Technical Acoustics

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  • A measurement device for sound field sampling in rooms

    Master Thesis of Thevißen, Florian
    Forschungsgebiet: Raum- und Bauakustik
    Betreuer: Witew, Ingo / Vorländer, Michael
  • A wavelet-synthesis model for the auralization of moving sound sources

    Master Thesis of Wenhuan Duan
    Forschungsgebiet: Akustische Virtuelle Realität
    Betreuer: Meng, Fanyu

    Moving sound sources are indispensable parts in acoustical environment and cause noise problems as the speed of the sources increases rapidly, such as high-speed trains and cars. Auralization is an efficient way for prediction and provides immerse audible sense. Therefore, it is important to find a sound synthesis approach to modeling moving sound sources and create perceptually convincing sounds for auralization. In this research, wavelet transform (WT) is proposed to synthesize moving sound sources in virtual reality environment. Compared to Fourier transform, WT has the advantage of remaining time information when transforming signals into the frequency domain, which benefits the received time-variant signals from moving sources. Due to frequency shift, the Doppler effect should be eliminated through interpolation before WT. With varying the parameters generated from WT, new signals can be synthesized based on several samples. The results need to be verified by on-site measurements listening tests. Finally, a synthesis model for auralization is established based on WT for moving sound sources.
  • Acoustic Surface Impedance Estimation with a Hybrid Measurement and Wave-Based Simulation Method

    Master Thesis of Müller-Giebeler, Mark
    Betreuer: Vorländer, Michael / Opdam, Rob

    Existing and commonly used methods to measure the sound reflection properties of acoustic surfaces have certain restrictions. Either they inherently do not provide enough information (for example phase information for wave- theory based simulations), or they only yield realistic results to a limited extent (for example in a perfectly diffuse sound field, under a plane wave incidence assumption or only for a limited frequency range) . More sophisticated methods to determine the complex angle-dependent reflection factors are often complicated and very time-consuming. This work presents an inverse method that only needs a single sound pressure measurement of a finite porous absorber sample, along with geometric information for simulation, as input data and takes into account the actual incident sound field as well as a potentially non-locally reacting material. With a non-linear fitting algorithm, the simulated complex pressure data is adjusted to match the measured data by changing the absorber model parameters (flow resistivity, porosity, etc.). Several factors that affect the measurement and/or the optimization process are investigated theoretically. Furthermore, an extension to the above mentioned approach is proposed, allowing for a edge effect correction of the finite material probe. Using iteratively refined FEM simulations that are based on the same geometric dimensions of the absorber sample as in the measurement, enables to compensate the introduced error and to determine the impedance as measured on an infinitely extended material probe. The method is validated based on simulations and applied in preliminary measurements.
  • Adaption of room acoustic auralizations to the reproduction environment

    Master Thesis of Voth, Markus
    Forschungsgebiet: Akustische Virtuelle Realität
    Betreuer: Kohnen, Michael

    This master thesis investigates how far virtual rooms can be adapted to reproduction environments. To achieve this, the properties of early and late reflections are used with respect to physics and hearing physiology. In case of insufficient absorptive materials, early reflections and long reverberation times occur in rooms. Thus, the reproduction of the virtual scene is distorted. To compensate for reverberation, there are various approaches. For early reflections, it has been shown that a wave based annihilation is highly sensitive to small disturbances. Therefore, in this thesis, early reflections of the reproduction room shall be integrated into the VR-scene as good as possible by using a mapping method. To visualize early reflections, a vector based figure is developed. Objective evaluation criterions or measures of error are explored to compare room impulse responses. To reduce these errors, the above described compensation strategies are developed. Though, compensation possibilities are limited by the room where signals are reproduced. To evaluate the results objectively, there are simulations and measurements. For the subjective evaluation, a headphone based listening test is executed.
  • Analysis and Design of a Matched Microphone Array for MIMO Applications in Room Acoustics

    Master Thesis of Berzborn, Marco
    Betreuer: Vorländer, Michael / Klein, Johannes

    Arrays of microphones and loudspeakers can be utilized to study spatial properties of acoustic wave fields in rOoms. For example, microphone arrays can be utilized to estimate the direction of sound incidents corresponding to single reflections, while loudspeaker arrays are capable of exciting single reflections in a room. Therefore, the combination of both to an acoustic mUltiple-input multiple-output (MIMO) system provides a powerful instrument for room acoustic analysis. The first part of this thesis focuses on an analytic formulation of such a MIMO system. In particular potential error sources such as spatial aliasing and model mismatch and their impact on the formulated system are studied. Based on the formulation of errors, a simulation framework is derived, aiding at the determination of a MIMO system that inherits the lowest total error for a given source array. F inally, a system fulfilling the minimal error criterion is identified. This thesis then concludes with the design of the spherical microphone array based on the results of the error simulations.
  • Analysis of Directional Decay Curves Based on Simulated Room Impulse Responses

    Bachelor Thesis of Bilitewski, Niclas
    Betreuer: Berzborn, Marco / Klein, Johannes
  • Analysis of Room Impulse Responses Measured with Compact Spherical Microphone and Loudspeaker Arrays

    Master Thesis of Haar gen. Epping, Christian
  • Atmospheric Ray Tracing based on altitude-dependent weather data

    Master Thesis of Schäfer, Philipp
    Forschungsgebiet: Akustische Virtuelle Realität
    Betreuer: Mecking, Jens / Stienen, Jonas

    This thesis addresses sound propagation in the atmosphere in the context of auralization of acoustic scenes. A common method to estimate sound paths between a given source and receiver is the so called ray tracing. With the help of these estimated paths, an impulse response can be derived, which allows the auralization of acoustic scenes in a virtual environment. In contrast to the acoustic medium in rooms, where ray tracing is commonly used, the atmosphere is neither homogeneous nor static. Main reasons for this are the variation of the sonic speed over space and movement of the medium, such as wind. These effects lead to refraction and translation of sound resulting in curved ray paths. Additionally, distances between source and receiver are rather large in outdoor scenarios. Therefore, ray density around the receiver is low and prediction of ray paths needs high computational effort. This impedes finding eigenrays - rays, that directly hit the receiver - since it is complex but needs to be efficient for fast computations of the impulse response. In the course of this thesis, a ray tracing algorithm for the simulation of atmospheric sound propagation and auralization is designed. Ray propagation is investigated to determine criteria for finding and neglecting rays, that are irrelevant for the receiver, in an early state to save computation time. Altitude-dependent weather data is used to model atmospheric properties assuming the atmosphere to be a stratified medium. In a second step, the influence of these properties on the impulse response is investigated. Therefore, an acoustic scene is rendered repeatedly while varying the weather parameters.
  • Auralization of Building Acoustic Filters

