Sound Radiation Pattern Research Articles

Modelling structure-borne sound and radiation of submerged structures at high frequencies

Predicting the vibroacoustic behaviour of structures in contact with water and at high frequencies can be a complex task due to the fluid-structure interaction. Computation time increases with frequency and the complexity of the structure. Being able to predict the sound radiated by a naval vehicle in contact with water could help in improving passengers' comfort as well as the impact on the marine fauna. We use a prediction method called Dynamic Energy Analysis (DEA), so far emloyed mainly to assess the vibrational energy levels in the structure itself. DEA is a phase-space based ray tracing method determining energy densities in terms of the ray densities in a structure. The method can be applied on FEM-meshes and thus needs no SEA type substructuring. We expand the DEA methodology here to take into account radiation into the fluid in contact with the structure. From structure borne DEA calculations, we can determine directional sound radiation patterns both inside and outside the structure. We will demonstrate the new technique using some simple model systems.

Investigation and comparison of heat pump noise in the lab and field

The presentation covers a contribution from the publicly funded HP-QUEEN MENESA project on the characterisation of a heat pump in the laboratory with comparisons in the field at comparable operation conditions. The data in the lab are obtained from a hemi-anechoic chamber that is equipped with temperature control to allow standardized measurements at -7 °C and 7 °C, for example. In this environment spherical sound radiation pattern are determined on a movable hemi-circle microphone arrangement allowing the assessment of source location and radiation contribution as well as sound power determination at the different operation points of the heat pump. These data are compared and analysed to measurements with the same heat pump in the field at model houses at the Fraunhofer-IBP location in Holzkirchen. Furthermore, we are also investigating the transmission path from the noise of the heat pump outdoors into the building taking sound reduction index of i.e., windows into account. It is planned to connect a psychoacoustic analysis together with a questionnaire to these investigations that allows assessment of the final sound characteristics inside the building.

Sound radiation patterns of the Sarasvati Veena and their relation with the modal behavior of its top plate

The large wooden resonator of the Sarasvati Veena amplifies and radiates the sound in almost all directions. The directional and spatial dependence of this radiation is studied in conjunction with the mode shapes of the top plate of the resonator. Sound radiation patterns are simulated theoretically using the nodal displacement data obtained from the numerical modal analysis of the resonator. The experimental analysis involves the manual plucking of the Veena string. The radiated sound is recorded by placing microphones around the resonator in circular arrays of different radii in the different planes. These combinations of arrays at different distances and planes provide a thorough knowledge of sound radiating out of the resonator. The intensities of different frequencies in the recorded spectral data as functions of direction and distance from the approximate center of the top plate of the resonator are studied. Experimentally measured patterns show the importance of the top plate over the body of the resonator. Theoretical and experimental radiation patterns for different harmonics of the plucked string are compared and a good match is observed. The behavior of the radiating sound in the different planes at different radial distances from the assumed center is discussed.

Application of the equivalent source method to preserve and reproduce the spatial characteristics of the sound source

Many works have been done to make a database of sound sources' radiation patterns, such as musical instruments. However, the conventional approaches were mainly based on the farfield measurement at some selected points on the spherical surface. A huge amount of data was presented in every spherical coordinate's angular direction. To overcome the problem, a method based on the equivalent source method(ESM) is proposed to record and exchange information on the spatial radiation characteristics from a sound source. By utilizing the principle of acoustical holography, complicated radiation patterns and strengths of an actual source can be approximately described by expanding the spherical harmonics in various orders. Such a method enables preserving the radiation pattern information of sound sources keeping only details on the position coordinate of equivalent sources and the coefficient of each order of spherical harmonics, which can be regarded as a standard format. If the proposed approach is used, a more precise and large amount of information can be stored with a smaller size of data than the conventional dataset.

Strategic Modelling of Industrial Noise with Limited Input Datav

Historically, strategic modelling of industrial noise exposure on a national scale has taken a wide range of approaches. Where sound emission data of industrial sites are not available, numerous assumptions are often made. These include simplified modelling of industrial sites and adoption of generic sound power levels for different industry types. In most cases such assumptions significantly increase the uncertainty in strategic noise mapping outcomes. This paper presents an alternative approach to strategic modelling of industrial sound which is based on the environmental permitting practice of large industrial sites in England. Drawing on this approach, a cost-effective and scalable modelling procedure has been developed to estimate sound emission levels and radiation patterns of industrial activities accounting for the local context of the site. This paper details the alternative modelling approach along with example prediction outputs. Potential future refinements to improve the modelling accuracy and opportunities to enhance site-specific input data in collaboration with national authorities are also discussed.

