Acoustic absorbing liners are efficient and commonly used measures to reduce sound levels in many fields of application. The sound reducingperformance of the liners is dependent on the acoustic state, defined by e.g. the flow and sound field interacting with the liner. To enable liner optimization the impact of these factors on the liner performance must be predictable. Studies of the impact of these factors were performed with existing experimental, analytical and numerical methods at low Mach number flows and material used in truck engine compartments. The study showed significant impact of both flow and sound field onthe liner performance. The size of the impact of the flow depends on which of the existing methods and models that was used, implying theneed of complementary methods. A new numerical method to model the boundary layer effect was for this reason developed in this work. The method was shown to predict the impact of flow correctly compared to the Pridmore-Brown solution and the method was computationally efficient. The sound reducing performance of a liner exposed to complex sound field and grazing flow can be predicted using existing methods together with the new proposed method. Extra care has to be taken when bulk reacting liners are considered since additional complications compared to locally reacting surfaces occur in presence the of grazing flow. / <p>QC 20130916</p>

Cochlear implant (CI) devices afford many profoundly deaf individuals worldwide partially restored hearing ability. Although CI users achieve remarkable speech perception with contemporary multichannel CI devices, their music perception ability is generally unsatisfactory. Improved CI-mediated music perception ability requires that the underlying constraints hindering processing of music-relevant information need to be identified and understood. This study puts forward a systematic approach, informed by the neurocognitive mechanisms underlying music perception in normal hearing (NH), for investigating implant-mediated music perception. Psychoacoustical experiments were used to explore the extent to which music-relevant information delivered to the central auditory system following peripheral electrical stimulation supports music perception. Task-specific stimuli and test procedures were developed to assess perception of pitch, rhythm and loudness information, both as separate and in combined form, in sound-field listening conditions. CI users’ unsuccessful judgement of the musical character of short, novel single-voice melodies suggests that insufficient information reaches the central auditory processing system to effect a unified musical percept. This is despite sound field frequency discrimination behaviour being better than had been expected and rhythm perception ability with regard to short tone sequences of varying pitch and rhythmic complexity being comparable to that of NH listeners. CI listeners also performed similarly to NH listeners during pitch-dependent loudness perception tasks. Within the framework of a hierarchical, modular processing system underlying music perception, it appears that early pitch processing deficits propagate throughout the music processing system to exert an overriding inhibitory perceptual effect. The outcomes of this study not only underline the importance of delivering sufficient pitch information to the electrically stimulated auditory system but also show that music perception in CI-mediated hearing should be investigated and understood as the outcome of an integrated perceptual system. / Thesis (PhD)--University of Pretoria, 2011. / Electrical, Electronic and Computer Engineering / Unrestricted

Environmental noise has for decades been a well known problem, especially in urban areas. As noise requirements for vehicles are sharpened, noise reducing concepts are needed in early design stages requiring accurate simulations to support the design. Specifically for optimization of noise treatments, the absorber performance must be simulated correctly. So called noise encapsulations are placed below the powertrain on heavy vehicles to enclose the engine and reduce noise radiation. The attenuation of the absorbers on these shields must be represented correctly in simulations, even in environments with complex sound field, cooling flow and high temperature variations which may affect the absorber performance. This thesis studies the performance variation due to different absorber representations and due to these factors and how to include this in simulations. It is shown that the material representation significantly affects the attenuation performance in the simulations. Assuming locally reacting absorbers neglects the full interaction between the sound field and the material, which was shown to affect the noise reduction considerably. A measurement method to determine the angular dependent surface impedance was evaluated. It was shown sensitive to small samples and a method to improve accuracy was suggested. Including the angular dependence, either by full resolution or an angular dependent impedance, the field-absorber interaction is included in the simulations and more accurate results are obtained. The influence of flow and temperature fields on the absorber performance was also investigated. A method to include these effects was developed and the attenuation performance shown significant, especially for materials with bulk reaction. In conclusion, thorough knowledge of the material behavior and the field in the applications is required to choose appropriate material representation to enable reliable simulation results.​ / <p>QC 20160311</p>

