JP5721483B2 - Acoustic characteristic measuring device - Google Patents

Description

  The present invention relates to an acoustic characteristic measuring apparatus that measures an acoustic characteristic of a specimen using an acoustic tube.

  Conventionally, this type of acoustic characteristic measuring apparatus is configured as shown in FIG. 5, for example (see Patent Document 1). In FIG. 5, reference numeral 1 denotes an acoustic tube for generating a standing wave. A test object (sound absorbing material) 2 to be measured is accommodated in the acoustic tube 1. A speaker 3 as a sound source is provided on one end side of the acoustic tube 1, and a piston 5 connected to the rigid wall 4 is provided on the other end side. The rigid wall 4 is for forming a back air layer 6 between the test body 2 and the piston 5 is moved in the longitudinal direction of the acoustic tube 1 to adjust the test body 2 and the rigid wall 4 to a specified distance. It is possible.

  Between the speaker 3 and the test body 2 in the acoustic tube 1, measurement microphones 7-1 and 7-2 for measuring the sound pressure in the acoustic tube 1 are connected to the microphone holders 8-1 and 8-2. It is installed and provided. These measurement microphones 7-1 and 7-2 are installed at two locations separated in the longitudinal direction of the acoustic tube 1, and measure the sound pressure at each position.

  Then, a stationary random sound wave, for example, white noise (incident wave) is generated from the speaker 3, propagated as a plane wave in the acoustic tube 1, and applied to the test body 2. The incident wave passes through the test body 2 and is reflected by the rigid wall 4, and a standing wave interference pattern is generated inside the acoustic tube 1 by superposition of the incident wave (forward wave) and the reflected wave (reverse wave). Two sound pressures of the acoustic tube 1 are measured by the measurement microphones 7-1 and 7-2 and input to an FFT (Fast Fourier Transform) analyzer to calculate a complex sound pressure transfer function. From this transfer function, the acoustic impedance of the front surface of the test body 2 is obtained using the acoustic impedance equation according to the two-point microphone method. Moreover, the acoustic impedance of the rear surface of the test body 2 can be calculated analytically. From these, the characteristic impedance and propagation constant of the specimen 2 are calculated.

  In the acoustic tube 1 having a general circular cross section as described above, it is premised that the plane wave from the speaker 3 proceeds and retreats in a circular cross section without being disturbed. The measurable upper limit frequency of the acoustic tube 1 depends on the relationship between the wavelength, the tube inner diameter φ1, and the inter-microphone distance ΔM. Usually, the inner diameter φ1 of the acoustic tube 1 is about 29 mm to 100 mm. For example, the inner diameter φ1 = 100 mm can be measured up to about 2 KHz, and the inner diameter φ1 = 29 mm can be measured up to about 6.8 KHz.

Japanese Patent Laid-Open No. 08-233649

  By the way, since the upper limit of the human audible range is as high as about 20 KHz, it is sometimes required to measure acoustic characteristics with a high frequency exceeding 10 KHz. In order to measure up to such a high frequency, it is conceivable to reduce the inner diameter φ1 of the acoustic tube 1 and the distance ΔM between the microphones. In this case, the microphone 7-1 to the acoustic tube 1, 7-2 and microphone holders 8-1 and 8-2 have a problem that the circular cross-sectional shape of the tube is greatly changed, and the plane wave traveling in the tube is disturbed, resulting in unstable measurement data.

  That is, as shown in FIG. 6, since the circular cross-sectional shape of the tube changes in the mounting portion of the measurement microphone 7-1 and microphone holder 8-1 on the acoustic tube 1, the plane wave traveling in the tube is disturbed. It becomes a factor. The same applies to the mounting portions of the measurement microphone 7-2 and the microphone holder 8-2. When the inner diameter φ1 of the acoustic tube 1 is large, the opening diameter D1 with respect to the inner diameter φ1 is small and can be ignored.

