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# Car audio

Car audio/video (car AV) is a term used to describe the sound or video system fitted in an automobile. A stock car audio system refers to one that was specified by the manufacturer when the car was built. A custom car audio installation can involve anything from the upgrade of the radio to a full-blown customization of a car based around its audio equipment. Events are held where entrants compete for the loudest or most innovative systems.

## History

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. It may be a surprise to some that this facility 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.

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 12 volts on their plates without a high voltage plate power supply.

Advances in electronics allowed additions to the basic radio and Motorola offered 45 rpm disc players fitted to some Chryslers from as early as 1956. 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 60's Lear invented and introduced the 8track cartdrige in competition with the cassette system. Other early manufacturers and enthusiasts began building extra audio 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. The company a/d/s also brought an amplifier to market in 1978.

In 1983, Zed Audio became the first company to build a 200 watt per channel car amplifier, 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. Modified drivers were developed to cope with these factors.

Today, advances in acoustic technology mean that even two 10-inch speakers in a well-designed efficient enclosure can produce more than 100 decibels SPL (sound pressure level) within the cabin.

Car audio competitions started in the early 1980s in a quest to find the loudest and/or most outrageous installations. For example, in 1985, Wayne Harris famously modified a 1960 Cadillac Hearse to feature three 24-inch subwoofers as well as eight 12-inch subwoofers. Little consideration was given to sound quality early on, but in the early 1990s, several organizations, including IASCA, began car audio competitions focusing on sound quality. The two styles -- SPL vs. sound quality -- have become almost mutually exclusive. The loudness competitions have become known as dB drag racing. Currently, MEASQ conducts Sound Quality Competitions nationally in Australia.

## Components

The most common and familiar piece of audio equipment is the radio/tape player/CD player/DVD Player which is generically described as a Head unit, which also can be called a head deck. It is also the most likely component to be upgraded with an after market item. A recent development in head unit technology has been the addition of CD players with MP3, Ogg, WMA, AAC, and USB, Bluetooth and Wi-Fi support.

Most modern cars include a CD player, and some have the option for a CD changer, which holds multiple discs either in the head unit itself or in a separate unit usually located in a trunk or console. More recent is the addition of DVD players and LCD screens. The LCD screen is either integrated such that it slides out and folds up, or integrated into the instrument console. Otherwise, the DVD head unit feeds video output into separately mounted displays, either folding down from the roof, or mounted into the headrest for viewing by rear seat passengers. The video screen may also show video output of an other components such as a navigation system, gaming console or parking camera that could be automatically activated when the car is put into reverse.

Head units generally offer some crossover(Audio_crossover) and Equalization capabilities. Generally included are parametric and/or graphic equalizers. The crossovers generally use high pass and low pass filters to only send specific frequency ranges to specific components. The subsonic filter is generally handled at the amplifier, not the head unit.

Head units are mainly found in two sizes, Single and Double DIN. Some single DIN units are Alpine's(Alpine_car_audio) CDA-9887, Kenwood's(Kenwood_Electronics) KDC-X991, and Pioneer's(Pioneer_Corporation) DEH-880mp.

### Speakers

Car speakers are generally located in doors and rear parcel shelves of a sedan in modern cars. High-end or competition stereo systems often have speakers mounted in "kick panel" enclosures, allowing for larger drivers and better driver placement. Before stereo radio was introduced, the most common speaker location was in the middle of the dashboard pointing through perforations towards the front windshield.

Car speakers come in a range of sizes, most commonly between 4 inch and 12 inch, and also in non circular sizes such as 6 X 9. The most common impedance for car speakers is 4 Ohms. Speaker power rating is usually between 35W (common head unit output) and 250W. High-end audio systems include Component Speakers that consist of a matched tweeter (high frequency), midrange (medium frequency) and woofer (low frequency) set. These component pairs are available in two speaker and three speaker combinations, and include an audio crossover which limits the frequency range that each component speaker must handle. This allows each cone to produce its optimal frequency for maximum sound quality and volume. In addition subwoofer(s) may be installed for bass and sub bass (ultra low frequency), which is felt more than heard depending on the sub frequency. Crossover systems can be active or passive crossover networks. Active electronic crossovers divide the signals before they are sent to the amplifiers giving a dedicated amplifier channel to each individual driver in the component system. Passive crossover networks divide the signal after amplification, making it possible to run multiple speaker component sets using just one channel.

5.1 and even 7.1 channel surround sound systems, as well as THX II Certified, are now being integrated into some cars by both aftermarket enthusiasts and car manufacturers themselves. These systems include the full complement of front left, right and center speakers along with rear right and left surround speakers (7.1 systems include left and right side surround speakers) along with digital surround sound processors. They can allow you to turn your car into a virtual rolling theater. This is becoming increasingly popular with the advent of SACD and DVD Audio which contain music encoded in 5.1.

