Characteristics Of Sound Field Research Articles

Calculated sound field characteristics in air gaps of noncontact ultrasonic motor fabricated using two square bending vibrators(Acoustical Letter)

Calculated sound field characteristics in air gaps of noncontact ultrasonic motor fabricated using two square bending vibrators(Acoustical Letter)

Energy Harvesting with Piezoelectric Element Using Vibroacoustic Coupling Phenomenon

This paper describes the vibroacoustic coupling between the structural vibrations and internal sound fields of thin structures. In this study, a cylindrical structure with thin end plates is subjected to the harmonic point force at one end plate or both end plates, and a natural frequency of the end plates is selected as the forcing frequency. The resulting vibroacoustic coupling is then analyzed theoretically and experimentally by considering the dynamic behavior of the plates and the acoustic characteristics of the internal sound field as a function of the cylinder length. The length and phase difference between the plate vibrations, which maximize the sound pressure level inside the cavity, are clarified theoretically. The theoretical results are validated experimentally through an excitation experiment using an experimental apparatus that emulates the analytical model. Moreover, the electricity generation experiment verifies that sufficient vibroacoustic coupling can be created for the adopted electricity generating system to be effective as an electric energy-harvesting device.

Simulation and Experimental Study of Ultrasonic Cleaning Based on Multi-Field Coupling

In current Ultrasonic Cleaning simulation, high calculation complexity and low precision is a big problem. The disadvantages of reflecting the sound field characteristics inaccurately and quantitative difficulties exist in the sound field measurements. Firstly, the two-dimensional and three-dimensional models of Ultrasonic Cleaning are established in COMSOL Multiphysics and corresponding cleaning effects under different frequencies are simulated, then the frequencies of cleaning machine suitable for remanufactured components are determined. Finally, by means of staining method, sound field distribution on different work cross-sections in the Ultrasonic Cleaning process is studied. Halcon and Matlab are used in our investigation to deal with the experiment results in order to provide a new idea on the measurement of the sound field of Ultrasonic Cleaning.

Sound Field Simulation and Optimization at an Underground Subway Station

The noise of underground subway stations has a great influence on the passengers and workers. The finite-element based software Actran is introduced to analyze the acoustical performance of an underground subway station in this paper. A sample station named Xingzhong Road from metro line 9 in Shanghai is considered. The finite element models for analysis of sound field characteristics are established at the two common working conditions of the subway train: coming and going. The sound pressure levels (SPLs) and energy distributions are calculated and verified by field noise tests. Based on the established models, furthermore, an optimizing scheme based on the orthogonal experimental algorithm is presented and performed. The simulation results show that the proposed method is effective and useful for improving the sound environment and reducing the harm of noise to the passengers and workers at underground subway stations.

Architectural treatments for improving sound fields for public address announcements in underground station platforms

This study investigates the effects of subway platform design elements, such as finishing materials, on the temporal and spectral characteristics of public address (PA) announcements. To reproduce the acoustic conditions of the simulation model, acoustic-fitting using ray-tracing models was performed for two existing subway stations with island platforms using field measurement data. A systematic investigation using a computer station model was then carried out to clarify variations in the sound field characteristics when modifying station dimension and replacing finishing materials. It was found that smaller station dimensions yielded a higher speech transmission index (STI) and sound pressure level (SPL) with low early decay time (EDT), whereas higher absorption materials yielded a higher STI with lower SPL and EDT in the platform sound fields. In particular, a smaller station cross-sectional area obtained by modifying the station width and corridor height was the most effective for improving STI. More absorption on the floor and ceiling surfaces in the platform area had a marked influence on improving STI. In addition the auralized PA sounds with anechoic male and female announcements were analyzed using spectrogram and auto-correlation/interaural cross-correlation factors. It was found that the absorptive treatments contributed to clearer temporal characteristics of the PA sounds with decreased binaural dissimilarity and without any changes in spectral components.

