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Views: 163772 - Replies: 1
| 08-02-07, 08:22 PM
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A Comprehensive Guide to Splicing Speaker Wire
A Comprehensive Guide to Splicing Speaker Wire
It’s probably happened to all of us at some point. You’ve rearranged your home theater and now one of the speaker wires is too short. Or you just bought a new house that was “pre wired” for surround sound, but the sheetrockers cut the wire and only left you a few inches coiled up in the box.
The scenario are endless, but the question is the same: "Can I splice an extension? Will I loose any resolution or audio quality?" The answer is “yes” and “no” respectively. More to the second issue, if you can hear the difference between a spliced and unspliced wire, you should apply for a job at Boston Acoustics immediately!
As a former installer of professional and commercial audio systems, I can assure you that splicing is fine. The only problem with splicing is that (obviously) the structural integrity of a cable is compromised. Therefore if there is ever a problem in the future where that cable is involved, the splice point is the first thing to check.
As far as how to accomplish a splice, there are several methods, all with their own specific strength and weaknesses. We'll fully explore each of them.
Twist and tape
This method, twisting two wires together and wrapping with electrical tape for insulation against short circuits, is by far the easiest spice to accomplish. It’s also the most unreliable method and therefore generally not recommended. Even a moderate amount of tension on the wire will usually make the splice separate.
Furthermore, electrical tape, especially the cheap stuff, tends to loosen over time as the adhesive breaks down. This is especially true in attics or the automotive environment, where the tape is subjected to extreme and constant changes in temperature and humidity.
If you must twist and tape, use only the most best 3M electrical tape - usually around $3 a roll at the hardware store. It's the only kind I've found that won't loosen with time - indoors at least.
Twist-on wire nuts
Wire nuts are designed primary for use with solid wire, like the Romex used for your house electrical. Aside from that, they are the best choice for splicing a solid and a stranded wire together. Wire nuts typically don’t work as well for splicing two stranded wires together. It’s better to use one of the other crimping devices or methods mentioned below, but wire nuts can work if you’re careful.
The key to a good wire nut connection is selecting the correct one for the gauge of wire you are using. Red nuts are usually best for 12 ga. wire, yellow for 14 ga., orange for 16 ga., etc. (Please note these are guidelines for solid wire and therefore may not be exacting with speaker wire, which will be physically larger for any given gauge, due to the stranded construction. Also, the more individual strands there are in a wire of a given gauge, the thicker it is physically, thus possibly requiring a larger wire nut.) If you are splicing more than two wires of any given gauge or combination of gauges, you will naturally want to move up to a larger wire nut.
The next key to a good wire nut connection is to use only those with a coiled metal insert. These function to slightly “bite” into the wire with a threading action as you twist them on, which insures a more stable connection. I’m not entirely certain, but I expect the threading action will be better accomplished with solid wire than with stranded – another reason to proceed with caution using wire nuts with speaker wire.
Do not twist the wires together before they are inserted into the nut – let the action of the nut do that as you twist it on. The nut should twist on very tightly, to the point where it will no longer turn. If the nut never stop turning, it will not be a secure connection and will easily come off, leaving you susceptible to shorts. Usually this is an indication that the nut you’ve selected is too large, but it can also happen if you use the cheap nuts without the metal inserts, or if it’s an old nut that has been used before (typically you don’t want to recycle wire nuts).
A wire nut that won’t tighten is often the situation you end up with when both of the wires are stranded. Again, that’s why it’s best to use other methods for splicing two stranded wires. If you must use a wire nut for stranded wire, it’s probably a good idea to fully wrap the connection with good-quality electrical tape, for an additional measure of security.
Aside from use with stranded wire, wire nut connection does not need to be taped if done properly. The insulation on the wire should not be stripped back so far that bare wire extends below the base of the nut.
