title: In situ measurements of the oblique incidence sound absorption coefficient for finite sized absorbers.
abstract: Absorption coefficients are mostly measured in reverberation rooms or with impedance tubes. Since these methods are only suitable for measuring the random incidence and the normal incidence absorption coefficient, there exists an increasing need for absorption coefficient measurement of finite absorbers at oblique incidence in situ. Due to the edge diffraction effect, oblique incidence methods considering an infinite sample fail to measure the absorption coefficient at large incidence angles of finite samples. This paper aims for the development of a measurement method that accounts for the finiteness of the absorber. A sound field model, which accounts for scattering from the finite absorber edges, assuming plane wave incidence is derived. A significant influence of the finiteness on the radiation impedance and the corresponding absorption coefficient is found. A finite surface method, which combines microphone array measurements over a finite sample with the sound field model in an inverse manner, is proposed. Besides, a temporal subtraction method, a microphone array method, impedance tube measurements, and an equivalent fluid model are used for validation. The finite surface method gives promising agreement with theory, especially at near grazing incidence. Thus, the finite surface method is proposed for further measurements at large incidence angles.
authors.affiliation: Müller-BBM GmbH, Robert-Koch-Strasse 11, Planegg, 82152, Germany.
authors.forename: Marco
authors.initials: M
authors.lastname: Ottink
authors.affiliation: Acoustic Technology, DTU Electrical Engineering, Technical University of Denmark, Ørsteds Plads 352, DK-2800 Kongens Lyngby, Denmark.
authors.forename: Jonas
authors.initials: J
authors.lastname: Brunskog
authors.affiliation: Acoustic Technology, DTU Electrical Engineering, Technical University of Denmark, Ørsteds Plads 352, DK-2800 Kongens Lyngby, Denmark.
authors.forename: Cheol-Ho
authors.initials: CH
authors.lastname: Jeong
authors.affiliation: Acoustic Technology, DTU Electrical Engineering, Technical University of Denmark, Ørsteds Plads 352, DK-2800 Kongens Lyngby, Denmark.
authors.forename: Efren
authors.initials: E
authors.lastname: Fernandez-Grande
authors.affiliation: Lloyds Register Consulting-Engineering Dynamics, Strandvejen 104A, DK-2900 Hellerup, Denmark.
authors.forename: Per
authors.initials: P
authors.lastname: Trojgaard
authors.affiliation: Brüel and Kjær Sound and Vibration Measurement A/S, Skodsborgvej 307, Nærum, DK-2850, Denmark.
authors.forename: Elisabet
authors.initials: E
authors.lastname: Tiana-Roig