Signal processing method, signal processing system and loudspeaker system

Abstract

An acoustic processing system includes: a signal processing unit that determines an input voltage on the basis of a target parameter including a volume flow rate of an acoustic port by using a nonlinear model that simulates a relationship in which acoustic impedance of the acoustic port for acoustic radiation based on Helmholtz resonance depends on the volume flow rate of the acoustic port; and a voltage supply unit that supplies an input voltage to the speaker device.

Description

Technical Field

[0001] This invention relates to a technique for reducing nonlinear distortion of sound radiated from a loudspeaker device. Background Technology

[0002] Nonlinear distortions, such as high-order harmonic distortion, can occur in the sound emitted from a loudspeaker device. For example, Patent Document 1 discloses a technique that reduces nonlinear distortion of the sound by using a nonlinear model that simulates the loudspeaker unit of the loudspeaker device.

[0003] Patent Document 1: US Patent No. 10,547,942 Summary of the Invention

[0004] A loudspeaker device is equipped with an acoustic port (e.g., a bass reflex port) for sound radiation based on Helmholtz resonance. For the sound played from the loudspeaker device, in addition to the nonlinear distortion caused by the loudspeaker unit, there may also be nonlinear distortion caused by the acoustic port. Considering the above, one objective of this invention is to reduce nonlinear distortion in the sound played from the loudspeaker device.

[0005] To address the above issues, one aspect of the present invention relates to a signal processing method that utilizes a nonlinear model to simulate the relationship between the acoustic impedance of an acoustic port for acoustic radiation based on Helmholtz resonance and the volumetric velocity of that acoustic port. Based on target parameters including the volumetric velocity of the acoustic port, the method determines an input voltage and supplies the input voltage to a loudspeaker device.

[0006] One aspect of the present invention relates to a signal processing system comprising: a signal processing unit that uses a nonlinear model to simulate the relationship between the acoustic impedance of an acoustic port for acoustic radiation based on Helmholtz resonance and the volumetric flow velocity of the acoustic port, and determines an input voltage based on target parameters including the volumetric flow velocity of the acoustic port; and a voltage supply unit that supplies the input voltage to a loudspeaker device.

[0007] One aspect of the present invention relates to a loudspeaker system comprising: a loudspeaker unit; an acoustic port for acoustic radiation based on Helmholtz resonance of radiated sound from the loudspeaker unit; and a signal processing system comprising: a signal processing unit that determines an input voltage based on target parameters including the volumetric flow rate of the acoustic port using a nonlinear model simulating a relationship dependent on the volumetric flow rate of the acoustic port; and a voltage supply unit that supplies the input voltage to the loudspeaker device. Attached Figure Description

[0008] Figure 1This is a schematic diagram of the loudspeaker system according to the first embodiment.

[0009] Figure 2 This is a side view of the speaker unit.

[0010] Figure 3 This is a block diagram of a signal processing system.

[0011] Figure 4 This is a schematic diagram of a nonlinear model.

[0012] Figure 5 This is a flowchart of the distortion reduction process.

[0013] Figure 6 This is the flowchart for the second process.

[0014] Figure 7 This is part of the flowchart of the distortion reduction process in the second embodiment.

[0015] Figure 8 This is a schematic diagram of the loudspeaker system according to the third embodiment.

[0016] Figure 9 This is part of the flowchart of the distortion reduction process in the second embodiment.

[0017] Figure 10 This is a cross-sectional view of a modified loudspeaker device.

[0018] Figure 11 This is a cross-sectional view of a modified loudspeaker device. Detailed Implementation

[0019] A: Implementation Method 1

[0020] Figure 1 This is a schematic diagram illustrating the structure of the loudspeaker system 100 according to the first embodiment. The loudspeaker system 100 of the first embodiment includes a signal processing system 10 and a loudspeaker device 20. An acoustic signal X is supplied to the signal processing system 10 from a signal supply device 30. The acoustic signal X is a signal representing the waveform of an acoustic sound. For example, the acoustic signal X is a sample sequence of waveforms representing the singing or playing sounds of a piece of music.

[0021] The signal supply device 30 is, for example, a playback device that supplies an audio signal X recorded on a recording medium to the signal processing system 10. Furthermore, a communication device that supplies an audio signal X received from a transmission device (not shown) via a communication network to the signal processing system 10, or a pickup device that generates an audio signal X by picking up ambient sound, is also used as the signal supply device 30. Additionally, the signal supply device 30 can also be incorporated as an element of the loudspeaker system 100.

[0022] The signal processing system 10 generates an audio signal Y by processing the audio signal X, and supplies the audio signal Y to the loudspeaker device 20. The loudspeaker device 20 is a sound-emitting device that radiates the sound represented by the audio signal Y.

[0023] The loudspeaker assembly 20 has a frame 40 (cabinet), a loudspeaker unit 50, and an audio port 60. The frame 40 is a hollow structure that supports the loudspeaker unit 50 and the audio port 60. The loudspeaker unit 50 and the audio port 60 are mounted on a plate 41 (baffle) located on the front surface side of the frame 40. Alternatively, the audio port 60 may be located on the back of the frame 40.

[0024] The loudspeaker unit 50 radiates sound according to the sound signal Y supplied from the signal processing system 10. Figure 2 This is a cross-sectional view of the loudspeaker unit 50. The loudspeaker 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.

[0025] Frame 51 is the external structure constituting the loudspeaker unit 50. Magnet 52 is a ring-shaped permanent magnet. Voice coil 53 is a coil capable of axial displacement within the magnetic field generated by magnet 52. Vibrating plate 54 is a frustum-shaped structure. The inner periphery of vibrating plate 54 is fixed to voice coil 53. The outer periphery of vibrating plate 54 is connected to frame 51 via edge 55. Furthermore, vibrating plate 54 and frame 51 are connected via damper 56. Edge 55 and damper 56 are ring-shaped elastic bodies. Sound waves are radiated by the axial reciprocating motion of vibrating plate 54.