    Forschungsgebiet: Raum- und Bauakustik
    Betreuer: Imran, Muhammad

    In building acoustics auralization, the implementation of sound transmission (i.e. airborne and structure borne transmission etc.) is an important phenomena to be incorporated in virtual buildings from where we can evaluate the performance of the building elements in terms of noise and comfort. The sound transmission through building elements influence the perception to a listener in listening rooms, therefore, there is a requirement to design the filters for building elements as acoustic sources to predict their influence. In the receiving room these building elements act as secondary sound sources and these secondary sources are obtained from transfer functions of sound transmission through building structures. This research topic focuses on handling the virtual building geometries and rendering the secondary sound sources in addition to the room acoustic filters to auralize the perception of the buildings under study. The potential applications of this research are the auralization of building in virtual reality and video games. Requirements ? Interest in the topic and independent work ? Knowledge of Room Acoustic ? Familiar with Matlab Optional skills ? C# Skills ? Working in Unity
  • Auralization of Sound Insulation in Virtual Reality

    Forschungsgebiet: Raum- und Bauakustik / Akustische Virtuelle Realität
    Betreuer: Imran, Muhammad

    In this research, we investigate the auralization of airborne sound transmission in complex buildings to develop the corresponding auralization filters chain for the evaluation of the performance of these building in terms of noise and comfort. This study focuses on the implementation of airborne sound transmission based on ISO-EN: 12354-1, and comprehends the calculation procedures for sound insulation metrics (i.e. sound reduction index for direct transmission of the different structures and the vibration level differences across junctions) and the development of sound insulation filters. These filters calculates the sound transmission between dwellings by partitions and by flanking structures to estimate the transfer functions between the sources and receivers during auralization process. Example buildings would be taken as a test case that consists of different type of building elements and their constructions. These buildings would be presented in virtual reality and the insulation filters will be applied to different scenarios (i.e. different source and receiver positions in different coupled rooms) and as a result synthesized room impulse responses (RIRs) will be obtained for these scenarios. Perceptual studies will be conducted to evaluate the performance of these buildings and to predict the comfort and annoyance. The potential applications of this research are the auralization of building in virtual reality and video games.
  • Automatische Geometrievereinfachung für Raumakustiksimulationen

    Bachelor Thesis of Durand, Christopher
    Forschungsgebiet: Akustische Virtuelle Realität / Raum- und Bauakustik
    Betreuer: Aspöck, Lukas
  • Building acoustics simulation based on semantic models

    Forschungsgebiet: Akustische Virtuelle Realität / Raum- und Bauakustik
    Betreuer: Stienen, Jonas / Imran, Muhammad

    Room acoustics simulations are mostly based on geometry meshes with polygonal faces that are linked to acoustic materials, such as absorption and scattering coefficients. Unfortunately, building acoustics simulations require also sound transmission through walls and ducts. Here, polygonal meshes are inherently insufficient, because solid structures can not be described efficiently. In building and architectural modeling, semantic data structures based on the BIM approach are widely used and well integrated into the design and model workflow. In this master thesis, the employment of IFC-compatible semantic input data for building acoustics simulation will be investigated. Ways to extract room meshes for room acoustic simulation are investigated. A derivation of sound transmission paths between rooms will be formulated that can be readily used for building acoustics simulations with flanking paths. Requirements  Basic C++ programming skills  Basic knowledge of technical acoustics  Basic knowledge of acoustic simulation  Interest in the topic and independent work Optional skills  Familiar with SketchUp, FreeCAD, Revit  Knowledge of semantic data structures (namely IFC)  Familiar with Visual Studio
  • Characterization of simulated jet noise by means of spherical harmonics decomposition

    Master Thesis of Cappellotto, Francesco
    Forschungsgebiet: Lärmforschung / Akustische Virtuelle Realität
    Betreuer: Mecking, Jens

    This thesis presents a research on the source modeling of aircraft’s jet noise, the goal of which is to reproduce the sound of aircraft in simulated Virtual Reality environments with a high degree of fidelity. At the moment, the acoustical modeling of jet noise follows semi-empirical models, partially derived from fly-over measurements and optimized to include a set of variable configurations, e.g. noise reducing chevrons. However, this method has some limitations. In fact, its spectral resolution is limited to one-third octave bands, and the correlation of single noise components is not defined. Moreover, ground measurements require some approximations to account for the cutback phase (a reduction in the power level right after take-off). This affects not only the power level, but also the directivity of the jet noise, which cannot be approximated due to lack of information. Finally, ground measurements are normalized to standard atmosphere, thus the uncertainty derived from the current weather at the time of the measurements is included in the directivity. In the scope of this thesis a method will be researched, to model the noise of jet engines in a more precise way, using simulated data to compute physically valid directivity patterns, rather than empirical or semi-empirical models, and to achieve results that are independent from meteorological conditions and not restricted to one-third octave bands. To do so, simulated data on a 3d-grid in the near far-field around the jet will be used as input data. A set of points has to be chosen and modeled using spherical harmonics decomposition. Since it is expected that the model will reach high-order spherical harmonics, an acoustic centering of the source will be evaluated to reduce the computational cost. With the use of this method, it is expected to achieve a better auralization, which can be used for more realistic VR simulations.
  • Characterizing and Analyzing Auralizations of Complex Acoustical Scenes

    Bachelor Thesis of Reffgen, Matthias
    Forschungsgebiet: Akustische Virtuelle Realität
    Betreuer: Aspöck, Lukas / Stienen, Jonas
  • Comparing inverse absorption coefficient methods to traditional reverberation chamber measurements

