View source for Vehicle audio

{{short description|Entertainment electronics in cars}}
{{Redirect|Car radio|the Twenty One Pilots song|Car Radio (song)}}

[[File:Autoradio panasonic.jpg|thumb|A [[ISO 7736|DIN]] [[Automotive head unit|head unit]] with a radio and CD player]]

'''Vehicle audio''' is equipment installed in a [[car]] or other vehicle to provide [[in-car entertainment]] and information for the occupants. Such systems are popularly known as '''car stereos'''. Until the 1950s, it consisted of a simple [[AM radio]]. Additions since then have included [[FM radio]] (1952), [[8-track tape]] players, [[Cassette deck]]s, [[record player]]s, [[CD player]]s, [[DVD player]]s, [[Blu-ray player]]s, [[Automotive navigation system|navigation systems]], [[Bluetooth]] telephone integration and audio [[Streaming media|streaming]], and smartphone controllers like [[CarPlay]] and [[Android Auto]]. Once controlled only from the dashboard with a few buttons, today they can be controlled by [[steering wheel controls]] and [[voice command]]s.

Initially implemented for listening to music and radio, vehicle audio is now part of car [[telematics]], [[telecommunications]], in-vehicle security, [[handsfree]] calling, [[Automotive navigation system|navigation]], and [[Remote diagnostics|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 example, making a small engine sound bigger.{{Citation needed|date=March 2024}} Vehicle audio systems have begun to move to digital platforms utilizing bus networks and optical cables for signal transfer rather than traditional analog cables.

==History==
===Radio===
[[File:Een Philips Autoradio veraangenaamt den rit en houdt den geest frisch.jpg|thumb|upright|1937 Philips Auto Radio. Weighing 24&nbsp;kg and taking 8 litres of space, it was floor mounted with a wired remote control to be fitted to the dashboard.]]

In 1904, before commercially viable technology for mobile radio was in place, [[United States|American]] [[inventor]] and self-described "Father of Radio" [[Lee de Forest]] demonstrated a car radio at the 1904 [[Louisiana Purchase Exposition]] in [[St. Louis, Missouri|St. Louis]].<ref>{{cite web |last=Erb |first=Ernst |title=First Car radios-history and development of early Car Radios |url= https://www.radiomuseum.org/forum/first_car_radios_history_and_development_of_early_car_radios.html |website=radiomuseum.org |date=30 April 2012 |access-date=10 February 2020}}</ref>

Around 1920, [[vacuum tube]] technology had matured to the point where the availability of [[radio receiver]]s made radio broadcasting viable.<ref>{{cite journal|last=Guarnieri|first=M.|year=2012|title=The age of vacuum tubes: the conquest of analog communications |journal=IEEE Ind. Electron. Mag. |pages=52–54 |doi=10.1109/MIE.2012.2193274 |s2cid=42357863}}</ref> A technical challenge was that the vacuum tubes in the radio receivers required 50 to 250 [[Voltage|volt]] [[direct current]], but car batteries ran at 6V. Voltage was stepped up with a [[Vibrator (electronic)|vibrator]] that provided a pulsating DC which could be converted to a higher voltage with a [[transformer]], [[Rectifier|rectified]], and filtered to create higher-voltage DC.{{Citation needed|date=March 2024}}

In 1920 [[Guglielmo Marconi]] demonstrated a car wireless receiver in Chelmsford, Essex, England where his company had installed an experimental 6&nbsp;kW [[longwave]] transmitter on 2750 meters (109&nbsp;kHz).

In 1924, Kelly's Motors in NSW, Australia, installed its first car radio.<ref>{{cite web|url= http://www.carhistory4u.com/the-last-100-years/parts-of-the-car/car-radio |title=Car History 4U – History of the Car Radio in Motor Cars |date=2012-12-09 |access-date=2018-08-17 |archive-url= https://web.archive.org/web/20121209064343/http://www.carhistory4u.com/the-last-100-years/parts-of-the-car/car-radio |archive-date=2012-12-09}}</ref><ref>{{cite web|url= https://www.radioinfo.com.au/news/lessons-history-inform-acma-thinking-today-radcomms-conference |title=Lessons of history inform ACMA thinking today: RadComms Conference|date=30 April 2009 |website=radioinfo.com.au |access-date=17 August 2018 |author1=Iamadmin }}</ref><ref>{{cite web|url= https://www.autoguru.com.au/car-advice/articles/10-aussie-auto-facts-you-probably-didnt-know |title=10 Aussie Auto Facts You Probably Didn't Know |website=autoguru.com.au |access-date=2018-08-17}}</ref>

