A ¼ inch cable is a ¼ inch cable, right? Not so. Despite their nearly identical looks, an instrument cable and speaker cable are actually very different under their jacket and are not meant to work interchangeably. This means that if you use the wrong cable, there’s a good chance you’re going to run into unwanted trouble.
The Right Cable for the Right Job
An instrument cable and speaker cable are built to best handle the type of signal that they’ll be working with. In the case of an instrument cable, they are designed to work with the low level signal of an instrument, one that is also susceptible to a wide range of outside noise interference such as RFI/EMI from cell phone and radio towers, electrical transformers, dimmers, fluorescent lights and other sources that are always around us. Because of this, instrument cables are built with a shield that is meant to protect an instrument’s signal from outside interference. Speaker cables are not built with this shield, meaning that using one in place of an instrument cable will generally cause a lot of noise. You won’t risk damaging anything from using a speaker cable to connect your instrument to an amp, but you most likely won’t get a clean, noise-free sound either.
On the other hand, using instrument cables should not be used to connect speakers to an amplifier because they don’t have a low enough resistance to allow the speaker voltage flow easily. By using an instrument cable instead of a speaker cable, you most likely won't hear a difference or have any problems at low volumes but if you happen to have a very powerful amp and crank up it up, you will probably hear some slight distortion as the amp will have to work much harder and deliver less power to drive the speaker. Since an instrument cable wasn't designed to deliver that amount of power, it could potentially melt the cable jacket and even create an electrical short circuit with the real possibility of also ruining your amplifier, speaker or both.
Under the Hood
It can be easy to lose track of your many cables, especially while setting up a gig. The last thing you need during a live performance is trouble created something as easily avoidable as accidentally using the wrong cable. Luckily, most cables should say whether they are meant for an instrument or speaker in small white lettering on their jacket. A speaker cable is also usually slightly thicker than an instrument cable. If all else fails or you just want to be absolutely sure, you can always unscrew the connector barrel and take a closer look under the hood.
An instrument cable is made of a single small gauge conductor, usually copper, surrounded by an insulator. This insulator is then covered by a braided or foil shield that also acts as a second conductor. All of this is then covered by a plastic or rubber outer jacket. Speaker cables meanwhile are composed of two conductors but are of a much higher gauge, both of which are encased in their own insulating jacket. These two individually insulated conductors, usually twisted, are then covered by a plastic or rubber outer jacket as well. So if you see two similarly sized individually insulated wires, you're holding a speaker cable; if you see one insulated wire wrapped in a copper shield, you have an instrument cable.
So if you ever happen to find yourself in a situation where you need an instrument cable but only have a speaker cable or vice versa, remember: its not worth it! Investing in a few spare instrument and speaker cables is a much better idea, one that can potentially save both your tone and your gear.
Your Turn to Sound Off!
Have you ever used a speaker cable instead of an instrument cable (or vice versa)? Were there any problems or differences you noticed?