    Forschungsgebiet: Akustische Virtuelle Realität
    Betreuer: Aspöck, Lukas

    Absorption coefficients as a description of the boundary conditions for room acoustics simulations are usually very challenging to determine. A standardized method estimates the random incidence absorption coefficient of a material sample by placing the material in a reverberation chamber, conducting an acoustical measurement and comparing it to another measurement of the empty chamber. As this method has some drawbacks and limitations, a novel approach uses a room acoustics simulation and matches the input parameters until a match is found for a room acoustics measurement of the identical situation. In this work, both methods should be applied for at least two samples and their results should be analyzed and compared. Especially the problems of non-diffuse sound fields and non-linear decay curves should be investigated.
  • Continuous measurement of room impulse responses with Spherical Loudspeaker Arrays

    Bachelor Thesis of Palenda, Pascal
    Forschungsgebiet: Akustische Messtechnik
    Betreuer: Klein, Johannes

    The results of a room impulse response (RIR) measurement are used in acoustic research for auralization, room reflection analysis or sound field analysis. When measuring a single RIR, the measurement system has an intrinsic directivity. Under the assumption that the room complies with the linear-time-invariant-system (LTI-system) prerequisites, superposing single RIRs, taken at specific directions, can synthesize a RIR with arbitrary directivity. The current state of the art is to measure the single RIRs sequentially using a spherical loudspeaker array (SLA) and spherical microphone array (SMA). Nevertheless, hundreds of single RIRs have to be measured for a high-resolution RIR with arbitrary directivity. Due to the long measurement time, the room is subject to changes in temperature and humidity. This in turn invalidates the time-invariance of the assumed LTI-system. The current goal is to minimize the time to complete the measurement. One proposed way is a continuous measurement. With this method the SLA is rotated continuously therefore we can simplify the problem to a measurement with an SLA and a single microphone. RIRs for different spatial directions, corresponding to the sequential measuring direction, can then be extracted from the captured signal. This would in turn eliminate the time of mechanical free travel and oscillations caused by adjusting the SLA and thus reducing the measurement duration. This thesis will examine the viability of continuous measurements for RIR measurements. A comparison methodology will be explored, subsequently the results of the continuous measurements can be compared to the sequential measurements. Furthermore, this thesis explores the limitations of a continuous measurements. Different excitation signals will be implemented, simulated, measured and post-processed using a single-input multiple-output (SIMO) measurement set-up with an SLA.
  • Creation of auditory scenes for multimodal listening experiments

    Bachelor Thesis of Geusen, Holger
    Forschungsgebiet: Raum- und Bauakustik / Akustische Virtuelle Realität
    Betreuer: Aspöck, Lukas / Vorländer, Michael

    Zur Bewertung und Validierung von raumakustischen Simulationen können diese mit Referenzmessungen verglichen werden. Ein solcher Vergleich soll zukünftig mit Hilfe von audiovisuellen Experimenten durchgeführt werden. Sowohl für akustische Simulation als auch für die visuelle Darstellung einer virtuellen Szene gibt es jedoch eine Vielzahl an Lösungen, was Hard- und Software betrifft. Aus diesem Grund sollen in dieser Abschlussarbeit verschiedene Tools und Umgebungen für das akustische und visuelle Rendering recherchiert und basierend auf einem erstellten Kriterienkatalog für die Eignung in den geplanten Experimenten bewertet werden. Dazu werden drei Raumszenen jeweils in mehreren Systemen erzeugt und in Pilotversuchen evaluiert.
  • Development of a measurement method for the analysis of surface vibrations

    Bachelor Thesis of Peckert, Fabian
    Betreuer: Mecking, Jens / Klein, Johannes

    Mikrospeakers, which are normally designed as dynamic loudspeakers, are very compact and can be found in portable devices. Therefore, many approximations of conventional loudspeakers are only partially valid for microspeakers. In particular the assumption of a loudspeaker membrane as an in-phase vibrating piston radiator does not apply for the whole frequency domain, since for certain frequencies vibrating-modes propagate in form of bending waves on the membrane. In order to investigate the position-dependent surface velocity of a loudspeaker membrane, this bachelor thesis presents a method to measure the membrane. Furthermore, with the help of the developed method the vibration pattern of the membrane can be visualized and analyzed. The scanning of the membrane is done by a laser-vibrometer that measures the velocity of the membrane. The measurement position is shifted by with two step motors which are attached to a measurement table. The measurements take place all over the membrane with an adjustable resolution of the measurement grid. A broad-band excitation signal which covers the whole human perceptible frequency range is used. This study is limited to the measurements of micro-loudspeakers, but can also be extended to analyze other vibrating surfaces. The analysis can be done for arbitrary frequencies by visualizing the different measurements with 2-D or 3-D graphic tools. Moreover transfer functions or impulse responses for individual measurelnent points on the Illmnbrane can be illustrated in order to study the formation of modes in the surface. Additionally a method for the creation of a video was made that shows the vibration characteristics of the membrane for different frequencies. Hereby the propagation of vibrating modes and the phase differences between input and output signal can be studied and analyzed which can help to modify micro-loudspeakers and its radiation characteristics. With regard to the future, the aim is to use the developed measurement method and the visualization tools for teaching purposes. Hereby the methods shall be integrated into the 'Akustische Praktikum'-lab course and further research on microspeakers at the Institute of Technical Acoustics.
  • Development of Sound Insulation Toolbox (GUI)

    Forschungsgebiet: Raum- und Bauakustik
    Betreuer: Imran, Muhammad

    The development sound insulation models for airborne transmission are important for evaluating the performance of building structures in terms of noise evaluation. The sound insulation models describe the performance of the building elements. The basic parameters that are necessary for the development of these models are based on measurements and/or on calculations and material properties of the building elements, according to the ISO standards. Once the sound insulation models are developed these models are implemented in graphic software such as Sketch Up and Unity. This research focuses on developing a graphical user interface (GUI) based toolbox for calculating the sound insulation parameters for virtual building geometries in Matlab software and rendering the corresponding sound transmission filters to auralize the perception of the buildings under study. This toolbox will be used for education and research purpose in the area of building acoustics. Requirements ? Interest in the topic and independent work ? Knowledge of Room Acoustics ? Matlab Optional skills ? Knowledge of Building Acoustics
  • Diffraction simulation in Geometrical Acoustics