In 1930, the American [[Galvin Manufacturing Corporation]] marketed a [[Motorola]]-branded [[radio receiver]] for $130.<ref name="caranddriver">{{cite web|title=The History of Car Radios|url= http://www.caranddriver.com/features/the-history-of-car-radios |work=Car and Driver|date= 25 October 2010 |access-date=14 January 2016}}</ref> The cost of these early radios was expensive, relative to the price of a car: the contemporary [[Ford Model A (1927–31)|Ford Model A]] cost about $540. A Plymouth sedan, "wired for Philco Transitone radio without extra cost," was advertised in ''[[Ladies' Home Journal]]'' in 1931. In 1932 in Germany the [[Blaupunkt]] AS 5 [[medium wave]] and [[longwave]] radio was marketed for 465 Reichsmark, about one-third of the price of a small car. Because it took nearly 10 litres of space, it could not be located near the driver and was operated via a steering wheel remote control.<ref>{{cite web |title=Blaupunkt: Success Story |url=http://www.blaupunkt.com/us/about-us/success-story/ |website=blaupunkt.com |access-date=2016-01-14}}</ref> In 1933, [[Crossley Motors]] offered a factory fitted car radio for £35.<ref name="guinness">{{cite book |title=Guinness book of car facts and feats |publisher=Guinness Superlatives |year=1977 |isbn=0-900424-54-0 |location=London}}</ref> By the late 1930s, push button AM radios were considered a standard feature. In 1946, there were an estimated 9 million AM car radios in use.<ref>{{cite web|title=When the Car Radio Was Introduced, People Freaked Out |url = http://mentalfloss.com/article/29631/when-car-radio-was-introduced-people-freaked-out |work=MentalFloss |date=3 January 2012 |access-date=2016-08-10}}</ref>

An [[Frequency modulation|FM]] receiver was offered by Blaupunkt in 1952. In 1953, Becker introduced the AM/FM Becker Mexico with a Variometer tuner, basically a station-search or scan function.<ref name="The History of the Car Stereo">{{cite web|title=The History of the Car Stereo |url= https://www.pcmag.com/article2/0,2817,2399878,00.asp |work=PCMag |access-date=2016-01-14}}</ref>

In April 1955, the [[Chrysler|Chrysler Corporation]] announced that it was offering a [[Mopar]] model 914HR branded [[Philco]] all-transistor car radio,<ref>{{cite web|title=Mopar 914-HR Ch= C-5690HR Car Radio Philco, Philadelphia |url= http://www.radiomuseum.org/r/philco_mopar_914_hr_ch_c_5690hr.html |website=radiomuseum.org |access-date=2016-01-14}}</ref> as a $150 option for its 1956 Chrysler and Imperial car models. Chrysler Corporation had decided to discontinue its all-transistor car radio option at the end of 1956, due to it being too expensive, and replaced it with a cheaper hybrid (transistors and low voltage vacuum tubes) car radio for its new 1957 car models.<ref name="Hirsh">{{cite web|last=Hirsh |first=Rick |url= https://www.allpar.com/threads/1955-chrysler%E2%80%99s-all-transistor-mopar-car-radio.228494/?post_id=1085222592&nested_view=1&sortby=oldest#post-1085222592 |title=Philco's All-Transistor Mopar Car Radio |website=allpar.com |date=November 16, 2020 |access-date=February 13, 2024}}</ref> In 1963, Becker introduced the Monte Carlo, a tubeless [[Solid-state electronics|solid state]] radio with no vacuum tubes.<ref name="The History of the Car Stereo"/>

