Some people are more attuned to certain frequencies, and are bothered by them. From your position, you’re getting the full spectrum of sound, whereas he may only be getting the bass. He hones in on this, and decides it bugs him. Rather than trying to deal with you on a level befitting his age, he’s taking out his frustration on you (likely some of which has nothing to do with you).
If he’s unwilling to deal with you in a reasonable manner, go to the manager of the apartments and ask him/her to be the moderator. Try to beat him there as this will show your willingness to rectify the situation, rather than the manager hearing the complaint of an angry tenant first.