Acoustic characteristic calculation device, acoustic characteristic calculation method, and program

Abstract

Provided is a technique for precisely measuring the acoustic characteristic of a parametric array. This acoustic characteristic calculating device comprises: a first calculation unit that calculates a complex amplitude d of an optical phase at a frequency fd from a variation amount φs of the optical phase due to a demodulation sound S; a second calculation unit that uses qdiff(ξ',η') as a function defined by using the Gaussian beam expansion method and calculates a function value qdiff(ξ,η) at a point X and a line integral value ∫Lqdiff(ξ',η)dξ' of a function qdiff(ξ',η) along an optical path L; and a third calculation unit that uses the complex amplitude d, the function value qdiff(ξ,η) and the line integral value ∫Lqdiff(ξ',η)dξ' to calculate the complex amplitude p of the demodulation sound at the frequency fd at the point X.

Description

[Technical field]

[0001] The present invention relates to a technique for measuring the acoustic characteristics of a parametric array. [Background technology]

[0002] A parametric array is a nonlinear acoustic phenomenon in which sound is generated in a space due to the nonlinearity of a medium (see Non-Patent Document 1). More specifically, a parametric array is a phenomenon in which, when sounds with two different frequencies are propagated, a sound with a frequency represented by the difference between the two frequencies is generated nonlinearly. Parametric array speakers, which utilize this phenomenon to reproduce audible sounds, are used for reproducing sound in limited spaces, spatial audio expression technology, noise control, etc.

[0003] It is known that when a microphone is used to measure audible sounds (hereafter referred to as demodulated sounds) generated by a parametric array, noise called onomatopoeia is generated. Onomatopoeia is nonlinear noise in a sound receiving system including a microphone, which is generated by large amplitude ultrasonic waves in a parametric array. In principle, the frequency of onomatopoeia matches that of demodulated sounds, so the demodulated sounds being measured and onomatopoeia are superimposed and detected in a form that makes them indistinguishable. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Woon-Seng Gan, Jun Yang, and Tomoo Kamakura, “A review of parametric acoustic array in air,” Applied Acoustics, Vol.73, Issue 12, pp.1211-1219, 2012. Summary of the Invention [Problem to be solved by the invention]

[0005] In order to measure the acoustic characteristics of the demodulated sound, a method of removing onomatopoeia can be considered, using an acoustic filter that attenuates the ultrasonic components that enter the microphone, which cause onomatopoeia, in space and transmits the demodulated sound components. However, the effect of removing onomatopoeia using an acoustic filter is limited, and it is not possible to completely remove onomatopoeia. In other words, it is not possible to accurately measure the acoustic characteristics of the demodulated sound.

[0006] Therefore, an object of the present invention is to provide a technique for accurately measuring the acoustic characteristics of a parametric array. [Means for solving the problem]

[0007] In one aspect of the present invention, L is an optical path in a sound field measuring device that measures a phase change of light caused by an audible sound (hereinafter referred to as demodulated sound) S generated by a parametric array using a transducer that is a substantially circular sound source, C is a point where the optical path L intersects with a straight line that passes through the transducer and is parallel to the propagation direction of the demodulated sound S, X is a point on the optical path L that is a distance x from point C, z is the distance from the transducer to the optical path L, a is the radius of the transducer, and f is the distance from the transducer to the optical path L. d = |f1-f2| (where f1 is the carrier frequency and f2 is the sideband frequency) is the frequency of the demodulated sound S, c is the speed of sound, and the amount of change in the optical phase due to the demodulated sound S is φ s Then, frequency f d A first calculation unit for calculating a complex amplitude d of an optical phase at q diff Let (ξ',η') be a function defined using the Gaussian beam expansion method, and the function value q diff (ξ,η)(where ξ=x / a, η=2z / ka 2 , k1=f1 / c, k2=f2 / c, k=(k1+k2) / 2) and the function q along the light path L diff Line integral value of (ξ',η) ∫ L q diff A second calculation unit for calculating (ξ', η)dξ' and a frequency f d The complex amplitude d of the optical phase at point X and the function value q at point X diff (ξ,η) and function q along the light path L diff Line integral value of (ξ',η) ∫ L qdiff Using (ξ',η)dξ', the frequency f at point X is d and a third calculation unit that calculates a complex amplitude p of the demodulated sound. Effect of the Invention

