There is a difference in volume between the left and right sides, or the bass (low frequency) sound is insufficient.

If you feel that the bass (low frequency) sound is low or there is a difference in volume levels between the left and right sides of the headphones, change the earbuds to another size that comfortably and snugly fit both ears.

NOTES:

• M-sized earbuds come attached to the left and right units of the headset at the time of purchase.
• Try the earbud sizes in order from the larger sizes to the smaller sizes, and use the ones that feel more sealed. The best size earbuds may be different for left and right ear.
• Make sure that you are wearing the earbuds properly.
  Example of using the WF-SP800N headset, as you insert the headset units into each ear, twist the headset to secure the arc supporter into your ear grooves.
  
  1. Ear grooves
  2. Arc supporter