Vehicle audio
Vehicle audio is equipment installed in a car or other vehicle to provide in-car entertainment and information for the vehicle occupants. Until the 1950s it consisted of a simple AM radio. Additions since then have included FM radio (1952), 8-track tape players, cassette players, record players, CD players, DVD players, Blu-ray players, navigation systems, Bluetooth telephone integration, and smartphone controllers like CarPlay and Android Auto. Once controlled from the dashboard with a few buttons, they can now be controlled by steering wheel controls and voice commands. Initially implemented for listening to music and radio, vehicle audio is now part of car telematics, telecommunication, in-vehicle security, handsfree calling, navigation, and remote diagnostics systems. The same loudspeakers may also be used to minimize road and engine noise with active noise control, or they may be used to augment engine sounds, for instance making a smaller engine sound bigger. In 1904, well before commercially viable technology for mobile radio was in place, American inventor and self-described "Father of Radio" Lee de Forest demonstrated a car radio at the 1904 Louisiana Purchase Exposition in St. Louis. Around 1920, vacuum tube technology had matured to the point where the availability of radio receivers made radio broadcasting viable. A technical challenge was that the vacuum tubes in the radio receivers required 50 to 250 volt direct current, but car batteries ran at 6V. Voltage was stepped up with a vibrator that provided a pulsating DC which could be converted to a higher voltage with a transformer, rectified, and filtered to create higher-voltage DC. In 1924, Kelly's Motors in NSW, Australia, installed its first car radio. In 1930, the American Galvin Manufacturing Corporation marketed a Motorola-branded radio receiver for 540. A Plymouth sedan, "wired for Philco Transitone radio without extra cost," was advertised in Ladies' Home Journal in 1931.
