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Vehicle audio

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Title: Vehicle audio  
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Subject: Eugene Polley, Music technology, Cabin (truck), Automotive electronics, In-car entertainment
Collection: American Inventions, Audio Players, In-Car Entertainment, Radio Hobbies, Sound Production Technology
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Vehicle audio

Vehicle audio includes mobile audio, car audio, 12-volt (sometimes other voltages such as 6-volts for pre-1950s vintage cars and 24-volt for civilianized military vehicles or heavy-duty commercial civilian trucks or for light vehicles such as golf carts that use 24-volt electric motors) audio and other terms are used to describe sound systems fitted to an automobile or other vehicle.

A car stereo head unit in a dashboard

The focus of this article is the use in automobiles (hence car radio or car stereo), though the term can be used referring to similar systems fitted to marine and aviation craft, motorcycles, or heavy industrial equipment. The primary use of such equipment is usually entertainment, but can also include communications equipment, public address, and other similar applications.

Modern vehicle manufacturing nearly always includes a complete system of some kind from the factory when the car is assembled. This is referred to as the 'stock' system, or original equipment manufacturer (OEM) system. These systems can be supplied by an exclusive vendor to automakers specifications, or other company that specializes in design or production of such equipment. Additionally, there is a large market of products sold directly to consumers to replace, upgrade, or expand the vehicle's stock sound system capabilities.


  • History 1
    • 1920s-1940s 1.1
    • 1950s-1970s 1.2
    • Chrysler all-transistor car radio 1.3
    • Hybrid car radio 1.4
    • Car record and 8-track tape players 1.5
    • 1980s–Present 1.6
  • Common components and terms 2
    • Stock system 2.1
    • Head unit 2.2
    • Speakers 2.3
    • Amplifiers 2.4
    • Subwoofers 2.5
    • Capacitors 2.6
    • Damping 2.7
    • Other components 2.8
  • Legality 3
  • See also 4
  • Notes 5
  • References 6


An amateur radio set installed in a car, New York 1919.
1937 Philips Auto Radio
1942 Lincoln Continental Cabriolet radio
1964 Mercedes-Benz W110 190c dashboard with original FM Blaupunkt "Frankfurt" head unit.
BLAUPUNKT Köln Radio - German 1958 FORD Taunus 17M P2 deLuxe
1968 AMC Rebel 770 with optional AMC AM/FM radio


Broadcasting began in 1920, about the time vacuum tube radio receivers became available, sparking a "radio craze" during the early Roaring 20s. Many car owners installed home radio sets in their cars as a novelty.[1] The commercial introduction of the fitted car radio came in the 1930s from the Galvin Manufacturing Corporation. Galvin Manufacturing was owned and operated by Paul V. Galvin and his brother Joseph E. Galvin. The Galvin brothers purchased a battery eliminator business in 1928 and the corporation's first product was a battery eliminator that allowed vacuum tube battery-powered radios to run on standard household electric current (see also Rogers Majestic Batteryless Radio). In 1930, the Galvin Corporation introduced one of the first commercial car radios, the Motorola model 5T71, which sold for between $110 and $130 (2014: $1,800) and could be installed in most popular automobiles. Founders Paul Galvin and Joe Galvin came up with the name 'Motorola' when his company started manufacturing car radios. The Motorola prefix "motor-" was chosen because the company's initial focus was in automotive electronics. The name Motorola is derived from the words "motor" and "victrola".

In Germany Blaupunkt fitted their first radio to a Studebaker in 1932 and in the United Kingdom Crossley offered a factory fitted wireless in their 10 hp models from 1933. The early car radio receivers used the battery voltage (6.3 volts at the time) to run the vacuum tube filaments, and generated the required high voltage for the plate supply using a vibrator to drive a step-up transformer. The receivers required more stages than the typical home receiver in order to ensure that enough gain was available to allow the AGC to mask signal fading as the car was driven. When cars switched to 12-volt batteries, the same arrangement was used, with tubes with 12-volt heaters. In 1952 Blaupunkt became the first maker to offer FM receivers.


