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HOW TO


AUDIOVISUAL SYSTEMS

Low-voltage audiovisual wiring is the connecting link for cable TV and radio, satellite TV, stereo components and speakers, and a combination of all the above: home theater.


CABLE CLOSE-UP
That familiar round, black lifeline that drives both TV and FM signals is called coaxial cable. Cable comes in several varieties, but all types have similar components: an insulating core surrounds a thin copper conductor; woven shielding goes around the core to block radio interference; then an outer, rubberized sheath wraps everything up. Some cable types include solid foil wraps or multiple insulating/shielding layers to cut interference further. Cable for audiovisual use is rated at 75 ohms (coaxial used for data transmission is rated at 50 ohms). There are two main types: RG-59 and RG-6. The latter is fatter with an 18-gauge core instead of RG-59's 22-gauge, so there's less resistance over long distances. So-called quad cable (RG-6 quad cable) has four times the normal shielding for minimal interference; it's popular outdoors for satellite feeds and, to indoors for high-end home theaters.

ROUTING LOGISTICS: Coaxial cable may be routed through walls, floors, and ceilings, just like standard NM cable; or it can be strung atop baseboards, along carpet edges, or even down a wall (you can paint it to match). Use insulated cable staples to secure coaxial without damaging its insulation. Run the cable a minimum of 2 inches away from electrical wires; whenever possible, increase this distance to several feet.
When roughing-in new wiring, some professionals make a practice of running NM cable down the face of one wall stud and low-voltage cable down the facing surface of the adjacent stud. When crossing NM cable or conduit, try to do so at right angles. Don't place cable inside a housing box that has standard electrical wires, that's not only a source of interference, but it's also dangerous.


MAKING CONNECTIONS: Cable splices, or terminations, as they are sometimes called, are made with male couplings and female F-connectors. It's simplest to buy set lengths of coaxial cable with integral F-connectors. However, if you need a nonstandard length or have to make repairs, you can also add your own connectors-either by crimping (see below) or by using twist-on models (although they aren't as reliable as crimp-ons). Note that RG-59 and RG-6 cables require different connectors. Cable junctions are handled with "splitters," which come in two-way, three-way, and four-way versions. A splitter with a built-in amplifier boosts the signal, which would otherwise drop with each new splice. The amplifier is best placed where cable enters the house.

1. Remove the sheath
First cut back about %z inch of the cable's outer, rubberized sheath, exposing the insulating core. Score the sheath with a utility knife; then simply twist the sheath off the cable, leaving the core intact.
2. Strip the core
Some connectors require you to fold back the inner foil wrap or woven shielding; with others (like this one), simply remove the shielding. Then strip about 3/s inch of the inner
core off the copper conductor as shown. A wire stripper makes a clean cut.
3. Position the connector
Next, slip the cable connector overthe exposed cable end, twisting as necessary until about 1/16 inch of conductor protrudes past the connector's end.
4. Crimp the connector
Finally, squeeze the connector onto the cable as shown. A cable crimper works best, but in a pinch you could also use a multipurpose tool or lineman's pliers.

DIGITAL SATELLITE DISHES just a few years ago, state-of-the-art satellite dishes that allowed you to bring in long-distance TV channels were about 7 feet in diameter. Now they're an unobtrusive 18 inches and can be conveniently mounted to a house wall, eave, or chimney (depending on the model) with the appropriate installation kit. The only firm requirement is that the dish must have an unobstructed line of sight to the southern sky, where the sending satellite is located.
COMPONENTS: As shown at left, the key parts of a digital satellite system (DSS) are the dish and a DSS receiver located inside the house. The dish meets the receiver by way of coaxial cable, preferably RG-6 quad cable, which has four times the shielding of standard cable.
The quad cable runs from the dish to a wall-mounted, exterior grounding block, as shown, then from the block to the inside receiver. Exterior drip loops keep water from running directly down the cable and into either the connectors or the house. A solid copper grounding wire connects the grounding block to your home's grounding electrode conductor at the service entrance panel.
Inside, you'll need a 120-volt receptacle to power the receiver and a phone jack (this is how ordering and billing are done). If you want to hook up more than one TV to the satellite, the simplest way is via a cable splitter (see page 146) between the receiver and the first TV (you can't split the cable before it reaches the DSS receiver).
The drawback is each TV will receive the same channel. If you'd like the flexibility to watch a different channel on the second TV, installation gets a little messy: you'll need a second LNBF feedhorn (a signal receiver) at the dish, a second RC-6 quad cable, and an additional DSS receiver.

LOCAL PROGRAMMING: If local programming is important to you, you may need an additional off-the-air antenna wired with coaxial cable. This roof-mounted antenna follows a separate path into the house and, depending on the components, connects to either the DSS receiver, a VCR, or the "antenna in" port on your TV.
If an off-the-air antenna is already installed, it's likely to be wired with flat, twinlead wire; if that's the case, you'll need to add an impedance-matching transformer inside, connecting the twin-lead and 75-ohm coaxial, then run coaxial to one of the components listed above

WARNING Antennas are extremely efficient conductors. When working with any satellite dish or offthe-air antenna, you must not contact any electrical wires in the area. Do not work when there is any threat of lightning.

