ランダム入射吸音率測定におけるエッジ効果回避のためのDeep-well処理

概要

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Errors and scatters in usual absorption measurement in a reverberation room are mainly caused by non-diffusion condition and edge effect, which unfortunately differ from room to room. This paper presents a method termed"PLD/Deep-well"which eliminates these error sources and finally yields random incident absorption coefficient, α_∞, by two procedure:(1)mounting"Deep-well, "reflective panel taller than the thickness of the specimen, closely around its perimeter to eliminate the edge effect, and(2)applying"PLD(Power-law decay)approach"which compensates the lack of diffusion including what may be aggravated by procedure(1)through numerical evaluation of the curvature on the space-ensemble average decay process{<S^2(t)>}_<NO>, i.e., through direct prediction of total room absorption for perfect diffusion. Several α_∞ measurements were made to examine the validity of the proposed method, as well as computer simulation to confirm it from the qualitative viewpoint. The results imply the method gives α_∞ with high precision and reproducibility, independent of the area, shape and location of the specimen, diffusion condition, and the height of the well H only if H≧H_0+t, where t is the thickness of the specimen and H_0 the minimum required height of the well which turned out about 0.8 m for usual reverberation room.
社団法人日本音響学会の論文