You can improve the sound quality on your device by using an Equaliser which uses software to enhance specific frequency ranges.  There are many varying apps, with this one being suggested as very popular.

Equalizer & Bass Booster

Improve the sound quality of your android device with the first true global Equalizer, Bass Boost and Surround Sound. Make your android device sound like never before.  Equalizer & Bass Booster consists of a volume slider, live music stereo led VU meter, five-band Equalizer, Bass Booster, and Virtualizer effects.  Equalizer & Bass Booster lets you adjust sound effect levels so that you get the best out of your Music or Audio coming out of your phone.
Use with headphones for the best results.  As with most of these apps, you have to put up with promoted adverts in the free version.