Sound Field Distribution Research Articles

Errors in the measurement of transmission loss in a standing wave tube

The four-microphone method of the standing wave tube can be used to effectively measure the transmission loss (TL) of acoustic materials. However, large errors in the measurement results may be observed at specific frequencies. To investigate the mechanism and lower the error, in this paper, experiments are conducted with a standing wave tube, fabricated for these experiments, using a four-microphone method. Specific factor analysis for the error is carried out. Three structure parameters of the standing wave tube are varied to minimize measurement errors. A finite element method (FEM) is employed to calculate the internal sound field distribution and TL in the standing wave tube. Based on the comparison between the experiments and the calculations, the orthogonal experimental design (OED) is performed to optimize the three structure parameters and improve the measurement accuracy to reduce the error in testing TL. The result of this work can be used as a reference for the measurement of acoustic material, which can benefit the noise control community.

원통형 진동자 내부의 이중관 중심에서의 음압해석

유체로 채워진 원통형 압전진동자 내부에서 중심축으로 집속되는 음파에 대해 진동자 내부에 삽입된 동심원의 고체튜브가 음장분포에 미치는 영향을 해석하였다. 원통형 압전진동자의 내부로부터 방사된 음파는 유체매질을 지나 고체튜브의 벽면에서 반사 및 투과를 하여 중심축에 집속된다. 이때 고체튜브의 음향임피던스 및 두께 등에 의해 중심에 집속되는 음장 분포가 변한다. 이를 이론적으로 해석하기 위하여 각 매질에 대한 전달행렬을 도출하였고 이를 적용하여 중심축에서의 음압수준을 이론적으로 해석하였다. 여러 가지 두께를 갖는 아크릴 튜브에 대해서 중심축 상에서 측정한 음압수준의 변화는 이론해석의 결과와 잘 일치하였으며 중심에 형성되는 음압은 고체튜브의 두께에 따라 매우 민감하게 변화함을 확인하였다. The effect of the concentric solid tube inserted inside the vibrator on the sound field distribution was analyzed for the sound waves focused on the center axis in the fluid - filled cylindrical piezoelectric transducer. The sound waves radiated from the inside of the cylindrical piezoelectric vibrator are transmitted through the fluid medium and are reflected or transmitted on the wall surface of the solid tube, and are focused on the central axis. At this time, the sound field distribution centered on the acoustic tube varies depending on the acoustic impedance and the thickness of the solid tube. In order to theoretically analyze this, the transfer matrix for each medium is derived, and the sound pressure level at the center axis is theoretically analyzed. For the acrylic tube with various thicknesses, the changing trend in the sound pressure level measured on the central axis agrees well with the result of the theoretical analysis, and it confirmed that the sound pressure formed at the center changes very sensitively with the thickness of the solid tube.

Broadband asymmetric acoustic transmission through an acoustic prism

Narrow bandwidth and complex structure are the main shortcomings of the existing asymmetric acoustic transmission devices. In this letter, a simple broadband asymmetric acoustic transmission device is proposed by using an acoustic prism filled with xenon gas. The sound pressure field distributions, the transmission spectra, and the prism angle effect are numerically investigated by using finite element method. The proposed device can always realize asymmetric acoustic transmission for the wave frequency larger than 480 Hz because the wave paths are not influenced by the wave frequencies. The asymmetric acoustic transmission is attributed to normal refraction and total reflection occur at different interfaces. Besides, relatively high transmission efficiency is realized due to the similar impedance between the acoustic prism and background. And the transmitted wave direction can be controlled freely by changing the prism angle. Our design provides a simple method to obtain broadband asymmetric acoustic transmission device and has potentials in many applications, such as noise control and medical ultrasound.

Spatial distribution of sound field scattered from the rough seafloor interface

The scattering coefficient of rough seafloor interface is calculated using first order perturbation theory. The interface roughness considered here is described by the isotropic power law spectrum for isotropic rough seafloor interface and anisotropic Gaussian spectrum for the rippled seafloor interface. The characteristic of spatial distribution is shown by the scattering coefficient of the scattered field with forward scattering and backward scattering, which depend on the frequency and the grazing angle of the incident wave, and the roughness of the interface. The dependence of spatial distribution of the scattered field on these parameters is analyzed by Bragg scattering of the sinusoidal interface.