Sound radiation of a GLARE panel at elevated temperature

In this work, the effect of nodal and anti-nodal shifts on the sound radiation pattern of a uniformly heated square baffled GLARE panel is analyzed. The panel is examined with a 1 N harmonic force at the center and offset locations under elevated temperature using the finite element method. The effect of load location and temperature on sound radiation pattern is computed using Rayleigh integral method. It is observed that the panel's natural frequencies reduced with an increase in temperature and changes in sound radiation pattern due to modes nodal and anti-nodal shift.

Spherical correlation as a similarity measure for 3-D radiation patterns of musical instruments

We investigate the use of spherical cross-correlation as a similarity measure of sound radiation patterns, with potential applications for their study, organization, and manipulation. This work is motivated by the application of corpus-based synthesis techniques to spatial projection based on the radiation patterns of orchestral instruments. To this end, we wish to derive spatial descriptors to complement other audio features available for the organization of the sample corpus. Considering two directivity functions on the sphere, their spherical correlation can be computed from their spherical harmonic coefficients. In addition, one can search for the 3-D rotation matrix which maximizes the cross-correlation, i.e. which offers the optimal spherical shape matching. The mathematical foundations of these tools are well established in the literature; however, their practical use in the field of acoustics remains relatively limited and challenging. As a proof of concept, we apply these techniques both to simulated radiation data and to measurements derived from an existing database of 3-D directivity patterns of orchestral instruments. Using these examples we present several test cases to compare the results of spherical correlation to mathematical and acoustical expectations. A range of visualization methods are applied to analyze the test cases, including multi-dimensional scaling, employed as an efficient technique for data reduction and navigation. This article is an extended version of a study previously published in [Carpentier and Einbond. 16th Congrès Français d’Acoustique (CFA), Marseille, France, April 2022, pp. 1–6.https://openaccess.city.ac.uk/id/eprint/28202/].

On sound propagation along an infinite rectangular duct-like structure with a finite slot opening and its modelling.

The sound propagation across a sound leaking section along an infinite rectangular duct-like structure near to the lower order duct eigenfrequencies is investigated numerically in the present study. The sound leakage is achieved by finite length rectangular slots located at a corner of the duct-like structure cross section. The finite-element simulations are performed, in the first place, to gain insights into the modal development inside the structure. A semi-analytical model, which considers the wavy air motions along the slots with oblique sound radiation patterns, is developed. An empirical framework is also proposed to estimate the complex longitudinal wavenumber along the slot using the numerical results and dimensional analysis. The performance of the proposed semi-analytical model, together with the complex wavenumber prediction framework, is tested using two duct-like structures with different cross section aspect ratios. The results show that the present proposed approach gives predictions close to the finite-element simulations. The deviations are well within engineering tolerance.

Comparison of sound radiation between classical and pop singers

The directional characteristics of six soprano opera singers and five pop singers in the horizontal and vertical planes were measured in an anechoic room. Sound radiation measurements were made across the whole frequency range at 44 positions in the hemispherical array around the head at a distance of 120 cm while the singer's mouth was the centre. The scales through two octaves (C4–C6) in four dynamics and gradual increase of loudness (crescendo) in nine pitch positions were measured for the Czech vowels /a/, /i/, and /u/. The main aim was to describe differences in sound radiation between both groups of singers and verify the results of a preliminary study.The study confirmed that classical singers have more omnidirectional sound radiation patterns. A different type of pattern was found when singing /i/ in the middle voice range A4–F5#. The analysis of sound radiation in octave bands confirmed the main influence of the position and levels in the frequency bands of the first formant or first harmonic level, which is made by the difference in vocal technique between both groups of genres. When pitch and SPL levels are higher, the level of sound radiation is attenuated in the rear directions in general. The different trends of sound radiation, connected with the change of pitch and SPL, are probably caused by the shape and size of the singer's mouth. Those relations will be examined in the follow-up study.

