Until WWII put an end to production, German hi-fi stalwarts Bayerdynamic invented the world’s first dynamic headphones for home listening. Launched in 1937, the DT-48 remained in production (in one form or another) until 2012.
Meanwhile, across the border in Vienna, AKG (established in 1947) was busy inventing the thoroughly modern K120s. Neither pair made much of an impression but the original poster provided the template for all headphone ads since – the perfect balance of impressive-sounding tech specs and marketing mumbo-jumbo.