When you unplug the earphone from the earphone jack, make sure to grip the plug and gently pull the plug out from the device. Do not attempt to pull the plug without gripping, it will damage the cable.
Some foreign material (e.g. earwax, dust, etc.) might be accumulated in the earbuds, resulting in lower sound quality. When this happens, please clean it with a blower, by removing the earbud as shown below: