Sound measurement device

Abstract

Provided is a technique for measuring the sound pressure of a sound field by means of a discretionary sound present in a Fabry-Perot resonator. The present invention includes: a measurement light source that can be frequency-modulated and that emits laser light used for measurement (hereinafter referred to as measurement light); an optical resonator that has a sound field formed therein by a sound (hereinafter referred to as measurement target sound) to be subjected to sound pressure measurement, and that emits reflected light or transmitted light of the incident measurement light; a first photodetector that converts reflected light or transmitted light of the measurement light into a detection signal constituting an electric signal; a frequency control unit that, on the basis of the detection signal, controls the measurement light source so that the frequency of the measurement light matches the resonance frequency of the optical resonator; a frequency fluctuation measurement unit that measures frequency fluctuations of the measurement light; and a sound pressure calculation unit that calculates the sound pressure of the measurement target sound from the frequency fluctuations of the measurement light.

Description

Sound measuring device

[0001] The present invention relates to a sound measurement technique using light.

[0002] In recent years, sound pressure measurement methods using light have been used as an alternative to sound pressure measurement methods using microphones. Non-Patent Document 1 proposes a method for measuring sound pressure by measuring the resonant frequency fluctuation of a Fabry-Perot resonator caused by sound when a sound field due to standing waves exists within the Fabry-Perot resonator. Specifically, an acousto-optic modulator (AOM) is used to frequency lock the resonant frequency of the Fabry-Perot resonator, and the resonant frequency fluctuation is measured using a frequency counter.

[0003] Chijioke, A., Allen, R., Fick, S., Long, D., Reschovsky, B., Strait, J. and Wagner, R., "Optical-cavity-based primary sound standard," 28th International Congress on Sound and Vibration 2022 (ICSV28), 2022.

[0004] However, commonly available acousto-optic modulators have limited range and speed of frequency modulation, making it impossible to lock the frequency of a specific sound and measure sound pressure.

[0005] Therefore, an object of the present invention is to provide a technique for measuring the sound pressure of a sound field caused by any sound present in a Fabry-Perot resonator.

[0006] One aspect of the present invention includes a frequency-modulatable measurement light source that emits laser light used for measurement (hereinafter referred to as measurement light), an optical resonator in which a sound field is formed by the sound whose sound pressure is to be measured (hereinafter referred to as measurement target sound) and that emits reflected light or transmitted light of the incident measurement light, a first photodetector that converts the reflected light or transmitted light of the measurement light into a detection signal which is an electrical signal, a frequency control unit that controls the measurement light source based on the detection signal so that the frequency of the measurement light matches the resonant frequency of the optical resonator, a frequency fluctuation measurement unit that measures frequency fluctuations of the measurement light, and a sound pressure calculation unit that calculates the sound pressure of the measurement target sound from the frequency fluctuations of the measurement light.

[0007] According to the present invention, it is possible to measure the sound pressure of a sound field due to any sound existing in a Fabry-Perot resonator.

[0008] FIG. 1 is a diagram showing an example of an optical resonator. FIG. 2 is a block diagram showing an example of the configuration of the sound measuring device 100. FIG. 3 is a flowchart showing an example of the operation of the sound measuring device 100. FIG. 4 is a block diagram showing a first configuration example of the sound measuring device 100. FIG. 5 is a block diagram showing a second configuration example of the sound measuring device 100. FIG. 6 is a block diagram showing a third configuration example of the sound measuring device 100. FIG. 7 is a block diagram showing a fourth configuration example of the sound measuring device 100. FIG. 8 is a block diagram showing a fifth configuration example of the sound measuring device 100. FIG. 9 is a block diagram showing a sixth configuration example of the sound measuring device 100. FIG. 10 is a diagram showing an example of the functional configuration of a computer that realizes the sound measuring device 100 in an embodiment of the present invention.

[0009] Hereinafter, an embodiment of the present invention will be described in detail. Note that components having the same functions are given the same numbers and redundant explanations will be omitted.

