"The DT 48 was the first dynamic headphone in the world. It served as a basis for all hi-fi stereo headphones throughout the world.
In 1937 nobody, however, knew that this headphone was suitable as a hi-fi headphone. Therefore, Eugen Beyer called the DT 48 not headphone, but "Dynamic Telephone" which is abbreviated as "DT". It was in 1950 that the headphone and its inventor showed what was really going on: the first public demonstration of an artificial head with the DT 48 took place and the stereophonic DT 48 proved to be the world's first hi-fi stereo headphone! This was an acoustic sensation after 13 years. The DT 48 is still in production and one of the most popular professional headphone for reporters throughout the world! "
And I'd guess the K in AKG means Kopfhorer