Somewhere along the line somebody probably told you “Don’t ever use guitar cables for speakers and vice versa!” If not you will be glad you noticed this article because it might save you some trouble down the road. What seems confusing is that from outward appearances the two cables can look much the same, if not identical. The plugs are interchangeable in most cases as well. So let’s take a look at why they are different, what they are optimized for, and why they don’t make good substitutions for one another.
Instrument (guitar) cables are designed to transfer the very small signal your guitar pickups generate or the line level signals from a preamp or mixer to an amplifier input. They need to do this without collecting a lot of outside interference. This is important because any small electrical signals it picks up on the way to your amp input will be amplified right along with your instrument! To prevent this, guitar cables have a small central conductor to carry the low level signal to the amp and a large outer shield of twisted or braided copper to ground out interference before it gets into your signal chain.Speaker cables must carry a much more powerful signal as they come after your amplifier has boosted the signal level many times over (how loud is your amplifier compared to what your electric guitar sounds like unplugged?) Those high AC currents allow your power amp to move large, heavy speakers and a lot of air to create sound. So speaker cables must have very large conductors compared to instrument cables. On the other hand because the signal level they carry is so high, outside interference isn’t a problem (without being amplified it can’t compete with your amp’s output), so speaker cables do not have an outer ground shield like your instrument cables.
It is easy to see how both cables have different designs so they can handle different jobs. But why is it so important not to confuse the two?
If you were to use a speaker cable to plug in your guitar it would collect all the electrical interference around you like an antenna and inject it into your amp input along with your guitar signal because it doesn’t have the outer shield. By the time that noise was boosted by your entire amp it would come out just as loud as your guitar and would probably only be useful for getting club managers to fire the band.
Now if you put an instrument cable between your amp output and the speaker, the small center conductor cannot handle the high power output current and can overheat, generate resistance that affects your output load (bad for your amplifier’s output section!), and might even melt down or catch fire in extreme cases! The shielding on an instrument cable creates a capacitor with the inside conductor that your amplifier may not like. This could send your amp into an oscillation and potentially cause damage. Because of this it is very important for you to know which of your cables are which and that you can tell them apart even under low light stage conditions.
If you are unfamiliar with a cable, in a pinch you can often tell the difference by unscrewing the end of the cable and looking at the wire coming in. If the cable splits into two fairly thick even wires that are side-by-side, it is a speaker cable. If it has one wire in the middle and many strands of twisted or braided copper wire wrapped around the outside the other, it is an instrument cable. Some fancy, high quality cables might have extra center conductors, so don’t let that confuse you- they’re wired in parallel. The outer shield is what is important no matter how many wires are in the middle. Fortunately most quality cable makers also print the type of cable on the wire itself which can be a big help if the end of the cable isn’t designed to unscrew.
Take some time out to check all your cables so you know which are which. You might even want to mark them with colored tape so they are easy to tell apart next time you’re fishing in your gig bag for a replacement only moments before downbeat. Knowing every part of your system is wired correctly will give you added confidence, and you will be rewarded with great sound and reliability in the future.