[0010] <Technical Background> In an embodiment of the present invention, sound pressure is measured by measuring the resonant frequency fluctuation of a Fabry-Perot resonator caused by an arbitrary sound using a laser light source capable of frequency modulation over a wide range and at high speed. Specifically, sound pressure is measured by measuring the frequency fluctuation of a laser light caused by making the frequency of the laser light follow the resonant frequency of the Fabry-Perot resonator using a laser light source different from the above laser light source.

[0011] The principle of sound pressure measurement will be explained below. Consider a Fabry-Perot resonator (hereinafter referred to as optical resonator) that includes two opposing mirrors, a coupler for guiding laser light, and an aperture for guiding sound inside (see Figure 1). A sound field is formed inside the optical resonator by guiding sound from a sound source through the aperture. If the coupler is sufficiently small compared to the wavelength of the sound and the sound pressure inside the optical resonator can be considered uniform, the sound pressure p inside the optical resonator can be calculated using equation (1). where n0 is the refractive index of air in the absence of sound, γ is the specific heat ratio of air, P0 is the atmospheric pressure, and ν q is the resonant frequency of the optical resonator (where q represents the mode number), and Δν q is the resonant frequency fluctuation of the optical resonator.

[0012] The refractive index n0, the specific heat ratio γ, and the atmospheric pressure P0 are parameters that are determined when measuring the frequency fluctuation. q is the value obtained as the average frequency, which is the time average of the frequency of the laser light. q is a value obtained by making the frequency of the laser light follow the resonance frequency of the optical resonator. q Measure and calculate the sound pressure p.

[0013] First Embodiment A sound measuring device 100 measures the resonance frequency fluctuation of an optical resonator as the frequency fluctuation of the laser light using laser light emitted from a laser light source, and calculates the sound pressure of a sound field due to sound present in the optical resonator.

[0014] The sound measurement device 100 will be described below with reference to FIGS. 2 and 3. FIG. 2 is a block diagram showing an example of the configuration of the sound measurement device 100. FIG. 3 is a flowchart showing an example of the operation of the sound measurement device 100. As shown in FIG. 2, the sound measurement device 100 includes a measurement light source 110, an optical resonator 120, a first photodetector 130, a frequency control unit 140, a frequency fluctuation measurement unit 150, and a sound pressure calculation unit 160. The measurement light source 110 is a laser light source capable of externally modulating the oscillation frequency over a wide range and at high speed. The measurement light source 110 changes the oscillation frequency based on a control signal generated by the frequency control unit 140, as described below. As described in the "Technical Background" section, the optical resonator 120 is a Fabry-Perot resonator including two opposing mirrors, a coupler for guiding laser light, and an opening for guiding sound into the resonator. A sound field is formed inside the optical resonator 120 (i.e., the space between the two mirrors) by guiding sound from a sound source through the opening. Here, the sound of the sound source refers to the sound whose sound pressure is to be measured (hereinafter referred to as the measurement target sound). Any speaker can be used as the sound source. The sound field formed inside the optical resonator 120 changes the refractive index of air, causing a resonant frequency fluctuation of the optical resonator 120. The sound measuring device 100 includes a recording unit (not shown). The recording unit is a component that appropriately records information necessary for processing by the sound measuring device 100. The recording unit pre-records, for example, parameters determined when measuring the frequency fluctuation of the laser light from the measurement light source 110 and the average frequency of the laser light from the measurement light source 110. Parameters determined when measuring the frequency fluctuation of the laser light from the measurement light source 110 include, for example, the refractive index of air in the absence of sound, the specific heat ratio of air, and atmospheric pressure.

[0015] The operation of the sound measuring device 100 will be described with reference to FIG.

[0016] In S110, the measurement light source 110 emits laser light used for measurement (hereinafter referred to as measurement light).