If they are done right, wire nuts are reasonably sturdy and can withstand a good amount of stress on the cable. Indeed, each splice should be given a sharp tug to make sure the connection is secure. The final product is rather bulky and unseemly, and as such wire nuts are best for “out of sight” splices: in-wall, attics, etc. (although that would only apply only to low voltage applications like speaker wiring – there are codes and regulations for electrical splicing).
Crimped closed end caps or sleeves
Also known as pig-tail sleeves, these connectors are somewhat similar in application to twist-on wire nuts, in that there are specific sizes for the gauge of wire you are using (although not necessarily color-coded). And as with other splicing connectors, the insulation on the wire should not be stripped back so far that bare wire extends beyond the base of the sleeve.
Crimped caps should be used with a proper crimping tool. There are nice crimpers available with a ratcheting action, but I’ve never had any problem using one like this, which is readily available at any hardware store for no more than $10-15.
As an added bonus, this variety of crimper typically includes a built-in insulation stripper that works well for most stranded wire.
To perform the splice, both wires are stripped and slipped inside the sleeve. They don’t need to be twisted together first, although that’s okay. The cap should be firmly and fully crimped with a correct-sized jaw of the crimping tool, and the connection should be subjected to a pull-test afterwards.
Crimped caps, if done properly, are more sturdy than twist-on nuts and require no taping, but they are also bulky and unattractive and therefore primarily suited for out-of-site applications.
Insulated butt connectors
Commonly called “butt splices,” these crimped connectors have a metal tube inside a plastic sleeve and are installed in-line. Like wire nuts, there are specific and color-coded sizes for specific wire gauges: Yellow for 10-12 ga., blue for 14-16 ga., red or pink for 18-20 ga.
The big advantage of butt splices is that they result in the most streamlined and attractive appearance of any splicing method, and as such are the best choice when there are concerns for physical space or aesthetics. For instance, butt connectors would most assuredly be the way to fly for speaker wire running under carpet or in a wire-channel. To further streamline the finished product, the two splice points can be staggered. (NOTE that these butt spices are not crimped – the photos are mock-ups for illustration purposes only! The yellow marks show the proper crimping locations.)
The insulation should be stripped back far enough for the bare wire to fully seat in the metal tube. The wire’s insulation should ideally butt up against the metal tube, or at least be fully covered by the outer plastic sleeve. In other words, no bare wire should be exposed. The butt splice will have two crimps, each at a little less than half way between the center and the end (the “less” being closer to the center, not the end). That is, the crimp should ”bite” the internal metal tube and not the plastic sleeve extension that covers any bare wire.
Like crimped sleeves, butt splices should be firmly and fully crimped with a correct-sized jaw, and the connection should be subjected to a pull test afterwards. Butt splices, if done correctly, are about as sturdy as crimped sleeves and require no taping. The same tool recommended above for sleeves works fine for butt splices as well as all other insulated crimp-on terminals such as ring lugs, spade lugs, etc.
The only downside that may be a concern, butt splices do not maintain copper-to-copper contact between the two wires being spliced. This is because the metal tube has a “stop” in the center that prevents the stripped wire from being inserted past the halfway point. Thus the wires do not make physical contact; their electrical continuity will come via the body of the butt splice.
An important note, crimped devices are designed to be used solely with stranded wire. Under no circumstance should butt splices or sleeves ever be used with solid-core wire like Romex, etc.
All the various methods of splicing except butt splices can fully accommodate splicing wire of differing gauges. Butt splices are more limited - you can step up or step down a gauge only as long as it is the same size wire that the butt splice is designed for (see color/gauge code above). In other words, using a blue butt splice, you could transfer from 14 or 16 gauge, but not to gauges larger or smaller than that. Using too small a wire in a butt splice runs the risk of an unsecured crimp that can easily separate or pull out of the butt splice.
Soldering is undoubtedly the most robust method of splicing, but also the most difficult and expensive. It’s the most time consuming as well. A successfully soldered splice will be as strong as the cable itself, so in certain applications it might be preferable or appropriate. However, soldering requires considerably more skill than crimped or wire nut splices and requires specialized tools, namely an adequate soldering iron.
