Comparative study of sound transmission loss enhancement in double-leaf walls using inertial amplifier and resonator

This paper investigates the sound transmission loss (STL) characteristics of double-leaf walls incorporating different mechanical impedance elements within the cavity, including a spring, a spring–mass–spring (SMS) resonator, and an inertial amplifier (IA). This study presents a novel investigation of cavity-integrated spring–mass–spring resonators and inertial amplifiers for enhancing the sound transmission loss of double-leaf walls, together with their systematic optimization under an equal-mass constraint. A theoretical model is developed and validated through impedance tube experiments performed on baseline single-leaf and double-leaf walls, together with modified double-leaf configurations containing a spring, a SMS and an IA resonator in the air gap. A genetic algorithm-based optimization is further carried out to identify the optimal resonator parameters for the different configurations while maintaining a constant total mass of the wall and inserted mechanism. The results show that all mechanical insertions significantly enhance the STL relative to the baseline double-leaf wall. The optimized spring, SMS resonator, and IA configurations provide net STL improvements of 30%, 37.4%, and 40.3%, respectively. Although the IA yields the highest improvement, its advantage over the SMS resonator is found to be marginal, while both configurations exhibit superior sound insulation to the spring configuration. A parametric investigation reveals that increasing spring stiffness improves STL in the cavity-controlled region, whereas increasing the SMS auxiliary mass enhances low-frequency performance but introduces a pronounced resonance peak. For the IA configuration, increasing the inclination angle between the rod and spring reduces STL, while increasing spring stiffness produces the opposite effect. The increase in auxiliary mass improves STL in the mid-frequency range, but this benefit diminishes in the pre-coincidence region due to the dominance of plate impedance. The study highlights the effectiveness of embedded mechanical impedance elements for enhancing acoustic insulation and provides guidance for the optimal design of lightweight double-leaf wall systems.