How to Make a Double-Wire Loop

© March 2004 by Neil Bauman, Ph.D.

To make a double wire loop, get a roll of standard 18 gauge speaker wire. (With speaker wire, the two wires lay side by side like in a normal extension cord.) I use Radio Shack's speaker wire (Catalogue No. 278-1104) which costs $13.99 for a 100 foot roll.

If you look at the wire carefully (and feel it too), you'll notice that on one side the wire is smooth and on the other side, the wire is ribbed with the ribs running the length of the wire.

You need to know this so you can hook up one end of the ribbed wire to the smooth wire at the opposite end of the roll to make the double loop.

See the loop diagram. There I've shown it as a black wire (ribbed) and a broken red wire (smooth). With other wire products, you may have a black wire and a white wire, or a clear ( or copper) wire and a white (or silver) wire. In any case the black/copper/clear/ribbed wires are considered the "hot" side and the white/white strip/silver/smooth wire is the "ground" side. This is standard wiring practice.

Common Question Asked about Double-Wire Loops

It seems that some people get confused about the total length of wire in a double wire loop. One man wrote: "I am confused about one thing. The Univox 2A says that 80' is the maximum loop size, but you recommend using a double loop, and as I see it, 80' double-looped makes the loop length 160'."

I can see why you are confused. You are confusing the physical size of the loop with the length of wire used in making a double wire (or multi-wire) loop.

The maximum size of a loop is determined by the output of a particular loop amplifier. (The Univox 2A can drive a 80' loop.) This means the distance around the perimeter of the room (or looped area) can't exceed 80 lineal feet.

However, when we talk about a double wire loop, we are not talking about the physical size of the loop, but the number of times (the technical term is "turns") the wire makes around the room.

Thus if the room is 30 x 10 feet, that would make a physical loop of 80 feet. If you want a double-wire loop, you keep the loop the same physical size, but you take a second "turn" around the room. As a result, the loop is still 80', but now it consists of two coils (turns) of wire around the room (for a total of 160 lineal feet of wire).

This is perfectly ok. In actual fact, you can go around the room as many times as you like as long as you don't make the actual loop bigger than 80 feet for the Univox 2A. (Keep it within reason though. Between 1 to 8 turns is ok. After that, the inductance reactance builds up and negates any advantage gained by having multiple turns of wire in the loop.)

So the important thing is the size of the loop, not the number of lineal feet of wire used when you take multiple turns around the room.

Prepare the Double-wire Loop as follows

• Split each end of the wire to separate the individual wires for a distance of about 5 feet.
   
• At one end, cut the smooth (white) wire about 3 inches from the split. At the other end, cut the ribbed (black, copper) wire also about 3 inches from the split.
   
• Take about half an inch of insulation off the ends of each of the wire.
   
• Twist together the ends of the 3 inch stubs and screw a wire nut on. (See connection photo). This makes it easy to connect and disconnect the loop whenever you set it up or move it.
   
• The two long "tails" that are left go to the amplifier terminals. With 5-foot tails, you can have your amplifier up on a table or on your TV and the loop will still lay flat on the floor.
   

Setting up the Loop

For temporary loops, place the loop around the perimeter of the room or area you want to loop.

For permanent installation, put the edge of the loop under the carpet, behind the baseboard or around the edge of the ceiling. Better yet, if you have an unfinished basement, string the loop up in the joists under the floor. Alternatively, you could do the same if you have a crawl space under your roof and lay the loop above the ceiling of the area you want looped.

Connect the ends of the loop as described above and you are in business.

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