Method of operating a papermaking machine and papermaking machine

A paper-processing machine has two cylinders (12, 14) forming a nip gap through which a paper web feeds continually. The nip gap (16) is esp. monitored by a sound emitter and detector (18) in air close to an elastic cylinder (12). The sound detector (18) is located in the immediate vicinity of the gap and operates on a continuous, semi-continuous or intermittent basis. The detector is coupled to a measurement and control unit (22) which gives a warning when the sound passes a pre-determined threshold linked to the barring effect associated with the onset of faulty paper quality. The measurement and control unit is further linked to a cooling water supply to the cylinder.