Against the backdrop of accelerated global aging, urban elderly populations face severe challenges posed by the fracturing of social capital. This study focuses on the restructuring mechanism of singing activities on elderly social networks, innovatively proposing a “behavior-space-network” three-dimensional analytical framework. It reveals for the first time the biosociological pathway through which sound wave synchronization effects catalyze group trust by activating the neural mirror system. Addressing the shortcomings of existing research lacking quantitative tools, this study pioneers a dynamic cohesion index that integrates three dimensions: network density, emotional trust, and reciprocal behavior, breaking through the limitations of traditional subjective measurements. Methodologically, a tracking sample of 300 elderly members was constructed through multi-stage stratified sampling, combining portable GPS trajectory recording, sound spectrum analysis, and social network matrices to establish an empirical testing system with nine formulas. The key innovations lie in: 1) discovering the threshold effect of spatial acoustic comfort, proving that it amplifies the benefits of singing by enhancing sound wave synchronization rates; 2) constructing a causal chain between vocal part rotation intensity and network density; 3) verifying the predictive efficacy of the cohesion index for group persistence. Empirical results show that high-frequency singing significantly increases social network density by 68%, and vocal part cross-training transforms collaboration efficiency into emotional capital through precise reciprocal relationships. The spatial adjustment mechanism reveals that the network density of users in dedicated rehearsal rooms is doubled compared to open-air venues, and walking time ≤ 10 minutes can enhance the behavioral transformation benefit by 53%. The mediation model confirms that sound wave synchronization rates bear 34.8% of the emotional transmission function, while education level amplifies collaboration benefits through knowledge capital. The research contribution lies in establishing a “acoustic coordination-neural activation-capital precipitation” transmission mechanism at the theoretical level, creating a verifiable assessment tool for elderly social capital at the methodological level, and providing quantitative evidence for urban aging-friendly space renovation and cultural pension policies at the practical level.