Sound Incidence Angle Research Articles

Sound transmission loss and bending properties of sandwich structures based on triply periodic minimal surfaces

Four types of triply periodic minimal surfaces sandwich structures (TPMS-SS), namely, G-SS, D-SS, D1-SS, and IWP-SS, have been proposed. The bending properties were evaluated by experiments and numerical simulations, and their sound insulation performance was investigated using theoretical, numerical and experimental methods. Firstly, the bending performance of four TPMS-SS was compared. Then, the acoustic vibration control equation of TPMS-SS was established and the theoretical solution for the sound transmission loss (STL) was derived based on Reissner's theory combined with the fluid-solid coupling condition. Next, experimental study was conducted on the STL performance of TPMS-SS using the impedance tube method, and the numerical model was verified using theoretical and experimental results. Finally, parametric studies were carried out to investigate the effects of parameters such as relative density (RD), panel thickness (hf), and sound incidence elevation angle (φ), as well as the type of structure, on the STL performance. The results show that TPMS-SSs can achieve >30 dB of STL in the frequency range of 1 Hz to 10 kHz. The STL value increases with relative density (RD), panel thickness (hf), and sound incident elevation angle (φ), while the location of the dips in the STL curves is affected by relative density and panel thickness. G-SS has the best bending performance, while D1-SS has the best acoustic performance. The results could be used for the optimization design of lightweight sandwich structures.

Low Costs Electrical Calibration System of SLM with the Uncertainty Measurements Compared with Primary System Platform Brūel & Kjær type 3630

Sound level meter (SLM) calibration according to IEC61672-1, 2, 3: 2013 is an essential step in the measurement process. It ensures that the SLM meets its specifications. There is a strong need for an efficient and cheap calibration system device for the electrical calibration of SLM since it avoids the body effect and angle sensitivity of the microphone membrane to the sound incidence angle for free field calibration. As well as, it avoids leakage errors due to the microphone fitting in the coupler and the coupler effect in pressure field calibration. This work gives an alternative system device used in the electrical calibration of SLM. This system consists of individual tools; PULSE signal generator, universal frequency counter, HP Dynamic signal analyzer, and DMM voltmeter. All system tools are complying with the IEC17025. The calibration procedures follow the second edition of IEC61672-2. Calibration measurements of frequency, time-weightings, and linearity of range parameters as the major features of SLMs are tested in the frequency range of 31.5 Hz to 16 k Hz. The calibration was repeated 5 times on different days and different warm-up times for devices to estimate the associated uncertainty measurement values in accordance with Part 2 and Part 3 of IEC 61672. The obtained results show that, the calibration measurement deviations are in the allowable tolerance of the IEC 61672-1 and they are comparable with that obtained from the primary Brüel & Kjær (B & K) platform 3630. The computed uncertainty of measurements is in accepted limits that are required by IEC 61672-1 which is determined to the level of confidence of 95%, using coverage factor 2.

Auditory Spatial Bisection of Blind and Normally Sighted Individuals in Free Field and Virtual Acoustics.

Sound localization is an important ability in everyday life. This study investigates the influence of vision and presentation mode on auditory spatial bisection performance. Subjects were asked to identify the smaller perceived distance between three consecutive stimuli that were either presented via loudspeakers (free field) or via headphones after convolution with generic head-related impulse responses (binaural reproduction). Thirteen azimuthal sound incidence angles on a circular arc segment of ±24° at a radius of 3 m were included in three regions of space (front, rear, and laterally left). Twenty normally sighted (measured both sighted and blindfolded) and eight blind persons participated. Results showed no significant differences with respect to visual condition, but strong effects of sound direction and presentation mode. Psychometric functions were steepest in frontal space and indicated median spatial bisection thresholds of 11°-14°. Thresholds increased significantly in rear (11°-17°) and laterally left (20°-28°) space in free field. Individual pinna and torso cues, as available only in free field presentation, improved the performance of all participants compared to binaural reproduction. Especially in rear space, auditory spatial bisection thresholds were three to four times higher (i.e., poorer) using binaural reproduction than in free field. The results underline the importance of individual auditory spatial cues for spatial bisection, irrespective of access to vision, which indicates that vision may not be strictly necessary to calibrate allocentric spatial hearing.

