On monitors, both speakers reach both ears. On headphones, they don’t. And that makes center content about 3dB quieter in your cans than it does when you listen to your mix in the open air. If your vocals keep coming in hot when you check your mix, this might be why.

It’s not a flaw in your ears or your headphones — it’s physics. And you can compensate. Not with a fancy plug-in or an expensive piece of equipment, but simply armed with knowledge.