[0008] According to the present invention, it is possible to accurately measure the acoustic characteristics of a parametric array. [Brief description of the drawings]

[0009] [Figure 1] FIG. 8 is a block diagram showing the configuration of a sound field measuring device 800. [Diagram 2] FIG. 1 is a block diagram showing a configuration of an acoustic characteristic calculation device 100. [Diagram 3] 4 is a flowchart showing the operation of the acoustic characteristic calculation device 100. [Figure 4] FIG. 2 is a diagram showing the position of point X. [Diagram 5] FIG. 2 is a diagram illustrating an example of a functional configuration of a computer that realizes each device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described in detail. Note that components having the same functions are given the same reference numbers and duplicated explanations will be omitted.

[0011] Before describing each embodiment, the notation used in this specification will be described.

[0012] ^ (caret) represents a superscript. For example, x y^z Yes z is a superscript to x, and x y^z Yes z is a subscript to x. Also, _ (underscore) represents a subscript. For example, x y_z Yes z is a superscript to x, and x y_z Yes zis a subscript on x.

[0013] The superscripts "^" and "~" such as ^x and ~x for a certain letter x should actually be written directly above the "x", but due to the constraints of the description in the specification, they are written as ^x and ~x. <Technical background> In an embodiment of the present invention, a measurement that, in principle, does not produce onomatopoeia is realized by measuring a parametric array in a non-contact manner using optical sound measurement technology (see Reference Non-Patent Document 1). As explained in the [Background Art], onomatopoeia is caused by the nonlinear response of the diaphragm of a microphone. Since there is no equivalent to a diaphragm in optical sound measurement technology, in principle, onomatopoeia is not produced. (Reference Non-Patent Document 1: Kenji Ishikawa, Kohei Yatabe, Nachanant Chitanont, Yusuke Ikeda, Yasuhiro Oikawa, Takashi Onuma, Hayato Niwa, and Minoru Yoshii, “High-speed imaging of sound using parallel phase-shifting interferometry,” Optics Express, Vol. 24, Issue 12, pp. 12922-12932, 2016.) First, a method for measuring a sound field using the change in the refractive index of a medium caused by sound, known as the acousto-optic effect, will be described. According to the acousto-optic effect, the amount of change in the optical phase caused by sound, φ s is expressed by the following equation.

[0014]

number

[0015] Where k lis the wave number of light, n0 is the refractive index of air in the steady state, P0 is the atmospheric pressure in the steady state, and γ is the specific heat ratio of air. The integral in equation (1) represents the line integral of the sound pressure p along the light propagation path (hereinafter referred to as the light path) L. Here, the x-axis is defined to be parallel to the light path L. Also, the sound pressure p is the sound pressure at a certain time. Note that k l , n0, P0, and γ are constants determined by the physical conditions at the time of measurement.

[0016] As can be seen from equation (1), the amount of change in optical phase due to sound, φ s is not a quantity that represents the sound pressure at a point in space, but is a quantity that is proportional to the line integral value of the sound pressure along the optical path L.

[0017] In the embodiment of the present invention, the Gaussian Beam Expansion (GBE) method is used to measure the change in the optical phase, φ s The complex amplitude p of the demodulated sound at a point in space is calculated from . Specifically, the carrier wave and sideband waves that cause the demodulated sound are each approximated by the sum of Gaussian beams. Here, a Gaussian beam is a wave whose complex amplitude, obtained by Fourier transforming the sound pressure over a certain time interval, is expressed by a Gaussian function. In addition, waves generated from a sound source with piston motion can be approximated as the sum of Gaussian beams.

[0018] In the following, a circular sound source, such as a parametric array speaker configured by arranging multiple microphones in a circle, is assumed as the sound source that generates a parametric array. The sound source does not have to be a perfect circle, but may be an approximately circular sound source. The waves generated from a sound source with piston motion that is handled in the embodiment of the present invention are generated when all the microphones that make up the parametric array speaker emit the same sound.

[0019] The frequency f produced by the interaction of the carrier wave of frequency f1 and the sideband wave of frequency f2 dLet p be the complex amplitude of the demodulated sound of |f1-f2|. According to Reference Non-Patent Document 2, the complex amplitude p of the demodulated sound generated by a circular sound source can be expressed as follows using the Gaussian beam expansion method.