DE-based capacitive micro-speakers for generating directional audible sound

Although silicon is the most used material in micro-electro-mechanical-systems, due to the excellent mechanical properties, it has poor performance for generating audible sound by capacitive micro-speakers. This paper studies the capability of dielectric elastomer material instead for generating the directional sound in the human hearing regime. Dielectric elastomers are a branch of smart materials with high desired and practical specifications such as large deformation, energy-efficient, lightweight, biocompatible, and fast response which share the common characteristics of changing their shape under an applied electrical voltage or charge. An elastic circular dielectric elastomer micro-plate with compliant electrodes on both sides suspended over the unmoving plate as a capacitive micro-structure has been modeled as a diaphragm of the micro-speaker. Then the Bessel panel array has been considered in a square matrix form composed of the number of dielectric elastomer micro-speakers. The nonlinear equation of the vibrations of a micro-speaker’s diaphragm under an electrostatic loading and equations of the sound pressure and sound radiation pattern have been presented and solved. The results have shown that utilizing dielectric elastomer-based micro-speakers in a Bessel panel array can generate a directional audible sound pressure in the human hearing range. In addition, the results clear that the desired sound waves in the human audible range and a private or personal listening zone can be produced through adopting an optimal value among the excitation frequencies, diaphragm numbers, radii and inter-element spaces of a Bessel panel array.

Application of the Electrostatic Micro-Speakers for Producing Audible Directional Sound

In recent years, the demand for control of sound power and radiation patterns in personal messaging, calls, automotive entertainment, and gaming has brought a new interest in the audio world. The aim of this paper is to investigate the feasibility of producing the sound waves in the audible range and directing them in the desired listening zone by electrostatic micro-speakers. Therefore, a capacitive circular micro-plate has been modeled as an electrostatic micro-speaker. Then a Bessel panel array has been developed using a number of these plates arranged in a square array. The equations governing the vibrations of the micro-speaker’s diaphragm, as well as radiation pattern of the sound waves, have been introduced and solved. The results have shown that the Micro-Electro Mechanical Systems (MEMS) electrostatic diaphragms have the capability of producing the directional sound in the human hearing range. Moreover, we have investigated the effect of different excitation frequencies, radii size and the number of the diaphragms as well as the inter-element spacing on the sound radiation pattern of the Bessel panel array.

Sound radiation pattern of the advertisement call of the highly territorial poison frog Allobates femoralis

Sound radiation patterns have ecological implications in the effective communication between conspecifics, like optimization of the sound propagation, increase the likelihood to reach mates and to mitigate effects of sound scattering by environmental factors like vegetation. The territorial frog Allobates femoralis advertises its territory against conspecific males and attract females with advertisement calls. Here we report the nearly omnidirectional sound-radiation pattern of the advertisement call of A. femoralis. This sound spreading pattern allows the males to attract mates and repel rivals in all directions. Furthermore, A. femoralis males direct the advertisement call to conspecific neighbours after phonotactic orientation.

Directional Acoustic Antennas Based on Valley-Hall Topological Insulators.

Realizing directional acoustic signal transmittance and reception robust against surrounding noise and competing signals is crucial in many areas such as communication, navigation, and detection for medical and industrial purposes. The fundamentally wide-angled radiation pattern of most current acoustic sensors and transducers displays a major limitation of the performance when it comes to precise targeting and probing of sound particular of interest in human speaking and hearing. Here, it is shown how topological acoustic valley transport can be designed to enable a unique beamforming mechanism that renders a superdirective needle-like sound radiation and reception pattern. The strategy rests on out-coupling valley-polarized edge states, whose beam is experimentally detected in the far-field with 10° width and a sound-intensity enhancement factor ≈10. Furthermore, anti-interference communication is proposed where sound is received from desired directions, but background noise from other directions is successfully suppressed. This type of topological acoustic antenna offers new ways to control sound with improved performance and functionalities that are highly desirable for versatile applications.

Subwoofer array modeling and optimization

In the last few years, configuring subwoofer arrays in order to achieve a desired sound radiation pattern has become one of the most discussed topics in the sound reinforcement industry. The directivity of such arrays of low-frequency loudspeakers can typically be controlled by means of delay, gain, and polarity settings applied to the individual elements. A new software solution is presented that allows modeling and optimizing such setups, including various cardioid configurations as well as end-fire and steered setups. Frequencies down to 20 Hz can be investigated. It is also explained how coherent sound superposition at low frequencies and incoherent interaction of sound waves at high frequencies can be simulated consistently by means of a cross-over frequency band. Finally, an optimization method is presented that allows computing elemental delays automatically based on a user-defined coverage angle for the array.

