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Completed Project

Effect of Diffusers on Sound Field Diffusivity in a Reverberation Chamber

Nathaniel Ross, Vassar College ’18, Samuel Gilbert, Vassar College ’18, José Herrera Jr., Vassar College ’18, Mallory Morgan, Vassar College ’17, Jonathan Snyder, Vassar College ’18, Jacob Adelgren, Vassar College ’15, Gabriel Kardos, Vassar College ’19 and Prof. David T. Bradley

An ideal diffuse sound field is one in which all acoustic properties are independent of position (homogenous) and invariant with respect to direction (isotropic). In acoustically sensitive spaces, such as performing arts halls and classrooms, it is important to achieve the appropriate level of sound field diffusivity and to accurately quantify that diffusivity. Diffusers, which are rough surfaces that disperse sound temporally and spatially, are often incorporated into such spaces to achieve a more diffuse sound field. The state-of-the-art currently quantifies a diffuser’s spatial dispersion using the diffusion coefficient. There is currently no method for quantifying diffusivity as a function of any diffuser quantifier, including the diffusion coefficient. Computational models that characterize the effect of the diffusion coefficient on sound field diffusivity exist, but corresponding experimental data do not.

In the current project, an increasing number of diffusers have been installed in a half-scale reverberation chamber, which is a room used to measure various acoustics quantities. Data have been collected for various configurations of two types of diffusers using two measurement techniques. In the first measurement technique, a linear three-dimensional microphone grid was used to characterize homogeneity based on the relative standard deviation of sound decay rate, according to measurement standard ASTM C423. In the second measurement technique, a spherical microphone array was used to characterize isotropy; however, a quantifier for isotropy has yet to be developed. Preliminary data suggest that a greater number of diffusers actually decreases sound field homogeneity if steps are not taken to control for the absorptive behavior of the diffusers. It is anticipated that the measured data will aid in achieving the long-term goal of developing a single objective measure that characterizes both the homogenous and isotropic aspects of sound field diffusivity.