Variability of the sound field interference pattern due to horizontal refraction in shallow water

Variability of the ocean waveguide’s parameters in horizontal plane (bathymetry, sound speed profile, etc.) can lead to some set of effects in the sound propagation, which are specified as horizontal refraction, or in more general form, as 3D effects. These effects are being studied both in shallow and deep water, some of them were registered in experiments, or were analyzed using different theoretical models. In given paper main attention is drawn to the theory and experimental manifestation of spatial and temporal variations of interference pattern formed by narrow-band signals. Theoretical analysis is carried out using approach “Vertical Modes and Horizontal Rays” and “Vertical Modes and PE in horizontal plane.” It is shown, that dependence of the sound field distribution in horizontal plane (both in a ray or PE approaches) on frequency and mode number, combined with possible multipath propagation, may lead to rather specific observable effects: variations of the amplitude and phase fronts, evolution o...

A Liquid Level Measurement Technique Outside a Sealed Metal Container Based on Ultrasonic Impedance and Echo Energy.

The proposed method for measuring the liquid level focuses on the ultrasonic impedance and echo energy inside a metal wall, to which the sensor is attached directly, not on ultrasonic waves that penetrate the gas–liquid medium of a container. Firstly, by analyzing the sound field distribution characteristics of the sensor in a metal wall, this paper proposes the concept of an "energy circle" and discusses how to calculate echo energy under three different states in detail. Meanwhile, an ultrasonic transmitting and receiving circuit is designed to convert the echo energy inside the energy circle into its equivalent electric power. Secondly, in order to find the two critical states of the energy circle in the process of liquid level detection, a program is designed to help with calculating two critical positions automatically. Finally, the proposed method is evaluated through a series of experiments, and the experimental results indicate that the proposed method is effective and accurate in calibration of the liquid level outside a sealed metal container.

The Relationship between Structural Intensity and Sound Field Characteristics of Cylindrical Shells

It is an important subject in many engineering areas to recognize the vibro-acoustic behaviors of vibrational structures. Many researches have been done to study this characteristics of plane structure with structural intensity (SI) analysis. This paper extends the subject to study this subject by structural intensity approach in cylindrical shell structure and present a method of controlling the sound energy transmission. Structural intensity, a powerful method, can not only quantitatively reflect power flow strength, but also can provide the energy flow directions and distributions. The structural intensity patterns vary under different load and damping conditions, and thus affects the energy level of radiation sound field in cylindrical shell. In this paper, Numerical simulation system was built to represent the simply supported thin cylindrical shell coupled vibration and acoustical radiation structure which excited by harmonic normal point force. We get the corresponding results of structural intensity distribution, sound pressure and acoustic intensity of internal radiation sound field by adjusting damper positions, and calculating the sound field energy. The characteristics of SI of thin cylindrical shell are investigated, and the relationships between SI and sound field are established. We hope that our works could provide researchers new ideas for noise reduction of similar shell structures in potential applications.

A broadband low-frequency sound insulation structure based on two-dimensionally inbuilt Helmholtz resonator

Helmholtz resonator(HR) has already been demonstrated both theoretically and experimentally to be a metamaterial with negative mass density and negative bulk modulus simultaneously. The HR can resonate at a frequency corresponding to a wavelength much longer than its geometrical parameters. At this time, the incident acoustic energy can be located. Therefore, the HR structures are considered to be good choices for controlling low-frequency sound waves. Furthermore, existing results indicate that the wide forbidden band could be formed by a one-dimensional structure shunted with detuned HRs. Based on these aforementioned theories, a man-made acoustical structure with broadband low-frequency sound insulation effect is designed by circularly inbuilt HRs. Beyond this structure's surface, a two-dimensional quiet zone can be created. With the same simulated model, an experimental structure is fabricated based on PVC plastic material. The structure consists of five layerd circular plates. In the top four plates, two kinds of holes are drilled. The smaller holes in the top plate act as shot necks of the HR, while the bigger holes in the middle three plates serve as the cavities of the HR. They can construct 60 resonators with different resonant frequencies. Experiments are carried out to study its sound insulation properties. In the experiments, three kinds of HRs with resonant frequencies 785, 840 and 890 Hz from inner loop to outer loop, respectively, are formed. The experimental results are very coincident with the simulation results from the software of COMSOL Multiphysics based on finite element method, which shows that this structure has an excellent sound insulation effect in a frequency band of 680-1050 Hz, and the maximum insulation sound pressure level can reach 41 dB. Meanwhile, the distribution of the two-dimensional sound field is measured. The results point out that the range of the insulation area can be changed with the incident frequency. In addition, the sound insulation effect is sensitive to the resonant state of the HRs. When all of the resonators at the same loop resonate simultaneously, the insulation sound pressure level will be higher. On the contrary, the insulation sound pressure level will be lower because of the energy leaking through the positions where the HRs do not resonate with the others. This work will be of help for designing new sound protection devices for low-frequency sound waves.

