Application of the ISO 13472-1 in situ technique for measuring the acoustic absorption coefficient of grass and artificial turf surfaces

This paper presents the applicability of an in situ technique based on ISO 13472-1 standard for measuring the acoustic absorption coefficient of grass and artificial turf surfaces for normal incidence from a sound source. The in situ method is based on acoustic impulse response measurement of the material surface. A maximum length sequence (MLS) signal is played through a loudspeaker and the acoustic response from the surface is recorded using a single microphone. The fast Hadamard transform and fast Fourier transform based digital signal post-processing algorithm provides the acoustic absorption coefficient of the surface under test. The normal incidence acoustic absorption coefficient of a commercial artificial quash surface of Dow Co. obtained from this method was compared with the results from the ASTM E1050 impedance tube method for the same surface. The acoustic absorption coefficients of a test-site grass surfaces were measured for 30 mm and 100 mm length of grass blades in wet and dry soil conditions. Substantial difference in the acoustic absorption coefficient was observed for a similar grass-like artificial surface used for estimating sound power of commercial garden equipments and lawnmowers. The advantage of the in situ method lies in its ability to measure the normal incident acoustic absorption coefficient of any planar surface as installed or in situ. Additionally a quick testing time of less than a minute with the use of a laptop sound card based inexpensive data acquisition system is the main feature of this robust method.