[0026] Figure 1 The acoustic port 60 is a bass-reflex port that amplifies the low-frequency acoustic components radiated from the speaker unit 50 to the rear side of the frame 40 via Helmholtz resonance. That is, the speaker device 20 of the first embodiment is a bass-reflex type. The acoustic port 60 is located inside the frame 40, connecting the internal space 42 of the frame 40 to the external space. Specifically, the acoustic port 60 is an approximately cylindrical tube including an outer opening 61 and an inner opening 62. The outer opening 61 is an opening end communicating with the opening of the plate 41. The inner opening 62 is an opening end located inside the frame 40.

[0027] In the above structure, the sound radiated from the speaker unit 50 to the rear side is transmitted from the internal space 42 of the housing 40 to the speaker port 60, and then radiated to the external space through the speaker port 60. As described above, the playback sound produced by the speaker device 20 includes the radiated sound from the speaker unit 50 and the radiated sound from the speaker port 60.

[0028] The sound produced by the loudspeaker device 20, especially the high-frequency components, is accompanied by nonlinear distortion caused by the nonlinear characteristics of the various components constituting the loudspeaker device 20. The signal processing system 10 generates an audio signal Y based on the audio signal X to reduce the nonlinear distortion caused by the nonlinear characteristics of the loudspeaker device 20. Specifically, the signal processing system 10 reduces nonlinear distortion by using a nonlinear model M that simulates the operation of the loudspeaker device 20.

[0029] Figure 3 This is a block diagram illustrating the structure of the signal processing system 10. For example... Figure 3 As illustrated, 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 can be implemented, for example, by an information device such as a smartphone, tablet computer, or personal computer. Furthermore, the signal processing system 10 can be implemented not only as a single device, but also by multiple devices configured separately from each other.

[0030] The control device 11 consists of one or more processors that control the various elements of the signal processing system 10. For example, the control device 11 consists of one or more processors such as CPU (Central Processing Unit), SPU (Sound Processing Unit), DSP (Digital Signal Processor), FPGA (Field Programmable Gate Array), or ASIC (Application Specific Integrated Circuit).

[0031] Storage device 12 is one or more memory devices that store programs executed by control device 11 and various data used by control device 11. Storage device 12 is constructed from known recording media such as magnetic recording media or semiconductor recording media. Storage device 12 may also be constructed from a combination of various recording media. In addition, as storage device 12, a portable recording medium that can be detached from signal processing system 10 or a recording medium that control device 11 can read or write via a communication network (e.g., network hard drive) may also be used.

[0032] Input device 13 receives audio signal X from signal supply device 30. For example, input device 13 may utilize input interfaces such as USB (Universal Serial Bus), HDMI (High-Definition Multimedia Interface), MIDI (Musical Instrument Digital Interface), or headphone jack. Furthermore, in the case where analog audio signal X is supplied from signal supply device 30, an A / D converter that converts the audio signal X from analog to digital is provided on input device 13.

[0033] Output device 14 supplies the audio signal Y to speaker device 20. Specifically, output device 14 has a D / A converter that converts the audio signal Y from digital to analog and an amplifier that amplifies the audio signal Y. Furthermore, output device 14, which is separate from signal processing system 10, can also be connected to signal processing system 10 via wired or wireless means. Output device 14 is an example of a "voltage supply unit".

[0034] Figure 4 This is a schematic diagram of the nonlinear model M used by the signal processing system 10 when generating the audio signal Y. The nonlinear model M is an equivalent circuit simulating the speaker unit 50 and the audio port 60 of 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 simulating the speaker unit 50, and the second model M2 is a nonlinear mathematical model simulating the audio port 60.

[0035] In Model 1 M1, the input voltage u is the voltage supplied to the voice coil 53. That is, the signal value of the audio signal Y is equivalent to the input voltage u. Additionally, the input current i is the current flowing through the voice coil 53.

[0036] like Figure 4 As illustrated, the first model M1 includes the axial displacement x and velocity v of the diaphragm 54, the 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 of the voice coil 53 and the winding width l, and varies nonlinearly with respect to the displacement x of the diaphragm 54.

[0037] In addition, model M1 includes the mechanical impedance R of the vibrating system. ms Quality M ms Compliance C ms (x). Cis-C ms (x) is the spring constant K of the vibrating system, as expressed by the following mathematical expression. msThe reciprocal of (x). The spring constant K. ms (x) and cis C ms (x) varies nonlinearly according to the displacement x of the vibrating plate 54.

[0038] [Mathematical Expression 1]

[0039] The second model M2 of the nonlinear model M includes volumetric flow velocity V and volumetric flow velocity V p Acoustic compliance C af The volumetric flow velocity V is the flow rate (volume flow rate) of the airflow generated within the internal space 42 of the frame 40 due to the vibration of the vibrating plate 54. p This refers to the airflow rate (volume flow rate) generated within the speaker port 60. Acoustic compliance C af It refers to the acoustic compliance of the internal space 42 of the frame 40.

[0040] Additionally, model M2 includes the acoustic impedance R of the audio port 60. ap and sound quality M ap The acoustic impedance R related to acoustic radiation from the audio port 60 to the external space rad and sound quality M rad The nonlinear acoustic impedance R of the audio port 60 ap2 (V) p ).

[0041] Inside the speaker port 60, the sound flows in a fluid manner. Furthermore, in the flow path from the internal space 42 to the interior of the speaker port 60, the cross-sectional area decreases discontinuously at the boundary between the internal space 42 and the speaker port 60 (near the inner opening 62). Therefore, a constriction effect occurs near the inner opening 62 within the speaker port 60.

[0042] Due to the current-shrinking effect within the audio port 60, the audio impedance R of the audio port 60 is... ap2 (V) p According to the volumetric flow rate V within the audio port 60 p And change. As understood from the above explanation, the nonlinear model M (specifically, the second model M2) changes with respect to the acoustic impedance R of the audio port 60. ap2 (V) p The volumetric flow rate V depends on the audio port 60. p The relationship is simulated. Acoustic impedance R ap2 (V) p This is also manifested in the acoustic impedance within the audio port 60, which depends on the volumetric flow velocity V. p The ingredients.

[0043] In the nonlinear model M described above, equations (1) to (3) hold true.

[0044] [Mathematical Expression 2]

[0045] Furthermore, the acoustic impedance R in equation (3) ap and sound quality M ap It is expressed by the following formula (4).