A common feature of modern car radios is the "seek" function which allows tuning from one station to the next at the push of a button. This was a popular option on some Ford products in the 1950s. It was known as the "Town & Country" radio since it used a pair of switches marked "Town" and "Country." Pressing the Town button actuated a motor to rotate the tuning mechanism while the receiver sensitivity was reduced so that only local (stronger) signals would be received. When a station was tuned, the motor stopped. Pressing the Country button had the same effect except that full sensitivity was enabled so that the very next available station would be selected. In addition, for repeated seeking operations, pressing a foot switch on the driver's floor up to the left where the "dead pedal" is located on modern cars would reactivate the Seek at whatever sensitivity was last selected.

Chrysler all-transistor car radio

1955: World's first All-Transistor car radio - Chrysler Mopar 914HR / Philco model C-5690
A 1950s Philips car radio using both transistor and valves
GM Delco Transistorized "Hybrid" (vacuum tubes and transistors), first offered as an option on the 1956 Chevrolet Corvette car models.

Chrysler and Philco announced an all-transistor car radio in April 1955 as an option for the 1956 model year.[2] This all-transistor car radio was the first tubeless auto set in history, to be developed and produced.[3] It was a $150 "option" for 1956 Chrysler and Imperial cars with sales starting October 1955.[4][5][6]

Hybrid car radio

The early production costs of all-transistor car radios were high. One solution to lower the costs was by designing a "hybrid" car radio, that contained both vacuum tubes and transistors in 1956. The introduction of semiconductors (transistors) allowed the output stage to change to a transistor, which soon lead to the elimination of the vibrator, and the use of "space charge" tubes that only required 6 or 12-volts on their plates without a high voltage plate power supply (typical examples were the 6DR8/EBF83, 6GM8/ECC86, 6DS8/ECH83, 6ES6/EF97 and 6ET6/EF98). Chrysler had discontinued its all-transistor (Mopar model 914HR) optional car radio for its 1956 Chrysler and Imperial car models, and started using "hybrid" car radios for its new 1957 car models.[4]

Car record and 8-track tape players

1990 Ford Sierra CLX Radio-Cassette head unit in a dashboard with cassette storage
1978 AMC Matador sedan factory AM-FM-stereo-8-track unit with album by The Blues Brothers

Advances in electronics allowed additions to the basic radio and Motorola offered 16 2/3 rpm disc players fitted to some Chryslers known as Highway Hi-Fi from as early as 1956[7][8] and ran through 1958. Records were produced under license by Columbia "Special Products" division and sold exclusively through Chrysler dealers. The 45 rpm record player was introduced in 1959 and ran through the early 1960s under the RCA and ARC brand.

Earl "Madman" Muntz introduced the "4-track" tape player in the early 1960s using a continuous loop cartidge and was the first commercially available "car stereo". Tape players using reel to reel equipment followed, but their bulk ensured limited popularity. This changed in 1964 when Philips launched the Compact Cassette. During the 1960s, Lear invented and introduced the 8-track tape in competition with the cassette system. Players were available in many cars and trucks and the 8-track cassettes were popular because of convenience and portability through the early 1980s.

Other early manufacturers and enthusiasts began building extra audio power amplifiers to run on 12 volts (the standard voltage in automotive electrical systems). Jim Fosgate, later to become the founder of Rockford Fosgate, was one such pioneer.


In 1983, Zed Audio became the first company to build a 200-watt per channel car amplifier, the HiFonics Zeus, which was invented by company founder Steven Mantz. At first, speakers from the home audio and professional markets were simply installed into vehicles. However, they were not well suited to the extremes of temperature and vibration which are a normal part of the environment of an automobile. Different manufacturing techniques, and different component materials, were used in construction to adapt to these conditions.

Sound quality in car audio

By the mid-1980s, vacuum tube amplifiers had been completely supplanted by transistorized models. In 1986, toward the goal of maximum sound quality, Milbert Amplifiers introduced a 30-watt-per-channel all-tube audio power amplifier, born in high-end home audio a decade prior and subsequently adapted for use in automobiles. Receiving mention in hundreds of newspaper and magazine articles,[9] several car audio champion cars used Milbert tube amplifiers. By the early 2000s, a few companies had introduced "hybrid" amplifiers using vacuum tube voltage amplification coupled to transistorized power stages for driving loudspeakers. This trend toward sound quality continued as Fender Amplification entered the car audio market in 2012.