Optimal Search for Underwater Targets for Ships Equipped with Hull Mounted Sonar Using Genetic Algorithm

When a surface ship utilizes a hull-mounted sonar (HMS) to search for a target located in the water at sea, the maneuver path of the surface ship depends on the maximum detection range of the sonar. Because sonar utilizes sound waves, it is significantly influenced by the marine environment and the detection probability depends on the location and sound wave incident angle of the target. This study aims to calculate the detection probability by applying the actual marine environment, and proposes an optimal search path calculation method that maximizes the detection probability based on a genetic algorithm. The proposed optimal search path calculation method was proven to be effective via simulations in determining the optimal search.

Airborne sound insulation of single-leaf partitions under hygric load

In buildings of all types the use of single-leaf partitions are recommended, not least for reasons of cost efficiency and possible resource optimisation. In addition to the familiar building physics topics they play also a particularly important role in noise protection. Numerous factors influence the acoustic properties of single-leaf, plate-shaped and dry partitions. These include the mass, the bending stiffness, the position of the critical frequency and the total loss factor of the partition as well as the stimulating frequency of the airborne sound, the sound incidence angle or the characteristic impedance of the air. Each mineral wall-building material has its own product-specific pore structure. In the usual calculation of the airborne sound insulation of single-leaf, airtight and dry partitions, this has so far not been taken into account. It is precisely in these building material pores that a hygrothermal, continuous adjustment of the moisture content takes place in addition to the production-related water quantities. This changes the mass of the building component and thus the airborne sound insulation of the wall. In addition to this well-known mass effect, a further mechanism, which has not yet been considered, increases airborne sound insulation: the smaller the pore sizes in the building material, the greater the mechanical forces caused by stored pore water. The existing equations for airborne sound insulation do not take these effective forces into account and must therefore be extended. The wall building material is considered as a porous medium with solid and fluid components. The new calculation approach allows the calculation of the airborne sound reduction index for single-leaf partitions under hygric load for saturated and partially saturated moisture conditions with high accuracy. The calculation results provide valuable information for the planning and product development of new building materials.

Sensitivity to interaural time differences and localization accuracy in cochlear implant users with combined electric-acoustic stimulation.

ObjectivesIn this study, localization accuracy and sensitivity to acoustic interaural time differences (ITDs) in subjects using cochlear implants with combined electric-acoustic stimulation (EAS) were assessed and compared with the results of a normal hearing control group.MethodsEight CI users with EAS (2 bilaterally implanted, 6 unilaterally implanted) and symmetric binaural acoustic hearing and 24 normal hearing subjects participated in the study. The first experiment determined mean localization error (MLE) for different angles of sound incidence between ± 60° (frontal and dorsal presentation). The stimuli were either low-pass, high-pass or broadband noise bursts. In a second experiment, just noticeable differences (JND) of ITDs were measured for pure tones of 125 Hz, 250 Hz and 500 Hz (headphone presentation).ResultsExperiment 1: MLE of EAS subjects was 8.5°, 14.3° and 14.7°, (low-, high-pass and broadband stimuli respectively). In the control group, MLE was 1.8° (broadband stimuli). In the differentiation between sound incidence from front and back, EAS subjects performed on chance level. Experiment 2: The JND-ITDs were 88.7 μs for 125 Hz, 48.8 μs for 250 Hz and 52.9 μs for 500 Hz (EAS subjects). Compared to the control group, JND-ITD for 125 Hz was on the same level of performance. No statistically significant correlation was found between MLE and JND-ITD in the EAS cohort.ConclusionsNear to normal ITD sensitivity in the lower frequency acoustic hearing was demonstrated in a cohort of EAS users. However, in an acoustic localization task, the majority of the subjects did not reached the level of accuracy of normal hearing. Presumably, signal processing time delay differences between devices used on both sides are deteriorating the transfer of precise binaural timing cues.

The Third Frequency Range of the Sound Insulation Plot of the Single-Layer Partitions

