After further use with these I can now relate to your previous post about the L adaptor. While using the earphones and the adaptor on my Nexus 7, the sound is muffled and horrible. However just as you had said, sliding the adaptor lead out a little bit results in everything sounding as it should. BUT, this is what I find really confusing. When using the adaptor plugged into my desktop computer, the adaptor needs to be plugged in fully along with the original earphone lead. If it sits out a bit like listening to music on my Nexus, the sound becomes muffled.
Very, very weird.
Be sure that the headphone jack is not full of lint or other obstruction. This can prevent plug from fully seating. Try using a wooden toothpick to clean out jack.