Study on measurements of acoustic properties of turf and typical surfaces and on characteristics of sound propagation above turf field

摘要

Turf fields in a foot ball stadium and grass filed in a university campus were chosen as thernrepresentative ground surfaces with soft impedance, and some sites and objects werernchosen for basic field measurements of acoustical properties on sound reflection orrnabsorption by using a pair of particle velocity sensor and a microphone. Also investigationsrnof sound propagation above the turf field were carried out. Acoustical properties of the turfrnfields have typical characteristics of porous materials: acoustic impedance values are highrnat low frequency and decrease as they reach the value in the air at higher frequency. Theirrnsound absorption coefficients are increased by increasing frequency. In frequencyrncharacteristics of sound propagation, wide and deep dips were shown clearly at low andrnmiddle-range frequencies, at 300-1kHz for distance 10m-80m, caused by the interferencernbetween direct sound and reflected sound from the turf surface. As for application study,rncalculations on sound propagation above turf field were done using acoustic impedancernvalues obtained by measurements and ideal estimations. For fair matches of calculatedrnfrequency characteristics of sound propagation to those measured in fields, re-analyzing ofrnthe acoustic impedance by ideally changing of geometrical surface to the equivalent soundrnreflection surface are proposed. Moreover, the experiments of the sound propagationrnconstant and the acoustic impedance were done using a sound tube for the samples cut outrngrass as the fundamental study. Some obtained acoustical properties in this study and fairrncalculation ways for sound propagation characteristics on turf fields are introduced.