1958 · Stereo
Koss dates the SP/3 stereophone to 1958.
Koss’s retrospective places the device within a stereo phonograph demonstration.
John C. Koss and Martin Lange Jr. developed a portable stereo record player; the SP/3 became part of this music-listening story.
The milestone shifts the timeline’s focus from communication to personal stereo music.
Koss calls it the first stereo headphone. We attribute that priority claim to the manufacturer rather than treating it as independently settled.
No cleared reproduction; view the source collection.
manufacturer · Reviewed 2026-09-27 · primary-source
Primary-source confidence means the source directly documents the statement, not that every historical priority or performance claim has been independently established.