Compact Disc technology also began appearing in vehicles after its use in home audio proved popular. Stock and aftermarket CD players began appearing in the late 1980s, competing with the cassette. The Ford Motor Company was the first automobile manufacturer to offer an OEM compact disc player in the 1987 Lincoln Town Car. It was integrated into the lower part of the dashboard, directly under the car's stereo radio controls. Use of the CD in a moving vehicle faced challenges that compromised playback quality of early units. Shock and vibration inherent with driving a vehicle would cause the laser to lose its track and skip around, interrupting playback. Innovations in passive, active, and digital skip protection improved on these conditions in the 90s. However, in general CDs were only put in cars for practicality, rather than fidelity reasons since cars had road and engine noise that defeated high fidelity. And also so that a music library of store-bought CD albums didn't have to be converted to audio cassette, or so store-bought CDs would be reissued from vinyl albums which had little to no tolerance in automotive environments for a similar reason.

Car audio competitions started in the early 1980s

The first known occurred in 1981 in Bakersfield, California and evolved into an annual event. It was called The Summertime Car Show and Sound Off Competition, which at its height drew upwards of 300 contestants and continued into the 1990s. The Summertime Car Show and Sound Off Competition began as a promotional event for Cars on Camera, a magazine founded by owners Steve Silver and Scott Burud. Since the magazine derived a large part of its advertising revenue from local car stereo shops (TransLex, AutoSounds and others), it made sense to hold a sound-off competition in order to create higher demand for magazine ad space. The original event took place in the parking lot of the local Zody's chain store on Ming Avenue, in Bakersfield. However, the following year it was moved to the Kern County fairgrounds in order to accommodate the thousands of participants. By the second year, the event added a men's great legs contest and a bikini contest that attracted contestants from all over California. Cars on Camera changed its name to Camera Ads, which was then sold to Buck Owens Productions.

The most important of these were CAN (formed by Alpine) and NACA (supported by shop owners and amp manufacturers). Both organizations sanctioned countrywide regional events and hosted National Championship events in the late 1980s. They merged to form IASCA in 1990. Despite the move to "quality"-based judging, volume was still a significant portion of most early 1990s competitions. Since then, the two styles—SPL vs. sound quality—have become almost mutually exclusive. The loudness competitions have become known as dB drag racing. Currently, Mobile Electronics Australia, an independent organisation, conducts Sound Quality Competitions (MEASQ) and SPL Competitions (Bass Battle) nationally in Australia. These formats were developed by enthusiast Marc Rushton, the founder of one of the largest enthusiast organizations known as Mobile Electronics Australia.

Common components and terms

Stock system

A stock car audio system refers to the OEM application that the vehicle's manufacturer specified to be installed when the car was built.

These components can be sourced exclusively by the car manufacturer. They can also be contracted to a third party specializing in such applications who then build to spec. Examples of third party manufacturers who produce stock car stereos include Bang & Olufsen, Bose and Harman (through its various brands including Harman Kardon, JBL, and Infinity).

Stock systems can be very minimalist and basic or very comprehensive, depending on the intent of the vehicle manufacturer. Common components found in most basic modern vehicles are the stereo sound head unit, AM/FM receiver, CD player, a pair of speakers mounted in the interior panels, and an auxiliary input jack or USB jack for external playback devices or smartphones.

Head unit

A single DIN head unit, combining radio, CD and MP3

In modern cars, the primary control device for an audio system is commonly referred to as a head unit, and is installed in the center of the dash panel between the driver and the passenger. In older vehicles that had audio components as an option, such devices were mounted externally to the top of or underneath the dash. In rarer occasions, head units have also been mounted vertically directly between the driver and passenger.

