The voice coil former material affects thermal resistance, rigidity, weight, heat dissipation and mechanical stability of the voice coil.

Kapton — a lightweight, heat-resistant and non-conductive material. It is widely used in voice coils for speakers, woofers, midrange drivers and subwoofers. It offers a good balance between weight, thermal resistance and reliability.

Fiberglass — a glass-fiber composite former material. It is more rigid than Kapton and provides good mechanical stability and heat resistance. It can be useful when a stronger structure is required.

Aluminum — a rigid material with good heat dissipation. It helps transfer heat away from the winding more efficiently, but because aluminum is electrically conductive, it may affect some electrical parameters of the coil and speaker. It is often used where rigidity and cooling are important.

Black aluminum / Black Al — an aluminum former with a black surface treatment or coating. It keeps the advantages of aluminum, such as rigidity and heat dissipation, and may improve surface stability and adhesion depending on the type of treatment.

Titanium — a lightweight, rigid and heat-resistant material. It is used in specific designs where high mechanical stability and low weight are important.

Paper — a lightweight traditional material, mostly found in vintage speakers or lower-power designs. It has lower thermal resistance compared with Kapton, fiberglass and metal formers.

Important: the final thermal resistance of the voice coil does not depend only on the former material, but also on the wire, insulation, adhesive, winding height, speaker ventilation and real operating conditions.

The wire material affects the weight of the voice coil, electrical conductivity, outer winding diameter, moving mass of the speaker and repair-related characteristics.

Copper (Cu) offers the best electrical conductivity among the most commonly used voice coil wire materials. Copper wire provides good efficiency and stable electrical parameters, but it is significantly heavier than aluminum and CCA. The increased coil weight can raise the moving mass of the speaker, which is especially important in midrange drivers, midwoofers and other applications where high sensitivity and fast response of the moving system are important.

Aluminum (Al) is much lighter than copper and helps reduce the weight of the voice coil. This can be useful when the goal is to reduce the moving mass of the speaker and improve response. However, aluminum has lower electrical conductivity than copper, so a larger wire cross-section may be required to achieve similar resistance. As a result, the outer diameter of the coil may be larger than that of an equivalent copper coil. Aluminum wire is also more difficult to solder, so the connection method of the lead-out wires should be considered during repair.

CCA, or copper-clad aluminum, combines the lower weight of aluminum with improved surface conductivity and better solderability thanks to the copper coating. CCA is lighter than copper, but usually heavier than pure aluminum. It is a compromise between weight, conductivity, cost and ease of assembly. The actual performance of CCA depends on the wire cross-section and the thickness of the copper coating.

When choosing a voice coil, it is important to consider not only the wire material, but also the inner diameter, outer diameter, winding height, former height, impedance, number of layers and compatibility with the original speaker construction.

Temperature index indicates the thermal class of the enameled wire used for the voice coil. This value shows the temperature at which the wire insulation can operate continuously without significant degradation of its electrical and mechanical properties.

Class 200

Enameled wire with insulation based on polyester / polyesterimide and an outer polyamide-imide coating.

Temperature index: ≥200°C
Thermal shock: approximately 220°C
Thermoplasticity temperature of the insulation: approximately 320°C

Class 240

Wire with aromatic polyimide insulation, used for applications with higher operating temperatures.

Temperature index: ≥240°C
Thermal shock: approximately 260–300°C
Thermoplasticity temperature of the insulation: approximately 350–400°C

Important: the temperature index should not be interpreted as the guaranteed maximum temperature of the entire voice coil. The final thermal resistance also depends on the former material, adhesive type, winding quality, speaker ventilation and real operating conditions.

Thermal shock — indicates the ability of the insulation to withstand higher temperatures for a short time without cracking or breaking.

Thermoplasticity temperature — indicates the temperature at which the insulation may begin to soften or lose mechanical stability.

The wire cross-section shape affects winding density, fill factor, outer coil diameter, resistance, weight and production cost.

Round wire — the standard and most common option for voice coils. In multilayer windings, the turns of the next layer sit in the spaces between the turns of the previous layer, but because of the round shape, more empty space remains between the wires. As a result, the fill factor is lower than with flat or rectangular wire.

Voice coils made with round wire are usually easier and less expensive to produce and are suitable for most speaker, woofer, midwoofer and subwoofer repairs.

Flat / rectangular wire — allows the available space in the magnetic gap to be filled more efficiently. Thanks to the higher fill factor, it is possible to place more conductive material in the same volume, reduce the outer winding diameter or lower the resistance when the wire size is selected correctly.

Voice coils made with flat or rectangular wire can be more efficient in high-power speakers and professional applications, but they are more complex and more expensive to manufacture. The final parameters depend on the wire size, number of layers, winding height and winding method.

Fill factor — indicates how efficiently the wire occupies the available space in the winding. The higher the fill factor, the more conductive material can be placed in a given volume.