Abstract: Disclosed herein is a linear actuator for controlling the movement of a payload along a linear trajectory. Such actuator is particularly useful, for example, in controlling the radial position of a write/read head in an optical or magnetic recorder/player. The actuator comprises a simple elongated ferromagnetic member, preferably having a substantially triangular cross-section. Such member is surrounded by a coil to which a payload-bearing carriage is rigidly connected. Bearing devices are provided for slidably mounting the carriage for movement on and along the ferromagnetic member. A plurality of magnets serve to establish a magnetic field through which the coil, upon applicaiton of a current, is advanced along the ferromagnetic member. The ferromagnetic member serves the dual function of conducting magnetic flux and guiding the payload along the linear trajectory.

Abstract: A body of foam substance forming a head-rest, for example a head restraint for an automobile seat, an aircraft seat, or the like, provides a housing and support for the loudspeaker; the forward or head-supporting surface has at least one recess, open to the front, formed therein in which the loudspeaker is located and supported. The portion of the foam material in the recess behind the loudspeaker has open pores whereas the outer or remaining surfaces of the body are essentially airtight, for example by having their pores closed or by being covered with an essentially airtight upholstering material, perforated only in the region through which the sound from the loudspeaker is to be transmitted. This arrangement permits flexible or soft membrane suspension of the loudspeaker and thus better transducing fidelity.