Loop wire vs copper tape: choosing the conductor

Most hearing loops are laid in round insulated wire or flat copper tape. The choice depends mostly on where the conductor goes and what will cover it, but it also changes the load the driver sees, through the copper's resistance and the loop's inductance. This guide covers both, plus the feeder cable.

Key points

• Where the loop goes usually decides. Tape lies flat under carpet and other floor coverings. Round wire suits ceilings, conduit, trays, saw-cut grooves and concrete.
• The conductor does not set the field. Current, turns and the loop's path do.
• Resistance follows copper area. Thin tape can hold less copper than the wire it replaces, so check its cross-section, not its width.
• Wide tape has a little less inductance, which trims the driver voltage needed at high frequencies. The gain is real but modest.
• The feeder counts too. Use twisted pair or star-quad cable, keep it short, and include it in the driver calculation.

Round wire and copper tape at a glance

Round loop wire is insulated copper, solid or stranded, typically 1.5 to 4 mm² (about 16 to 12 AWG). Copper tape is a thin insulated copper strip, commonly 10 to 20 mm wide and about 0.1 mm thick.

Installation: under carpet, in screed, in ceilings

Under carpet and floor coverings

Copper tape is made for this. It goes down on the subfloor before the carpet or tiles, held with adhesive and covered with protective tape.

• Start with a dry, sealed, thoroughly vacuumed floor; dust defeats adhesion.
• Keep the tape clear of carpet tack strips, seat fixings and thresholds, where nails, bolts and sharp edges can cut it.
• Turn corners with a flat fold rather than a cut and joint, where the tape's instructions allow.
• Solder with a broad, heavy iron tip held flat on the foil, keep the solder thin so it leaves no ridge, and insulate every joint. Covering tape is not joint insulation.
• Leave a small slack fold across moving cracks; flexing boards can fatigue foil into hidden breaks.
• Join tape to feeder in an accessible box with strain relief, not by clamping foil into a driver terminal.

Thin vinyl can show tape in low-angle light; for a critical finish, consider round wire in a shallow saw-cut groove. Floor fitters do cut loop tape, so show them the routes, keep a cut-wire alarm on the loop while they work, and photograph the routes before they are covered.

In screed, saw-cut grooves and concrete

For a new slab or screed, use round cable with insulation suited to being cast into concrete and to the moisture it will see, tough enough to survive boots, shovels and the pour itself. Tough cable made for vehicle-detector loops is one option, in a version rated for that concrete exposure; a traffic-loop or burial label alone does not settle it. Copper tape is not burial cable. Label both ends of every circuit, consider a spare circuit on the same route, and leave a spare insulated and disconnected, never joined into a closed turn.

In an existing slab, find out before any cutting where the reinforcement, post-tensioning cables, heating pipes and other services are, and agree the routes and cutting depths with the building owner. Fine-stranded, flexible round wire settles into narrow saw-cut grooves more easily than stiff cable. Allow extra depth at corners and crossovers.

In ceilings and along walls

Round wire is the usual choice above a ceiling, on tray, in conduit or trunking, or along a wall at floor level. Follow the local wiring code for cable in air-handling spaces. Prefer non-metallic conduit, trunking or tray where the code allows: steel containment puts metal right against the conductor, and if it is bonded into a continuous ring around the room it can weaken the field badly; see metal loss. A ceiling loop sits at a different distance from listeners' heads than a floor loop, and standing listeners are closer to it than seated ones, which changes the current needed and how even the field is; see listening height.

Whatever the method, test before anything is covered: with the driver disconnected, measure continuity, loop resistance and insulation to earth, then, where you can, run a test driver and listen with a receiver. A site survey that records the floor finish, ceiling access and slab type tells you which method you are planning for.

Resistance, inductance and the high frequencies

Resistance depends on copper cross-section and length: a metre of copper with a 1 mm² cross-section is about 0.017 Ω at 20 °C, and twice the cross-section has half the resistance. A 10 mm × 0.1 mm tape holds 1 mm² of copper, less than half that of 2.5 mm² wire, so on the same path it has more than twice the resistance. Wider or thicker tapes close the gap.

Inductance depends mostly on the loop's size and shape, and a little on the conductor. A wide, flat conductor spreads the current across its width, which lowers its inductance. Compared with 2.5 mm² wire, tape 10 to 20 mm wide is roughly 10 to 20 percent lower in a single-turn room loop.