Optimal design of a sound reflector by particle swarm optimization

For room acoustic design, the shape of the room and the materials need to be well considered. Designing such rooms requires extensive experience. Numerical analyses can minimize designers’ burdens by the automatic generation of many room candidates and the selection of an optimized one on the basis of objective measurements. Research on both numerical analysis methods and optimal design methods is required, but few studies are done regarding the latter. This paper proposes an optimal method by combining geometrical acoustic simulation with an optimization technique known as “particle swarm optimization.” Although the final aim is to achieve a global acoustic design, this paper is limited to local shape design, which is still important, considering that local shapes affect the characteristics of the global sound field. The proposed method is used for designing sound reflectors, whose aim is to scatter first reflected sound waves across the entire field. Hence, the optimization variables are sound reflectors shapes and materials, and the objective function is to evaluate the uniformity of a sound field in terms of room acoustic indices (T20, C80, and Ts). Compared with the initial reflectors, the optimized sound reflectors exhibited a higher uniformity in the room acoustic indices.

G101043 音振動連成現象を利用した発電システム([G101-04]機械力学・計測制御部門,一般セッション(4))

This paper describes the vibroacoustic coupling between the structural vibrations and internal sound fields of thin structures. In this study, a cylindrical structure with thin end plates is subjected to a harmonic point force at one end plate and a natural frequency of the end plates is selected as the forcing frequency. The resulting vibroacoustic coupling is then analyzed by theoretically and experimentally by considering the dynamic behavior of the plates and the acoustic characteristics of the internal sound field as a function of the cylinder length. The length and phase difference between the plate vibrations, which maximize the sound pressure level inside the cavity, are clarified theoretically. The theoretical results are validated experimentally through an excitation experiment using an experimental apparatus that emulates the analytical model.Moreover, the electricity generation experiment verifies that sufficient vibroacoustic coupling can be created for the adopted electricity generating system to be effective as an electric energy-harvesting device.

An experimental study of the sound field in a large atrium

In large atria acoustic comfort is an important consideration, but it is less studied compared to other physical environmental factors. In this study, sound distribution and reverberation in a typical large atrium have been experimentally examined, revealing the basic sound field characteristics. The results show that in terms of sound distribution, at all frequencies there is a continuous decrease in sound pressure level (SPL) with increasing distance to the source, both vertically with increasing floor level, and horizontally at each floor. The patterns of SPL decrease with increasing source–receiver distance are rather complicated, and also vary considerably at different frequencies. There is a considerable difference between the maximum and minimum SPL at each floor, ranging from 31 dBA to 18 dBA from ground to top floor, but in terms of the average SPL across each floor, the decrease is only 4.4 dBA from ground to top floor. With different source positions, the average SPL in the whole atrium could be rather different, up to about 10 dBA. In terms of reverberation, at all frequencies there is generally a continuous increase with increasing source–receiver distance. With a source at the ground floor, the reverberation time variation on the ground floor could be about 100%, and in the side corridors, the reverberation time is rather long, up to about 5 s across frequencies. The decay curves are generally not linear, and the non-linearity is more significant in side corridors and also, at lower frequencies. The above features suggest the non-diffuse characteristics of such a typical atrium.

Sound field characteristics of underground railway stations – Effect of interior materials and noise source positions

In the case of most underground railway stations, no acoustical solutions are used to reduce train noise. Because the reflecting features of train noise in an underground station are not known, appropriate methods for controlling these features have yet to be established. The aim of this study was to clarify the sound field characteristics of underground stations by putting a sound source and receiver on the railway track and platform, respectively. The impulse responses for two vacant underground stations were measured to clarify the effects of the interior materials of the station (Comparison I), and the sound source was put in each station and tunnel to clarify the effect of the noise source positions (Comparison II). Results showed that the sound fields were similar between the stations whose lateral walls were covered with either metallic or fire-resistant wooden panels (Comparison I), and that the sound field for the sound sources near or in the tunnel presented a higher strength (G) by 5.1dB and longer reverberation time (EDT) by 0.7s compared to the sound source in the station (Comparison II). The sound sources in the tunnel presented strong and long reverberations at around 500Hz due to the convergence effect of the tunnel. Therefore, this study proposes a platform screen with doors to limit noise transmission into the platform.

