Characterisation of noise counter-measures for cabin floors

A growing attention has been devoted to acoustical problems on board of ships, particularly in connection with the recent, extensive production of high standard cruise vessels. Severe specifications on the maximum noise levels in the various areas of the ship and in particular in the living and working areas are now common. This brought the need, since the first steps of the design, for a careful acoustical planning, based on a detailed analysis of the various elements of the “acoustic circuit”. This approach implies in general to consider sources on board (power and location), transmission paths and receiving positions. The work concentrates on the final part of the transmission path and regards the anti-noise measures that are utilised for the cabin walls (particularly on the floor) to reduce the noise radiated inside the room. Such measures have been applied since a long time by the shipyards, but mostly with empirical methods, based on a trial-and-error procedure. The aim of the present work is to summarise the physical concepts that are at the bases of the noise counter-measures and to review the physical quantities that can be used to quantify their effectiveness. The case of the application of viscoelastic materials in a constrained layer arrangement to the cabin floor is discussed in particular, with a description of the main material and geometrical parameters and an evaluation of their influence on the performance of the treatment. A description is included of a simplified procedure for a comparative testing of different viscoelastic materials and of some results of this procedure.