โ Scribed by R.A. Novak
No coin nor oath required. For personal study only.
In this paper, results from measurements and theoretical calculations of the sound reduction index of some double walls are presented. The walls are lightweight (many o f them made from gypsum boards), uncoupled and fitted with sound-absorbing material in the gap. The results from measurements and calculations show very good agreement for low frequencies, from 50 Hz up to a certain characteristic frequency. This frequency corresponds to a Helmholtz number of one with respect to the wavenumber of sound in air and the gap width. A t higher frequencies the agreement between measured and calculated results are rather poor. However, it is shown that a fairly good agreement can be obtained if a much lower value of the flow resistance than the actual one is used for the calculations. The measurements have been carried out using the intensity technique as well as the standard technique. The results obtained with the intensity technique are somewhat higher than those obtained from pressure measurements. This difference tends to increase with increasing sound reduction index.
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