|
akutek.info |
|
The Acoustic www Conference site |
|
Methods for computer assisted prediction of acoustics is very important to research in the field of room acoustics, and for development and design of new performance spaces. Computational capacity in computers has increased since Krokstad et al started out in the 1960’s, but so have our demands. Prediction of reverberant sound Reverberant sound affects the perception of room acoustics in many ways, and is physically very complex. For frequencies higher than the absorption-dependent Schroeder Frequency Fc~2000·(T/V)1/2 ~800/A1/2 , where, T is the reverberation time, V the volume in cubic meters, and A the total (Sabine) absorption area of the room, the reverberant sound field is dominated by conditions that can be predicted by geometrical acoustics (GA), e.g. with ray-tracing methods. This means that sound in many ways acts like light, only with slower propagation speed, and thus sound rays and sound particles can be helpful models in frequency domain and time domain respectively. In a 20.000 cubic meter hall with T~2.0s, the Schroeder frequency is 20Hz, so GA applies in the practical frequency range of most concert halls. For frequencies lower than Fc, modes can be expected to dominate the room acoustic conditions, thus wave acoustics must be taken more into account, especially to predict the effects of standing wave patterns (hot spots, cold spots) over the room and peaks and dips in the frequency response. In practice this is significant to recording studios and rehearsal rooms. Effectivity of absorption The conclusion from the paper Diffusivity and its effect on concert hall seat absorption is presented below: Different rooms have different diffusivity. Therefore, one and the same absorbing surface, e.g. concert hall seats, will in general have different effective absorption coefficients. We have to deal with three different sets of absorptions coefficients when predicting acoustics, namely the input coefficients in the prediction algorithm, the lab-test coefficients, and the in-situ coefficients. A sound absorbing object does not have absolute absorption coefficients. There exists only relative absorption coefficients, related to the measuring conditions, whether in different laboratories, or in different halls as measured in-situ. This paper suggests a method to predict the relation between absorption coefficients. In concert hall planning this method can be used to take diffuse field differences between laboratory and a concert hall into account. (more) Computational Acoustics (misc papers) NEW! An improved low frequency radiation model for finite sound reflectors by Rathsam et.al Acoustical Modelling with Sonel Mapping, by Kapralos, Jenkin and Milios. 25.09.2007 Edge Diffraction in Room Acoustics Computer Modeling, by Peter Svensson and Paul Calamia An Improved Energetic Approach to Diffraction Based on the Uncertainty Principle, by Uwe Stephenson and Peter Svensson. 21.09.2007
|
|
Computational acoustics |
