The history of high-end sound began with the HD 414. The world's first open headphones revolutionised the headphones market in 1968. For the first time, the ears could hear in a way that they are accustomed to: open and free in space. The sound can travel to the ear drum much more naturally and clearly than in closed models. With its new principle, the HD 414 triggered an absolute boom in headphones sales. More than 100,000 sets of headphones had already been sold by the end of 1969. Even today, the HD 414, which has long since gained cult status, is still the bestselling headphones in the world, with sales of over 10 million units to date. The open principle has also become firmly established in the development of high-end headphones.