[0046] [Mathematical Expression 3]

[0047] In addition, the volumetric flow velocity V and displacement x p Defined as in equation (5) below. As understood from equation (5), the displacement x p It is the volumetric flow velocity V p The time integral is equivalent to the displacement of the air within the speaker port 60.

[0048] [Mathematical Expression 4]

[0049] By applying equation (5), equation (2) is transformed into equation (6), and equation (3) is transformed into equation (7).

[0050] [Mathematical Expression 5]

[0051] As understood from the above explanation, the nonlinear model M contains nonlinear parameters (Bl(x), K) related to the speaker unit 50. ms (x)) and the nonlinear parameter (R) associated with the audio port 60 ap2 (V) p Nonlinear parameters (R) associated with audio port 60 ap2 (V) p )) is an example of the "first nonlinear parameter", a nonlinear parameter (Bl(x), K) associated with speaker unit 50. ms (x) is an example of the "second nonlinear parameter".

[0052] The control device 11 uses the nonlinear model M described above to determine the input voltage u, thereby reducing both the nonlinear distortion caused by the speaker unit 50 and the nonlinear distortion caused by the audio port 60. The nonlinear distortion caused by the speaker unit 50 is due to the force coefficient Bl(x) and the spring constant K. ms(x) High-order harmonic distortion generated in the radiated sound of the loudspeaker unit 50, depending on the nonlinear characteristics of the displacement x of the diaphragm 54. The nonlinear distortion caused by the audio port 60 is due to the audio impedance R. ap2 (V) p Depends on volumetric flow rate V p The nonlinear characteristics of the sound result in high-order harmonic distortion in the radiated sound from the audio port 60.

[0053] Specifically, the control device 11 determines the input voltage u for each specified sampling period by utilizing the calculation of the nonlinear model M. That is, the audio signal Y supplied from the output device 14 to the speaker device 20 is a voltage signal with the signal value set to the input voltage u.

[0054] Figure 5 This is a flowchart of the process (hereinafter referred to as "distortion reduction process") performed by the control device 11 to determine the input voltage u. It is performed for each specified sampling period. Figure 5 Distortion reduction processing.

[0055] The distortion reduction process includes a first process S1 and a second process S2. The first process S1 is the process of 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 playback sound of the speaker device 20. In the first embodiment, the volumetric flow rate V required at the audio port 60 to reduce the nonlinear distortion of the playback sound corresponding to the audio signal X is... p This is exemplified as a target parameter.

[0056] In the first process S1, the control device 11 generates the volumetric flow velocity V using the target generation model F. p The target generation model F is a mathematical model that linearizes the nonlinear parameters of the nonlinear model M. Linearization is a process to ignore the nonlinear characteristics of the nonlinear model M.

[0057] The target generation model F in the first embodiment is a mathematical model that virtually ignores the nonlinear characteristics of the speaker unit 50 and the audio port 60 in the nonlinear model M. That is, in the target generation model F, the nonlinear parameters (Bl(x), K) related to the speaker unit 50 in the nonlinear model M are ignored. ms (x)) and the nonlinear parameter (R) associated with the audio port 60 ap2 (V) p Linearization is performed. Specifically, the target generation model F is represented by the following equations (8a), (9a) and (10a).

[0058] [Mathematical Expression 6]

[0059] [Target Generation Model F]

[0060] In equations (8a) and (9a), the nonlinear parameter of the loudspeaker unit 50 in equations (1) and (6), namely the force coefficient Bl(x), is replaced by a specified constant Bl. Furthermore, in equation (9a), the nonlinear parameter of the loudspeaker unit 50 in equation (6), namely the spring constant K, is replaced by a constant Bl. ms (x) is replaced by the specified constant K ms In equation (10a), the nonlinear parameter of the audio port 60 in equation (7) is the audio impedance R. ap2 (V) p (To be precise, acoustic impedance R) ap 'and acoustic impedance R ap2 (V) p The sum of ) is replaced by a specified constant R. ap '.

[0061] In the first process S1, the control device 11 uses the signal value of the acoustic signal X as the input voltage u and applies it to equations (8a) to (10a) of the target generation model F, thereby calculating the volumetric flow rate V when the acoustic signal X is supplied to the loudspeaker device 20, which is assumed to be a linear system. p .

[0062] As explained above, the target parameter of the first embodiment is the volumetric flow rate V under ideal conditions without nonlinear distortion caused by the nonlinear characteristics of the speaker unit 50 and the audio port 60. p That is, in the first embodiment, in an ideal environment where the nonlinear characteristics of the loudspeaker unit 50 and the audio port 60 are ignored, the volumetric velocity V required for the loudspeaker device 20 to radiate sound corresponding to the audio signal X is calculated. p .

[0063] Furthermore, the solution of simultaneous differential equations can be arbitrarily achieved using well-known methods such as the common state-space model. For example, for the analytical solution utilizing the state-space model, see 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.

[0064] As understood from the above description, 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 that linearizes the nonlinear parameters of the nonlinear model M (signal generation model G) related to the speaker unit 50 and the audio port 60.

[0065] like Figure 5 As illustrated, the control device 11 executes the second process S2 after performing the first process S1. The second process S2 determines the input voltage u using the signal generation model G. The processing. Specifically, the control device 11 will process the volumetric flow rate V calculated by the first processing S1. p (i.e., the target parameter) is applied to the signal generation model G, thereby calculating the volumetric flow rate V to achieve this. p Required input voltage u The signal generation model G is equivalent to the aforementioned nonlinear model M. Specifically, the signal generation model G is represented by the following equations (11a), (12a), and (13a). Furthermore, the notation " "" refers to the ideal value of a virtual environment that does not produce nonlinear distortion.

[0066] [Mathematical Expression 7]

[0067] [Signal Generation Model G]

[0068] Equation (11a) corresponds to Equation (7) mentioned above, and Equation (12a) corresponds to Equation (6) mentioned above. Additionally, Equation (13a) corresponds to Equation (1) mentioned above. As explained above, the signal generation model G (nonlinear model M) includes nonlinear parameters related to the speaker unit 50, namely the force coefficient Bl(x) and the spring constant K. ms (x) The nonlinear parameter related to the audio port 60, namely the audio impedance R. ap2 (V) p ).

