JP5044798B2 - High speed air flow noise prevention microphone device - Google Patents

Description

  The present invention relates to a high-speed airflow noise prevention microphone device that detects sound in a high-speed airflow without generating a self-generated sound of a microphone.

Anti-phase / same amplitude of noise emitted from jet fan for ventilation in road tunnels, noise emitted from automobile engine exhaust pipe, or wheel rolling noise emitted from high-speed traveling vehicle There is an active noise control system that emits speaker sound from the vicinity of a noise generation source to interfere and mute the noise. In order to efficiently mute noise with this system, the noise must be detected by a jet fan in a high-speed air flow of about 30 m / sec or detected by a microphone installed on a vehicle traveling at high speed. . When a strong wind directly hits the microphone, a large amount of wind noise generated by the microphone itself is input, and the quality of the detected noise signal is significantly degraded. Therefore, a nose cone type windshield microphone and a sound collector that detects sound by installing a small hole at a position where wind noise is difficult to occur are installed to reduce the effect of wind noise, or the acceleration sensor vibrates the noise source. A method for eliminating the influence of wind noise has been proposed, such as obtaining sound signals for control by detecting the noise (Patent Document 1 and Patent Document 2).
JP 2001-356777 A Japanese Patent Laid-Open No. 9-269263

  However, installing the nose cone type windshield microphone in the jet fan casing to detect noise inserts protrusions into the airflow path of the high-speed airflow, so pressure due to wind pressure or turbulence in the airflow This may be a fatal obstacle for jet fans that require efficient discharge of high-speed jets, such as loss, new noise, or poor maintainability due to the insertion of protrusions on the inner wall surface.

  In addition, a method using a sound collector installed at a position where wind noise is difficult to generate or an acceleration sensor that detects periodic noise by detecting periodic vibrations is used when a noise signal is detected and a canceling sound is output from a speaker. There arises a problem that it is difficult to correlate the sound propagation properties of both at the interference point between the noise and the canceling sound. Especially when dealing with noise including wideband frequencies, detection of noise signals in active noise control systems that need to output loudspeakers with the exact opposite phase and amplitude over the entire band of emitted and discharged noise As a means, there has been a problem that it has a difficult problem from the initial stage of detecting a control signal.

  In an apparatus for detecting sound in a high-speed air flow without generating self-generated sound, a microphone, a cylindrical cover for storing the microphone, a first opening provided on the high-speed air flow side of the cylindrical cover, A second opening provided on the stationary or low-speed airflow side of the cylindrical cover, and the cross section of the air passage between the microphone and the inner wall of the cylindrical cover and the second opening are sufficiently larger than the first opening. As a result, an atmospheric pressure difference is generated from the flow velocity difference between the first opening and the second opening, that is, the high-speed airflow side and the stationary or low-speed airflow side, and the high pressure side second opening is formed in the cylindrical cover. A high-speed airflow noise prevention mask that creates a flow path for airflow flowing to the first opening on the low-pressure side and sufficiently lowers the flow velocity of the airflow passing near the microphone than the flow velocity of the airflow passing through the first opening. It is a Kurohon apparatus.

  In the above high-speed airflow noise prevention microphone device, an inner wall surface of the cylindrical cover that surrounds the first opening and the microphone is an elliptical surface having first and second focal points, and is located at the center of the first opening. The first focal point of the elliptical surface is disposed, and the second focal point of the elliptical surface is disposed at the center of the microphone, whereby the sound signal component that is input from the first opening and propagates radially is transmitted by the microphone. Collect sound.

The microphone device for preventing high-speed airflow noise according to the present invention can detect noise discharged together with high-speed airflow, noise outside the vehicle body of a high-speed traveling body, etc. without generating wind noise. If there is a strong wind hitting the microphone using the property of the fluid flow that the pressure is small at a high speed and the flow rate per unit time when the fluid flows through the pipe line does not change. It is configured so that there is no.
Because noise is taken in from a small hole provided in a plane parallel to the flow of airflow, pressure loss is not applied to the high-speed airflow flowing through the pipeline, and detection of external noise such as wheel rolling noise of high-speed traveling vehicles is noise. It can be detected at the nearest position that can be regarded as the source of In particular, the present invention is effective as a noise detection method for active noise control in which the characteristics of wave propagation of sound that changes from moment to moment are strictly grasped and acoustically processed appropriately.

Embodiment 1

The best mode for carrying out the present invention will be described below in detail with reference to the drawings.
In addition, in each figure, the same part attaches | subjects the same code | symbol and the overlapping description is abbreviate | omitted.

