CN110501427B - Portable device and method for measuring sound absorption coefficient of material based on short sound tube pulse method - Google Patents
Portable device and method for measuring sound absorption coefficient of material based on short sound tube pulse method Download PDFInfo
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Abstract
The invention provides a portable device and a method for measuring the sound absorption coefficient of a material based on short sound tube and superimposed pulse extraction. The method has the advantages that the used tube length is short, the problem of frequency limitation of a transfer function method and the problem of sound attenuation of a pulse separation method are avoided, convenience of experimental operation is improved, and conditions are provided for a portable pulse method.
Description
Technical Field
The invention relates to the field of measurement of material vertical incidence sound absorption coefficients, in particular to a portable device for measuring a material sound absorption coefficient based on short sound tubes and superposed pulse extraction and a measurement method.
Background
In the field of acoustic parameter measurement of materials, the conventional measurement technologies for the vertical incidence sound absorption coefficient of the materials mainly comprise a standing wave ratio method, a transfer function method and a time domain pulse separation method.
The standing wave ratio method determines the reflection coefficient, the surface acoustic impedance rate or the acoustic admittance rate and the vertical incidence sound absorption coefficient of a sample by utilizing the ratio of the maximum value and the minimum value of the amplitude of the standing wave formed by the plane wave in the impedance tube and the position where the minimum value appears. The method has the advantage of high measurement precision. However, it requires pure sound as the measurement signal, and in general engineering application, the sound absorption coefficient in the wide frequency range of the acoustic material is required to be obtained, so the measurement step of the method is time-consuming in the wide frequency test.
The transfer function method adopts broadband random signals with stationarity and ergodicity of various states as excitation, and calculates parameters such as complex reflection coefficient, sound absorption coefficient and the like of the surface of the material by measuring the transfer function between the double microphones on the wall of the standing wave pipe. The matching problem between two microphones is the main problem encountered by a transfer function method, the transfer function can be exchanged and measured by using the two microphones so as to eliminate the mismatching between the two microphones, and the problem of phase and amplitude mismatching can not exist by using a single-microphone method for sequential measurement.
Although calibrating the transfer function eliminates the mismatch problem of the two microphones, this approach still has limitations: the spacing between the two microphones will affect the upper and lower limits of the test frequency, and for parameters in different frequency ranges, different microphone spacing combinations will need to be used.
For the time domain pulse separation method, the applicant previously filed the invention patent with application number 201310013381.2, a device and a measurement method for measuring the sound absorption coefficient of an acoustic material by adopting the pulse method, which mainly generate an ideal broadband short pulse through an inverse filtering technology, and select a proper microphone position in a sound tube with a proper length, thereby directly separating incident waves and reflected waves on the surface of the material from collected sound pressure time domain signals, and then calculating to obtain a complex reflection coefficient and the sound absorption coefficient. The method only uses one microphone, the calibration problem of the transfer function does not exist, and simultaneously, because the incident wave and the reflected wave are directly obtained, the distance between the microphones does not influence the testing frequency range. However, in order to directly separate incident waves and reflected waves in a time domain, the length of the sound tube used in the method is longer and is more than 1360mm, and because loss exists in the sound tube, the longer the tube is, the larger the loss is, and then errors are introduced into the sound pressure obtained by testing, so that the testing result of the final sound absorption coefficient is influenced; and the longer sound tube also has certain limitation in the practical operation, for example, in some occasions needing field test, the longer sound tube is inconvenient to carry.
Disclosure of Invention
In the existing measurement technology, the standing wave ratio method is low in broadband test efficiency, the distance between microphones in the transfer function method limits the upper limit and the lower limit of the test frequency, and the time domain pulse separation method is high in test efficiency, and the distance between the microphones does not influence the test frequency range, but the length of a used sound tube is long, so that inconvenience is brought to the experiment, and under the condition that the length of the sound tube is shortened, the pulse method is not suitable any more due to superposition of primary reflected waves and incident waves. In order to solve the problems existing in the prior art. The invention provides a method for measuring sound absorption coefficient in a continuous wide-frequency range based on a short sound tube and superimposed pulse extraction. The method has the advantages that the used tube length is short, the problem of frequency limitation of a transfer function method and the problem of sound attenuation of a pulse separation method are avoided, convenience of experimental operation is improved, and conditions are provided for a portable pulse method.
