In flawless gear boxes relatively prominent tones appears at gearmesh frequency, i.e. number of cogs multiplied with the rotational speed (RPM frequency) of the gear box. When the gear box has been used for a while the level of the gear mesh component decreases as the edges of the cogs are slightly rounded. Continued wear increases the level och gear mesh again. The level is also affected by the alignment of the pinion axles.
| Source of vibration | Exciting frequency | Dominating direction | Amplitude | Spectral characteristic | Comments |
| Bad gear mesh | X times number of cog | Radial, axial | Constant, sometimes with variations | Narrow band | Often with 1X on each side of gear mesh frequency |
| Eccentric pinion | 1X, gear mesh | Radial | Narrow band | Wheel may be balanced but mounted on anunbalanced rotor. 1X sideband around gear mesh frequency. | |
| Bad alignment | 2X, gear mesh | Axial | Constant | Narrow band | 1X side band around gear mesh |
| Out of true, unbalance or damaged cog | 1X and gear mesh | Radial for cut cogs and axial for one or two arrow cogs | Constant | Narrow band | 1X side band around gear mesh |
| Production fault | Gear mesh “Ghost frequency” normally not synchron with 1X | Radial, axial | Constant | Narrow band | Production fault due to gear mesh fault in the production machine drive can give “ghost frequencies”. |
| Problem with planetary gear box | Very dependent on gear box geometry | Radial | Constant | Narrow band | It is common with side bands around gear mesh frequency with an interval as the planets rotational frequency. |
