Last modified on Thu 18 Mar 2021 15.30 EDT Lou Ottens, who has died aged 94, invented the audio tape cassette, and thus was instrumental in making music both more portable and more personal for millions of people around the world. The transistor radio had allowed listeners to carry their preferred radio stations around with them, but the advent of the audio cassette provided them with an easy means of recording radio broadcasts or dubbing from LP records into an easily portable format. Ottens had already developed portable tape recorders for his employers, the Dutch electronics company Philips, but he pursued a simpler format, as he put it, “simply out of irritation” with the awkwardness of handling reel-to-reel tape. He never foresaw the changes his 1962 invention would bring. “We expected it to be a success, not a revolution,” he said.