¡§Phononic crystal,¡¨ a binary-composite medium composed of a square array of parallel circular steel cylinders in a air matrix is studied. Phononic crystal exists full band-gaps phenomenon which is caused by strongly constructive interference of Bragg reflection in their acoustic transmission spectrum. The Bragg reflection theorem is also a basis for searching the full band-gaps in this thesis. This thesis applies the boundary element simulation software BEASY to analyze the sound field characteristics of solid/fluid composite medium, phononic crystal. The forbidden bands of the band gap are shown by the relative amplitude in the incidence before and after. First, the study by Varadan and Faran aims at scattering sound field of the single rigid sphere and the circular cylinder in water which constructed a simulation of the boundary element model. It is compared to under the different kr change result of its scattering sound field and it has demonstrated that our simulation work was feasible. Second, the study constructs the boundary element model for a two-dimensional phononic crystal which was studied by Sánchez-Pérez etc. with experimentation, constituted of rectangular and triangular array of parallel circular stainless steel and aluminum cylinders in air. The study is compared with the forbidden bands of the band gap in the reference which performs the simulations with the mono-frequency by sweep. The full band gaps are determined from the combination of the results in both the [100] and [110] direction. Finally, the study aimed at the scattering pattern of sound field in phononic crystal to make discussion. In order to understand the sound source acts on the phononic crystal, the status of the sound pressure is distributed over the spatial. So it could get up to reduce the influence of the noise by way of the improvement the structure in phononic crystal. The study has successfully shown the boundary element simulation for the solid/fluid phononic crystal. The study of experiment in the reference is compared with the BEM simulation in this thesis. The results have demonstrated that the boundary element method is a good tool for the design of phononic crystal in application to new type sound absorption (isolation) material in the future.

The development and improvement of 3-D immersive audio is gaining momentum through the growing interest in virtual reality. Possible applications reach from recreating real world environments to immersive concerts and performances to exploiting big data acoustically. To improve the immersive experience several measures can be taken. The recording of the sound field, the spatialization and the development of the loudspeaker arrays are some of the greatest challenges. In this thesis, these challenges for improving immersive audio will be explored. First, there will be a short introduction about 3D audio and a review about the state of the art technology and research. Next, the thesis will provide an introduction to 3D loudspeaker arrays and describe the systems used during this research. Furthermore, the development of a new 16-element 3rd order sound field microphone will be described. Afterwards, different spatial audio algorithms such as higher order ambisonics, wave field synthesis and vector based amplitude panning will be described, analyzed and compared. For each spatialization algorithm, the quality of soundfield reproduction will be quantified using listener perception tests for clarity and sound source localization. / Master of Science

Research Doctorate - Doctor of Philosophy (PhD) / Sound field distribution is becoming increasingly known as a method to overcome problems associated with noise, distance, and reverberation in classrooms. No robust research on this intervention has been conducted in the New Zealand context. Changing pedagogies in the education of New Zealand children and young people have been observed particularly since the 1970’s, resulting in noisier classrooms (Wilson, 2000). Acoustic standards for New Zealand classrooms that were adopted in 2003 apply only to new or renovated classrooms, and not to the majority of existing classrooms (Ministry of Education, 2003a). This study investigated: (a) the efficacy of sound field distribution in 30 New Zealand classrooms from five schools and compared outcome measures with a representative control group; (b) the variations of benefit for groups from specific populations, in particular children from five different socio-economic backgrounds and those with histories of middle ear dysfunction; and (c) the effects on teachers who use this equipment. Data were collected from standardized objective measurement tools and from the teachers and students who were participating in the study. Results revealed that sound field distribution, with the equipment configuration of boom microphones and four speakers, can enhance the listening and learning environment resulting in significant positive benefits in raising the achievement levels of children and young people. These results were observed in listening comprehension, which has a flow-on effect on the overall scholastic achievement of all students. Evidence of improved outcomes in areas with a strong link to mastery of literacy were significant, in particular in the areas of phonologic skills, reading comprehension, and reading vocabulary. Results of the study strongly support the use of sound field distribution in all mainstream school settings irrespective of whether the children and young people belong to a particular ethnic group, have had a history of middle ear dysfunction, or attend schools of a particular socio-economic status. Classroom sound field distribution seemingly benefits all children and young people. As a result of the positive results of this study and given the stated goals for education by the New Zealand Ministry of Education (Ministry of Education, 2003b), sound field distribution needs to be considered at a policy level as an intervention to assist in reducing disparity and to improve learning outcomes for all young New Zealanders in mainstream school settings.