Testing equipment based on the propagation of elastic waves are commonly used for measuring specific material properties. As a prerequisite for accurate measurements a reliable acoustic coupling of probe and specimen is highly important. Therefore, high-resolution testing equipment is using fluids as couplant. In certain conditions, only non-contacting methods can be considered. This is the case for example, if particular high or low temperatures are present, if topographic features impede the use of ultrasonic probes, diffusion or solubility processes exist, measurements at vacuum are addressed and if high purity requirements need to be fulfilled. Hence, subject of this work is a method which offers to handle these constraints. With the emergence of modern laser systems the scientific basics for a non-contacting, laser-acoustic excitation of ultrasound were discovered. The tremendous development of commercially available laser systems during the last decade was taken as reason to investigate, to which extent former scientifically designed laboratory setups can now be merged into one single application oriented measuring system. All considerations are based on the thermoelastic excitation of ultrasound in combination with a likewise laser-based detection. By this, a self-contained measuring chain is built which combines the attributes non-destructive, non-contacting and application oriented within one ultrasonic measurement system for the first time. Thermal calculations lead to more precise equations which predict a laser-induced, local temperature rise of about 100 K. The examination of sound field simulations, as a prerequisite for the design of ultrasonic systems, identified an additional complex of problems. Although existing calculation approaches presuppose laser intensity profiles what can be described in analytical terms, real-world laser sources exhibit a complex shaped spatial distribution of laser energy. Based on a preceding CEFIT simulation, the developed CPSS method enables the calculation of the time resolved, 3D wave propagation of arbitrary shaped sources. A comparison to measured data successfully validated the results of simulation. By presenting selected scenario of measurements, the practical suitability of this non-contacting method is demonstrated. Using a transmission setup enables the characterization of open-pore ceramic coatings as well as the deduction of longitudinal and transversal speeds of sound. Equally, the imaging and estimation of the depth position of artificial defects with 0.7 mm in diameter is shown. Measurements based on a reflection setup provided evidence of a resolution limit of at least FBH = 1 mm in 4.5 mm depth. Additional examples demonstrate the ability to detect close-surface defects, the analysis of the challenging lamb waves zero-group-velocity S1 mode as well as the utilization of buried laser-acoustic sources. / Prüfsysteme, welche die Ausbreitungseigenschaften elastischer Wellen zur Ableitung spezifischer Messgrößen nutzen, sind etablierte Messverfahren. Voraussetzung für zuverlässige Ergebnisse ist stets die sichere akustische Kopplung zwischen Sensor und Material. Daher arbeiten hochauflösende Prüfsysteme mit Fluiden als Koppelmedium. Unter bestimmten Bedingungen scheiden kontaktierende Ultraschallsysteme allerdings ersatzlos aus. Dies ist beispielsweise der Fall, wenn die Probe eine besonders niedrige oder hohe Temperatur besitzt, topografische Eigenschaften ein sicheres Ankoppeln der Kontaktprüfköpfe erschweren, Diffusionsvorgänge oder Löslichkeiten zu beachten sind, in Vakuum zu arbeiten ist oder erhöhte Reinheitsanforderungen vorliegen. Gegenstand der vorliegenden Arbeit ist eine Technik welche hilft, diese Einschränkungen zu umgehen. Mit dem Aufkommen der ersten Laserquellen entstanden die wissenschaftlichen Grundlagen zur kontaktlosen Anregung und Detektion von Ultraschall. Die rasante Entwicklung kommerziell verfügbarer Lasersysteme der vergangenen Dekade wurde zum Anlass genommen zu untersuchen, in wie weit sich die einst wissenschaftlich orientierte Laboraufbauten zu einem anwendungsnahen Messsystem zusammenführen lassen. Basis der Arbeiten ist die thermoelastische Anregung von Ultraschall in Kombination mit einer ebenfalls kontaktlosen Detektion. Damit entsteht eine geschlossene Messkette welche erstmals die Eigenschaften zerstörungsfrei, kontaktlos und anwendungsorientiert in einem Ultraschallmesssystem vereint. Ausgangspunkt stellt die thermische Simulation der Anregung dar. Mit Hilfe präzisierter Gleichungen wird eine lokale Erwärmung von lediglich 100 K vorausgesagt. Für die zur Auslegung eines akustischen Messsystems notwendige Schallfeldsimulation wurde eine weitere Problematik identifiziert. Während bekannte Rechenansätze stets analytisch beschreibbare Strahlprofile des Lasers voraussetzen, zeigen reale Laserquellen kompliziert gestaltete räumliche Intensitätsverteilungen. Auf Basis einer vorangestellten CEFIT-Simulation ist mit der entwickelten CPSS-Methode eine zeitdiskrete Berechnung der 3D-Wellenausbreitung beliebiger Quellgeometrien möglich. Vergleiche mit realen Messdaten bestätigen die Simulationsrechnungen. Anhand ausgewählter Messszenarien wird die Praxistauglichkeit der kontaktlosen Arbeitsweise demonstriert. Neben der Charakterisierung einer offenporigen keramischen Beschichtung erlauben Transmissionsmessungen die Berechnung der longitudinalen und transversalen Schallgeschwindigkeiten. Ebenso ist die Abbildung wie auch die Beurteilung der Tiefenlage von Referenzfehlern mit lediglich 0,7 mm Durchmesser möglich. In Reflexionsmessungen wurde eine Auflösungsgrenze von mindestens KSR = 1 mm in 4,5 mm Tiefe nachgewiesen. Weitere Beispiele zeigen die Sensitivität hinsichtlich oberflächennaher Fehler, die Auswertung der anspruchsvollen „Zero Group Velocity“ S1-Mode der Lambwelle wie auch die Nutzung eingebetteter Quellen.

