TFL may claim that the very high sound levels may not lead to deafness in the long term. However, this is not the only problem. Very loud noise can also trigger bouts of tinnitus.

In addition there is an additional problem on the Northern Line.

The PA system in the carriages has very powerful amplifiers, and sometimes the sound levels due to these can be ear-shattering. The volume settings very wildly and unpredictably, depending on (a) in which part of the line you are travelling in, and (b) whether you are in a station or not.

The illogical thing is that it appears that the PA announcements use the full frequncy range. There is little or no low frequency reduction, so the lower frequencies, which have the most sound power, and which carry the least information, cause distortion and so make the higher frequencies, which carry the most information, difficult to hear.

In contrast, on the Picadilly line, the announcements are not loud, but are perfectly audible, because the relative frequency levels are done correctly.

So, on the NOrthern Line, as well as the noise due to the wheels and the condition of the rails, passengers have to needlessly and pointlessly submit to even more discomfort when the announcements occur, and have to put up with the reduced intelligibility.