Quick answer: Speaker level is a high current, low impedance link with no differential receiver, so a speaker cable cannot be balanced in the line sense. The products sold as balanced speaker cable are two-conductor cables with XLR or TRS connectors, and the connector does not make the link balanced. The safety question is the amplifier: a bridged output has no ground terminal, and the wiring must not ground either leg.
Balanced Speaker Cable: The Speaker Link Is Not Balanced
A balanced speaker cable is a name that describes a connector rather than a circuit, and the distinction matters for the wiring. The speaker link carries a high current at a low impedance, and the two conductors are the two ends of the voice coil rather than a signal and its inverse. There is no differential input at the speaker to subtract anything, so the rejection that a balanced line provides does not exist in this link. What the products sold under the name contain is a two-conductor cable with a balanced connector, and the wiring has to respect what the amplifier expects. This guide covers the physics, the products, the bridged amplifier case, and the cable to buy.
Why Speaker Level Is Different
The speaker link is different from the line link in the three properties that decide the cable: the impedance, the current, and the absence of a receiver. The impedance is four to eight ohms rather than ten kilohms, the current is amps rather than milliamps, and the load is a voice coil rather than a differential input. The first two set the gauge, and the third removes the reason for the balanced arrangement, because there is nothing at the far end to subtract the two legs.
Low Impedance, High Current
The low impedance is the reason the speaker cable is thick and short. A four ohm load draws several amps at a normal level, and the resistance of the cable is in series with the load, so a thin cable loses a fraction of the power and damps the speaker less. The gauge and the length are the two numbers that matter, and the construction is the third. The balanced question does not appear in any of them.
No Differential Pair
The speaker has two terminals and they are the ends of the voice coil, and neither of them is a signal against a reference. The amplifier drives the pair, and the speaker responds to the current through it, so there is no common-mode component to reject and no receiver to do the rejection. The two conductors are the two ends of one circuit, not a signal and its inverse. The balanced arrangement is a line-level idea and it does not transfer.
What the Products Contain
The products sold as balanced speaker cable contain a two-conductor cable of a heavy gauge with a connector that belongs to the balanced family, usually the XLR or the TRS jack. The cable is not a balanced pair, and the connector does not change that. The reason the products exist is the convenience of the connector in an installation that already uses XLR wall plates, and the reason to be careful is that the connector implies a convention that the speaker link does not follow.
Two Conductors in a Balanced Connector
The two conductors go to two of the three contacts, and the third is unused or tied to the shell. The arrangement works, because the speaker needs two conductors, and it is a mechanical convenience rather than an electrical improvement. The risk is the convention, because an XLR on a speaker line looks like a line-level connection to the next installer. The labelling is the mitigation and it is worth the tape.
The Marketing
The marketing borrows the word balanced from the line interface and applies it to a link that has no differential receiver. The claimed benefit is the rejection of interference, and the mechanism does not exist at the speaker level, because the impedance is too low for the picked-up voltage to matter and the load would not reject it anyway. The audible difference between a good two-conductor cable and a good balanced speaker cable is the gauge and the length, not the word.
The Bridged Amplifier Case
The bridged amplifier is the case where the speaker wiring has a real safety rule, and it is the one case where the balanced vocabulary causes damage. The bridged output drives both speaker terminals, and neither is at ground potential. A cable or a connector that ties either terminal to the chassis, or to a common ground, shorts one half of the amplifier. The rule is the same as the headphone case, at a much higher current.
Floating Outputs
The floating output is the design in which neither speaker terminal is referenced to ground, and the bridged amplifier is the common example. The two terminals carry equal and opposite voltages, and the speaker sees the difference. A meter from either terminal to ground reads half the signal, which is the reading that leads installers to think one terminal is grounded. The pair is the circuit and the chassis is the only ground.
The Safe Wiring
The safe wiring keeps the two conductors of each channel together and separate from the other channel and from the chassis. The connector shell is tied to the chassis at the amplifier end and left open at the speaker end, where the shell is not part of the circuit. The speaker switch, the headphone adapter, and the common-ground patch panel are the parts to avoid, because they tie the two channels together. The rule is the same as the four-wire headphone link.
