Sound Intensity Vector Research Articles

Design of a hydro sound intensity probe for quantification and localization of acoustic sources — Applied to a hubless marine rim drive

The reduction of hydro noise emission by ship propulsion systems is of importance since background noise levels in the oceans have increased by 21 dB in the past decades. Thus, the acoustical improvement of ship propulsion systems is a necessary and challenging task. It involves not only the ship propeller but also the components of the entire drive train like diesel or electrical engines, electrical inverters as well as gearboxes. Acoustical measurement systems for the quantification and localization of noise sources are essential for any kind of optimization and are state of the art in the airborne noise field. This is not the case in the hydro acoustic field and measurements are mostly limited to the recording of the hydro sound pressure using single hydrophones. The objective of this paper is the presentation of a new three dimensional hydro sound intensity probe capable of acoustical sound power quantification and noise source localization. The probe can be used for the determination of the hydro sound pressure, the 3D sound intensity vector and the sound power. Furthermore, the probe can be utilized for hydro sound source localization purposes using beamforming methods based on virtual acoustical arrays. The developed probe was used for hydro acoustic investigations of a full scale marine rim drive during a measurement campaign in the river Warnow in Rostock, Germany. The results indicate the different hydro sound generating mechanism of the rim drive.

The estimation of distance and power of multiple sound sources by combining three-dimensional sound intensity and beamforming

The problem of identifying multiple sound sources occurs in various fields. This study proposes a method for multi-source localization and sound power estimation based on three-dimensional sound intensity (3DSI) measurement combined with high-precision beamforming. First, according to the propagation law of the point source in the free field and 3DSI measurement method, a mathematical model of the sound intensity vector, sound power, and source location in 3D space for multiple sources is derived. The 3DSI components can be measured by 3DSI probes. To reduce the computational cost required to solve the mathematical model, the angles of the sources are estimated via compressive sensing beamforming orthogonal matching pursuit for the method. Moreover, the sound intensity components and angles are used as inputs in the multiple sound source identification model, and the dimensions of the model are significantly reduced. The model was solved to obtain sound source distance and sound power. Two tetrahedral intensity probes and a 16-channel microphone array were used for experiments in a semi-anechoic chamber. The results demonstrate that the method can accurately identify the locations of multiple sound sources and determine the sound power. Considering three sound sources, the maximum angular error is 1.41°, while the maximum distance error is 0.08 m. This method can use a small number of probes to obtain the sound sources spatial position and sound source power, and it improve the resolution and calculation efficiency.

Сравнение результатов измерений уровней подводного шума источника, полученных прямым методом и с использованием векторно-фазовой обработки

Object and purpose of research. Moving broadband source underwater noise level estimations obtained by direct and indirect methods using a receiver for the measurement of sound pressure and sound particle velocity components combined. Materials and methods. Theoretical research using computer simulation, full-scale experiments in real measurement conditions, statistical analysis of experimental results. Main results. The noise level estimations obtained by the direct method, only through the sound pressure channel, and by the indirect method with recalculating the values of sound intensity were compared based on representative samples under ideal conditions and in real water area conditions. Conclusion. Under ideal measurement conditions a statistically significant difference between the two estimation methods occurs only at frequencies below 16 Hz. The results of a full-scale experiment in real conditions show that the estimate obtained on the basis of the spatial selective sound intensity vector is characterized by greater reliability and accuracy since it is less affected by reflections from the boundaries of the water area.

Research on the Detection Technology of Audible Noise Sources of UHVDC Transmission Lines

In order to directly and deeply study the law and characteristics of audible noise sources of UHVDC transmission lines, a method of detecting the sound intensity vector at the source position in the bundle conductor is proposed. First, the structure of the sound intensity detection device is designed, and the method for calculating the sound intensity vector is deduced based on this prototype. Then, the simulation of the electric field distribution on the surface of the device in the UHV extreme electric field environment is carried out. The change of the maximum electric field intensity and the influencing factors are obtained, which proves that the proposed detection device has the adaptability of the UHV electric field environment. Finally, the measurement error of the proposed detection device is analyzed. The results show that in the frequency range of 100∼5000Hz, the theoretical error of the sound intensity vector components and the total sound intensity level obtained by the measurement device in three directions are less than 2dB, which can meet requirements of sound intensity detection at the sound source.

