how about music in one x?
They go a little loud. Around as loud as most high end phones go these days. They're not too loud though, so if there are background noises around you such as people talking, you may not hear them too clearly. One thing I noticed, if I'm showing a comedic video to more than 1 person, the laughter often covers the sound of the video, making us miss a joke or 2.
The speaker on the One X is pretty clear. It's one of the best phone speakers I've heard in terms of quality. However, I rarely use the loud speaker for music, so my opinion may not be the best.
However, if you're talking about using headphones, here's my opinion:
Having the Beats equalizer actually makes the music sound a little better than when you disable it. Overall, I've really enjoyed listening to music from the One X through headphones.