a method and a device to be used in the process of manufacturing plates , such as fibreboards or the like boards , where the raw material in form of bio - mass particles , such as wood fibres or the like , applied with a thermosetting binder is spread onto a forming belt to form a mat , and where said mat by means of a hot press is compressed into the desired thickness of the finished plate and the thermosetting binder is hardened . according to the inventing a system and corresponding method for manufacturing biomass - based products is provided that has enhanced efficiency due to the application of ultra sound .