A theoretical method based on mutual radiation impedance is proposed to compute the sound absorption performance of a Helmholtz resonator array in the low-frequency range. Any configuration of resonator arrangement can be allowed in the method, while all the resonators may or may not be identical. Comparisons of the theoretical predictions with those done by the past studies or experiments show that the present method can accurately predict the absorption performance in more general cases.

This study aims to examine some kinds of plans to solve the ploblem of noise and vibration transmitted to adjacent rooms, especially to the downstairs, when using SMT (surface mount technology) equipment. To achive this, a kind of system for preventing noise and vibration was applied, and the effects of sound insulation performance for that were tested and analyzed. To reduce floor impact noise, a floating floor system using a plastic pallet and rubber was applied. The applied plastic pallet is 30 cm wide, 60 cm deep, and 6 cm high and designed to array on a concrete slab. Above this plastic pallet, a 14-cm-thick concrete slab was constructed. After installation of this system the floor impact sound was reduced about 7 dB(A). For more reduction, a ceiling with a 5-cm-thick glass wool and twofold of 0.9-cm-thick plywood was constructed at the directly below downstairs. According to this, 4 dB(A) was additionally reduced.

The floating floors used to reduce floor impact sound in European countries are not as compatible with Korean style floors because every residential floor in Korea is heated up by the floor heating method. In this case, considering the floor heat radiation effect, the cement screen is constructed to be about 40 to 50 mm thick. So constructing the low-density damping materials, such as glasswool, under the cement screen over 20 mm definitely makes some cracks. To prevent this kind of floor crack and to improve the impact insulation performance, the floating floor system using a plastic pallet and rubber was developed. The developed plastic pallet is 30 cm wide ×60 cm deep ×4 cm high and is designed to array on a concrete slab; above this plastic pallet, a 2-cm thick thermal insulator is constructed. On this, the insulator heating coil is installed, and finally the 4-cm-thick cement screen is constructed over that. The test results of impact insulation performance for the developed system show good improvement, about 15 dBa between before and after installation of the system.