[0069] Figure 6 This is a flowchart illustrating the specific process of the second process S2. If the second process S2 is started, the control device 11 will apply the volumetric flow rate V calculated from the first process S1. p Equation (11a) is applied to the signal generation model G, thereby calculating the ideal displacement x of the vibrating plate 54. (S21).

[0070] The control device 11 controls the displacement x of the vibrating plate 54 By performing differentiation, the ideal velocity v of the vibrating plate 54 can be calculated. (S22). Additionally, the control device 11 will use the volumetric flow rate V calculated through the first process S1. p Applying this to equation (5), the ideal displacement x associated with the audio port 60 is calculated. p (S23). Furthermore, in the above explanation, the volumetric flow rate V... p The target parameter was explained, but the volumetric flow rate V at the audio port 60 can also be considered. p and displacement x p The combination of these parameters can be interpreted as the target parameters. Alternatively, the volumetric flow rate V at the audio port 60 can also be considered. p Displacement x p and the displacement x of the vibrating plate 54 and speed v The combination of these parameters is interpreted as the target parameter. As illustrated above, the target parameter is, for example, the volumetric flow rate V including the acoustic port 60. p The parameters included in the performance are reflected in the performance.

[0071] The control device 11 controls the displacement x of the vibrating plate 54. and speed v The volumetric flow rate V at the audio port 60 p and displacement x p The mathematical formula (12a) applied to the signal generation model G is used to calculate the ideal input current i. (S24). Then, the control device 11 will adjust the displacement x of the vibrating plate 54. and speed v and input current i Equation (13a) is applied to the signal generation model G, from which the input voltage u is calculated. (S25). Input voltage u This is to achieve the ideal displacement x of the audio port 60. p and volumetric flow rate V p The required voltage.

[0072] If the first process S1 and the second process S2 are executed, then the control device 11 will... Figure 5 As illustrated, the signal value is set to the input voltage u. The audio signal Y is supplied from the output device 14 to the speaker device 20 (S3). That is, the output device 14 supplies the input voltage u Supply to loudspeaker device 20.

[0073] As understood from the above description, the control device 11 of the first embodiment utilizes the acoustic impedance R of the audio port 60. ap2 (V) p Depends on volumetric flow rate V p The input voltage u is determined by a nonlinear model M that simulates the relationship between the two. The signal processing unit (SMU) functions to reduce non-linear distortion caused by the audio port 60. Based on this structure, non-linear distortion caused by the audio port 60 can be reduced for the sound played from the speaker device 20.

[0074] Furthermore, in the first embodiment, the nonlinear parameters (Bl(x), K) related to the speaker unit 50 in the nonlinear model M are... ms (x)) and the nonlinear parameter (R) associated with the audio port 60 ap2 (V) p The linearized target generation model F was used to calculate the target parameters (volume flow rate V). p Therefore, in addition to reducing the nonlinear distortion caused by the audio port 60, it is also possible to reduce the nonlinear distortion caused by the speaker unit 50.

[0075] B: Implementation Method 2

[0076] The second embodiment of the present invention will be described. Furthermore, for elements in the following embodiments that function the same as those in the first embodiment, the same reference numerals as in the description of the first embodiment will be used, and detailed descriptions of each will be omitted as appropriate.

[0077] In the second embodiment, the signal generation model G (nonlinear model M) applied to the second process S2 is different from that in the first embodiment. Specifically, the signal generation model G in the second embodiment is represented by the following equations (11b), (12b), and (13b).

[0078] [Mathematical Expression 8]

[0079] [Signal Generation Model G]

[0080] Equation (11b) of the signal generation model G is the same as equation (11a) of the first embodiment. That is, the signal generation model G of the second embodiment includes the nonlinear parameter of the audio port 60, namely the audio impedance R. ap2 (V) p Furthermore, the signal generation model G in the second embodiment incorporates the nonlinear parameters (Bl(x), K) related to the speaker unit 50 in the signal generation model G of the first embodiment. ms (x)) is a linearized mathematical model. That is, in the signal generation model G, as in equations (12b) and (13b), the nonlinear parameter of the signal generation model G, namely the force coefficient Bl(x) The parameter ) is replaced by a specified constant Bl, and the nonlinear parameter of the signal generation model G is the spring constant K. ms (x) The value is replaced by the specified constant K. ms .

[0081] Control device 11 controls the target parameter (volume flow rate V) by... p The second process S2, applied to the signal generation model G described above, calculates the input voltage u. Furthermore, in the first process S1, the target parameters (volume flow rate V) are calculated using the same target generation model F as in the first embodiment. p ).

[0082] As explained above, in the second embodiment, the acoustic impedance R of the audio port 60 is also utilized. ap2 (V) p Depends on volumetric flow rate V p The signal generation model G (nonlinear model M) simulates the relationship between the input voltage u and the signal generation model G (nonlinear model M). Therefore, similar to the first embodiment, nonlinear distortion can be reduced for the playback sound of the speaker device 20.

[0083] Furthermore, the signal generation model G in the first embodiment, besides the nonlinear parameters (R0) of the audio port 60, also includes... ap2 (V) pIn addition to the above, it also includes the nonlinear parameters of the speaker unit 50 (Bl(x), K). ms (x)), therefore, in addition to the nonlinear distortion caused by the audio port 60, the nonlinear distortion caused by the speaker unit 50 can also be reduced. On the other hand, the nonlinear parameters included in the signal generation model G of the second embodiment are only the nonlinear parameters of the audio port 60 (R). ap2 (V) p Therefore, in the second embodiment, the reduction in the playback sound from the speaker device 20 is due to the nonlinear distortion caused by the audio port 60.

[0084] As explained above, from the viewpoint of further reducing nonlinear distortion caused by the speaker unit 50, the first embodiment is more effective than the second embodiment. On the other hand, in the second embodiment, the number of nonlinear parameters of the signal generation model G is reduced, thus reducing the generation of the audio signal Y (input voltage u) compared to the first embodiment. The advantages of the required processing load.

[0085] C: Third Implementation Method

[0086] 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 represented by the following equations (8b), (9b), and (10b). In the first process S1, the control device 11 uses the target generation model F exemplified below to calculate the target parameters (specifically, the volumetric flow rate V of the acoustic port 60). p ).