[0020]

number

[0021] where ξ=x / a, η=2z / ka 2 , k=(k1+k2) / 2, k d =k1-k2, where a is the radius of the sound source, k1 is the wave number of the carrier wave, k2 is the wave number of the sideband wave, and p0 (1) is the amplitude of the carrier, p0 (2) is the amplitude of the sideband, β is the nonlinear coefficient of air, ρ is the density of air, c is the speed of sound, and i is the imaginary unit. The z-axis is defined to be parallel to the propagation direction of the demodulated sound. The wave numbers k1 and k2 can be expressed as k1=f1 / c and k2=f2 / c, respectively. Therefore, k d =f d / c.

[0022] Also, q diff (ξ, η) is a term that represents the beam shape of the demodulated sound,

[0023]

number

[0024]

number

[0025] Here, m is a parameter representing the Gaussian beam used to approximate the carrier wave, and m' is a parameter representing the Gaussian beam used to approximate the sideband wave. As can be seen from equation (3), the carrier wave and the sideband wave are each approximated using 10 Gaussian beams. This is based on the fact that it is empirically known that sufficient approximation accuracy can be obtained by using 10 Gaussian beams. In addition, A m , A m’ (m=1, …, 10, m'=1, …, 10) are the coefficients of the Gaussian beam. For example, A in Table 1 of Reference Non-Patent Document 3 n The value of r1 can be used. E1(x) is the exponential integral function. (mm’) , r2 (mm’) , s1 (mm’) , s2 (mm’) (m=1, ..., 10, m'=1, ..., 10) are defined by the following equations (see Reference Non-Patent Document 2).

[0026]

number

[0027]

number

[0028]

number

[0029]

number

[0030]

number

[0031]

number

[0032] where k a =k1 / k, k b =-k2 / k. Also, B m (1) , B m’ (2) (m=1, ..., 10, m'=1, ..., 10) is a predetermined constant. For example, B in Table 1 of Reference Non-Patent Document 3 n The value of i / δ can be used. δ represents the normalized radius of curvature of the sound source. If the sound source is planar, δ becomes infinite and the term i / δ becomes zero.

[0033] In other words, equation (2) represents the complex amplitude of the demodulated sound generated by the interaction between the carrier wave and the sideband wave when the carrier wave and the sideband wave are approximated by the sum of Gaussian beams. (Reference Non-Patent Document 2: Desheng Ding, “A simplified algorithm for the second-order sound fields,” The Journal of Acoustical Society of America, Vol. 108, Issue 6, pp. 2759-2764, 2000.) (Reference Non-Patent Document 3: JJ Wen and MA Breazeale, “A diffraction beam field expressed as the superposition of Gaussian beams,” The Journal of Acoustical Society of America, Vol. 83, Issue 5, pp. 1752-1756, 1988.) By integrating equation (2) along the optical path L, the frequency f d The complex amplitude d of the optical phase at

[0034]

number

[0035] However, C ao =k l (n0-1) / γP0.

[0036] The complex amplitude d in equation (4) is the change in the optical phase φ s is the frequency spectrum of the optical phase change φ s is Fourier transformed at a certain time interval to obtain a predetermined frequency f d This corresponds to the components extracted from the above.

[0037] From equations (2) and (4), the frequency f d The complex amplitude p of the demodulated sound can be calculated by the following formula:

[0038]

number

[0039] The complex amplitude d in equation (5) is the change in the optical phase obtained as the measurement result φ s The value obtained from C ao is a value determined by the physical conditions at the time of measurement. Also, the function q diff The value of and its integral value can be calculated by determining the number of Gaussian beams used to approximate the carrier wave and the sideband wave, respectively, and setting the radius a and the radius of curvature δ of the sound source.

[0040] As can be seen from the above, by assuming that the carrier wave and the sideband wave can be expressed as the sum of Gaussian beams, the complex amplitude p of the demodulated sound can be defined as a function of position and wave number (see equation (2)). The complex amplitude p of the demodulated sound at a point in space is expressed as the change in the optical phase φ obtained as the measurement result. s can be approximately calculated from

[0041] By using optical sound measurement technology to realize measurements that are theoretically free of onomatopoeia, it is possible to accurately measure the acoustic characteristics of a parametric array. Since the effects of onomatopoeia are particularly prominent near the transducer, it has been difficult to measure the acoustic characteristics of a parametric array near the transducer. Measuring the sound field using the above method makes it possible to measure the sound source radiation characteristics in detail, so the above method is useful for inspecting transducers and developing high performance. In addition, the above method also makes it possible to accurately measure the sound pressure level and quality of reproduced sound in situations where listening is required near the parametric speaker due to restrictions on the installation location. First Embodiment The acoustic characteristic calculation device 100 receives as input the amount of change in optical phase due to sound, which is the output of a sound field measuring device 800 that uses light to measure a sound field, and outputs the complex amplitude of a demodulated sound at a point in space. First, the sound field measuring device 800 will be described with reference to FIG.