Subjective spatiotemporal matrix as a new measure of sound field distribution in a room

A new approach for representing the acoustic quality of classroom is presented in this paper. The subjective spatiotemporal measure was developed from a 3D scanning plane by using a dedicated scanning gear to measure the subjective volumetric sound field of a listener inside the room. Calculated coherence matrix is derived from spectral comparison on the appropriate scanning planes. It then could be used for indicating the subjective perception of a listener which is may differ to another listener at adifferent position inside the rooms.

Features of sound propagation in the ocean with fine-structure inhomogeneities

We analyze the results of an experiment using an explosive sound source in the tropical part of the Indian Ocean. We consider the time structure of sound signals in geometric shadow zones to a distance of 270 km and the scheme of how the sound field in the shadow zone is formed by rays reflected from horizontally extended fine-structured sound velocity layers. From the results of calculation using a wave program that realizes the method of psuedodifferential parabolic equations, we analyze the influence of signal scattering by fine-structure sound velocity inhomogeneities on the sound field distribution in a waveguide. We show that the field formed by spots of light in each of the shadow zones is generated by a regular field and propagates in parallel to it, taking energy from the regular zone in the near field and in each subsequent convergence zone. This mechanism causes an additional decrease in the field in illuminated zones, which can be interpreted as additional attenuation of the regular sound field.

Active Noise Control for Dishwasher noise

The dishwasher is a useful home appliance and continually used for automatically washing dishes. It's commonly placed in the kitchen with built-in style for practicality and better use of space. In this environment, people are easily exposed to dishwasher noise, so it is an important issue for the consumers, especially for the people living in open and narrow space. Recently, the sound power levels of the noise are about 40 - 50 dBA. It could be achieved by removal of noise sources and passive means of insulating acoustical path. For more reduction, such a quiet mode with the lower speed of cycle has been introduced, but this deteriorates the washing capacity. Under this background, we propose active noise control for dishwasher noise. It is observed that the noise is propagating mainly from the lower part of the front side. Control speakers are placed in the part for the collocation. Observation part of estimating sound field distribution and control part of generating the anti-noise are designed for active noise control. Simulation result shows proposed active noise control scheme could have a potential application for dishwasher noise reduction.

Waveform-preserved unidirectional acoustic transmission based on impedance-matched acoustic metasurface and phononic crystal

The waveform distortion happens in most of the unidirectional acoustic transmission (UAT) devices proposed before. In this paper, a novel type of waveform-preserved UAT device composed of an impedance-matched acoustic metasurface (AMS) and a phononic crystal (PC) structure is proposed and numerically investigated. The acoustic pressure field distributions and transmittance are calculated by using the finite element method. The subwavelength AMS that can modulate the wavefront of the transmitted wave at will is designed and the band structure of the PC structure is calculated and analyzed. The sound pressure field distributions demonstrate that the unidirectional acoustic transmission can be realized by the proposed UAT device without changing the waveforms of the output waves, which is the distinctive feature compared with the previous UAT devices. The physical mechanism of the unidirectional acoustic transmission is discussed by analyzing the refraction angle changes and partial band gap map. The calculated transmission spectra show that the UAT device is valid within a relatively broad frequency range. The simulation results agree well with the theoretical predictions. The proposed UAT device provides a good reference for designing waveform-preserved UAT devices and has potential applications in many fields, such as medical ultrasound, acoustic rectifiers, and noise insulation.

