The noise treatments weight reduction strategy, which consists in combining broadband absorption and insulation acoustic properties in order to reduce the weight of barriers, depends strongly on surface to volume ratio of the absorbing layers in the reception cavity. Indeed, lightweight technologies like the now classical Absorber /Barrier /Absorber layup are extremely efficient behind the Instrument Panel of a vehicle, but most of the time disappointing when applied as floor insulator behind the carpet.
This work aims at showing that a minimum of 20 mm equivalent “shoddy” standard cotton felt absorption is requested for a floor carpet insulator, in order to be able to reduce the weight of barriers. This means that a pure absorbing system that would destroy completely the insulation properties and slopes can only work, if the noise sources are extremely low in this specific area, which is seldom the case even at the rear footwells location. The proposed Carpet hybrid foam spacer technology is answering to the question by using the hybrid foam-foam 3D solution, applied as floor insulator with encapsulated rigid EPS or EPP foam spacers in the PUR foam spring layer, depending on the overall available thicknesses.
The ultra-absorbing properties are obtained thank to the upper dense (90 to 140 kg/m3), resistive, tortuous and stiff foam layer having an average thickness of more than 15 mm up to 20 mm. The latter layer is also working as an equivalent barrier of its weight per unit area thank to its bending stiffness and to the airtight hybrid intermediate interpenetration layer between the upper absorbing and lower insulating foam layers (18 dB/oct slopes). All existing floor insulator technologies will be compared to one another using the Finite Transfer Matrix Method, as well as poroelastic finite elements method for various overall thicknesses from 30 mm to 100 mm. A Ray-Tracing model will be used as well, in order to quantify the absorption effects at ear point of this floor carpet insulator.