In order to improve the floor impact sound insulation of a cross laminated timber (=CLT) floor slab, several variations of double ceiling systems with cross laminated timber panels of its thickness 90mm were attached under the CLT floor slab. These floor and ceiling specimens were installed in the laboratory, and their floor impact sound levels were measured. Results of those experiments are as follows.
(1) In case of attaching a double ceiling system of CLT panels of panel thickness 90mm with its air back cavity thickness 120mm and closed, heavy/soft floor impact sound levels didn't increase in 63Hz band. This result is different from the case of the common double ceiling system with gypsum boards. In this case, heavy/soft floor impact sound insulation performance was almost the same to that in case without a ceiling system. On the contrary, about 10dB improvement was observed in light floor impact sound insulation performance.
(2) As for the same CLT panel double ceiling system, in case of attaching a double ceiling system of CLT panels with its air back cavity opened to the sound receiving room in the lower side, air pressure increasing in the back cavity and vibration of ceiling panels were suppressed. However, both heavy/soft floor impact sound level and light floor impact sound level in the sound receiving room became higher than that of the case mentioned above with its air cavity closed. Therefore, to make the air cavity opened to the sound receiving room is quite inadequate for the purpose of floor impact sound insulation.
(3) In case of attaching a double ceiling system of CLT panels with its air back cavity (thickness 158mm) closed to the sound receiving room in the lower side but opened to horizontal direction, air pressure increasing in the back cavity and vibration of ceiling panels were suppressed. In this case, heavy/soft floor impact sound insulation performance was improved.
(4) Further, by loading weights of several sand bags on the upper surface of CLT ceiling panels with its air cavity thickness 196mm and doubling the air opening surface to the horizontal direction, heavy/soft floor impact sound level index (= L number) decreased by eight points from the case without a ceiling system.
