 The Diatone brand currently sees limited use on aftermarket car stereos and speakers manufactured by Mitsubishi Electric exclusively for the Japanese domestic market.In the 1940s Mitsubishi Electric successfully developed a hard-ferrite (permanent-magnet) OP magnet and began to prepare for the commercial production of ferrite.The Diatone speaker was developed in the fall of 1945 at Mitsubishi Electric's Ofuna Factory.