Why the volume of earbuds is so week ,hardly can hear ? 

1. If you're using Apple, the volume is set only through the phone, making sure your volume setting on the phone is appropriate
2. If you're using Android system, the volume setting is separately from the phone and the earbubs, make sure the volume setting is between 20%-80% on the phone and then press long the left earbud is decreasing the volume, press long the right earbud is increasing the volume.