Analysis of Acoustic Performance of Compound Muffler by Finite Element Method

Since the theory of one-dimensional plane wave can not accurately predict the internal sound field of the complex structure muffler. The three-dimensional finite element method is adopted to establish the acoustic model of the composite muffler based on the application of composite muffler model. Transmission loss and characteristics of internal sound field of the composite muffler's are calculated through acoustic vibration software Sysnoise. The calculation shows that the muffler under the interference of fluid flow has the higher transmission loss compared with the absence of liquidity function with an additional silencer band. The analysis method and conclusions provide a basis for the design of composite muffler.

Sound field of typical single-bed hospital wards

The aim of this paper is to investigate the basic characteristics of sound fields in the increasingly concerned single-bed hospital wards, the effects of commonly used furniture, and the feasibility and strategic use of acoustic simulation techniques for such spaces. Two typical single-bed wards at a Critical Care Unit were selected as the case study site. Eight different room acoustic conditions were created by gradually moving pieces of furniture out of the ward. It has been shown that in the ward without acoustic ceiling, under empty room condition the RT ranged from 0.8s, typically at low frequency, to 2.3s at 630Hz; the variations in both SPL and RT at different receivers were insignificant except at low frequencies, so that in such single-bed wards a diffuse field could be assumed; and longer RT and higher SPL were found when furniture was gradually moved out of the ward. In the ward with acoustic ceiling, the effect of furniture was less. There was a good agreement between measured and simulated RT and SPL, showing the usefulness of computer simulation for this kind of spaces. In the simulation, the effect of surface diffusion coefficient was generally insignificant, whereas the effect of edge diffusion should be taken into account, especially for the RT prediction. The feasibility of geometric simplification was also demonstrated.

Acoustic cues used by blind travelers

People with vision loss rely heavily on subtle environmental sound cues for safe and efficient travel (“Wayfinding”). Using our laboratory-developed instruments, the acoustic cues available to blind individuals, with and without hearing loss, during real-life pedestrian travel were recorded. Acoustic signals picked up by electret condenser microphones in the ear canals were fed to a wearable digital audio recorder. Head and body movements were monitored by accelerometers and gyroscopes mounted on the heads and torsos of subjects during typical travel situations such as walking along a corridor with an open doorway. A skilled wayfinder can detect the presence of an open doorway from the acoustic characteristics of the ambient sound field (the “acoustic signature”). The salient characteristics of the acoustic signature when passing an open door were found to be below 1500 Hz. These data confirm previous work regarding ambient room noise near a wall and an opening (Ashmead, 1999). Unlike previous work, the current study also measured the interaural characteristics of the acoustic signature. The results of this investigation will be used to develop the design requirements of a special-purpose hearing aid for people with both vision and hearing loss. (Funded by NIDRR and Smith-Kettlewell Eye Research Institute.)

S056025 プラズマアクチュエータを用いた平板翼列から発生する空力音の制御

In order to reduce an aerodynamic noise generated from the flat plate cascade, we attempted to flow and noise control by using plasma actuator. In the case of non-resonance condition (such as the Aeolian tone noise generated from a single flat plate), aerodynamic noise levels increase by using PA. This is considered because that PA supply the momentum to the separated flow near the leading edge, flow separations are suppressed and the share flow becomes stronger than that of without PA. As a result, aerodynamic noise is increased by using PA in non-resonance condition. The effect of noise control is proportional to the supplied voltage and driven frequency of PA. On the other hand, in the case of resonance condition of flow and sound fields, sound level can be reduced by using PA. When the acoustic resonance occurs in flat plate cascade, phase of vortex shedding is locked by the generated sound. The experimental results showed that PA was control the phase and intensity of the vortex shedding near the reading edge, and it is less likely to become strong acoustic resonance field is formed. These facts indicate that the control of unsteady aerodynamic flow and sound field characteristics must be discussed when the effectiveness of noise control with PA is evaluated.