[0042] FIG. 1 is a diagram showing an example of the configuration of a sound field measuring device 800. As shown in FIG. 1, the sound field measuring device 800 includes a transducer 810, a light source 820, and a phase change measuring device 830. Here, the transducer 810 is a substantially circular sound source that generates demodulated sound by generating a parametric array, and can be configured as a parametric array speaker configured by arranging a plurality of microphones in a circle, for example. In addition, a component including the light source 820 and the phase change measuring device 830 is called an optical measurement device. The optical measurement device measures the amount of change in optical phase caused by the demodulated sound used to obtain the acoustic characteristics of the parametric array. As the optical measurement device, any device that can measure the amount of change in optical phase may be used, and for example, the devices described in Reference Non-Patent Document 1 and Reference Non-Patent Document 4 can be used. Note that the optical path L is set so as to be perpendicular to the propagation direction of the ultrasonic wave (radiated sound) emitted from the transducer 810, as shown in FIG. 1. (Reference non-patent document 4: A. Torras-Rosell, S. Barrera-Figueroa, and F. Jacobsen, “Sound field reconstruction using acousto optic tomography,” The Journal of Acoustical Society of America, Vol. 131, Issue 5, pp. 3786-3793, 2012.) The operation of sound field measuring device 800 will be described below. First, transducer 810 generates demodulated sound and generates a sound field. Next, light source 820 emits light. The light emitted from light source 820 is phase-modulated by the sound as it passes through the sound field. The light phase-modulated by the sound is input to phase change measuring device 830, which causes a change in the amount of light depending on the amount of phase modulation, and phase change measuring device 830 outputs the distribution of this changed light amount, i.e., the amount of change in the optical phase caused by the demodulated sound.

[0043] The acoustic characteristic calculation device 100 will be described below with reference to Figs. 2 and 3. Fig. 2 is a block diagram showing the configuration of the acoustic characteristic calculation device 100. Fig. 3 is a flowchart showing the operation of the acoustic characteristic calculation device 100. As shown in Fig. 2, the acoustic characteristic calculation device 100 includes a first calculation unit 110, a second calculation unit 120, a third calculation unit 130, and a recording unit 190. The recording unit 190 is a component that appropriately records information necessary for the processing of the acoustic characteristic calculation device 100. Note that an apparatus including the sound field measuring device 800 and the acoustic characteristic calculation device 100 is referred to as an acoustic characteristic measurement device 1000.

[0044] In the following, L is the optical path in the sound field measuring device 800 that measures the phase change of light due to demodulated sound S generated by a parametric array using a transducer 810 that is a substantially circular sound source, C is the point where the optical path L intersects with a line that passes through the transducer 810 and is parallel to the propagation direction of the demodulated sound S, X is a point on the optical path L that is a distance x from point C, z is the distance from the transducer 810 to the optical path L, a is the radius of the transducer 810, and f is the distance from the transducer 810 to the optical path L. d=|f1-f2| (where f1 is the frequency of the carrier wave, and f2 is the frequency of the sideband wave) is the frequency of the demodulated sound S, and c is the speed of sound. FIG.

[0045] The operation of the acoustic characteristic calculation device 100 will be described with reference to FIG.

[0046] In S110, the first calculation unit 110 calculates the amount of change φ in the optical phase due to the demodulated sound S that is the output of the sound field measuring device 800. s is input, and the change in optical phase φ s to frequency f d Specifically, the first calculation unit 110 calculates a complex amplitude d of the optical phase at s is Fourier transformed in a certain time interval to obtain frequency f d The complex amplitude d is obtained by extracting the components of

[0047] In S120, the second calculation unit 120 calculates a function q diff Using (ξ',η'), the function value q at point X diff (ξ,η)(where ξ=x / a, η=2z / ka 2 , k1=f1 / c, k2=f2 / c, k=(k1+k2) / 2) and the function q along the light path L diff Line integral value of (ξ',η) ∫ L q diff Calculate (ξ',η)dξ'.