[0017] In S120, the optical resonator 120 receives the measurement light emitted in S110 as incident light and emits reflected light or transmitted light of the measurement light. As described above, a sound field is formed inside the optical resonator 120 due to the sound to be measured, and the resonant frequency of the optical resonator 120 varies due to the sound to be measured.

[0018] In S130, the first photodetector 130 receives the reflected or transmitted measurement light emitted in S120 as incident light, converts the reflected or transmitted measurement light into a detection signal, which is an electrical signal, and outputs it.

[0019] In S140, the frequency control unit 140 receives the detection signal output in S130 as input, and generates and outputs a signal (hereinafter referred to as a control signal) for controlling the measurement light source 110 based on the detection signal so that the frequency of the measurement light matches the resonance frequency of the optical resonator 120. The frequency control unit 140 generates the control signal using, for example, the Pound-Drever-Hall method. The control signal output in S140 is input to the measurement light source 110. Then, the measurement light source 110 operates in accordance with the control signal so that the frequency of the measurement light matches the resonance frequency of the optical resonator 120.

[0020] In S150, the frequency fluctuation measurement unit 150 uses the measurement light emitted by the measurement light source 110 as incident light, measures the frequency fluctuation of the measurement light, and outputs the measured value. The frequency fluctuation measurement unit 150 measures the frequency fluctuation of the measurement light at a sampling rate higher than twice the frequency of the sound to be measured. For example, the frequency fluctuation measurement unit 150 can measure the frequency fluctuation of the measurement light by interfering the measurement light with light emitted by a reference laser light source with low frequency fluctuation and measuring the time fluctuation of the beat frequency of the interference light. Here, the reference laser light source can be, for example, a frequency-stabilized optical frequency comb. Alternatively, the frequency fluctuation measurement unit 150 can frequency-lock the measurement light using an optical frequency comb controller capable of high-speed laser frequency control (i.e., by matching the frequency of the laser light emitted by the optical frequency comb with the frequency of the measurement light), and then calculate the frequency fluctuation of the measurement light by measuring the RF signal output by the optical frequency comb. Here, the optical frequency comb controller can be, for example, composed of an optical frequency comb and a controller that controls the oscillation frequency of the optical frequency comb.

[0021] In S160, the sound pressure calculation unit 160 receives the frequency fluctuation of the measurement light output in S150 as input, calculates the sound pressure of the measurement target sound from the frequency fluctuation of the measurement light using parameters determined during measurement and the average frequency of the measurement light, and outputs the calculated sound pressure. The sound pressure calculation unit 160 calculates the sound pressure using, for example, Equation (1).

[0022] An example of the configuration of the sound measuring device 100 will be described below with reference to FIGS.

[0023] (Configuration Example 1) Figure 4 is a block diagram showing Configuration Example 1 of the sound measuring device 100. As shown in Figure 4, the sound measuring device 100 in Configuration Example 1 includes a measurement light source 110, an optical resonator 120, a first photodetector 130, a frequency control unit 140, a frequency fluctuation measurement unit 150, a sound pressure calculation unit 160, a beam splitter 170, and an optical circulator 180. The frequency control unit 140 includes an electro-optic modulator (EOM) 140-1, a local oscillator 140-2, and a PDH laser lock unit 140-3. The frequency fluctuation measurement unit 150 includes an optical frequency comb 150-1, a beam splitter 150-2, a beam splitter 150-3, a second photodetector 150-4, a frequency counter 150-5, and a fluctuation calculation unit 150-6. The optical frequency comb 150-1 is the reference laser light source described in the process of S150.

[0024] The operation of the sound measuring device 100 will be described with reference to Fig. 4. First, the operation of the measurement light source 110, the optical resonator 120, the first photodetector 130, the frequency control section 140, the beam splitter 170, and the optical circulator 180 will be described.

