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 May 15, 2005 Stereo at Home Away from HomeNo picture of an Edwardian picnic would be complete without a wind-up Victrola in the background. Almost as soon as there was sound equipment for the home, there was an urge to take it outdoors, and the earliest equipment was not ill suited for that. The first record players were totally mechanical, and early radios, although electric, ran on batteries. The problem with the early devices, however, was that they were bulky, and reducing them to a practical size usually meant serious compromises in performance. Still, the desire for sound on the go has been a powerful one from the beginning. In the 1920s, car radios became popular, powered by the automobile’s battery, and with the electronics stowed safely in the trunk. True portable radios -- ones you could carry around -- were another matter. In the 1930s there were radios with handles, but they were too heavy to carry for long because their vacuum tubes required so much power that large batteries had to be accommodated. Not until transistors began to replace tubes in the 1950s did true portability become possible. These solid-state devices were tiny, used little power, and produced almost no heat, making them ideal for pocket-sized radios. Until recently, Victrolas aside, audio outside the home was restricted to radio. Vinyl records were the chief audio storage medium for most of the last century, and they were notoriously unsuitable for anything but the steadiest conditions. Only when magnetic tape became popular did audio free itself from the home for good; the compact disc and other digital storage media have refined the possibilities even further. The car radio relieved boredom, gave useful information, and created a captive audience for radio stations. All of this was possible with fairly minimal performance, and that’s what most early autosound equipment delivered. But when broadcast authorities decreed that all radios had to be able to receive FM broadcasts, and listeners realized that the now-accessible stations were broadcasting in stereo, they demanded the extra channel, and car stereo was born. At about the same time, prerecorded tapes became widely available, and players for them began to appear. Tape had been around for a couple of decades before it showed up in cars, but it was packaging it in plastic shells that could be shoved into a slot that made tape so popular. The first version to gain popularity on this continent was the four-track cartridge, an endless loop of tape containing two stereo pairs of recordings; a bit of metal leader tape triggered a mechanism that switched the playback heads from one program to another (usually in mid-song), allowing hands-off reproduction of a whole record. This was soon replaced by the eight-track cartridge, which was physically similar but held twice as much music. It was difficult to record on an eight-track cartridge, and it was inconvenient to manipulate the tape during playback -- there was no rewind, and only a limited sort of fast forward -- but the format reigned supreme in North American vehicles during the first decade or so of the autosound boom. Eventually, it gave way to the cassette, which had long since become the standard elsewhere in the world. Exotic tape formulations and Dolby noise reduction had turned the cassette into a true high-fidelity medium, although such niceties were late to show up in cars. Still, there were lots of home cassette decks, so car stereo enthusiasts began to discover the joys of recording their own tapes for playing in the car. The central component of any autosound system is the head unit. This contains all the electronics, and need only be hooked up to speakers elsewhere in the car; in more elaborate setups, some of the electronics may be external, the head unit being used as a control center. Head units come in a number of physical formats, both in-dash and under-dash; the one to use in any situation will depend on the car itself. Many head units are designed for the European DIN (for Deutsche Industrie-Normen, or German Industrial Standards) mount, in which the equipment fits a rectangular opening in the dash. Special requirements, such as the addition of extra components -- an equalizer or external CD player, say -- may make the use of mini-chassis equipment a reasonable choice. If the head unit contains only an AM/FM tuner and an amplifier, it’s simply a car radio; if there’s no amplifier, it’s a tuner. A head unit with tuner, amplifiers, and tape player is called a cassette receiver; without the amps, it’s a cassette tuner (and similarly for the CD receiver and the CD tuner). Without a tuner but with or without amps, these become cassette or CD players. Multi-disc CD changers have long been popular; these are usually mounted in the trunk and run by a CD controller in the front, which may have the ability to play tapes or CDs on its own. A relative newcomer is the single- or multi-disc DVD player for the car, which of course can also play CDs. Most head units provide preamp outputs for feeding extra amplifiers, and some also include line inputs for extra signal sources. In cases where such inputs are lacking, things such as Apple iPods and other MP3 players can use a cassette-shaped interface, or broadcast a low-power FM signal, to feed music to the system. A few head units contain equalizers for shaping the system’s frequency