The invention relates to an acoustic structure which complies with protection standard IP 67 and which can be used to provide hands-free capability e.g. in cellular terminals or small radio receivers. The acoustic structure comprises, in a device body (100), two interconnected, separate cavities for speaker means (151, 152, 153) and isolating means (120, 125, 130, 140). An isolating diaphragm (125) belonging to the speaker arrangement according to the invention is utilized simultaneously as an isolating means against dust and water and as a sound-reproduction element.