[0025] The measurement light emitted from the measurement light source 110 enters the beam splitter 170 and is split into two beams of light (hereinafter referred to as the first light and the second light) by the beam splitter 170. The first light is the measurement light that enters the frequency control unit 140, and the second light is the measurement light that enters the frequency fluctuation measurement unit 150. Specifically, the first light enters the electro-optic modulator 140-1, and the second light enters the beam splitter 150-3. The first light passes through the electro-optic modulator 140-1 and enters the optical circulator 180. The first light emitted from the optical circulator 180 enters the optical resonator 120. The reflected light or transmitted light of the first light emitted from the optical resonator 120 enters the optical circulator 180 and is emitted in a direction different from the first light that entered the optical circulator 180. The reflected or transmitted first light emitted from the optical circulator 180 enters the first photodetector 130 and is converted into a detection signal by the first photodetector 130. The detection signal output from the first photodetector 130 is input to the PDH laser locking unit 140-3. The PDH laser locking unit 140-3 also receives a signal output from the local oscillator 140-2 that drives the electro-optic modulator 140-1. The PDH laser locking unit 140-3 generates and outputs a control signal using these two signals. The control signal is input to the measurement light source 110, which modulates the oscillation frequency in accordance with the control signal so that the frequency of the measurement light matches the resonant frequency of the optical resonator 120. Through the process described above, the frequency of the measurement light is maintained at the resonant frequency of the optical resonator 120 while the sound to be measured is being reproduced from the sound source. Note that a beam splitter can be used instead of the optical circulator 180.

[0026] Next, the operation of the frequency fluctuation measurement unit 150 and the sound pressure calculation unit 160 will be described. The light emitted from the optical frequency comb 150-1 enters the beam splitter 150-3 via the beam splitter 150-2 and is superimposed on the second light. The beam splitter 150-3 emits interference light between the light emitted from the optical frequency comb 150-1 and the second light. The interference light emitted from the beam splitter 150-3 is input to the second photodetector 150-4. The second photodetector 150-4 converts the interference light into a detection signal, which is an electrical signal. When the repetition frequency of the optical frequency comb 150-1 is 100 MHz, the first-order beat frequency of the interference light appears between 0 and 50 MHz. The detection signal output from the second photodetector 150-4 is input to the frequency counter 150-5. The frequency counter 150-5 uses the detection signal to measure and output the first-order beat frequency of the interference light. The frequency counter 150-5 is a frequency counter capable of setting the sampling rate for beat frequency measurement higher than half the frequency of the sound to be measured to prevent aliasing. The beat frequency measured by the frequency counter 150-5 is recorded in a recording unit (not shown) as a frequency measurement value at each time. The fluctuation calculation unit 150-6 calculates and outputs the time fluctuation of the beat frequency as the frequency fluctuation of the measurement wave from the beat frequency recorded in the recording unit. Here, since the state in which the frequency of the measurement light matches the resonant frequency of the optical resonator 120 is maintained, the frequency fluctuation of the measurement wave output by the fluctuation calculation unit 150-6 matches the resonant frequency fluctuation of the optical resonator 120. The sound pressure calculation unit 160 calculates and outputs the sound pressure of the sound to be measured from the frequency fluctuation of the measurement wave output by the fluctuation calculation unit 150-6.

[0027] (Configuration Example 2) Fig. 5 is a block diagram showing Configuration Example 2 of the sound measuring device 100. The sound measuring device 100 in Configuration Example 2 differs from the sound measuring device 100 in Configuration Example 1 in the configuration of the frequency fluctuation measuring unit 150. As shown in Fig. 5, the frequency fluctuation measuring unit 150 includes an optical frequency comb 150-1, a beam splitter 150-2, a beam splitter 150-3, a second photodetector 150-4, and an FM demodulator 150-7.

[0028] The operation of the sound measuring device 100 will be described with reference to Fig. 5. However, since the operation up to the point where the second photodetector 150-4 included in the frequency fluctuation measuring unit 150 converts the interference light into a detection signal is the same as in Configuration Example 1, the operation thereafter will be described.