[0087] [Mathematical Expression 9]

[0088] [Target Generation Model F]

[0089] Equations (8b) and (9b) of the target generation model F are the same as those of equations (8a) and (9a) of the first embodiment. That is, in the target generation model F of the third embodiment, the nonlinear parameters (Bl(x), K) related to the speaker unit 50 in the nonlinear model M are... ms (x) is linearized. Specifically, in the target generation model F, the force coefficient Bl(x) of the loudspeaker unit 50 is replaced by the constant Bl, and the spring constant K of the loudspeaker unit 50 is linearized. ms (x) is replaced by the constant K ms .

[0090] On the other hand, as understood according to equation (10b), in the target generation model F of the third embodiment, the nonlinear parameter (R) related to the audio port 60 in the nonlinear model M...ap2 (V) p The target generation model F of the third embodiment is maintained as nonlinear. As understood from the above description, the target generation model F includes nonlinear parameters (R) related to the audio port 60. ap2 (V) p )).

[0091] In the third embodiment, the signal generation model G applied to the second process S2 is the same as in the first embodiment. That is, the signal generation model G in the third embodiment includes nonlinear parameters (Bl(x), K) related to the speaker unit 50. ms (x)) and the nonlinear parameter (R) associated with the audio port 60 ap2 (V) p The control device 11, similar to the first embodiment, uses the target parameters (specifically, the volumetric flow rate V) calculated by the first process S1. p The second process S2, applied to the signal generation model G, calculates the input voltage u. .

[0092] As explained above, in the third embodiment, the acoustic impedance R of the audio port 60 is also utilized. ap2 (V) p Depends on volumetric flow rate V p The signal generation model G (nonlinear model M) simulates the relationship between the input voltage u and the signal generation model G (nonlinear model M). Therefore, similar to the first embodiment, nonlinear distortion can be reduced for the playback sound of the speaker device 20.

[0093] In the target generation model F of the third embodiment, the nonlinear parameters (R) of the audio port 60 of the nonlinear model M are included. ap2 (V) p On the other hand, the nonlinear parameters (Bl(x), K) related to the speaker unit 50 in the nonlinear model M are... ms (x)) linearization. Therefore, in the third embodiment, it is possible to reduce the nonlinear distortion caused by the speaker unit 50 from the playback sound of the speaker device 20.

[0094] However, in the target generation model F, the nonlinear parameters of the audio port 60 (audio impedance R) are included. ap2 (V) p In a linearized structure (e.g., the first embodiment), the displacement x of the diaphragm 54 of the speaker unit 50 It might be overestimated. The displacement x of the vibrating plate 54. An excessively large evaluation result may lead to insufficient reduction of nonlinear distortions such as high-order harmonic distortion of the played sound. In the third embodiment, the target generation model F includes nonlinear parameters of the audio port, thus suppressing the displacement x of the diaphragm 54 during distortion reduction processing. It was overrated. Therefore, it has the advantage of being able to reduce nonlinear distortion caused by the speaker unit 50 in the playback sound of the speaker device 20 with high precision.

[0095] D: Fourth Implementation Method

[0096] In the fourth embodiment, the signal generation model G (nonlinear model M) applied to the second process S2 is different from that in the first embodiment. Specifically, the signal generation model G in the fourth embodiment is represented by the following equations (11c) to (13c).

[0097] [Mathematical Expression 10]

[0098] [Signal Generation Model G]

[0099] Equations (12c) and (13c) of the signal generation model G are the same as those (12a) and (13a) of the first embodiment. In equation (11c) of the signal generation model G in the third embodiment, the acoustic compliance C, which is set as a constant in the first embodiment, is... af The change is to a nonlinear parameter (acoustic compliance C) that varies nonlinearly based on the displacement x of the diaphragm 54. af (x)). Acoustic compliance C af (x) is the acoustic compliance of the internal space 42 of the frame 40. Furthermore, the acoustic compliance C... af (x) is an example of the "third nonlinear parameter".

[0100] Control device 11 controls the target parameter (volume flow rate V) by... p The second process S2, applied to the signal generation model G described above, calculates the input voltage u. Furthermore, in the first process S1, the target parameters (volume flow rate V) are calculated using the same target generation model F as that expressed in the third embodiment by equations (8b) to (10b). p That is, the target generation model F of the fourth embodiment includes the nonlinear parameters (R) of the audio port 60. ap2 (V) p ), and the nonlinear parameters (Bl(x), K) of speaker unit 50 ms (x)) and the nonlinear parameter (C) related to the acoustic compliance of the interior space 42. af (x) linearization.

[0101] As explained above, in the fourth embodiment, the acoustic impedance R of the audio port 60 is also utilized. ap2 (V) p Depends on volumetric flow rate V p The signal generation model G (nonlinear model M) simulates the relationship between the input voltage u and the signal generation model G (nonlinear model M). Therefore, similar to the first embodiment, nonlinear distortion can be reduced for the playback sound of the speaker device 20.

[0102] Furthermore, in the fourth embodiment, the nonlinear parameter related to the internal space 42 of the frame 40, namely the acoustic compliance C, is... af (x) is included in the signal generation model G, and the acoustic compliance C is included in the target generation model F. af (x) Linearization. Therefore, according to the fourth embodiment, in addition to reducing the nonlinear distortion caused by the speaker unit 50 in the same way as in the third embodiment, it is also possible to reduce the distortion caused by the acoustic compliance C in the playback sound. af (x) causes nonlinear distortion.

[0103] E: Fifth Implementation

[0104] Figure 7 This is a flowchart of the distortion reduction process in the fifth embodiment. If the ideal volumetric flow rate V at the audio port 60 relative to the audio signal X is calculated through the first process S1... p Then the control device 11 will control the volumetric flow rate V p The limitation is within a specified range (hereinafter referred to as the "limited range") (Sa). The limited range is the range from the minimum value Vmin to the maximum value Vmax. The minimum value Vmin and the maximum value Vmax are set experimentally or statistically to suppress high-frequency noise components that cannot be reduced in the distortion reduction process of the first embodiment.

