• Speaker vs. Instrument Cables - A Simple Guide

    10 comments / Posted by Bruce Ohms



    Even the most experienced musicians forget essential parts of their rig from time to time. A drummer I know forgot his drum sticks at an out of town gig, and I myself have showed up to play at a local show having forgotten to bring my bass amp head (I had to use a DI that night)! It’s something that happens to the best of us. Fortunately, if there are other bands on the lineup or a helpful soundman, they may be obliged to help you out lending you the item you forgot, especially if it is something like a cable.

    Use the Right Cable for the Job

    If you’re at the gig or studio and realize that you’ve made the understandable mistake of forgetting your speaker or instrument cables, or you’ve found out one of your cables has gone bad, it’s essential to make sure that the new cable that you borrow or buy is the proper one for the job. While standard ¼-inch speaker and instrument cables may look similar, they have a few key differences in construction that make it so you cannot use them interchangeably.

    The construction of a cable is fairly simple. It consists of a copper core coated with polyester or rubber, with nickel, gold, or other metal connectors. High-end cables like Carvin Audio’s C20P shielded guitar cable utilize an oxygen free copper core for optimal signal transfer and to reduce the aging process of the copper. The key difference between instrument cables and speaker cables are instrument cables are shielded with much smaller wires and speaker cables are unshielded with larger wire gauges.

    Since an instrument cable is used to connect your instrument to the amplifier in a high impedance environment, shielding is essential. Shielding surrounds the signal wire in the cable and “shields” it, reducing interference from other electronics and radio signals nearby. Speaker cables do not need shielding since the signal from your amp is so large and the impedance of your speaker is so low, that any additional RF noise and outside interference will be insignificant.

    What Happens if You Use the Wrong Cable?

    Using a speaker cable in place of an instrument cable will add a lot of unwanted noise to your setup. Since it’s unshielded, your guitar signal will be accompanied by buzz, hum, and interference from the surrounding electronics- including hum and buzz from your own amplifier’s transformer, your band mates’ amplifier and the PA speakers. Not to exclude the lighting system, cell phones and those cool beer neon signs hanging all around the bar. You’ll be a one person noise rock band, and not in a good way.

    Using an instrument cable in place of your speaker cable can cause catastrophic damage to your amplifier. While your amp will still work initially, the high amount of current going through the instrument cable’s small gauge wire can actually melt the cable! Furthermore, this may cause a short, damaging your amplifier.

    Another issue with using shielded cables for speaker cables is they introduce a capacitive element that can destabilize your amplifier. Most amplifiers have improved to withstand using the wrong type of cable for a short time, but no one likes to test their amplifier’s stability at a show. This can cause some crazy results in some amplifiers leaving the amplifier damaged and you paying the repair bill.

    Telling the Two Cables Apart

    While most manufacturers make it clear which cable is which by labelling it clearly on the cable, there may be instances where you won’t be sure. If this is the case, simply unscrew an end of the cable. A speaker cable has two independent wires, one connected to the tip and one to the sleeve. These wires will likely be red and black or white and black. There should be no braided wires or a foil rap present let alone connected to any pin. The two wires should be of significant size also. Typical wire gauge for a 1/4-inch speaker cable is 16 or maybe 18 gauge. If it’s an instrument cable, you will see one or two wires covered in some form of shielding. The shielding can be a braided wire mesh or foil wrap around the one or two wires. If the ¼-inch connector is a TRS end (this is a stereo end with a Tip, Ring, and Sleeve, like on head phones) then you know it is not a speaker cable.

    If you’re in a bind, make sure you use the proper cable! While it’s easy to be tempted to substitute one for the other, it’s never worth it.

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