WO2025150093A1 - Sound measurement device - Google Patents

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

The present invention relates to optical sound measurement technology.

　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 of measuring sound pressure by measuring the resonant frequency fluctuation of a Fabry-Perot resonator caused by sound when a sound field caused by 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 a frequency counter is used to measure the resonant frequency fluctuation.

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.

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

The present invention aims to provide a technology for measuring the sound pressure of a sound field caused by any sound present inside a Fabry-Perot resonator.

One aspect of the present invention includes a frequency-modulatable measurement light source that emits a laser light (hereinafter referred to as measurement light) used for measurement, an optical resonator in which a sound field is formed by the sound (hereinafter referred to as the measurement target sound) whose sound pressure is to be measured and that emits reflected or transmitted light of the incident measurement light, a first photodetector that converts the reflected or transmitted light of the measurement light into a detection signal that 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 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.

The present invention makes it possible to measure the sound pressure of a sound field caused by any sound present inside a Fabry-Perot resonator.

FIG. 1 illustrates an example of an optical resonator. FIG. 1 is a block diagram showing an example of the configuration of a sound measuring device 100. 4 is a flowchart showing an example of the operation of the sound measuring device 100. FIG. 1 is a block diagram showing a first configuration example of a sound measuring device 100. FIG. 11 is a block diagram showing a second configuration example of the sound measuring device 100. FIG. 11 is a block diagram showing a third configuration example of the sound measuring device 100. FIG. 11 is a block diagram showing a fourth configuration example of the sound measuring device 100. FIG. 11 is a block diagram showing a fifth configuration example of the sound measuring device 100. FIG. 11 is a block diagram showing a sixth configuration example of the sound measuring device 100. FIG. 2 is a diagram illustrating an example of a functional configuration of a computer that realizes the sound measuring device 100 according to an embodiment of the present invention.

Below, an embodiment of the present invention will be described in detail. Components having the same functions will be given the same numbers, and duplicate explanations will be omitted.

<Technical background>
In an embodiment of the present invention, a laser light source capable of performing frequency modulation over a wide range and at high speed is used to measure a resonance frequency fluctuation of a Fabry-Perot resonator caused by an arbitrary sound, thereby measuring the sound pressure. Specifically, the sound pressure is measured by measuring the frequency fluctuation of a laser light caused by making the frequency of the laser light follow the resonance frequency of the Fabry-Perot resonator, using a laser light source different from the above-mentioned laser light source.

The principle of sound pressure measurement will be explained below. Consider a Fabry-Perot resonator (hereinafter referred to as an optical resonator) that includes two opposing mirrors, a coupler for introducing laser light, and an opening 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 opening. If the coupler is sufficiently small compared to the wavelength of the sound and the sound pressure inside the optical resonator can be considered to be uniform, the sound pressure p inside the optical resonator can be calculated using formula (1).
Here, n ₀ is the refractive index of air in the absence of sound, γ is the specific heat ratio of air, P ₀ is the atmospheric pressure, 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.

The refractive index _n0 , the specific heat ratio γ, and the atmospheric pressure _P0 are parameters that are determined when measuring the frequency fluctuation. The resonance frequency _vq is a value obtained as an average frequency that is the time average of the frequency of the laser light. The resonance frequency fluctuation _Δvq is a value obtained by making the frequency of the laser light follow the resonance frequency of the optical resonator. That is, in the sound pressure measurement in the embodiment of the present invention, the resonance frequency fluctuation _Δvq is measured and the sound pressure p is calculated.

First Embodiment
The sound measuring device 100 measures the resonance frequency fluctuation of an optical resonator as the frequency fluctuation of the laser light using a laser light emitted from a laser light source, and calculates the sound pressure of a sound field due to sound existing within the optical resonator.

The sound measuring 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 measuring device 100. Fig. 3 is a flowchart showing an example of the operation of the sound measuring device 100. As shown in Fig. 2, the sound measuring device 100 includes a measurement light source 110, an optical resonator 120, a first optical detector 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 modulating the oscillation frequency from the outside 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 <Technical Background>, the optical resonator 120 is a Fabry-Perot resonator including two opposing mirrors, a coupler for inputting laser light, and an opening for guiding sound inside. A sound field is formed inside the optical resonator 120 (i.e., the space between the two mirrors) by guiding the sound of the sound source through the opening. Here, the sound of the sound source refers to the sound that is the subject of sound pressure measurement (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 the air, causing a change in the resonant frequency 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 required for processing by the sound measuring device 100. The recording unit records, for example, parameters determined when measuring the frequency fluctuation of the laser light of the measurement light source 110 and the average frequency of the laser light of the measurement light source 110 in advance. Parameters determined when measuring the frequency fluctuation of the laser light of 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.

