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Subwoofer Cable FAQ:
Here are some frequently asked questions about subwoofer cable. Should you find your question isn't answered here, by all means give us a call; we're happy to help.
What kind of cable do I need for my subwoofer?
Well, there are two basic possible answers to that question, depending on what sort of subwoofer you have. Most subwoofers in consumer use, from the cheapest to the extremely high-end, are powered subwoofers. These subwoofers have their own power supply which is plugged in to a wall outlet, and the signal is fed to them by a line-level cable, typically through RCA (almost universal) or XLR (reasonably common, but not always present) jacks on the panel of the subwoofer. The signal goes into the subwoofer at the same low signal level that it would go from, say, a tape deck into an amplifier. It is then amplified in the cabinet of the subwoofer and fed directly to the speaker internally.
But while that’s the usual arrangement, it’s not universal. Sometimes a subwoofer is a "passive" subwoofer, meaning that just like any other ordinary speaker, it’s made to accept a powerful, speaker-level signal. In such cases, the input will usually go through a conventional speaker cable and into a set of binding posts, though other connectors, e.g., Neutrik Speakons or 1/4 inch connectors, are sometimes seen. And no, in such a case you can't feed the subwoofer from an RCA or XLR line-level output -- the signal level will be far too low to be acceptable without adding an amplifier along the way.
The remaining questions and answers in this FAQ are about line-level subwoofer cable. If you have a passive subwoofer and need speaker cable, see our speaker cable department.
My sub has stereo inputs. Do I need to use them both?
It depends. If your sub has left and right audio inputs and outputs and you're "looping through" the full-range audio, passing it through the sub on the way to the main amp, then yes, you'll want to feed both inputs and connect the signal out of both outputs.
But the more typical configuration is to have a single subwoofer line-level out signal (e.g., coming from an amp or preamp). If that's your situation, take a look at the manual for your sub. The vast, vast majority of subwoofers are set up to take a mono signal, and this usually calls for plugging the subwoofer signal in to the "left" channel side and leaving the right channel unconnected. When this is the case, there's really no advantage to also feeding the right channel.
If the sub manual does recommend feeding both channels in such a situation, the easiest way to do that in the case of a single output from the system is a simple Y-cable which will feed a single signal out to two inputs. But, again: this is usually unnecessary.
What are the important features of a subwoofer cable?
The biggest factor in subwoofer cable quality, in the case of an unbalanced ("RCA") cable, is simply shielding: shielding is the only method of noise rejection in an unbalanced line, and the length of subwoofer cables sometimes can mean that they are vulnerable to some induced noise pickup. Heavy shielding also has an added benefit in relation to the possibility of ground loop hum: the lower the resistance between the signal grounds on the devices, the lower the difference in ground potential will be.
In the case of a balanced connection (typically XLR to XLR), noise rejection is not dependent only on shielding; it mostly comes from common-mode noise rejection, which depends on how well balanced the circuits on each end of the line are and on how consistent and symmetrical the cable is, both physically and electrically. These are the same attributes which make for a good balanced audio cable in general -- nothing is really different about the subwoofer application.
Are subwoofer cables shielded?
Well, they certainly should be, especially in the case of an unbalanced ("RCA") connection. In unbalanced connections, there's no common mode noise rejection, and the shield is the one obstacle to induced noise. We do occasionally see people using unshielded cables, and we also sometimes see people who misunderstand the nature of common-mode noise rejection and think that a twisted pair cable, such as is commonly used in balanced audio, will provide noise rejection so that shielding is unnecessary, even when going in to an RCA input. It won't. The problem is that common mode noise rejection is not simply a function of the cable; it only works if the circuits at both ends of the cable are balanced, and RCA-type connections are always unbalanced.
My sub has both XLR and RCA inputs. Which should I use?
In theory, at least, the XLR connection should always be superior -- that is, if it is an XLR connection at both ends. It's always better, if you have only an RCA input, to join that to an RCA output, and if you have only an XLR input, to join that to an XLR output.
That said, it is also entirely possible for the RCA connection to be superior, for reasons that have more to do with hard-to-guess aspects of circuit design than anything else.
