JP2001352598A - Acoustic calibrator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a user-friendly acoustic calibrator by reducing the height without lowering calibration accuracy, and making the calibrator into form stable for calibration work. SOLUTION: In the acoustic calibrator in which a pressure type microphone 8 is inserted into a coupler 7 and the sensitivity of the pressure type microphone 8 is calibrated by generation a calibration sound inside the coupler 7 by means of an electromagnetic type earphone 6, a signal for minimizing the waveform distortion of the calibration sound generated by the electromagnetic type earphone 6 is supplied to the electromagnetic type earphone 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an acoustic calibrator for calibrating the sensitivity of an acoustic measuring instrument such as a sound level meter having a pressure type microphone.

[0002]

2. Description of the Related Art In order to maintain the accuracy of a sound measuring device such as a sound level meter using a microphone, it is necessary to periodically perform a sound calibration of the microphone. For this reason, a sound calibrator is generally used.

A conventional sound calibrator is shown in FIG.
A cylindrical case 10 with a diameter of 2 inches and a height of about 4 inches
0, a coupler 101 for inserting a microphone to be calibrated into the case 100, a speaker 102 for generating sound pressure in the coupler 101, and a sine wave having a predetermined frequency and a predetermined amplitude in the speaker 102. A printed circuit board 103 on which electronic components for supplying signals are mounted, and a battery holder 1 for holding a battery serving as a power supply of the printed circuit board 103
04 and so on.

However, when the sound calibrator shown in FIG. 4 is used to calibrate the sound level of the sound level meter, the sound level of the sound level meter is higher than the diameter of the sound level meter. When this is released, there is a problem that sufficient stability cannot be obtained and it is difficult to perform acoustic calibration. One of the reasons why the height is higher than the diameter is that a speaker 102 having a relatively high overall height is incorporated.

[0005]

In order to solve this problem, it is conceivable to use an electromagnetic earphone that is smaller than a speaker as an electroacoustic transducer. However, small electromagnetic earphones have a narrow dynamic range,
If an attempt is made to generate a sound pressure of about SPL, the output sound pressure waveform is distorted, and there is a problem that the calibration accuracy is reduced.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to reduce the height of the calibration work without lowering the calibration accuracy. Sometimes with a shape that has good stability,
It is intended to provide an easy-to-use acoustic calibrator.

[0007]

According to the present invention, a pressure-type microphone is inserted into a coupler, and a calibration sound is generated by an electro-acoustic conversion means in the coupler, and the sensitivity of the pressure-type microphone is increased. And a signal for minimizing the waveform distortion of the calibration sound generated by the electro-acoustic conversion means, to the electro-acoustic conversion means.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is a configuration diagram of an acoustic calibrator according to the present invention, and FIG. 2 is a system configuration diagram for obtaining waveform data stored in a waveform data table.

As shown in FIG. 1, an acoustic calibrator according to the present invention includes a storage unit 1, a control unit 2, a D / A converter 3, a low-pass filter 4, an amplifier 5, an electromagnetic earphone 6, a coupler 7, and the like. Be prepared. Reference numeral 8 denotes a pressure type microphone to be calibrated.

The storage unit 1 has a waveform data table,
Non-sinusoidal waveform data of a predetermined frequency is stored in the waveform data table in advance. The control unit 2 extracts waveform data that is not a sine wave from the waveform data table provided in the storage unit 1, and outputs the waveform data.

The D / A converter 3 D / A converts the non-sinusoidal waveform data output from the control unit 2 into an analog signal. The low-pass filter 4 cuts off a frequency component higher than half the sampling frequency of the analog signal output from the D / A converter 3.

The amplifier 5 amplifies the signal output from the low-pass filter 4 to a predetermined level. Electromagnetic earphone 6
Receives the signal output from the amplifier 5 and generates a calibration sound in the coupler 7.

