JP2008261700A - Sound wavelength measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure a fundamental wavelength of a sound for determining a fundamental frequency of a normal facility which is required when diagnosing the existence of a facility abnormality of a power facility or the like based on a sound generated from the facility. <P>SOLUTION: This sound wavelength measuring device is equipped with a cylindrical pipe 12 having one closed end; a microphone 14a mounted in the pipe slidably in the pipe axis direction, for measuring a sound pressure on the mounting position; and a detection device 16 for detecting the sound pressure measured by the microphone. The device is also equipped with a cylindrical pipe 12 having one closed end; the first microphone 14a and the second microphone 14b mounted in the pipe, for measuring a sound pressure on the mounting position; an adjustment mechanism capable of adjusting a distance between the first microphone and the second microphone; and a detection device 16 for detecting a sound pressure difference measured by the first microphone and the second microphone. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a sound wavelength measuring apparatus, for example, a sound wavelength for obtaining a fundamental frequency of normal equipment required for diagnosing the presence or absence of equipment abnormality such as power equipment based on sound generated by the equipment. It relates to a measuring device.

One method of diagnosing abnormalities in equipment such as train wheels and electric power equipment is to try to find abnormalities from the sound generated by the equipment. In addition to the human diagnostic method (sensory test method) in which a trained worker taps the wheel of a train with a hammer and diagnoses the abnormality from the sound, the frequency of the sound generated from the equipment has been increased in recent years. A method of diagnosing the presence or absence of abnormality by measuring and performing frequency analysis by Fourier analysis is used.
In this case, in the frequency analysis by Fourier analysis, data that changes with 2π as one period is the object of analysis, and therefore the basic frequency of normal equipment is required as reference data.

As an invention aimed at discovering an abnormality of an apparatus by measuring a sound generated from equipment, there is, for example, an “abnormal sound inspection method and apparatus” of Patent Document 1. In this invention, the abnormal sound inspection for judging whether the abnormal sound of the product is good or not is performed by using the sound data of the product that the person has determined as normal sound from the measurement data as a reference value, and the measurement data of the sound generated from the actually measured product. By comparing with the reference sound data, anomalies are to be found from the degree of coincidence.
JP 2005-283227 A

When measuring sound generated from equipment and performing frequency analysis by Fourier analysis, the fundamental wavelength of sound generated by equipment is assumed, and this is assumed to be one period, and frequency analysis is performed. Naturally, an error occurs in the analysis result from the deviation from the actual fundamental wavelength.
In order to suppress this error as much as possible, there is a method of performing “window function” processing on the data. However, such processing cannot completely eliminate the analysis error.
In Patent Document 1, since a normal sound is sensuously determined and the sound data is used as a reference value, the presence of a skilled person is indispensable.

  The present invention has been conceived to solve the above-described problems, and has an object to provide a wavelength measuring device for measuring the wavelength of sound. For example, the present invention measures sound generated from equipment. When frequency analysis is performed by Fourier analysis or the like, this is an apparatus that is effective in actually measuring and obtaining the wavelength rather than assuming the fundamental wavelength of sound generated by normal equipment. By performing frequency analysis based on the actually measured fundamental wavelength, it is possible to detect abnormalities in equipment with higher reliability with almost no analysis error.

  In order to achieve the above object, the present invention includes a cylindrical pipe (12) closed at one end, a first microphone (14a) attached to the pipe and measuring sound pressure at the attachment position, and a second microphone. A microphone (14b), an adjustment mechanism capable of adjusting the distance between the first microphone and the second microphone, and a detection device (16) for detecting a sound pressure difference measured by the first microphone and the second microphone; And a sound wavelength measuring device characterized by comprising:

  Here, the second microphone (14b) is fixedly attached to the closed end of the pipe (12), and the adjusting mechanism slides the first microphone (14a) in the pipe axial direction within the pipe. It is assumed that the tube length between the first microphone (14a) and the second microphone is changed.