Why it matters at high frequencies. Reactance, the part of the loop's opposition to current that comes from its inductance, grows in step with frequency, and the frequency-response target in IEC 60118-4 runs up to 5 kHz. In most room loops, inductance rather than resistance sets the driver voltage at the top of that range, so lower inductance helps a driver near its voltage limit hold the treble. Skin effect changes little here: at 5 kHz the skin depth in copper is about 0.9 mm, roughly the radius of 2.5 mm² wire, so the wire's resistance stays close to its DC value, and the loop's reactance is far larger than its resistance anyway.

The field does not change. For the same current on the same path, tape and wire give practically the same field at listening height, so tape does not reduce the current you need. See sizing a loop driver.

Worked example: Community Hall

An example with a synthetic room and rounded figures, not a real job. Your loop will differ.

Community Hall is 15 m × 10 m, with a single-turn perimeter loop of 50 m driven at 5.5 A: the 1 kHz current for 400 mA/m at 1.2 m above the middle of the room, with no metal loss. A 15 m star-quad feeder adds about 0.17 Ω and 2 µH, and is included in the voltages.

The wide tape needs about 17 percent less voltage at 5 kHz than the round wire, despite its higher resistance. The narrow tape needs the most voltage at 1 kHz, where its higher resistance counts most, yet still a little less than the wire at 5 kHz. These differences are modest: a second turn, or a few dB of metal loss, would each change the voltage demand more than the conductor does.

Feeder cable: why twisted pair or star-quad matters

The feeder carries the full loop current but adds no useful field, and its resistance and inductance use up driver voltage.

• Keep the legs together. Outgoing and return conductors that run apart form a stray loop, adding inductance and putting field into places such as the equipment room. Twisted pair or star-quad cable makes their fields cancel.
• Wire star-quad correctly. Parallel two diagonally opposite cores for each leg, not neighbouring cores. Each channel of a phased array needs its own feeder; never share a return.
• Count it, and keep it short. On a 15 m route, a single 1.5 mm² pair adds about 0.34 Ω, as much as the whole 2.5 mm² loop above. Four-core 1.5 mm² star-quad halves that.

Choosing for the job

• Carpeted floor: copper tape under new carpet or tiles is usually the simplest route.
• Hard or thin finishes: round wire in shallow saw-cut grooves, or a ceiling or wall route.
• New slab or screed: round cable rated for concrete, with a spare circuit.
• Large loop, tight voltage budget: wide tape or a heavier conductor buys a little headroom; fewer turns usually buy more, and a short star-quad feeder wastes less of what you have.
• Phased arrays: either conductor works, with insulated crossings; see phased array hearing loops.

Pick a size that puts the loop resistance within the driver's stated load range, and record the conductor, size, length and measured resistance for the handover. The design method shows where this step sits in the whole process.

Planning the conductor in Hearing Loop Designer

In Hearing Loop Designer you choose round wire or copper tape, its size, and the feeder cable and length. The app works out resistance, inductance, impedance and drive voltage at 1 kHz, 1.6 kHz and 5 kHz for each channel. The materials list carries the conductor length, with adhesive tape for copper tape, and the drawings include installation guidance for the method you choose; see drivers and wire. The design is still a plan: installed performance is confirmed by commissioning.

Common questions

Does copper tape give a stronger field than round wire?

No. The field depends on the current, the turns and the loop's path. Tape's advantages are its flat profile and slightly lower inductance.

Can one loop use both tape and round wire?

Yes. A common case is tape under the carpet and round wire where the route rises up a wall to the driver. Make each transition in an accessible box, soldered or crimped, insulated and strain-relieved, and include each length in the resistance calculation.

Can copper tape go in screed or concrete?

Not unless the tape's maker approves that product for that use. For a new slab, round cable rated for concrete is the usual choice.

Why measure the loop resistance before it is covered?

A reading close to the design figure confirms the conductor, length and joints before they disappear. Loop resistances are often below 1 Ω, so use a meter that reads to hundredths of an ohm and subtract the resistance of its test leads. A high reading points to a poor joint or the wrong conductor; low insulation to earth points to damage. Both are quick to fix now and slow to fix later.