First, waveform data that is not a sine wave is stored in the storage unit 1.
The reason for memorizing the information is described below. When a sine wave is input to the electromagnetic earphone 6, the electromagnetic earphone 6 generates a calibration sound including a harmonic component in the coupler 7 due to its characteristics. This harmonic component is an element of the distortion of the calibration sound.

Therefore, a non-sinusoidal waveform is prepared in advance as the input waveform of the electromagnetic earphone 6 and supplied to the electromagnetic earphone 6, so that the calibration sound having a small harmonic component, that is, a small waveform distortion is obtained. Is to be generated in the coupler 7.

As shown in FIG. 2, a system for obtaining non-sinusoidal waveform data includes a synthesizer 10, a low-pass filter 4, an amplifier 5, an electromagnetic earphone 11 for measuring distortion, a coupler 7, a microphone 12, an amplifier 13, It consists of a rate meter 14.

The strain-measuring electromagnetic earphone 11 is the same type of electromagnetic earphone used for the acoustic calibrator. The components having the same reference numerals as those in FIG. 1 are the same as the components used in the acoustic calibrator.

The operation of the system for obtaining non-sinusoidal waveform data will be described. The signal output from the synthesizer 10 is subjected to the same processing as that of the acoustic calibrator by the low-pass filter 4 and the amplifier 5, and is input to the distortion measuring electromagnetic earphone 11. Then, the distortion-type electromagnetic earphone 11 generates a sound pressure in the coupler 7, the microphone 12 converts this sound pressure waveform into an electric signal, and the amplifier 13 amplifies the signal. The total 14 measures.

The non-sinusoidal waveform data is created by superimposing the second harmonic and the third harmonic on the sine wave, and sampling and quantizing it. Hereinafter, procedures (1) to (10) for obtaining waveform data that is not a sine wave will be described. (1) Prepare a plurality (for example, 10) of electromagnetic earphones of the same type as that used for the acoustic calibrator.

(2) The phase and amplitude of the second harmonic component to be superimposed on the sine wave and the third harmonic component for each of the prepared electromagnetic earphones by using the following procedures (3) to (8). Determine the phase and amplitude of. (3) The electromagnetic earphone used for the measurement is installed at the same position as the distortion measuring electromagnetic earphone 11 shown in FIG.

(4) A signal obtained by superimposing a second harmonic component having an appropriate amplitude on a sine wave (for example, 1 kHz) having a frequency used in the acoustic calibrator, while shifting the phase of the second harmonic component to be superimposed on the signal. , And the distortion of the sound pressure generated in the coupler 7 is measured using the distortion factor meter 14.
Then, the phase of the second harmonic component that minimizes the sound pressure distortion is found.

(5) Next, a second harmonic component having an appropriate amplitude is superimposed on a sine wave having a frequency used in the acoustic calibrator at the phase found in step (4). Then, the signal is output from the synthesizer 10 while shifting the amplitude of the second harmonic component to be superimposed, and the distortion of the sound pressure generated in the coupler 7 is measured using the distortion factor meter 14. Then, the amplitude of the second harmonic component that minimizes the sound pressure distortion is found.

(6) Next, a waveform is prepared by superimposing the second harmonic component of the amplitude and phase found in steps (4) and (5) on the sine wave of the frequency used in the acoustic calibrator. A signal obtained by superimposing a third harmonic component having an appropriate amplitude is output from the synthesizer 10 while shifting the phase of the third harmonic component to be superimposed. It is measured using a total of 14. Then, the phase of the third harmonic component that minimizes the sound pressure distortion is found.

(7) Next, a waveform is prepared by superimposing the second harmonic component of the amplitude and phase found in steps (4) and (5) on the sine wave of the frequency used in the acoustic calibrator. A third harmonic component having an appropriate amplitude is superimposed on the third harmonic component with the phase found in step (6). Then, while shifting the amplitude of the third harmonic component to be superimposed, the signal is output from the synthesizer 10, and the distortion of the sound pressure generated in the coupler 7 is measured using the distortion factor meter 14. Then, the amplitude of the third harmonic component that minimizes the sound pressure distortion is found.

