The original midrange and tweeter cones were paper. In 1961 the B-209 midrange cone was changed to a radical new design. The material was very thin spun aluminum which took much of its strength from its curvilinear profile along the radius. The cone received a thin coating of latex in order to damp the surface reflections that otherwise would occur on a metal surface which is vibrated rapidly. The design was patented and was largely responsible for the superb transient response of the Bozak B-209B and B-209C midrange.