[0048]

number

[0049]

number

[0050] (However, r1 (mm’) =(k a B k_bm’ +k b B k_am )+i(k a +k b)η'B k_am B k_bm’ , r2 (mm’) =(k a B k_am +k b B k_bm’ )η'-i(k a +k b ), s1 (mm’) =(k a +k b ) 2 B k_am B k_bm’ , s2 (mm’) =-i(k a +k b )k a k b (B k_am -B k_bm’ ) 2 , B k_am =B m (1) / k a +i / δ, B k_bm’ =B m’ (2) / k b +i / δ, k a =k1 / k, k b =-k2 / k, and A m , A m’ , B m (1) , B m’ (2) , δ is a given constant) That is, the function q diff (ξ', η') is a function defined using the Gaussian beam expansion method.

[0051] In addition, A m , A m’ , B m (1) , B m’ (2) (m=1, . . . , 10, m'=1, . . . , 10), and δ may be recorded in the recording unit 190 in advance.

[0052] In S130, the third calculation unit 130 calculates the frequency f d The complex amplitude d of the optical phase at point X, the function value q at point X calculated in S120 diff(ξ,η) and function q along the light path L diff Line integral value of (ξ',η) ∫ L q diff (ξ',η)dξ' is input, and the frequency f at point X is calculated by the following equation. d Calculate the complex amplitude p of the demodulated sound.

[0053]

number

[0054] (However, C ao is a value determined by the physical conditions at the time of sound field measurement) In addition, C ao =k l (n0-1) / γP0, and the constant C ao The wave number k of light used in the calculation l The refractive index of air in the steady state n0, the atmospheric pressure in the steady state P0, and the specific heat ratio γ of air may be recorded in the recording unit 190 in advance.

[0055] According to an embodiment of the present invention, by using the amount of change in optical phase due to demodulated sound obtained using optical sound measurement technology, it is possible to accurately determine the complex amplitude of the demodulated sound, which is an acoustic characteristic of a parametric array.

[0056] An example of application of this embodiment will be described below. (Application example 1) Using this embodiment, the frequency characteristics of a parametric speaker are measured. The parametric speaker to be measured is installed at a desired position. One frequency is extracted from a vector (hereinafter referred to as a demodulated sound frequency vector) whose elements are the frequencies of the demodulated sound, and the complex amplitude at that frequency at a certain point is calculated using this embodiment. By repeating this calculation for all elements of the demodulated sound frequency vector, a vector (hereinafter referred to as a demodulated sound complex amplitude vector) whose elements are the complex amplitudes of the demodulated sound at each frequency at a certain point is generated. This results in a pair of the demodulated sound frequency vector and the demodulated sound complex amplitude vector that represent the frequency characteristics of the parametric speaker. (Application example 2) Using this embodiment, the sound pressure of the time signal of the parametric array is measured. The amount of change in the optical phase, φ, which is a discrete time signal measured by the sound field measuring device 800, is s A discrete Fourier transform is performed on the discrete frequency spectrum to obtain a discrete frequency spectrum. For the complex amplitudes at all frequencies in the discrete frequency spectrum, the complex amplitude of the demodulated sound at a certain frequency at that point is calculated according to this embodiment to generate a discrete frequency spectrum at that point. An inverse Fourier transform is performed on the generated discrete frequency spectrum at that point to obtain the time waveform of the sound pressure at that point, i.e., the sound pressure of the time signal of the parametric array.

[0057] In addition, the discrete-time signal φ s A discrete Fourier transform may be performed on the discrete time signal of the number of samples obtained in advance. The time waveform of the sound pressure at a certain point is obtained by performing the above process on the discrete time signal of the number of samples. At this time, by performing the calculation in the second calculation unit 120, which takes time to calculate, in advance, it becomes possible to obtain the time waveform of the sound pressure at a certain point in real time. By repeating the process for each of the above predetermined number of samples until the measurement is completed, the sound pressure of the time signal of the parametric array can be measured in real time. The time waveform of the sound pressure of the demodulated sound obtained in real time can be used as an input to, for example, an active sound field control device, an online diagnosis device, or an optimization device for installation conditions and driving signals. <Additional Notes> 5 is a diagram showing an example of a functional configuration of a computer 2000 that realizes each of the above-mentioned devices. The processing in each of the above-mentioned devices can be performed by having a recording unit 2020 load a program for causing the computer 2000 to function as each of the above-mentioned devices, and having the control unit 2010, the input unit 2030, the output unit 2040, etc. operate.

