A tonal component in gear noise or vibration at a frequency that is not a whole multiple of the gear's own mesh frequency. It comes from periodic errors copied onto the teeth by the hobbing or grinding machine, typically from its index worm gear, so the tone corresponds to the machine's tooth count rather than the part's. Ghost tones can be heard as whine even when the gear checks within tolerance on standard charts.
There's a tone at 87 orders and nothing in the box has 87 teeth, that's a ghost frequency, ask which hobber cut it.
Also heard as
- ghost tone
- ghost noise
- ghost order
Related terms
GMF
Gear mesh frequency: tooth count times shaft speed, the frequency at which teeth enter mesh.
Hob
A gear cutter shaped like a worm with gashes across its threads, used on a hobbing machine.
Pitch deviation
Errors in tooth spacing, either from one tooth to the next or accumulated around the gear.
Whine
A steady, pitch-changing tonal noise from gears, rising with speed and caused by tooth meshing errors.