It should work exactly the same as speakers. Unless the phones are bad too or something. I assume you used phones you know are good and the volume is up. There is a setting under sounds and audio devices where you can change the type of speaker you have connected, but it really shouldn't matter, that just kind of tweaks the sound quality.
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If your equation requires either a complex combination of variables to get the desired result OR you can't seem to get the result regardless of the variables....it ain't your variables, it's your constant.