[0105] Specifically, the control device 11 calculates the volumetric flow rate V through the first process S1. p When the volumetric flow rate V is less than the minimum value Vmin, p Set to the minimum value Vmin. On the other hand, at the volumetric flow rate V... p When the flow rate is greater than the maximum value Vmax, the control device 11 will reduce the volumetric flow rate V. p Set to the maximum value Vmax. The volumetric flow rate V after applying the constraint. p The second process S2 is the same as the methods described above.

[0106] In the fifth embodiment, the same effect as in the first embodiment can be achieved. Furthermore, in the fifth embodiment, the volumetric flow rate V applied to the nonlinear model M... pBeing limited to a certain range, it is possible to suppress the energy of nonlinear distortion in the sound played by the speaker device 20 that is difficult to sufficiently reduce through the nonlinear model M.

[0107] F: Implementation Method 6

[0108] Figure 8 This is a schematic diagram of the loudspeaker system 100 according to the sixth embodiment. (As shown) Figure 8 As illustrated, the speaker system 100 of the sixth embodiment is a method in which a sensor 70 is added to the first embodiment.

[0109] Sensor 70 measures the volumetric flow rate V inside the audio port 60. p A flow rate sensor for measurement. For example, as sensor 70, a flow rate meter such as an LDV (Laser Doppler Velocity Meter) is used to optically detect the flow of air within the acoustic port 60.

[0110] Figure 9 This is a flowchart of the distortion reduction process in the sixth embodiment. If distortion reduction processing begins, the control device 11 (signal processing unit) acquires the measured value (Sb) from the sensor 70. The control device 11 uses the measured value from the sensor 70 as the volumetric flow rate V of the nonlinear model M. p The second processing step S2 determines the input voltage u. Specifically, the non-linear acoustic impedance R of the audio port 60 ap2 (V) p The value is set based on the measured value of sensor 70.

[0111] The specific process of the second process S2 (S21-S25) is the same as that of the first embodiment. Therefore, the sixth embodiment also achieves the same effect as the first embodiment. In the sixth embodiment, especially in determining the input voltage u... The sensor 70 inside the audio port 60 detects the volumetric flow rate V. p The result is that the actual sound wave action at the audio port 60 determines the input voltage u. The time is also taken into account. Therefore, the input voltage u is determined by calculation. Compared to using all numerical values ​​at the time, it can reduce nonlinear distortion caused by the audio port 60 with high precision.

[0112] G: Variation

[0113] The following examples illustrate specific variations of the methods shown above. Two or more methods selected from the examples below can be appropriately combined without contradiction.

[0114] (1) In the fifth embodiment, by using the volumetric flow rate V p While the nonlinear distortion is suppressed by limiting the range, the structure and processing used to suppress the energy that is difficult to sufficiently reduce in the nonlinear model M are not limited to the examples above. For example, nonlinear distortion can also be reduced by signal processing for the audio signal X. Specifically, the control device 11 performs signal processing on the audio signal X to suppress the high-frequency audio components that are difficult to sufficiently reduce in the nonlinear model M. The signal processing is, for example, equalization processing that adjusts the intensity of each frequency band of the audio signal X. The control device 11 determines the input voltage u by applying the calculations (Sa1 to Sa5) of the nonlinear model M of the signal-processed audio signal X.

[0115] (2) In the sixth embodiment, a flow meter for measuring volumetric flow velocity was exemplified as sensor 70, but the type of sensor 70 is not limited to the example above. For example, a pressure sensor (e.g., a MEMS sensor) utilizing a detection element such as a piezoelectric element or electrostatic capacitance can be used as sensor 70 inside the audio port 60. The control device 11 calculates the volumetric flow velocity V based on the pressure measured by sensor 70. p By applying this volumetric flow rate V p The calculation determines the input voltage u.

[0116] Furthermore, in the sixth embodiment, a sensor 70 is shown installed inside the audio port 60, but this installation is not mandatory. For example, the sensor 70 can be installed near the audio port 60. For example, a sensor 70 for picking up radiated sound can be installed near the outer opening 61 of the audio port 60. For example, an external microphone that detects ambient sound pressure, such as a moving-coil microphone or a condenser microphone, can be used as the sensor 70. The control device 11 calculates the volumetric flow velocity V based on the sound pressure detected by the sensor 70. p By applying this volumetric flow rate V p The calculation determines the input voltage u.

[0117] As understood from the above description, sensor 70 is generally described as detecting acoustic characteristics of the interior or vicinity of acoustic port 60. In addition to the volumetric flow rate illustrated in the sixth embodiment, acoustic characteristics also include pressure or sound pressure illustrated in this variation.

[0118] (3) Among the aforementioned methods, a bass-reflex type loudspeaker device 20 with a bass reflex port as an audio port 60 is shown as an example, but the form (casing form) of the loudspeaker device 20 is not limited to the above examples.

[0119] For example, the aforementioned methods can be similarly applied to, for example... Figure 10 As illustrated, sound radiated to the front of the speaker unit 50 is radiated through the speaker port 60 in a Kelton-type speaker device 20. Furthermore, the aforementioned methods can also be similarly applied to... Figure 11 The illustrated bandpass speaker device 20 has an audio port 60 for sound radiating to the front of the speaker unit 50 and an audio port 60 for sound radiating to the rear.

[0120] As understood from the above examples, the audio port 60 of the present invention is generally described as a port for sound radiation using the Helmholtz resonance of the radiated sound from the loudspeaker unit 50, and the port for which sound radiated from the loudspeaker unit 50 passes through is not limited in the present invention.

[0121] (4) In the sixth embodiment, the volumetric flow rate V is shown as an example for distortion reduction processing. p While the method utilizes the measurements from sensor 70, it is not limited to the examples described above. For instance, it is also conceivable to use the measurements from sensor 70 to pre-identify the volumetric flow rate V. p and acoustic impedance R ap2 (V) p The way in which they relate to each other.

[0122] (5) The method of determining the input voltage u using the nonlinear model M is not limited to the methods exemplified in the foregoing. For the calculation of the input voltage u using the nonlinear model M, any known technique may be used.

[0123] (6) Among the aforementioned embodiments, a speaker system 100 in which the signal processing system 10 and the speaker device 20 are separately configured is shown. However, the aforementioned embodiments can also be applied to a speaker system 100 (active speaker) in which the signal processing system 10 is disposed inside the housing 40. In addition, the speaker system 100 can be implemented not only as a fixed system, but also as a portable information device such as a smartphone, tablet terminal or personal computer.

