Voice coil

a typical coil consists of two or four layers of copper wire or aluminum block. The copper has a higher density and a lower electrical resistance, so that equals size coils and electrical resistance, the copper coils has more and more inductance. In general the copper is more suitable, but where it is important to the high frequency response is better to use aluminum for its lower mass and its lower inductance. To eliminate some of the difficulties with building the aluminum, you can use aluminum covered with copper (with a heat treatment) so combining the strength and lightness of this material to the best electrical characteristics of copper.

Another factor that may further reduce the efficiency of speakers, in itself already very low, is increasing the temperature of the core, causing a consequent increase in resistance (about 0.4% / C°). Various methods are used to help heat dissipation accumulated by the coil: the use of iron in the fluid gap of magnet, the magnet ventilated (eg patent Super Vented Gap of JBL). We have seen a decrease in mass of the core can increase the efficiency of the system and an alternative to the use of different materials to use different sections of wire, thus increasing the factor of "impaccamento" the windings (note that this way you can get to increased efficiency of 2 dB). The voice coil is generally cylindrical section and can be composed of different materials, in this case are the determinants strength of the material and its ability to resist heat developed by the coil without any deformations.