An in situ transfer function technique for the assessment of the acoustic absorption of materials in buildings

A method for measuring the absorption properties of materials in situ at mid to high frequencies is proposed. It is an adapted version of the well known free-field two-microphone transfer function technique to in situ conditions. The novel features of the method are presented: noise-immune acquisition technique, proper time windowing — both windowing strategy and window choice — practical geometrical transducer setup at oblique incidence. A rigorous study of measurement conditioning as a function of incidence is given using the conformal mapping technique. Experimental results are ultimately provided in realistic in situ conditions showing the viability of the method with comparison to standing wave tube measurements.