Buscando-se a aplicação prática da teoria de Wave Field Synthesis (WFS) na música, foi feita uma pesquisa visando à modelagem de um sistema de sonorização capaz de criar imagens sonoras espaciais com a utilização desta técnica. Diferentemente da maioria das outras técnicas de sonorização, que trabalham com uma região de escuta pequena e localizada, WFS permite projetar os sons de cada fonte sonora - como instrumentos musicais e vozes - em diferentes pontos do espaço de audição, em uma região de escuta que pode abranger quase toda a área compreendida por este espaço, dependendo da quantidade de alto-falantes instalados. O desenvolvimento de um código de estrutura modular para WFS foi baseado na plataforma orientada a patches Pure Data (Pd), e no sistema de auralização AUDIENCE, desenvolvido na USP, sendo integrável como ferramenta para espacialização sonora interativa. A solução emprega patches dinâmicos e uma arquitetura modular, permitindo flexibilidade e manutenabilidade do código, com vantagens frente a outros software existentes, particularmente na instalação, operação e para lidar com um número elevado de fontes sonoras e alto-falantes. Para este sistema também foram desenvolvidos alto-falantes especiais com características que facilitam seu uso em aplicações musicais. / Seeking the practical application of the theory of Wave Field Synthesis (WFS) in music, a research aimed at modeling a sound system capable of creating spatial sound images with the use of this technique was made. Unlike most other techniques for sound projection that work with a small, localized listening area, WFS allows projecting the sounds of each sound source - such as musical instruments and voices - at different points within the hearing space, in a region that can cover almost the entire area comprised by this space, depending on the amount of installed speakers. The development of a modular structured code for WFS was based on the patch-oriented platform Pure Data (Pd), and on the AUDIENCE auralization system developed at USP, and it is integrable as a tool for interactive sound spatialization. The solution employs dynamic patches and a modular architecture, allowing code flexibility and maintainability, with advantages compared to other existing software, particularly in the installation, operation and to handle a large number of sound sources and speakers. For this system special speakers with features that facilitate its use in musical applications were also developed.

