The sound is slightly deep/full for “bass” and less so for “treble”. Is that all?
Basically, yeah.
Sounds that are lower in pitch (like the bass parts) have longer wavelengths. Any sound, whether it’s music, speech, or that annoying car alarm are just vibrations in the air made up of different wavelengths.
An equalizer can boost certain wavelengths, so when you “turn up the bass” you are amplifying the longer wavelengths but not the shorter ones.