From 1974 to 2005, the [[Autofahrer-Rundfunk-Informationssystem]] was used by the German [[ARD (broadcaster)|ARD]] network.<ref>{{cite web |title=Institut für Rundfunktechnik Historic Milestones |url= http://www.irt.de/en/irt/milestones.html |website=irt.de |access-date=2009-05-17 |archive-url= https://web.archive.org/web/20090420084023/http://www.irt.de/en/irt/milestones.html |archive-date= 20 April 2009 | url-status= live}}</ref> Developed jointly by the {{lang|de|[[Institut für Rundfunktechnik]]}} and Blaupunkt,<ref>{{cite web|title=March 2009: RDS is now 25 – the complete history |url= http://www.rds.org.uk/rds98/pdf/RDS_25_090327_4.pdf |website=rds.org.uk |date=2009-03-27 |page=1 |access-date=2009-05-17 |url-status=dead |archive-url= https://web.archive.org/web/20091007182550/http://www.rds.org.uk/rds98/pdf/RDS_25_090327_4.pdf |archive-date=October 7, 2009 }}</ref> it indicated the presence of traffic announcements through manipulation of the 57{{spaces}}[[kHz]] [[subcarrier]] of the station's FM signal.<ref>{{cite patent|country=EP|number=1432157|title=Method for separating a RDS signal component and signal receiver|pubdate=2004-06-23|assign=[[Sony|Sony International (Europe) GMBH]]|inventor1-last=Wildhagen|inventor1-first=Jens}}</ref> ARI was replaced by the [[Radio Data System]].<ref>{{cite web |title=Das Autofahrer-Rundfunk-Informationssystem wird abgeschaltet |url=http://www.shortnews.de/start.cfm?id=562110 |website=shortnews.de |location=Regensburg, Germany |date=2005-02-28 |language=de |access-date=2009-05-17 |archive-date=2013-02-11 |archive-url=https://archive.today/20130211234146/http://www.shortnews.de/start.cfm?id=562110 |url-status=dead }}</ref>

The AM/FM radio combined with a CD player has remained a mainstay of car audio, despite being obsolescent in non-car applications.<ref>{{cite web|url= https://www.crutchfield.ca/learn/is-the-car-cd-player-dead.html |title=Is the car CD player dead?|first=Dominic |last=DeVito |work=Crutchfield |access-date=February 13, 2024}}</ref><ref>{{cite web|url= https://www.hagerty.com/articles-videos/Articles/2018/01/08/obsolete-car-audio-part-5 |title=History of obsolete car audio, part 5: What's old is new (or, at least, in vogue) |first=Rob|last=Siegel |website=hagerty.com |date=8 January 2018 }}</ref>

In the 2010s, [[internet radio]], [[Satellite radio system|satellite radio]], [[music streaming service|streaming]], and [[podcasting]] came into competition with AM/FM radio. By this time some models were offering [[5.1 surround sound]].{{Citation needed|date=March 2024}}

In 2023, several automobile manufacturers, including [[Ford Motor Company]], announced plans to discontinue offering the AM radio band in new vehicles, starting with the 2024 model year. Ford later reversed its announcement, with chief executive officer [[Jim Farley (businessman)|Jim Farley]] citing the importance of AM's [[emergency alert system]]. Audi, BMW, Volvo, and Tesla had already started to not offer the AM band on their entertainment systems, specifically on their electric vehicles.<ref>{{cite web|title=Ford Not Nixing AM Radio in 2024 Models after All, CEO Says |work=Car and Driver |date=May 23, 2023 |url= https://www.caranddriver.com/news/a43980143/2024-ford-lincoln-models-keep-am-radio/ |first=y Eric |last=Stafford |access-date=February 13, 2024}}</ref> The previous announcement had several lawmakers introduce bipartisan legislation to require that automobile manufacturers include the AM band on their audio/entertainment systems.<ref>{{cite web|url= https://www.reuters.com/business/autos-transportation/us-lawmakers-want-bar-automakers-eliminating-am-radio-new-vehicles-2023-05-17/ |title=US lawmakers want to bar automakers from eliminating AM radio in new vehicles |first=David |last=Shepardson |date=May 17, 2023 |work=Reuters |access-date=February 13, 2024}}</ref>