The head unit itself is usually a multi-purpose device that houses multiple components in its housing. The most common components are a radio receiver/tuner usually with AM and FM bands, and a small amplifier for driving an audio signal to speakers. Other possible components include various media devices, such as (in older vehicles) a tape player (either 8-track or cassette), CD player, DVD player, HD Radio, Satellite Radio, USB flash memory, and even a portable hard disk drive typically used in notebook computing. Many head units also feature a DSP component, and equalization component (such as bass and treble controls), or a control interface for another feature on the car (such as a back-up/parking camera, navigation system, trip odometer, etc.).

Car stereos generally lag behind audio technology. Cassette decks have been found in cars as late as the 2008 Acura TL, and even in the 2010s the CD player is still a standard part of most car stereos, although their non-car counterparts (i.e. Walkmans) have long disappeared from consumer shelves. Car audio has since adapted to consumer preferences for MP3 players and smartphones since the late 2000s, by adding USB jacks and Bluetooth Streaming Audio; nonetheless consumer studies showed that a significant number of motorists still listen to CDs. In retaining the CD player, a Honda product planner was quoted as saying "It's obviously a horizontal line in the dashboard, very short in height — [a] quarter of an inch. We've never had an issue where a designer has said, you know, we can make it better if you didn't have a CD player. It's relatively small in space." A Chrysler designer had an opposing view, saying "The center stack is such precious real estate — it's like the waterfront in Chicago. Every millimeter, not just every inch, counts", also noting that clustering the dashboard components (radio and air-conditioning ducts) too close together would complicate packaging or risk overheating. Some manufacturers have removed the CD players from their vehicles.[10]

For decades most vehicle dashboards had a rectangular "cutout" where the head unit was installed (which went above another rectangular cutout for the HVAC controls), and this allowed for straightforward replacement of the stock system with an aftermarket stereo, since audio technology improves faster than model updates from car companies. These cutouts, however, also allowed for easy theft of the car radio.[11] Due to auto manufacturing differences over the years, aftermarket headunit products are manufactured in multiple form factors. The primarily used size is mostly referred to by its legacy name of DIN, which refers to ISO 7736. DIN headunits come as single DIN or double DIN. A third less common standard is used mostly by Chrysler group and for a time Mitsubishi in their OEM devices.

Since the mid-2000s many manufacturers have integrated cutout-free stereos into ever-more seamless dashboards, which can be controlled through steering-wheel audio controls and various vehicle sensors. The 2006-2011 Honda Civic (United States) did away with the dashboard cutout for all trims but the base DX (which had no radio) and the Navi models (due to the form factor of the stock audio/navigation system); similarly the 2009-13 Honda Fit (United States) retained the dashboard cutout only for Navi models. Although the car stereo can still be replaced after the intricately designed dashboard coverings are removed, it is a challenge for aftermarket vendors to make the new stereo work with the car's audio controls and sensors. The trend away from dashboards with cutouts, along with improving car audio technology, has eroded sales from the aftermarket stereo industry.[11]


A factory headrest on a Pontiac Fiero embedded with stereo speakers. Eliminated on later models due to cost.
A set of speaker drivers removed from a passenger vehicle

Car speakers [12] [13] are largely functionally identical to any other loudspeaker design with key components specialized for use in mobile environments, and generally serve an identical purpose. One major key design difference is multi-axial mounting of different types of loudspeakers in the same footprint, such as a tweeter directly mounted over a woofer. Another key difference is non-circular cone shapes, such as square, oval, or even triangular. Both of these features reflect a significant reduction in space and size that a speaker may occupy in a vehicle cabin.

Material construction may also include more exotic and hearty components more suitable to mobile use. Marine speakers may have plating for corrosion resistance. Cones may be coated with a substance to resist expansion and contraction under high vehicle cabin temperatures, known to reach 140 °F (60 °C) in the sun. Subwoofers may also be found in mobile audio applications where a cabin speaker may lack the desired low frequency response on its own.

Before stereo radio was introduced, the most common speaker location was in the middle of the dashboard pointing through perforations towards the front windshield. In most modern applications, speakers are mounted certain common locations including the bottom of the doors, the front deck (or dash), the rear deck (or parcel shelf), and the kick panel (located in the footwell below the A-pillar). In the case of subwoofers, mountings are usually under the seat or in the trunk. Each position has certain strengths and limitations from both a quality of sound, and a vehicle manufacturing perspective.


