CAR AUDIO

Car audio

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.

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 more than one channel to be used (one channel)


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.


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.


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.


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.

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