===Physical media and connectivity===
Mobile players for physical media have been provided for [[vinyl record]]s, [[8-track tape]]s, [[cassette tape]]s, [[compact disc]]s, and [[MP3]]s. The increased sophistication of the vehicle audio system to accommodate such media has made the audio unit a common target of car break-ins, so these are equipped with [[anti-theft system]]s too.{{Citation needed|date=March 2024}}

Attempts at providing mobile play from media were first made with vinyl records, beginning in the 1950s. The first such player was offered by Chrysler as an option on 1956 Chrysler, Desoto, Dodge, and Plymouth cars. The player was developed by [[CBS Labs]] and played a limited selection of specially provided {{convert|7|in|adj=on}} discs at {{frac|16|2|3}} [[RPM]]. The unit was an expensive option and was dropped after two years. Cheaper options using commonly available [[45 rpm record]]s were made by [[RCA Victor]] (available only in 1961) and [[Norelco]]. All of these players required extra pressure on the [[Gramophone needle|needle]] to avoid skipping during vehicle movement, which caused accelerated wear on the records.<ref>{{cite web |url= https://www.consumerreports.org/cro/news/2014/04/record-players-were-the-infotainment-systems-of-the-1950s-and-60s/index.htm |title=Record players were the infotainment systems of the 1950s and '60s |first=Sharon |last=Riley |date=April 12, 2014 |work=Consumer Reports |access-date=April 16, 2020}}</ref>

In 1962, Muntz introduced the Wayfarer 4-track cartridge tape player. Celebrities, including Frank Sinatra, had these units installed in their cars.

In 1965, [[Ford Motor Company|Ford]] and Motorola jointly introduced the in-car [[8-track tape]] player as optional equipment for 1966 Ford car models. In 1968, a dashboard car radio with a built-in [[cassette tape]] player was introduced by Philips. In subsequent years, cassettes supplanted the 8-track and improved the technology, with longer play times, better tape quality, auto-reverse, and [[Dolby noise-reduction system|Dolby noise reduction]]. They were popular throughout the 1970s and 1980s. Cassette players were still found in vehicles as late as the 2005–06 [[Honda CR-V]] and 2008 [[Acura TL]]. There have also been vehicle audio units that accept both compact cassettes and CDs.{{Citation needed|date=March 2024}}

Pioneer introduced the CDX-1, the first car [[CD]] (compact disc) player, in 1984. It was known for its improved sound quality, instant track skipping, and the format's increased durability over cassette tapes. Car CD changers started to gain popularity in the late 1980s and continued throughout the 1990s, with the earlier devices being trunk-mounted and later ones being mounted in the head unit, some able to accommodate six to ten CDs.<ref>{{cite web|url= http://ca.complex.com/music/2015/02/the-evolution-of-playing-music-in-your-car/1980s-1990s-the-rise-of-the-cd |title=The Evolution of Playing Music in Your Car 1980s–1990s: The Rise of the CD |first=Meaghan |last=Garvey |date=February 10, 2015 |work=Complex CA |access-date=February 13, 2024}}</ref> Stock and aftermarket CD players began appearing in the late 1980s, competing with the cassette. The first automaker to offer a CD player in their cars from the factory was Mercedes, who offered a Becker Mexico radio with an integrated CD player as an option on most of their models starting in either 1985 or 1986.<ref>{{cite web|url=https://www.auto-preisliste.de/download-preislisten-aller-marken/file/31100-1986-09-preisliste-mercedes-benz-s-klasse|title=1986-09_preisliste_mercedes-benz_s-klasse|access-date=13 May 2025}}</ref><ref>{{cite web|url=https://www.auto-preisliste.de/download-preislisten-aller-marken/file/30173-1986-09-preisliste-mercedes-benz-190|title=1986-09_preisliste_mercedes-benz_190|access-date=13 May 2025}}</ref><ref>{{cite web|url=https://autocatalogarchive.com/mercedes/|title=Das neue Programm der S-Klasse. Mercedes-Benz 260 SE, 300 SE/SEL, 420 SE/SEL, 500 SE/SEL. 560 SEL (1985)|work=Auto Catalog Archive &#124; Car Brochures |date=8 June 2016 |access-date=13 May 2025}}</ref> Soon after, Lincoln introduced an OEM CD player in the 1987 [[Lincoln Town Car]], built in collaboration with JBL. The last new cars in the American market to be factory-equipped with a cassette deck in the dashboard were the 2010 Lexus SC430,<ref>{{cite news|title=For Car Cassette Decks, Play Time Is Over |url = https://www.nytimes.com/2011/02/06/automobiles/06AUDIO.html |newspaper=The New York Times |date=2011-02-04|access-date=2016-01-14 |first=Stephen |last=Williams}}</ref> and the Ford Crown Victoria.<ref>{{cite news|title=The in car cassette deck lives on for one more year |url= https://www.autoguide.com/auto-news/2011/03/the-in-car-cassette-deck-lives-on-for-one-more-year.html |first=Amy |last=Tokic |date=March 26, 2011 |access-date=February 13, 2024}}</ref> A car cassette adapter allowed motorists to plug in a portable music player (CD player, MP3 player) into an existing installed cassette tape deck.<ref>{{Cite web|url= https://www.vice.com/en/article/the-car-cassette-adapter-was-an-unsung-hero-at-the-dawn-of-the-digital-age/ |title=The Car Cassette Adapter Was an Unsung Hero at the Dawn of the Digital Age |first=Ernie |last=Smith |date=November 6, 2019}}</ref>