  However, since the opening diameter D1 is determined and fixed by the outer diameters of the microphone holders 8-1 and 8-2, if the acoustic tube 1 is thinned to, for example, 14 mm or less, a relatively large change occurs in the circular cross-sectional shape of the tube. The turbulence of the plane wave traveling in the tube cannot be ignored. Therefore, it is difficult for the general acoustic tube 1 to measure the acoustic characteristics stably up to a high frequency range exceeding 10 KHz.

  The present invention has been proposed in view of the above, and an object thereof is to provide an acoustic characteristic measuring apparatus capable of measuring acoustic characteristics stably up to a high frequency range.

In order to solve the above-described problem, the acoustic characteristic measuring apparatus according to the first aspect of the present invention provides a sound source 12 at one end of an acoustic tube 11 in which a test object 13 to be measured is accommodated. A plane wave is excited to measure a complex sound pressure transfer function between two longitudinal positions between the sound source 12 and the test body 13 by the measurement microphones 18-1, 18-2, 18 and this complex. An acoustic characteristic measuring apparatus capable of calculating an acoustic characteristic from a sound pressure transfer function, wherein an inner diameter φ2 of the acoustic tube 11 is 14 mm or less, and the measurement microphones 18-1 and 18 to the acoustic tube 11 are provided. -2 and 18 have an opening diameter D2 of 1/3 or less of the inner diameter φ2 of the acoustic tube 11 , and the measurement microphones 18-1, 18-2, and 18 are respectively microphone holders 17-1. , The microphone holders 17-1, 17-2, and 17 are attached to the acoustic tube 11 through 17-2 and 17, and end portions of the microphone holders 17-1, 17-2, and 17 are in bottomed holes 22 formed in the outer peripheral portion of the acoustic tube 11 The microphone opening 23 is disposed at the bottom of the bottomed hole 22, and the microphone holder 17 accommodates the O-ring 19 on the inner surface so that the O-ring 19 can be moved up and down when the measurement microphone 18 is attached and removed. An inner groove 20 and an inner pressure adjusting hole 21 provided at the bottom of the inner groove 20 and communicating with the outside of the acoustic tube 11 are provided .

In the present invention, by forming a microphone opening having an opening diameter sufficiently smaller than the inner diameter of the acoustic tube in the mounting portion of the measurement microphone, the cross-sectional shape of the acoustic tube is disturbed even if the inner diameter of the acoustic tube is reduced. Can be reduced, and the disturbance of the measurement value due to this can be reduced. Therefore, stable acoustic characteristics can be measured up to a high frequency range.

Furthermore, fitted one end of Ma Ikurohonhoruda in a bottomed hole formed in the outer periphery of the acoustic tube, by arranging the microphone opening in the bottom of the bottomed hole, you need to penetrate the microphone holder to the acoustic tube Therefore, the disturbance in the cross-sectional shape of the acoustic tube can be reduced.

When the microphone is attached / detached, the pressure change in the acoustic tube can be suppressed by the internal pressure adjusting hole, so that the microphone can be safely replaced.

It is a cross-sectional view of the mounting part of the microphone and the microphone holder to the acoustic tube in the acoustic characteristic measuring apparatus according to the embodiment of the present invention. It is a longitudinal cross-sectional view which shows the acoustic characteristic measuring apparatus which concerns on the Example of this invention. It is a figure which shows the example of a measurement of characteristic impedance when changing the ratio of the internal diameter of an acoustic tube and opening part diameter in an acoustic characteristic measuring apparatus. FIG. 6 shows a microphone and a microphone holder mounting portion on an acoustic tube in an acoustic characteristic measuring apparatus according to another embodiment of the present invention, wherein (a) is a cross-sectional view when the microphone is mounted, and (b) is a microphone removal. FIG. It is a longitudinal cross-sectional view of the conventional acoustic characteristic measuring apparatus. It is a cross-sectional view of the mounting part of the microphone and the microphone holder to the acoustic tube in the conventional acoustic characteristic measuring apparatus.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 and FIG. 2 are each for explaining an acoustic characteristic measuring apparatus according to an embodiment of the present invention, and FIG. 1 is a cross-sectional view showing an extracted portion of a microphone and a microphone holder attached to an acoustic tube, FIG. 2 is a longitudinal sectional view of the entire apparatus. As shown in FIG. 2, in this acoustic characteristic measuring apparatus, a speaker 12 as a sound source is installed on one end side of an acoustic tube 11 for generating a standing wave, and a test object (sound absorbing material) 13 to be measured is placed in the tube. Contained.