  If necessary, it is also preferable to connect the attachment pipe (12 ') to the pipe (12) to extend the entire length of the pipe.

In the sound wavelength measuring apparatus of the present invention, a standing wave that is a combined wave of an incident wave and a reflected wave reflected at the closed end is introduced into a cylindrical pipe that closes one end (end). The fundamental wavelength of the standing wave is obtained by measuring the change in sound pressure (amplitude) of the sound wave while moving the microphone provided in the pipe.
For this reason, the first microphone is fixed to the closed end of the pipe, and a second microphone that can adjust the separation distance from the first microphone is provided. Then, by measuring the change in the sound pressure difference between the two microphones as the microphone moves, one wavelength (λ) is actually obtained from the tube length from the position where the sound pressure is minimized to the position where the sound pressure is minimized next. From this, the fundamental frequency of the sound wave can be calculated.

  Here, the adjustment mechanism for adjusting the separation distance between the first microphone and the second microphone is, for example, a pipe having a double-pipe structure in addition to the one that slides the second microphone in the pipe axial direction within the pipe. There is one that changes the tube length of the pipe between the first microphone and the second microphone, and thus the fundamental wavelength can be easily measured by a device having a simple structure.

  Although it is possible to continuously measure the sound pressure at each position in the pipe with a single microphone, the use of two microphones makes it easy to minimize the difference in sound pressure measured with each microphone. Can be detected.

  In addition, by connecting and connecting, for example, a helical attachment pipe that opens at both ends to the open end of the pipe and extending the entire length of the pipe, it is possible to measure the fundamental wavelength even for low frequency and long wavelength sound. .

In the present invention, when a sound wave propagating in the air is introduced into a cylindrical pipe whose end is closed, an incident wave and a reflected wave reflected at the end of the pipe are combined, and one cycle length is included in the pipe. Applies the same standing wave as the incident wave. When an incident wave is reflected at the end of the pipe, a combined wave of the incident wave and the reflected wave is generated in the pipe, but this wave does not move in the pipe but appears to change only in magnitude. This wave is called standing wave.
The measurement of the fundamental wavelength by the sound wavelength measuring apparatus of the present invention is to measure one period length of a standing wave (fundamental wave) measured using this theory.

FIG. 1 shows a conceptual diagram of a sound wavelength measuring apparatus according to the first embodiment.
The wavelength measuring apparatus 10 of the present embodiment is attached to a cylindrical pipe 12 whose one end is closed, a microphone (first microphone 14a) which is slidably mounted in the pipe axial direction within the pipe, and a closed end. And a detection device 16 for detecting the sound pressure difference between the sound pressures measured by the first microphone 14a and the second microphone 14b.

The pipe 12 is a straight cylinder having an inner diameter of about 10 cm and made of a transparent acrylic resin or the like, and has an overall length of about 1 m, for example. One end of the pipe 12 is open and the other end (termination) is closed. The pipe 12 has a scale (not shown) for measuring the distance from the end, with the closed end (end) being 0.
As shown in FIG. 2, an attachment pipe 12 ′ for extending the entire length of the pipe can be connected and connected to the open end portion of the pipe 12. The attachment pipe 12 ′ is the same pipe as the pipe 12, and can be smoothly connected and connected without a step by being screwed into the opening end portion of the pipe 12. In FIG. 2, the attachment pipe 12 ′ connected to the pipe 12 is illustrated as a straight pipe, but a pipe formed in a spiral shape may be used. The attachment pipe 12 'has a scale (not shown) for measuring the distance from the closed end of the pipe when connected to the pipe 12.
The attachment pipe 12 'is used when measuring the fundamental wavelength of a sound having a low frequency and a long wavelength, and its length (tube length) is about several meters (note that the attachment pipe 12' is a curved pipe). Is also good).