A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing the configuration of the present invention. FIG. 2 is a cross-sectional view of a silencer actuator using the present invention, and FIG. 4 is a schematic diagram of a jet fan noise reduction apparatus and an evaluation apparatus using the present invention.
1, 2, and 4, 1 is a microphone, 2 is a cylindrical cover, 3 is a first opening, 4 is a second opening, 5 is an elliptical wall surface, 6 is a sound wave guide wall, 7 is a sound wave rectifier, 8 Is an air flow introducing cylinder, 9 is a sound absorbing material, 10 is a filter, 11 is a silencer actuator, 12 is a speaker, 13 is an enclosure, 14 is a canceling sound discharge port, 15 is a control circuit, 16 is an amplifier, 21 is a jet fan, 22 Is an axial blower.

  As shown in FIG. 1, the microphone device 1 of the present invention is housed in the approximate center of the inner wall surrounded by the cylindrical cover 2. One opening 3 is provided, and a second opening 4 is provided on the stationary or low-speed airflow side. The cross section of the ventilation path sandwiched between the microphone 1 and the inner wall surface of the cylindrical cover 2 and the opening surface of the second opening 4 are sufficiently larger than the opening surface of the first opening 3.

  The inner wall surface of the cylindrical cover 2 that surrounds the first opening 3 and the microphone 1 is an elliptical wall surface 5 having first and second focal points, and the first wall of the elliptical wall surface 5 is located at the center of the first opening 3. The second focal point of the elliptical wall surface 5 is disposed at the center of the microphone 1. The elliptical wall surface 5, the sound wave guiding wall 6, and the sound wave rectifying body 7 are made of a highly reflective material that reflects sound well, and the air flow introducing cylinder 8 has a porous sound absorbing material 9 attached to the inner wall surface of the air flow introduction tube 8. 4 is provided with a dust-proof filter 10.

  In such a high-speed airflow noise prevention microphone device of the present invention, the outside of the first opening 3 faces the flow of the high-speed airflow, and the outside of the second opening 4 is the flow of the stationary or low-speed airflow without the airflow. Although the air pressure difference is generated between the first opening 3 and the second opening 4, the first opening 3 side where the airflow is fast has a low air pressure and the airflow is slow. The atmospheric pressure on the side increases. Therefore, a flow path for an airflow flowing from the second opening 4 on the high pressure side to the first opening 3 on the low pressure side is formed in the cylindrical cover 2.

  Since the airflow flowing through the cylindrical flow passage in the cylindrical cover 2 is continuous and the flow rate per unit time does not change at any position in the flow passage, it passes through the opening of the first opening 3 having a small opening surface. Since the flow velocity of the airflow is fast and the periphery of the microphone 1 and the opening surface of the second opening 4 are sufficiently larger than the opening surface of the first opening 3, the flow velocity of the passing airflow is slow. The ratio of the speed of the passing airflow is inversely proportional to the size of the cross section of each airflow passage portion.

  FIG. 2 shows a silencer actuator 11 in which the microphone device for preventing high-speed airflow noise of the present invention is incorporated in an enclosure 13 as a noise detection device in high-speed airflow. As shown in FIG. 4, the silencer actuator 11 is attached to the outer periphery of the intake / exhaust port of the jet fan 21 and is used as a jet fan noise reduction device for road tunnel ventilation.

  In the high-speed airflow that is discharged from the axial blower 22 and is sent out, for example, toward the exhaust port of the jet fan 21, noise that propagates using the high-speed airflow as a medium is also released simultaneously. Noise is introduced into the cylindrical cover 2 from the first opening 3 provided in the silencer actuator 11, and diffuses and propagates radially. Noise radiated from the first opening 3, that is, the first focal point of the elliptical wall surface 5 is corrected by the sound wave guiding wall 6 and the conical acoustic wave rectifier 7, and reflected by the elliptical wall surface 5. The signal converges again to the second focal point of the elliptical wall surface 5, that is, the microphone 1, and the sound signal component is strengthened and input to the microphone 1. The output signal of the microphone 1 is supplied to a control circuit 15 that performs active silencing control, and a canceling sound is output from the speaker 12 via the amplifier 16 by the output of the control circuit 15, and the canceling sound is a canceling sound emission port 14. Released.

  Noise that is emitted from the axial blower 22 and propagates straight through the high-speed airflow is input from the first opening 3 to the position of the canceling sound discharge port 14 and the input from the first opening 3 and the elliptical wall surface 5 The propagation distance on the cancellation sound side, which is the sum of the propagation distance from the speaker 12 to the microphone 1 and the propagation distance from the speaker 12 to the cancellation sound emission port 14, is distorted at the interference point due to the difference in the propagation route of both sounds. Both sounds are interference-muted while the acoustic propagation properties that do not occur are equivalent.

  As described above, according to the present invention, it is possible to detect a high-quality noise signal in a high-speed air flow without generating a self-generated sound generated by the microphone itself when a strong wind directly hits the microphone. A high-speed airflow is flowing around the opening of the first opening 3 and wind hits the opening edge of the first opening 3, and there is concern about the generation of wind noise. However, the noise around the intake and exhaust ports of the jet fan 21 Since the noise generated by the rotation of the fan of the axial blower 22 is much higher than the noise generated by the flow of the air, the noise of the jet fan 21 can be handled as the dominant noise of the fan.

