Car stereo

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), CD players (1984), 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. It is also used to create fake engine noise. For the 2015 Ford Mustang EcoBoost, an "Active Noise Control" system was developed that amplifies the engine sound through the car speakers. A similar system is used in the F-150 pickup truck. Volkswagen uses a Soundaktor, a special speaker to play sounds in cars such as the Golf GTi and Beetle Turbo. BMW plays a recorded sample of its motors through the car speakers, using a different samples according to the engine’s load and power.

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.

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