[0029] The detection signal output from the second photodetector 150-4 is input to the FM demodulator 150-7. The FM demodulator 150-7 detects the first-order beat frequency of the interference light from the detection signal, generates a demodulated signal representing the frequency fluctuation of the measurement light, and outputs it. Here, since the frequency of the measurement light is maintained in a state where it matches the resonant frequency of the optical resonator 120, the demodulated signal output by the FM demodulator 150-7 is a signal representing the resonant frequency fluctuation of the optical resonator 120. Note that the FM demodulator 150-7 can be, for example, a high-speed phase-locked loop. The demodulated signal output by the FM demodulator 150-7 is recorded in a recording unit (not shown). The sound pressure calculation unit 160 calculates the sound pressure of the sound to be measured from the demodulated signal recorded in the recording unit and outputs the calculated value.

[0030] The sound measuring device 100 in the second configuration example is capable of measuring frequency fluctuations with higher precision than the sound measuring device 100 in the first configuration example, and is therefore capable of measuring sound pressure more accurately.

[0031] (Configuration Example 3) Figure 6 is a block diagram showing Configuration Example 3 of the sound measuring device 100. The sound measuring device 100 in Configuration Example 3 differs from the sound measuring device 100 in Configuration Example 2 in that it includes a sine wave oscillator 190 and in the configuration of the frequency fluctuation measuring unit 150. As shown in Figure 6, the frequency fluctuation measuring unit 150 includes an optical frequency comb 150-1, a beam splitter 150-2, a beam splitter 150-3, a second photodetector 150-4, an FM demodulator 150-7, and a lock-in amplifier 150-8. In the sound measuring device 100 in Configuration Example 3, a sine wave signal generated by the sine wave oscillator 190 is reproduced from the sound source as the sound to be measured.

[0032] The operation of the sound measuring device 100 will be described with reference to Fig. 6. However, since the operation up to the point where the FM demodulator 150-7 included in the frequency fluctuation measuring unit 150 generates a demodulated signal is the same as in Configuration Example 2, only the operation thereafter will be described.

[0033] The demodulated signal output by the FM demodulator 150-7 is input to the lock-in amplifier 150-8. A signal having the same frequency as the sine wave signal generated by the sine wave oscillator 190 is also input to the lock-in amplifier 150-8 as a reference signal. The lock-in amplifier 150-8 measures and outputs the amplitude of the frequency fluctuation of a signal having the same frequency as the sine wave signal (hereinafter referred to as a fluctuation signal) contained in the demodulated signal. The amplitude of the frequency fluctuation of the fluctuation signal measured by the lock-in amplifier 150-8 is recorded in a recording unit (not shown). The sound pressure calculation unit 160 calculates and outputs the sound pressure of the sound to be measured from the amplitude of the frequency fluctuation of the fluctuation signal recorded in the recording unit.

[0034] Therefore, when a sine wave signal is reproduced from a sound source as the sound to be measured, the operations of frequency fluctuation measuring section 150 and sound pressure calculating section 160 are as follows.

[0035] In S150, the frequency fluctuation measuring unit 150 uses the measurement light emitted by the measurement light source 110 as incident light, and measures and outputs the amplitude of the frequency fluctuation of a signal (hereinafter referred to as a fluctuation signal) having the same frequency as the sine wave signal reproduced as the sound to be measured from the sound source, which is included in the signal representing the frequency fluctuation of the measurement light.

[0036] In S160, the sound pressure calculation unit 160 receives as input the amplitude of the frequency fluctuation of the fluctuation signal output in S150, and calculates and outputs the sound pressure of the sound to be measured from the amplitude of the frequency fluctuation of the fluctuation signal using parameters determined during measurement and the average frequency of the measurement light.

[0037] The sound measuring device 100 in configuration example 3 can measure sound pressure more accurately than the sound measuring device 100 in configuration example 1 or 2 when a sine wave signal is reproduced from a sound source as the sound to be measured.