  In this example, the acoustic tube 11 is formed of a transparent acrylic pipe, the inner diameter φ2 is 14 mm, and the total length L is about 150 mm. By forming the acoustic tube 11 with a transparent material, it is possible to easily confirm whether the state of the test body (deformation, position, etc.) and the position of the microphone are correct after the test body is set. The speaker 12 excites a plane wave in the acoustic tube 11, and various sizes of speaker units can be used by joining to one end of the acoustic tube 11 via an adapter, for example, 1/4 inch. Alternatively, a small speaker such as a 1 / 2-inch size condenser microphone or headphone may be used.

  A hollow cylindrical spacer ring 15-1 for forming a back air layer 14 is provided on the back surface of the test body 13, and a spacer 16-1 serving as a rigid wall is provided behind the spacer ring 15-1. ing. A spacer ring 15-2 and a spacer 16-2 are housed behind the spacer 16-1. Various widths are prepared for the spacer rings 15-1 and 15-2 and the spacers 16-1 and 16-2, and the spacer rings 15-1 and 15-2 and the spacers 16-1 and 16-2 are respectively provided. The distance from the test body 13 to the rigid wall (spacer 16-1) can be adjusted by changing or increasing / decreasing.

  On the side surface of the acoustic tube 11 between the speaker 12 and the test body 13, measurement microphones 18-1 and 18-2 inserted into microphone holders 17-1 and 17-2 are central axes of the acoustic tube 11. It is installed in a direction substantially orthogonal to AX. Then, the complex sound pressure transfer function between the two longitudinal positions is measured by the two measurement microphones 18-1 and 18-2, and the acoustic characteristics can be calculated from the transfer function.

  As shown in FIG. 1, a microphone opening 23 is provided in a portion where the measurement microphone 18-1 and the microphone holder 17-1 are attached to the acoustic tube 11. The opening diameter D2 of the microphone opening 23 is set to 1/3 or less of the inner diameter φ2 of the acoustic tube 11. The same applies to the mounting portions of the measurement microphone 18-2 and the microphone holder 17-2.

  That is, conventionally, as shown in FIG. 6, the through hole 9 is formed in the acoustic tube 1 to form the microphone opening 10 equal to the outer diameter of the microphone holder 8-1. A microphone holder 17-1 is mounted so as not to penetrate the tube 11, and a microphone opening D2 that is substantially equal to or smaller than the outer diameter of the measurement microphones 18-1 and 18-2 is formed.

  In order to obtain such a structure, for example, a circular bottomed hole 22 that is substantially equal to the outer diameter of the microphone holders 17-1 and 17-2 and does not reach the inner wall is provided on the outer periphery of the microphone mounting portion of the acoustic tube 11. Then, the ends of the microphone holders 17-1 and 17-2 are fitted into the bottomed hole 22. The outer diameters of the measurement microphones 18-1 and 18-2 are substantially equal to the inner diameters of the microphone holders 17-1 and 17-2, and are inserted into the microphone holders 17-1 and 17-2 for measurement. The tip portions of the microphones 18-1 and 18-2 are disposed at positions corresponding to the inner surface of the acoustic tube 11. In this example, the opening diameter D2 on the inner surface of the acoustic tube 11 is smaller than the outer diameter of the measurement microphones 18-1 and 18-2.

