CN104683906B - For the phonon crystal filter of high directivity audio speaker measuring system - Google Patents
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- CN104683906B CN104683906B CN201310627177.XA CN201310627177A CN104683906B CN 104683906 B CN104683906 B CN 104683906B CN 201310627177 A CN201310627177 A CN 201310627177A CN 104683906 B CN104683906 B CN 104683906B
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- 239000013078 crystal Substances 0.000 title claims abstract description 12
- 238000005259 measurement Methods 0.000 claims description 28
- 238000001914 filtration Methods 0.000 claims description 10
- 238000009413 insulation Methods 0.000 claims description 9
- 239000004038 photonic crystal Substances 0.000 claims description 7
- 230000002238 attenuated effect Effects 0.000 claims description 5
- 230000003247 decreasing effect Effects 0.000 claims description 3
- 230000000149 penetrating effect Effects 0.000 claims description 3
- 238000002604 ultrasonography Methods 0.000 abstract description 6
- 238000010521 absorption reaction Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 230000005236 sound signal Effects 0.000 description 2
- 238000003491 array Methods 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
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Abstract
The present invention relates to a kind of phonon crystal filter for high directivity audio speaker measuring system, including：Limited cylinder volume array, frame, stent and microphone；Wherein, frame is a hollow cuboid, it includes at least top surface, bottom surface, left surface and right flank；The limited cylinder volume array is located between top surface and the bottom surface of frame, and it includes multiple equidistant longish horizontal cylinders；The stent is mounted on the frame, and center is equipped with one for wearing the pipe of the microphone, and limited cylinder volume array is located at the front end of the microphone.Phonon crystal filter provided by the invention has band gap properties, there is greater attenuation to ultrasound, and the audio frequency sound shadow sound of band gap center frequency remotely of adjusting the distance is smaller.Therefore, it can effectively be reduced in high directivity audio speaker measuring system and pseudo noise is measured caused by microphone, and audio frequency sound is not had much influence.
Description
Technical Field
The invention relates to the technical field of acoustic measurement, in particular to a photonic crystal filtering device for a high-directivity audio speaker measurement system.
Background
The high-directivity audio speaker system is a novel speaker system based on the parametric array principle and can emit high-directivity audio sound to a specific direction. The basic principle is that the audio signal is modulated onto ultrasonic carrier wave, and after being transmitted by ultrasonic transducer array, the audio signal is nonlinearly demodulated in air to form audio sound. The audio sound generated by the demodulation inherits the high directivity of the ultrasonic wave, and therefore has high directivity. The high-directivity audio speaker can be widely applied to the fields of sound wave directional transmission, material acoustic characteristic measurement and the like.
When the two column frequencies are f1And f2(assume f)1＞f2) After the ultrasonic wave is transmitted by the ultrasonic transducer array, a plurality of differences (f) comprising two frequencies can be generated due to the nonlinear action in the air1-f2) Sound waves of different frequencies including the sum of the two frequencies, higher harmonics, etc. Because the attenuation coefficient of the sound wave is in direct proportion to the square of the frequency, other high-frequency components are attenuated quickly in the process of propagation, and therefore the difference frequency sound wave occupies a main position after the sound wave is propagated for a distance. If the frequency range of the difference frequency sound wave is in the sound frequency range, sound is formedAnd (4) frequency sound. However, two ultrasonic waves and an acoustic frequency sound wave exist in the near field region at the same time, and because the sound pressure level of the two ultrasonic waves is higher and can reach more than 115dB generally, pseudo noise is generated when the microphone is directly used for measurement in the region. The frequency of the generated pseudo noise is the difference (f) between the frequencies of the two ultrasonic waves1-f2) The amplitude being proportional to the product of the amplitudes of the two lines of ultrasound at the point of measurement, i.e. pn∝p1p2Wherein p is1And p2The amplitudes of the two lines of ultrasonic waves at the measuring point are respectively. It follows that the spurious noise caused by the measurement system is at the same frequency as the audible difference frequency sound produced by the highly directional audio speaker, but the amplitude is independent of the frequency of the difference frequency; the relationship between the audible difference frequency sound amplitude and the difference frequency wave frequency generated by the high-directivity loudspeaker isWherein n is more than or equal to 1 and less than or equal to 2. n is determined by the ratio of the rayleigh distance to the absorption distance, and when the rayleigh distance is far greater than the absorption distance, n is 2; when the absorption distance is much greater than the rayleigh distance, n is 1. Therefore, whether the pseudo noise is filtered or greatly reduced can be judged according to the measured frequency response curve of the difference frequency acoustic wave.