[0038] (Configuration Example 4) FIG. 7 is a block diagram showing Configuration Example 4 of the sound measuring device 100. The sound measuring device 100 in Configuration Example 4 differs from the sound measuring device 100 in Configuration Example 1 in the configuration of the optical resonator 120 and the configuration of the frequency fluctuation measurement unit 150. As shown in FIG. 7, the optical resonator 120 includes a thermocontroller 120-1. The thermocontroller 120-1 is a controller capable of adjusting temperature, and is attached to the optical resonator 120 to adjust the temperature of the optical resonator 120. The frequency fluctuation measurement unit 150 also includes an optical frequency comb 150-1, a beam splitter 150-2, a beam splitter 150-3, a second photodetector 150-4, a frequency counter 150-5, a fluctuation calculation unit 150-6, a slow locking unit 150-9, and a local oscillator 150-10.

[0039] 7, the operation of the sound measuring device 100 will be described. However, only the operation of the low speed locking unit 150-9, the local oscillator 150-10, and the thermocontroller 120-1, which is different from the first configuration example, will be described.

[0040] The detection signal output from the second photodetector 150-4 is input to the slow locking unit 150-9. The slow locking unit 150-9 also receives an RF signal generated by the local oscillator 150-10. Using these two signals, the slow locking unit 150-9 generates and outputs a signal that matches the first beat frequency of the interference light with the frequency of the RF signal. Here, the signal that matches the first beat frequency of the interference light with the frequency of the RF signal serves as a signal (hereinafter referred to as a control signal) that controls the thermocontroller 120-1. The control signal output from the slow locking unit 150-9 is input to the thermocontroller 120-1. The thermocontroller 120-1 controls the temperature of the optical resonator 120. This cancels out slow environmental fluctuations that occur in the measurement environment, stabilizing the beat frequency at the desired set value. The RF signal output from the local oscillator 150-10 is input to the frequency counter 150-5. The frequency counter 150-5 measures the beat frequency using the RF signal as a reference, thereby improving the stability of the measurement of frequency fluctuations.

[0041] Note that, although an example in which the slow locking unit 150-9, local oscillator 150-10, and thermo controller 120-1 are added to the sound measuring device 100 in configuration example 1 has been described here, the slow locking unit 150-9, local oscillator 150-10, and thermo controller 120-1 may also be added to the sound measuring device 100 in configuration example 2 or configuration example 3. In this case, the RF signal output from the local oscillator 150-10 is input to the FM demodulator 150-7. The FM demodulator 150-7 generates a demodulated signal based on the RF signal.

[0042] (Configuration Example 5) Fig. 8 is a block diagram showing Configuration Example 5 of the sound measuring device 100. The sound measuring device 100 in Configuration Example 5 differs from the sound measuring device 100 in Configuration Example 1 in the configuration of the optical resonator 120. As shown in Fig. 8, the optical resonator 120 includes a storage device 120-2. The optical resonator 120 is stored in the storage device 120-2. The storage device 120-2 is, for example, a thermostatic bath that keeps the temperature constant or a chamber that keeps the air condition constant.

[0043] By storing the optical resonator 120 in the storage container 120-2, fluctuations in the air temperature and atmospheric pressure can be kept low for a relatively short period of time, and the beat frequency is stabilized at a desired set value. This improves the stability of frequency fluctuation measurements, as in Configuration Example 4.

[0044] Although an example in which the storage device 120-2 is added to the sound measuring device 100 in the first configuration example has been described here, the storage device 120-2 may be added to the sound measuring device 100 in the second or third configuration example.

[0045] (Configuration Example 6) Figure 9 is a block diagram showing Configuration Example 6 of the sound measuring device 100. The sound measuring device 100 in Configuration Example 6 differs from the sound measuring device 100 in Configuration Example 1 in the configuration of the frequency fluctuation measurement unit 150. As shown in Figure 9, the frequency fluctuation measurement unit 150 includes a beam splitter 150-2, a beam splitter 150-3, a second photodetector 150-4, an optical frequency comb control unit 150-11, a frequency measurement unit 150-12, and a fluctuation calculation unit 150-13. The optical frequency comb control unit 150-11 is the optical frequency comb controller described in the processing of S150.

