ABSTRACT
To generate noise from gears the primary cause must be a force variation which generates a vibration (in the components), which is then transmitted to the surrounding structure. It is only when the vibration excites external panels that airborne noise is produced. Inside a normal sealed gearbox there are high noise levels but this does not usually matter since the air pressure fluctuations are not powerful enough to excite the gearcase significantly. Occasionally in equipment such as knitting machinery there are gears which are not sealed in oiltight cases and direct generated noise can then be a major problem.