In highly directional audio speaker measurement systems, the presence of spurious noise severely interferes with the measurement of the actual demodulated audio sound, and particularly in the near field, spurious noise tends to be much larger than the audio sound actually produced by the highly directional audio speaker, i.e., pn＜＜pdTherefore, it is necessary to design an acoustic filtering device to filter the ultrasonic wave, so as to remove the pseudo noise and obtain the real audio sound by measurement. While at the same time not having as great an influence on the acoustic sound as possible.
Disclosure of Invention
The invention aims to overcome the defects that the prior art cannot remove pseudo noise and keep audio sound at the same time, thereby providing a device for filtering the pseudo noise and keeping the audio sound wave to the maximum extent.
In order to achieve the above object, the present invention provides a photonic crystal filtering apparatus for a highly directional audio speaker measuring system, comprising: the microphone comprises a limited long cylinder array 1, a frame 2, a bracket 3 and a microphone 4; wherein,
the frame 2 is a hollow cuboid, and at least comprises a top surface 21, a bottom surface 22, a left side surface 23 and a right side surface 24; the limited long cylinder array 1 is positioned between the top surface 21 and the bottom surface 22 of the frame 2 and comprises a plurality of limited long cylinders at equal intervals; the support 3 is arranged on the frame 2, a round pipe used for penetrating the microphone 4 is arranged at the center of the support, and the limited long cylinder array 1 is positioned at the front end of the microphone 4.
In the above technical solution, the distance between each limited long circular cylinder included in the limited long circular cylinder array 1 is determined according to the actual ultrasonic signal frequency that needs to be attenuated, that is: a ═ c0A/2 f, where a is the pitch, c0For sonic velocity, f is the center frequency at which ultrasonic waves are expected to be filtered, and the height of the finite long cylinder is greater than 30 mm.
In the technical scheme, the row number and the column number of the limited long cylinder array 1 are increased or decreased according to actual needs so as to correspond to ultrasonic sound insulation quantities with different sizes and be suitable for different measuring distances.
In the above technical scheme, the frame 2 at least comprises 4 identical rectangular plates, the rectangular plates are perpendicular to each other to form a hollow rectangular body, and the thickness of the rectangular plate is less than 1 mm.
In the technical scheme, the support 3 comprises a circular tube and at least 4 identical small rectangular plates, the circular tube is used for fixing the microphone 4, the length of the circular tube is greater than 30mm, and the distance between the top end of the circular tube and the limited long cylindrical array 1 is less than 5 mm; the small rectangular plate is vertically arranged on the frame 2 and used for connecting the circular tube with the frame 2, the length of the small rectangular plate is greater than 20mm, and the thickness of the small rectangular plate is smaller than 1 mm.
In the above technical solution, the diameter of the circular tube included in the support 3 is related to the size of the selected microphone.
The invention has the advantages that:
the photonic crystal filtering device provided by the invention has a band gap characteristic, has larger attenuation to ultrasound, and has smaller influence on audio frequency sound at a position far away from the center frequency of the band gap. Therefore, measurement pseudo noise caused by the microphone can be effectively reduced in the high directivity audio speaker measurement system without much influence on the audio sound.
Drawings
FIG. 1 is an embodiment of a photonic crystal filtering apparatus of a highly directional audio speaker measurement system of the present invention;
FIG. 2 is a graph showing the measurement results of the sound insulation amount of ultrasonic waves in the embodiment;
fig. 3 is a graph showing the measurement results of the sound insulation amount of an acoustic sound wave in the embodiment;
FIG. 4 is an amplitude response curve at 1 meter for 256 measured ultrasound transducer arrays;
FIG. 5 is a graph of actual measurements taken for a high directivity audio speaker without the use of a filter;
fig. 6 is a graph of actual measurements for a highly directional audio speaker using an embodiment.
The figures are numbered:
1 finite long cylinder array 2 frame 3 support
4 top surface 22 and bottom surface of microphone 21
23 left side 24 right side
Detailed Description
For a better understanding of the present invention, reference is made to the following detailed description of the invention taken in conjunction with the accompanying drawings.
Referring to fig. 1, the phononic crystal filtering apparatus for a highly directional audio speaker measuring system of the present invention includes: the microphone comprises a limited long cylinder array 1, a frame 2, a bracket 3 and a microphone 4; wherein, the frame 2 is a hollow cuboid, which comprises four surfaces, namely a top surface 21, a bottom surface 22, a left side surface 23 and a right side surface 24; the limited long cylinder array 1 is positioned between the top surface 21 and the bottom surface 22 of the frame 2 and comprises a plurality of limited long cylinders at equal intervals; the support 3 is arranged on four surfaces of the frame 2, and a circular tube for penetrating the microphone 4 is arranged at the center of the support, so that the limited long cylindrical array 1 is positioned at the front end of the microphone 4.
