The question usually arrives after something hummed. An installer finishes a small distributed system, hears a buzz, and someone on site says the cable should have been shielded. Sometimes that is right. Often it is not, and the shielded cable goes in without the hum being found.
Short answer
Most amplifier-to-loudspeaker runs do not need a shield. A speaker line carries a high-level, low-impedance signal, and the noise that a shield is designed to drain is a problem for low-level, high-impedance circuits such as microphone and line inputs. What a speaker pair does need is the right conductor section for the run and a construction that keeps the pair together — which is what a twisted pair does.
A shield becomes the right answer when the interference is being coupled into the pair in a way the twist cannot reject, or when the project specification demands a shielded construction regardless of the physics. Both cases exist, and they are decided before the cable is ordered, not after the hum starts.
What a shield does, and what it does not do
A shield is a conductive layer around the conductors that is bonded to a reference potential — normally the chassis or connector shell — so that interference reaching the cable is drained to that reference instead of being induced into the signal path. Two consequences follow, and both are practical:
- A shield that is not bonded at the connector does almost nothing. Floating foil in a cable is packaging, not shielding.
- A shield only addresses interference that arrives through the electric field around the cable. It does not reduce loop resistance, it does not add current capacity, and it does not repair a ground loop.
Twisting works differently. Two conductors twisted together see the same interfering field from the same direction, so the induced voltage appears as a common-mode signal on both conductors and largely cancels at the load. That is a geometric effect, and it is the reason an unshielded twisted pair is a legitimate speaker construction rather than a cheap one: the pair is already rejecting the most common form of induced noise on a speaker run.
Where a shielded speaker run is genuinely the right answer
The honest list is short and specific:
- Long runs sharing a tray or trunking with mains or dimmer feeds. The closer and longer the parallel path, the more the pair is exposed; a shield plus separation is the usual measure.
- RF-dense environments. Transmitter sites, rooms full of wireless systems and broadcast positions put energy on the cable that a twist alone is not intended to handle.
- Project specifications that name a shielded construction. A consultant’s specification is a requirement to meet, not a claim to argue with. If the drawing says shielded, the cable is shielded.
- Runs inside racks or dimmer rooms where the cable passes close to switching equipment for part of its length.
On distributed 100 V line systems the same question comes up, because those runs are long and live in the same containment as other services. The construction choices on a distributed line are set out in speaker cable for 100 V line distributed audio.
Deciding by run and environment
| Run and environment | Published unshielded twisted pair | What actually decides it |
|---|---|---|
| Amplifier to loudspeaker inside one room, cable kept away from mains | Adequate | Conductor section for the run, and keeping the pair together |
| Fixed installation in conduit or on tray, ordinary building services nearby | Adequate | Jacket and containment, plus separation from power runs |
| Long run parallel to mains or dimmer feeds | Not the first choice | Separation first; a shielded construction where that cannot be achieved |
| Dimmer room, rack interior, or next to switching equipment | Not the first choice | Whether the cable can be routed away from the equipment |
| 100 V line through a building alongside other services | Commonly used | The project specification and the route, not the audio signal level |
| Specification names a shielded construction | Does not apply | The specification is the requirement |
The comparison between the two unshielded geometries — flat parallel zip cord and twisted pair — is covered in figure-8 zip cord vs twisted pair speaker wire.
The published LBS speaker construction for this decision
LBS publishes a twisted pair unshielded speaker family in five sections, unjacketed, with 4N OFC conductors and PVC insulation. The values below are the published specification of the family, not an extrapolation:
| Model | Section | AWG | O.D. | Conductors | Insulation |
|---|---|---|---|---|---|
| LBSRVS-T-0.5 | 2 × 0.5 mm² | 20 AWG | 2.5 × 5 mm | 2 | PVC |
| LBSRVS-T-0.75 | 2 × 0.75 mm² | 19 AWG | 2.8 × 5.6 mm | 2 | PVC |
| LBSRVS-T-1.0 | 2 × 1.0 mm² | 18 AWG | 3 × 6 mm | 2 | PVC |
| LBSRVS-T-1.5 | 2 × 1.5 mm² | 16 AWG | 3.3 × 6.6 mm | 2 | PVC |
| LBSRVS-T-2.5 | 2 × 2.5 mm² | 14 AWG | 3.8 × 7.6 mm | 2 | PVC |
Standard colour pairing is blue/red, black/red, white/red, yellow/black, green/black, brown/blue, grey/white and orange/black, with custom colour coding available on request. Because the construction is unjacketed, the pair is intended for installation where it is protected by the containment, not for trailing across a stage floor.
