8 x 21 db does not give you how loud it is gonna be. If a person yells and you can barely hear them, 10 people yelling is not going to increase the volume 10 times. There is a physics equation to determine all of this, but I won't get into that. Just know that 2 fans at 21 db does not sound like 1 at 42 db. Just the same as 8 fans at 21 db does not sound like 1 at 168 db, because that is REALLY FRIGGEN LOUD. Just know that your computer definitely won't be quiet.