In the early 21st century, compact digital storage media – [[Bluetooth]]-enabled devices, [[thumb drive]]s, [[memory cards]], and dedicated hard drives – came to be accommodated by vehicle audio systems. Around this time auxiliary input jacks and USB ports were added to connect [[MP3 player]]s to the vehicle's speakers. Minivans and three-row SUVs have an available rear entertainment system with a [[DVD player]] to entertain passengers.<ref>{{cite web| url= https://www.hondainfocenter.com/2022/Odyssey/Feature-Guide/Interior-Features/Advanced-Rear-Entertainment-System-RES/ |title=Advanced Rear Entertainment System (RES) ... – 2022 Honda Odyssey &#124; Honda Info Center }}</ref>

The automobile head unit became increasingly important as a housing for front and [[backup camera|backup]] [[dashcam]]s, [[Automotive navigation system|navis]], and operating systems with multiple functions, such as [[Android Auto]], [[CarPlay]] and [[MirrorLink]], allowing a smartphone's music library and navigation apps to be controlled via the [[In-car entertainment|vehicle's infotainment system]].<ref>{{cite web |last=Bruzek |first=Joe |date=January 27, 2016 |title=2015 Honda Fit Apps Remind Us Why Apple CarPlay, Android Auto Rock |url= https://www.cars.com/articles/2015-honda-fit-apps-remind-us-why-apple-carplay-android-auto-rock-1420683234115/ |access-date=September 29, 2023 |website=cars.com}}</ref> Latest models are coming equipped with features like Bluetooth technology along with HDMI port for better connectivity. Screen size varies from {{convert|5|to|7|in|adj=on}} for the double Din car stereos.<ref>{{cite web|url= https://stereoauthority.com/best-double-din-stereo/ |title=Best Double Din Stereo 2019 – Top 5 Reviews|date=2019-01-01 |work=Stereo Authority |access-date=2019-01-16}}</ref>

