# Experimental/Numerical Acoustic Assessment of Aircraft Beat Headsets Based on Electrospupn Mats
## 1 Introduction
Furthermore, the nanofiber layers act as an acoustic resonance membrane: the nanofibrous membrane resonates at given frequencies, consequently increasing the rate of sound energy conversion into thermal energy. Because of these characteristics and thanks to recent advances in the field of nanotechnology and the introduction of different types of nanomaterials, nanofiber-based sound absorbers are considered a promising solution, especially for aeronautic and automotive applications in which noise reduction requirements in new products are becoming more and more strict. In light of this trend, research effort is devoted to the experimental assessment of the sound absorption properties of nanofiber layers [20; 21; 22]. Reducing in-cabin noise can be achieved by using high performance materials in combination with advanced computational approaches to evaluate upfront the performances of several PNC (Passive Noise Control) implementations. Aircraft interior noise characteristics depend on both the mission profile (comprising run-up, taxiing, take-off, cruise, etc.) and on the type of propulsion. For propeller-driven aircrafts, the dominant noise sources are the rotating fans and the striking pistons, which create periodic sound waves on the fuselage at the known Blade-Passage Frequency (BPF). For jet engine-driven aircrafts (including turbofan, turboprop and turbojet), the primary noise source is the roar of the jet exhaust and the high-pitched noise generated by the engine's turbomachinery system, compressors, and engine blades. In most cases, noise generated by an aircraft engine can be considered as proportional to its exhaust stream velocity. During the cruising phase of the flight, the broadband interior noise due to the Turbulent Boundary Layer (TBL) excitation [23] dominates the overall Sound Pressure Level (SPL) and negatively affects the Speech Interference Level (SIL) inside the aircraft. Grounding on preliminary numerical investigations already presented by some of the authors [22; 24], this work concerns the numerical and experimental investigation of PNC technologies to enhance the acoustic comfort of aircraft seat headrests. A similar investigation can be found in [25], in which a 1:1 fuselage mock-up and BEM simulationswere compared experimentally and numerically, respectively. In [25], nanofiber textiles and lateral caps for the headrests were investigated as two possibilities for reducing the noise for passengers during different flight conditions (take-off, cruise, etc.). Similarly, two PNC concepts were evaluated here to assess their performance for the reduction of the Sound Pressure Level (SPL) perceived at the passengers' ears. One concept was based on the shape optimization of the seats' headrests, whereas the second was based on the adoption of a high absorbing material, i.e., a nanofiber textile, to improve the absorbing performances of the headrests. An experimental campaign was conducted in a semi-anechoic chamber by using a binaural dummy head and microphones at various positions around different configurations of headrest. In parallel, simulations based on the Boundary Element Method (BEM) were performed for each configuration so as to provide a cross comparison of results. The rest of this document is organized as it follows. The next section develops the experimental campaign conducted in the semi-anechoic chamber together with some information on the nanofibrous textiles (see [20; 21; 22] for further details). Section 3 presents the numerical investigation performed for a comparison with experiments (see [22; 24] for further details). Section 4 discusses the comparison of both numerical and experimental results. Finally, Section 5 concludes with the remarks of this document.