The various components of the device are described further below.
The distance between each limited long cylinder included in the limited long cylinder array 1 needs to be determined according to the actual ultrasonic signal frequency needing to be attenuated, that is: a ═ c0(ii)/2 f; wherein a is the pitch, c0F is the central frequency of the ultrasonic wave which is expected to be filtered out, so that the ultrasonic signal with f as the central frequency is effectively attenuated by utilizing the characteristic band gap characteristic of the phononic crystal, and the ultrasonic signal which is far away from the central frequency f has no obvious attenuation effect, thereby the acoustic sound can be kept to the maximum extent. In practical application, c is defined as the equation0And on the basis of a obtained by/2 f, the size of a can be finely adjusted according to actual needs. The limited long cylinder is higher than 30 mm.
In the present embodiment, the finite long cylinder array 1 is a 5 × 5 array, in other embodiments, the number of rows and columns of the array may be increased or decreased according to actual needs, and different numbers of rows and columns correspond to different sizes of ultrasonic sound insulation quantities, and are suitable for different measurement distances.
Frame 2 includes 4 the same rectangular boards, and mutually perpendicular between these 4 rectangular boards forms a hollow cuboid, and each rectangular board thickness is less than 1 mm. In this embodiment, the number of the rectangular boards included in the frame 2 is 4, and in other embodiments, 5 or 6 rectangular boards may be included.
In this embodiment, the support 3 includes a circular tube and 4 identical small rectangular plates, wherein the circular tube is used for fixing the microphone 4, the length of the circular tube is greater than 30mm, and the distance between the top end of the circular tube and the limited long cylindrical array is less than 5 mm; the 4 small rectangular plates are used for connecting the circular tube and the frame 2, are distributed around the circular tube in a cross shape, are perpendicular to four surfaces of the frame 2, and are longer than 20mm and thinner than 1 mm. In this embodiment, the number of the small rectangular plates included in the bracket 3 is 4, and in other embodiments, other numbers, such as 3, or 5, 6, etc., are also possible. The diameter of the circular tube is related to the size of the selected microphone 4, and can be designed according to actual conditions. In the present embodiment, the diameter of the circular tube for fixing the microphone 4 is slightly larger than 1.27cm, and in other embodiments, the circular tube can be designed according to the size of the microphone 4.
The effect of the phononic crystal filter device of the present invention is verified by experiments below.
Fig. 2 and 3 are schematic diagrams of the measurement results of the sound insulation amount of the phononic crystal filter device of the present invention shown in fig. 1 for ultrasonic sound and acoustic sound, respectively. As can be seen from the figure, the average sound insulation quantity of the filtering device in the ultrasonic frequency band of 32.5kHz-50.5kHz of the directional loudspeaker is above 15dB, and the maximum value is near 42.6 kHz; the sound insulation quantity in the sound wave frequency band of 0kHz-16kHz is within 3dB, and the sound insulation quantity in the frequency band of 0kHz-4kHz is within 1 dB. This embodiment is seen to be effective in attenuating ultrasound but has less of an acoustic effect.
To verify the effectiveness of the above embodiments, actual measurements were made on the high directivity audio speakers in the muffling chamber. The high-directivity audio speaker is composed of 256 ultrasonic transducer units with the diameter of 16mm, the carrier wave is 40kHz, a single-sideband modulation technology is adopted, and the amplitude response curve at 1m is shown in figure 4. The microphone was used with 1/2 inch model numbers from B & K: 4189 the microphone was placed at 1m from the axis of the high directivity speaker, and the frequency response of the high directivity speaker was measured. FIG. 5 is a measurement result of an unfiltered device, in which the measured low-frequency response is substantially independent of frequency, since the low-frequency band spurious noise is much larger than the audible sound generated by the directional speaker, and the magnitude of the spurious noise is proportional to the product of the ultrasonic waves; for the high frequency band, due to the narrow-band characteristic of the ultrasonic transducer array, the product of the amplitudes of the two ultrasonic waves generating the high frequency is not enough to cause the nonlinearity of the measuring microphone, namely, the pseudo noise problem is basically eliminated at the moment, so that the frequency response of the high frequency band is approximately consistent with the 1.6 power trend of the difference frequency wave frequency. Fig. 6 shows the measurement results after the above embodiment is added, and the whole frequency response curve of the directional loudspeaker is consistent with the 1.6 power trend of the difference frequency wave frequency, which proves that the pseudo noise is basically filtered.
