Why my speaker is very bad

Dust, dirt and/or water damage could quite easily make your speaker sound distorted or poorer quality than it initially did (I presume this is your complaint). If you have any tools use a small plastic needle nose tool to gently clean your speaker ports, being careful not to damage them. Avoid using compressed air, especially at high pressure as this could damage the speakers further, a light blow (of your breath) does help clear a debris, after your clean with the needle nose tool. A microfibre cloth also is helpful to wipe out the speakers.