There is this thing called "Burn in" Burn is quite subjective and people can either believe in it or not. Burn in is when you play music, sine waves, pink noise etc... through your new headphones(Or IEMs). People believe that you need to burn in dynamic drivers to make the driver used and make how the makers wanted it to sound. However, balanced armature drivers doesn't seem to need it, whilst some models apparently do. So before you actually judge the sound of the headphones(Or IEMs) and then return them, wait and play around 100 hours of burn in to see if you really like them. I approve of burn in, since my IE8s need 350+ hours of it. ¬____¬ So if you are wondering if your new pair of headphones(Or IEMs) need burn in, simply put it in your post and I will try to reply to you.