The operation of the sound measuring device 100 will be explained with reference to Figure 3.

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

In S120, the optical resonator 120 receives the measurement light emitted in S110 as incident light and emits reflected 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 fluctuates due to the sound to be measured.

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.

In S140, the frequency control unit 140 receives the detection signal output in S130, and generates and outputs a signal (hereinafter referred to as a control signal) that controls the measurement light source 110 based on the detection signal so that the frequency of the measurement light matches the resonant 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 resonant frequency of the optical resonator 120.

In S150, the frequency fluctuation measurement unit 150 measures and outputs the frequency fluctuation of the measurement light emitted by the measurement light source 110 as the incident light. 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 use a method of measuring the time fluctuation of the beat frequency of the interference light obtained by interfering the measurement light with light emitted by a reference laser light source with little frequency fluctuation as the frequency fluctuation of the measurement light. Here, for example, a frequency-stabilized optical frequency comb can be used as the reference laser light source. In addition, the frequency fluctuation measurement unit 150 can use a method of frequency-locking the measurement light using an optical frequency comb controller that can control the frequency of the laser light at high speed (i.e., making the frequency of the laser light emitted by the optical frequency comb match the frequency of the measurement light) and calculating the frequency fluctuation of the measurement light by measuring the RF signal output by the optical frequency comb. Here, the optical frequency comb controller is composed of, for example, an optical frequency comb and a controller that controls the oscillation frequency of the optical frequency comb.

In S160, the sound pressure calculation unit 160 receives the frequency fluctuation of the measurement light output in S150 as input, and calculates and outputs the sound pressure of the sound to be measured from the frequency fluctuation of the measurement light using parameters determined during measurement and the average frequency of the measurement light. The sound pressure calculation unit 160 calculates the sound pressure, for example, using formula (1).

Below, an example configuration of the sound measurement device 100 will be described with reference to Figures 4 to 9.

(Configuration Example 1)
FIG. 4 is a block diagram showing a first configuration example of the sound measuring device 100. As shown in FIG. 4, the sound measuring device 100 in the first configuration example includes a measurement light source 110, an optical resonator 120, a first optical detector 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 optical detector 150-4, a frequency counter 150-5, and a fluctuation calculation unit 150-6. Optical frequency comb 150-1 is the reference laser light source described in the process of S150.

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 optical detector 130, the frequency control unit 140, the beam splitter 170, and the optical circulator 180 will be described.

The measurement light emitted from the measurement light source 110 enters the beam splitter 170 and is split into two lights (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-optical modulator 140-1, and the second light enters the beam splitter 150-3. The first light passes through the electro-optical 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 is incident on the first optical detector 130 and converted into a detection signal by the first optical detector 130. The detection signal output from the first optical detector 130 is input to the PDH laser locking unit 140-3. The signal output from the local oscillator 140-2 that drives the electro-optical modulator 140-1 is also input to the PDH laser locking unit 140-3. 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 state in which the frequency of the measurement light matches the resonant frequency of the optical resonator 120 is maintained 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.

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 is incident on the beam splitter 150-3 via the beam splitter 150-2 and is superimposed with 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 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 beat frequency of the interference light. In addition, the frequency counter 150-5 is a frequency counter that can set the sampling rate for the 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.

(Configuration Example 2)
Fig. 5 is a block diagram showing a second configuration example of the sound measuring device 100. The sound measuring device 100 in the second configuration example differs from the sound measuring device 100 in the first configuration example 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.

The operation of the sound measuring device 100 will be described with reference to FIG. 5. However, 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, so the operation thereafter will be described.

The detection signal output from the second optical detector 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, and generates and outputs a demodulated signal representing the frequency fluctuation of the measurement light. Here, since the state in which the frequency of the measurement light matches the resonant frequency of the optical resonator 120 is maintained, 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 may 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 it.