===Active noise control and noise synthesis===
The automobile sound system may be part of an [[active noise control]] system which reduces engine and road noise for the driver and passengers. One or more microphones are used to pick up sound from various places on the vehicle, especially the engine compartment, underside, or exhaust pipes, and these signals are handled by a [[digital signal processor]] (DSP) and then sent to the loudspeakers in such a way that the processed signal reduces or cancels out the outside noise heard inside the car. An early system focused only on engine noise was developed by [[Lotus Cars|Lotus]] and licensed for the 1992 [[Nissan Bluebird]] models sold in Japan.<ref>{{cite web |last1=Peachey |first1=Colin |title=Noise Optimization Technology with Colin Peachey of Lotus Engineering |url= https://www.automotive-iq.com/alternative-powertrains/interviews/noise-optimization-technology-with-colin-peachey-o |work=Automotive IQ |date=1 October 2013 |access-date=25 March 2021}}</ref> Lotus later teamed with [[Harman International Industries|Harman]] in 2009 to develop a more complete noise reduction system, including road and tire noise as well as chassis vibrations.<ref>{{cite web |last1=Filipponio |first1=Frank |title=Lotus and Harman partner on noise-cancelling, noise-creating tech |url= https://www.autoblog.com/2009/04/16/lotus-and-harman-partner-on-noise-cancelling-noise-creating-tec/ |publisher=Autoblog |access-date=25 March 2021 |date=16 April 2009}}</ref> One benefit of active noise control is that the car can weigh less, with less sound-deadening material used, and without a heavy [[balance shaft]] in the engine. Removing the balance shaft also increases fuel efficiency.<ref>{{cite web|url= https://www.automotive-iq.com/alternative-powertrains/interviews/active-noise-control-with-colin-peachey-of-lotus-e |title=Active Noise Control with Colin Peachey of Lotus Engineering |first=Colin |last=Peachey |date=October 7, 2013 |work=Automotive IQ |access-date=25 March 2021}}</ref> The 2013 Honda Accord used an active noise control system, as did the 2013 Lincoln luxury line and the Ford C-Max and Fusion models.<ref>{{cite web |url= http://beta.usatoday.com/story/money/cars/driveon/2012/09/26/cars-noise-cancellation-technology/1590703/ |title= Automakers shush cars with noise cancellation technology |work= USA Today }}{{Dead link|date=July 2025 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Other operating data, such as the engine's speed in revolutions per minute (RPM) or the car's highway speed, may also play a part in the DSP. A multiple source reduction system may reach as much as 80% of the noise removed.{{Citation needed|date=June 2023}}

The same system may also be used to synthesize or augment engine noise to make the engine sound more powerful to the driver.<ref>{{cite news|title = America's best-selling cars and trucks are built on lies: The rise of fake engine noise|url= https://www.washingtonpost.com/business/economy/americas-best-selling-cars-and-trucks-are-built-on-lies-the-rise-of-fake-engine-noise/2015/01/21/6db09a10-a0ba-11e4-b146-577832eafcb4_story.html |newspaper=The Washington Post |date=2015-01-21 |access-date=2016-01-16 |first=Drew |last=Harwell}}</ref> For the 2015 [[Ford Mustang]] EcoBoost Fastback and EcoBoost Fastback Premium, an "Active Noise Control" system was developed that amplifies the engine sound through the car speakers. A similar system is used in the [[Ford F-Series|F-150]] [[pickup truck]]. [[Volkswagen]] uses a [[Soundaktor]], a special speaker to play sounds in cars such as the [[Volkswagen Golf|Golf]] GTi and [[Volkswagen New Beetle|Beetle]] Turbo. [[BMW]] plays a recorded sample of its motors through the car speakers, using different samples according to the engine's load and power.<ref>{{cite web|title= The Rise of the Fake Engine Roar |url= http://www.popularmechanics.com/cars/a7923/the-rise-of-the-fake-engine-roar-11291754/ |work=Popular Mechanics |date=2012-08-02 |access-date = 2016-01-16}}</ref>

==Components and terms==
The stock system is the [[OEM]] application that the vehicle's manufacturer specified to be installed when the car was built.

Aftermarket components can also be used.

* [[Head unit]]: Headunit products includes the screen and buttons and are manufactured mainly in DIN form factor, which refers to [[ISO 7736]]. Head units come as single DIN or double DIN.
* Connectors for car audio, where [[ISO 10487]] Harness Adapter is used.
* [[Capacitor]]s.
* Mobile [[audio power amplifier]]s.