    Forschungsgebiet: Akustische Virtuelle Realität
    Betreuer: Stienen, Jonas

    Acoustic diffraction off and around geometrical obstacles is an important phenomenon that occurs if the compared wave length is not small or big against the geometrical dimensions. Simulating acoustic diffraction is usually done in the time or frequency domain using simulation methods that solve the wave equation, i.e. naturally take this effect into account. Calculating a sound field this way results in a high spatial resolution but is yet so computationally expensive, that it is not suitible for almost any non-fundamental problem. Acoustic simulations using the Geometrical Acoustics principle, on the other hand, are able to rapidly generate sound transmission information for distinct solitaire positions of a source and a receiver, which makes this approach feasible for real-time auralization. In this master thesis, acoustic sound diffraction shall be investigated using geometrical techniques.
  • Direction of Arrival Estimation of Early Reflections Using Compressive Sensing

    Bachelor Thesis of Förster, Jonas
    Betreuer: Berzborn, Marco / Berzborn, Marco
  • Dynamic Crosstalk-Cancellation with Room Compensation for Immersive CAVE-Environments

    Master Thesis of Röcher, Eric
    Forschungsgebiet: Akustische Virtuelle Realität
    Betreuer: Kohnen, Michael / Stienen, Jonas

    Auralization of virtual scenes using binaural synthesis enables a realistic reproduction of auditory events, which intensifies the feeling of immersion in Virtual Reality applications. Headphones are usually used with binaural synthesis; however, they tend to constrain the users immersion. To retain the immersion, a speaker setup with a proceeding Crosstalk-Cancellation filter can be used. In large CAVE-VR-Systems with extensive acoustically hard projection surfaces, which partly or completely surround the user, challenging acoustical conditions are to be expected. Not only is the speaker’s placement limited to positions above the hard projection surfaces but furthermore, due to the non-absorbent surfaces, distinct early reflections superimpose the useful signal. This results in a not insignificant change in the overall reverberation time. Therefore a CTC filter design is proposed which compensates those early reflections. Based on the simple room geometry in CAVE-Environments, sound transmission paths can be easily estimated. These estimations can then be used to integrate room characteristics into the design of a dynamic CTC-system and lead to an improved playback quality for rooms with challenging acoustical conditions. The proposed procedure will be instrumentally reviewed for its performance in the aixCAVE, the VR-Environment of the RWTH Aachen University. The tests will focus on accuracy and introduced errors for each individual hardware as well as software component of the system. Inherent System latencies and positional inaccuracies like for example the CAVE’s tracking device and transmission path delays will be taken into consideration.
  • Dynamische Modenkompensation in Quaderräumen

    Bachelor Thesis of Voth, Markus
    Forschungsgebiet: Akustische Virtuelle Realität
    Betreuer: Kohnen, Michael / Stienen, Jonas

    In small rooms, especially with parallel and perfect reflecting walls, there occur distinct standing waves. Due to standing waves, there are constructive and destructive interferences for single, deep frequencies. In respect of the position, this inhomogeneous spread of sound pressure is perceived by the listener as an unbalanced an unpleasant soundfield. Especially in the aixCAVE the causes for standing waves exist, as mentioned above. The only possible optimization is a software solution, because walls and floor are used for rear projections. Up to now, only static software solutions are considered for the compensation of room- and transducer effects. So in this bachelor thesis it is explored, how far the spectral course of sound pressure level may be equalized in cuboid rooms with a listening position adaptive compensation of modes. Therefore an analytical frequency response estimation and an adaptive IIR-filter concept with adapted sampling rate is implemented. To reduce the computational complexity, also a symmetry optimized lookup-table concept is developed. The results of the compensation are validated with suitable simulations and measurements. In the process, the estimation of modes in the aixCAVE is proved as difficult, because of the complicated boundary conditions, appearing by an open and absorbing ceiling. With a perfect estimation, the developed software compensation of modes in the aixCAVE provides a realistic improvement of more than 20dB.
  • Embedded Microphone Equalization for Array Applications

    Master Thesis of Maintz, Thomas
    Betreuer: Berzborn, Marco

    The analysis of a sound field with an array of microphones reveals detailed information about its directional properties. To achieve a high spatial resolution many microphones are required, typically resulting in high costs when using standard electret microphones. To reduce costs, Micro Electro Mechanical System (MEMS) microphones are used. These, however, show a non-ideal frequency response. Thus, the frequency- and phase response of all individual microphones have to be equalized for their application in microphone arrays. The internal logic of Field Programmable Gate Arrays (FPGA) can be customized to implement a live-equalization of microphones. In this thesis the Xilinx Zynq FPGA is choosen for this purpose. In addition to the programmable logic block the Xilinx Zynq platform includes two ARM-processors which connect to the programmable logic block via standardized protocols. These can be used to interface the FPGA logic and program the filter coefficients into the programmable logic. Further, optimized atomic architectures for digital signal processing are provided within the Zynq FPGA. This thesis outlines the conception and implementation of a scalable convolution kernel with minimum latency for the equalization of larger scale microphone arrays in hardware. The implementation is carried out on the Xilinx Zynq FPGA platform relying on pipelining. Parallel FIR- and Biquad-Filters are implemented and can be customized for each microphone channel individually. By applying a hybrid convolution technique with time and frequency domain convolution, the length of the equalization filters can be extended. To reduce the total number of FFT operations the symmetry properties in the spectra of real valued time signals are used. The solution will be used inside a spherical microphone array yielding a live-equalization of the individual microphone signals. Eventually, the output signals are converted to a MADI stream allowing for a standardized interface to a measurement PC. Further, the implementation is analyzed with respect to the limitations of the used fixed-point arithmetic. Finally, results are compared to computational results of a Golden Reference Modell implemented in floating-point arithmetic.
  • English: Physics-based real-time auralization with the game and VR environment ‘Unity’