Both the first microphone 14a and the second microphone 14b are small sound collecting microphones for measuring the sound pressure (amplitude) in the tube. Here, the second microphone 14b is fixedly attached to the center of the closed end of the pipe, and the first microphone 14a slides on the central axis of the pipe 12, which is a circular pipe. That is, as shown in FIG. 3 showing an adjustment mechanism for movement, the first microphone 14a is radially arranged on a thin-walled (about 1 mm) circular frame 21 having the same outer diameter as the inner diameter of the pipe 12. It is attached to the center of the cross column 23 which is a thin rod attached in a cross shape. Further, a cord 25 for transmitting sound pressure data of the collected sound to the detection device 16 extends from the microphones 14a and 14b. Here, the cord 25 extending from the first microphone 14a extends along the inner peripheral wall of the circular tube, and the circular frame 21 arranged on the back side (closed end side) of the pipe 12 opens by pulling the cord. Slide to the end side. The slide movement of the circle frame 21 may be performed by providing a dedicated string instead of the code 25. Further, if the circular frame 21 is slid using a thin rod or the like, the circular frame can be slid in the direction of pushing the circular frame inward.
In the present embodiment, the microphone 14a is slid so as to be positioned at the center of the pipe 12. However, the microphone 14a may be slid in the axial direction along the inner periphery of the pipe.

  The detection device 16 connected to the first microphone 14a and the second microphone 14b is a device that detects a sound pressure difference measured by each microphone, and an amplification circuit that amplifies sound pressure data from the cord 25 connected to each microphone. And a sound pressure difference detection circuit including a display device such as an LED lamp and an indicator hand that can visually discriminate a change in the difference in sound pressure amplified by the amplifier circuit.

Next, a wavelength measurement method using the sound wavelength measurement apparatus 10 described above will be described.
First, the circular frame 21 to which the first microphone 14a is attached is pushed from the open end of the pipe 12 to which the second microphone is attached to the closed end to the deepest portion (closed end). In this state, the opening of the pipe is directed toward the sound source. If the fundamental wavelength of the sound to be measured here is long, an attachment pipe 12 ′ is connected in advance to the pipe opening end. Then, by slowly pulling the cord 25 of the first microphone 14a, the first microphone attached to the circular frame 21 is gradually slid to the open end side. At this time, a change in the difference between the sound pressure measured by the first microphone 14a and the sound pressure measured by the second microphone 14b is observed by the display device of the detection device 16. And the position of the 1st microphone 14a when the sound pressure difference becomes the minimum is recorded by reading the scale written in the pipe 12.

  It can be seen that when the first microphone 14a is slid to record the change in sound pressure, the minimum value of the sound pressure difference appears repeatedly at regular intervals. That is, since a standing wave is generated in the pipe 12, this interval (distance) is the fundamental wavelength λ to be measured. From this, the fundamental wavelength of sound is obtained, and the fundamental frequency f (= 1 / T) is obtained.

That is, the speed of sound V (m / s) is given by equation (a), and the basic period T (s) is given by equation (b). Here, λ is the fundamental wavelength (m), and t is the air temperature (° C.).
V = 331.5 + 0.6t (a)
T = λ / V (b)
From these equations, the fundamental frequency f (= 1 / T) is obtained.

When applying to frequency analysis, when the sound is measured at the sampling time st (s), the basic period T (s) is obtained by the equation (b), so that the following equation (c) is satisfied, or this If the frequency analysis is performed with the number of data close to m, the analysis accuracy will be improved.
m = n × T / st (n = 1, 2, 3...) (c)