Influence of room modes on low-frequency transients: Theoretical modeling and numerical predictions

In the low-frequency range, a sound reproduction in enclosures is strongly influenced by excited room modes. While the spectral impact of acoustic modes on a room response is well recognized, there is no sufficient knowledge on how these modes affects transients. In the paper this issue has been examined theoretically and numerically for a room excited by a tone burst by using a modal expansion method supported by a computer implementation. To quantify a temporal accuracy of a sound reproduction, the new metrics referred to as the tone burst reproduction error was introduced. The basis for determining this quantity was a deviation between the tone burst amplitude and the amplitude of a sound pressure computed via the Hilbert transform. A numerical simulation was performed for an irregularly shaped enclosure having a form of two-room coupled system. Calculation results have proved that a high inaccuracy of a tone burst reproduction occurs at receiving points corresponding to sharp dips in a distribution of the steady-state sound pressure level. This is because in these points an amplitude of transient sound is much bigger than a tone burst amplitude. It was discovered that strong narrow peaks in the tone burst reproduction error are located at centers of vortices in the active sound intensity vector field. An influence of a sound damping in a room on a reproduction of a tone burst was also examined and it was found that a substantial increase in a wall sound absorption does not significantly improves a tone burst reproduction because it does not eliminate sharp dips in a distribution of the steady-state sound pressure level.

Spatial sound intensity vectors in spherical harmonic domain.

Sound intensity is a fundamental quantity describing acoustic wave fields and it contains both energy and directivity information. It is used in a variety of applications such as source localization, reproduction, and power measurement. Until now, intensity is defined at a point in space, however given sound propagates over space, knowing its spatial distribution could be more powerful. This paper formulates spatial sound intensity vectors in spherical harmonic domain such that the vectors contain energy and directivity information over continuous spatial regions. These representations are derived with finite sets of closed form coefficients enabling ease of implementation.

Localizing multiple targets with a single particle velocity sensor

The acoustic velocity sensor (AVS) measures the direction of a propagating plane wave by measuring instantaneously the particle velocity over a small volume in space. When multiple sound sources are present, the AVS no longer reports the correct directions as the sound intensity vectors (the product of pressure and velocity vector) get mixed up nonlinearly. A few methods have been proposed to extract the individual components from just one sensor by assuming, for example, spectral separability or nongaussianity. This paper shows it is in fact possible to extract the components without making such assumptions. The approach here is to constrain the signal with the acoustic impedance equation for multiple superposing plane waves and, applying various techniques, such as sparsity decomposition, to solve the derived least squares problem.

Eulerian motion magnification applied to structural health monitoring of wind turbines

Several types of defects may occur in wind turbines, as physical damage of blades or gearbox malfunction. A wind farm monitoring and damage prediction system is built to observe abnormal vibrations of elements of wind turbine: blades, nacelle, and tower. Contactless methods are developed which do not require turbine stopping. In this work, structural health monitoring of a wind turbine is evaluated using a conversion from the captured and processed video to the acoustic signal, employing the method of Eulerian motion magnification in video. It was assumed that this task can be achieved using a stabilized high-speed video camera only, directed at the wind turbine without any additional sensors mounted on windmill blades or on its body. Moreover, the developed vector sound intensity probe was used for spatial measurements in order to recover the vibration modes of wind turbines. Finally, statistical methods were applied to the processing of computed features reflecting vibrations in order to determine wind turbine technical condition. The developed method was evaluated empirically in real wind farm. [Research was subsidized by the Polish National Centre for Research and Development within the grant “STEO—System for Technical and Economic Optimization of Distributed Renewable Energy Sources,” No. POIR.01.02.00-00-0357/16.]

Torsional wave band gap properties in a circular plate of a two-dimensional generalized phononic crystal

The torsional wave band gap properties of a two-dimensional generalized phononic crystal (GPC) are investigated in this paper. The GPC structure considered is consisted of two different materials being arranged with radial and circumferential periodicities simultaneously. Based on the viewpoint of energy distribution and the finite element method, the power flow, energy density, sound intensity vector together with the stress field of the structure excited by torsional load are numerically calculated and discussed. Our results show that, the band gap of Bragg type exists in these two-dimensional composite structures, and the band gap range is mainly determined by radial periodicity while the circumferential periodicity would result in some transmission peaks within the band gap. These peaks are mainly produced by two different mechanisms, the energy leakage occurred in circumferential channels and the excitation of the local eigenmodes of certain scatterers. These results may be useful in torsional vibration control for various rotational parts and components, and in the application of energy harvesting, etc.

