1. Field of the Invention
The present invention relates to a technology for visualizing sound source energy distribution, particularly to a system utilizing an inverse operation technology to visualize sound source energy distribution and a method thereof.
2. Description of the Related Art
With the advance of science and technology, people demand higher and higher living-environment quality. However, the living environment is full of the noise induced by structural vibration, which may cause physiological and psychological problems.
The effect of noise control correlates closely with the correctness of positioning and identifying noise sources. Therefore, it is essential for noise control to accurately trace and correctly identify the sources of noise. Only after the position, source strength distribution, particle velocity distribution, and intensity distribution of a structural-vibration-induced noise have been obtained should the noise be correctly estimated, optimally controlled and effectively reduced. When the noise-control technology is applied to the diagnosis of power machines, it can assist the engineers to correctly identify the source of a malfunction and estimate the influence thereof.
As to the conventional technologies of sound source identification, there is an article “Determination of Directivity of a Planar Noise Source by Means of Near Field Acoustical Holography, 2: Numerical Simulation” by M. A. Rowell and D. J. Oldham, J. Sound and Vibration, 1995, which utilizes a nearfield acoustical holography to determine noise sources. However, the nearfield acoustical holography can only identify the distribution of the acoustic field on a nearfield plane. Further, the calculation thereof needs to perform coordinate transformation several times, which is apt to cause a spatial aliasing. Besides, such a technology is also disadvantaged by needing a multitude of microphones. There is also a US patent of Publication No. 20050225497 proposing a sound source-identification method implemented by a beam forming array technology. However, the beam forming array technology can only identify a farfield acoustic field and is not so effective in identifying an unstable-state sound source. Besides, such a technology is also disadvantaged by that it cannot perform calculation instantly, that it cannot synchronically identify the acoustic fields of different coordinate systems, and that it needs to modify the configuration of the microphone array to avoid a spatial aliasing.
Accordingly, the present invention proposes a system for visualizing sound source energy distribution and a method thereof to overcome the abovementioned problems.
The primary objective of the present invention is to provide a system for visualizing sound source energy distribution and a method thereof, which utilizes an inverse-operation technology to establish a sound source energy distribution reconstructor in order to obtain the energy distributions of nearfield/farfield stable-state/unstable-state sound sources or the sound source energy distribution of an arbitrary frequency band.
Another objective of the present invention is to provide a system for visualizing sound source energy distribution and a method thereof, which can utilizes fewer in-array microphones to obtain the energy distributions of planar or non-planar sound sources and is advantaged by wide identifiable frequency band, no reference signal, less spatial aliasing, allowance of an irregular microphone array, the capability of instant calculation, and the capability of synchronically obtaining the energy distributions of the sound sources of different coordinate systems.
In the present invention, a propagation matrix and a window matrix are obtained via assigning values to the coordinates of arrayed microphones and assigning values to the coordinates of the retreated focus points on the retreated focus point surface; next, an inverse operation of the propagation matrix is performed; next, a multiplication operation of the window matrix and the result of the inverse operation is performed; then, the result of the multiplication operation is displaced from the frequency domain to the time domain by an Inverse Fast Fourier Transform operation. Thereby, a sound source energy distribution reconstructor is established. Next, arrayed microphones are used to receive the signals of sound sources, and a multi-channel capture device is used to transform the sound source signals into digital sound source signals. Next, a convolution operation of the digital sound source signals and the sound source energy distribution reconstructor is performed to obtain the sound source energy distribution on the retreated focus point surface, and the sound source energy distribution is presented on an output device. The propagation matrix is obtained with the formula:
wherein rMN is the distance between the coordinate of the Nth retreated focus point and the coordinate of the Mth in-array microphone, and k is the wave number
The window matrix is obtained via: defining a boundary of the retreated focus point surface, assigning 1 to the coordinates of the retreated focus points inside the boundary, and assigning 0 to the coordinates of the retreated focus points outside the boundary. The sound source energy distribution reconstructor utilizes ERA (Eigensystem Realization Algorithm) to transform the convolution operation to a state space to undertake a synchronic MIMO operation. Further, the retreated focus point surface method is used to obtain the sound source energy distribution on a reconstructed surface and accomplish a higher accuracy of the sound source energy distribution.
To enable the objectives, technical contents, characteristics, and accomplishments of the present invention to be more easily understood, the embodiments of the present invention are to be described in detail in cooperation with the attached drawings below.
The present invention proposes a system for visualizing sound source energy distribution and a method thereof, which utilizes an inverse-operation technology to establish a sound source energy distribution reconstructor and obtain the energy distributions of sound sources.
