共鳴器仕様の違いが重量床衝撃音遮断性能に及ぼす影響に関する実験的検討

－Helmholtz共鳴器を有する高性能乾式遮音二重床の開発　その２－

抄録

 We have developed a high-sound-insulation double floor structure using Helmholtz resonators, along with a two-particle theory to predict the vibration characteristics of the structure. In this paper, experiments using a small unit structure partially taken out from the whole double floor structure were performed as a first step to thoroughly grasp the actual vibration phenomenon. Helmholtz resonators were made of square lightweight steel pipes and particle boards. The main findings obtained through the experiments are summarized below.
 To obtain clear two peaks and one dip in the vibration transmissibility as calculated from the two-particle theory, the following items are important.
 (i) The rigidity of the resonator walls should be sufficiently large.
 (ii) The excess damping in the resonator necks should be restrained by some measures such as increasing the number of the necks.
This excess damping in item (ii) is probably due to the short distance between the opening of the resonator neck and its facing wall.
 Regarding other factors affecting the vibration transmissibility, the following items were confirmed.
 (iii) The horizontal displacement of the resonator necks hardly affects the vibration transmissibility.
 (iv) The vertical displacement of the resonator necks hardly affects the vibration transmissibility when the resonator walls are sufficiently large.
 (v) The effects of other factors such as the neck length and neck number are qualitatively predictable by the two-particle theory if the above-mentioned items (i) and (ii) are satisfied.
 In addition to the experiments, to improve the predictability of the vibration characteristics by the two-particle theory, various damping effects in the double floor structure were investigated through identification of the effective values of the damping coefficients used in the two-particle theory. The findings are summarized below.
 (vi) The calculation results with the identified values and the measured results were consistent well.
 (vii) The identified values of the damping coefficients for the vibration-isolating rubbers and resonator necks were several times larger than the theoretical values. When Helmholtz resonators are used for vibration control, it should be noted that the damping effect is different from that for sound absorption use.
 (viii) As for the damping coefficients for the perimeter of the double floor structure, large differences in the identified value were observed among the unit structure samples. It is important to stably control the construction conditions for the perimeter of the double floor structure.
 (ix) All identified values of the resonator neck end correction were 0. This is probably because the distance between the opening of the resonator neck and its facing wall is too short and the movement of the air mass in the neck is considerably restricted.
 In future works, we will investigate various effects caused by the spread plane floor, i.e., the effects of the natural vibration and bending of the floor slab and the upper floor structure on it.