Android's built-in Music app is pretty capable -- and for Jelly Bean users (both 4.1 and 4.2), you'll find the ability to equalize your music has been baked right in. Once you're playing a song, hit the three dots in the upper-right corner and select "Equalizer." You'll be able to select from presets such as "Folk" and "Heavy Metal," and you can even drag the five sliders yourself to fine-tune based on what you're listening to at the moment. Down below are extra controls: drag to adjust the amount of bass boost applied. There’s also a "3-D effect," some software processing that makes the music sound a little deeper. Those options are only available when headphones are plugged in, since they wouldn't make much of a difference to the sound quality of your phone's built-in speaker.
If your device isn't running Jelly Bean, check out the free "Equalizer" app in the Google Play store -- it offers many of the same features.