response to suit a car’s acoustic properties, although these are more often found as separate components. In many cases, the equalizer is combined with an external amplifier; if this is meant to be fed from the built-in amplifier rather than the preamp outputs, it’s usually known as a booster amplifier. External amplification is often used where numerous speakers are placed about the car, sometimes bridged to mono to increase output. Because amplification tends to consume considerable power, some of the more elaborate autosound systems include heavy-duty alternators and batteries to handle the load. Various noise-suppression circuits are sometimes necessary as well, to overcome electrical interference generated by the car itself. The cassette player (or tuner or receiver) is still common in autosound systems today, and more and more of them are reaching the technical sophistication of their homebound cousins. Noise reduction is becoming very common; it’s doubtful that such noise reduction is very effective in the noisy environment of a car, but it makes for compatibility between home and car players. Two useful features that are almost universal are auto reverse play, which reduces the amount of tape fumbling, and auto eject, which disengages the cassette when the car’s ignition is turned off. This preserves the pinch roller and lessens the likelihood of wow and flutter. Some players are claimed to be able to play back "metal" tapes, although any player that will play Type II tapes can handle metal as well. Considerable effort has gone into improving the performance of car FM tuners, which may be more susceptible to reception problems than home tuners. Multipath distortion and its most common mobile manifestation, picket-fencing, have been tamed in some advanced systems by means of diversity tuning, which constantly monitors the signals from two or more antennas and feeds the best to the tuner. Input overload is sometimes dealt with by a Local/DX switch, and the inherent noise of weaker stations is countered by FM Blend (or Auto Blend), which reduces channel separation and noise in the higher frequencies. Selecting the station you wish to hear is usually aided by presets, which can range in number from a handful to dozens. Many tuners are able to scan the band as well, choosing the strongest stations. In the US, and presumably soon in Canada, satellite radio signals from XM or Sirius are becoming increasingly popular, providing hundreds of signals and continent-wide digital coverage. As with every sort of audio, good car stereo speakers are critical for good sound. In the simplest systems, sound is reproduced by a single pair mounted near the front seats (frequently in the doors), or by a similar pair in the rear deck. Often both are used, and most head units can control them by means of a fader. Such systems may employ full-range speakers, either in the form of single-cone drivers or drive-units with extra diaphragms, called whizzers, to help with the higher frequencies. While these are sometimes called "dual-cone" speakers, they should not be confused with true two-way systems, in which the high-frequency tweeter and low-frequency woofer are fed separately through a crossover network (if a third driver, for the midrange, is added, it’s a called a three-way). Often the drivers are mounted together, the tweeter in front of the woofer, to fit in a standard speaker cutout; such speakers are called coaxial (triaxial if a midrange is included). Individual drivers may be positioned separately rather than combined, and this often requires biamplification: the tweeters and woofers amplified separately, the signals to them split by means of an electronic crossover. More speakers may require triamplification, but even if only full-range units are employed, extra amplifiers may be advisable, as car speakers tend to have rather low nominal impedances -- typically 4 ohms -- and can be hard to drive when used in numbers. Powered speakers -- drivers with their own built-in amplifiers -- are often a solution to problem loads. Sometimes subwoofers -- extra speakers used for the lowest octave -- are powered this way, although a conventional crossover is often used. Speakers can be installed several different ways. Often the most satisfactory method is to drop the speaker into a hole that lets its rear wave vent into the trunk. Such flush-mount speakers are probably the most common, and most cars have cutouts to accommodate them. In some cases this is inadequate, and speakers with their own enclosures must be used. These surface-mount systems are affixed to the car’s interior by brackets. A larger variant of this is the truck box, for use in vehicles lacking suitable surfaces for conventional mounting, such as vans and pickups. These may be full-range units or contain only woofers, and they may or may not include their own amplifiers. A car stereo system often includes features that have little to do with sound quality. Many feature some form of security arrangement to discourage thieves; two popular ones are the pullout chassis, which lets you remove the head unit easily, and the security code, which disables the equipment if it’s stolen. Car components can also be used to control such things as overall security systems and power antennas. A few even offer circuits that interrupt the audio when the cellular phone is in use. ...Ian G. Masters
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