SubwooferThis is the speaker that goes boom. A subwoofer generates sound at a frequency of about 100Hz to 20Hz. It needs an enclosure, otherwise known as a box, to achieve the best performance. Some might be sold already built into an enclosure that looks like a box (such as the MTX MagnaForm),or might resemble a cylinder (such as the Bazooka Bass Tube). Most subwoofers,however, are purchased separately from an enclosure that needs to be custom-fitted to the subwoofer. The design of the enclosure depends on the specific frequency range the subwoofer needs to generate, where the subwoofer has to fit in the vehicle, and other factors. Enclosure types include sealed, vented or ported, band pass, dual reflex, and isobaric (which is not an enclosure so much as a way to mount the sub in a vehicle). Don't buy into the idea that you need a bigger subwoofer for big bass. Size does matter, but it's only half of the equation. Much of the performance is in the subwoofer's enclosure.
MultimediaIt used to be that if passengers wanted to keep themselves occupied on a long road trip, they would stare out the car window and count the cows or risk car sickness by reading a book. And then there is that old standby - sleeping. Nowadays, however, video is becoming a mainstay of mobile entertainment. Multimedia systems will usually share some components with the sound system in a vehicle in the same way the TV in a home theater system is plugged into the stereo. A media player, such as a DVD or VCP, or a TV tuner and antenna feed a movie or broadcast into the head unit - if it has DVD, VCP, or TV tuner controls - which will operate both the audio and video in the vehicle. From there, the audio signal is routed through the sound system while video is shown on liquid crystal displays (LCDs). An A/V switcher might give you more flexibility when you have multiple media players feeding into multiple monitors, allowing junior sitting in back to watch SpongeBob SquarePants, while The Matrix plays up front.
You can buy prefabricated multimedia systems that include a VCP, monitor, and controls, and that bolt into the vehicle's ceiling or replace the center console. Or, you can have monitors custom-fitted into your headrests, visors, and elsewhere. The considerations for choosing a monitor are similar to those of a laptop monitor, with the viewing angle at the top of the list. TFT LCDs offer the best viewing angle, but cost more. If possible, go large and get a 7-inch monitor.
Wiring & PowerWires are mobile entertainment's nervous system, and are just as differentiated as our own, particularly when it comes to the diameter, or gauge, of a wire or cable. Power and wire length dictate what gauge of wire a certain application requires. The wire connecting the battery to a head unit or amplifier carries a lot of current, so it is thick, measuring perhaps 1/0 and 8 gauge. Speaker wire, on the other hand, doesn't carry as much power, so it is thinner, maybe 12 or 16 gauge (the higher the gauge, the thinner the wire)
Electronic systems generate a lot of electromagnetic interference. Wires, such as antennas, can pick up this interference, which will translate as unwanted noise. Various wiring designs shield the wires from such interference. The most common type of wire, coaxial cable, is one small-gauge wire jacketed by a braided cable, both of which are wrapped in a plastic jacket. Twisted-pair cables take two small-gauge cables and twist them around each other so the noise in one cancels the same noise in the other. While both work fine for most situations, twisted-pair is usually the better choice.