After a thorough market research and reading the good reviews on this website, I decided to buy the AKG K420 headphone about a year ago. It seemed perfect for my needs: low price, good sound quality, very portable and rather bad sound isolation, which I need so that I can hear the cars when riding my bike. As always, I bought it second hand because you usually get much better deals buying second hand; I still cannot believe the kind of great stuff I got for incredibly cheap prices.   So I got the headphone. They looked as new and they sounded as...