    Bachelor Thesis of Andreas, Maurice
    Forschungsgebiet: Akustische Virtuelle Realität
    Betreuer: Stienen, Jonas

    For the creation of virtual environments not only technical and artistic abilities are needed. Without the use of State-of-the-Art-Software the enormous effort of modeling, scripting and developing individual extension scripts is not viable. The highly specialized development environment \grqq Unity\grqq{} by Unity Technologies Inc. offers an extensive base for easy implementation not only for the gaming industry but also for Virtual Reality. For this purpose integrable modules are ready to use a number of VR-Devices like the Oculus Rift, LLC or the \grqq HTC Vive\grqq{}. Furthermore Unity offers extensive possibilities to program plugins and gather objects of the virtual environment with scripts written in C\#. This bachelor thesis deals with the creation of a connection between Unity and VA. This enables the usage of physically based realtime auralization and all other available reproduction methods in combination with VR glasses. The result will be a full-fledged multi-modal VR system which can be used to demonstrate interactively environment noise or for building and room acoustic studies. On top of that it can be used for studies about multi modal perception which have to be executed under controllable and reproducible conditions.
  • Estimation of room geometry based on impulse responses

    Bachelor Thesis of Maintz, Thomas
    Forschungsgebiet: Akustische Virtuelle Realität / Raum- und Bauakustik
    Betreuer: Aspöck, Lukas

    Virtual Reality methods are used to create an immersive environment where the user is able to freely interact. Besides visual perception acoustic perception is of high importance. The process of auralization makes scenes audible and aligns the acoustic and visual feedback. For this procedure simulated room impulse responses are required which represent the room's acoustical characteristics. Room impulse responses contain early reflections within the first 50 ms. Those reflections occur on bounding surfaces and appear as peaks in room impulse responses. These peaks can be approximated by the image source model which is based on the principles of geometric acoustics. An algorithm was developed which calculates the bounding surfaces and in this way estimates the room geometry. No a priori knowledge is required except for the speed of sound and the constellation of receivers. Since the identification of higher order image sources is not trivial, mainly convex room geometries are investigated. In these spaces independent of the source and the receiver positions all first order image sources are audible. Peaks of the room impulse response are converted into estimated propagation paths using methods of Euclidean Distance Matrix and Multidimensional Scaling. Based on estimated positions of the original source and image sources bounding surfaces are calculated. In order to validate the result of the estimates, a measure of the error is introduced taking into account acoustic and geometric deviations.
  • Evaluation of audio signal synthesis and network transmission for real-time auralization in Virtual Reality

    Bachelor Thesis of Heimes, Anne
    Forschungsgebiet: Akustische Virtuelle Realität
    Betreuer: Stienen, Jonas

    In virtual reality applications, technical challenges are the biggest obstacle when producing a virtual scene in a quality standard, which achieves a satisfactory immersion. For this purpose, various components are integrated into an overall system, which separates the tasks and divides the burden of complicated calculations. Typical examples are CAVE systems, which usually use dedicated computers for visualization, tracking and auralization. They communicate exclusively via network interfaces. Extensions, which require a correspondingly high calculation effort, can be integrated via the acquisition of additional computing units without slowing the system down. An important aspect of interactive VR applications is the systems reaction to user action. In sound propagation simulation, these changes lead to new calculation of the parameters for the digital signal processing, which imprints the effects of the propagation on an input signal. These input signals of the real-time processing are usually read out directly from the main memory without significant expenditure. A different situation occurs if the input signal is not directly available, but must be generated from an artificial parameterizable calculation model or a complex physical model by means of modal analysis and synthesis. In this case, mathematical operations are carried out that additionally burden the processor and thus compete for resources. In this bachelor thesis, the aim is to examine under which preconditions the generation of signals from a virtual sound source on a dedicated computer and the subsequent transmission to the auralization computer via a network interface are reasonable. System components and complexity of signal generation as well as latency and transmission rates are taken into account in order to formulate a general recommendation.
  • Extention of a Model of Open Pit Mines for Optimization of Noise Emissions

    Master Thesis of Uber, Thomas
    Betreuer: Vorländer, Michael / Aspöck, Lukas
  • Filter design of diffraction in auralization of urban environments

    Bachelor Thesis of Filbert, Daniel
    Forschungsgebiet: Akustische Virtuelle Realität
    Betreuer: Stienen, Jonas

    The acoustic propagation of sound in the open field or in the interior can be calculated effectively and in high quality by geometric simulation methods. However, phenomena that are mainly due to wave-based properties are implemented insufficiently or only with comparatively complex calculation models by these approaches. In this bachelor theses, well-known methods for the filter design of diffraction simulation in geometric acoustics will are investigated and applied for the auralization of urban environments, in which mainly wave fronts of low order come to account.
  • Filteroptimisation for 3D-audio reproduction

    Bachelor Thesis of Klein, Simon
    Forschungsgebiet: Psychoakustik
    Betreuer: Kohnen, Michael / Stienen, Jonas

    Nowadays, head-mounted displays (HMD) like the Oculus Rift or the HTC Vive allow an immersive experience of virtual environments even for the consumer market. To present a correct audio stimulus beside these visual reproductions loudspeaker-based reproduction methods can be used. In this thesis such loudspeaker-based reproduction method should be optimized in terms of computational efficiency by investigating the possibilities of simplifying or shortening the used filters. Furthermore the results of such an optimization will be investigation in terms of subjective audibility (i.e. a short listening experiment) and objective parameters (e.g. change in energy of the filters). Both the optimization and listening test can be coded in MATLAB using the ITA-Toolbox. Requirements - Programming skills (MATLAB) - Work independendly - Interest in the topic - Basics of Acoustics (e.g. ‘Einführung in die Akustik’)
  • How much does the sound field in auditoria change from one position to the next?

