not to hijack this, but you guys will be deaf faster than a biker, or members of 'the who'! 140 db is supposed to cause instant hearing damage. dbs are logarhythmic and i think each 20 db is ten times the power of the last eg: 40db is 10 times 20db, 60db is 10x 2 more powerful etc. and so 140db is 10 x 6 more powerful. i think really loud stereos should be banned myself, especially if it sets of alarms and makes people jump. but thats just me, im old and cranky 
i didnt have it that loud all the time, and db is measured in pressure, yep it could blow your ear drums etc
if you are subjected to it for long periods of time the hairs inside your ear can be damaged and its this that will give you damaged hearing.
when i go to a SPL (Sound pressure level) contest i stand outside the car,
the other things to conside is the frequency that you play the tune at, the Higher the frequency the more damage likly,
Quick physics bit
Everything has a harmonic frequency and if you match that frequency you can damage the item. the hairs in your ear are set to a higher frequency than any bass can produce thats why it hurts your ears when subjected to a very high frequency and not to a very low frequency and sound cars are normally set to low frequency. the only damage that can be caused is your ear drums exploding due to the pressure built up in a confind enclosure, just like a deep sea divers would if he wasnt properly protected. i can remember he exact equasion but its nearly impossible to do it in a car as there is too much panel flex and too many places for the air to escape from to get this much pressure.
but if you can reproduce 7hz or lower you will boil your internal organs in about 10mins most high end speakers and only turely (regardless of what the box says) go down to 20hz,
the other magic frequency is 33hz, legend has it that if you can reproduce this frequency exactly, any female in range of this air movement will start to smile as it is the same freqiency of their clitoris.
Franco, good luck with the CAD studying if you need any help just ask.