Why the legislation to require mufflers on your car.   It only makes it slightly quieter.    About the same amount quieter that a suppressor makes a firearm. It's the same technology.   If something is 70 db and is reduced to db  by way of a muffler that helps.   A lot actually.   A suppressor on a firearm reduces the Db level from around 150 to 120db.  Or slightly more than really good hearing protection ear muffs. This is similar to a reduction in noise level from a fully packed stadium or rock concert down to a lawn mower.   Or an unmuffled motorcycle down to vacuum cleaner level of sound.    The lawnmower and vacuum cleaner aren't 'silent' but they are much quieter than the counterpart.