Amplifiers increase the power level of audio signals. Some head units have built-in stereo amplifiers. Other car audio systems use a separate stand-alone amplifier. Every amplifier has a rated power level sometimes noted on the head unit with the built-in amplifier, or on the label of a stand-alone unit.{{Citation needed|date=March 2024}}

# Coaxial speakers: These are the most common type of car speakers and are often factory-installed. They usually consist of a woofer and a tweeter mounted on the same axis, and are designed to reproduce a wide range of frequencies.
# Component speakers: These speakers are designed for higher-end car audio systems and typically consist of separate woofers, tweeters, and crossovers. This allows for more precise sound tuning and a higher level of sound quality.
# Subwoofers: These speakers are designed to reproduce low-frequency sounds, particularly bass. They come in various sizes and power levels, and can be used to enhance the bass in a car audio system.
# Mid-range speakers: These speakers are designed to reproduce mid-range frequencies, such as vocals and instruments like guitars and pianos.
# Tweeters: These speakers are designed to reproduce high-frequency sounds, such as cymbals and other high-pitched instruments.
# Sound-deadening material is often used in the door cavities and boot area to dampen excess vibration of the panels in the car in response to loud subwoofer bass tones, especially the boot (trunk).
# [[Optical disc drive|Optical drive]]s with [[Optical disc drive#Tray and slot loading|slot-loading mechanism]].
# Digital Sound processors also known as DSP chips to enhance or alter the sound signal being reproduced.

== Add-ons ==
[[File:Project 365 -267- 240922 Trailing Cables.jpg|thumb|A [[digital radio]] adapter add-on for a car, designed for listening to [[Digital Audio Broadcasting|DAB]] radio broadcasts on vehicles that would otherwise lack the feature]]
Vehicles can be [[retrofitted]] or upgraded with additional, non-fixed audio systems. [[FM transmitter (personal device)|FM transmitters]] provide a way of listening to audio output from a device using the car's FM radio.<ref>{{Cite web |title=You Don't Need CarPlay in Your New Car. You Need $11 |url=https://www.motor1.com/features/727619/apple-carplay-bluetooth-general-motors/ |access-date=2025-03-01 |website=Motor1.com |language=en}}</ref><ref>{{Cite web |last=Stegner |first=Ben |date=2018-02-01 |title=How to Play Music From Your Phone to a Car Stereo |url=https://www.makeuseof.com/tag/how-to-play-music-from-phone-to-car/ |access-date=2025-03-01 |website=MUO |language=en}}</ref> [[Cassette tape adapter]]s give the ability of an auxiliary input on a car cassette deck, being able to output audio on the car stereo from a smartphone, [[portable CD player]] and any other equipment using the standard [[headphone jack]]. There also exist cassette adapters that make use of [[Bluetooth]].<ref>{{Cite web |date=2010-12-29 |title=Mobile Fun Bluetooth Cassette Adapter |url=http://www.allaboutsymbian.com/reviews/item/12429_mobile_fun_bluetooth_cassette_.php |access-date=2025-03-01 |website=All About Symbian |language=en}}</ref> Older cars that may lack Bluetooth in its stereo unit can also be fitted with a Bluetooth adapter through e.g. the car's [[Automobile auxiliary power outlet|cigarette power outlet]].<ref>{{Cite web |title=How to add Bluetooth to your car |url=https://www.drive.com.au/caradvice/how-to-add-bluetooth-to-your-car/ |access-date=2025-03-01 |website=Drive |language=en}}</ref>

Newer cars that may lack a native [[CD]] player may also be upgraded using a portable CD player outputting through the car stereo's auxiliary port, or through Bluetooth or an FM transmitter.<ref>{{Cite web |date=2017-05-11 |title=Dear Wirecutter: Can I Add a CD Player to a Car Stereo? |url=https://www.nytimes.com/wirecutter/blog/add-cd-player-car-stereo/ |access-date=2025-03-01 |website=Wirecutter: Reviews for the Real World |language=en-US}}</ref> Some companies, including car manufacturers themselves, have offered external CD players as add-ons, designed specifically for use in the car.<ref>{{Cite web |title=How to Keep Playing CDs in Your Modern Car: Top Solutions Explored {{!}} Kunes Auto Group Blog |url=https://shopkunes.com/blog/how-to-keep-playing-cds-in-your-modern-car-top-solutions-explored |access-date=2025-03-01 |website=Kunes Auto Group |language=en}}</ref>

