John C. Koss, Stereo Headphone Innovator, Is Dead at 91

John C. Koss, a trumpet player and onetime teenage bandleader who with a friend invented stereo headphones and provided people with a new high-quality — and personal — way to listen to music, died on Dec. 21 in Milwaukee. He was 91.

His son Michael confirmed the death.

Koss headphones became standard equipment for music listeners, disc jockeys and recording artists in the studio — even for members of the House Judiciary Committee when they heard White House tapes in 1974 during President Richard M. Nixon’s impeachment inquiry. For many years they were virtually all Mr. Koss’s company made, until an unsuccessful expansion into other audio products in the 1980s nearly put it out of business.

Mr. Koss and his friend Martin Lange Jr., an engineer, developed a portable stereo phonograph in 1958 that they called a “private listening station.” It had a turntable, speakers and a privacy switch that let users plug headphones into a jack. But most of the headphones available, such as those used by telephone operators, shortwave radio users and pilots, were incompatible and were not stereophonic.

So they rigged up cardboard cups that contained three-inch speakers and chamois pads from a flight helmet, and they attached them to a headband made of a bent clothes hanger covered with a rubber shower hose.

“And, oh man, whew, it was just bouncing in my ears,” Mr. Koss said in an undated video interview on the Koss Corporation’s website. “It was a great sound. Now the whole thing was there. Anybody that listened to it, it was like the first time you drove in a car or the first time you did anything.”

Mr. Koss, whose own taste ran toward the music of the big band era, added, “Enclosing yourself in just the music — it gets to be even more thrilling.”

When the two men brought the Koss Model 390 phonograph to a Wisconsin hi-fi show soon after, the headphones were a hit; the larger unit, not so much. The SP-3 headphones, which sold for $24.95, became the first of many versions that Koss would manufacture over the next six decades.

“For many industry professionals, the Koss Pro/4 headphone was the entry into good stereophonic sound that could be heard on headphones,” Jim Anderson, a professor at New York University’s Clive Davis Institute of Recorded Music, said in an email, referring to a product first produced in 1962. “Koss set a standard for construction quality and audio for many years and had the market virtually to themselves.”

The company became known in the 1970s for cheeky billboards that included various figures wearing Koss headphones. With Lincoln’s head wrapped in a pair, the tagline said, “Not all stereophones are created equal.” Another ad showed three owls on a tree limb, the middle one listening on headphones. “Give your neighbors the silent treatment,” it said.

During that decade, the company hired Doc Severinsen, the colorfully dressed trumpeter and bandleader of “The Tonight Show Starring Johnny Carson,” as a spokesman. A set of Koss headphones became part of the Smithsonian Institution’s permanent collection.

John Charles Koss was born on Feb. 22, 1930, in Milwaukee. His father, Earl, was a teacher, a cookie salesman and later the bookkeeper at his son’s company; his mother, Eda (Kenkel) Koss, was a teacher. As a youngster, John started playing a cornet that he had inherited from a grandfather; he later switched to trumpet.

While attending Riverdale High School in Milwaukee, Mr. Koss started a big band that played at schools and churches. After his graduation, he served in the Air National Guard and became a salesman at an appliance store. One day, when he was home sick from his job, he got the idea to start a business renting television sets to hospitals, a business that branched into renting them to schools. Then, in 1958, he and Mr. Lange created the portable phonograph and its headphones.

“At first, you had to buy the whole system to get the headphones,” Michael Koss, who replaced his father as the company’s chief executive in 1991 (the elder Mr. Koss remained chairman), said in a phone interview. “Fortunately, for our family, Dad looked in the mirror and talked to the marketing department and said, ‘I have to be in the headphone business.’”

Headphones sustained the company even as competition emerged, especially from Japan. In 1979, John Koss brought in a new president, James Dodson. Mr. Koss remained chief executive but gave Mr. Dodson the freedom to make substantial changes.

Believing the headphone business to have matured, Mr. Dodson moved Koss into loudspeakers, challenged the Sony Walkman with the Koss Music Box, bought a company that made record and tape care products and developed a digital radio.

But the audio market contracted, causing sales of headphones to shrink, and manufacturing problems in Taiwan damaged hopes of success with the Music Box and the digital radio. By 1983, the company was losing money and its stock was faltering. Late the next year, after Mr. Dodson’s five-year contract ended, Koss filed for Chapter 11 bankruptcy protection.

Mr. Koss, whose net worth was tied entirely to the company, was broke.

“I felt awful,” Mr. Koss told Inc. magazine in 1988. “My board had agreed, my family had agreed, but I was the guy who had to sign the papers. I just walked around in a daze, angry at myself.”

A year later, Koss emerged from bankruptcy after taking measures like liquidating the Music Box and digital radio inventory and selling the company that made record and tape care products. It refocused on headphones, and it has not changed its strategy since then.

The company overcame another hurdle when shareholders and the Securities and Exchange Commission sued it after it emerged that an executive had embezzled more than $30 million. The suits were settled in 2011.

Two years ago, Koss sued several of its competitors, including Apple and Bose, for infringing on its wireless headphone patents. The cases remains open.

In addition to his son Michael, Mr. Koss is survived by another son, John Jr.; his daughters, Debra Fulton, Linda Moore and Pamela Geimer; 15 grandchildren; 15 great-grandchildren; and his brother, G. Peter Koss. His wife, Nancy (Weeks) Koss, died in 2018.

Mr. Koss retired as chairman in 2015, but Michael Koss said the company used him as a “secret weapon” until 2016 because of his standing in the audio industry.

“If I took him to a trade show, people would bring their headphones for him to sign, especially if we were overseas,” he said. “People would line up to meet him.”