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

@appletree wrote:
I think more expensive earphone will promising the better sound. (More price means better quality). I have 2 pair of Philips IEM (SHE-9700 and SHE-9800). I purchased SHE-9700 for $20 and SHE-9800 for $60. The frequency range of SHE-9700 (6Hz-23KHz) is wider than SHE-9800 (12Hz-22KHz), but for the overall sound quality, the SHE-9800 is far better than SHE-9700.

Although not always the case, I’ve generally found the more expensive brands tend to be a bit more honest (realistic?) in their spec claims.