For reference, the results of the frequency analysis of the sample sound using the sound wavelength measurement device of the present example are shown in the figure. The length of the pipe is 44 cm without attaching an attachment pipe.
FIG. 4 shows an example in which a sample sound having a frequency f of 880 Hz and a wavelength λ of 38.6 cm is incident from the pipe opening end, and the sound waveform detected by the second microphone at the pipe closing end is displayed on an oscilloscope. . Since seven wavelengths (7λ) appear at the time indicated by the arrow (7.95 ms), it can be seen that the period T is about 1.136 ms, and f is obtained as f = 1 / T≈880 Hz, which is It matches the frequency of the sample sound. Here, if the speed of sound V is 340 m / s, the wavelength is obtained as λ = V / f = 340/880 = 38.6 cm.
FIG. 5 shows a waveform obtained by detecting the same sample sound with the first microphone and the second microphone of the sound wavelength measuring apparatus of the present embodiment on an oscilloscope. The separation distance L (see FIG. 1) between the first microphone and the second microphone here is 0 cm. Since 8 wavelengths (8λ) appear at the time indicated by the arrow (9.08 ms), the period T is found to be about 1.135 ms, and f is obtained as f = 1 / T≈881 Hz, It almost matches the frequency of the sample sound.

  FIGS. 6 to 10 show sample sounds measured with the wavelength measuring apparatus of the present embodiment. FIG. 6A shows temporal changes in the sound pressures detected by the first microphone and the second microphone. ) Represents a temporal change in the sound pressure difference between the sounds detected by the first microphone and the second microphone. 6 shows a case where the distance L (see FIG. 1) between the first microphone and the second microphone is set to L = 0, FIG. 7 shows a case where L = λ / 4, and FIG. 8 shows a case where L = λ. FIG. 9 shows the sound pressure (a) and the sound pressure difference (b) when L = 3λ / 4, and FIG. 10 shows the sound pressure difference (b) when L = λ.

  As is clear from this result, it can be seen that the sound pressure difference between the sounds detected by the first microphone and the second microphone is substantially zero when the separation distance L is L = nλ.

According to the sound wavelength measuring apparatus of the present embodiment described above, the fundamental frequency can be calculated from the actually measured fundamental wavelength. Therefore, for example, when measuring sound generated from equipment and performing frequency analysis by Fourier analysis etc., frequency analysis is based on the fundamental wavelength actually measured, not assuming the fundamental wavelength of sound generated by normal equipment. It is possible to detect the abnormality of the equipment with higher reliability with almost no analysis error.
Further, the sound wavelength measuring apparatus of this embodiment has a simple measurement principle, and the operation of the apparatus is extremely simple, and the fundamental wavelength can be directly read by simply taking sound directly from the open end of the pipe. Furthermore, since the structure of the device itself is simple, it can be manufactured lightly and inexpensively. This eliminates the need for an expensive measuring instrument such as an oscilloscope or a complicated data autocorrelation processing / frequency counter device required for conventional wavelength measurement.
Further, since the attachment pipe can be connected and connected, it is possible to measure the wavelength even when the wavelength of the sound is long.

FIG. 11 shows a conceptual diagram of the sound wavelength measuring apparatus according to the second embodiment. In addition, about the structure similar to Example 1, the duplicate description is abbreviate | omitted by attaching | subjecting the same code | symbol.
The sound wavelength measuring device 10 is attached to a cylindrical pipe 12 whose one end is closed, a microphone (first microphone 14a) which is slidably mounted in the pipe axial direction within the pipe, and a closed end. A microphone (second microphone 14b) and a detection device 16 for detecting the sound pressure difference between the sound pressures measured by the first microphone 14a and the second microphone 14b are provided.

  The pipe 12 is a straight cylinder made of a transparent acrylic resin having an inner diameter of about 10 cm, and an outer cylinder 12a having a length of about 1 m that is closed at one end, and both ends that are inserted into the inner circumference of the outer cylinder 12a without a gap. It has a double-cylindrical structure consisting of a thin-walled inner cylinder 12b with a length of slightly over 1 m. Here, the inner cylinder 12b is inserted and removed while sliding with respect to the outer cylinder 12a, and a large step cannot be formed at the tip of the inner cylinder inserted into the outer cylinder. The outer cylinder 12a has a scale (not shown) for measuring the distance from the closed end.

