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Computer Modeling of a Large Fan-Shaped Auditorium

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

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Title: Computer Modeling of a Large Fan-Shaped Auditorium


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
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4
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 users web page)
  • Coupled room
  • Transmission coefficients for some surfaces

5
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6
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

7
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8
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

9
Comparisons
CATT Model
EASE Model
C-50 C-80 STI
Measured -2.89 -0.81 0.47
CATT -.21 2.8 0.58
EASE -3.45 -0.18 0.57
Measured
10
Source Omnidirectional loudspeaker
Receiver KEMAR manikin with microphones at
opening of artificial ear canal
11
Refining Absorption in the Model
  • Experimentally measure absorption coefficients
    for surfaces that have a large effect on total
    absorption
  • Seats
  • Seated Audience
  • Ceiling treatment

12
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)

13
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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