1. Headphones, problems solved.

In all fairness though, your scenario suffers from an continunity problem. Did the neighbor pop out of nowhere? I'll go on that possibility because there's a severe continunity problem if not. I'll mention one continunity issue is that the neighbor doens't have to deal only with your music - there's plenty of other things they'd need to avoid. Washing the dishes? Taking a shower? Playing their own music? There's simply too many things that produce a strong enough sound that your music would be equal if not lower than what they can perceive.

Also, ome people here said that you'll be cooperating. I say you're being defecated on. Because their situation simply isn't really going anywhere - everyone MUST go down or else.. wahh, my ears.

Least convinient possible world, where my aforementioned continuty problem is not a problem, I'd say that they still need to cover for themselves - it's still their issue. They certainly need to solve it themselves, fair's fair. That doesn't allow you to be a dick, but I see no reason you should bend down while not getting anything in return.