The spider is usually made of a corrugated fabric disk, generally with a coating of a material intended to improve mechanical properties. Unusually, a German manufacturer, Klangfilm, used bakelite for spiders in some of its early drivers, and another German company currently offers a spider made of wood. The surround can be a roll of rubber or foam, or a ring of corrugated fabric (often coated), attached to the outer circumference of the cone and to the frame. The choice of suspension materials affects driver lifetime, especially in the case of foam surrounds which are susceptible to aging and environmental damage.
Very few manufacturers use electrically powered field coils as was common in the earliest designs. The size and type of magnet and details of the magnetic circuit differ, depending on design goals. For instance, the shape of the pole piece affects the magnetic interaction between the voice coil and the magnetic field, and is sometimes used to modify a driver's behavior. As well, a 'shorting ring' or cap is sometimes used near the magnetic gap to reduce adverse distortion effects of high current in the voice coil.
