## 1 Introduction
Furthermore, if the floor impact sound insulation performance does not meet the standards set forth in the official guidelines, the inspection authority may recommend corrective measures, such as additional construction or compensation for damages, to the project owner. These changes in the floor impact sound regulations necessitate the implementation of corresponding administrative procedures, and the project owner will incur additional burdens in terms of manpower, resources, and time to comply with the evolving standards. With the introduction of the post-certification system for floor impact sound in multi-family housing, the most significant changes have occurred in two main areas. The first change concerns the impact source. In the pre-certification system, the standard impact force characteristics of a one-person hanging machine, as specified in KS F 2810-2 [14], were used. However, under the post-certification system, a rubber ball--as referenced in both KS F ISO 16283-2 [15] and KS F 2810-2--is employed. The second change involves the method of evaluating floor impact sound. In the pre-certification system, the frequency octave band results, as outlined in KSF 2863-1 and KS F 2863-2 [16; 17], were used to calculate a weighted floor impact sound level (\(L^{\prime}_{i,Fmax,AW}\)) using an inverse A-weighted curve to derive a single numerical rating. However, under the post-certification system, the single numerical rating for floor impact sound is derived by applying A-weighting maximum floor impact sound level (\(L^{\prime}{}_{iA,Fmax}\)) through the A-weighted 1/3 octave band correction, as specified in KSF ISO 717-2. The third change concerns the classification of floor impact sound; specifically, the distinction between lightweight and heavy-impact sounds. In the pre-certification system, the minimum threshold for heavy-impact sound was set at 50 dB, whereas under the post-certification system, this minimum threshold has been revised to 49 dB. Various studies have been conducted in relation to the changes in the measurement and evaluation methods for floor impact sound in multi-family housing. One study analyzed the correlation between the use of the banging machine employed in the pre-certification system and the rubber ball used in the post-certification system in a multi-family housing unit with a slab thickness of 120 mm [18; 19; 20]. The results indicated a coefficient of determination (R\({}^{2}\)) of 0.76 between the two indicators. Furthermore, studies on the correlation of floor impact sound among various impact sources [21; 22; 23; 24; 25; 26; 27] have suggested that the characteristics of the impact sound from different sources can affect the floor impact sound insulation performance. The evaluation method used to derive the single numerical rating for the resulting impact sound, along with the impact source, may cause variations in the values obtained [28; 29; 30; 31; 32]. Therefore, further research is required to objectively measure and evaluate the impact sound reduction performance of resilient materials floor structures. Furthermore, when deriving the single number quantity for floor impact sound, it is essential to analyze the correlation between impact sources and evaluation methods. The presentation of such results suggests that the project owner in multi-family housing will be able to identify frequency bands that are particularly susceptible to floor impact sound. By analyzing the vulnerable frequency bands of the floor structure, strategies for improvement can be designed. From the perspective of residents, it is expected that the high-performance design of floor resilient materials structures by the project owner will minimize the adverse effects of floor impact sound. Therefore, in this study, the analysis was conducted on heavy-impact sound in multi-family housing units in South Korea with a minimum floor area of 16 m\({}^{2}\) and a maximum of 84 m\({}^{2}\).