Patent ID: 8542865

Claim:
A transducer motor structure for generating acoustic vibrations in response to an electrical audio signal, comprising: a voice coil former having an open interior lumen with an inside surface adapted to carry a single conductive voice coil having first and second electrical connections; said voice coil former being configured to be driven in a linear excursion and drive a diaphragm; wherein said single voice coil is carried entirely within said former's interior lumen and has a selected axial length or height; a magnetic circuit comprising a permanent magnet configured to generate a permanent magnetic field, a pole piece having a central axis, a magnetic field return path, and a magnetic gap defining plate, wherein said pole piece, said return path and said magnetic gap defining plate are all configured to constrain lines of magnetic flux from said permanent magnetic field across a magnetic gap; wherein said magnetic gap is annular and dimensioned to receive said voice coil former in coaxial alignment, such that said voice coil having said first and second electrical connections is immersed in the magnetic field in said magnetic gap; wherein said pole piece projects into said former's lumen and is coaxially aligned with said voice coil former, such that said voice coil is constrained to move axially over said pole piece in response to an audio signal; wherein said pole piece has an axial length projecting into said former's lumen that is greater than said voice coil's selected length; and wherein said magnetic gap defining plate is configured to define a magnetic gap having a selected thickness, said thickness being less than said voice coil's selected length.