If two metal plates have molten wax poured between them and a high DC voltage is sent across the two plates, this assembly yields a permanent electric field, in the same way that a magnet produces a permanent magnetic field. It is hypothesized that the polar molecules in the wax align, producing the electric field. An assembly of this type is used to provide a polarization voltage for small condenser microphones so that they do not require phantom power at 48V, but operate instead at a small pre-amplified voltage of 5V-12V. Microphones constructed in this way are called electret microphones.