If you are experiencing bad or no audio from your Edifier W820NB Plus, you might need to replace one or both drivers. The drivers are the part responsible for producing sound in headphones, See this troubleshooting page for more information.
This guide requires soldering. If you're unfamiliar with soldering, review the How to Solder and Desolder Connections guide and take appropriate precautions before beginning.
This guide will use the left driver as an example but the same steps can be mirrored when replacing or removing the right driver. The battery is under the left driver, while the motherboard and daughterboard are under the right driver.