The main concepts of sound insulation theory of the massive plates were developed in the mid-20th-century. There were obtained the frequency dependence of sound insulation from the plate mass and the plate stiffness [1, 2]. The multiple researches on dependence of insulation from sound incidence angle [1, 2, 3, 4] and coefficients of internal friction for plates materials were carried out [1, 2, 3, 4]. The comparison of theoretical and experimental results showed the generally statistical matching, but in the same time, there were frequently observed their considerable differences [1, 2].There was a necessity in additional studies in that period. Due to the electronics development and perfect appliances on its base, the observational researches begun to prevail, such as in issues [5, 6, 7, 8, 9, 10]. Thereafter, the reference curves with the three frequency ranges for sound isolation calculation were obtained, due to the large mass of experimental data processing. The first two ranges are divided by the wave coincidence frequency, and the third one limits the maximum possible insulation irrespective of frequency.The articles [11, 12, 13] show, that the existing formulas of sound propagation through the interface of two media and the flat layers, which are developed from the continuity conditions, mismatch to these conditions on all incident angles, except of the normal. So the present insulation theories, which are depending from the sound incident angle, make no sense.The issue [14] shows, that the calculation sound insulation method, which is based on discrete (concentrated) models of sound propagation with the application of momentum conservation law and the kinetic energy for the plates with the mass more than 50kg/m2, gives the more exact results of comparison with the experimental data [15, 16], than with the calculation data by the standard curve. The contributions [15, 16] contains the evidences about the sound insulation values mainly in first two frequency ranges. The third frequency range is become beyond the limits of measurements. This article contains the results of publication materials, involving the sound insulation data at the third frequency range.

Lung-to-ear sound transmission does not improve directional hearing in green treefrogs (Hyla cinerea).

Amphibians are unique among extant vertebrates in having middle ear cavities that are internally coupled to each other and to the lungs. In frogs, the lung-to-ear sound transmission pathway can influence the tympanum's inherent directionality, but what role such effects might play in directional hearing remains unclear. In this study of the American green treefrog (Hyla cinerea), we tested the hypothesis that the lung-to-ear sound transmission pathway functions to improve directional hearing, particularly in the context of intraspecific sexual communication. Using laser vibrometry, we measured the tympanum's vibration amplitude in females in response to a frequency modulated sweep presented from 12 sound incidence angles in azimuth. Tympanum directionality was determined across three states of lung inflation (inflated, deflated, reinflated) both for a single tympanum in the form of the vibration amplitude difference (VAD) and for binaural comparisons in the form of the interaural vibration amplitude difference (IVAD). The state of lung inflation had negligible effects (typically less than 0.5 dB) on both VADs and IVADs at frequencies emphasized in the advertisement calls produced by conspecific males (834 and 2730 Hz). Directionality at the peak resonance frequency of the lungs (1558 Hz) was improved by ∼3 dB for a single tympanum when the lungs were inflated versus deflated, but IVADs were not impacted by the state of lung inflation. Based on these results, we reject the hypothesis that the lung-to-ear sound transmission pathway functions to improve directional hearing in frogs.

In-situ impedance and absorption coefficient measurements using a double-layer microphone array

Acoustic impedance is typically measured using an impedance tube, which requires a material sample physically fitted to the tube. However, the impedance can vary greatly between the material mounted in the tube and the material located in a real environment, where the mounting conditions are likely to be different. Also, oblique incidence cannot be measured in an impedance tube. In this paper, we investigate the use of a double-layer microphone array for in-situ measurement of surface impedance and absorption coefficient. With the array positioned near the material surface, a source emits broad-band sound towards the array and the material. A measurement is taken, and the sound pressure and the surface-normal particle velocity at the material surface are calculated using Statistically Optimized Near-field Acoustical Holography (SONAH). From the surface pressure and velocity, the impedance across a selected area is calculated, and finally the absorption coefficient is calculated from the impedance. A set of tests has been performed on porous material samples in an anechoic chamber as well as in a fitted room. Different sample sizes and different sound incidence angles have been considered. The results show consistency between the measurements in the anechoic room and the ordinary room as well as good agreement with Miki’s model up to large oblique incidence angles.

Errors when assuming locally reacting boundary condition in the estimation of the surface acoustic impedance

Numerical simulations usually require boundary conditions in terms of surface acoustic impedance. The surface acoustic impedance depends on the porous material acoustic properties (e.g., characteristic impedance and wave number) and its thickness as well as the type of wave front impinging on its surface. The locally reactive behaviour hypothesis is often assumed to simplify the choice of proper boundary conditions assigning a constant acoustic impedance value on the porous material surface at a given frequency and for each angle of sound incidence. This hypothesis is also used in measurement procedures or for the estimation of the edge effects.In this paper, it is shown that, in general, a porous material behaves partly as a locally reactive and partly as a non-locally reactive material depending on the ratio between the sound velocities in the free air and in the porous material. By using numerical FEM simulations it is shown that, given a porous material, the acoustic impedance may change or not along the material surface depending on the type of wave front that impinges on its surface.The error when assuming the locally reactive behaviour for porous materials backed by a hard surface and planar incident wave front to compute surface acoustic impedance values has been investigated comparing results yielded by theoretical models available in the literature and the one proposed for non-locally reactive behaviour materials. The last one is validated by means of FEM simulations and experimental results.

