Dirk Schröder

Virtual reality system with integrated sound field simulation and reproduction

A real-time audio rendering system is introduced which combines a full room-specific simulation, dynamic crosstalk cancellation, and multitrack binaural synthesis for virtual acoustical imaging. The system is applicable for any room shape (normal, long, flat, coupled), independent of the a priori assumption of a diffuse sound field. This provides the possibility of simulating indoor or outdoor spatially distributed, freely movable sources and a moving listener in virtual environments. In addition to that, near-to-head sources can be simulated by using measured near-field HRTFs. The reproduction component consists of a headphone-free reproduction by dynamic crosstalk cancellation. The focus of the project is mainly on the integration and interaction of all involved subsystems. It is demonstrated that the system is capable of real-time room simulation and reproduction and, thus, can be used as a reliable platform for further research on VR applications.

Synthesis, characterisation and catalytic activity of Pd(II) and Ni(II) complexes with new cyclic α-diphenylphosphino-ketoimines. Crystal structure of 2,6-diisopropyl-N-(2-diphenylphosphino-cyclopentylidene)aniline and of 2,6-diisopropyl-N-(2-diphenylphosphino-cyclohexylidene)aniline

Abstract New cyclic α-diphenylphosphino-ketoimines have been synthesised by deprotonation of the corresponding imine and subsequent reaction with chlorodiphenylphosphine. The crystal structures of two of these compounds containing a cyclopentylidene and cyclohexylidene backbone are discussed. Reaction of these bidentate phosphorus–nitrogen (P∧N) ligands with (cod)Pd(CH3)Cl leads to neutral complexes of the general formula (P∧N)Pd(CH3)Cl which have been reacted with AgSbF6 to yield cationic complexes of formula [(P∧N)Pd(CH3)(NCCH3)]SbF6. Reaction of these ligands with (1,2-dimethoxyethane)NiBr2 yields neutral nickel(II) complexes that have been characterised by IR and elemental analysis. Cationic Pd(II) complexes as well as MAO-activated neutral nickel(II) complexes have been used as ethylene oligomerisation catalysts. The cationic palladium(II) complexes show a marked pressure dependence of TOF, with α-olefin fraction and Schulz-Flory α-values explainable in the light of the accepted mechanism for analogous complexes. By increasing the steric bulkiness of the substituent on the imine, or by using ligands with cyclohexylidene or cycloheptylidene backbone instead of cyclopentylidene, a drop in catalytic activity is observed. Nickel(II) complexes of the title ligands activated with MAO permit to confirm the latter conclusions. In comparison with palladium their use brings to comparable linearities but higher oligomerisation grades as well as α-olefin fraction. Cationic palladium(II) complexes are also active in the propene and 1-butene oligomerisation.

Virtual reality for architectural acoustics

Over the last decades, powerful prediction models have been developed in architectural acoustics, which are used for the calculation of sound propagation in indoor and/or outdoor scenarios. Sound insulation is predicted rather precisely by using direct and flanking transmission models of sound and vibration propagation. These prediction tools are already in use in architectural design and consulting. For the extension towards virtual reality (VR) systems, it is required to accelerate the prediction and simulation tools significantly and to allow an adaptive and interactive data processing during the simulation and 3D audio stimulus presentation. This article gives an overview on the current state-of-the-art of acoustic VR and discusses all relevant components in terms of accuracy, implementation and computational effort. With the progress in processing power, it is already possible to apply such VR concepts for architectural acoustics and to start perceptual studies in integrated architectural design processes.

Modeling (non-)uniform scattering distributions in geometrical acoustics

In most cases, a surface is not ideally smooth. It rather contains regular and irregular dents, bumps and other textures that influence the reflection of the incident wave. A reflection on such a corrugated surface causes a frequency-dependent redirection of the incident sound energy outside the specular direction, called scattering. While the computation of the specular part is well elaborated today, a model that thoroughly captures the wave phenomenon of scattering is still under discussion. Here, the most common assumption is that scattered energy follows a uniform Lambert distribution, which has proven to be a good approximation, especially in room acoustical applications. In this contribution, we will discuss Lambert-based scattering models (specular/diffuse sound field decomposition and vector mixing) and their implementations in methods of Geometrical Acoustics. We will analyze benefits and flaws of the respective models and investigate possibilities to introduce angle-dependent scattering for use cases where the uniform Lambertian distribution becomes invalid.

Open measurements of edge diffraction from a noise barrier scale model

Until today, all known simulation methods for the wave phenomenon of edge diffraction are just approximations, based on either Geometrical Acoustics or the numerical solving of the wave equation. Although these methods work fine for simple test scenarios and a certain frequency range, they fail to simulate the effect of diffraction in its whole complexity. This leads to false predictions especially for more complex geometries where the influence of multiple wave diffraction and sound scattering has to be taken into account as well. Consequently, huge effort is currently put into the development of improved simulation methods. Here, a basic need is an all-embracing validation of simulation results, which also includes the comparison with real-world measurements. Unfortunately, there is a lack of such data which is the reason why the Institute of Technical Acoustics (ITA), RWTH Aachen University, Germany, and the Centre for Quantifiable Quality of Service in Communication Systems (Q2S), NTNU Trondheim, Norway, have started an initiative called openMeasurements, which is aimed to be an internet platform for free acoustic measurement data of any kind, together with their respective simulation models (CAD-model, detailed information on sources and receivers, material data) and helpful tools. As initial step, various measurement series of a scaled-down model of a noise barrier were carried out. These series aim to give researches, developers, and common application users, the possibility to thoroughly test their prediction models of edge diffraction. The measurements were carried out in a full anechoic chamber and a turntable was used to rotate the scale-model during the measurements in steps of one degree. The scale-model was constructed with a changeable ground layer in order to massively influence the objects acoustical properties and, thus, create measurement datasets that considerably differ. Here, datasets for five different ground layers were obtained: 3 absorbers, 1 rigid surface and 1 self-constructed skyline-diffuser. A skyline diffuser was chosen as it is a well reproducible geometrical pattern, which enables a simulation of sound scattering in two ways: stochastic and deterministic. In this contribution, detailed information on the measurement setup is given and measurement procedures are described thoroughly. Measurement uncertainties are briefly discussed and first comparisons with simulations are presented. All measurements together with geometrical models of the scale-model (with/without diffuser), detailed information on sources and receivers, material data (absorption- and scattering coefficients) and useful Matlab tools are freely available for download (www.openmeasurements.net).