The technical scheme of the invention is as follows:
the portable device for measuring the sound absorption coefficient of the material based on the short sound tube pulse method is characterized in that: the device comprises a loudspeaker, a microphone, a portable air sound tube, a power amplifier, a signal generating device and a data acquisition device;
the portable air sound tube consists of a section of large-diameter cylindrical tube and a small-diameter cylindrical tube at one end; the loudspeaker is arranged in the large-diameter cylindrical pipe; the large-diameter cylindrical pipe and the small-diameter cylindrical pipe are in nested fit, and the inner end of the small-diameter cylindrical pipe faces the loudspeaker; the inner diameter of the small-diameter cylindrical pipe is less than 30mm, and the thickness of the pipe wall of the small-diameter cylindrical pipe is more than 3 mm; two through holes which are perpendicular to the central axis of the small cylindrical tube and used for installing the microphone are formed in the side wall of the small-diameter cylindrical tube, the diameter of each through hole is equal to that of the microphone, and a ring-shaped silica gel sheet is placed in each through hole to fix the microphone and seal a gap between the microphone and the small-diameter cylindrical tube; for the through hole close to the loudspeaker on the side wall of the small-diameter cylindrical tube, the axial distance from the center of the through hole to the surface of the loudspeaker is not less than 90mm, and the axial distance from the center of the through hole to the outer end of the small-diameter cylindrical tube is not less than 170mm and not more than 250 mm; an annular silicon sheet is sleeved at the outer end of the small-diameter cylindrical tube, and the outer end surface of the annular silicon sheet is flush with the outer end surface of the small-diameter cylindrical tube;
the signal generator provides an excitation signal for the loudspeaker through the power amplifier; and a microphone is used for measuring sound pressure signals in the pipe at the positions of two through holes on the wall surface of the small-diameter cylindrical pipe respectively and transmitting the sound pressure signals to the data acquisition device.
Further preferred scheme, the portable equipment based on material sound absorption coefficient is measured to short sound pipe pulse method, its characterized in that: the loudspeaker is coaxially arranged in the large-diameter cylindrical pipe, and the inner diameter of the large-diameter cylindrical pipe is the same as the diameter of the loudspeaker.
Further preferred scheme, the portable equipment based on material sound absorption coefficient is measured to short sound pipe pulse method, its characterized in that: the thickness of a ring-shaped silica gel sheet in the through hole in the side wall of the small-diameter cylindrical tube is not less than 1mm, and the diameter of the ring-shaped silica gel sheet is equal to that of the microphone; the thickness of the annular silica gel sheet sleeved at the outer end of the small-diameter cylindrical pipe is not less than 2mm, and the inner diameter of the annular silica gel sheet is equal to the outer diameter of the small-diameter cylindrical pipe.
Further preferred scheme, the portable equipment based on material sound absorption coefficient is measured to short sound pipe pulse method, its characterized in that: the handle is installed to major diameter cylinder pipe outer end, overlaps on the minor diameter cylinder pipe outer wall and has the handle.