Embodiment 2

A second embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a structural diagram of the inside of a windshield using the present invention. The second embodiment of the present invention is used for an evaluation device for sound in a high-speed air stream emitted from a jet tunnel noise reduction device for road tunnel ventilation.
23 is a windshield tower and 24 is a tunnel ceiling wall surface.

FIG. 3 shows the high-speed airflow noise prevention microphone apparatus of the present invention housed in the windshield 23. The windshield 23 is a cylindrical windshield in which the front tip and the rear tip are sharpened and the trunk portion has a streamlined ship-like cross section in order to prevent airflow disturbance and separation caused by the wind pressure of the high-speed airflow.
As shown in FIG. 4, the windbreak tower 23 is suspended from the tunnel ceiling wall surface 24 together with the noise reduction device-equipped jet fan 21 in which the silencer actuator 11 is attached to the outer periphery of the intake and exhaust ports. The windshield 23 is installed in front of the opening on the central axis of the jet fan 21 so that the lower end of the windshield 23 coincides with a position several meters away.

  When the axial blower 22 rotates, noise is also discharged from the exhaust port of the jet fan 21 together with a high-speed air stream having an average air speed of about 30 m / sec. The high-speed air current hardly changes in the speed of the air current at the position near the opening of the jet fan 21 and the position near the lower end of the windshield 23 installed in front of the opening, and the wind speed hardly decreases. Therefore, the flow velocity of the airflow facing the outside of the first opening 3 provided on the flat surface at the lower end of the windshield 23 is about 30 m / sec. On the other hand, since the airflow introduction cylinder 8 is extended to the tunnel ceiling wall surface 24 near the second opening 4, the outside of the second opening 4 is directly affected by the high-speed airflow like the outside of the first opening 3. Therefore, the flow velocity is much slower than the flow velocity of the airflow outside the first opening 3.

  The pressure on the first opening 3 side where the airflow is fast is low, and the pressure on the second opening 4 side where the airflow is slow is high. In the cylindrical cover 2, an airflow passage is formed from the second opening 4 on the high pressure side to the first opening 3 on the low pressure side. The flow velocity of the airflow passing through the opening of the first opening 3 having a small opening surface is high, and the flow velocity of the airflow passing through the flow passage around the microphone 1 sufficiently larger than the opening surface of the first opening 3 is low. Therefore, since strong wind does not directly hit the microphone 1, noise can be detected while preventing the self-generated sound generated by the microphone 1 itself.

  In the above embodiment, the case where the present invention is applied to a road tunnel ventilation jet fan noise reduction device and a sound evaluation device in a high-speed airflow has been described. Noise emitted from a high-speed traveling vehicle can be detected while suppressing generation of wind noise. Further, the fluid serving as the sound propagation medium may be a high-speed water flow instead of the high-speed air flow, and the present invention can be applied similarly to the above embodiment. Even when the present invention is applied as described above, the same effects as those of the above-described embodiment can be obtained.

  It is sectional drawing which shows the structure of this invention.   It is sectional drawing of the silencer actuator using this invention.   It is a structure figure inside a windshield tower using the present invention.   1 is a schematic diagram of a jet fan noise reduction device and an evaluation device using the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Microphone, 2 ... Cylindrical cover, 3 ... 1st opening, 4 ... 2nd opening, 5 ... Ellipse wall surface, 6 ... Sound wave guide wall, 7 ... Sound wave rectifier, 8 ... Air flow introduction cylinder, 9 ... Sound absorption material, DESCRIPTION OF SYMBOLS 10 ... Filter, 11 ... Silencer actuator, 12 ... Speaker, 13 ... Enclosure, 14 ... Canceling sound discharge port, 15 ... Control circuit, 16 ... Amplifier, 21 ... Jet fan, 22 ... Axial fan, 23 ... Windshield tower, 24 ... Tunnel ceiling wall

Claims (1)

Microphone (1) ,
A cylindrical cover (2) for housing the microphone (1) ;
A first opening (3) provided on the high-speed airflow side of the cylindrical cover (2) ;
A second opening (4) provided on the stationary or low-speed airflow side of the cylindrical cover (2) ,
A high-speed airflow noise-preventing microphone device in which the cross section of the air passage between the microphone (1) and the inner wall of the cylindrical cover (2) and the second opening (4) are sufficiently larger than the first opening (3). In
An inner wall surface of the cylindrical cover (2) surrounding the first opening (3) and the microphone (1) is an elliptical surface having first and second focal points, and the first opening (3) A high-speed airflow noise-preventing microphone device, wherein the first focal point of the elliptical surface is disposed at the center and the second focal point of the elliptical surface is disposed at the center of the microphone (1) .

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