Theoretical Investigation of ‘Open’ Sound Absorption and Its Comparison with ‘Closed’ Damping

The conditional equation for the linear propagation constant of ‘open’ sound absorption damping is discussed in which the absorption material is described through its flow resistance, its porosity and its structure factor. For different ratios of covering and flow resistance the normal damping diagrams are given. At low frequencies, the damping coefficient for a definite flow resistance has a minimum. The propagation constant of higher modes is investigated at low and high frequencies. The explicit approximate formulae for the propagation constant at low and high frequencies are compared with the accurate results. Finally the absorption coefficient of “open” sound damping is compared with that of ‘boxed’ sound damping.