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The analysis of the spatio-temporal features of sound fields is of great interest in the field of room acoustics, as they inevitably contribute to a listeners impression of the room. The perceived spaciousness is linked to lateral sound incidence during the early and late part of the impulse response which largely depends on the geometry of the room. In complex geometries, particularly in rooms with reverberation reservoirs or coupled spaces, the reverberation process might show distinct spatio-temporal characteristics. In the present study, we apply the analysis of directional energy decay curves based on the decomposition of the sound field into a plane wave basis, previously proposed for reverberation room characterization, to general purpose performance spaces. A simulation study of a concert hall and two churches is presented uncovering anisotropic sound field decays in two cases and highlighting implications for the resulting temporal evolution of the sound field diffuseness.

As an alternative for the common geometric room acoustical models, a wave theory-based model has been developed derived from the so-called WRW scheme, often used in seismic modelling [1, 2]. In this model, the wave properties of sound are appropriately taken into account. The proposed model is similar to the Boundary Element Method (BEM). Other than in BEM, in the WRW scheme non-locally reacting room boundaries can be included in the modelling process using only the fluid domain. The results of sound field modelling in rooms with locally as well as non-locally reacting boundaries are presented. The differences are analysed and their relevance is discussed.

Achieving a diffuse sound field in a reverberation chamber is crucial for measurements of acoustic quantities such as sound absorption coefficient, scattering coefficient, and sound power level. Toward this aim, diffusing elements such as hanging panels or rotating diffusers are typically installed in the chamber. However, previous research has suggested that hanging panels violate certain theoretical assumptions regarding diffusivity. Also, rotating diffusers cause the chamber to be a time-variant system, precluding the use of some measurement approaches such as sine-sweep integrated impulse response techniques. Boundary diffusers are offered as an alternative in the current study. The effects of both hanging panels and boundary diffusers on sound field diffusivity in a scale reverberation chamber are systematically and comparatively analyzed. The field diffusivity is characterized based on the guidelines set forth in American and international standards, including ISO 354, ASTM C423, and ASTM E90. Resulting data suggests that these standardized methods do not adequately or rigorously quantify diffusivity. The relative effectiveness of hanging diffusers vs. boundary diffusers will be discussed.

In order to characterize surfaces with respect to their sound reflecting properties, the absorption and the scattering or diffusion coefficient can currently be measured under standardized laboratory conditions. However, it is questionable whether the data from measurements performed under such laboratory conditions can be used to accurately model the actual sound field in rooms. Additionally, it is not always possible to obtain a transportable sample of a material. In-situ measurement methods can overcome these shortcomings, as they measure the desired quantities at the location where the material is installed. For this purpose, a portable setup was built that allows for a complete hemispherical measurement of the sound pressure distribution using less than 30 sensors. This contribution will present the setup together with the challenges for post-processing of the acquired data. First measurement results will be presented and discussed.

Humans experience their environment in various working, educational and living situations and in concert halls and opera houses. Whether the environment is considered acoustically appropriate or not depends on many factors. The research unit SEACEN is currently working on a coordinated effort to improve the complete signal chain from the numerical modelling, the data acquisition within numerical or real sound fields, the coding and transmission to the electro-acoustic reproduction by binaural technology or by sound field synthesis. A novel approach for the comparative evaluation of real and simulated environments will also enable the evaluation of the plausibility and/or the authenticity of virtual acoustic environments and a contribution to the development of better physical metrics to predict the qualities of concert halls and opera houses. These activities are relevant not only for concert hall acoustics but for acoustic spaces in general. The activities of SEACEN are summarized. The benefit from having these projects coordinated in a consortium is in the connection between all projects through perception studies and knowledge and data transfer between the groups. The commonly used factors in ISO 3382-like applications in classical room acoustics for concert hall design and consulting will be re-visited, and an extended parameter set will lead to progress in coding and reproduction of 3D sound fields in general. It is hoped that in the end room acoustics and audio engineering will benefit from this cooperation.

In a number of independent empiric studies it was shown that room acoustic single number parameters vary severely with small changes of the source and microphone position. Presently there is no evidence that these spatial fluctuations can be modelled using simulated impulse responses. As a result there is limited knowledge about the origin and the contributing influence factors of this variance over space. In this contribution the results of simulations using wave based as well as ray tracing simulations are compared to each other. It will be discussed if these simulations are able to predict the fluctuations that were found in measurement series taken in a number of different auditoria.

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 object's 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 ).

In the last decade computer simulations of sound fields in rooms have been developed for application in research and consulting. Some programs are commercially available. Most computer models are based on geometrical room acoustics and/or on statistical (radiosity) methods, thus not including wave phenomena such as diffraction. The uncertainty of typical simulation software was investigated in an international verification test in 1994 and 1995. The results were partly promising although some programs were not as reliable as the operators expected. These round robin tests have been continued until today with simulations and measurements in a concert hall in Jönköping in Sweden. In this paper the basic algorithms of room acoustical computer simulations, the verification in round robin tests and the observed accuracy and limitations are summarised. Finally, possible improvements are discussed.

A survey test method was developed for measuring the airborne and impact sound insulation and the noise from equipment in buildings. The method is based on manual scanning to obtain the average sound pressure level in a room and on the use of tabular reverberation time data. The uncertainty produced by manual scanning is quite small. The influence of the reverberation time table can also be kept small if a certain complexity of the table is taken as the limit of simplification. Furnished rooms, and several types of unfurnished room constructions are therefore treated separately. The basic principle of the CEN survey method was recently agreed upon by the working group responsible. Additional field measurements should be carried out with reference to ISO 140-4, –5 and –7 to obtain more reliable data on the accuracy in all cases of furnished and unfurnished rooms. If, with reference to the methods of ISO 140, the preliminary estimated uncertainty of single number quantities of ±2 dB proved to be correct, the CEN survey method would be a useful alternative for measurements and verification tests in the field. As to the measurement of noise from housing equipment, some open questions remain to be solved.