A numerical simulation of acoustic field within liquids subject to three orthogonal ultrasounds

When one beam of ultrasound propagates along a single direction in liquids, the cavitation effect is always confined to a limited volume close to the ultrasonic source. This greatly limits the application of power ultrasound in liquid processing and materials fabrication. In this study, a methodology for applying three orthogonal ultrasounds within liquids has been proposed. By solving the Helmholtz equation, the sound field distribution characteristics are investigated in 1D (one dimensional), 2D (two dimensional) and 3D (three dimensional) ultrasounds at their resonant frequencies, which show that the coherent interaction of three beams of ultrasounds is able to strikingly promote the sound pressure level and reinforce the mean acoustic energy density as compared with that in 1D case. Hence, the potential cavitation volume is enlarged remarkably. This opens new possibilities for the design and optimization of ultrasonic technology in fabricating materials.

The acoustical role of vocal tract in the horseshoe bat, Rhinolophus pusillus.

The sound field distribution in the vocal tract with a single sound source in the glottis and the transfer function of the supraglottal vocal tract of the horseshoe bat, Rhinolophus pusillus, have been obtained using the finite-element method (FEM) technique. The models of vocal tracts used for FEM calculation are constructed by tomography scanning. These models are used to set up a finite-element model for calculating the sound field distribution by loading the unit sound source in the glottis. By changing the frequency of the unit sound source, the frequency response was figured out and the acoustic role of vocal tract chambers was examined by obtaining the transfer function and sound pressure distribution before and after filling the chambers using voxels. Sound pressures in the trachea and nostrils are recorded and some analysis of the acoustics of the subglottal and vocal tract was made to find the function of the construction in the vocal tract and subglottal parts. The results show nasal chambers can effectively improve the Q (quality factor) value near the second harmonic, and alternate the sound distribution in the supraglottal part. Whereas the tracheal chambers can reduce the amplitude second harmonic in the subglottal part, its function is like a notch filter which can block the second harmonic component of the back propagation sound under the glottis.

A controllable circular ring acoustic focused field

Based on Huygens principle about the aspect of phased array, this paper presents a structure of cylindrical acoustic transducer consisting of circular ring piezoelectric transducer elements in radial vibration mode, which can be used to achieve the ultrasonic nondestructive test for the cylindrical scanning acoustic field in three-dimensional space. By analyzing the acoustic field of a single ring line source and a single element, the sound field distribution of the phased array is obtained for constructing circular ring acoustic focused field. By means of the phased array incentive mode, the phase difference of driving signals is generated and forms a regular time delay; with the accomplishment of sound field scanning in cylindrical three-dimensional space, the circular ring acoustic focused field can be controlled in real time.Theoretical analysis and finite element simulation results demonstrate that the size of the circular ring acoustic focused field can be controlled by the numbers of the excited array elements, which are 4, 8, 16 and 32 respectively in our work. We find that with more array element numbers, the circular ring acoustic field has better focused features. The radius size of the circular ring acoustic focused field can be controlled by the different locations of the focus positions which are 30 and 50 mm respectively in our work. And we find that as the distance between the focus positions and the center of piezoelectric wafer becomes longer, the radius of the circular ring acoustic focused field becomes bigger, and the position of the focus is equivalent to the radius of the circular ring acoustic focused field. The movement along the axial direction of circular ring acoustic focused field can be controlled by the angle of deflection, which are set as 0, 10 respectively in our work. And we find that the circular ring acoustic focused field is deflected in a corresponding deflection angle along the Z-axis, and the moving distance is FZ = F/sin . With the theoretical analysis and the experimental simulation, it can be shown that the structure of cylindrical acoustic transducer array presented in this paper could create an adjustable circular ring acoustic focused field and can potentially provide an acoustic field scan method in detection ultrasound, medical ultrasound and other areas of a cylindrical space.