The sound measuring device 100 in configuration example 2 is capable of measuring frequency fluctuations with higher precision than the sound measuring device 100 in configuration example 1, making it possible to measure sound pressure more accurately.

(Configuration Example 3)
6 is a block diagram showing a configuration example 3 of the sound measuring device 100. The sound measuring device 100 in the configuration example 3 differs from the sound measuring device 100 in the 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 FIG. 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 the 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.

The operation of the sound measuring device 100 will be described with reference to FIG. 6. However, the operation up to the point where the FM demodulator 150-7 included in the frequency fluctuation measuring unit 150 generates the demodulated signal is the same as in configuration example 2, so the operation thereafter will be described.

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 the 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.

Therefore, when a sine wave signal is reproduced from a sound source as the sound to be measured, the operation of the frequency fluctuation measurement unit 150 and the sound pressure calculation unit 160 is as follows.

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

In S160, the sound pressure calculation unit 160 receives 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 at the time of measurement and the average frequency of the measurement light.

The sound measuring device 100 in configuration example 3 is capable of measuring 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.

(Configuration Example 4)
7 is a block diagram showing a fourth configuration example of the sound measuring device 100. The sound measuring device 100 in the fourth configuration example differs from the sound measuring device 100 in the first configuration example in the configuration of the optical resonator 120 and the configuration of the frequency fluctuation measuring 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 the temperature, and is attached to the optical resonator 120 to adjust the temperature of the optical resonator 120. 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, a frequency counter 150-5, a fluctuation calculation unit 150-6, a slow locking unit 150-9, and a local oscillator 150-10.

The operation of the sound measuring device 100 will be described with reference to FIG. 7. However, only the operation of the low-speed lock unit 150-9, local oscillator 150-10, and thermocontroller 120-1, which differs from configuration example 1, will be described.

The detection signal output from the second photodetector 150-4 is input to the slow locking unit 150-9. The RF signal generated by the local oscillator 150-10 is also input to the slow locking unit 150-9. The slow locking unit 150-9 uses these two signals to generate and output a signal that makes the first beat frequency of the interference light and the frequency of the RF signal coincident. Here, the signal that makes the first beat frequency of the interference light and the frequency of the RF signal coincident becomes 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, and the beat frequency is stabilized 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. This improves the stability of the frequency fluctuation measurement.

Note that, although an example in which a slow locking unit 150-9, a local oscillator 150-10, and a thermo controller 120-1 are added to the sound measuring device 100 in configuration example 1 has been described here, a slow locking unit 150-9, a local oscillator 150-10, and a 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.

(Configuration Example 5)
Fig. 8 is a block diagram showing a configuration example 5 of the sound measuring device 100. The sound measuring device 100 in the configuration example 5 differs from the sound measuring device 100 in the 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.

By storing the optical resonator 120 in storage 120-2, it is possible to keep the air temperature fluctuations and atmospheric pressure fluctuations low for a relatively short period of time, so the beat frequency is stabilized at the desired set value. This improves the stability of frequency fluctuation measurements, as in configuration example 4.

Note that, although an example of adding the storage device 120-2 to the sound measuring device 100 in configuration example 1 has been described here, the storage device 120-2 may also be added to the sound measuring device 100 in configuration example 2 or configuration example 3.

(Configuration Example 6)
9 is a block diagram showing a sixth configuration example of the sound measuring device 100. The sound measuring device 100 in the sixth configuration example differs from the sound measuring device 100 in the first configuration example in the configuration of the frequency fluctuation measuring unit 150. As shown in FIG. 9, the frequency fluctuation measuring 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 process of S150.

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 configuration example 1, the operation of the frequency fluctuation measuring unit 150 will be described.

The light emitted from the optical frequency comb control unit 150-11 enters beam splitter 150-3 via beam splitter 150-2 and is superimposed with the second light. 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 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 frequency or carrier envelope frequency of the optical frequency comb so that the beat frequency of the interference light is 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 resonant 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 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 light output by the fluctuation calculation unit 150-13.

(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. Then, the sound pressure of the sound reproduced from the sound source is measured using the sound measurement device 100. In addition, 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. In addition, the time delay and phase characteristic 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.