Non-impulsive signal deconvolution for computation of violin sound radiation patterns and applications in sound synthesis

This work presents a method to compute violin body impulse responses (BIR) based on deconvolution of non-impulsive signals. This newly conceived approach is based on a frame-weighted deconvolution of excitation and response signals. The excitation, consisting of bowed glissandi, is measured with piezoelectric transducers built into the violin bridge and the response is measured as sound pressure with microphones. Based on this method, several research works have been carried out in the areas of acoustics and sound synthesis. First, by placing multiple microphones at different angles around the violin, we were able to compute a dense grid of 3D sound radiation patterns without restrictions in the frequency range. Second, the computed BIRs can be convolved with a source signal (captured with the same bridge-transducer and using the same violin), obtaining a highly realistic violin sound very similar to that of a microphone recording. The multiple impulse responses at different directions make has been used to enhance sound synthesis with spatialization effects. Finally, a bowing machine was built to perform repeatable glissandi and therefore be able to compute BIRs across different violins. The bowing machine has been used to compute cross-BIRs that map the pickup signal of electric violins to the radiated acoustic sound of acoustic violins, which allows to imitate the sound of any measured acoustic violin with an electric counterpart.

Conversion of sound radiation pattern via gradient acoustic metasurface with space-coiling structure

We designed, fabricated, and experimentally demonstrated a gradient acoustic metasurface to manipulate sound radiation patterns. The gradient metasurface is constructed on the basis of a coiling-up space in a tunable interdigitated structure, which exhibits relative refractive index in a discretized classic hyperbolic secant profile. Capable of generating secondary sound sources with desired gradient phase shifts, the metasurface shows the ability of controlling sound radiation such as by cylindrical-to-plane-wave conversion, plane wave focusing, and effective tunable acoustic negative refraction. Owing to its deep-subwavelength thickness, the metasurface may reduce the size of acoustic devices and offer potential applications in imaging and scanning systems.

COMPRESSION DRIVER AND HORN STRUCTURE

A loudspeaker driver 100 with new horn throat configuration 120 has a phase plug summation plane radius that is also the effective throat of the driver. The selected plane “D” where the elements of the horn that provide directional information to the wave front are implemented is made part of the geometry of the magnetic return circuit back plate 108 . The portion of the back plate that is coincident with the selected plane “D” has a lumen or opening that is made equal to the radius of the circle defined by the phase plug summation plane. The geometry of the back plate's lumen controls projected sound's radiation pattern.

Experimental investigation into sound and vibration of a torpedo-shaped structure under axial force excitation

In this study, the sound radiation patterns and vibration characteristics of a torpedo-shaped structure are determined experimentally using a proof mass actuator to allow pure axial excitation of the model. Using this method, the second energy path found in previous designed structures is eliminated. Input power and driving forces are measured using four force transducers and four accelerometers, while the vibration response and mode shapes are measured using an array of accelerometers. The sound pressure and its directivity are captured by a spatially distributed microphone array inside an anechoic chamber. Motivations for this work are to investigate the effect of the complex boundary constraints: a semispherical head and conical tail on the two meter long model when compared to existing analytical solutions for simple geometries, and later the measurement will be performed in an underwater experiment to contrast the effect of fluid loading.

High resolution radiation pattern measurements of a grand piano—The effect of attack velocity

The sound radiation pattern of a grand piano is highly complex and depends on the shape of the soundboard, construction of the frame, reflections from the lid, and other parts of the instrument’s structure. The spectral energy generated by and emitted from the instrument is further complicated by the sound production mechanism (hammers, strings), the attack velocity, and results in independently complex behaviors depending on the register of the piano. This paper presents the acoustic measurements of the radiation pattern of a grand piano using a high spatial resolution measurement technique. Measurements of a Yamaha Diskclavier were taken using a 32-channel microphone array with a 2-in. spacing between capsules. The complex radiation patterns and overtone structure is analyzed for middle-C at three attack velocities—pianissimo, mezzo forte, and forte. Comparisons of the effect of attack strength on frequency response and radiation pattern are presented.

Active Control of Radiated Sound from Stiffened Plates Using IDE-PFC Actuators

It has been a practice in modern day aircraft and automobile industries to manufacture a stiffened structure for significantly enhancing efficiency and strength without incurring a considerable weight increase. In the present study, an attempt is made to understand the effect of stiffeners on the sound radiation pattern of a vibrating plate. Subsequently, a velocity feedback control algorithm based on Linear Quadratic Regulator (LQR) methodology is developed to attenuate the radiated sound power from the vibrating structures with surface bonded piezo fibre composite (PFC) patches with interdigitated electrodes (IDE) as actuators and polyvinylidene fluoride (PVDF) films as sensors. Results are obtained for different orientations of stiffeners and various locations of PFC patches and are discussed. 1,2,3