  Both the first microphone 14a and the second microphone 14b are small sound collecting microphones, and the second microphone is fixedly attached to the center of the closed end of the outer cylinder 12a as in the second embodiment. On the other hand, the first microphone 14a is attached to the center of the opening end of the inner cylinder 12b on the side inserted into the outer cylinder 12a by a cross column 23 which is a thin rod attached in a cross shape in the radial direction.

Next, a wavelength measurement method using the sound wavelength measurement apparatus 10 described above will be described.
First, the inner cylinder 12b to which the first microphone 14a is attached is pushed in from the opening end of the outer cylinder 12a to which the second microphone 14b is attached at the closed end to the deepest part (closed end). Turn to. Then, by slowly pulling out the inner cylinder 12b to which the first microphone 14a is attached, the first microphone 14a is gradually moved away from the second microphone 14b. At this time, a change in the difference between the sound pressure measured by the first microphone 14 a and the sound pressure measured by the second microphone 14 b is observed by the display device of the detection device 16. And the position of the 1st microphone 14a when a sound pressure difference becomes the minimum is recorded by reading the scale written in the outer cylinder 12a.

  The fundamental wavelength to be measured is obtained from the fact that the distance (scale value of the first microphone 14a) between the first microphone 14a and the second microphone 14b when the sound pressure difference is minimized is λ. The fundamental frequency f (= 1 / T) is obtained from the above equation.

  According to the sound wavelength measuring apparatus of the present embodiment described above, the fundamental wavelength can be measured even when the sound pressure of the sound generated from the equipment is not stable, as in the effect of the apparatus of the above-described embodiment. It becomes. It is also possible to connect the attachment pipe of Example 2 to the inner cylinder.

  The configuration of the present invention is not limited to that described in the above embodiment, and can be changed as appropriate without departing from the spirit of the present invention. For example, it is of course possible to attach an attachment pipe to the apparatus of Example 1 or Example 2.

1 is a conceptual diagram of a sound wavelength measuring apparatus according to Embodiment 1. FIG. It is the figure which showed a mode that the attachment pipe was connected with a pipe. It is a perspective view showing an adjustment mechanism. This is the waveform of the sample sound displayed on the oscilloscope (closed end). This is the waveform of the sample sound displayed on the oscilloscope (closed end and open end). It shows the temporal change of the sound pressure detected by each microphone and the temporal change of the sound pressure difference. It shows the temporal change of the sound pressure detected by each microphone and the temporal change of the sound pressure difference. It shows the temporal change of the sound pressure detected by each microphone and the temporal change of the sound pressure difference. It shows the temporal change of the sound pressure detected by each microphone and the temporal change of the sound pressure difference. It shows the temporal change of the sound pressure detected by each microphone and the temporal change of the sound pressure difference. FIG. 6 is a conceptual diagram of a sound wavelength measuring apparatus according to a second embodiment.

Explanation of symbols

12 pipe 12 'attachment pipe 12a outer cylinder 12b inner cylinder 14a first microphone 14b second microphone 16 detection device 21 circular frame 23 cross column 25 cord

Claims (4)

A cylindrical pipe (12) closing one end;
A first microphone (14a) and a second microphone (14b) mounted in the pipe and measuring the sound pressure at the mounting position;
An adjustment mechanism capable of adjusting the distance between the first microphone and the second microphone;
A sound wavelength measurement device comprising: a detection device (16) for detecting a difference in sound pressure measured by the first microphone and the second microphone. The second microphone (14b) is fixedly attached to the closed end of the pipe (12),
The sound wavelength measuring device according to claim 1, wherein the adjusting mechanism is configured to slide the first microphone (14a) in the pipe axial direction within the pipe. The second microphone (14b) is fixedly attached to the closed end of the pipe (12),
The sound wavelength measuring device according to claim 1, wherein the adjusting mechanism changes a tube length between the first microphone (14a) and the second microphone.   The sound wavelength according to any one of claims 1 to 3, wherein an attachment pipe (12 ') is connected to the pipe (12) so as to extend the entire length of the pipe. measuring device.