Patent ID: 7142685

Claim:
A loudspeaker motor structure comprising: a magnetic pole piece comprising a first end elongated along an axis and a second end; a magnetic structure comprising: a magnet comprising a first magnetic pole and a second magnetic pole, the second magnetic pole being magnetically coupled to the second end of the pole piece, and portions defining an opening along the axis, the first end of the pole piece being positioned in the opening of the magnetic structure to form a gap between the first end of the pole piece and the portions defining the opening of the magnetic structure proximate to the first end of the pole piece, the portions defining the opening that are proximate the first end of the pole piece being magnetically coupled to the first magnetic pole, resulting in a magnetic field in the gap; and a voice coil sliding on the first end of the pole piece along the axis in the gap; wherein: the pole piece and the portions defining the opening of the magnetic structure proximate to the first end of the pole piece are capable of being rotated relative each other around the axis under predetermined conditions; and the magnetic field in the gap varies with rotation of the pole piece and the portions defining the opening of the magnetic structure proximate to the first end of the pole piece relative each other around the axis.