Abstract: A vessel for bulk materials is described whose level can be continuously determined from outside during the filling or emptying process. To this end, at least one AE (acoustic emission) transducer is mounted at each of the levels of the vessel which determine full or empty states. An acoustic waveguide is provided between the two AE transducers defining full and empty states. Preferably, however, the vessel wall serves as an acoustic waveguide. The AE transducers are connected with an electronic signal processing unit which determines the movement of the bulk material by localization from the difference between the arrival times of the signals generated by friction noises of the bulk material at the acoustic waveguide, which are detected by the two AE transducers.