Sound intensity probe for ultrasonic field in water using light-emitting diodes and piezoelectric elements

The sound intensity vector provides useful information on the state of an ultrasonic field in water, since sound intensity is a vector quantity expressing the direction and magnitude of the sound field. In the previous studies on sound intensity measurement in water, conventional piezoelectric sensors and metal cables were used, and the transmission distance was limited. A new configuration of a sound intensity probe suitable for ultrasonic measurement in water is proposed and constructed for trial in this study. The probe consists of light-emitting diodes and piezoelectric elements, and the output signals are transmitted through fiber optic cables as intensity-modulated light. Sound intensity measurements of a 26 kHz ultrasonic field in water are demonstrated. The difference in the intensity vector state between the water tank with and without sound-absorbing material on its walls was successfully observed.

The Use of Acoustic Vectors Decomposition of Sound Fields to Vibroacoustic Protection on Ships

Abstract In this paper, numerous examples will be illustrated as principles of applying the sound intensity measurements to practical problems at the noise abatement on ships and offshore constructions. The paper presents the results of transmission loss measurements together with flanking transmission for ship bulkheads and partitions with doors and windows. Investigations carried out with sound intensity measurement techniques will be compared against those made by classical methods. Finally for a few examples, the graphic presentation of spatial distribution of sound intensity vectors risen close to vibrating ship cabin partitions and inside the cabin will be shown in 2D and 3D graphical form. As a result, a two-dimensional acoustic wave flow map of time-averaged active intensity vectors propagated along curved streamlines and a vector perpendicular to measured plane are graphically illustrated. The technique of acoustic vectors decomposition of sound fields described, can enrich the knowledge of the mechanism of acoustic energy flux through ship partitions.

Spatial analysis and auralization of room acoustics using a tetrahedral microphone

A compact tetrahedral microphone array is used to measure several controlled sound fields and compare the analysis of spatial room impulse responses with two methods: spatial decomposition method (SDM) and IRIS, a commercial system based on sound intensity vector analysis. Results suggest that the spatial accuracy of both methods is similar and in most cases the error is comparable to the localization uncertainty of human listeners. Furthermore, a listening test is conducted comparing three 3D-sound fields and their SDM auralizations. Results suggest that the similarity of the auralized and original sound fields depends on the target room and stimulus.

Optimized vector sound intensity measurements with a tetrahedral arrangement of microphones in a spherical shell.

Recent times have seen the introduction of small spherical arrays whose usefulness as sound intensity probes is the focus of this paper. The presented probe consists of a spherical shell, 30 mm in diameter, housing four 14 in. microphones arranged in a regular tetrahedral configuration. Classical formulae may be used to estimate the sound intensity vector, as may methods based on spherical harmonics decomposition. Results are shown to be comparable to those obtained from classical sound intensity probes. The existence of an analytical model for a plane wave's diffraction about a sphere provides a means for adopting common optimization techniques for potentially improving the intensity vector estimate, however. This paper examines the validity of non-linear least squares optimization in conjunction with the proposed spherical sound intensity probe when placed in the following sound fields: (1) a simple plane wave; (2) a plane wave corrupted by noise; and (3) multiple incident plane waves. Under certain conditions, the probe is shown to greatly extend the operational frequency range of classical sound intensity probes. The optimization algorithm is found to lack robustness against deviations from plane wave conditions, however.

One-dimensional and three-dimensional propagation analyses of acoustic characteristics of Japanese and French vowel /a/ with nasal coupling

In this paper, we describe a comparison of the acoustic characteristics of one-dimensional and three-dimensional models of vocal tracts with nasal coupling. One-dimensional acoustic propagation is computed using an electric analog model. A finite element method is used for three-dimensional acoustic simulation. The comparison of these two approaches involves the vocal-tract shape of two subjects, one Japanese male and one French male pronouncing the vowel /a/ in their native language. Results show that the pole/zero pairs ascribed to the nasal coupling for both simulations appeared at almost the same frequency, at least below 2 kHz. Little difference between the one-dimensional and three-dimensional simulations in the transfer functions for the French subject is observed, since the three-dimensional mesh for the French subject is smoother. An extra pole exists in the transfer function of the three-dimensional model for the Japanese subject, possibly caused by the asymmetric structure of the laryngeal cavity. In the three-dimensional distribution of the active sound intensity vectors for the French subject, sound energy fluxes circulate between oral and nasal cavities coupled in the vicinity of the lips and nostrils.