  In the configuration as described above, when a steady random sound wave, for example, white noise, is generated from the speaker 12 and propagates as a plane wave in the acoustic tube 11 and hits the test body 13, the incident wave passes through the test body 13 and is rigid. Reflected by the wall (spacer 16-1), a standing wave interference pattern is generated in the acoustic tube 11 by superposition of the incident wave and the reflected wave.

  Then, the two sound pressures of the acoustic tube 11 are measured by the measurement microphones 18-1 and 18-2, and input to, for example, an FFT (Fast Fourier Transform) analyzer to calculate a complex sound pressure transfer function. From this transfer function, the acoustic impedance of the front surface of the test body 13 is obtained using a well-known acoustic impedance equation according to the two-point microphone method. Further, the acoustic impedance of the rear surface of the test body 13 can be calculated analytically. From these, the characteristic impedance and propagation constant of the test body 13 are calculated.

FIG. 3 shows a measurement example of characteristic impedance when the ratio of the inner diameter φ2 and the opening diameter D2 of the acoustic tube 11 in the acoustic characteristic measuring apparatus described above is changed. Here, the characteristic impedance (Z / ρc ₀ ) at a frequency of 4 KHz to 10 KHz is measured with the inner diameter φ2 of the acoustic tube 11 kept constant and the opening diameter D2 changed. Here, ρ is the density of air, and c ₀ is the speed of sound in the air. The broken line 30 is the real part data when the opening diameter is large, the broken line 31 is the imaginary part data when the opening diameter is large, the solid line 32 is the real part data with a small opening diameter, and the solid line 32 is the opening diameter. This is the imaginary part data when is small.

  As is clear from FIG. 3, when the opening diameter D2 is large, the data disturbances Δ1 and Δ2 are large in both the real part and the imaginary part, and the measurement data is not stable, resulting in a large disturbance. On the other hand, when the opening diameter D2 is reduced, the data disturbances Δ3 and Δ4 can be reduced. An experiment was conducted by changing the ratio between the inner diameter φ2 of the acoustic tube 11 and the opening diameter D2. As a result, the opening diameter D2 of the microphone opening 23 was set to 1/3 or less of the inner diameter φ2 of the acoustic tube 11 to obtain an acoustic tube. The influence on the plane wave traveling in 11 can be reduced, and a favorable result was obtained.

  Therefore, according to the configuration as described above, the microphone holders 17-1 and 17-2 are not allowed to penetrate the acoustic tube 11, and the mounting portions of the measurement microphones 18-1 and 18-2 are attached to the acoustic tube 11. Since the microphone opening 23 having an opening diameter D2 sufficiently smaller than the inner diameter φ2 is formed, the disturbance of the cross-sectional shape of the acoustic tube 11 can be reduced, and even if the inner diameter φ2 of the acoustic tube 11 is reduced, it is stable to a high frequency range. Measurement of acoustic characteristics becomes possible. As a result, stable measurement can be performed up to a high frequency exceeding 10 KHz, which is difficult to measure with a general acoustic tube.

Figure 4 (a), (b) shows a mounting portion of the microphone and microphone holder to the acoustic tube in their respective acoustic characteristic measuring apparatus, (a) Figure is a cross-sectional view of the time of the microphone mount, (b The figure is a cross-sectional view when the microphone is removed. In this embodiment, the microphone holder is provided with an internal pressure adjusting hole that can be opened and closed by moving the O-ring. Since other basic configuration is the same as the above mentioned, the detailed description thereof is omitted.

  That is, an inner groove 20 is provided on the inner surface of the hollow tubular microphone holder 17 so as to accommodate the O-ring 19 so as to be movable up and down when the measurement microphone 18 is attached and removed, and an inner pressure adjusting hole 21 is provided at the bottom of the inner groove 20. Is provided. The internal pressure adjusting hole 21 communicates from the inner surface of the microphone holder 17 to the outer peripheral portion (outside of the acoustic tube 11).

