headphones By mike_N Mar 1, 1885 first headphone Mar 8, 1910 second improvement Mar 8, 1949 third improvement Mar 8, 1958 forth improvement Mar 8, 1959 fifth improvement Mar 8, 1968 sixth improvement Mar 8, 1980 seventh improvement Mar 8, 2001 8 th improvement Mar 8, 2008 ninth improvement Mar 8, 2012 tenth improvement
