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@PHDTHESIS{MllerTrapet:540025,
      author       = {Müller-Trapet, Markus},
      othercontributors = {Vorländer, Michael and Embrechts, Jean-Jacques},
      title        = {{M}easurement of surface reflection properties : concepts
                      and uncertainties},
      volume       = {23},
      school       = {RWTH Aachen, Dissertation},
      type         = {Dissertation},
      address      = {Berlin},
      publisher    = {Logos-Verl.},
      reportid     = {RWTH-2015-05681},
      isbn         = {978-3-8325-4120-0},
      series       = {Aachener Beiträge zur technischen Akustik},
      year         = {2015},
      note         = {Druckausgabe: 2015. - Auch veröffentlicht auf dem
                      Publikationsserver der RWTH Aachen University 2016;
                      Dissertation, RWTH Aachen, 2015},
      abstract     = {Although the quality of room acoustic simulations has
                      increased significantly in recent years, an entirely
                      realistic result is seldom achieved in complex scenarios.
                      Among the factors influencing the degree of realism of such
                      simulations, the boundary conditions concerning sound
                      reflection are considered most important as they determine
                      the sound field to a great extent. Standardized measurement
                      methods exist but they contain inherent uncertainties or do
                      not always yield enough information for a correct modeling
                      of the sound field. To ameliorate the situation, acoustic
                      measurement techniques related to the absorbing as well as
                      the scattering properties of architectural surfaces are
                      investigated in this thesis.The research is divided into two
                      parts: the first part consists of determining the most
                      relevant causes of uncertainty for the standardized
                      measurement methods of random-incidence absorption and
                      scattering coefficients. The difficulties of obtaining
                      accurate results that are often encountered in practice are
                      explained by analytically relating the variation of the
                      input quantities --- such as sample surface area or
                      reverberation time --- to the variation of the absorption
                      and scattering coefficient. Special focus is set on the
                      spatial variation of reverberation times as the primary
                      uncertainty factor. The predicted uncertainty is
                      successfully validated with measurements in both full-scale
                      and small-scale reverberation chambers. Based on the
                      uncertainty analysis, a method is developed to determine the
                      necessary minimum number of source-receiver combinations in
                      the sound field to ensure a specified precision of the
                      absorption or scattering coefficient.The second part of the
                      thesis focuses on signal processing steps related to the
                      measurement of angle-dependent reflection properties in the
                      free-field. For this purpose a hemispherical microphone
                      array is described and validated in this thesis.
                      Improvements to the subtraction method are presented that
                      allow to include the source and receiver directivity. Sound
                      reflection models of different accuracy and calculation
                      complexity are considered to deduce the surface impedance
                      from measured reflection factors. Array processing
                      techniques are investigated as an alternative method to
                      obtain a source reference signal in-situ and to process the
                      spatial response of the reflection measurement.Measurements
                      show that the array setup can be used to obtain the
                      angle-dependent absorbing properties of samples with few
                      source positions. The results indicate that for receivers
                      close to the surface the simplified plane wave model should
                      not be used as it leads to large errors, especially at low
                      frequencies. Some uncertainty remains in the phase angle of
                      the complex reflection factor, which is due to incomplete
                      knowledge of the source and receiver positions. Nonetheless,
                      relatively stable results can be obtained even for samples
                      of finite extent. With the help of array-processing methods,
                      the setup can also be used to determine the directional
                      diffusion and scattering coefficient of small samples,
                      yielding the same result as established far-field methods.},
      cin          = {613510},
      ddc          = {621.3},
      cid          = {$I:(DE-82)613510_20140620$},
      typ          = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
      urn          = {urn:nbn:de:hbz:82-rwth-2015-056810},
      doi          = {10.18154/RWTH-2015-05681},
      url          = {https://publications.rwth-aachen.de/record/540025},
}