[0046] The operation of the sound measuring device 100 will be described with reference to Fig. 9. However, since the operations other than the operation of the frequency fluctuation measuring unit 150 are the same as those in the first configuration example, the operation of the frequency fluctuation measuring unit 150 will be described.

[0047] The light emitted from the optical frequency comb control unit 150-11 enters the beam splitter 150-3 via the beam splitter 150-2 and is superimposed on the second light. The beam splitter 150-3 emits interference light between the light emitted from the optical frequency comb control unit 150-11 and the second light. The interference light emitted from the beam splitter 150-3 is input to the second photodetector 150-4. The second photodetector 150-4 converts the interference light into a detection signal, which is an electrical signal. The detection signal output from the second photodetector 150-4 is input to the optical frequency comb control unit 150-11. The optical frequency comb control unit 150-11 uses the detection signal to control the optical frequency comb so that the frequency of the light emitted by the optical frequency comb matches the frequency of the measurement light. Specifically, the optical frequency comb control unit 150-11 uses the detection signal to control the repetition rate or carrier envelope frequency of the optical frequency comb so that the beat frequency of the interference light becomes a constant value. The frequency measurement unit 150-12 measures and outputs the repetition frequency and carrier envelope frequency of the optical frequency comb. The repetition frequency and carrier envelope frequency of the optical frequency comb measured by the frequency measurement unit 150-12 are recorded in a recording unit (not shown). The fluctuation calculation unit 150-13 calculates and outputs the frequency fluctuation of the measurement light from the repetition frequency and carrier envelope frequency of the optical frequency comb recorded in the recording unit. Here, since the state in which the frequency of the measurement light matches the resonance frequency of the optical resonator 120 is maintained, the frequency fluctuation of the measurement wave output by the fluctuation calculation unit 150-13 matches the resonance frequency fluctuation of the optical resonator 120. The sound pressure calculation unit 160 calculates and outputs the sound pressure of the sound to be measured from the frequency fluctuation of the measurement light output by the fluctuation calculation unit 150-13.

[0048] (Application Example) Here, a microphone calibration device using the sound measurement device 100 will be described. When the sound measurement device 100 is used as a microphone calibration device, the optical resonator 120 includes at least two openings. A sound source is placed in one of the openings, and a microphone to be calibrated is placed in the other. The sound measurement device 100 is then used to measure the sound pressure of the sound reproduced from the sound source. The output signal from the microphone to be calibrated is also measured. The sound pressure sensitivity of the microphone can be obtained by dividing the amplitude of the output signal from the microphone by the measured sound pressure. Furthermore, the time delay and phase characteristics of the microphone can be calibrated by calculating the time difference and phase difference between the waveform of the output signal from the microphone and the waveform of the measurement wave.

[0049] According to an embodiment of the present invention, it is possible to measure the sound pressure of a sound field due to any sound present in a Fabry-Perot resonator. This makes it possible to measure sound pressure accurately and quantitatively using the frequency of light, a physical quantity that can be measured accurately and quantitatively. Furthermore, it becomes possible to directly measure Pascals, which are the physical unit of sound pressure, which has not been realized in sound pressure measurement methods using microphones.

[0050] Furthermore, application of the present invention makes it possible to calibrate any microphone based on measurements of light frequencies.

[0051] <Additional Notes> Some of the functions performed by the components described in this specification may be implemented in circuitry or processing circuitry, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), CPUs (Central Processing Units), conventional circuits, and / or combinations thereof, programmed to perform the described functions. A processor includes transistors and other circuits and is considered to be circuitry or processing circuitry. A processor may also be a programmed processor that executes a program stored in a memory.

[0052] In this specification, a circuitry, unit, or means is hardware that is programmed to realize or performs the described functions, which may be any hardware disclosed herein or any hardware known to be programmed to realize or perform the described functions.