    Bachelor Thesis of Hasti, Henry
    Forschungsgebiet: Raum- und Bauakustik / Akustische Messtechnik
    Betreuer: Witew, Ingo

    Room acoustical measurements with microphone arrays have shown that the sound field in auditoria changes significantly from one position to the next. This gives rise to the question how valid acoustical measurements in architectural acoustics are. This question that is of core relevance when it comes to characterizing the sound field in rooms based on a small number or singular measurements. At the Institute of Technical Acoustics, a measurement robot was designed, capable of conducting automated high-resolution sound-field measurements in auditoria over a larger area (5.5 x 8.0 m). This data can be used to investigate how severely the sound field changes from one position to the next. In this thesis acoustical measurements are to be conducted in different auditoria (lecture rooms and concert halls) to collect data that can serve as the foundation to derive a relationship between the change in acoustic conditions an the distance between two measurement positions. Goal of this thesis will be to answer two important questions: • For what size a region is a single measurement in a room valid? • How accurate need measurements to be documented so that the results are reproducible? This knowledge is of special interest to make acoustical measurements in architectural acoustics more efficient.
  • Implementation of VBAP and DBAP with Evaluation using Measurements and Binaural Simulation Model

    Bachelor Thesis of Bassiri, Sina
    Betreuer: Vorländer, Michael / Kohnen, Michael

    To create an acoustic virtual reality with the best possible realistic perception of sound sources for a listener in a closed space, it is necessary to analyse the spatial sound in certain areas. In this thesis two methods are considered: Vector Base Amplitude Panning (VBAP) and Distance-Based Amplitude Panning (DBAP). Thesc techniques arc able to create virtual sound sources for a listener by controlling several speakers. Important cues like the Interaural Time Difference (ITD) and the Interaural Level Difference (ILD) together with the frequency spectrum are analysed and evaluated. This aspects will be investigated by looking at the head direction and at the movement of the virtual source. The aim of this bachelor thesis is to implement the methods VBAP and DBAP in MatLab and to write a corresponding test script which plays different sounds with different methods and sound source locations. These sounds are recorded by a dummy head and they are evaluated in terms of ITD, ILD and frequency spectrum within the test script. With existing recordings of Head Related Transfer Functions (HRTFs) of the dummy head the evaluation is accomplished. In addition there will be a comparison with an auditory model by Dietz, which represents a model of the human hearing. The dependence of the speaker positions and position in the head related coordinatesystem are very important for the perception of the sound source. The results for DBAP's evaluation were unfavourable. However, VBAP works for the greater part very solid.
  • In-Situ determination of room acoustic boundary conditions based on invese simulation techniques

    Master Thesis of Knauber, Fabian
    Forschungsgebiet: Akustische Virtuelle Realität
    Betreuer: Pelzer, Sönke / Vorländer, Michael

    The acoustical transformation from a real existing room into a congruent simulation model requires a precise room model replication and appropriate wall boundary conditions, which replicate the wall material distribution of this room. The room model is easy to build, whereas the wall boundaries are challenging to measure in-situ. Typical room acoustic simulation software uses a room model and the absorption coefficients to calculate an impulse response. While trying to find the best possible match of the simulation result to a given impulse response measurement, certain absorption coefficients have to be set. This problem can not be analytically solved, but it can be formulated as a non-linear minimization problem, which can be iteratively solved using optimization algorithms. In this work a MATLAB tool was developed that implements an absorption coefficient determination, by using the optimization toolbox together with a new method for the fast generation of energy decay curves from a given set of absorption coefficients. Furthermore, the optimization was improved by formulating an acoustically reasonable cost function. The implementation was validated versus simulated rooms as well as applied to measurements of different rooms.
  • Investigation of Thermal and Nonlinear Distortions in Small Loudspeakers

    Master Thesis of Mecking, Jens
    Forschungsgebiet: Elektroakustik
    Betreuer: Behler, Gottfried / Müller-Trapet, Markus

    This thesis deals with the characterization and modeling of small dynamic loudspeakers which are relevant due to their use in mobile devices (smart phones, tablet computers, etc.). These so-called microspeakers show considerable deviations from the idealized model of a linear time-invariant system which allows its electrical, mechanical and acoustical characterization by means of a time- independent transfer function. Although the reasons for these deviations are well-known for the case of large dynamic loudspeakers the transferability of the results to the case of microspeakers is questionable due to the altered mechanical composition concerning structure, material and size. An exact description of the occuring distortions would eventually allow their compensation and thus lead to an improved playback quality. During operation the temperature of the system rises which leads to changes in the electrical and mechanical properties and therefore also in the linear transfer properties of the transducer. An uncontrolled temperature increase can cause mechanical damage and eventually even the destruction of the device. An accurate description of the speaker’s thermal behavior is therefore necessary to compensate these undesired effects. In order to carry out thermal investigations on the system, a precise knowledge of the device temperature is essential. Therefore, a method to measure the temperature via the DC resistance of the voice coil was validated regarding accuracy and reproducibility. This method was subsequently used to characterize a loudspeaker in the framework of thermal models which predict the temperature as a function of the electical input power. Furthermore, the temperature dependence of the linear Thiele-Small parameters was investigated. In addition to thermal effects, microspeakers show nonlinear distortions in their transfer characteristic if operated in the large-signal domain. The Harmonic-Balance method was used in order to characterize the loudspeaker in the framework of an extended nonlinear model. Therefore, generalized transfer functions for higher orders of the input signal were derived and fitted to measurement data obtained in the nonlinear regime. A special focus was laid on the integration of the linear loudspeaker parameters into the nonlinear model.
  • Investigation on headphone reproduction using individual and non-individual HRTFs

    Master Thesis of Reffgen, Matthias
    Betreuer: Vorländer, Michael

    The use of binaural synthesis to generate virtual aeoustieal environments for numerous eontexts is nowadays of peeuliar interest. Many studies foeus on the preeise determination of individual head-related transfer functions (HRTF ) , the investigation of anthropometrie data as well as its influenee in time and frequeney domain. Alternatively different proeedures based on simplified geometrieal models approximate speeifie indiviudual HRTFs to reduee the measurement effort related to the determination of individual HRTFs. This seems to be essentially for the eommereial use of binaural teehnology. To evaluate the performance of different individualizations, well known and new investigation methods were implemented to be used together with a head-mounted display and applied in several listening tests. Along with the employment of individualization teehniques, such as headphone equalization or ITD-adjustment, also the influence of additionally presented visual stimuli and possible applications of head-mounted displays in listening tests were discussed. The results of these investigations should be used to evaluate possible applications of binaural technology in non-scientific multimedia contexts.
  • Listening test on acoustic immersion in virtual reality

