In   situ evaluation of aircraft interior noise reduction technologies

In order to quantify the performance of interior noise treatments under flight conditions, it is desirable to evaluate the noise reduction due to treatment of a limited portion of an aircraft fuselage. However, radiation from the untreated areas of the fuselage can corrupt an intensity measurement in front of the treated area. In the past, this problem of corrupting noise has been solved by acoustically isolating the treated area from the rest of the fuselage. In this presentation, a method to evaluate the performance of an acoustic treatment applied to an aircraft fuselage in situ using correlation analysis is documented. The insertion loss of the acoustic treatments is estimated from the ratio of the intensity, correlated to reference transducers, measured with and without the treatment applied. The formulation is presented for both single and multiple reference transducers. Several experimental studies and numerical simulations have been conducted, and the results are documented. Through these case studies, it is demonstrated that this method can be used to evaluate the insertion loss of fuselage treatments without having to acoustically isolate the treated area.