[0058] The device of the present invention has, as a single hardware entity, an input section to which a keyboard or the like can be connected, an output section to which a liquid crystal display or the like can be connected, a communication section to which a communication device (e.g., a communication cable) capable of communicating with the outside of the hardware entity can be connected, a CPU (which may also have a central processing unit, cache memory, registers, etc.), memories such as RAM and ROM, an external storage device such as a hard disk, and buses connecting the input section, output section, communication section, CPU, RAM, ROM, and external storage device so that data can be exchanged between them. If necessary, the hardware entity may also be provided with a device (drive) capable of reading and writing a recording medium such as a CD-ROM. A physical entity equipped with such hardware resources is, for example, a general-purpose computer.

[0059] The external storage device of the hardware entity stores the programs required to realize the above-mentioned functions and the data required in the processing of these programs (not limited to the external storage device, but for example the programs may be stored in a ROM, which is a read-only storage device). Data obtained by the processing of these programs is stored appropriately in the RAM, the external storage device, etc.

[0060] In the hardware entity, each program stored in an external storage device (or ROM, etc.) and the data required for processing each program are loaded into memory as necessary, and interpreted, executed, and processed by the CPU as appropriate, so that the CPU realizes a predetermined function (each component represented as the above, "unit," "means," etc.).

[0061] The present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the spirit of the present invention. In addition, the processes described in the above-described embodiment are not limited to being executed in chronological order according to the order described, but may be executed in parallel or individually depending on the processing capacity of the device that executes the processes or as necessary.

[0062] As described above, when the processing functions of the hardware entities (the devices of the present invention) described in the above embodiments are realized by a computer, the processing contents of the functions that the hardware entities should have are described by a program. Then, by executing this program on a computer, the processing functions of the hardware entities are realized on the computer.

[0063] The program describing the processing contents can be recorded on a computer-readable recording medium. The computer-readable recording medium may be, for example, a magnetic recording device, an optical disk, a magneto-optical recording medium, a semiconductor memory, or any other suitable recording medium. Specifically, for example, a hard disk drive, a flexible disk, a magnetic tape, or the like can be used as the magnetic recording device, a DVD (Digital Versatile Disc), a DVD-RAM (Random Access Memory), a CD-ROM (Compact Disc Read Only Memory), a CD-R (Recordable) / RW (ReWritable), or the like can be used as the optical disk, an MO (Magneto-Optical disc), or the like can be used as the magneto-optical recording medium, and an EEP-ROM (Electronically Erasable and Programmable-Read Only Memory) or the like can be used as the semiconductor memory.

[0064] The program may be distributed, for example, by selling, transferring, lending, etc. portable recording media such as DVDs and CD-ROMs on which the program is recorded. Furthermore, the program may be distributed by storing the program in a storage device of a server computer and transferring the program from the server computer to other computers via a network.

[0065] A computer that executes such a program, for example, first stores the program recorded on a portable recording medium or the program transferred from a server computer in its own storage device. Then, when executing a process, the computer reads the program stored in its own storage device and executes a process according to the read program. As another execution form of the program, the computer may directly read the program from the portable recording medium and execute a process according to the program, or may execute a process according to the received program each time a program is transferred from the server computer to the computer. The server computer may not transfer the program to the computer, but may execute the above-mentioned process by a so-called ASP (Application Service Provider) type service that realizes the processing function only by issuing an execution instruction and obtaining the result. Note that the program in this embodiment includes information used for processing by an electronic computer that is equivalent to a program (data that is not a direct instruction to the computer but has a nature that specifies the processing of the computer, etc.).

[0066] In addition, in this embodiment, a hardware entity is configured by executing a specific program on a computer, but at least a part of the processing contents may be realized by hardware.

