CALCULATION AND MEASUREMENT OF THE PROPAG ATIONVELOCITY OF SOUNDWAVESIN RECTANGULAR DUCTS

This paper treats an interesting problem in technical practise, the fr equency dependent velocity of propagation for low frequency soundwaves in rectangular airducts. To calculate the propagation of disturbancie s or to study resonating problems in these ducts, neglection of this p henomen can lead to wrong conclusions. This can complicate or prevent the solution of the; problem. This study introduces the fundamental eq uations of the problem and a method to calculate the propagationveloci ty of soundwaves in dependence of fluid, ductgeometrie, ductmaterial a nd frequency of excitation. The results of the calculations are compar ed with measurements. For the measurements, the shape of the cross sec tion and length of the duct segments are varied. A good agreement betw een calculation and measurement is found as a result. Building on thes e fundamentals, a method is described based on the fourierintegral to calculate the propagation of a pressurewave in the above used duct. Re flections at the boundaries of the duct are considered and the calcula tions were also compared with measurements.