According to an embodiment of the present invention, it is possible to measure the sound pressure of a sound field caused by any sound present inside a Fabry-Perot resonator. This makes it possible to measure sound pressure precisely and quantitatively using the frequency of light, a physical quantity that can be measured precisely and quantitatively. It also makes it possible to directly measure the Pascal, which is the physical unit of sound pressure, something that was not possible with sound pressure measurement methods that use microphones.

In addition, by applying an embodiment of the present invention, it becomes possible to calibrate any microphone based on measurements of light frequencies.

<Additional Notes>
Some of the functionality provided by the components described herein 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 provide the functionality described. Processors include transistors and other circuits and are considered to be circuitry or processing circuitry. A processor may be a programmed processor that executes a program stored in a memory.

In this specification, a circuitry, unit, or means is hardware that is programmed to realize or executes the described functions. The hardware may be any hardware disclosed in this specification or any hardware known to be programmed to realize or execute the described functions.

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

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 FIG. 10, and operating the control unit 2010, input unit 2030, output unit 2040, display unit 2050, etc.

The program describing this processing can be recorded on a computer-readable recording medium. Examples of computer-readable recording media include magnetic recording devices, optical disks, magneto-optical recording media, and semiconductor memories.

The program may be distributed, for example, by selling, transferring, or lending portable recording media such as DVDs or 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.

A computer that executes such a program, for example, first stores in its own storage device the program recorded on a portable recording medium or the program transferred from a server computer. Then, when executing processing, the computer reads the program stored in its own storage device and executes processing according to the read program. As another execution form of the program, the computer may read the program directly from the portable recording medium and execute processing according to the program, or may execute processing according to the received program each time a program is transferred to the computer from the server computer. Alternatively, the server computer may not transfer the program to the computer, but may execute processing by a so-called ASP (Application Service Provider) type service that realizes processing functions only by issuing execution instructions and obtaining results. Furthermore, the terminal processing may be executed by using a so-called SaaS (Software as a Service) type service that allows users to use part of the server computer together with the program. In this embodiment, the program includes information used for processing by a computer that is equivalent to a program (such as data that is not a direct command to a computer but has properties that dictate computer processing).

In addition, in this embodiment, the device is configured by executing a specific program on a computer, but at least a portion of the processing may be realized by hardware.

The present invention is not limited to the above-described embodiment, and appropriate modifications can be made without departing from the spirit of the present invention. Furthermore, the processes described in the above embodiment are not limited to being executed chronologically in the order described, but may be executed in parallel or individually depending on the processing capacity of the device executing the processes or as necessary.

Claims (4)

a frequency-modulated measurement light source that emits a laser beam used for measurement (hereinafter referred to as measurement light);
an optical resonator in which a sound field is formed by a sound to be measured for sound pressure (hereinafter referred to as a measurement target sound) and which emits reflected light or transmitted light of the incident measurement light;
a first photodetector for converting the reflected 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 coincides with the resonance frequency of the optical resonator;
a frequency fluctuation measuring unit for measuring a frequency fluctuation of the measurement light;
a sound pressure calculation unit that calculates the sound pressure of the measurement target sound from the frequency fluctuation of the measurement light;
A sound measuring device comprising: The sound measuring device according to claim 1,
The frequency control unit is
The laser includes an electro-optic modulator, a local oscillator, and a PDH laser lock unit;
a detection signal input to the PDH laser lock unit and an output signal of a local oscillator that drives the electro-optic modulator are used to generate a signal that controls the measurement light source so that the frequency of the measurement light matches the resonance frequency of the optical resonator. The sound measuring device according to claim 1,
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 a first-order beat frequency of the interference light using a detection signal obtained by converting interference light between the light emitted from the optical frequency comb and the measurement light, the interference light being output by the second photodetector; and
The sound measuring device according to claim 1 , wherein the fluctuation calculation unit calculates a frequency fluctuation of the measurement light from a first-order beat frequency of the interference light. The sound measuring device according to claim 1,
the frequency fluctuation measurement unit includes an optical frequency comb, a second photodetector, and an FM demodulator;
the FM demodulator detects a first-order beat frequency of the interference light using a detection signal obtained by converting the interference light between the light emitted from the optical frequency comb and the measurement light output by the second photodetector, and generates a demodulated signal representing a frequency fluctuation of the measurement light.