Whole House Wiring Basics
Brought to you by Impact Acoustics
"Music is a discipline, and a mistress of order and good manners, she makes the people milder and gentler, more moral and more reasonable." - Martin Luther
One of the hottest business sectors associated with consumer electronics today is the distribution of audio, video and control signals throughout the home or office. Multi-room multi-zone is a mantra that is heard from the architect's offices to the builder's model, from electricians to data network specialists. As with so much in life, there are several levels of distribution from "bare bones" functional to extravagant touch-panel control, from background music to multi-room discrete surround sound. What you want in your home will be strictly controlled by the infrastructure you install. Get the wiring right and the rest is easy.
It can't get much easier than distributing sound, can it? It's just speakers, right? Oh, if life were so easy… For just two conductors covering a distance of a few feet to a few yards there is much that can go wrong. Fortunately for us, getting this part right is both inexpensive and easy to accomplish.
Most folks want background music distribution to be relatively inconspicuous. A common desire is to install in-wall or in-ceiling speakers in one or more rooms, and have the speakers driven from the "B" speaker port on an audio/video receiver. The first concern is the in-wall wiring. The National Electrical Code (NEC) prescribes the properties of the wire to be used as it relates to the primary goals of the NEC, which are:
- Reduce the spread of fire and smoke.
- Prevent shock
- Comply with other requirements of the NEC
All wiring used behind walls, under floors or otherwise installed as a structural component of the building must be properly rated. Speaker wires used for this type of installation are rated as either Class 2 or Class 3. The only difference between classes is that Class 3 rated wiring is rated for a maximum of 300 volts and Class 2 has no such voltage rating. Is this important? An audio amplifier driving a pair of 8-ohm speakers, and delivering 300 volts peak-to-peak will provide an incredible 26 amperes (I=E/R) of current for a total RMS power delivery of something like 5600 watts (P=I2R). Since it is HIGHLY unlikely that you will be driving in-wall speakers with 5 Kilowatts of power you probably don't need to be concerned with Class 3 ratings!
Now that we know we don't need to shell out extra money for Class 3 wiring, we still need to decide on wire gauge and conductor count. How do we know what's right for the job? Distance and anticipated performance are the critical factors. Let's examine each in turn.
The distance from the audio amplifier to the anticipated speaker location is a major factor in deciding which in-wall wire is the right one for the installation. Every foot of speaker wire adds a bit more resistance, capacitance and inductance to the performance equation. While these parameters by themselves have minor sonic effects, the total impedance of the wiring network has a larger effect - especially on the amplifier. The trick is to minimize the effects of the wiring, so here's a good rule of thumb:
- For less than 50 feet to the speakers or volume control, 16AWG is fine
- From 50 feet to 100 feet use 14AWG
- For 100 feet or more use 12AWG
Don't forget to account for the expected bass response and volume at which the speakers will be played. For primary sound where dynamic range is at a premium and full range sound is desired, use more copper. For background sound you can drop copper. In other words, you are unlikely to compromise the performance of a pair of 5-inch coaxial in-ceiling speakers placed in the master bathroom by using 16AWG, even if the run is 100 feet. On the other hand you may want to use 12AWG if you're wiring your main theater speakers - even if the run is only 30 feet.
In addition to considering the gauge of the wire used, it is also wise to consider the conductor count. Each and every room should have the ability to support a local volume control. This control is best placed somewhere near the main lighting controls for that room. A 4-conductor cable should be strung from the equipment closet to the volume control location. A single 4-conductor cable is much easier to run - and less expensive - than two 2-conductor cables. 2-conductor cable should then be run from the volume control location to each speaker location.
In addition to a volume control, which can be mechanical or electrical, each remote location should provide the infrastructure to support infrared remote control or keypad remote control. There are many control solutions from manufacturers including Xantech, Niles , Sonance, Crestron, AMX and others. Some of these are extremely sophisticated and require professional installation and proprietary wiring. Most, however, will work well with simple uninsulated twisted pair wiring (UTP). A great solution is to use CAT5e wiring for the control system.
Composite cables are cable assemblies blending two or more different cable types. One good composite to use for audio distribution is 14/4 & CAT5e composite. This gives you control capability and speaker level audio distribution in one easy-to-pull cable. You can also get 14/4 & Dual Cat5e for more sophisticated systems or in instances where you want to distribute Telco as well as IR and speaker level audio.
Some systems will benefit from the installation of IR targets or IR repeaters. These devices allow you to aim your infrared remote controls at a small IR window built into a cabinet, speaker grill or wall box to relay those commands to the equipment closet. A single CAT5e run is more than sufficient for most contemporary IR management systems. Keep in mind that even if you don't plan on installing keypads or IR control systems right away it is important to include the wiring in your installation. You will not have a chance to remove the drywall and insulation to do it later!
RF, Antenna and Satellite Distribution
Sending music from room to room isn't enough for most of us. We live in a world of sound and image. Contemporary systems require audio, control and video distribution of some sort. There are four variations of video distribution and most systems will use at least one - often two or more - to fulfill expectations. Let's start with the simplest first.
RF distribution refers to the availability of antenna, CATV, satellite and local modulated video content in various rooms and areas throughout the house. RF distribution takes place on coaxial cable. RG-6u is best, though RG-59u is acceptable. The primary difference between the two is the high frequency attenuation, as related to the length of the run, and the quality of the shielding. A good quad-shield RG-6u is the very best choice for RF distribution.
There are two ways to handle a simple MATV or CATV distribution system - tapped or home run. Tapped systems have a single trunk line with 75-ohm drops used for each antenna feed location. Taps have a feed-through port and a drop that costs about 3.5 decibels of signal strength (in this case the signal is voltage dependent and not power dependent - in voltage dependent systems the total voltage is halved when the signal drops 6dB). Taps are easy to install and will service most simple antenna needs.
Home run systems require that a coaxial cable be run from each antenna location to the equipment closet. This can be a more flexible system in that IR controls, satellite IF and other signals can be "piggy backed" on the RF signal. Also, specific sources can be modulated and delivered to only certain locations. The disadvantages of a home run are the additional wiring and labor costs - as well as the need for distribution amplification. The use of RF amplification is a subject fit for an article in and of itself and is a topic we will explore in a future column.
DBS distribution is a bit trickier as it requires sweep-tested components capable of passing a full 3GHz bandwidth - with bidirectional capability. If you plan on installing a DBS satellite dish make sure you run a MINIMUM of two coaxial cables to the dish location from the equipment closet. In this way you can utilize a dual-feed LNB system with a phased array reflector for reception of signals from multiple satellite orbital locations. This is critical to getting the full measure of local-into-local or HDTV broadcast programming.
Our next column will explore the basics of composite video, S-video and component video distribution, line-level audio distribution, and digital signal distribution.
We would like to thank Impact Acoustics for allowing us to reprint this informative article.
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