waves - Why do you only hear the bass when someone nearby is wearing earphones?

When someone nearby is listening to music through earphones or headphones, usually you can only hear the bass (unless it's really loud where you can hear the singer's voice and the other instruments too).

Why are the bass sounds more audible?

The answer probably has to do with the bass sound waves having the highest wavelengths. I was able to gain some insight from this question however not a real answer as it focuses on the way sound waves travel across a room and through walls and not on ear/headphones.

Answer

You don't.

You actually hear the high frequency notes from headphones. The bass really doesn't travel at all well, but the attack noise from the drum or bass guitar is what leaks from headphones.

This is why on the tube you hear "tsss tsss tsss tsss" and very little else.

From @leftaroundabout's answer on the post that valerio92 linked:

Normal headphones are basically dipole speakers, and especially for bass frequencies (wavelength much larger than the speakers) this describes their behaviour well. So the amplitide decreases ∝ 1/r⁴. At higher frequencies, they also have some monopole components which decay more slowly, with the familiar inverse-square. So if you're listening from far away, you'll mostly hear those treble frequencies and little or no bass. OTOH, while wearing the headphones there's little difference since you're in the near field where neither frequency range has decayed substantially at all.