Flat diaphragm for sound transducers and method for manufacturing it

Claim 2

A substantially flat diaphragm to be used in sound transducers, made of a cellular, strong, stiff platelike member, having a flat front face, a rear face and side faces connecting said front and rear faces, a layer including said front face, additional layers between said layer including said front face and said rear face, said front face defining a front face plane, said layer including said front face being pretensioned in a direction substantially perpendicular to said front face plane and in a direction within said front face plane and said additional layers of said platelike member between said front face and said rear face are gradually under minor stresses from said front face towards said rear face.

Claim 3

The diaphragm as claimed in claim 1, further comprising a marginal vibration damper portion, a figure portion, a central stiffer portion, and wherein said platelike member defines said marginal vibration damper portion which substantially circumscribes said figure portion on said rear face, said figure portion including said central stiffer portion at a zone out of the geometric center of said figure portion, and said central stiffer portion defining a center for capturing vibrations.

Claim 4

The diaphragm as claimed in claim 2, wherein said platelike member is made of granular expanded-bonded cellular, strong, stiff, plastics.

Claim 5

The diaphragm as claimed in claim 1, wherein said front face is sheathed with a tensioned thin sheet member having marginal portions anchored on said side faces.

Claim 6

The diaphragm as claimed in claim 4, wherein said side faces are irregular to increase the anchoring surface for said marginal portion of said sheetlike member.

Claim 7

The diaphragm as claimed in claim 4, wherein said sheetlike member is adhesively adhered to said front face and said side faces.

Claim 8

The diaphragm as claimed in claim 4, wherein said sheetlike member is paper.

Claim 9

The diaphragm as claimed in claim 4, wherein said sheetlike member is a fabric. 9. The diaphragm as claimed in claim 2, wherein said figure portion is ear shaped.

Claim 10

The diaphragm as claimed in claim 2, wherein said central stiffer portion is of larger width than the remaining portions of said figure portion.

Claim 11

The diaphragm as claimed in claim 10, further comprising a cylindrical projection and wherein said central stiffer portion is integral with said cylindrical projection, said cylindrical projection is adapted for supporting a voice coil.

Claim 12

The diaphragm as claimed in claim 2, wherein said platelike member has a blind bore, a thin short metal insert inserted in said platelike member and accessible from said rear face through said blind bore present in said platelike member, and said metal insert passing through said marginal vibration damper portion and being partially housed in said figure portion.

Claim 13

The diaphragm as claimed in claim 3, wherein said plastics platelike member has predetermined zones formed by preexpanded granules of different sizes.

Claim 14

A loudspeaker comprising a substantially flat diaphragm made of a granular expanded-bonded cellular, strong, stiff plastics platelike, imperforate member, having a flat front face, a rear face and side faces connecting said front and rear faces, said platelike member defining a marginal vibration damper portion, a figure portion on said rear face, said marginal vibration damper portion substantially circumscribing said figure portion, a layer including said front face and defining a front face plane, said layer being pretensioned in a direction substantially perpendicular to said front face plane and in a direction within said front face plane, additional layers between said layer including said front face and said rear face, said additional layers of said platelike member between said front face and said rear face are gradually under minor stresses from said front face towards said rear face, a central stiffer portion, said figure portion including said central stiffer portion at a zone out of the geometric center of said figure portion, a frame having a rear portion, at least a part of said side faces being rigidly framed in said frame, said frame projecting with its rear portion beyond said rear face of said diaphragm, a nonmagnetic crossbar mounted in said frame and spaced away from said rear face of said diaphragm, a magnetic assembly including a voice coil supported by said nonmagnetic crossbar and in vibration-transmitting relationship with said central stiffer portion, a tensioned thin sheet member having marginal portions, said front face of said diaphragm being sheathed with said sheet member, said marginal portions being anchored on said side faces of said diaphragm.

Claim 15

A loudspeaker comprising a substantially flat diaphragm made of a granular expanded-bonded cellular, strong, stiff plastics platelike, imperforate member, having a flat front face, a rear face and side faces connecting said front and rear faces, said platelike member defining a marginal vibration damper portion, a figure portion on said rear face, said marginal vibration damper portion substantially circumscribing said figure portion, a layer including said front face and defining a front face plane, said layer being pretensioned in a direction substantially perpendicular to said front face plane and in a direction within said front face plane, additional layers between said layer including said front face and said rear face, said additional layers of said platelike member between said front face and said rear face are gradually under minor stresses from said front face towards said rear face, a central stiffer portion, said figure portion including said central stiffer portion at a zone out of the geometric center of said figure portion, a frame having a rear portion, at least a part of said side faces being rigidly framed in said frame, said frame projecting with its rear portion beyond said rear face of said diaphragm, a nonmagnetic crossbar mounted in said frame and spaced away from said rear face of said diaphragm, a magnetic assembly including a voice coil supported by said nonmagnetic crossbar and in vibration-transmitting relationship with said central stiffer portion, a tensioned thin sheet member having marginal portions, said front face of said diaphragm being sheathed with said sheet member, said marginal portions being anchored on said side faces of said diaphragm.

Claim 16

The loudspeaker as claimed in claim 14, further comprising a cover lid including frustoconical damping projections, said rear portion of said frame being closed by said cover lid, said frustoconical damping projections being directed towards the rear face of said diaphragm, said frame having a bore connecting the inside between said diaphragm and said cover lid with the outside.

Claim 17

The loudspeaker as claimed in claim 14, wherein a damper plate is mounted on said marginal vibration damper portion of said diaphragm.

Claim 20

The method as claimed in claim 17, comprising the additional step of subjecting said platelike member to heat in order to remove moisture from said platelike member and sealing by spray said faces of said platelike member from the outside prior to adhering said sheetlike member.

Claim 21

The method as claimed in claim 17, wherein said platelike member is bent prior to adhering said sheetlike member thereto.

Claim 22

The method as claimed in claim 17, wherein said sheetlike member is of the shrinkable type and is adhered by adhesive to said flat front face to produce the bending of said platelike member by shrinkage of said sheetlike member.