[0053] If the hardware is a processor considered to be a type of circuitry, the circuitry, means, or unit is a combination of the hardware and software used to configure the hardware and / or processor.

[0054] The various processes described above can be implemented by loading a program that executes each step of the above method into the recording unit 2020 of the computer 2000 shown in Figure 10, and operating the control unit 2010, input unit 2030, output unit 2040, display unit 2050, etc.

[0055] The program describing the processing contents can be recorded on a computer-readable recording medium, which 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.

[0056] The program may be distributed by, for example, selling, transferring, lending, etc. portable recording media such as DVDs and CD-ROMs on which the program is recorded. Furthermore, the program may be stored in a storage device of a server computer, and then transferred from the server computer to other computers via a network, thereby distributing the program.

[0057] A computer that executes such a program may first temporarily store the program recorded on a portable recording medium or transferred from a server computer in its own storage device. Then, when executing a process, the computer reads the program stored in its storage device and executes the process in accordance with the read program. Alternatively, the computer may read the program directly from a portable recording medium and execute the process in accordance with the program. Furthermore, the computer may execute the process in accordance with the program each time a program is transferred from a server computer to the computer. Alternatively, the server computer may not transfer the program to the computer, but may instead execute the process through a so-called ASP (Application Service Provider) service, which realizes the processing function by issuing an execution instruction and obtaining the results. Furthermore, the server computer may execute the process at the terminal using a so-called SaaS (Software as a Service) service, which allows users to use part of the server computer along with the program. In this embodiment, the program includes information used for processing by an electronic computer that is equivalent to a program (such as data that is not a direct instruction to a computer but has properties that dictate computer processing).

[0058] Furthermore, in this embodiment, the device is configured by executing a predetermined program on a computer, but at least a part of the processing contents may be realized by hardware.

[0059] The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Furthermore, the processes described in the above embodiments may not only be executed in chronological order according to the order described, but may also be executed in parallel or individually depending on the processing capacity of the device that executes the processes or as needed.

Claims

1. A sound measurement device including: a measurement light source capable of frequency modulation that emits a laser beam (hereinafter referred to as measurement light) used for measurement; an optical resonator in which a sound field formed by a sound (hereinafter referred to as measurement target sound) to be measured by a sound pressure meter is formed inside, and that emits reflected light or transmitted light of the incident measurement light; a first photodetector that converts the reflected light or transmitted light of the measurement light into a detection signal which is an electrical signal; a frequency control unit that controls the measurement light source so that the frequency of the measurement light matches the resonance frequency of the optical resonator based on the detection signal; a frequency fluctuation measurement unit that measures the frequency fluctuation of the measurement light; and a sound pressure calculation unit that calculates the sound pressure of the measurement target sound from the frequency fluctuation of the measurement light.

2. The sound measurement device according to claim 1, wherein the frequency control unit includes an electro-optic modulator, a local oscillator, and a PDH laser lock unit, and generates a signal for controlling the measurement light source so that the frequency of the measurement light matches the resonance frequency of the optical resonator by using the detection signal input to the PDH laser lock unit and the output signal of the local oscillator that drives the electro-optic modulator.

3. The sound measurement device according to claim 1, wherein the frequency fluctuation measurement unit includes an optical frequency comb, a second photodetector, a frequency counter, and a fluctuation calculation unit. The frequency counter measures the first beat frequency of the interference light by using a detection signal obtained by converting the interference light between the light emitted from the optical frequency comb and the measurement light output from the second photodetector. The fluctuation calculation unit calculates the frequency fluctuation of the measurement light from the first beat frequency of the interference light.

4. The sound measurement device according to claim 1, wherein the frequency fluctuation measurement unit includes an optical frequency comb, a second photodetector, and an FM demodulator. The FM demodulator detects the first beat frequency of the interference light by using a detection signal obtained by converting the interference light between the light emitted from the optical frequency comb and the measurement light output from the second photodetector, and generates a demodulated signal representing the frequency fluctuation of the measurement light.

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