Silencers in Flow Ducts

Abstract

Chapters 4–10 describe sound absorbing elements with regard to their

• a ) acoustical performance

• b ) mechanical robustness and

• c ) optical appearance

in numerous embodiments and in relation to other additional functions. In closed rooms (see Chaps. 11 and 12), the amount of space required for a specific absorption aspect (a) plays an important role particularly in view of low frequencies, because this can directly influence the construction costs of a building. The durability aspect (b) and design aspect (c) of porous/fibrous damping materials can be improved by acoustically transparent covering or lining as described e.g. by Leistner and Drotleff (2004). Properties (a) and (b) gain much more significance if the absorbers are installed in the form of lining and/or splitters in ducts, where they are exposed to highly turbulent flow of a, possibly chemically aggressive, fluid and probably additional strong vibration impact . Moreover, if there are suspended particles carried with the fluid, for example dust, there is the risk that deposits on the silencer may diminish its acoustic efficiency (a). In such a case “coated” materials (see Sect. 4.2), in particular reactive, completely “sealed” metal cassettes according to Sects. 6.3 and 10.7 offer distinct advantages, see Fuchs et al. 1999. The latter two, just as the “sintered” porous glass foam described in Sects. 4.3 and 11.14.9 b, can be made to also withstand very high temperatures and flow velocities in ducts.