Buscando-se a aplicação prática da teoria de Wave Field Synthesis (WFS) na música, foi feita uma pesquisa visando à modelagem de um sistema de sonorização capaz de criar imagens sonoras espaciais com a utilização desta técnica. Diferentemente da maioria das outras técnicas de sonorização, que trabalham com uma região de escuta pequena e localizada, WFS permite projetar os sons de cada fonte sonora - como instrumentos musicais e vozes - em diferentes pontos do espaço de audição, em uma região de escuta que pode abranger quase toda a área compreendida por este espaço, dependendo da quantidade de alto-falantes instalados. O desenvolvimento de um código de estrutura modular para WFS foi baseado na plataforma orientada a patches Pure Data (Pd), e no sistema de auralização AUDIENCE, desenvolvido na USP, sendo integrável como ferramenta para espacialização sonora interativa. A solução emprega patches dinâmicos e uma arquitetura modular, permitindo flexibilidade e manutenabilidade do código, com vantagens frente a outros software existentes, particularmente na instalação, operação e para lidar com um número elevado de fontes sonoras e alto-falantes. Para este sistema também foram desenvolvidos alto-falantes especiais com características que facilitam seu uso em aplicações musicais. / Seeking the practical application of the theory of Wave Field Synthesis (WFS) in music, a research aimed at modeling a sound system capable of creating spatial sound images with the use of this technique was made. Unlike most other techniques for sound projection that work with a small, localized listening area, WFS allows projecting the sounds of each sound source - such as musical instruments and voices - at different points within the hearing space, in a region that can cover almost the entire area comprised by this space, depending on the amount of installed speakers. The development of a modular structured code for WFS was based on the patch-oriented platform Pure Data (Pd), and on the AUDIENCE auralization system developed at USP, and it is integrable as a tool for interactive sound spatialization. The solution employs dynamic patches and a modular architecture, allowing code flexibility and maintainability, with advantages compared to other existing software, particularly in the installation, operation and to handle a large number of sound sources and speakers. For this system special speakers with features that facilitate its use in musical applications were also developed.