The method for measuring the sound absorption coefficient of the material based on the short sound tube pulse method is realized by utilizing the device, and is characterized in that: the method comprises the following steps:
step 1: a microphone is arranged in a through hole which is close to the loudspeaker and arranged on the side wall of the small-diameter cylindrical pipe, and a plastic cylinder with the same diameter as the microphone is arranged in the other through hole; keeping the nesting state of the large-diameter cylindrical pipe and the small-diameter circular pipe, and vertically abutting an opening at the outer end of the small-diameter circular pipe on the surface of a sample to be detected;
step 2: the signal generator sends a broadband pulse signal to the loudspeaker, the Fourier transform of which is H1(ω) measuring the sound pressure signal in the tube by means of a microphone close to the loudspeaker, obtaining the Fourier transform of the measured signal into H2(ω); the impulse response function of the whole measuring system is then obtained as: h (omega) ═ H2(ω)/H1(ω)；
And step 3: moving the microphone to a through hole on the side wall of the small-diameter cylindrical tube far away from the surface of the loudspeaker, and installing a plastic cylinder with the same diameter as the microphone in the other through hole; signal generator transmissionTime domain signal S (t) to the loudspeaker, and measuring the sound pressure signal in the pipe by using a microphone far away from the loudspeaker to obtain Fourier transform H of the measured signaly(ω); wherein the time domain signal S (t) is formed by H0(ω) is obtained by inverse Fourier transform, and H0(ω)＝H1(ω)/H(ω)；
And 4, step 4: h is to bey(omega) substitution formula
Hy′(ω)＝[Hy(ω)-H0(ω)e-jks]·(1+e-jk2s)
To obtain H'y(ω) where s represents a distance between centers of two through holes on a sidewall of the small-diameter cylindrical tube, k represents a complex wave number obtained by a formula k of 2 π f/c, f represents a frequency, and c represents a wave velocity in air;
and 5: h'y(omega) performing inverse Fourier transform, intercepting the primary reflected wave signal from the obtained time domain signal, performing Fourier transform on the extracted primary reflected wave signal, and recording the Fourier transform as Hf(ω), the normal incidence sound absorption coefficient α (ω) is calculated by substituting the following formula:
further preferred scheme, based on the measuring method of short sound pipe pulse method measurement material sound absorption coefficient, its characterized in that: step 4Hy(omega) substitution formula
Iterative calculation is carried out until H'yn(ω) the time-domain signal obtained by performing the inverse fourier transform can be directly separated into a primary reflected wave signal, where n is 1,2,3, … representing the number of iterations.
Advantageous effects
(1) The invention can extract the primary reflected wave in the superposed sound field under the conditions that the tube length is shortened and the incident wave and the reflected wave are superposed.
(2) The invention greatly shortens the length of the used sound tube, controls the length of the sound tube in the experimental measurement device within 400mm, and reduces the influence of loss on the test result.
(3) Because the length of the tube is controlled within 400mm, the invention realizes the test of a pulse method by utilizing the portable short sound tube, thereby being capable of applying the device to the field test.
(4) Compared with a transfer function method, the invention eliminates the limitation of the microphone spacing on the test frequency range.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1: the invention is a schematic diagram of an experimental measuring device;
wherein, 1 represents a handle mounted on a large-diameter cylindrical pipe; 2 represents a large-diameter cylindrical pipe; 3 represents a small-diameter cylindrical tube; 4 represents a through hole near the surface of the speaker; 5 represents a through hole away from the speaker surface; 6 represents a handle mounted on the outer wall of the small-diameter cylindrical tube; and 7 represents a silica gel sheet sleeved on the end of the small-diameter cylindrical pipe.
FIG. 2: measurement of the sound absorption coefficient at normal incidence of the polymer material.
Detailed Description
The following detailed description of embodiments of the invention is intended to be illustrative, and not to be construed as limiting the invention.
In this example, the sound absorption coefficient of the polymer material at normal incidence was measured:
as shown in fig. 1, the portable device for measuring the sound absorption coefficient of a material based on a short sound tube pulse method proposed in this embodiment includes a speaker, a microphone, a portable air sound tube, a power amplifier, a signal generating device, and a data collecting device;
the loudspeaker model is Wheatstone M3N, the diameter is 90mm, and the response is flat in the frequency range of 300-7000 Hz. The portable air sound tube is composed of a section of large-diameter cylindrical tube and a small-diameter cylindrical tube at one end, the sound tube is made of rigid materials, the inner diameter of the large-diameter cylindrical tube is 90mm, the wall thickness is 6mm, the inner diameter of the small-diameter cylindrical tube is 29.5mm, and the wall thickness is 6 mm.
The speaker is coaxially arranged in the large-diameter cylindrical pipe, and the handle is arranged at the outer end of the large-diameter cylindrical pipe. The large-diameter cylindrical tube is in nested fit with the small-diameter cylindrical tube, and the inner end of the small-diameter cylindrical tube faces the loudspeaker. Two through holes which are perpendicular to the central axis of the small cylindrical tube and used for mounting the microphone are formed in the side wall of the small-diameter cylindrical tube, the diameter of each through hole is 1/4 inches, and a ring-shaped silicon sheet with the thickness of 2mm is placed in each through hole and used for fixing the 1/4-inch microphone and sealing a gap between the microphone and the sound tube.