[0067] The foregoing description of the embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings. The embodiments have been chosen and depicted to provide a best illustration of the principles of the invention and to enable those skilled in the art to utilize the invention in various embodiments and with various modifications as may be suitable for the practical use contemplated. All such modifications and variations are within the scope of the invention as defined by the appended claims interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Claims

1. L is the optical path in a sound field measuring device that measures the phase change of light caused by audible sound (hereinafter referred to as demodulated sound) S generated by a parametric array using a transducer that is an approximately circular sound source, C is the point where the optical path L intersects with a straight line that passes through the transducer and is parallel to the propagation direction of the demodulated sound S, X is a point on the optical path L whose distance from point C is x, z is the distance from the transducer to the optical path L, a is the radius of the transducer, and f d =|f 1 -f 2 | (where f 1 is the carrier frequency, f 2 is the frequency of the sideband) is the frequency of the demodulated sound S, c is the speed of sound, The amount of change in optical phase caused by demodulated sound S is φ s Then, frequency f d A first calculation unit that calculates a complex amplitude d of an optical phase at q diff Let (ξ',η') be a function defined using the Gaussian beam expansion method, Function value q at point X diff (ξ,η) (where ξ=x / a, η=2z / ka 2 , k 1 =f 1 / c, k 2 =f 2 / c, k=(k 1 +k 2 ) / 2) and the function q along the light path L diff Line integral value of (ξ',η) ∫ L q diff A second calculation unit for calculating (ξ', η)dξ'; frequency f d The complex amplitude d of the optical phase at point X and the function value q at point X diff (ξ,η) and function q along the light path L diff Line integral value of (ξ',η) ∫ L q diff Using (ξ',η)dξ', the frequency f at point X is d A third calculation unit for calculating a complex amplitude p of the demodulated sound; An acoustic characteristic calculation device comprising:

2. 2. The acoustic characteristic calculation device according to claim 1, Function q diff (ξ', η') is a function defined by the following equation: ##EQU00016## ##EQU00017## (However, r 1 (mm’) = (k a B k_bm’ + k b B k_am ) + i(k a + k b )η’B k_am B k_bm’ , r 2 (mm’) = (k a B k_am + k b B k_bm’ )η’ - i(k a + k b ), s 1 (mm’) = (k a + k b ) 2 B k_am B k_bm’ , s 2 (mm’) = -i(k a + k b )k a k b (B k_am - B k_bm’ ) 2 , B k_am = B m (1) / k a + i / δ, B k_bm’ = B m’ (2) / k b + i / δ, k a = k 1 / k, k b = -k 2 / k, where A m , A m’ , B m (1) , B m’ (2) , δ are predetermined constants) The third calculation unit calculates a complex amplitude p by the following formula: [0018] (However, C ao is a value determined by the physical conditions at the time of sound field measurement) 2. An acoustic characteristic calculation device comprising:

3. L is the optical path in a sound field measuring device that measures the phase change of light caused by audible sound (hereinafter referred to as demodulated sound) S generated by a parametric array using a transducer that is an approximately circular sound source, C is the point where the optical path L intersects with a straight line that passes through the transducer and is parallel to the propagation direction of the demodulated sound S, X is a point on the optical path L whose distance from point C is x, z is the distance from the transducer to the optical path L, a is the radius of the transducer, and f d =|f 1 -f 2 | (where f 1 is the carrier frequency, f 2 is the frequency of the sideband) is the frequency of the demodulated sound S, c is the speed of sound, The acoustic characteristic calculation device calculates the amount of change in the optical phase φ due to the demodulated sound S. s Then, frequency f d a first calculation step of calculating a complex amplitude d of the optical phase at q diff Let (ξ',η') be a function defined using the Gaussian beam expansion method, The acoustic characteristic calculation device calculates a function value q diff (ξ,η) (where ξ=x / a, η=2z / ka 2 , k 1 =f 1 / c, k 2 =f 2 / c, k=(k 1 +k 2 ) / 2) and the function q along the light path L diff Line integral value of (ξ',η) ∫ L q diff a second calculation step of calculating (ξ',η)dξ'; The acoustic characteristic calculation device calculates the frequency f d The complex amplitude d of the optical phase at point X and the function value q at point X diff (ξ,η) and function q along the light path L diff Line integral value of (ξ',η) ∫ L q diff Using (ξ',η)dξ', the frequency f at point X is d A third calculation step of calculating a complex amplitude p of the demodulated sound; The acoustic characteristic calculation method includes:

4. A program for causing a computer to function as the acoustic characteristic calculation device according to claim 1 or 2.

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