(8) The values of the amplitude of the second harmonic component, the phase of the second harmonic component, the amplitude of the third harmonic component, and the phase of the third harmonic component that minimize the sound pressure distortion are recorded. . (9) Prepare these four values, that is, the amplitude of the second harmonic component, the phase of the second harmonic component, the amplitude of the third harmonic component, and the phase of the third harmonic component that minimize the sound pressure distortion. Average over all earphones you did.

(10) The waveform is calculated using the average value of the amplitude of the second harmonic component, the phase of the second harmonic component, the amplitude of the third harmonic component, and the phase of the third harmonic component. Is sampled and quantized to obtain waveform data.

By the above procedure, non-sinusoidal waveform data for generating a sound pressure with little waveform distortion in the coupler 7 can be obtained. Next, a digital data string representing an amplitude value for one wavelength of the obtained non-sinusoidal waveform data is written in the waveform data table of the storage unit 1.

FIG. 3 shows an example of one waveform of non-sinusoidal waveform data. A solid line is an example of waveform data in which a sine wave is used and a dot is not a sine wave. For non-sine wave data,
As shown in FIG. 3, the waveform shape is sharper than a sine wave, and has a feature that the tip of the positive region is sharper than the tip of the negative region. The waveform data shown in FIG. 3 is exaggerated for the sake of explanation.

The operation of the acoustic calibrator according to the present invention using non-sinusoidal waveform data will be described. First, the control unit 2 reads a discrete value signal from a digital data string representing an amplitude value for one wavelength of non-sinusoidal waveform data written in the waveform data table of the storage unit 1 at predetermined time intervals. Is output to the D / A converter 3 at predetermined time intervals.

The D / A converter 3 converts the input discrete value signal into continuous data and outputs it to the low-pass filter 4. The low-pass filter 4 cuts off frequency components higher than half the sampling frequency of the input signal and outputs the signal to the amplifier 5. Thereby, the input signal of the amplifier 5 becomes smooth. Then, the amplifier 5 amplifies the input signal and outputs the amplified signal to the electromagnetic earphone 6. Then, the electromagnetic earphone 6 generates a calibration sound with little distortion in the coupler 7.

In the above-described embodiment, the case where the balanced electromagnetic earphone 6 is used as the electro-acoustic transducer has been described. An electroacoustic transducer, such as a shape, may be used.

Although the procedure for obtaining waveform data other than a sine wave has been described up to the third harmonic, it may be applied to higher harmonics in the same manner. Also, in the procedure for obtaining waveform data that is not a sine wave, the case where the amplitudes and phases of a plurality of electromagnetic earphones are averaged has been described, but the waveform data according to the characteristics of each individual earphone is not averaged. May be created.

[0032]

As described above, according to the present invention, a small-sized electroacoustic transducer having a relatively small dynamic range can be used, so that the acoustic calibrator can be reduced in size and weight.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an acoustic calibrator according to the present invention.

FIG. 2 is a system configuration diagram for obtaining waveform data stored in a waveform data table.

FIG. 3 shows an example of waveform data that is not a sine wave.

FIG. 4 is a configuration diagram of a conventional acoustic calibrator.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Storage part, 2 ... Control part, 3 ... D / A converter, 4 ... Low-pass filter, 5 ... Amplifier, 6 ... Electromagnetic earphone, 7 ...
Coupler, 8: Pressure type microphone, 10: Synthesizer, 11: Electromagnetic type earphone for strain measurement, 12: Microphone, 13: Amplifier, 14: Distortion rate meter.

Claims (1)

[Claims] 1. A sound calibrator for inserting a pressure-type microphone into a coupler and generating a calibration sound in the coupler by electro-acoustic conversion means to calibrate the sensitivity of the pressure-type microphone. An acoustic calibrator, characterized in that a signal that minimizes waveform distortion of a generated calibration sound is supplied to the electroacoustic conversion means.