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Insertion loss of enclosures with lined slits
An air slit with one of the boundaries created by an absorbing lining is an acoustic system that can introduce the transmission loss (TL) of high values, especially in the high frequency range. The aim of this paper is evaluation of overall insertion loss (IL) in acoustic enclosures caused by air slits. For this purpose, two MDF sound insulating enclosures with dierent sizes were constructed. Enclosures were elevated in order to create slits with adjustable height. Because enclosures were acoustically adapted, an absorbing boundary was naturally created. Mechel's model was utilized to predict TL of that kind of absorbing slits. The insertion losses of both enclosures were measured according to ISO 11546-1. Next, simulation of insertion loss has been performed (two models have been used: a well-known simple formula and a SEA model). It was noticed, that dierence between results obtained with using simple formula and with SEA model is negligible, because a transmission across slits (modelled in SEA as an non-resonant transmission) is much higher than a transmission across enclosure walls in a wide frequency range. Results of simulations and measurements have been compared. A good agreement occurs in a case of narrow slits. Furthermore, results conrmed the importance of providing high modal overlap conditions while using statistical models in acoustic simulation.