EFFECT OF WATER-FILMS ON THE ABSORPTION OF MEMBRANE ABSORBERS

The membrane absorber is a fibre-free absorber which consists of vibra ting metal membranes on a lightweight metal honeycomb structure. An ad vantage of this absorber is that the smooth cover-membrane seals the c omponent against humidity and solid particles. In some cases the cover -membrane still needs to be frequently cleaned, and a flowing water-fi lm can be used for this purpose. In this research the effects of such a water-film on the absorption characteristics of the membrane absorbe r have been experimentally investigated in a reverberation room. The r esults show that with a water-film the absorption coefficient of a mem brane absorber is generally decreased, and the frequency of maximum ab sorption becomes slightly lower. It is noted, however, that when the w ater-film is relatively thin, say 1 mm, with which a membrane absorber can be effectively cleaned, its effect on sound absorption is negligi ble. Generally speaking, a vertically flowing water-film has less effe ct on the absorption of membrane absorbers than a horizontal water-fil m. Measurements also show that the noise level caused by a flowing wat er-film is acceptable in practice. (C) 1998 Elsevier Science Ltd. All rights reserved.