To the through-hole that is close to the speaker on the minor diameter cylinder pipe lateral wall, its axial distance from the speaker surface of center is 90mm for the decay of higher order wave, and is 180mm apart from the axial distance of minor diameter cylinder pipe outer end, and to the through-hole of keeping away from the speaker surface, the axial distance from minor diameter cylinder pipe outer end is 160 mm.
An annular silica gel sheet with the thickness of 3mm is sleeved at the outer end of the small-diameter cylindrical tube, the inner diameter of the annular silica gel sheet is equal to the outer diameter of the small-diameter cylindrical tube, and the outer end surface of the annular silica gel sheet is flush with the outer end surface of the small-diameter cylindrical tube; the outer wall of the small-diameter cylindrical pipe is sleeved with a handle.
The signal generator provides an excitation signal for the loudspeaker through the power amplifier; and a microphone is used for measuring sound pressure signals in the pipe at the positions of two through holes on the wall surface of the small-diameter cylindrical pipe respectively and transmitting the sound pressure signals to the data acquisition device.
The method for measuring the sound absorption coefficient of the material based on the short sound tube pulse method is realized by utilizing the device, and is characterized in that: the method comprises the following steps:
step 1: a microphone is arranged in a through hole which is close to the loudspeaker and arranged on the side wall of the small-diameter cylindrical pipe, and a plastic cylinder with the same diameter as the microphone is arranged in the other through hole; the outer end handle of the large-diameter cylindrical pipe and the outer wall handle of the small-diameter circular pipe are respectively held by two hands of a tester to keep the nesting state of the large-diameter cylindrical pipe and the small-diameter circular pipe, and the outer end opening of the small-diameter circular pipe is vertically abutted to the surface of a sample to be tested.
Step 2: the signal generator sends a broadband pulse signal to the loudspeaker, the Fourier transform of which is H1(ω) measuring the sound pressure signal in the tube by means of a microphone close to the loudspeaker, obtaining the Fourier transform of the measured signal into H2(ω); the impulse response function of the whole measuring system is then obtained as: h (omega) ═ H2(ω)/H1(ω)。
And step 3: moving the microphone to a through hole on the side wall of the small-diameter cylindrical tube far away from the surface of the loudspeaker, and installing a plastic cylinder with the same diameter as the microphone in the other through hole; the signal generator transmits a time domain signal S (t) to the loudspeaker, and a microphone far away from the loudspeaker is used for measuring a sound pressure signal in the pipe to obtain Fourier transform H of a measurement signaly(ω); wherein the time domain signal S (t) is formed by H0(ω) is obtained by inverse Fourier transform, and H0(ω)＝H1(ω)/H(ω)。
In this regard, we further explain the principle:
fourier transform of signal acquired near the through hole on the surface of loudspeaker1(ω), the Fourier transform H of the signal that the signal generator needs to output0(ω) can be expressed as: h0(ω)＝H1(ω)/H (ω); to H0And (omega) performing inverse Fourier transform to obtain a time domain signal S (t), and sending the obtained time domain signal S (t) to a loudspeaker by a signal generator, namely generating a broadband pulse signal with an ideal waveform at a position close to a through hole on the surface of the loudspeaker for subsequent measurement.
