Phased Geometrical Acoustics using Low / High Frequency Reflection Coefficients with Applications to Absorption Measurements

The prediction of sound and noise in everyday environments is of utmost importance for comfort as well as for personal health. Although measurements give invaluable information about the behavior of existing environments, designers and engineers are also in need of predictive models that are both accurate and efficient. These simulations provide detailed analysis before construction or prior to renovations and thus yield a huge return on investment. Geometrical acoustics (GA) simulations are used throughout industry for the design of acoustic comfort in offices, classrooms, concert halls, music studios and more. Despite its prevalence, limitations of geometrical acoustics methods are still present. Most deficiencies stem from the high frequency assumptions of the method, meaning that GA traditionally only calculates the sound energy and is only an approximation to the wave equation. Expanding geometrical acoustics to lower frequencies by adding wave behavior such as scattering, diffraction and interference -- phenomena that are common in everyday experience -- is a need by practitioners and an important aim for researchers. A main focus of this work is on interference effects, which requires phase information so that sound pressures can be calculated instead of energy. An important source of information for phased geometrical acoustics comes from reflections from acoustical boundaries. While a plane wave assumption is valid at high frequencies, sound propagates more as a spherical wave when obstacles/walls/observers are close to the source, making spherical wave reflection coefficients important for low frequency sound prediction in geometrical acoustics. Including this behavior is more accurate and results in changes to acoustic parameters that are clearly noticed by most listeners. Previous work has shown that the uncertainty in sound absorption data has a strong influence on the accuracy of geometrical acoustics simulations. It is even known that the uncertainty in measured absorption coefficients alone is enough for simulations to give audible differences. This puts great importance on improving measurement techniques of acoustic absorption coefficients or even coming up with new methods. This motivates the second part of this thesis, which works to combine phased geometrical acoustics models with absorption measurement techniques.

Jaar van publicatie:2017

Toegankelijkheid:Closed