<div>Near-Field Acoustical Holography (NAH) is an inverse process in which sound pressure measurements made in the near-field of an unknown sound source can be used to reconstruct the sound field so that source locations can be identified. Usually a large number of measurements is required for the usual NAH methods since a large number of parameters in the source or field model need to be determined. However, a large-scale microphone measurement is costly and hard to perform, so the use of NAH is limited by practical experimental conditions. In the present work, with the motivation of decreasing the number of microphone measurements required, and thus facilitating the measurement process, two sparse Equivalent Source Method (ESM) algorithms were studied: i.e., Wideband Acoustical Holography (WBH) and l_1-norm minimization. Based on these two algorithms, a new hybrid NAH procedure was proposed and demonstrated.To study and verify the above mentioned algorithms, simulations of different sources were conducted and then experiments were conducted on different sources: i.e., a loudspeaker cabinet and a diesel engine.</div>

Sound-field amplification systems (SFA) have proven effective in overcoming classroom listening difficulties associated with noise, distance and reverberation. However, whether improving the classroom listening environment is sufficient to enhance young children’s learning in areas critical to early reading acquisition, such as awareness of the sound structure of spoken words (phonological awareness: PA), is unclear. This study aimed to examine the effectiveness of an enhanced listening environment combined with PA intervention which aimed to specifically increase children’s PA compared to an enhanced listening environment alone. Participants were 38 children aged 5-6 years from two classes at a low-decile primary school. All children were hearing screened at baseline, pre- and post-intervention. PA, letter-sound knowledge, real and non-word decoding were measured three times over 10 weeks (Term 1) prior to SFA installation in both classrooms, as well as pre- and post-intervention. In Term 2, children in class 1 were randomly assigned to receive SFA and an eight-week class-based teacher-administered PA programme. Class 2 received SFA only. A significant learning effect for all children occurred during the first phase of the monitoring period. Yet, a plateau was reached for most children between assessment times two and three prior to intervention. Following intervention, class 1 demonstrated a significant difference compared to class 2 in one PA assessment. Other measures failed to show any differences between classes. Visual data analyses revealed particular (non-significant) improvements for poor readers in class 1. These children outperformed poor readers in class 2 on all measures. Teacher questionnaires indicated that children’s listening skills improved with SFA. The significant difference observed in one measure of PA between classes demonstrated that the combination of enhanced classroom acoustic environment and PA intervention actively improved PA development. The results of this study have implications for: (a) facilitating attention to sound structure, (b) optimal intervention for early PA development, (c) early reading acquisition in New Zealand classrooms, and, (d) the use of typical models of professional teacher development.

Preliminary studies have stirred the hope that sound-field stimulation through auditory steady state evoked potentials can be used to assess aided thresholds in the difficult-to-test population. Before the introduction of ASSEP into the clinical field, as a technique for the prediction of aided thresholds in the difficult-to-test population, a question arises concerning its clinical validation. The application of ASSEP through sound field stimulation, in the determination of aided thresholds and for the evaluation of amplification fittings, is dependent on the determination of unaided responses. Subsequently the estimation of unaided thresholds in the hearing impaired population is dependent on the establishment of normative data from the normal hearing population. The aim of this study was to determine the influence of insert earphones and sound field speaker presentation on threshold estimations using monotic auditory steady state evoked potentials, in a group of normal hearing adults. To achieve the aim of the study, a comparative, within-group experimental design was selected. The results of the current study indicated that the monotic single ASSEP technique under both insert earphone- and sound field conditions provided a reasonable estimation (25-35 dB HL for inset earphones; 20-33 dB HL for sound field speaker presentation) of the behavioural pure tone thresholds. The minimum response levels obtained under insert earphone conditions differed significantly from those obtained under sound field conditions for all the frequencies tested except 2 kHz (p < 0.01). Subsequently, the current study indicates that minimum response levels obtained using a specific transducer should serve as the basis of comparison with behavioural thresholds obtained under the same transducer. Therefore, behavioural pure tone thresholds obtained under insert earphone conditions will not suffice as a basis of comparison for minimum response levels obtained for the ASSEP technique under sound field conditions, and vice versa. This research endeavour concluded that the monotic ASSEP technique under both insert earphone and sound field conditions provide useful information for the estimation of frequency specific thresholds, but that the results are transducer specific and that comparison across transducers should be avoided. / Dissertation (M (Communication Pathology))--University of Pretoria, 2006. / Speech-Language Pathology and Audiology / Unrestricted

Tese de mestrado. Multimédia. Faculdade de Engenharia. Universidade do Porto. 2012

Since the micro-electro mechanical system microphone, MEMS microphone, has the advantages of superior sound quality, low power consumption, higher temperature resistance and anti-noise ability in used. The researchers therefore have studied the functions of MEMS microphone since 1980s. The MEMS microphones is applied as the part of 3G mobile phone in the market. Though the functions of microphone are improved by manufacturing process technique and new material designed, this study tends to provide a new, low-cost and rapid design idea to gain the performance in chamber of microphone. Taguchi method and BEASY software, which is boundary element method, are combined to evaluate the results of the design in sound field. Taguchi method is a famous method in industrial design to find out relations between system parameters and chamber size. BEASY is a tool for sound field analysis in the research. The result from Taguchi method appears the sound pressure level gain about 2.2 dB to 2.4 dB due to the change of microphone chamber size only. It is also interested in studying the optimization design for position of microphone. It is displayed that the location of port is closer to the boundary of chip will also increase about 0.3 dB to 0.6dB sound pressure level in sound field. The higher frequency of sound source will also create larger sound pressure level at two corners on the port.

