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 the representative ground surfaces with soft impedance, and some sites and objects were chosen for basic field measurements of acoustical properties on sound reflection or absorption by using a pair of particle velocity sensor and a microphone. Also investigations of sound propagation above the turf field were carried out. Acoustical properties of the turf fields have typical characteristics of porous materials: acoustic impedance values are high at low frequency and decrease as they reach the value in the air at higher frequency. Their sound absorption coefficients are increased by increasing frequency. In frequency characteristics of sound propagation, wide and deep dips were shown clearly at low and middle-range frequencies, at 300-1kHz for distance 10m-80m, caused by the interference between direct sound and reflected sound from the turf surface. As for application study, calculations on sound propagation above turf field were done using acoustic impedance values obtained by measurements and ideal estimations. For fair matches of calculated frequency characteristics of sound propagation to those measured in fields, re-analyzing of the acoustic impedance by ideally changing of geometrical surface to the equivalent sound reflection surface are proposed. Moreover, the experiments of the sound propagation constant and the acoustic impedance were done using a sound tube for the samples cut out grass as the fundamental study. Some obtained acoustical properties in this study and fair calculation ways for sound propagation characteristics on turf fields are introduced.