### Amplifiers

Car audio amplifiers are used to give extra power to speakers in the system that need more power than what the stereo or head unit can produce. The most common amplifiers are used for subwoofers. Preferences for amplifiers greatly vary. Today there are countless brands and prices to choose from. The most common amps are one-channel (mono-block) or 2, and 4 channels. Some top brands in car audio amplification are: Pioneer, Kicker, MTX, Sundown Audio, RD Audio, Incriminator Audio, Digital Designs (DD), US Amps, JL Audio, and Rockford Fosgate.

Amplifiers are classified by how they make the power. There are Class D, Class A, Class A/B, Class B, and many variations on the Class D such as Class X, Class TX, etc. The internal components of an amplifier are generally referred to as "Amp Guts" and by how stout the amp looks on the inside you can get a VERY general idea on the power output.

Also, a general rule of thumb is the amplifier can only produce around the power it is fused for. Many amps claim 3000 watts, but only have 140 amps of fusing. For 3000 watts you would still need about 200 amps of fusing, but that is considering the amp is 100% efficient. No amplifier on the market is 100% efficient, with most Class D mono-blocks being from 60-90% efficient depending on the impedence of the speaker. Don't just go by the ratings on the box, add up the fuses and look for some real-world clamp tests and bench tests to see what it can actually put out. Many manufactures "bend the truth" when rating their amps. Generally you multiply the amperage on the fuse(s) by 10 to get potential wattage. The true formula would be $Fuse Rating*14.4*Efficiency$ where the fuse rating is in amps, 14.4 is the normal charging voltage of a car, and efficiency being the amplifier's rated efficiency.

### Subwoofers

Subwoofer brands are just as vast as everything else in car audio. There are literally thousands of brands to choose from. The most common sizes range anywhere from 8" to 18" but can go as high as 21"(Incriminator Audio's 21" Death Penalty Sub) and 34"(Audiobahn's 34" Sub). Pricing can range anywhere from \$20 from brands like Soundstorm, Lightning Audio and Boss, to \$3000 like the AudioPulse LMT. Subwoofers have single, dual, or quad voice coils and have resistance in ohms, most commonly seen in the voice coils are 0.7, 1, 1.4, 2, 2.4, and 4 ohm loads. Top brand names today producing subwoofers are: Rockford Fosgate, JL Audio, MTX Audio, Pioneer, Incriminator Audio, Kicker, MA Audio, RE Audio, Sundown Audio, Fi Car Audio, AudioPulse, and Memphis Car Audio. Every company offers their own unique design elements, power handling and looks. Deciding what is right for you will depend on how loud you wanna go, the music you mainly listen to and of course your price range. The fact that bigger subwoofers cannot produce tight and accurate bass is simply a myth, to an extent. An 18" Sub can be just as accurate as a 10" sub can be, it will just cost more and be of a much higher quality and have a much higher power handling most likely because just about any 10" can keep a tight punch, but once you get bigger the lower end subs will not reproduce frequencies cleanly, and tend to get 'sloppy'.

### Capacitors

Capacitors are used to store energy for the amplifier to draw on demand. They come in many different sizes ranging from .5 Farads to well over 100.

### Rattle-reduction

Sound deadening is often used in the door cavities and boot/trunk area to provide less rattling of the metal in the car, especially the boot/trunk. The most common type of deadening is either Butyl or rubberized asphalt which as an adhesive quality and can be applied by simply pressing it into place with a roller and use of a heat gun (or hair dryer) if needed. Other types of deadening can be sprayed on, but they're less common because of the additional difficulty in their installation. The most popular sound deadening brand would be Dynamat, with others that are not as well known but offer sound deadening products in which some have been proven to be superior in performance such as Second Skin's Damplifier Pro, FatMat, and RAAMat to name a few other companies.

### Other components

Other components that make up high-end car audio installations may include:

### Common myths

• It is a common myth that the amplifier power rating should be less than the speaker rating. In fact it is the opposite: as the power amplifier reaches clipping, its output changes to a square wave, which can damage the speaker due to the increased power content.
• Adding an extra battery will increase load, since the alternator will have to charge two batteries. In fact, the battery comes fully charged when bought, and would get no more drained than a single battery.
• More subwoofers are better then less. This isn't true, if you do not have the proper air space for the drivers to breath, the output may be far less then the proper amount of drivers for the airspace you have available.
• You should always look at peak ratings. This is falser then anything else that's spread around. Peak ratings mean nothing, and are in essence a made up number by the amplifier manufacturer to sell more product.
• 18" subs only offer sloppy bass. This is in no way true, there is a sub for every application, and there are some very nice SQ 18" subs with very accurate outputs.