L'objectif de ce travail de thèse est la conception d'un système de haut-parleurs transportable, capable de générer un champ sonore prédéfini et focalisé avec un contraste spatial élevé. Ce système doit permettre à terme d'effectuer différents types d'études, par exemple des essais de transparence acoustique ou encore des essais vibratoires en conditions non-anéchoïques. La minimisation du nombre de canaux à piloter ainsi que du nombre des transducteurs est l'un des enjeux principaux du travail. Le choix du nombre de sources et la sélection de leurs positions optimales afin de générer un champ acoustique cible n'a pas de solution triviale. Pour répondre à cette question, la méthode proposée se base sur la décomposition du rayonnement d’une source en série de fonctions orthogonales indépendantes (les"modes de rayonnement"), construits numériquement via une décomposition en valeurs singulières de la matrice d'impédance. En filtrant les termes évanescents, le champ lointain peut être reconstruit à l'aide d'un faible nombre de termes. De plus, la méthode permet d'estimer une distribution de débit efficace pour générer le champ cible. La méthode proposée étant relativement peu étudiée dans la littérature, la première partie de la thèse a été consacrée au problème de la validation expérimentale de la méthode directe et à l'étude des principaux paramètres en influençant le résultat. La problématique du positionnement des sources permettant de synthétiser un champ sonore prédéfini et focalisé est abordée dans la deuxième partie du travail. / The goal of this thesis is the design of a transportable speaker system, able to generate a predefined and focused sound field with a high spatial contrast. This system has eventually to allow carrying out different types of studies, for example acoustic transmission loss tests or vibration tests in non-anechoic conditions. The minimization of the number of driven channels and the number of transducers is one of the main goals of the work. The choice of the number of sources and the selection of their optimal positions in order to generate a target acoustic field has no trivial solution. To answer this question, the proposed method is based on the decomposition of the source radiation into a series of independent orthogonal functions (the "radiation modes"), constructed numerically via a singular value decomposition of the impedance matrix. By filtering the evanescent terms, the far field can be reconstructed using a small number of terms. In addition, the method allows the estimation of an efficient flow distribution to generate the target field. With the proposed method having been scarcely studied in the literature, the first part of the thesis is devoted to the problem of the experimental validation of the direct method and the study of the main parameters that are influencing the result. The problem of sources positioning in order to synthesize a predefined and focused sound field is discussed in the second part of the thesis.

Orientador: Vera Lúcia da Silveira Nantes Button / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-21T00:54:44Z (GMT). No. of bitstreams: 1 Gasparini_ReynaldoTronco_M.pdf: 4522453 bytes, checksum: a5e3883976604a06aa2fd8dcffb6cd3b (MD5) Previous issue date: 2012 / Resumo: O estudo do campo acústico gerado por um transdutor ultrassônico é fundamental para sua construção e caracterização, pois permite prever qual será seu comportamento antes mesmo de ser construído e indica se ele realmente é viável para aplicação para a qual foi projetado, e se são necessárias modificações para que se comporte como o esperado. O presente estudo teve como objetivo o desenvolvimento de um software, em ambiente MATLAB®, para a simulação computacional de campos acústicos gerados por transdutores ultrassônicos de diferentes configurações, utilizando dois modelos que descrevem o campo, o de Zemanek e o de Stepanishen. Os campos de transdutores com focalização, apodização e meios com atenuação também poderão ser simulados. Para a simulação do modelo de Zemanek é utilizado o método matemático de discretização e para o de Stepanishen é empregada uma solução analítica para a resposta impulsiva de cada geometria de transdutor. As simulações foram validadas com resultados obtidos anteriormente por alunos do DEB/FEEC/UNICAMP e os programas desenvolvidos foram agregados em um pacote computacional. Estes programas têm seus códigos abertos para que futuramente sejam implementadas outras funções e configurações de transdutor. O software pode auxiliar no projeto de transdutores e também no estudo da modelagem do campo acústico pelos diferentes modelos que o descrevem / Abstract: The study of the acoustic field generated by an ultrasonic transducer is fundamental to its construction and characterization, because it allows to predict how it will behave before being built and whether it is really feasible or not for the application to which it was designed, and to suggest modifications to behave as expected. The present study describes the development of a software implemented in MATLAB®, for computational simulation of acoustic fields generated by ultrasonic transducers, of different configurations, using two models that describe the field, Zemanek and Stepanishen. Transducers with focusing, apodization and attenuation environment may also be simulated. For Zemanek's model simulation is used the mathematical method of discretization and for Stepanishen's model, an analytical solution for the impulse response of each transducer geometry is employed. The simulations were validated with results obtained previously by students from DEB/FEEC/UNICAMP and the developed programs were aggregated into a computer package. These programs have their code available so that, in a near future, other functions and transducer configurations can be implemented. The software can support the transducer design and also the study of the acoustic field modeling by different models that describe it / Mestrado / Engenharia Biomedica / Mestre em Engenharia Elétrica