetric flow velocity at the acoustic port; and a voltage supply unit that supplies the input voltage to a speaker device.

9. The signal processing system of claim 8, further comprising: a target generation unit, the nonlinear model including a first nonlinear parameter representing the dependence of the volumetric flow velocity on the acoustic resistance, and generating the target parameter using a target generation model in which the first nonlinear parameter in the nonlinear model is linearized.

10. The signal processing system of claim 9, wherein the nonlinear model further includes a second nonlinear parameter related to a speaker unit of the speaker device, and the target generation model is a model in which the first nonlinear parameter and the second nonlinear parameter in the nonlinear model are linearized.

11. The signal processing system of claim 8, further comprising: a target generation unit that generates the target parameters using a target generation model that includes the first nonlinear parameter in the nonlinear model and in which the second nonlinear parameter is linearized, the nonlinear model including a first nonlinear parameter representing the dependence of the volumetric flow velocity on the acoustic resistance and a second nonlinear parameter relating to a speaker unit of the speaker device.

12. The signal processing system of claim 8, further comprising: a target generation unit that generates the target parameters using a target generation model that includes the first nonlinear parameter in the nonlinear model and in which the second nonlinear parameter and the third nonlinear parameter are linearized, the nonlinear model including a first nonlinear parameter representing the dependence of the volumetric flow velocity on the acoustic resistance, a second nonlinear parameter relating to a speaker unit of the speaker device, and a third nonlinear parameter relating to acoustic compliance in the internal space of the speaker device.

13. A speaker system comprising: a speaker unit; an acoustic port for acoustic radiation utilizing Helmholtz resonance of sound radiated from the speaker unit; and a signal processing system, the signal processing system including: a signal processing unit that determines an input voltage from target parameters including a volumetric flow velocity at the acoustic port by utilizing a nonlinear model that simulates a relationship that depends on the volumetric flow velocity at the acoustic port; and a voltage supply unit that supplies the input voltage to a speaker device.

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