Effect of Machined Surface Shape on Sound Reflection

Sound reflection of materials is influenced by many factors, e.g. by material type, density, thickness, porosity, angle of sound incidence, surface shape and excitation frequency of acoustic wave. The aim of the paper is to investigate the surface shape effect of expanded polyvinylchloride material on sound reflection. For this reason polyvinylchloride samples of different surface shapes and perforations were produced on universal and CNC machine tool. The material ability to reflect sound of the investigated polyvinylchloride samples was experimentally measured by means of the transfer function method on Kundt's impedance tube. The material samples were subsequently compared in terms of their sound reflection. It was verified that the highest sound reflection was obtained in case of the smooth surface polyvinylchloride sample.

Verification of mathematical formulae applied to overhead stage canopy design

Abstract This paper presents a comparison of the experimental research concerning overhead stage canopies with a numerical approach based on selected mathematical models. The numerical predictions are made using the simplified asymptotic curves suggested by Rindel and modified by Skalevik. For singular cases a prediction with detailed calculations based on the Fresnel–Kirchhoff approximation is also given. The aim of the work is to verify proposed algorithms for designing reflective panels as well as to determine the conditions of conducting such procedures. It is shown that based on Rindel’s approximation one may determine some substantial information about sound reflection from the panels i.e. the value of upper limit frequency as well as the relative sound reflection level. On the other hand, the lower cut-off frequency should be calculated using Skalevik’s model as the value obtained from Rindel’s formula is undervalued. Such an approach could be applied to design reflective structures. However, it has some limitations for example for arrays of perturbed symmetry or sparse arrays as well as in the case of non-perpendicular angles of sound wave incidence. Then it may be necessary to apply more accurate numerical models.

The emergence of resonance within acoustic fields of the float gyroscope suspension

The formation nature of resonance phenomena, which give rise to the rapid growth of the gyro errors in hypersonic flight conditions in the suspension of a two-stage float gyroscope is revealed. On the example of the industrial design of the float gyroscope, computational models are built. They allowed determining the influence of the antisymmetric and symmetric impedance of the housing on the emergence of resonance conditions in the suspension. The influence of the propagation direction of acoustic radiation on the occurrence of the features, leading to the rapid growth of additional autonomous positioning errors is determined. The resonance content at high (above the cutoff) and low (below the cutoff) frequencies is revealed. It is shown that at high frequencies the resonance is formed by only bending vibration of the housing in the sound field provided that the antisymmetric impedance is much lower than the symmetrical impedance. It is found that the low-frequency resonance can be formed only by the circumferential vibration of the housing depending on the sound wave incidence angles. It appears in the form of the wave coincidence of the trace of the incident and circumferential waves, or coincidence of the circumference of the frame and the circumferential wave on the plane of the incident wavefront. The resonance methods of dealing with the influence of the sound fields as the only effective ones in the resonance conditions of hypersonic flight are analyzed.

Signal response of rib-stiffened plates covered by decoupling coating layers

This paper proposes a fully elastic theoretical model for the signal response of a periodically rib-stiffened plate covered with a decoupling coating layer, in which the elastic plate and the coating layer are modeled by adopting the plain strain elasticity theory. The fluid loadings on the two sides of the structure are taken into account, which thus enables the model to handle the case that the coated structure is immersed in two different fluids. The periodicity introduced by the parallel distribution of rib-stiffeners is considered by utilizing the space harmonic series to express the solutions. The resultant equations are formulated by the displacement and stress continuity conditions at the fluid/coating, coating/plate and plate/fluid interfaces. The signal response of the structure can be obtained by solving these resultant equations, built upon which numerical investigation is conducted. Specific interests are focused on the investigation for the signal velocity component distributions with the sound incident angle, frequency, location through the coating thickness, as well as the effect of coating material properties. The drawn conclusions provide useful guidance for the vector velocity measurement and optimal design of the rib-stiffened plate covered with the decoupling coating layer.