I have an XLR input on my sub and I've heard XLR is superior to RCA. Should I use it even though my signal is coming from an RCA output?
No, unless there's no other alternative. When XLR connections are superior to RCA connections, it's because of the balanced nature of the connection; and a connection between an unbalanced circuit and a balanced circuit is NEVER a balanced connection. If there is no alternative, it can be done, though problems sometimes result. We offer cables for this here: Balanced to Unbalanced Cables.
How long should a subwoofer cable be? Is there a maximum?
Abraham Lincoln, asked how long a man's legs should be, said they should be long enough to reach the ground. That's pretty much the rule here. Establish your equipment locations on the basis of other criteria such as best placement for the sub, and then make sure the sub cable is long enough to reach. That said, there may be times when getting that connection to be shorter can help with management of ground-loop hum.
What causes a subwoofer to hum, and how can I fix it?
Subwoofers are great at reproducing low frequencies. It's unfortunate, then, that one of the most ubiquitous signals in this world is the annoying 60-cycle hum (or, in many countries, 50-cycle) of our normal household AC supply current. Once that gets into the signal path, one way or another, a subwoofer does a marvelous job of amplifying it.
There are several possible causes of hum in a subwoofer, addressed in this article: Bah! The Subwoofer Hum Bug. The most common cause is some sort of ground loop situation, usually best resolved by addressing the system's grounding. However, when that fails or when it's difficult or impractical to do, sometimes the handiest answer is a line-level audio isolation transformer, which breaks the flow of ground current along the signal path.
Is a subwoofer cable the same as an RCA cable?
"RCA" in this usage really is just the term for a connector type, originated by RCA (Radio Corporation of America) in the 1930s for phonograph inputs to radio amplifiers. There's no such thing as a standard RCA cable -- these cables vary in internal structure and electrical characteristics. Some are better suited to a subwoofer than others. But if this often-asked question means "can I use any cable with RCAs on it to hook up my subwoofer," the answer is yes, so long as your sub has RCA connections.
Is a subwoofer cable the same as a coaxial cable?
In the case of an RCA-terminated cable, usually. But let's be clear about terms.
"Coaxial" is a reference to cable geometry, not to connector types or anything else. All that defines a coaxial cable is that there's a center conductor, an insulating dielectric around that conductor, then a shield on the outside of that dielectric and (ordinarily, but not invariably) a jacket around that shield. Frequently, in common usage, when people say "coaxial cable" they mean a 75 ohm cable terminated with F connectors: the little screw-thread connectors that attach television antennas and cable TV outlets. But a coaxial cable can be many things. It can be an SDI cable for high-bandwidth digital video, a CATV drop coax, an audio cable, a 50 ohm radio transmitter cable, and so on, and so on. It may be equipped with any of a huge number of different connectors, depending upon the connection requirements. There are differences between these which may, in a particular application, be important. For example, CATV drop coax is not as well shielded (typically 60% aluminum braid over foil) as something like an SDI cable, which may or may not be an issue in a particular installation.
The best geometry for an RCA-connector subwoofer cable is coaxial, but that doesn't necessarily mean that the cable stock used in a subwoofer cable will be one suited for those other applications; and a cable made for CATV connections will have the wrong doggoned connectors on it for use as a subwoofer cable (though adapters do exist that will allow one to do it).
I hear a radio station through my subwoofer. What's happening and what can I do about it?
Alas, radio-frequency interference (RFI) is as old as radio. Various types of radio sources -- AM broadcast, CB, and ham, among others -- can get into home audio circuits, become rectified, and come out as audio. The question here is always what the entry point is. If the signal is getting in to the subwoofer itself directly, a change in cable won't help; the problem has to do with inadequate shielding of the subwoofer's internal circuit.
In some cases, however, the cable is the pickup point; cables, being long, can effectively operate as antennas, picking up such things. If you're getting RFI through the sub cable, we recommend going to a sub cable with a foil shield. Our normal recommendation, LC-1, has two braid shields but no foil, because those braid shields are highly effective at audio frequencies, while foil is not. But if radio frequencies are the problem, the advantage shifts to a braid-over-foil cable, such as Belden 1694A.