Sound Pressure Distribution Research Articles

1109 穴あき矩形カバーの遮音性能予測に関する研究

Noise and vibration control are the one of important issues for engineering. A sound insulation cover which envelops a sound source is very useful for the noise reduction. When large noise and high temperature heat are emitted from the sound source, we have to consider the heat cooling as well as the noise reduction. The purpose of the present study is to investigate the acoustic characteristic of a sound insulation cover with and without a small hole using acoustic/structure coupled analysis. The effect of hole size and position were also investigated. Although a lot of sound leaked from a large size hole, a small size hole hardly influenced the sound insulation performance of the cover. It is clearly that sound pressure distributions around the cover changed obviously according to the input frequency of a sound source.

G1010502 木琴の放射音特性に関する研究([G101-05]機械力学・計測制御一般セッション(5))

This research is directed to xylophone. Xylophone is musical instrument that has side-by-side wooden sound board in general, it is intended for those with resonance tubes under sound boards in this research. I taken out one set of the resonance tube and sound board, treated as system, which led the resonance tube and sound board. Theory of the system that led the two has not been established yet. This research is finally aimed establishment of theory. I was produced in resonance tube and sound board based on the 'la' of the sound of basic. Sound boards of xylophone are carved arched lower, but I was using the aluminum, using rectangular solid in this research. Resonance tube was using vinyl chloride. The result of hanging the sound board, measuring some points sound pressure with or without the resonance tube, I found that there are differences in sound pressure distribution. Therefore, I can be seen that the resonance tube has brought something to the effect space or sound board.

Experimental and numerical characterization of the sound pressure in standing wave acoustic levitators

A novel method for predictions of the sound pressure distribution in acoustic levitators is based on a matrix representation of the Rayleigh integral. This method allows for a fast calculation of the acoustic field within the resonator. To make sure that the underlying assumptions and simplifications are justified, this approach was tested by a direct comparison to experimental data. The experimental sound pressure distributions were recorded by high spatially resolved frequency selective microphone scanning. To emphasize the general applicability of the two approaches, the comparative studies were conducted for four different resonator geometries. In all cases, the results show an excellent agreement, demonstrating the accuracy of the matrix method.

Optimization of acoustic emitted field of transducer array for ultrasound imaging

A method is proposed to calculate the weight vector of a transducer array for ultrasound imaging to obtain a low-sidelobe transmitting beam pattern based on the near-field response vector. An optimization problem is established, and the second-order cone (SOC) algorithm is used to solve the problem to obtain the weight vector. The optimized acoustic emitted field of the transducer array is then calculated using the Field II program by applying the obtained weight vector to the array. The simulation results with a 64-element 26 MHz linear phased array show that the proposed method can be used to control the sidelobe of the near-field transmitting beam pattern of the transducer array and achieve a low-sidelobe level. The near-field sound pressure distribution of the transducer array using the proposed method focuses much better than that using the standard delay and sum (DAS) beamforming method. The sound energy is more concentrated using the proposed method.

Object Characterization Based on Multispectral Acoustic Imaging

In previous studies, acoustic imaging was conducted using a single frequency or a limited number of frequencies that were not sufficient to clearly describe and explain the object characteristics. In this study, multispectral acoustic imaging (MSAI) is proposed to reveal rich information of object characteristics. An experimental study on object surfaces is conducted to verify the validity of the technique. Acoustic imaging of object surfaces is performed on the basis of a significant number of spectra over a wide frequency range. Using the frequency-swept irradiation from 1 to 20 kHz at 30 Hz intervals, we demonstrate the visualization of the following three different object surfaces: a rigid surface with small holes with and without a piece of thin paper covering the surface, and a boundary between wood and rubber plates. The distributions of sound pressure reconstructed at each frequency by a near-field acoustic holography (NAH) technique are shown. In multispectral acoustic imaging, frequency dependence provides us rich information about the surface shape and material properties of the objects; thus, the characteristics of the surfaces are successfully visualized.

Sound field alteration through cavity shape design using a Wavelet-Galerkin Method

The general problem of internal sound field prediction along with the manipulation of the cavity boundary shape to alter the sound pressure distribution is dealt with in this paper. Owing to the compactly supported orthogonal property of the wavelet and its extraordinary fitting capability, Daubechies wavelet scaling function is used as a global basis function to expand the unknown sound pressure under the general Galerkin framework. The proposed formulation is shown to offer high accuracy on the numerical calculation of the sound pressure field with the use of a remarkably small number of messing points. A genetic based shape optimization algorithm is proposed and demonstrated. As an example, an enclosure with an inner rigid acoustic screen is investigated. By optimizing the shape of the screen, the sound pressure level within a chosen area is successfully reduced. Results show the remarkable potentials of the proposed approach as a topology optimal tool for the general inner sound field problems.