Effect of Amplification on Acoustic and Vibration Energy with Vibroacoustic Coupling

In order to apply acoustic energy to industrial fields, its amplification is essential and vibroacoustic coupling is one of best ways of amplifying acoustic energy. In the present study, we consider a cylindrical structure with thin plate at both ends and investigate vibroacousitc coupling between the plate vibrations and internal sound field when an external harmonic force is applied to one end plate, regarding such a coupling phenomena as one of the available measures to amplify acoustic energy. This coupling is theoretically and experimentally investigated by considering the behavior of both plates and the acoustic characteristics of the internal sound field for varying dimensions of the end plates and the cylinder. In the analytical model, the end plates are supported circumferentially by springs in order to obtain support conditions that are as close as possible to the actual condition in the experiment due to adjustments of spring stiffnesses. The cylinder length and phase difference, which maximized the sound pressure level inside the cavity, are clarified theoretically. These theoretically results are verified experimentally through an excitation experiment using an experimental apparatus that is emulated by the analytical model. The above-describe results reveal such a vibroacoustic coupling phenomenon is useful for the amplification of the acoustic energy.

G090014 外部周期力を受ける連結円筒構造の音振動特性

In order to apply acoustic energy to industrial fields, its amplification is essential and vibroacoustic coupling is one of best ways of amplifying acoustic energy. The present paper describes vibroacoustic coupling between the plate vibrations and the internal sound fields of a cylindrical structure connected two cylinders with thin plates, and the coupling phenomena are investigated experimentally by considering the behavior of the plates and the acoustic characteristics of the internal sound fields with variations in the cylinder length, when external periodical forces are applied to both end plates. The acoustic characteristics are evaluated based on the sound pressure level, which is maximized while changing the phase difference between the plate vibrations. Moreover, the experiment of electricity generation is carried out with piezoelectric elements, which are installed on the plates. These results reveal that vibroacoustic coupling is effective in increasing the acoustic energy and can extract the acoustic energy via the plate vibrations.

Investigation into Noise Frequency Spectrum Characteristics Corresponding to Blade Nonsynchronous Vibration in Multi-Stage Axial Compressor

Unsteady flow phenomenon occurs in a multi-stage axial compressor. The unsteady flow not only has significant influence on the performance of compressor and the stability of flow, but also can be an excitation source inducing Nonsynchronous vibration (NSV) of rotor blade. NSV is an aeroelastic phenomenon where the rotor blades vibrate at nonintegral multiples of the shaft rotational frequencies in operating regimes where classical flutter is not known to occur. Recently, more and more scholars pay attention to Rotating instabilities (RIs) as one of the unsteady flow phenomenon. RIs have been observed in axial flow fans and centrifugal compressors as well as in low-speed and high-speed axial compressors. They are responsible for the excitation of high amplitude rotor blade vibrations and noise generation. This research aims at revealing the relationships among the unsteady flow behaviors, characteristics of inner sound field and propagation, the vibration of rotor blade in multi-stage axial compressor. The noise in compressor and the vibration of rotor blade have been measured on a high pressure compressor rig testing. The transducer system is connected to the interior casing wall through the acoustic waveguide pipes. The noise is measured by 1/4 inch condenser microphones in different operating of the compressor. The time-domain wave of noise acquired at different work status of the compressor is transformed into frequency spectrum by Fast Fourier Transform (FFT) to investigate characteristics of sound field in multi-stage axial compressor. And the emphasis is focused on the frequency characteristics of the noise corresponding to blade nonsynchronous vibration. It is found that the vibration amplitude of the rotor blade suddenly increases in a pre-arranged structure adjustment and specific rotating speed, and noise signal with special frequency structures appears simultaneously. High amplitude levels of blade vibration have occurred on the first rotor of a multi-stage high pressure compressor. The frequencies are not in resonance with harmonics of the rotor speed. The frequency analysis show that the noise has a special frequency structures with combination of the appeared characteristic frequency and the blade pass frequency of rotor blade (BPF). Because the similarities between the frequency combination and the specific frequency structure of the fluctuating pressure when the rotating instability (RI) appears in the axial compressor have been identified, the acting mechanism of rotating instability may exist in this compressor, i.e. the vibrational excitation to the rotor blade may be aerodynamically caused and associated with a rotating flow instability in the compressor.

On Acoustic Radiation by Rotating Body Sources in Frequency Domain

For the complexity of the sound generated mechanism of rotating body source, this paper describes a frequency-domain numerical method for predicting sound radiation of rotating body sources based on the Kirchhoff integral equation with analytical Green's function of rotating monopole and dipole source in free space. The sound radiation model is established in free space and the relationship between characteristics of sound field and acoustic nature frequency of source, angular frequency and its harmonics can be revealed by the mathematical solution. Numerical simulation shows that sound field has a strong directivity, fundamental frequency transmitting in the rotary shaft direction and harmonics spreading along radial direction and frequency shift phenomena appearing clearly in higher rotating speed of source. The method has a theoretical significance for exploring the low-noise rotating machinery. Research about sound radiation of moving source originates from Lighthill. The first integral approach for acoustic propagation is the acoustic analogy. In the acoustic analogy, the governing Navier-Stokes equations are rearranged to be in wave-type form. There is some question as to which terms should be identified as part of the sound source and retained in the right-hand side of the equation and which terms should be in the left-hand side as part of the operator. The far-field sound pressure is then given in terms of a volume integral over the domain containing the sound source. However the major difficulty with the acoustic analogy is that the sound source is not compact in supersonic flows. Several modifications to Lighthill's original theory have been proposed to account for the moving sound source or other effects. The Ffowcs Williams and Hawkings (FW-H) equation was introduced to extend acoustic analogy in the case of solid surfaces. However, when acoustic sources are present in the flowfield a volume integration is needed. This volume integration of the quadrupole source term is difficult to compute and is usually neglected in most acoustic analogy codes. Errors could be encountered in calculating the sound field. Another alternative is the Kirchhoff method which assumes that the sound transmission is governed by the simple wave equation. Kirchhoff's method consists of the calculation of the nonlinear near- and mid-field, usually numerically, with the far-field solutions found from a linear Kirchhoff formulation evaluated on a control surface surrounding the nonlinear-field. The control surface is assumed to enclose all the nonlinear flow effects and noise sources. The sound pressure can be obtained in terms of a surface integral of the surface pressure and its normal and time derivatives. This approach has the potential to overcome some of the difficulties associated with the traditional acoustic analogy approach. The method is simple and accurate and accounts for the nonlinear quadrupole noise in the far-field. Full diffraction and focusing effects are included while eliminating the propagation of the reactive near-field. Kirchhoff's formula, published in 1882, is used in the theory of diffraction of light and in other electromaqnetic problems. It also has many applications to problems of wave in acoustics. One of the novel uses of this formula was proposed by Hawkinqs for predicting

On Acoustic Radiation by Rotating Dipole Sources in Frequency Domain

In order to deal with the acoustic radiation from rotating sources, this paper describes a frequency-domain numerical method for predicting sound radiation. The method is based on the analytical Green’s function of rotating monopole and dipole source in free space. Sound radiation model is established and characteristics of sound field are discussed by numerical simulation and the relationship between radiated sound frequencies and acoustic nature frequency of source, angular frequency and its harmonics can be revealed .The radiated sound field has a strong directivity, fundamental frequency transmitting in the rotary shaft direction and harmonics spreading along radial direction and frequency shift phenomena appearing clearly in higher rotating speed of source. The method has a theoretical significance for exploring the low-noise rotating machinery.

Research on the Planar Near-Field Acoustic Holography for Cyclostationary Sound Field

The conventional planar near-field acoustic holography is not suitable for cyclostationary sound field radiated by the rotating machines. When the cyclic spectral density (CSD), instead of the complex sound pressure, is adopted as reconstructed physical quantity, the modulating wave and carrier wave components of the cyclostationary sound field can be extracted exactly and so the cyclostationary planar near-field acoustic holography (CPNAH) technique was proposed. Simulation and experimental results show that the modulation characteristics of the cyclostationary sound field can be extracted effectively and the sound source can be localized accurately.

Acoustical Design and Measurement in Surround Sound Classroom

This paper covers the requirement and measurement of sound quality in the surround sound classroom. Based on the characteristics of the sound field, this paper specially deals with the design of acoustics requirement of the characteristics of reverberation frequency and sound propagation. In order to meet the requirements of recording in signal to noise ratio, comprehensive methods in noise decrease are adopted in design, which include the reduction of noise in room background. Through the checking of the testing data and the evaluation of the users, various acoustics norms meet the requirements of acoustics and the demands of the using.