Patent ID: 7831059

Claim:
An electro-magnetic transducer comprising: a diaphragm; a generally cylindrical bobbin defining an interior air chamber having a first end coupled to said diaphragm; an electrical winding on said bobbin toward a second end thereof forming a voice coil; a magnet assembly including a permanent magnet defining a center hole therethrough and a ferro-magnetic bottom plate magnetically coupled to a bottom of said permanent magnet with said bottom plate having a generally annular ferro-magnetic pole piece having a hollow center extending axially through said center hole of said permanent magnet arranged substantially coaxially with said bobbin around a distal end of said pole piece with said permanent magnet cooperable with a proximate end of said pole piece to drive said diaphragm via said bobbin in response to an electrical signal applied to said voice coil; and a cooling cap coupled to, and substantially closing said distal end of said hollow center of said pole piece with said cooling cap having at least one short narrow opening therethrough in communication with said hollow center of said pole piece and said interior air chamber of said bobbin with said at least one opening positioned to create, as air is drawn into said chamber, a vortex of air within said chamber as said bobbin is driven upward by said electrical signal applied to said voice coil.