Haoshuai Suo

Low-frequency impact sound control remains a critical challenge for floating floor systems. Conventional resilient underlayment materials exhibit insufficient damping and are prone to long-term deformation, making stable low-frequency sound insulation difficult to achieve. This study presents the development of a composite floating floor underlayment comprising recycled rubber granules, polymer resin, and quartz sand. Based on the constrained layer damping-inspired (CLD-inspired) perspective, the vibration attenuation and noise reduction mechanism is elucidated, and the material’s physical properties, mechanical behavior, microstructure, and acoustic performance are systematically investigated. The results indicate that excessively large rubber granules aggravate curing shrinkage cracking. Optimal processing characteristics are achieved with a binder content of 20 wt% and a rubber granule size of 50 mesh. Laboratory characterization reveals that, compared with conventional cross-linked polyethylene (XLPE) foam underlayments, the proposed composite underlayment reduces the impact sound pressure level by an average of 3–5 dB in the low-frequency band below 250 Hz, and the overall sound insulation performance is improved by 10.77%. Dynamic mechanical analysis shows the composite storage modulus declines from 280 MPa at −20 °C to 10 MPa at 80 °C, while the loss factor remains above 0.2 under typical indoor conditions. Such stable viscoelastic behavior enables efficient shear dissipation of low-frequency vibration energy under the CLD-inspired mechanism. Full-scale field testing combined with long-term observation over 3000 loading cycles demonstrates excellent structural compatibility between the underlayment and the gypsum screed, with no cracking or appreciable deformation observed during prolonged service. The weighted impact sound improvement index (ΔLw) attains 15 dB. These findings verify that the CLD-inspired composite underlayment simultaneously achieves efficient low-frequency impact sound control and superior long-term structural stability, providing an innovative material solution and design strategy for impact noise mitigation in residential floating floor applications.

Based on the three-parameter approximate JCAL analytical model (hereinafter referred to as the three-parameter model), this study conducted an in-depth analysis of the effects of porosity, median pore size, and pore size standard deviation on the acoustic performance of porous materials and developed a composite porous material composed of glass fibers and zeolite particles. Experimental results indicate that the pore size distribution significantly affects the acoustic performance of fibrous porous sound-absorbing materials. Specifically, smaller pores lead to better sound absorption at mid–low frequencies, with the optimal sound absorption performance observed when the median pore size is between 60 and 80 μm. Increasing the material density and decreasing the fiber diameter help reduce the internal pore size, thereby improving the material’s sound absorption performance. Additionally, the appropriate addition of zeolite can further optimize the internal pore size and effective sound-absorbing interface, thus enhancing the material’s sound absorption performance. When the material density is 120 kg/m³ and the zeolite substitution rate is around 10%, the material exhibits the best acoustic performance, with a noise reduction coefficient (NRC) reaching 0.65, which is a 10.17% increase compared to the material without zeolite. Comparing the simulation data from the three-parameter model with the actual measurement data shows that the model has excellent predictive performance for the sound absorption coefficient (SAC) of single-fiber porous materials (with an error of approximately 5%). However, for composite porous materials, due to the complex changes in interfaces, there is a certain prediction error (with the maximum error reaching 12.81%), indicating that the model needs further optimization and correction when applied to composite materials.