Under what specifications does the sound quality of a pair of earphones mostly depend?

simply put, you might have to purchase a few pair to find “the one” set for “you”. just like specs on headphones, your ears has it’s own specs. when buying a set of studio monitors for recording, you have to do the same thing, you listen to everything first. bad thing, i don’t know of any place that allows you to do this with earbuds. over the ears, maybe. if your ears hear 1k-6k better, getting a set that puts emphasis on the area will sound harsh and you’ll have to cut those frequencies. i went through 4 pair before i bought a set from CVS pharmacy made by Philips, they are the best yet.