Firstly, the principle and steps of establishing a sound source energy distribution reconstructor will be described below. Refer to
is used to work out a propagation matrix (2), wherein rMN is the distance between the coordinate of the Nth retreated focus point and the coordinate of Mth in-array microphone, and k is the wave number
In Step S3, based on the k value obtained by specifying the frequency and the distance between the coordinate of a retreated focus point and the coordinate of an in-array microphone, a propagation matrix (2) for a given frequency can be obtained with Formula (1); the propagation matrix (2) is expressed by:
wherein H(rMN) is obtained via Formula (1) and denotes the pressure that the Mth in-array microphone receives from the point source at the Nth retreated focus point. The relation of those three matrices is expressed by Formula (3):
Refer to
In Step S5, an inverse operation of the propagation matrix (2) is performed; next, a multiplication operation of the window matrix (4) and the result of the inverse operation is performed to obtain an inverse matrix CB×M 4; then, the inverse matrix CB×M 4 is transformed from the frequency domain to the time domain by an Inverse Fast Fourier Transform operation. Thereby, a sound source energy distribution reconstructor is established.
In Step S6, according to the requirement of the sound source energy distribution reconstructor, an array of microphones is arranged. Multiple sound source signals are received by the arrayed microphones and transformed into multiple digital sound source signals by a multi-channel capture device. A convolution operation of the digital sound source signals and the sound source energy distribution reconstructor is performed to obtain the sound source energy distribution {circumflex over (q)}1, {circumflex over (q)}2 . . . {circumflex over (q)}B on the retreated focus point surface 6, wherein the total number of them amounts to B.
Refer to
To speak briefly, the present invention firstly establishes a sound source energy distribution reconstructor, and next, an array of microphones is arranged according to the requirement of the reconstructor; next, an analog/digital conversion is performed to transform the received analog sound source signals into digital sound source signals; then, a convolution operation of the digital sound source signals and the sound source energy distribution reconstructor is performed to obtain the energy distribution of the sound source.
In the present invention, the window matrix is used to increase the identification accuracy in the boundary of the sound source so that the error of the estimated sound source energy distribution can be minimized. Refer to
When the coordinates of the arrayed microphones are less than those of the retreated focus points, the present invention utilizes an under-determined architecture to enable that the sound source energy distribution reconstructor can use a right inverse operation to obtain the result of the inverse operation of the propagation matrix HM×N. Thereby, a sound source energy distribution reconstructor, which is suitable for the case that the coordinates of the arrayed microphones are less those of the retreated focus points, can be established.
To reduce the calculation of the convolution operation of the digital sound source signals and the sound source energy distribution reconstructor, and to promote the efficiency of the sound source energy distribution reconstructor, the present invention utilize ERA (Eigensystem Realization Algorithm) to enable the convolution operation of the digital sound source signals and the sound source energy distribution reconstructor to be calculated in a state space. Firstly, the impulse responses of the sound source energy distribution reconstructor are arranged into a Hankel matrix, and an SVD (Singular Value Decomposition) operation is performed on the Hankel matrix. Refer to
Refer to
Refer to
wherein A is the sound source energy distribution 26 on the retreated focus point surface, r is the distance from the retreated focus point on the retreated focus point surface to the focus point on the reconstructed surface 42, and k is the wave number
Refer to
The acoustic field distribution not only can be observed in a sound source pressure distribution but also can be observed in a sound source particle velocity distribution or a sound source intensity distribution. Refer to
The present invention can further perform an image interpolation operation on a sound source energy distribution so that the sound source energy distribution can be output to an output device with a higher resolution. The image interpolation operation may be implemented with the sinc function or the gauss function;
In order to synchronically obtain the sound source energy distributions of different coordinate systems without moving the arrayed microphones and the test objects, the present invention further utilizes a synthetic aperture method to enable that the maximum rotation angle of a measurement aperture can reach 30 degrees. A convolution operation of the digital sound source signals originally received by the arrayed microphones and the sound source energy distribution reconstructor is performed to obtain a sound source energy distribution on the retreated focus point surface inside the rotated aperture. Refer to
In summary, the present invention obtains different propagation matrices via assigning different values to the frequency and has the advantage of wide identifiable frequency band. Further, the present invention needs fewer transformations so that the present invention can be advantaged in less spatial aliasing. Besides, the present invention is also advantaged in that no reference signal is needed.
The system and method of the present invention, which utilizes the abovementioned inverse operation technology and performs the operation within the time domain, can effectively identify the positions of sound sources and obtain the distribution of the acoustic field. The present invention can solve the problems of the conventional technologies that the nearfield and farfield sound source energy distributions cannot be synchronically obtained, and the operation cannot be instantly performed. The system for visualizing sound source energy distribution and the method thereof proposed by the present invention not only can obtain the energy distributions of nearfield/farfield stable-state/unstable-state sound sources or the sound source energy distribution of an arbitrary frequency band, but also can utilizes fewer microphones to obtain the energy distributions of planar or non-planar sound sources. Furthermore, the present invention is advantaged by wide identifiable frequency bands, no reference signal, less spatial aliasing, allowance of an irregular microphone array, the capability of instant calculation, and the capability of synchronically obtaining the energy distributions of the sound sources of different coordinate systems.
Those embodiments described above are to clarify the present invention to enable the persons skilled in the art to understand, make and use the present invention; however, it is not intended to limit the scope of the present invention, and any equivalent modification and variation according to the spirit of the present invention is to be also included within the scope of the claims stated below.
Number | Date | Country | Kind |
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95106887 | Mar 2006 | TW | national |