Car audio

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Car audio/video (car AV) is a term used to describe the sound and 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.

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, after older tape decks. 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. Even with the rampant ubiquity of solid state MP3 players, car audio systems with line-in jacks and other standards are only in their infancy, and that since tape adaptors are often used with tape players, people are now viewing car radios with built-in CD players as "misfeatures" of the audio system since people now often "rip" their CDs onto their computers.Other types include the video touch screen capable of controlling; navigation, dvd movies, mp3 players back up camera and other accessories.

Most modern cars include at least a CD player/ CD recorder, 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. Depending on the head unit, 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 integrated component such as a navigation system, 3G cell phone or parking cameras that could be automatically activated when the car is put into reverse.

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.

High-end audio systems include Component Speakers that consist of a matched tweeter (small, high frequency), midrange (medium, medium frequency) and woofer (large, 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) are provided for bass and sub bass (ultra low frequency), which is felt more than heard depending on the sub frequency, the lower the frequency the less the human ear picks it up, however the chance of "feeling" the vibration becomes greater. Sub bass is omni-directional, meaning that the human ear cannot distinguish where the sound is coming from. Humans can not hear subsonic frequencies (below the frequency of 20hz), we are however able to feel it (eg. An air rush when closing a door cannot be heard, it can be felt however). 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.

4Ω is the most commonly used impedance in car loudspeakers.

car audio amplifier
car audio amplifier

Contents

[edit] Amplifiers

Amplifiers provide the necessary power, measured in watts to drive the speakers. High Power amplifiers require a low gauge cable to provide adequate current to the amplifier. The amplifier is a very important component of a loud speaker system. Make sure that the total power handling capacity of the speakers connected to the amplifier or head unit is greater than or equal to the power of the amplifier or head unit. Amplifiers commonly come in two,four or six channels. Subwoofer amplifiers these days are generally Mono Amplifiers. However it is common that multiple channels be used for the exclusive use in allowing for mor ethan one channel to be used (one channel)

[edit] Capacitors

Capacitors are used to store extra energy for the amplifier to draw on demand. Capacitors are useful because they can reduce the voltage loss (small margin) on the other electrical components in the car. These large capacitors may not cure headlight and/or interior light dimming as this is a sign of too little amperage from the alternator. A capacitor is only good so far as the audio system isn't trying to pull too much from the electrical system. A capacitor doesn't provide more power, it's designed to 'stiffen' the voltage to the amp, nothing else. If the current isn't there, a cap won't help. The alternator must have at least 20% more amperage power than the entire vehicle and sound system combined for a capacitor to be of benefit which is ironically the same requirements for an amp to be efficient. A rule of thumb is that 0.5 farad of capacitance is needed for every 500 watts of power in your audio system. A capacitor does not affect sound in any way. It is strictly for power conditioning.

[edit] Power

There are two very different expressions of power; the first is known as PMPO (peak music power output) or "commercial watts." This is a misleading measurement and is often used to make audio components sound better than they actually are. PMPO is the peak amount of power that can be derived from an amplifier given perfect conditions and can only be sustained over a very short time (a few milliseconds). PMPO is also used to measure speaker output. Once again this is merely the peak amount of power that can be run through a speaker without blowing it. Should this amount of power be applied for more than a few milliseconds the speaker will blow. The next measurement for power is RMS (Root mean square) and is the maximum continuous power that can be derived from an amplifier or run through a speaker. This is a true measurement of what you can expect from any specific component of an audio system.

Since there are many ways for a company to measure the power output of their product, CEA(The organisation Consumer Electronics Association) created the CEA-2006 standard[1]. The standard provides a guideline for car audio manufacturers to follow. Although this is a voluntary standard, all major manufacturers have agreed to use it to measure their head unit and amplifier power output. The rating is also clearly stated on the product with the CEA2006 logo on the packaging box, which makes comparing two competing products easier.

[edit] RMS vs PMPO

There is a relation between RMS and PMPO as they will differ greatly from component to component; however it is agreed that on average if one wishes to derive RMS from PMPO the ratio is one into two, (or 2 watts PMPO = 1 watt RMS) this is however only an average and should not be deemed accurate.

[edit] Upgrading the vehicle's current capability

Alternators may be upgraded from the stock unit to increase the current capability of the vehicle's electrical system, often required of high-power audio system components. An additional deep cycle battery (or, for very large systems, banks of batteries) can be deployed (often charged via a Split charge relay) to limit voltage drop and allow the system to be played for long periods without the vehicle's engine being run.

As a genral rule, if your total system power is 1200 watts RMS or more, you will need to:

1. Upgrade the alternator to a high output alternator

2. Upgrade to a heavy duty deep cycle battery or a battery specific to car audio

3. Upgrade the "Big 3" - that is to replace (or add to) the power wire between the battery and alternator, the ground from the battery to the chassis and the ground strap from the engine/tranny to the chassis with at least 2 AWG wire.

Failure to do this could result in the early death of the alternator or other electrical problems.

A second battery is never a good idea for systems that are 3000 watts RMS or less as it's an added strain on the alternator to charge two batteries AND supply power for the car. The ONLY time a second battery is useful is if the audio system is to be used with the car off for show.

[edit] 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. It is a rubber or asphalt-like substance that can be sprayed on or glued on in sheets.

a powerful after-market audio system installation in a Toyota.
a powerful after-market audio system installation in a Toyota.

[edit] Other components

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

[edit] Common modifications

Common modifications in high-end car audio installations:

[edit] History

From the earliest days of radio, enthusiasts had adapted domestic equipment to use in their cars. 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 battery-powered radios to run on standard household electric current (see also Rogers Majestic Batteryless Radio). In 1930, the Galvin Corporation introduced the first commercial car radio, the Motorola model 5T71, which sold for between $110 and $130 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. A number of early companies making phonographs, radios, and other audio equipment in the early 20th century used the suffix "-ola," the most famous being Victrola; RCA made a "radiola"; there was also a company that made jukeboxes called Rock-Ola, and a film editing device called a Moviola. The Motorola prefix "motor-" was chosen because the company's initial focus was in automotive electronics.

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 filaments, and generated the required high voltage 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 around.

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 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.

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. 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.

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.

[edit] See also

[edit] References

  1. ^ CEA2006 website[1]

[edit] External links