枠組壁工法による床の振動と騒音の特性 : タッピングマシンによる衝撃の場合

A test wood joist floor was constructed with the two by four construction system. Floor size was 3700×2850 mm. Nominal 2 by 6 inch joists, spaced 18 inches, were straight-nailed. Plywood was laid with staggered joints with the longer sides perpendicular to the joist span. The floor was impacted with a tapping machine. Vibrations and noise of the plywood floor were measured before and after addition of carpeting.
The distribution of acceleration level generally showed radial decay but this decay did not show at low frequencies. The floor vibrated with nodes at the joists and antinodes at the plywood surface between joists. The difference of levels was about 6 dB. On the addition of carpet, vibration was damped above 500 Hz. The main effect of carpet on vibration was assumed to be absorption of impact energy. The impact sound level of the floor had a peak value at about 85 dB at 160-250 Hz above the floor. The spectrum was simllar to the vibration spectrum near the impact source. Below the floor, impact sound level showed a different spectrum from that found above the floor. This result was attributed to room modes being excited below the floor.