    Master Thesis of Jarmer, Fabian
    Forschungsgebiet: Akustische Virtuelle Realität / Psychoakustik
    Betreuer: Kohnen, Michael / Aspöck, Lukas
  • Listening test on acoustic immersion in virtual reality

    Bachelor Thesis of Lian Esthefany Gomez De Pasquale
    Forschungsgebiet: / Akustische Virtuelle Realität
    Betreuer: Aspöck, Lukas

    A realistic virtual reproduction of a room acoustic scene deeply relies on the accuracy of the used room model and the specified boundary conditions, in particular the absorption coefficients. The determination of the absorption coefficients is usually a challenge, in spite of the multiple available methods for its obtaining. A standardized method estimates the absorption coefficient of random incidence of a material's sample by performing an acoustic measurement when placing it in a reverberation chamber, and comparing the results with those of another measurement of the empty chamber. As this method has some drawbacks and limitations, innovative approaches have been proposed that use an acoustic simulation of the room and modify the input parameters until a match is found for an acoustic measurement of the room of the identical situation. This work presents, analyzes and compares the results obtained through the methods described when they are applied to different sample layouts, in shape and size, both in diffuse and non-diffuse sound fields. In addition, the accuracy of the results obtained through these methods is tested by altering the input parameters of the model of the simulated scenarios.
  • Method for the assessment of simulated electric car drives by means of psychoacoustic parameters

    Bachelor Thesis of Vermeulen, Markus
    Betreuer: / Vorländer, Michael
  • Modellierung und Evaluierung der Schallabstrahlung elektrischer Antriebe

    Forschungsgebiet: Maschinenakustik und Diagnose und Transpferpfadanalyse / Numerische Akustik
    Betreuer: Müller-Giebeler, Mark
  • Modelling of moving sound sources using compressive beamforming for auralization

    Master Thesis of Li, Yan
    Forschungsgebiet: Akustische Virtuelle Realität
    Betreuer: Meng, Fanyu

    Compressive beamforming (CB) is a method to reconstruct sparse signals using few measurements by solving a convex minimization problem. CB not only has good localization resolution, but is also able to reconstruct source signals with phase information. For moving sound sources, CB guarantees an acceptable localization resolution; Besides, phase information benefits auralization by completely reconstructing source signals. This paper focuses on obtaining the signals of moving sound sources for auralization using CB. A microphone array will be applied to record a pass-by moving sound source. The deployment of the array should be determined in terms of a better performance. Subsequently, the recordings are processed by CB to localize and reconstruct the source signal. Finally, the reconstructed signal will be added to the moving sound source in virtual reality (VR) for auralization.
  • Optimization of a sound insulation test bench regarding its measurement accuracy

    Bachelor Thesis of Mattern, Arne-Heinz
    Forschungsgebiet: Raum- und Bauakustik / Akustische Messtechnik
    Betreuer: Mecking, Jens

    One of the most important measures of sound insulation is the sound reduction index. It describes the property of a component regarding sound transmission as a function of frequency and is therefore decisive for the sound propagation in buildings. The sound reduction index is determined through measurements in a test bench according to EN ISO 10140. An important aspect that must be considered during measurements is the flanking transmission, i.e. the transmission of power through objects that are flanking the tested component. This additional power increases the measured sound pressure in the receiver room and thus the measured sound reduction index is lower than its true value. But, because the sound reduction index is supposed to be the property of a component and not dependent on the room itself, the flanking transmission must be suppressed as far as possible. The aim of this thesis is to improve the measurement accuracy of the test bench, which is primarily used during the acoustic lab course. For this purpose, a characterization of the test bench is achieved by comparing the measured and calculated values for the sound reduction index. Then the possible flanking paths are characterized and analyzed. Based on these results constructive solutions are derived and implemented. In the end, the proposed solutions should be evaluated. A before-and-after comparison of the measuring accuracy is suitable for this purpose.
  • Optimized sound propagation simulation for auralization of outdoor noise in urban environments

    Bachelor Thesis of Jansen, Julian
    Forschungsgebiet: Akustische Virtuelle Realität
    Betreuer: Stienen, Jonas

    Noise maps are key tools of noise protection in urban environments. The expected, averaged noise exposure is visualized for every location within the surveyed area. This visual representation, however, does not allow a statement about the characteristics of the perceived sounds. The aim of this thesis is a real-time simulation of the sound propagation from various sound sources to a receiver in a three-dimensional city model, to make an auralisation of the perceived sounds possible. The size of the city model datasets requires the implementation of optimization approaches, which limit the number of calculated propagation paths and geometric objects, if real-time calculation is to be achieved. Crucial to this is an a-priori analysis of the source signal properties.
  • Outdoor noise simulation based on CityGML models

    Forschungsgebiet: Akustische Virtuelle Realität
    Betreuer: Stienen, Jonas

    Sound scapes of cities are not only affected by typical sound sources, but also by the build environment. To simulate instant noise distribution or auralize an urban situation, acoustic (noise) simulations are required that incorporate physical sound propagation with correct reflections off building facades and around diffraction objects. In an attempt to describe the real world by means of computer models, CityGML can be helpful to define static build environment, traffic routes as well as dynamics in time-variant traffic. This Bachelor thesis will investigate how far CityGML models can be used for urban noise distribution and auralization, and which data processing is required to achieve this goal. Depending on skill and interest, the actual orientation of the topic can be suggested by the student’s favor, requiring a coordination with the supervior, a short literature review and exposé beforehand. Requirements  Basic C++ and/or Matlab programming skills  Basic knowledge of acoustics  Interest in the topic and independent work Optional skills  Familiar with SketchUp or other CAD modellers  Knowledge of XML and semantic data structures (namely CityGML)  Sound design or audio processing
  • Parallelisierung einer Echtzeit-Raumakustik-Simulation für Mehrkernprozessoren