==Legality==
Excessively loud sound systems in automobiles violate the [[Noise regulation|noise ordinance]] of municipalities, some of which have outlawed them.<ref>{{cite web|url= https://noisefree.org/boomcars.php |title=Boom Cars, Noise Free America |website=Noisefree.org |access-date=February 18, 2015 |archive-url= https://web.archive.org/web/20150219064546/http://noisefree.org/boomcars.php |archive-date=February 19, 2015 |url-status=dead}}</ref> In 2002, the [[United States Department of Justice|U.S. Department of Justice]] issued a guide to [[police officer]]s on how to deal with problems associated with loud audio systems in cars.<ref>{{cite book |url= http://www.cops.usdoj.gov/pdf/e05021550.pdf |title=Loud Car Stereos |first=Michael S. |last=Scott |publisher=U.S. Department of Justice, Community Oriented Policing Services |date=May 22, 2002 |access-date=February 18, 2015 |url-status=dead |archive-url= https://web.archive.org/web/20150923210515/http://www.cops.usdoj.gov/pdf/e05021550.pdf |archive-date=September 23, 2015 }}</ref>

==Gallery==
<gallery>
File:Autoradio Roehre.jpg|A 1950s Philips car radio using both transistor and valves. This model used a range of valves that only required 12 volts for their plate (anode) voltage.<ref>{{cite web |title=6DS8 |url= http://www.r-type.org/exhib/aaa0246.htm |website=r-type.org |date=28 January 2019 |access-date=25 March 2021}}</ref>
File:Chevrolet Corvette Transistorized Hybrid Car Radio-1956.JPG|GM Delco Transistorized "Hybrid" (vacuum tubes and transistors), first offered as an option on the 1956 Chevrolet Corvette car models
File:Kenwood KDC-W4527.jpg|A car stereo head unit in a dashboard
File:Lincoln Continental Cabriolet photo-58.JPG|1942 Lincoln Continental Cabriolet radio
File:VW Hebmüller (2015-09-12 3701).JPG|Dashboard of VW Hebmüller with Telefunken Radio (1949/50)
File:FORD Taunus 17M P2(TL) deLuxe Two door 1958 Radio Blaupunkt Köln.jpg|Blaupunkt Köln Radio - German 1958 Ford Taunus 17M P2 deLuxe
File:W110 Cockpit.jpg|1964 [[Mercedes-Benz W110]] 190c dashboard with original FM Blaupunkt "Frankfurt" head unit.
File:1978 AMC Matador sedan red NC detail of factory AM-FM-stereo-8-track unit.jpg|1978 AMC Matador sedan factory AM-FM-stereo-[[8-track tape|8-track]] unit with an album by [[The Blues Brothers]]
File:Ford Sierra CLX 1990 Radio.jpg|1990 Ford Sierra CLX Radio-Cassette head unit in a dashboard with cassette storage
BP74-Servicemenu-2008-05-31-03.jpg|Early 00's [[Blaupunkt]] car radio (close look)
File:2008-04-16 Car audio drivers.jpg|A set of speaker drivers removed from a passenger vehicle
File:Lightning Audio 750 Watts Car Audio Amplifier.JPG|A car audio amplifier
File:JLaudiosubwoofers.jpg|Two {{convert|10|in|adj=on}} subwoofers in the trunk of a car
File:Toyota Camry Factory Integrated (In-Dash) Head Unit.jpg|As technology keeps evolving, head units are now paired with the climate control system and other functions
File:SiriusXM_Display_on_Volkswagen's_RNS-510_Receiver.png|An example of the evolution: 2010's Volkswagen has a smart panel both with buttons and a touch screen to play [[music]].
</gallery>

==See also==
* [[Active sound design]]
* [[List of auto parts]]
* [[List of car audio manufacturers and brands]]

==References==
{{reflist|colwidth=30em}}

{{Audio players}}
{{Car-interior}}
{{Music technology}}

{{DEFAULTSORT:Vehicle Audio}}
[[Category:American inventions]]
[[Category:Audio players]]
[[Category:In-car entertainment]]
[[Category:Radio hobbies]]
[[Category:Automotive accessories]]
[[Category:Automotive technologies]]