INSTALLING A BUILT-IN SPEAKER

Cut a hole, fish wire
First cut a hole in the ceiling or wall for the speaker body; most speakers come with hole-cutting templates. Fish speaker cable through the hole and attach wires to speaker terminals (be sure each wire goes to the correct terminal).
Secure the speaker.
This speaker comes with integral clamping wings; simply slip the speaker into the hole and tighten the mounting screws-which in turn secure the wings to ceiling or wall material. Some speakers may require toggle bolts or plastic anchors instead.
Add the grill.
The hard work is done. To complete the job, simply push the speaker grill onto the speaker-it's much like securing a recessed downlight's trim ring or baffle.
When talking about stereo wiring, two terms matter: impedance and polarity.
Impedance, measured in ohms, is the resistance a speaker offers to the signal passing through it. Speakers are rated for a certain impedance-most are rated at 8 ohms, but the available range is 4 to 16 ohms. AV receivers often have specific sets of ports, or terminals, for different impedance ratings.
If your receiver supports multiple channels-such as A, B, and A-B-you can wire two sets of speakers directly from the receiver in home-run fashion. You simply wire the speakers to the correct ports. However, if you choose to run multiple speakers in series fashion, the impedance rating becomes the sum of the individual speakers' ratings. Two 8-ohm speakers are now a 16-ohm load. If you wire the speakers in parallel, the impedance is the speakers' individual ohm ratings divided by the number of speakers. Two 8-ohm speakers become a 4-ohm load.
Polarity refers to the direction that current flows through a device. The ports or terminals on a receiver, speakers, and other components are polarized: each set should have one input marked "+" or " L" and one marked -" or "R." Your wiring hookups must match up at both ends; that is, if a wire is connected to a negative terminal on a speaker it should also be connected to the negative terminal on the receiver. Most audio and speaker cables are color-coded or otherwise marked (ribbing is common): be sure that the red connector or the ribbed leg is connected to the same polarized terminal on both ends. Speaker cable comes in several grades and gauges commonly #10 to #16. Generally, the bigger the cable the better. For stereo, you'll need two cables-one to each speaker-each with two wires. Keep wire runs as short as possible.

HOME THEATER BASICS
LABEL THAT CABLE
Because of the sheer number of interwoven cables coming and going throughout a home theater installation, it's essential to keep some sense of order-as well as a firm sense of polarity. Be sure to mark all cables at both ends-either by using a permanent marker and masking tape or by purchasing specific cable labels, available at home electronics stores.

What transforms a TV, a VCR, and a pile of other black boxes into a formal home theater? It's the systematic relationship between several key devices, all tied together with the same cast of low-voltage wires and cables we've met already.
Typical home theater components are shown on the facing page. The TV and speakers are obvious stars, but it's the audiovisual receiver that's really "command central." A plethora of media signals may be routed to the AV receiver from components both inside and outside the home: a cable box, satellite dish, off-the-air antenna, VCR, or DVD player. The receiver allows you to choose which of these input sources you want, and then encodes and outputs signals to the TV and speakers. Consider the AV receiver as the axis of whatever wiring scheme you're planning.

VIDEO OPTIONS: TVs are available with a choice of features: direct view, rear-projection, front-projection, flat-screen, high-definition. You'll need some showroom help unraveling your options; and, just as important, you'll need the right cable and wiring connections that are compatible with your AV receiver.
Whenever possible, use shielded cable rather than coaxial cable to make hookups between your TV and receiver. Coaxial cable transmits RF (radio frequency) signals, while shielded cable sends cleaner baseband signals. Most connectors are RCA types (shown at left); newer video-S and connectors are RCA types (shown at left); newer video-S and composite jacks, which divide the video signal into multiple facets, may use 4-pin connectors.
To keep wire runs as short as possible, plan to cluster home theater components in a central location or nearby closet. Be sure to maintain at least 6 inches of clearance between audiovisual cables and standard electrical wires. Don't make loops in cable to take up wire slack; loops add interference.

AUDIO ASPECTS: Surround sound is the heart of the home theater experience. A battery of at least five and sometimes six speakers is driven by digital encoding supplied by the AV receiver. Matching speakers at front left and front right provide "stereo." A shielded center speaker, mounted above the TV or placed right on top, fills in the middle. (You could also use the TV's built-in speaker, but a separate center speaker usually sounds better.) Left-rear and right-rear speakers create the surround-sound effect. In addition, a sixth speaker-a specialized subwoofer-is often placed at rear center (although technically, it could be placed anywhere, as these low-frequency sounds have no clear "direction").

So how do you organize this potential tangle of speakers and speaker wires? If walls are open, simply run wires through house framing to wall jacks with stereo speaker inputs. In existing homes, you can use the same fishing tricks used for standard electrical wiring. If other avenues are closed, you can also route cable along baseboards, inside carpet tack strips, or through surface raceways.



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Updated: 07/2017   copyright 2012 U-Repair.com