    Master Thesis of Schallenberg, Ralf
    Betreuer: Pelzer, Sönke / Vorländer, Michael
  • Perception of Spherical Harmonics Source Directivity Patterns in Rooms

    Bachelor Thesis of Wolf, Gregor
    Betreuer: Klein, Johannes / Berzborn, Marco

    Room acoustical measurements according to the international standard ISO 3382 are executed with the requirement of directivity of source and receiver to be omni-directional to ensure the comparability of standardized parameters. Due to this, directivity patterns of ordinary sources, like human speakers or instruments, are not respected in these measurements. For realistic auralization and precise room acoustical analysis the measurement of room impulse responses including the desired directivity is required. Due to practical considerations, every room impulse measurement is limited in terms of the spatial resolution in spherical harmonics. In this regard, the question of the human perception accuracy of the spatial resolution arises. Listening tests have proven, that differences between strongly directive sources and rather omni-directional sources are audible. The goal of this thesis is to evaluate the human perception accuracy of sound directivity pattern in rooms with consideration of the spatial resolution of the directivity patterns. For this task, defined directivity patterns of different spatial resolutions are simulated in different scene models with the objective to create signals for a listening test. Based on these simulations a listening test of the concluded sources and scenes is implemented and executed. With the data it is possible to evaluate how detailed the perception is and to analyse a possible threshold of audibility regarding the spatial resolution of the different sources. .
  • Psychoacoustic assessment of simulated and measured rooms

    Forschungsgebiet: Raum- und Bauakustik
    Betreuer: Aspöck, Lukas

    Room acoustics simulations offer the possibility to predict the acoustical characteristics of a room before it has been built or in case of a planned modification. For existing rooms, the room acoustics can be captured by conducting a measurement of the room impulse response. To adjust for the human perception, a binaural room impulse response can be measured using a dummy head. These binaural room impulse responses can be applied for validations of simulated results of the same room. By convolution with an anechoic sound file, the measured or simulated room can be made audible – this process is called auralization. This thesis investigates the differences of simulated and measured binaural room impulse responses of various rooms. As a room acoustics simulation includes complex input data and various configuration possibilities, the measured results are used as a reference. By using an optimization process, one or more parameters of the simulated room impulse response can be selected and matched to the measurements. In this work a listening experiment has to be conducted which compares the perception of a simulated and a measured room. Weaknesses in the simulation engine and the filter synthesis should be identified. "earliest start: Middle of May/End of June 2017"
  • Psychoakustische Untersuchung der Geräuschqualität von Elektrofahrzeugen

    Forschungsgebiet: Maschinenakustik und Diagnose und Transpferpfadanalyse / Psychoakustik
    Betreuer: Müller-Giebeler, Mark
  • Real-time auralization of complex scenes

    Forschungsgebiet: Akustische Virtuelle Realität
    Betreuer: Stienen, Jonas / Aspöck, Lukas

    Auralization of virtual scenarios has been investigated for decades, however the total number of sound sources and sound reveivers considered is still imited in the approaches available to date. It is common that only one receiver is regarded and a few sound sources can be calculated. This Master thesis will deal with the design and implementation of a real-time auralization module that can cope with hundrets of sound sources. The main challenge will be to interactively route audio processing resources to most relevant sources, i.e. by culling approaches that require a-priori estimations on the relevance of a source. Also, clustering options will be examined that combine distant sources for propagation simulation. The evaluation of the results have to be conducted by either a benchmark or a listening experiment. Depending on skill and interest, the actual orientation of the implementation and evaluation part can be suggested by the student’s favor, requiring a coordination with the superviors, a short literature review and a written exposé beforehand. Requirements  Basic C++ programming skills  Basic knowledge of technical acoustics  Basic knowledge of acoustic simulation  Interest in the topic and independent work Optional skills  Basic Matlab skills  Real-time audio processing skills  Familiar with Visual Studio
  • Sound source localization on a car body based on beamforming using transfer functions

    Master Thesis of Havolli, Albulena
    Betreuer: Nau, Clemens / Berzborn, Marco

    The acoustic and vibro-acoustic-technical comfort of vehicles (NVH) raises in importance, especially in the premium segment. In order to fully exploit its own development potential and continue to make progress towards its competitors, the advancement of acoustic de-velopment tools is of central importance for OEM (Original Equipment Manufacturer). As a successful development tool for the localization and characterization of noise outside and inside the vehicle, the beamforming has proven to be the method. The localization of a sound source which inducts structure-borne sound into the car body, which is emitted as an air sound into the vehicle cabin by the interior boundary, is currently not possible. Thus, with the existing conventional beamforming algorithms (CBF), only a locating of the air-borne radiation, but not of the structure-borne sound generation, is possible. This master thesis is intended to contribute to the improvement of beamforming for sound source detection in the vehicle interior by using transfer functions. For this purpose, in the first step, the transfer functions of defined structural points of the car body are determined experimentally (by striking with the impact hammer). In the next step, these transfer func-tions are implemented in an existing beamforming environment. To validate the beamforming approach using transfer functions, the car body is excited with a shaker at the defined positions. The localization results of this approach and the corres-ponding method without the inclusion of transfer functions are recorded, compared and qualitatively evaluated.
  • Spatial variation of the acoustic field in auditoria

    Bachelor Thesis of Reich, Lennart
    Forschungsgebiet: Raum- und Bauakustik
    Betreuer: Witew, Ingo

    In room acoustics, several measurements have shown that the acoustic field in large rooms, such as auditoria, varies significantly depending on position. This raises the question of the practical validity of acoustical measurements, especially if single measurements are used to analyze the acoustical character of an extended area in an auditorium. In order to make this argument work it is necessary to know how much the sound changes from one position to the next. To establish this relationship empirically impulse responses are measured in an array of closely spaced microphone positions using a measurement apparatus capable of automatically sampling the sound field over an extended area. These impulse responses can be used to calculate acoustical quantities related to the perceived acoustical character of a room, which are then examined in a statistical analysis.