Study on Surface Radiation Noise of a Diesel Engine Based on FEM

To evaluate the noise of a diesel engine and provide the basis for the next step for noise reduction, a boundary element model of the diesel engine has been built and finite element software is used to analyze the noise of the engine. Surface vibration velocity distribution, radiation noise spectrum, sound pressure distribution and total noise level are calculated. The calculation results obtained show that the most representative three points of the peak of SPL (sound pressure level) are 500Hz, 1200Hz and 1950Hz; total SPL is 108.99dB; the main sources of the noise of the diesel engine are oil pan, gear chamber cover and flywheel housing, these three parts should be prior; the noise of the lower part and left and right part (the gear chamber cover side and flywheel housing side) of the engine is greater than the upper part and front and rear part; improving the suspension mechanism of the internal combustion engine, optimizing the oil sump, flywheel housing and gear chamber cover and strengthening the rigidity of the skirt of the engine body can be used as the primary means of noise reduction.

Research on near Field Acoustic Characteristic of a Compound Structure with Plate & Cylindrical Hull Subjected to Sound Excitation

In order to study the acoustic environment of a ship sonar platform, near-field acoustic characteristic of a compound structure with plates & a cylindrical shell (CSPCS) subjected to sound excitation is researched based on numerical simulation. Influence of frequency and sound incident angle on acoustic environment of CSPCS are studied. Study shows that the sound pressure field distribution of CSPCS is complicated. Sound pressure would be strengthened and weakened in different locations when sound pressure uniformly incident into CSPCS. Result shows that the sound pressure distribution is highly dependent on frequency and incident angle. Sound pressure field is more evenly distributed when sound wave frequency is low. Study also shows that the incident angle has considerable influence on the sound field distribution of strengthened and weakened area.

Study of Transmission Loss on Muffler

Transmission loss is the main method which measure silencer sound deadening capacity. The most effective noise elimination technique of compensator is muffler. Muffler is equipment which organizes sound transmission and permits airflow pass and must satisfy definite muffling amount and frequency property. The study builds model and theoretically studies and analyzes the internal sound problem and contrasts between FEM and transmission matrix method and computes transmission loss. On the basis of experimental verification, combining model analysis with sound pressure distribution graph, analyze muffling property deeply.

A polar-coordinate-discretized wave equation finite-difference time-domain simulation for controlling the emission characteristics of sound source

In sound field simulation with conventional WE-FDTD, the simulated field and wave equation are discretized with symbol time domain and spatial domain with Cartesian coordinate, and sound pressure distribution is calculated. Spatial-discretization with Cartesian coordinate easily achieves calculation and sound synthesis. However, the discretized Cartesian coordinate cannot model sound emission characteristic exactly, because the emission characteristics is under spherical diffusion and discretize Cartesian coordinate cannot define spherical. Emission characteristic of sound source is indispensable for sound field reproduction. Then, we propose a new approach for WE-FDTD method to simulate emission characteristic of sound source object. Polar coordinate discretization is employed in the new approach instead of Cartesian coordinate. The wave equation with spatial Cartesian coordinate is projected onto polar coordinates, and discretized. The discretized polar coordinate is better way to define spherical wave surface than Cartesian one, and it is expected that the emission characteristics are simulated more exactly. The objective evaluations were conducted for the proposed approach. According to the result, the sound field simulation with the new approach can flexibly define exact emission characteristics. However, the discretized interval of polar coordinate is coarse in distance. Verifying the interval limit is important issue in future work.

Directional sound source modeling by using spherical harmonic functions for finite-difference time-domain analysis

Directivity of a sound source originates from the source’s shape and its size relative to wavelength. Therefore, the directivity varies with a frequency of a sound. In order to precisely simulate a directivity of a source in the finite-difference time-domain analysis, basically, it is necessary to model the shape of the source geometrically in detail. In the case of sources with complex shapes, however, geometrically precise modeling of the source shape requires small size of spatial discretization, and such a fine mesh discretization results in huge computational costs. In this study, applying a basic theory of Fourier analysis in which arbitrary directivity can be constructed by linear combination of spherical harmonic function, the condition of the sound source for the finite-difference time-domain method to reduce computational cost and to enable efficient analysis against a source with complex directivity characteristics is investigated. Spatial distribution of sound pressure of initial condition for respective spherical harmonic function and correction method of spectral characteristics for the finite-difference time-domain analysis are described.

