I have seen these figures somewhere. Perhaps a chat to headset services will give some accurate figures but I thought it was around 100 decibels at full power.
24db of attenuation brings it down to 76 which is a bit like the sound of a loud television (I think). 60 Db is a wisper.
Sound is not linear. It doubles every 3 Db.
That said most pilots who have flown for a long time have suffered hearing loss and ringing due to ear damage. These figures make a good argument for spending £700 on a headset now. Presumably once you have lost your hearing you will happily pay £700 to get it back rather than wear a hearing aid. The active headsets boast an additional 15 ish db reduction.