Where a project calls for a shielded speaker construction, that is a construction question for the factory to answer against the project requirement rather than something to assume from a catalogue picture. The next step is a specification enquiry, not a guess.
If the system hums, check this before changing the cable
Changing to a shielded cable is the most expensive way to look for a fault, and it frequently does not fix one. In order:
- Is there a ground loop? Two pieces of equipment bonded to earth through different paths create a loop that carries current through the signal reference. The symptom follows the equipment, not the cable.
- Is an unbalanced connection hiding in the chain? One unbalanced link in an otherwise balanced path defeats the balance, and the shield then carries signal reference current instead of only draining interference.
- Is the cable routed along a dimmer feed or a mains trunking? Moving the cable is free; a new cable is not.
- Is the shield bonded at both ends? On a shielded run, bonding at both ends can create a loop through the shield itself. That is a termination decision, not a reason to abandon shielding.
- Is the fault in the loudspeaker or the amplifier? A faulty driver, a failing capacitor or a noisy source will follow the system to any cable.
An installed speaker run adds a constraint that shielded-versus-unshielded does not cover: the path itself. A loudspeaker cable sharing trunking or conduit with lighting and power circuits is both an interference question and a space question, and the larger multi-core speaker constructions are the ones that run out of conduit capacity first. The published outside diameters by core count and the conduit count table are in cable outside diameter and conduit fill.
What to put in an enquiry
A factory cannot choose a construction from the phrase “speaker cable”. The facts that change what gets supplied are: the application and where the run sits, the run length, the amplifier output or transformer tap, whether the route shares containment with power or dimmer feeds, whether the project specification names a shielded construction, and the packaging unit the order should be supplied in. With those six facts, a specification can be confirmed against published product data instead of a sample being guessed at.
A request is answered as a specification, not a catalogue line: request a cable specification.
Frequently asked questions
Do speaker cables need to be shielded?
Not for most amplifier-to-loudspeaker runs. A speaker line is a high-level, low-impedance circuit, and a twisted pair already rejects the common form of induced noise. A shield is justified where the run is exposed to interference the twist cannot reject, or where the project specification requires it.
Is twisted pair the same as shielded cable?
No. Twisting is a geometry: two conductors twisted together cancel common-mode interference. A shield is a conductive layer around the conductors, bonded to a reference. The LBS twisted pair unshielded speaker family is unshielded by construction, and its name says so.
Can I use a shielded microphone cable as a speaker cable?
It is the wrong tool. Microphone cable is built for low-level balanced signals with small conductors, and the shield adds capacitance that matters in that circuit. A speaker run needs conductor section for its length and current, which is what a speaker construction provides.
Will a shielded speaker cable stop hum?
Usually not, because hum more often comes from a ground loop or from a cable routed along a power feed than from the absence of a shield. Find the cause first; a shield drains interference but does not break a ground loop.
Does shielding change the sound of a speaker run?
The purpose of a shield is interference rejection, not tonal character. In a normal in-room run the deciding factors remain conductor section and the pair staying together. Where a specification asks for shielding, the reason is the electrical environment, not the sound.
Continue reading
- Twisted pair unshielded speaker cable 2 × 0.5 mm²
- Twisted pair unshielded speaker cable 2 × 0.75 mm²
- Twisted pair unshielded speaker cable 2 × 1.0 mm²
- Twisted pair unshielded speaker cable 2 × 1.5 mm²
- Twisted pair unshielded speaker cable 2 × 2.5 mm²
- Speaker cable for 100 V line distributed audio
- Balanced microphone cable: shielding and twisted pair
- How to choose speaker cable gauge
- Speaker cable range
The jacketed counterpart of the same decision is LBSRVS-2X1.5 — unshielded jacketed 2-core: an overall PVC jacket is mechanical protection, not a shield, so a jacketed cable is not a shielded cable and the two attributes have to be specified separately.