Some research of mapped radiation modes and its application in analyzing the radiation surface of vibrating structures

Acoustic radiation modes divide the velocity patterns into groups with effective and ineffective radiation efficiencies. It suggests a promising way in the computation of sound power and near field acoustic holography. However, obtaining the radiation modes based on eigenvalue analysis suffers from issues of CPU time and memory, especially for large-scale problems. Based on the idea of equivalent source method and boundary integral equation, it is mathematically and numerically proved that the spherical basis functions is a set of linearly independent patterns on an arbitrary surface. They are termed as mapped radiation modes. The analytical sound power of a structure vibrating in its mapped radiation modes is obtained. An efficient and accurate method to compute the sound power based on the mapped radiation modes is proposed. Based on the relationship between the mapped radiation modes of a vibrating structure and its field sound pressure distribution patterns on a sphere, an improved near field acoustic holography is also developed. It does not need the inverse process but requires microphones to locate at the integral points on a sphere. Numerical examples are presented to validate advantages of applying mapped radiation modes in the sound power evaluation and near field acoustic holography.

Multi-spectral acoustic imaging on object surface in air

Acoustical imaging has been performed using mono-frequency or a limited number of frequencies in the previous studies. The frequency dependence, however, may provide rich information on surface profiles, structures hidden under surfaces, and material properties of objects. In this study, acoustic imaging on object surfaces was conducted over a wide frequency range with a fine frequency step. A rigid surface with different profiles and a boundary between two objects composed of different materials were illuminated by sound wave swept over the frequency range from 1 kHz to 20 kHz with a 30-Hz step. The scattered sound field was recorded two-dimensionally using a scanning microphone, and the holographic method was used to reconstruct the sound pressure distribution on the surface from the recorded data. From the experimental results, the characteristics of the surfaces with respect to the shapes and material properties were demonstrated experimentally. The depth of the holes was identified by its own resonance frequency, and the two different materials were successfully distinguished by multiple images obtained at different frequencies.

Mechano-acoustical measurement and modeling of the outer and middle ear

Mechano-acoustical measurement and modeling have evolved together. Most early measurements of the behavior of the outer and middle ear produced either spatial averages or single-point observations, which were amenable to modeling with uniform transmission lines and lumped circuits. A major step forward was the measurement of displacement patterns on the eardrum, which called for the use of finite-element models. Other major experimental steps forward included measuring spatial sound-pressure distributions, 3-D displacement patterns, and intracochlear pressures. Use of the finite-element method made it desirable to obtain detailed 3-D shape measurements, which were made much easier by the introduction of magnetic-resonance microscopy and x-ray microCT. The finite-element method has also made it possible to exploit measurements of material properties, and several different approaches have been used recently for making such measurements. The greatest challenges may be in dealing with very small dimensions and non-linear visco-elastic behavior. There is a need for more and better 3-D multipoint vibration measurements, and for material-property measurements that are more localized and that span a broader frequency range. Important directions for modeling include better use of available shape and material-property data, more attention to experimental animals and to variability, and better integration with cochlear models.

A microacoustic analysis including viscosity and thermal conductivity to model the effect of the protective cap on the acoustic response of a MEMS microphone

An analysis is presented of the effect of the protective cover on the acoustic response of a miniature silicon microphone. The microphone diaphragm is contained within a small rectangular enclosure and the sound enters through a small hole in the enclosure's top surface. A numerical model is presented to predict the variation in the sound field with position within the enclosure. An objective of this study is to determine up to which frequency the pressure distribution remains sufficiently uniform so that a pressure calibration can be made in free space. The secondary motivation for this effort is to facilitate microphone design by providing a means of predicting how the placement of the microphone diaphragm in the package affects the sensitivity and frequency response. While the size of the package is typically small relative to the wavelength of the sounds of interest, because the dimensions of the package are on the order of the thickness of the viscous boundary layer, viscosity can significantly affect the distribution of sound pressure around the diaphragm. In addition to the need to consider viscous effects, it is shown here that one must also carefully account for thermal conductivity to properly represent energy dissipation at the system's primary acoustic resonance frequency. The sound field is calculated using a solution of the linearized system consisting of continuity equation, Navier-Stokes equations, the state equation and the energy equation using a finite element approach. The predicted spatial variation of both the amplitude and phase of the sound pressure is shown over the range of audible frequencies. Excellent agreement is shown between the predicted and measured effects of the package on the microphone's sensitivity.

