One earphone quieter than the other.

It must be the connection of your earphones that has been damaged or broken. If only the right side is faulty, it's probably the area between the right earphone itself and the cable that has an issue. There's nothing to be done unless you know how to repair it, and it might cost you if you have it repaired; it's better to buy a new one.
However, this could also be due to the device you are plugging your earphones into. If it's a computer or a music player, try to see if there’s an option to correct the issue. Maybe the program has been set up incorrectly.
In any case, and without needing to buy anything, given that the right earphone is working poorly, but again, and the problem is that it doesn't provide as much sound as the other earphone, you just need to adjust the device they are connected to by boosting the right earphone using the balance. You will need to adjust the settings.
For a PC running XP, go to start, control panel, sound and audio devices, volume, advanced settings, and then adjust the balance each time, this will correct the sound and restore the balance. Unfortunately, this is not possible with iPods, for example, but some MP4 players offer this option.
There you go, good luck ;)