FINITE ELEMENT DETERMINATION OF THE HEAD-RELATED TRANSFER FUNCTION

The auditory peripheral system, which takes care of collection and enlargement in hearing processing, is an important part of the overall auditory system. This system is the key of sound source identification and location, and an important basis for a variety of audio equipment design and sound quality evaluation. In order to better recognize the acoustic characteristics of the auditory peripheral system, and effectively guide the audio equipment design as well as the sound quality evaluation, this study presents a numerical model based on the finite element/infinite element method (FEM/IFEM) to compute the near-field head-related transfer function (HRTF) on a reversed head model. A spherical sound source is positioned at different locations in the horizontal, median and lateral planes. The HRTFs and sound field distributions are computed for a frequency range up to 6 kHz. The present model is qualitatively validated against experimental data from MIT database. The results confirm the potentiality of the proposed approach which can efficiently detect the diffraction region, diffraction angle and tails in the sound field.

Simulation and experiment for the inspection of stainless steel bolts in servicing using an ultrasonic phased array

The non-destructive testing of small-sized (M12–M20) stainless steel bolts in servicing is always a technical problem. This article focuses on the simulation and experimental research of stainless steel bolts with an artificial defect reflector using ultrasonic phased array inspection. Based on the observation of the sound field distribution of stainless steel bolts in ultrasonic phased array as well as simulation modelling and analysis of the phased array probes' detection effects with various defect sizes, different artificial defect reflectors of M16 stainless steel bolts are machined in reference to the simulation results. Next, those bolts are tested using a 10-wafer phased array probe with 5 MHz. The test results finally prove that ultrasonic phased array can detect 1-mm cracks in diameter with different depths of M16 stainless steel bolts and a metal loss of Φ1 mm of through-hole bolts, which provides technical support for future non-destructive testing of stainless steel bolts in servicing.

Sound quality inside small meeting rooms with different room shape and fine structures

This note is intended to understand relative importance of room shape and fine structures on the sound quality inside small meeting rooms in terms of the reverberation time, the sound field distribution and the speech transmission index with similar room volume, surface area and the absorption coefficients. First, different shaped rooms with smooth walls are modeled and simulated to investigate the effects of room shape on the sound quality, and then hyperboloid cells are made on the walls to examine the influence of fine structural surface on sound quality with both regular and random arrangements. It is found that the reverberation time is affected significantly by the room shape while is not sensitive to the hyperboloid cells. The sound field distribution is affected little by the room shape and the hyperboloid cells and the difference is smaller than the Just-Noticeable-Difference in most cases. The impact of the room shape and fine structural surface on the speech transmission index mainly lies in the transition area between the direct sound and the reverberant sound. The reliability of the simulation remarks is confirmed by the experiments carried out in two different meeting rooms. The main conclusion of the note is that when the room volume, the surface area and the absorption coefficients are kept constant, the room shape and fine structural surface have little impact on the sound field distribution and speech intelligibility inside small rooms with ordinary surface absorption, while the reverberation time is affected significantly by room shape but slightly by the fine structural surface.

A Directional Audible Sound System using Ultrasonic Transducers

In general the audible sound has the characteristics of spreading, however the ultrasound is directional. This study used amplitude-modulating technique for an array of 8 ultrasonic transducers to produce directional audible sound beam. In this study sound field distribution for the directional audible sound beam has been investigated. The effect of different weightings varied with different frequency for the transducers on the directivity of the sound beam has also been evaluated. An H (infinity) optimization method was used to calculate the optimal weightings of the transducers for better directivity of the sound beam. Different optimal weightings also added to the carrier and sideband frequencies to control the difference frequency’s beamwidth and sidelobe amplitude. The results showed that the beam width can be controlled and good directivity of the sound beam can be obtained by using the H_8 optimization method.

Influences of Ground Reflection on the Elevated Box Bridge Structure Noise

A 32 m simply supported concrete box bridge is taken as the research object. The box bridge structure noise induced by the static loads and how the ground reflection affects it are studied by the modal acoustic transfer vector (MATV) method. The results show that it is commendable to analyze the box bridge structure noise using the MATV method; the regularities of the sound field distribution are changed obviously by the ground reflection, and the directivity is very obvious in the far-field region and there has the stratification of the vertical sound field under the box bridge; the ground reflection enhances the overall sound level of the sound field except the region above the box bridge, and the vertical sound field in the far field is affected very obviously. The buildings, especially the high-rise buildings, are mostly in the far field area, so the influences of the ground reflection on the box bridge structure noise must be paid attention to.