Floor impact noise reduction in ship cabins by means of a floating floor

Floating floors are widely used to reduce the floor impact noise in ship cabins as well as in multi-dwelling buildings. The most common material for impact absorption in floating floor structure is mineral wool, where high density and sufficient thickness is also needed for fire-resistant requirement in ships. For proper design of floating floors, it is essential to understand how the performance of floating floor is affected by the design parameters such as changes of the mineral wool thickness, density, fiber direction and the use of viscoelastic layer. In this paper, noise reduction performance of the floating floor for use in cruise ship cabin is studied. A mock-up is built by using 6 mm steel plate, and two identical cabins are made of 25 mm sandwich panel inside the steel structure. Various floating floor systems are tested by employing the mock-up. The measurements show that viscoelastic layer is effective when it is used to form a constrained layer. However, viscoelastic layer becomes insignificant when mineral wool is present. It is found that impact noise becomes quieter by 7 dB when fiber direction of the mineral wool is changed from vertical to horizontal, and increasing density of mineral wool from 140 kg/m³ to 240 kg/m³ results in an increase of 9 dB. It is also observed that floor SBN (Structure-Borne Noise) is greater than side wall SBN by 10–15 dB up to 2000 Hz, which means that side wall SBN can be neglected in evaluating floor impact noise of ship cabin at frequencies up to 2000 Hz.