Whenever the noise source level or the expected acoustic comfort increases for diesel engines for example or for premium petrol vehicles, the required weight per unit area can be specified above 2000 g/m2 for the equivalent barrier of a mixed absorbing-insulating noise treatment. For an ABA foam/heavy layer/felt insulator, this is not a big issue, one has to increase the intermediate heavy layer weight. For hybrid stiff compressed felt backfoamed standard technologies, going above 2000 g/m2 is critical due to absorption properties loss following much too high airflow resistances and progressive porosity loss (above 250 kg/m3) as well as too high bending stiffness presenting resonant modes progressively and assembly manipulation issues. Last but not least, compressed felts begin to present too high costs at these weights against those of the heavy layers of ABA systems.
The chips urethanes give an answer to the aforementioned issues for high weights above 2000 g/m2 up to 3500 g/m2 typically for hybrid stiff backfoamed concepts in the same mold and with the same process as lower weights (called Polyfoam). The acoustic properties of these highly compressed chips urethane with standard isocyanate binder are good, even better with bi-component fibers, but the costs remain often too high against ABA systems. The Ecofelt tunable insulator is another answer to this high weights range above 2000 g/m2 up to 3500 g/m2, and even above, while maintaining the same processes and molds as for the light standard hybrid stiff insulators. The lay-up consists of a first compressed stiff felt layer of 1300 g/m2 8 mm thick typically backed by the powdered scraps of 400 g/m2 to 1200 g/m2 typically (and above) and backfoamed by an injected soft PUR foam of 50 kg/m3 classically.
The mass per unit area of the scraps allows to adjust the insulation performance and also to localize it where needed, whenever the upper felt is sufficiently stiff. Knowing that these carpet and heavy layer scraps are almost always available in manufacturing plants due to the 30% average cut out waste of carpets or trunk trims processes, these recycled materials are almost for free as long as they are not transported. This paper will show the acoustic performance of this Ecofelt tunable insulator technology on both laboratory flat samples and dash insulator parts measured in coupled reverberant rooms or in vehicle and also simulated using poroelastic finite elements.