* Check your volume settings on phone.
-Go to the main menu on the phone , go to settings, click on sound icon, and check volumes settings for music, videos, games, ringtones, alarms and other media.
* You can check the speaker and see if there is a problem with the speaker physically visible
-Check and see where your speaker is located and check if its free from dust or anything obstructing it.
* you can replace the Speaker
-Follow this guide ([guide|31971|Blu Studio 5.5 S Speaker Replacement])