In order to discuss acoustical quality of sound fields in a forest, measurements were carried out obtaining four orthogonal factors [Y. Ando, J. Acoust. Soc. Am. 74, 873-887 (1983)]. Results were compared with those in a concert hall. In the forest, for example, the subsequent reverberation time, T_(sub) was 1.66 s (500 Hz), and the interaural cross correlation (IACC) was 0.44 (1 kHz) at a point 40 m from the source. Such an outdoor space has specific acoustic properties being blended for certain sound sources involving the middle and higher frequency ranges. It was found that the value of the width of the interaural cross-correlation function, W_(IACC), which is related to the apparent source width (ASW) of sound fields in the forest, was smaller than that in the concert hall.
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