Inner-ear sound pressures near the base of the cochlea in chinchilla: Further investigation

The middle-ear pressure gain GMEP, the ratio of sound pressure in the cochlear vestibule PV to sound pressure at the tympanic membrane PTM, is a descriptor of middle-ear sound transfer and the cochlear input for a given stimulus in the ear canal. GMEP and the cochlear partition differential pressure near the cochlear base ΔPCP, which determines the stimulus for cochlear partition motion and has been linked to hearing ability, were computed from simultaneous measurements of PV, PTM, and the sound pressure in scala tympani near the round window PST in chinchilla. GMEP magnitude was approximately 30 dB between 0.1 and 10 kHz and decreased sharply above 20 kHz, which is not consistent with an ideal transformer or a lossless transmission line. The GMEP phase was consistent with a roughly 50-μs delay between PV and PTM. GMEP was little affected by the inner-ear modifications necessary to measure PST. GMEP is a good predictor of ΔPCP at low and moderate frequencies where PV >> PST but overestimates ΔPCP above a few kilohertz where PV ≈ PST. The ratio of PST to PV provides insight into the distribution of sound pressure within the cochlear scalae.

Vibration and acoustic response of an orthotropic composite laminated plate in a hygroscopic environment

This paper is a study of the vibration and acoustic response characteristics of orthotropic laminated composite plate with simple supported boundary conditions excited by a harmonic concentrated force in a hygroscopic environment. First the natural vibration of the plate with the in-plane forces induced by hygroscopic stress is obtained analytically. Secondly, the sound pressure distribution of the plate at the far field is obtained using the Rayleigh integral. Furthermore, the sound radiation efficiency is deduced. Third, different ratios of elastic modulus in material principal directions are set to research the effects of increasing stiffness of the orthotropic plate on the vibration and acoustic radiation characteristics. Finally, to verify the theoretical solution, numerical simulations are also carried out with commercial finite software. It is found that the natural frequencies decrease with the increase of the moisture content and the first two order modes interconvert at high moisture content. The dynamic response and sound pressure level float to lower frequencies with elevated moisture content. Acoustic radiation efficiency generally floats to the low frequencies and decreases with an increase of moisture content. The dynamic and acoustic responses reduce and the coincidence frequency decreases with the enhanced stiffness.

1101 音源位置を考慮した気柱共鳴現象の検討(OS11-1 流体関連振動・騒音,OS11 流体関連振動・騒音)

Noise and vibration control are the one of important issues. A sound insulation cover which covers a sound source is very useful for the noise reduction. The purpose of the present study is to investigate the acoustic characteristic of a sound insulation cover using acoustic/structure coupled analysis. It is clearly that sound pressure distributions inside and outside cover changed obviously according to the input frequency of a sound source. Several peaks of the sound pressure level were observed and these peaks were depended on the natural frequency and the resonance frequency of the insulation cover. Detail characteristic of the acoustic resonance phenomena was investigated and the mode of acoustic resonance changed by the sound source position.

The Realization for Sound Pressure Unit Using Laser Doppler Anemometry in a Travelling Wave Tube

Abstract. To realize the sound pressure unit directly, the method of sound pressure measurement based on acoustic particle velocity was described. In order to get a simple acoustic field, a travelling wave tube was designed. The sound pressure distribution obtained by microphone along the tube was measured. The result showed the acoustic field inside the tube could be considered as travelling wave and the sound pressure is equal to the product of the air density, sound speed and the particle velocity. The laser Doppler Anemometry was used to measure the particle velocity in the acoustic field. The modulated Doppler signal was obtained by measurement system. With the spectral analysis of Doppler signal and the signal model, the particle velocity was obtained with the Bessel function analysis. The comparison of sound pressure measured by microphone and the value deduced from the velocity measured by laser Doppler system shows that deviations between two methods were 0.04 dB at 650 Hz and discrepancies were less than 0.34 dB at frequencies from 300 Hz to 1k Hz.

Vibration Analysis of a Shell Structure by Finite Element Method

Plate-shell structures, especially cylindrical shells and spherical shells, are widely used in engineering fields, such as aircraft and tanks, missiles, submarines, ships, hydraulic pumps, infusion pipelines and gas pipelines, and so on. These structures are usually in a fluid medium, which are related to the structure fluid-solid coupling and acoustic radiation field. As many experiments show that enclosed air in a thin walled structure, just like the violin, affects some modes of vibration significantly, air coupling between vibrating sides of the structure cannot be neglected. In order to explore the sound pressure distribution of vibrational frequencies, this paper, considering the material anisotropy, analyzes a typical complex shell structure of the violin by finite element method, including acoustic-structure coupling analysis and post-processing, especially sound pressure vibration frequency extraction. Finally, we get the conclusion that the distribution of sound pressure vibration frequency is similar to the normal distribution.