In 1958, John C. Koss invented personal listening with the World’s First SP/3 Stereophone. Koss sought to replicate the excitement of a live musical performance and the original SP/3 stereophone allowed listeners to experience sound as they had never before, bringing them closer to the music they love.

Following the original Koss SP/3 in 1958, the improved SP/3X was released in 1960. Listeners of the era were experiencing stereo headphones for their first time. People were won over by this revolution in personal listening. It was around this same time that Koss coined the phrase "Hearing is Believing".

John C. Koss remembers the SP/3X, and the challenge of introducing the world to stereophones:

"Back then if someone handed you a headset, it had been designed for a telephone operator or a bombardier. The SP/3X meant nothing to anyone until they could actually hear it, and when they did, it was about as exciting as their first ride in a car, or flight on an airplane. The sound of the SP/3X Stereophone was about that exciting."

John C. Koss with the SP/3X

"Because the experience of stereo sound was so new, people would invite the whole neighborhood to come hear it. They wanted to run their own hi-fi show. That's kind of the way it worked all along. You had to hear it to believe it." - John C. Koss

Koss SP/3X with the Koss-390 Record Player.

The T-2 Headphone Adaptor Plate. These were included with every SP/3X, and served as headphone outlets in a time before headphone jacks. At the time there were no jacks on any amplifiers. Koss developed an adaptor that would tie onto the speaker outlets.