I dont know what is speaker enclosure but there are 3 reasons for bottom speaker problems.
1- Replace the buzzer ( it is black plastic part with two screws. It also has GSM antenna ribbon on it)
2- replace the charging port assembly. It has charging port, microphone and speaker connectors.
3- replace the headphone jack flex cable ( yes ... Shorcut in headphone jack supresses speaker sound )
Before that you can also clean connector between charging port and speaker.
Good luck ...