In summary, the photonic crystal filter device provided by the invention has a band gap characteristic, and has a large attenuation to ultrasound and a small influence to audio frequency sound. The measuring pseudo noise caused by the microphone in the high-directivity audio speaker measuring system can be effectively reduced.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and are not limited. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (6)
1. A photonic crystal filtering apparatus for a highly directional audio speaker measurement system, comprising: the microphone comprises a limited long cylinder array (1), a frame (2), a support (3) and a microphone (4); wherein,
the frame (2) is a hollow cuboid and at least comprises a top surface (21), a bottom surface (22), a left side surface (23) and a right side surface (24); the limited long cylinder array (1) is positioned between the top surface (21) and the bottom surface (22) of the frame (2) and comprises a plurality of equally spaced limited long cylinders; the support (3) is arranged on the right side face of the frame (2), a round pipe used for penetrating the microphone (4) is arranged in the center of the support, and the limited long cylinder array (1) is located at the front end of the microphone (4).
2. The phononic crystal filter device for highly directional audio speaker measurement system according to claim 1, wherein the distance between each limited long cylinder included in the limited long cylinder array (1) is determined according to the actual ultrasonic signal frequency to be attenuated, that is: a ═ c0A/2 f, where a is the pitch, c0For sonic velocity, f is the center frequency at which ultrasonic waves are expected to be filtered, and the height of the finite long cylinder is greater than 30 mm.
3. The phononic crystal filter device for high directivity audio speaker measurement system according to claim 1, wherein the number of rows and columns of the finite long cylinder array (1) is increased or decreased according to actual needs to correspond to different ultrasonic sound insulation amounts, and the device is suitable for different measurement distances.
4. The phononic crystal filter assembly for highly directional audio speaker measurement systems according to claim 1, wherein said frame (2) comprises at least 4 identical rectangular plates, said rectangular plates being perpendicular to each other to form a hollow rectangular parallelepiped, said rectangular plates having a thickness of less than 1 mm.
5. The phononic crystal filter device for highly directional audio speaker measurement system according to claim 1, wherein said support (3) comprises a circular tube for holding said microphone (4) and having a length of more than 30mm and a tip spaced from said limited long cylindrical array (1) by less than 5mm, and at least 4 identical small rectangular plates; the small rectangular plate is vertically arranged on the frame (2) and used for connecting the circular tube with the frame (2), the length of the small rectangular plate is greater than 20mm, and the thickness of the small rectangular plate is smaller than 1 mm.
6. The photonic crystal filter apparatus for highly directional audio speaker measurement systems as claimed in claim 5, wherein said frame (3) comprises a circular tube having a diameter related to the size of the microphone selected.
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| CN105306004B (en) * | 2015-10-29 | 2018-06-29 | 中国科学院长春光学精密机械与物理研究所 | A kind of method that vibration mode selection is carried out to phonon crystal resonator |
| CN105656446B (en) * | 2015-12-17 | 2018-09-04 | 东莞酷派软件技术有限公司 | A kind of SAW filter and preparation method thereof |
| CN109036360B (en) * | 2018-06-29 | 2023-03-31 | 中国船舶重工集团公司第七一五研究所 | Voltage-withstanding acoustic filter for truncated parametric array and design method |
| CN117294280B (en) * | 2023-11-24 | 2024-02-06 | 苏州清听声学科技有限公司 | Ultrasonic filter for removing pseudo noise of parametric array loudspeaker |
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| CN101777346A (en) * | 2010-01-21 | 2010-07-14 | 北京工业大学 | Two-dimensional Archimedes lattice acoustic band gap material |
| CN102075846A (en) * | 2010-12-22 | 2011-05-25 | 中国科学院声学研究所 | Acoustic filter device for high-directivity audio loudspeaker measuring system |
| EP2442301A1 (en) * | 2007-12-21 | 2012-04-18 | 3m Innovative Properties Company | Viscoelastic phononic crystal |
| CN202652159U (en) * | 2012-07-17 | 2013-01-02 | 中国科学院声学研究所 | Two-dimensional piezoelectric phononic crystal radio-frequency acoustic waveguide |
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| CN1635705A (en) * | 2003-12-31 | 2005-07-06 | 财团法人工业技术研究院 | Noise suppression method for filter |
| EP2442301A1 (en) * | 2007-12-21 | 2012-04-18 | 3m Innovative Properties Company | Viscoelastic phononic crystal |
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