+1 JohnO, if you've got good hearing then use plugs to protect it. Riding service bikes ruined mine well before fitted earplugs were in use.
The radio from the service bikes was obviously plumbed straight into the helmet on both sides. Why ruin just one ear? At a standstill with the engine running you could turn the radio to its lowest setting and it would be crystal. When running at high speed with wailers etc you could turn the radio to flat out and you still couldn't hear it, don't underestimate road noise, it is very very loud.
This experience was on both LT1100's with electric screens when they worked and ST11's with fixed higher screens.
If you were stationary and put the radio flat out it would hurt your ears it was that loud, multiply this volume by 100's or 1000's of hours and voilà , sorry what did you say, yes it's 7 o'clock etc.
Upt'North.