Why the speaker is very low?

Something could be jammed in the speaker or there could be alot of dust/crud build up in there. If its not clean try to clean it with a toothpick.

You need to clean your speaker. You can clean it very easily. To clean your speaker you need a dry toothbrush and play loud sound on your phone. Then slowly rub the brush into speaker. To applay this methode your speaker clean from dust. Hope you Understand 😊