And 4, step 4: h is to bey(omega) substitution formula
Hy′(ω)＝[Hy(ω)-H0(ω)e-jks]·(1+e-jk2s)
To obtain H'y(ω) wherein s represents a distance between centers of two through holes on a side wall of the small-diameter cylindrical tube, k represents a complex wave number obtained by a formula k of 2 π f/c, and f represents a frequencyAnd c represents the wave velocity in air;
in this regard, we further explain the principle:
h obtained in step 3yThe theoretical formula of (omega) is Hy(ω)＝H0(ω)·[e-jks+rme-jk(2l″-s)-rme-jk(2l″+s)-rm 2e-jk(4l″-s)+…]
Wherein l' represents the distance from the outer end opening surface (i.e., the sample surface) of the small-diameter sound tube near the through-hole of the speaker surface, and rmThe complex reflection coefficient of the material to be tested under the condition of hard backing support is shown. Then H is obtainedy(ω) after, if H is to be obtained close to the through hole of the loudspeaker surface0After (omega) displacement exp (-jks), H obtained at the through hole far from the loudspeaker surface is reusedy(ω) subtracting it; then, the subtraction result is shifted by exp (-jk2s) and added to the initial subtraction result. Then H 'is obtained'y(ω), the primary reflected wave can be extracted from the superimposed signal. I.e. Hy(omega) substitution formula
H′y(ω)＝[Hy(ω)-H0(ω)e-jks]·(1+e-jk2s)
To obtain H'y(ω)。
H′y(ω)＝[Hy(ω)-H0(ω)e-jks]·(1+e-jk2s)＝H0(ω)·[rme-jk(2l″-s)-rme-jk(2l″+3s)-rm 2e-jk(4l″-s)+…]…]
Considering that a reflected wave may still be superimposed by a subsequent signal after one of the above operations, it is preferable to add H herey(omega) substitution formula
Iterative calculation is carried out until H'yn(omega) the primary reflected wave signal can be directly separated from the time domain signal obtained by performing inverse Fourier transformWhere n-1, 2,3, … represents the number of iterations.
And 5: h'yn(omega) performing inverse Fourier transform, intercepting the primary reflected wave signal from the obtained time domain signal, performing Fourier transform on the extracted primary reflected wave signal, and recording the Fourier transform as Hf(ω), the normal incidence sound absorption coefficient α (ω) is calculated by substituting the following formula:
in the example, Butterworth broadband short pulse signals are generated at the through hole close to the surface of the loudspeaker, then measurement is carried out according to the measurement principle, and the measurement result is compared with the test result of the transfer function method and the test result of the traditional pulse separation method, the measurement result is shown in figure 2 and is the vertical incidence sound absorption coefficient of the polymer material measured in the example, and it can be seen that the result obtained by the measurement method is well matched with the measurement results of the transfer function method and the traditional pulse separation method at 6400Hz, and the effectiveness of the method is verified; compared with the traditional transfer function method, the method has the advantages that the upper limit and the lower limit of the testing frequency are not influenced by the distance between the microphones, the low-frequency measurement is more accurate, and compared with the traditional pulse separation method, the method obtains almost the same result on the premise of greatly shortening the length of the sound tube.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made in the above embodiments by those of ordinary skill in the art without departing from the principle and spirit of the present invention.
Claims (5)
1. A method for measuring the sound absorption coefficient of a material based on a short sound tube pulse method is characterized by comprising the following steps: implemented with the following portable device:
the portable device comprises a loudspeaker, a microphone, a portable air sound tube, a power amplifier, a signal generating device and a data acquisition device;
the portable air sound tube consists of a section of large-diameter cylindrical tube and a small-diameter cylindrical tube at one end; the loudspeaker is arranged in the large-diameter cylindrical pipe; the large-diameter cylindrical pipe and the small-diameter cylindrical pipe are in nested fit, and the inner end of the small-diameter cylindrical pipe faces the loudspeaker; the inner diameter of the small-diameter cylindrical pipe is less than 30mm, and the thickness of the pipe wall of the small-diameter cylindrical pipe is more than 3 mm; two through holes which are perpendicular to the central axis of the small cylindrical tube and used for installing the microphone are formed in the side wall of the small-diameter cylindrical tube, the diameter of each through hole is equal to that of the microphone, and a ring-shaped silica gel sheet is placed in each through hole to fix the microphone and seal a gap between the microphone and the small-diameter cylindrical tube; for the through hole close to the loudspeaker on the side wall of the small-diameter cylindrical tube, the axial distance from the center of the through hole to the surface of the loudspeaker is not less than 90mm, and the axial distance from the center of the through hole to the outer end of the small-diameter cylindrical tube is not less than 170mm and not more than 250 mm; an annular silicon sheet is sleeved at the outer end of the small-diameter cylindrical tube, and the outer end surface of the annular silicon sheet is flush with the outer end surface of the small-diameter cylindrical tube;
