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The rapidly increasing number of aircraft passengers requires improved techniques for aircraft manufacturers to provide high internal comfort for passengers and the crew. In this paper, the internal acoustic comfort was evaluated using binaural recordings inside three aircrafts of different sizes during regular flights. The parameters of sharpness, tonality and loudness, which are expected to be correlated with perceived sound quality, were calculated. The results of listening tests performed with or without loudness equalization were obtained applying the paired comparison technique. These results will be discussed in detail in this paper.

Within modern sound engineering the individual perception of sound events has to be considered and assessed by adequate means. Psychometric instruments are suitable for this objective and all over the world several instruments for the assessment of sound and sound quality have already been developed. Adaptation of such an instrument to the target population is not without problems and a successful adaptation process addresses complex issues, for instance, semantic structure. As the semantics of instruments can not simply be translated an investigation into the semantics related to the concept of interest is important. This article offers guidelines for this step, which can be described as an investigation of the attributes and items related to sound and sound quality. This part of the development procedure is, in constrast to the statistical validation procedure, not usually sufficiently described in the literature.

In this paper, four different configurations of plug type muffler are investigated. Three different evaluations methods are used; Finite Element Method, Transfer Matrix Method and experimental measurements. The results obtained for the transmission loss of each muffler are compared. No flow and temperature variation are considered.