木の音色に関する研究(2) : 粘性項を考慮したTimoshenko式による木材音響スペクトルの解析

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  • キ ノ ネイロ ニ カンスル ケンキュウ 2 ネンセイコウ オ コウリョシタ

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The dependence on frequency of sound pressure level radiated from the free end of a cantilever was caliculated using viscoelastic timoshenko equation. The effects of specific gravity (γ), specific dynamic Young's modulus (E/γ), tanδ, value of E/κG and height of beam (h) on the sound spectrum for longitudinal and radial specimens were also estimated in a wide frequency range. At lower frequencies, where shearing deformation is negligible, the sound pressure level (PL) could be represented by the following formula : PL (dB)=-Alog (γ×tanδ×h×√<E/γ>) where, A is constant. With elevation of vibration mode, peak sound pressure level decreased linearly as frequency increased logarithmically. The degree of decreased in peak level in both longitudinal and radial specimens was independent of variations in γ and tanδ, whereas it was magnified with increasing value of E/κG. It is speculated that E/κG contributes to the tone quality of radiated sound from wood in proportion to a share of shearing deformation in the deflection of beam.

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