An exact elasticity model for rib-stiffened plates covered by decoupling acoustic coating layers

This paper presents an exact elasticity model for a fluid-loaded periodically rib-stiffened plate covered by a decoupling acoustic coating layer, which is built upon the plain strain elasticity theory. The acoustical coating layer is assumed to be perfectly bonded to the parallelly rib-stiffened plate, which is impinged by a time-harmonic plane sound wave. The theoretical model begins with Navier–Cauchy equations of motion to describe the vibration behavior of the rib-stiffened plate and the acoustic coating layer, and utilizes the acoustic equation to model the fluid motion. Applying the continuities of displacements and stresses at the interfaces of the plate, the coating layer and the fluid mediums, the vibroacoustic governing equation can be solved to obtain the sound transmission loss (STL) of the structure. The plane strain model is verified by comparing with the thin-plate model, and good agreements have been achieved between the two predictions. Based upon the theoretical model, the influences of the geometrical parameters of the structure, sound incidence angle, the dilatation and shear wave speeds in the acoustic coating layer on the STL of the structure are numerically explored. Results reveal the significant effect of the decoupling acoustic coating layer on the noise reduction of the periodically rib-stiffened structures.

Spatial hearing in Cope’s gray treefrog: II. Frequency-dependent directionality in the amplitude and phase of tympanum vibrations

Anuran ears function as pressure difference receivers, and the amplitude and phase of tympanum vibrations are inherently directional, varying with sound incident angle. We quantified the nature of this directionality for Cope's gray treefrog, Hyla chrysoscelis. We presented subjects with pure tones, advertisement calls, and frequency-modulated sweeps to examine the influence of frequency, signal level, lung inflation, and sex on ear directionality. Interaural differences in the amplitude of tympanum vibrations were 1-4dB greater than sound pressure differences adjacent to the two tympana, while interaural differences in the phase of tympanum vibration were similar to or smaller than those in sound phase. Directionality in the amplitude and phase of tympanum vibration were highly dependent on sound frequency, and directionality in amplitude varied slightly with signal level. Directionality in the amplitude and phase of tone- and call-evoked responses did not differ between sexes. Lung inflation strongly affected tympanum directionality over a narrow frequency range that, in females, included call frequencies. This study provides a foundation for further work on the biomechanics and neural mechanisms of spatial hearing in H. chrysoscelis, and lends valuable perspective to behavioral studies on the use of spatial information by this species and other frogs.

About Some Misunderstandings in the Modern Theory of the Sound Isolation and Discrete Models of Sound Transmission

The present paper is a short critical review of the modern theory of the sound isolation by single-layered protections. It is shown that dependence of insulation upon angle of sound incidence is untenable. The author disproves existence possibility of «spatial frequency resonance» at wave coincidence and of « loss coefficient of a design» defining the abatement of the sound isolation on resonances.The substantiation of application of discrete models of sound transmission through a plate, in which the equations of laws of conservation of momentum and kinetic energy are used, is explained. On the basis of discrete models is offered a practical way of calculation of the sound isolation, not conceding accuracy to modern standard methods, but distinguishing itself in a greater universality and simplicity.

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.

Characterization of directional microphones in an arbitrary sound field

An acoustic characterization method for directional microphones is presented that does not require an anechoic chamber to provide a controlled plane wave sound field. Measurements of a directional microphone under test are performed in a nearly arbitrary sound field for several angles of sound incidence, and the corresponding sound pressure and pressure gradients in the vicinity of the test microphone are measured using an automated probe microphone scanning system. From these measurements, the total acoustic frequency response of the directional microphone can be decomposed into its sensitivities to sound pressure and pressure gradient using a least squares estimation technique. These component responses can then be combined to predict the directional response of the microphone to a plane wave sound field. This technique is demonstrated on a commercially available pressure gradient microphone, and also on a combination sound pressure-pressure gradient microphone. Comparisons with the plane wave responses measured in an anechoic environment show that the method gives accurate results down to 100 Hz.

Acoustical device using helmholtz resonator for the high-speed train noise barrier

This study is primarily aimed at developing a measure to overcome the limited shielding performance of the noise barriers for the high-speed train. Up to the train speed of 300km/h and more the noise incidence angle and the source height change due to the pronounced aerodynamic noise source parts located at the higher positions compared to the height of the conventional rolling noise source. By means of the experimental analysis on the sound radiation characteristics and the sound pressure distribution around the noise barrier, a prototype of an acoustical attachment is porduced based on the analytical model calculation and numerical analysis. The principle of the Helmholtz resonator is used to optimize the acoustical impedance on the surface of the upper dege of the noise barrier. Using the model it was possible to find an appropriate acoustical property for the impedance according to the target frequency,sound incidence angle relative to the barrier and the receiver position. In this paper the results of the experiment in an anechic room and from the out door experiment are shown and discussed.