Iron cores often become saturated 2 or 3 times faster than air core inductors. Magnetism is induced in an iron core when voltage is applied to it, magnetizing the core in one direction. Additional power is needed to reverse the magnetic field, and the reversal may not be instantaneous resulting in unwanted distortion. Therefore, air cores have substantially reduced hystereses distortion due to the fact that they have no magnetic core. Egewound coils can fit more turns of wire on a voice coil since the wire is flattened and wound on its edge.
Standard coils are just circular wire with no special properties.
Multi-layer are generally used in subwoofers where two channels are to come out of one speaker. The disadvantage of this and the resulting unsuitablility for small speakers is the increased inductance which reduces higher frequency output. Loudspeaker voice coils when driven at high power levels experience considerable heating which results in elevated voice coil resistance and subsequent damping loss. This is often called power compression. Most voice coils use copper wire, however, aluminum wire was used in some ribbon or edgewound coils to save even more weight.