Low-frequency impact sound transmission of floating floor: Case study of mortar bed on concrete slab with continuous interlayer

• Impact sound is isolated above the natural frequency of the floating floor system.
• Coupled wave field of floating floor exerts a strong influence on the impact sound field.
• Decoupled bending wave field disturbs sound insulation in vibration isolation region.
• Non-rectangular acoustic cavity mitigates the influence of axial room modes.

The vibroacoustic behavior of a commonly used floating floor installed in an actual multifamily housing unit was investigated to determine the factors that influence impact sound transmission at low frequencies. A finite element vibration model of the floor structure and an experimental sound field against a rubber ball impact were analyzed in combination. The results indicated that, in addition to isolation of the impact energy above the system's natural frequency, the aspect of coupled and decoupled wave fields of the floating floor influences the impact sound transmission. The coupled wave field below the natural frequency is dominated by the bending wave field of the base slab and exerts a strong influence on the sound field, in which the sound field is dependent on the modal space and impact location of the coupled motion. The decoupled wave fields generated in the floating plate or the base slab above the natural frequency may disturb the vibration isolation. The non-rectangular acoustic cavity is considered to mitigate the influence of axial room modes on the impact sound field.