Die vorliegende Arbeit untersucht, wie die genaue Kenntnis der Sende- und Empfangsschallfelder eines Ultraschallwandlers zur Entwicklung neuer Meßverfahren genutzt werden kann. Insbesondere werden dargestellt: - ein neuartiges, nichtscannendes Verfahren zur Bestimmung der Krümmung eines Reflektors, basierend auf der Analyse der Wellenfrontkrümmung reflektierter Schallfelder - ein neuartiges, nichtinvasives Verfahren zur Bestimmung der Schallgeschwindigkeit in einer Flüssigkeit durch Auswertung der Echosignale von im Ausbreitungsmedium vorhandenen Streupartikeln und - ein Verfahren zur Wandlercharakterisierung durch Messungen in Fluiden mit Streupartikeln, sowie verschiedene Zuordnungen von Schallfeldmerkmalen zu spezifischen Eigenschaften eines Ultraschallwandlers. Im Zusammenspiel von Simulation und Experiment konnten die Funktionstüchtigkeit aller Meßverfahren nachgewiesen und vielversprechende innovative Ansätze für zukünftige Entwicklungen angeregt werden: 1. Das nichtscannende Verfahren zur Krümmungsmessung erlaubt bei guter Justage eine Krümmungsbestimmung von Reflektoren mit Radien zwischen 6 und 11 mm mit einer Unsicherheit von ungefähr 0,5 mm. In Kombination mit herkömmlichen scannenden Verfahren bietet es Ansätze zur präzisen Größenbestimmung von Fehlern in der zerstörungsfreien Prüfung. 2. Das Verfahren zur nichtinvasiven Schallgeschwindigkeitsmessung erlaubt eine Bestimmung von Schallgeschwindigkeiten mit einer statistischen Meßunsicherheit von 0,1 %. Mögliche Weiterentwicklungen zur Messung der Schallgeschwindigkeit mit örtlicher Auflösung und zur Gewinnung neuer Diagnosemöglichkeiten in Metallurgie (nichtinvasive Charakterisierung von Mischungsvorgängen) und Biomedizintechnik (nichtinvasive Temperaturmessung in Körpergewebe zur Überwachung der Hyperthermiebehandlung, Gewebecharakterisierung) werden erläutert. Aus verschiedenen bekannten sowie einem neuartigen, leicht anwendbaren Meßverfahren werden neue Schlüsse gezogen a) zur Bestimmung der akustisch effektiven Elementgröße von Wandlerelementen mittels Schallfeldmessungen, b) zur Qualitätssicherung im Hinblick auf Schallkopfasymmetrien und c) zur Verbesserung von Schallfeldsimulationen. / The current thesis explores how the precise knowledge of the sending and receiving sound fields of an ultrasonic transducer can contribute to the development of novel measuring techniques. Emphasis is placed on: - a novel, non-scanning method for the determination of the curvature radius of a spherical reflector, based on the analysis of the wave front curvature of the reflected sound field, - a novel non-invasive method for sound velocity measurements in fluids using the echo signals from scattering particles, and - novel conclusions on how to use well-known sound field measurement methods for transducer characterisation, as well as an introduction to a novel easy-to-use method for transducer characterisation exploiting the echo signals from scattering particles. Proof of concept is shown for all methods by simulation and measurement, and different promising improvements for further techniques are suggested: - The non-scanning method for curvature measurements makes it possible to determine reflector radii between 6 and 11 mm with an uncertainty of about 0.5 mm, provided that there is a good reflector alignment. In combination with conventional methods, a novel approach for the determination of the size of discontinuities in non-destructive testing is outlined. - The method for non-invasive sound velocity measurements allows the determination of sound velocity in homogeneous fluids with a statistical uncertainty of 0.1 %. Future improvements are suggested to allow sound velocity measurements with local resolution, which enables novel approaches for metallurgy (non-invasive characterisation of mixing processes) and biomedical engineering (non-invasive temperature control for hyperthermia treatment, tissue characterisation). - New conclusions are drawn based on well-established and a novel easy-to-implement measurement method regarding a) the determination of the acoustically effective element size of transducer elements, b) transducer asymmetries, thereby improving quality control, and c) the improvement of sound field simulations.

In the first part of this master's thesis there is briefly presented the biomechanics of the human voice creation and an overview of the hitherto published computational models of the vocal tract and dissemination of the acoustic waves around the human head. The second part of the thesis deals with the creation of the computational model of a dissemination of the acoustic waves through vocal tract and further into a space around the head during the pronouncing of the Czech vowel /a:/. The vocal tract is excited by a harmonic signal in the place of vocal chords. On the surface of the vocal tract and the part of the head including hair and skin there is defined an acoustic absorption. The dissemination of the acoustic waves in the vocal tract, in the near field around the mouth, in the area around the head and in the points on the cheeks is detailed mapped. The dissemination of the acoustic waves is analyzed in the points where the speech microphones are placed. Acoustic pressure dependence on frequency, transmission functions between defined points and the acoustic pressure amplitudes depending on the distance from the mouth are obtained. In particular, the frequency distortion of the spectra is observed at the points indicated. Furthermore, the radiation impedance in the mouth area is evaluated. The results obtained are compared with the results of the hitherto published experimental measurements and can be used for the exact measurement of human voice or for the frequency correction of the microphones during the scann of the speech and sing placced in the analyzed points.

This thesis is dealing with problem and solution of simulation in room acoustics. At the beginning is introduction with sound as waves and his behavior in closed space. Following part of text is dealing with computional methods in room acoustics, statistics methods , ray-based methods, wave-based methods. Following are focused FDTD wave method, which serves as the basis for creating simulation algorithm.Last part of this work is practical sample of MATLAB aplication enviroment for simulation of sound waves in closed room by explicit sub-methods of method FDTD. The last section contains an example and discussion of the results of simulations.

The aim of this master´s thesis is to work out a comparison and evaluation of selected methods used for sound field mapping. Thesis will include software tools and results of sample measurement on test object for each mapping method.