[3] After a short time Koss was looking for new ideas, and partnered with Martin Lange to eventually develop a stereo headphone.

Being very durable, they required service for wear and tear on cords and earpads during their lifespan, by K&M Electronics (Klenworth & Midwest based in Minneapolis), working out of the TV Rental location.

Koss was considered a higher quality unit at the time, offering a wide line of models.

[citation needed] In the late 1970s, to accommodate rapid growth, Koss moved to its present location on the north side of Milwaukee.

[6] In December 2009, former vice president of finance Sujata "Sue" Sachdeva was charged in federal court with wire fraud after the firm discovered her embezzlement of US$34 million (equivalent to $48.29 million in 2023), and sentenced to eleven years in federal prison,[7] of which she served six years.

[8] In 2020, Koss sued Apple, Bose, JLAB Audio, Plantronics Inc., and Skullcandy for patent infringement.

[11] During the 2021 GameStop short squeeze, the executives and directors of Koss earned US$40 million by selling company stock.

[14] Since 1989, all headphones manufactured in North America by KOSS come with a limited lifetime warranty covering normal use by the initial owner.