A car audio amplifier

Basically a mobile audio power amplifier, a car 'amp' is a term used to refer to a dedicated electronic amplifier separated from the other components of the system. Though most head units have an amplifier, some do not, or lack the desired power or additional features (e.g., equalization controls or crossover systems). External amplification is available and most often used when existing amplification is insufficient. External amplifiers can be mounted in a different part of the car than the "head unit"; in many cases, an additional amp is mounted in the trunk. This is usually the case when powering a subwoofer, where desired wattage may be several multiples more compared to other cabin speakers.

Though less common, OEM external amplification can be found in 'premium' audio packages, or in luxury cars. More common is aftermarket amplification installed later to satisfy the expansion of an existing system in some way. During operation, it is common for a vehicle's charging system to fluctuate, so a regulated amplifier will maintain its power output regardless of voltage fluctuation. Amplifiers rated at 100 watts at 14.4 volts can not be regarded equal as to an amplifier that can maintain 100 watts at 12 volts. Outside of certain standards, it is not uncommon for manufacturers to list a 14.4 rating and not post a 12 volt value.


Two 10-inch sub-woofers in the trunk of a car

Subwoofers are a specific type of loudspeaker for low frequency reproduction. Mobile 'subs' are not very different from any other application of sub in terms of construction. However it is more common in aftermarket that visual aesthetics take on a more significant role in design than other types of sub drivers, including high contrast paint schemes, grill covers, translucent or refractive materials. Typical subwoofer drivers range in size from an 8" diameter to 10", 12" or 15". Subwoofer systems with 18" woofers were once common, but are rarely seen now. More rarely, some car systems may have 21", 22", 24" or even 32" subwoofers, but are very rare as these are often special order woofers.

A subwoofer is used when existing low frequency production is unsatisfactory, either in frequency range or in volume. Design goals have led to subwoofer, both drivers alone and whole packages, with some extreme difference from one another. Space conscious design has reduced some driver depth to 2" or less, or enclosure depth to 3". Pure loudness through increasing sound pressure has led to some drivers with excursions as great as 4" and vented components to cool the "motor" of the speaker. Quality and clarity has led to driver enclosures being tuned by construction to resonate or neutralize certain frequencies.


After-market speaker system in the cargo area
After-market speakers in the cargo area

Capacitors are used to store energy for the amplifier to draw on demand. They come in many different sizes ranging from 0.5 farad to well over 100 farads and their intended function is to temporarily cover the short-burst electrical demands of a car audio system that have exceeded the general electrical capabilities of the vehicle. As the demand for more power and bigger amplifiers become ever more present in today's vehicle, capacitors are a highly debated topic. Some professionals will claim that a capacitor integrated into certain systems will only hinder the electrical system rather than helping when installed with certain amplifiers. The common ground is they are beneficial with smaller amplifiers when the ability to change the alternator and main battery are not feasible.


Sound deadening material is often used in the door cavities and boot/trunk area to damp excess vibration of the panels in the car in response to loud subwoofer bass tones, especially the boot/trunk. The most common type of deadening is either butyl or rubberized asphalt, a product which has an adhesive quality and can be applied by simply pressing it into place with a roller and using a heat gun (or hair dryer).

Other types of deadening include:

  • Spray on Sound Dampening, less common because of the additional installation difficulties
  • Mass loaded vinyl
  • Closed cell foam

Other components

Radio scanner installed with aftermarket head unit

Other components that make up vehicle audio installations may include:


Extremely loud sound systems in automobiles, particularly the Noise Free America, a 501(c)(3) non-profit group, cites boom cars as one of the most problematic sources of noise pollution.[14] In 2002, the U.S. Department of Justice issued a guide to police officers on how to deal with problems associated with boom cars.[15]

See also


  1. ^ Retrieved March 7, 2014 from Frederick Siemens, "Radio on your motor car" in Popular Radio magazine, Popular Radio, Inc., New York, Vol. 2, No. 4, December 1922, p. 249 on Google Books
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  4. ^ a b
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