The Cable to Buy
The cable to buy is a two-conductor speaker cable of the right gauge for the length, with the connector that fits the amplifier and the speaker. The gauge is the first decision, and the length is the second, and the connector is the third. The word balanced does not enter the decision, and the premium for the balanced connector buys the connector rather than the signal.
Gauge and Length
The gauge follows the length and the impedance, and the rule of thumb is to keep the cable resistance below a small fraction of the load impedance. A four ohm load and a ten metre run call for a heavier gauge than an eight ohm load and a three metre run. The tables that the cable makers publish give the figure for each combination, and the number is the resistance rather than the gauge name. The length is measured along the path rather than in a straight line.
The Connector Choice
The connector choice is the mechanical interface, and the banana plug, the spade, and the bare wire are the speaker standards. The XLR and the TRS are the line connectors that some installations use for convenience, and they work where the wiring respects the floating output. The connector that ties a terminal to the shell is the one to avoid, because the shell is the chassis. The rule is the same in every case: the speaker connects across the pair and never to ground.
Speaker Link Against Line Link
| Factor | Speaker link | Balanced line link | Effect | Rule |
|---|---|---|---|---|
| Impedance | 4 to 8 ohms | 10 kilohms and above | Gauge | Heavy and short |
| Current | Amps | Milliamps | Heating | Check the connector rating |
| Receiver | Voice coil | Differential input | Rejection | No balancing possible |
| Reference | Floating pair | Differential pair | Grounding | Never ground a terminal |
| Connector | Banana, spade, bare | XLR, TRS | Convention | Label the speaker line |
| Bridged amplifier | Both terminals driven | Not applicable | Safety | Keep the channels separate |
Real-World Application Scenarios
The home system is the case the ordinary two-conductor cable serves. The amplifier and the speakers are three metres apart, the load is eight ohms, and a fourteen gauge cable carries the current without a measurable loss. The bridged subwoofer is the second, where the two terminals are both driven and the wiring has to keep them off the chassis. The installed system with the XLR wall plates is the third, and there the balanced connector is a convenience that works where the wiring is documented. The stage is the fourth, where the speakon connector is the standard and the shell is not part of the circuit.
Related Guides on This Site
The related guides on this site cover the wiring and the gauge. The XLR connector on a speaker line is examined at XLR speaker cable, the cable and impedance behind the link are at amp speaker cable guide, and the gauge for the run is at 14 gauge speaker cable guide.
Frequently Asked Questions (FAQ)
Q: Is speaker cable balanced?
A: No, in the sense that matters. The speaker link has two conductors carrying the same current in opposite directions into a low impedance load, and there is no differential receiver at the far end to subtract anything. The balanced arrangement is a line-level idea, and the speaker link does not have the receiver that makes it work.
Q: Can I use an XLR cable for speakers?
A: It works where the connector is rated for the current and the wiring keeps both terminals floating, and it is a convenience for an installed system rather than an improvement. The risk is the convention, because the XLR looks like a line connection. The speakon connector is the one designed for the job and it is the safer choice.
Q: Why does bridging an amplifier change the speaker wiring?
A: Because the bridged output drives both terminals, and neither is at ground potential. A cable or a connector that ties either terminal to the chassis shorts one half of the amplifier. The speaker connects across the pair, and the switch or the adapter that ties the two channels to a common ground is the part that damages the amplifier.
Q: Does a heavier speaker cable improve the sound?
A: It reduces the resistance between the amplifier and the speaker, which matters where the run is long or the load is low. On a three metre run into eight ohms the difference between a twelve and a fourteen gauge cable is below the audible threshold. The gauge is chosen for the resistance, and the length and the impedance are the two numbers.
Q: What is a balanced speaker cable used for?
A: It is a two-conductor speaker cable with a balanced-family connector, used where the installation already has XLR or TRS wall plates. The connector is the convenience and the link is not balanced. The purchase is the gauge and the length, and the connector is the mechanical interface.