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Computer Modeling of a Large Fan-Shaped Auditorium

Explore the complexities of modeling a large fan-shaped auditorium, with insights on absorption and scattering coefficients, challenges faced, refining strategies, and comparisons with CATT and EASE models.

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Computer Modeling of a Large Fan-Shaped Auditorium

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  1. Computer Modeling of a Large Fan-Shaped Auditorium Heather Smith Timothy W. Leishman Acoustics Research Group Department of Physics & Astronomy Brigham Young University

  2. Auditorium Characteristics • Large • Seats 21,000 people • Volume = 11,400,000 cu. ft • Fan-shaped • Curved and concavely oriented surfaces toward the rear of the hall based primarily on one center of curvature • Coupled Spaces • Large cavity behind the rostrum • Large cavity above the canopy ceiling • Transparent surfaces • Façade side walls • Façade ceiling • Large skylights

  3. Challenges in Modeling this Auditorium • Large number of faces • Curved surfaces approximated with planar surfaces • Sensitive to absorption & scattering coefficients • Large surfaces • “If in doubt, try with both high and low values [for scattering coefficients] and see if the results are sensitive or not (it depends on the hall shape and the absorption distribution and is very difficult to know in advance).” - Bengt-Inge Dalenbäck (CATT user’s web page) • Coupled room • Transmission coefficients for some surfaces

  4. Absorption Coefficients • Used published absorption coefficients when possible • Otherwise estimated values using similar materials or rough averaging • Used cumulative absorption curves to determine contributions of surfaces to total absorption • Because of their contributions to total absorption, larger surfaces are very sensitive to absorption coefficient choices

  5. Scattering Coefficients • Little or no published data on scattering coefficients for surfaces • Approximating scattering coefficients • Use approximations suggested by various authors • Measure surface dimensions and compare to the wavelength • Limitations of approximations • Do not specify which three-dimensional surface dimension(s) to use • Vague in assignment of scattering coefficient values based on the wavelength/surface dimension ratio

  6. Comparisons CATT Model EASE Model Measured

  7. Source: Omnidirectional loudspeaker Receiver: KEMAR manikin with microphones at opening of artificial ear canal

  8. Refining Absorption in the Model • Experimentally measure absorption coefficients for surfaces that have a large effect on total absorption • Seats • Seated Audience • Ceiling treatment

  9. Refining Scattering in the Model • Work to obtain better scattering coefficient values for important surfaces (i.e., seats, seated audience) • Experimental • Measure scattering coefficients in reverberation chamber using proposed standard ISO/DIS 17497-1 • Numerical • Use BEM package to predict scattering coefficients • Analytical • Solutions for arrays of simple scatterers (e.g. spheres)

  10. Conclusions • It appears to be feasible to model a very large hall using commercial geometric acoustics packages • Models need more refining in order to better match the measured results • Additional work is needed to determine more accurate values for scattering and absorption coefficients of surfaces

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