[0124] (7) The functions of the signal processing system 10 illustrated above are realized, as described above, through the coordinated operation of one or more processors constituting the control device 11 and the program stored in the storage device 12. The program involved in this invention can be provided and installed in a computer in the form of a computer-readable recording medium. The recording medium is, for example, a non-transitory recording medium, preferably an optical recording medium (optical disc) such as a CD-ROM, and also includes any known form of recording medium such as a semiconductor recording medium or a magnetic recording medium. Furthermore, as a non-transitory recording medium, any recording medium other than a transient propagating signal may be included, and volatile recording media may also be excluded. In addition, in a structure in which a transmission device transmits a program via a communication network, the storage medium for storing the program in that transmission device is equivalent to the aforementioned non-transitory recording medium.

[0125] (8) The use of “nth” (where n is a natural number) in this application is merely a convenient identifier (label) for distinguishing the forms of the elements in terms of expression, and has no substantive meaning. Therefore, the position or order of the elements should not be interpreted restrictively based solely on the expression “nth”.

[0126] H: Appendix

[0127] Based on the examples above, for instance, understand the following structure.

[0128] One aspect of the present invention (Aspect 1) involves a loudspeaker system that utilizes a nonlinear model simulating the relationship between the acoustic impedance of an acoustic port used for sound radiation based on Helmholtz resonance and the volumetric flow velocity of that acoustic port. Based on target parameters including the volumetric flow velocity of the acoustic port, an input voltage is determined and supplied to the loudspeaker device. In this aspect, the input voltage for the loudspeaker device is determined using a nonlinear model simulating the relationship between the acoustic impedance of the acoustic port and the volumetric flow velocity. Therefore, nonlinear distortion can be reduced for the sound played by the loudspeaker device.

[0129] In a specific example of Method 1 (Method 2), the nonlinear model includes a first nonlinear parameter representing the dependence of the volumetric flow rate on the acoustic impedance. Further, a target parameter is generated using a target generation model that linearizes the first nonlinear parameter of the nonlinear model. In the above methods, the target parameter is generated using a target generation model that linearizes the first nonlinear parameter, and the input voltage is determined based on this target parameter. Therefore, it is possible to reduce nonlinear distortion caused by the audio port for the playback sound of the speaker device.

[0130] Nonlinear models simulate the linear or nonlinear relationship between the displacement (and thus the velocity or acceleration) of the diaphragm of a loudspeaker unit and the various characteristics such as electromagnetic force, mechanical impedance, or elastic force acting on the loudspeaker unit.

[0131] In a specific example of Method 2 (Method 3), the nonlinear model further includes a second nonlinear parameter related to the speaker unit of the speaker device, and the target generation model is a model that linearizes the first and second nonlinear parameters of the nonlinear model. In the above methods, a target parameter is generated using a target generation model that linearizes both the first and second nonlinear parameters, and the input voltage is determined based on this target parameter. Therefore, in addition to the nonlinear distortion caused by the audio port, the nonlinear distortion caused by the speaker unit can also be reduced.

[0132] In a specific example of Method 1 (Method 4), the nonlinear model includes: a first nonlinear parameter representing the dependence of the volumetric flow rate on the acoustic impedance; and a second nonlinear parameter related to the speaker unit of the speaker device. The nonlinear model further generates the target parameter using a target generation model that includes the first nonlinear parameter and linearizes the second nonlinear parameter. In the above methods, the target parameter is generated using a target generation model that includes the first nonlinear parameter and linearizes the second nonlinear parameter, and the input voltage is determined based on the target parameter using the nonlinear model. Therefore, it is possible to reduce nonlinear distortion caused by the speaker unit for the playback sound of the speaker device.

[0133] In a specific example of Method 1 (Method 5), the nonlinear model includes: a first nonlinear parameter representing the dependence of the volumetric flow rate on the acoustic impedance; a second nonlinear parameter related to the speaker unit of the speaker device; and a third nonlinear parameter related to the acoustic compliance of the internal space of the speaker device. The nonlinear model further generates the target parameter using a target generation model that includes the first nonlinear parameter of the nonlinear model and linearizes the second and third nonlinear parameters. In the above methods, the target parameter is generated using a target generation model that includes the first nonlinear parameter and linearizes the second and third nonlinear parameters, and the input voltage is determined based on the target parameter using the nonlinear model. Therefore, it is possible to reduce nonlinear distortion caused by the speaker unit and acoustic compliance for the playback sound of the speaker device.

[0134] In a specific example (method 6) of any of methods 1 to 5, the volumetric flow rate is further limited to a specified range. According to the above methods, by limiting the volumetric flow rate applied to the nonlinear model to a specified range, it is possible to suppress the generation of noise caused by the audio port in the playback sound of the speaker device, which is difficult to suppress using a nonlinear model.

[0135] In a specific example (method 7) of any of methods 1 to 6, the detection result of a sensor that detects the acoustic characteristics inside or near the speaker port is obtained, and the input voltage is determined by calculation applying the detection result. According to the above method, the result of the sensor detecting the acoustic characteristics inside or near the speaker port is applied to the signal processing unit when determining the input voltage. That is, the actual sound wave movement of the speaker port is taken into account when the signal processing unit determines the input voltage. Therefore, compared to the method of determining all the values ​​used when determining the input voltage through calculation, nonlinear distortion can be reduced with higher accuracy.

[0136] "Acoustic characteristics" are variables applied to nonlinear models. Specifically, characteristics such as flow velocity (volume flow velocity) or pressure inside the acoustic port are detected by sensors as acoustic characteristics.

[0137] "Near the audio port" is, for example, the space on the input side of the audio port (i.e., the inside of the speaker unit's housing) or the space on the output side of the audio port (i.e., the outside of the speaker unit's housing).

[0138] "Calculations that apply the detection results" include the following two: (1) A method of calibrating the nonlinear function of a nonlinear model (e.g., the relationship between volumetric flow rate and acoustic impedance) using sensor detection results. (2) The way to control (e.g., real-time feedback control) the values ​​of variables in a nonlinear model based on the sensor's detection results.