the signal generator provides an excitation signal for the loudspeaker through the power amplifier; a microphone respectively measures sound pressure signals in the pipe at the positions of two through holes on the wall surface of the small-diameter cylindrical pipe and transmits the sound pressure signals to a data acquisition device;
the method comprises the following steps:
step 1: a microphone is arranged in a through hole which is close to the loudspeaker and arranged on the side wall of the small-diameter cylindrical pipe, and a plastic cylinder with the same diameter as the microphone is arranged in the other through hole; keeping the nesting state of the large-diameter cylindrical pipe and the small-diameter circular pipe, and vertically abutting an opening at the outer end of the small-diameter circular pipe on the surface of a sample to be detected;
step 2: the signal generator sends a broadband pulse signal to the loudspeaker, the Fourier transform of which is H1(ω) measuring the sound pressure signal in the tube by means of a microphone close to the loudspeaker, obtaining the Fourier transform of the measured signal into H2(ω); the impulse response function of the whole measuring system is then obtained as: h (omega) ═ H2(ω)/H1(ω)；
And step 3: moving the microphone to the side wall of the small-diameter cylindrical tube far away from the loudspeakerIn the through hole on the surface, a plastic cylinder with the same diameter as the microphone is arranged in the other through hole; the signal generator transmits a time domain signal S (t) to the loudspeaker, and a microphone far away from the loudspeaker is used for measuring a sound pressure signal in the pipe to obtain Fourier transform H of a measurement signaly(ω); wherein the time domain signal S (t) is formed by H0(ω) is obtained by inverse Fourier transform, and H0(ω)＝H1(ω)/H(ω)；
And 4, step 4: h is to bey(omega) substitution formula
H′y(ω)＝[Hy(ω)-H0(ω)e-jks]·(1+e-jk2s)
To obtain H'y(ω) where s represents a distance between centers of two through holes on a sidewall of the small-diameter cylindrical tube, k represents a complex wave number obtained by a formula k of 2 π f/c, f represents a frequency, and c represents a wave velocity in air;
and 5: h'y(omega) performing inverse Fourier transform, intercepting the primary reflected wave signal from the obtained time domain signal, performing Fourier transform on the extracted primary reflected wave signal, and recording the Fourier transform as Hf(ω), the normal incidence sound absorption coefficient α (ω) is calculated by substituting the following formula:
2. the method for measuring the sound absorption coefficient of the material based on the short sound tube pulse method according to claim 1, wherein the method comprises the following steps: step 4Hy(omega) substitution formula
Iterative calculation is carried out until H'yn(ω) the time-domain signal obtained by performing the inverse fourier transform can be directly separated into a primary reflected wave signal, where n is 1,2,3, … representing the number of iterations.
3. The method for measuring the sound absorption coefficient of the material based on the short sound tube pulse method according to claim 1, wherein the method comprises the following steps: the loudspeaker is coaxially arranged in the large-diameter cylindrical pipe, and the inner diameter of the large-diameter cylindrical pipe is the same as the diameter of the loudspeaker.
4. The method for measuring the sound absorption coefficient of the material based on the short sound tube pulse method according to claim 1, wherein the method comprises the following steps: the thickness of a ring-shaped silica gel sheet in the through hole in the side wall of the small-diameter cylindrical tube is not less than 1mm, and the diameter of the ring-shaped silica gel sheet is equal to that of the microphone; the thickness of the annular silica gel sheet sleeved at the outer end of the small-diameter cylindrical pipe is not less than 2mm, and the inner diameter of the annular silica gel sheet is equal to the outer diameter of the small-diameter cylindrical pipe.
5. The method for measuring the sound absorption coefficient of the material based on the short sound tube pulse method according to claim 1, wherein the method comprises the following steps: the handle is installed to major diameter cylinder pipe outer end, overlaps on the minor diameter cylinder pipe outer wall and has the handle.
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| CN113405650B (en) * | 2021-05-29 | 2023-02-10 | 西北工业大学 | Vector sensor correction method based on standing wave tube and sound absorption material |
| CN114414664A (en) * | 2022-01-08 | 2022-04-29 | 西北工业大学 | Sound absorption coefficient testing device and method based on embedded control system and short sound tube |
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