Localization of the Sound Source with the Use of the First-order Ambisconic Microphone

The paper presents results of determination of sound wave direction based on signals from rst-order ambisonic microphone. The experiment consisted in recording the test signals with the SoundField microphone positioned in the axis of the turntable in the anechoic chamber. The spherical coordinates of the sound intensity vector were calculated with use of three di erent conceptual and numerical approaches and were compared to actual values resulting from the geometry of the system. Accuracy of the localization of the sound source depending on the frequencies and the method for determination of the spherical coordinates as well as on the time constant and the parameters of the signal recording was presented. The obtained results show the e ectiveness of the calculation methods used for localization of the sound source.

음향파워 측정 시 오차에 대한 고찰

Noise power of large machineries, such as textile looms, winders, and twisting machines, is often measured in a reverberant space because they cannot be installed and operated in an anechoic chamber due to their size, weight, and operating conditions. Factors affecting the measurement error of an in-situ noise power measurement include the nonuniform reverberation time and the direction of sound intensity vector which is usually regarded as normal to the measurement surface. In this study errors due to these factors are estimated with the aid of numerical simulation based on the ray-tracing technique. The averaging of reverberation times measured at several points on the measurement surface is suggested to reduce the errors from nonuniform absorption. Also the direction cosine of each surface element is taken into account, which as a whole is represented as a solid angle of the measurement surface.

Sound-power flow

To understand sound-intensity measurement, it should be realized that sound intensity is sound-power flow per unit area in the direction of sound propagation. Sound intensity can be measured in fluids such as air or water. Generally measurements cannot be made inside a solid. However there may be ways of measuring sound intensity in a solid, if the solid is transparent. Also sound intensity can be computed in a solid and then measured in a surrounding fluid to collate with the calculated results. In general the measurement of sound-intensity is relatively new. It can be measured either as a vector in three or two dimensions or as a single vector component. These features are discussed, together with some examples of sound-intensity measurement. An important use of a single component of sound intensity is the measurement of the sound power of a noise source. Another use is locating the primary sources of noise in operating machinery. The full sound-intensity vector can determine the direction of a noise source. Two vectors can determine the location of the source in space.

Acoustic energy density distribution and sound intensity vector field inside coupled spaces

In this paper, the modal expansion method supported by a computer implementation has been used to predict steady-state distributions of the potential and kinetic energy densities, and the active and reactive sound intensities inside two coupled enclosures. The numerical study was dedicated to low-frequency room responses. Calculation results have shown that the distribution of energetic quantities in coupled spaces is strongly influenced by the modal localization. Appropriate descriptors of the localization effect were introduced to identify localized modes. As was evidenced by numerical data, the characteristic objects in the active intensity field are vortices positioned irregularly inside the room. It was found that vortex centers lie exactly on the lines corresponding to zeros of the eigenfunction for a dominant mode. Finally, an impact of the wall impedance on the quantitative relationship between the active and reactive intensities was analyzed and it was concluded that for very small sound damping the behavior of the sound intensity inside the room space is essentially only oscillatory.

Vector sound intensity measurements with a tetrahedral arrangement of microphones in a spherical probe

The three dimensional sound intensity vector may be measured using a number of microphone configurations, an example of which is an orthogonal arrangement of three matched pairs of microphones. This setup is prone to unwanted reflections, however, and uses more microphones than theoretically required. Results are therefore presented on the calculation of the sound intensity vector using atetrahedral arrangement of microphones housed within a solid sphere. The acoustic presence of the sphere is quantified; specifically, frequency dependent phase and pressure measurements due to diffraction are obtained for various incidence angles and compared with theoretical values. The proposed intensity probe is further evaluated against traditional arrangements for the calculation of the acoustic intensity vector and advantages of adopting the spherically mounted, tetrahedral arrangement are highlighted.

VECTOR SOUND-INTENSITY PROBES OPERATING IN A HALF-SPACE

Method and apparatus ( 333 ) for measuring the sound-intensity vector in a half space bounded by a surface such as a wall or the ground ( 100 ) using an acoustic vector probe (AVP) ( 40 ), where the AVP consists of four small omnidirectional microphones ( 1, 2, 3 and 4 ) supported on narrow straight tubes at the vertices of an imaginary regular tetrahedron. The tubes are attached perpendicularly to a ring ( 42 ) with the microphones all pointing into the half space. The sound-intensity vector measured by the AVP determines the direction of a sound source within the half space. Interference from echoes caused by reflections from the boundary of the half space and from surrounding objects on the boundary can be reduced by attaching a concave solid structure ( 55 ) to the base of the AVP at the supporting ring ( 42 ). The inside of the concave structure is lined with absorbing material ( 65 ) to reduce interference by reflections from the structure.