[0139] One aspect of the present invention relates to a signal processing system comprising: a signal processing unit that determines an input voltage based on target parameters including the volumetric flow velocity of an acoustic port, which is used to simulate the relationship between the acoustic impedance of an acoustic port for acoustic radiation based on Helmholtz resonance and the volumetric flow velocity of that acoustic port using a nonlinear model; and a voltage supply unit that supplies the input voltage to a loudspeaker device. In the above embodiment, the input voltage for the loudspeaker device is determined using a nonlinear model simulating the relationship between the acoustic impedance of the acoustic port and the volumetric flow velocity. Therefore, nonlinear distortion can be reduced for the sound played by the loudspeaker device. Furthermore, the various embodiments (embodiments 2 to 6) described above with respect to the signal processing method of the present invention are also applicable to the signal processing system of the present invention.

[0140] One aspect of the present invention relates to a loudspeaker system having a loudspeaker unit, an acoustic port, and a signal processing system. The acoustic port is used for acoustic radiation utilizing Helmholtz resonance of radiated sound from the loudspeaker unit. The signal processing system includes: a signal processing unit that determines an input voltage based on target parameters, including the volumetric flow rate of the acoustic port, using a nonlinear model simulating a relationship dependent on the volumetric flow rate of the acoustic port; and a voltage supply unit that supplies the input voltage to the loudspeaker device. In this embodiment, the input voltage for the loudspeaker device is determined using a nonlinear model simulating a relationship between the acoustic impedance of the acoustic port and the volumetric flow rate. Therefore, nonlinear distortion can be reduced for the sound played by the loudspeaker device.

[0141] Explanation of the label

[0142] 100… loudspeaker system, 10… signal processing system, 11… control device, 12… storage device, 13… input device, 14… output device, 20… loudspeaker assembly, 30… signal supply device, 40… frame, 41… plate, 50… loudspeaker unit, 51… frame, 52… magnet, 53… voice coil, 54… diaphragm, 55… edge, 56… damper, 60… audio port, 70… sensor.

Claims

1. A signal processing method implemented by a computer system, A nonlinear model is used to simulate the relationship between the acoustic impedance of an acoustic port based on Helmholtz resonance and the volumetric flow velocity at that port. The input voltage is determined based on target parameters, including the volumetric flow velocity at the acoustic port. The input voltage is supplied to the speaker device.

2. The signal processing method according to claim 1, wherein, The nonlinear model includes a first nonlinear parameter, which represents the dependence of the acoustic impedance on the volumetric flow rate. Furthermore, the target parameters are generated using a target generation model that linearizes the first nonlinear parameter of the nonlinear model.

3. The signal processing method according to claim 2, wherein, The nonlinear model also includes a second nonlinear parameter related to the speaker unit of the speaker device. The target generation model is a model that linearizes the first nonlinear parameter and the second nonlinear parameter of the nonlinear model.

4. The signal processing method according to claim 1, wherein, The nonlinear model includes: a first nonlinear parameter representing the dependence of the acoustic impedance on the volumetric flow rate; and a second nonlinear parameter related to the speaker unit of the loudspeaker device. Furthermore, the target parameters are generated using a target generation model that incorporates the first nonlinear parameter of the nonlinear model and linearizes the second nonlinear parameter.

5. The signal processing method according to claim 1, wherein, The nonlinear model includes: a first nonlinear parameter representing the dependence of the acoustic impedance on the volumetric flow rate; a second nonlinear parameter related to the loudspeaker unit of the loudspeaker device; and a third nonlinear parameter related to the acoustic compliance of the internal space of the loudspeaker device. Furthermore, the target parameters are generated using a target generation model that includes the first nonlinear parameter of the nonlinear model and linearizes the second and third nonlinear parameters.

6. The signal processing method according to claim 1, wherein, Furthermore, the volumetric flow rate is limited to a specified range.

7. The signal processing method according to claim 1, wherein, Furthermore, the sensor's detection results are obtained, and the input voltage is determined by applying the calculations based on these detection results. The sensor detects the acoustic characteristics inside or near the audio port.

8. A signal processing system, comprising: The signal processing unit, using a nonlinear model simulating the relationship between the acoustic impedance of an acoustic port based on Helmholtz resonance for acoustic radiation and the volumetric flow velocity of that acoustic port, determines the input voltage based on target parameters including the volumetric flow velocity of the acoustic port; and The voltage supply unit supplies the input voltage to the speaker device.

9. The signal processing system according to claim 8, wherein, The nonlinear model includes a first nonlinear parameter, which represents the dependence of the acoustic impedance on the volumetric flow rate. The signal processing system further includes a target generation unit that generates the target parameters using a target generation model that linearizes the first nonlinear parameter of the nonlinear model.

10. The signal processing system according to claim 9, wherein, The nonlinear model also includes a second nonlinear parameter related to the speaker unit of the speaker device. The target generation model is a model that linearizes the first nonlinear parameter and the second nonlinear parameter of the nonlinear model.

11. The signal processing system according to claim 8, wherein, The nonlinear model includes: a first nonlinear parameter representing the dependence of the acoustic impedance on the volumetric flow rate; and a second nonlinear parameter related to the speaker unit of the loudspeaker device. The signal processing system further includes a target generation unit that generates the target parameters using a target generation model that includes the first nonlinear parameter of the nonlinear model and linearizes the second nonlinear parameter.

12. The signal processing system according to claim 8, wherein, The nonlinear model includes: a first nonlinear parameter representing the dependence of the acoustic impedance on the volumetric flow rate; a second nonlinear parameter related to the loudspeaker unit of the loudspeaker device; and a third nonlinear parameter related to the acoustic compliance of the internal space of the loudspeaker device. The signal processing system further includes a target generation unit that generates the target parameters using a target generation model that includes the first nonlinear parameter of the nonlinear model and linearizes the second and third nonlinear parameters.

13. A loudspeaker system comprising: loudspeaker unit; The acoustic port for acoustic radiation is based on the Helmholtz resonance of the radiated sound from the speaker unit; and Signal processing system The signal processing system includes: The signal processing unit, using a nonlinear model simulating the relationship between the volumetric flow rate and the acoustic port, determines the input voltage based on target parameters including the volumetric flow rate of the acoustic port; and The voltage supply unit supplies the input voltage to the speaker device.

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