Why do Jubilee line trains make that noise?

[marmaduke]

On the tube, why do Jubilee line trains make that particular droning noise, not heard on any of the other trains?

[samwolf5]

if you mean the 'gear changing' type of noise which you hear as the train accellerates, this is due to the particular type of 'thyristor' (simplified - a sort of electronic switch) which is used to control the power supply to the traction motors (which drive the wheels). The type of thyristor used here is called a Gate Turn Off Thyristor - if you're interested a simple google of this will return thousands of results on the intricacies of these devices! NB - Northern Lines trains are similar in look to Jubilee ones but the power switching equipment is different - hence no noise.

[marmaduke]

I'm thinking more of as they enter the station, and slow down, they drone like a sort of air-raid signal. It's a depressing sound.

[Andyh-R6S]

What you can hear is the switching frequency resonating within the stator winding of the induction motor and to a small degree the motor cables, etc. A similar sound can be found in the Alstom Networkers, as the Jubilee Line inverter is based on this design. The ‘Grrrrrr’ you can hear on rheostatic braking, (Around 30 to 20 mph during deceleration and sometimes in acceleration too) is mechanical resonance (Vibration might be felt too.) being generated by noise getting into the phase CMD and being injected into the control PI loop. This will eventually destroy/cause issues in the coupling between the motor and the gearbox. Networker had the same issue originally and a Faraday cage had to be fitted adjacent to the phase CMD in each phase module. (23RA009B2)

Although many do not like the harmonic noise given out by the inverter, the noise does indicate the health condition of an inverter and can give clues to what is or not doing as the case may be. In essence what you can hear is the switching frequency shifting in tone due to the applied power being increased (acceleration) or decreased (deceleration) at a set frequency per gear. What sounds like a gear change is in fact the inverter control electronics changing the supply frequency to the motor, to enhance the torque range and power of the motor to keep it accelerating providing the air gap between the rotor and stator is constant and slip is in the region of 2 or 3% (ish). (Temperature compensation to air gap compensation algorithms are used as well.)

Hope the above helps.