  When the microphone 18 is attached, as shown in FIG. 4A, the O-ring 19 moves to the bottom of the inner groove 20 in accordance with the downward pressing operation (in the direction of arrow A) to the microphone 18 and the inner pressure adjusting hole 21 is moved. When the microphone 18 is removed, as shown in FIG. 4B, the O-ring 19 moves to the upper part of the inner groove 20 in accordance with the upward movement of the microphone 18 (in the direction of arrow B), so that the internal pressure adjusting hole is 21 is open.

  According to the configuration as described above, the pressure change in the acoustic tube 11 can be suppressed by the internal pressure adjusting hole 21 when the microphone 18 is attached / detached, so that the microphone 18 can be safely replaced. In particular, if the inner diameter of the acoustic tube 11 is reduced to 14 mm or less, the pressure in the tube changes greatly when the microphone 18 is attached or detached, so that the microphone 18 may be destroyed, and as the inner diameter of the acoustic tube 11 decreases. A big effect is acquired.

In the above embodiment, the case where the spacer rings 15-1 and 15-2 and the spacers 16-1 and 16-2 are used in order to form the back air layer 14 behind the test body 13 is taken as an example. As described above, it is a matter of course that a back air layer may be generated by the piston and the rigid wall.

Has been described in the following Uehon invention, the present invention is not limited to the above you施例, in an implementation stage can be variously modified without departing from the scope of the invention. Further, the upper you施例include inventions of various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. Be removed several of the constituent elements shown in if real施例example, the invention can be at least one of resolution of the problems described in the section of the problems to be solved, described in the section of the effects of the invention In a case where at least one of the obtained effects can be obtained, a configuration in which this configuration requirement is deleted can be extracted as an invention.

DESCRIPTION OF SYMBOLS 1 Acoustic tube 2 Test body 3 Speaker 4 Hard wall 5 Piston 6 Back air layer 7-1, 7-2 Microphone 8-1, 8-2 Microphone holder 9 Through-hole 10 Microphone opening 11 Acoustic tube 12 Speaker (sound source)
13 Specimen 14 Back air layer 15-1, 15-2 Spacer ring 16-1, 16-2 Spacer 17-1, 17-2, 17 Microphone holder 18-1, 18-2, 18 Measurement microphone 19 O-ring 20 inner groove 21 inner pressure adjusting hole 22 bottomed hole 23 microphone opening ΔM distance between microphones φ1, φ2 inner diameter of acoustic tube AX central axis of acoustic tube D1, D2 opening diameter

Claims (1)

A sound source (12) is provided at one end of an acoustic tube (11) containing a test object (13) to be measured, and a plane wave is excited in the acoustic tube (11) by the sound source (12), and a measurement microphone (18 -1, 18-2, 18), a complex sound pressure transfer function between two longitudinal positions between the sound source (12) and the test body (13) is measured, and from this complex sound pressure transfer function, An acoustic characteristic measuring apparatus capable of calculating an acoustic characteristic,
The inner diameter (φ2) of the acoustic tube (11) is 14 mm or less, and the opening diameter (D2) of the mounting portion of the measurement microphone (18-1, 18-2, 18) to the acoustic tube (11). Is 1/3 or less of the inner diameter (φ2) of the acoustic tube (11) , and the measurement microphones (18-1, 18-2, 18) are respectively microphone holders (17-1, 17-2, 17) is attached to the acoustic tube (11) via the bottom end of the microphone holder (17-1, 17-2, 17) formed in the outer periphery of the acoustic tube (11). (22) is fitted in, the microphone opening (23) is arranged at the bottom of the bottomed hole (22), and the microphone holder (17) is mounted on the inner surface of the measurement microphone (18). O-ring (19) can be moved up and down when removed An acoustic characteristic characterized by comprising an inner groove (20) that is accommodated in the capacity and an internal pressure adjusting hole (21) that is provided at the bottom of the inner groove (20) and communicates with the outside of the acoustic pipe (11). measuring device.

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