Good soldering irons or soldering guns usually start at about $30-40; my brand of preference is Weller. You can buy cheaper irons, but for speaker wire, especially if it’s larger than 16-ga. you’ll want at least a 40-watt iron. This Model WLC100 variable-temperature station from Weller is a relative bargain, only a few dollars more than their professional-grade 35-watt irons (the light blue ones), and will do everything from speaker wire down to circuit board work.
Soldering becomes more problematic as wire gauge increases; a 14-ga. splice (which will total 11 ga. when the two ends are twisted together) is the maximum sized wire that can reasonably be soldered with a 40-watt iron, and that’s pushing it. Lower-powered irons like the one pictured above will deliver the available heat most effectively with a large or broad tip, as opposed to a thin, pencil point tip.
Soldering a 12 ga. splice with a low-powered iron (40 watts or less) is not recommended, because the total AWG of two 12 ga. wires twisted together is a very substantial 9 ga. The problem with soldering heavy gauge wire with a light-duty iron is that the wire is very slow to heat, and consequently the insulation starts to melt before you get the wire up to temperature for the solder to melt. More powerful irons can heat up the wire quicker at the solder point, before it can fully transfer down to the insulation. Bottom line, if one has to solder two pieces of 12 ga. speaker wire, a 100 watt gun or iron is recommended.
Soldering 10 ga. or larger splice will probably require a torch, which will certainly ruin the insulation. Butt splices are the most practical and economical way to splice 10 ga. wire.
A problem with soldering to be aware of is that the flux residue over time becomes a corrosive element that can eventually eat through the wire and sever the connection. However, this is more a problem with very small-gauge wire (22 ga. or less) than with large gauge wire.
While twist-nuts and crimped connections provide their own built-in insulators for the splice connection, soldering does not, so soldered connections must be insulated after the fact. The best, most effective, and most durable insulator is heat shrink tubing.
Heat shrink comes in a variety of sizes, from very small to very large. You will need to choose the size that’s appropriate for the speaker wire you’re using; most good tubing shrinks down to about half its original size. Typically for speaker wire, either 3/8” or 1/2” tubing is what you’ll need (size indicators are typically before-shrinking.) My preference is the 3M brand, although others are available.
The tube is slipped over one of the wire leads before soldering, large enough in diameter to fully cover the splice, and long enough to lap over both sides of the splice onto the insulation. After soldering, the spliced section would be bent down with pliers to be parallel with the length of wire, and the heat shrink would then be slipped over to fully cover the splice and all bare wire. This makes for a somewhat more “streamlined” splice (although still pretty bulky compared to an in-line butt splice).
It is important for the heat shrink to be rather loose at the splice point before heating. If it is so tight that it barely fits, it will probably split when you apply the heat.
The heat shrink obviously needs a heat source to shrink. The best thing to use is a heat gun (yup, more specialized tools to buy!).
You can get special heat guns made for that purpose at electronics hobby shops (read expensive), but a common paint stripping heat gun from Wal-Mart will work fine, for about $20. Alternately, a cigarette lighter, fireplace lighter, etc. can be used with care. The heat shrink will take direct flame, but the insulation on the wire won’t, so extreme caution is recommended. For best results, make sure to fully turn the wire over and back and forth when heating the tubing, to even distribute the shrinking process.
Wrapping the wire electrical tape is not recommended for insulating a soldered connection because, as mentioned earlier, it does not hold up over time.
Now that you know the ins and outs of wire splicing, the same techniques can be applied to all sorts of wiring applications, such as hooking up electronics in your car, for instance (signal wiring and coax are out as far as splicing is concerned, however). Some applications, like telephone wire, do require specialized crimping devices. Just be sure and educate yourself on the correct protocol for the task at hand.
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