Electro-acoustic transducer causing sound waves to be in phase at any point by preventing reflection from the back end of the diaphragm to stress applying means

• US 4,395,598 A
• Filed: 07/16/1980
• Issued: 07/26/1983
• Est. Priority Date: 11/16/1978
• Status: Expired due to Term

• Current Assignee: Societe Audax
• Original Assignee: Societe Audax
• Inventors: Lesage, Philippe M.
• Primary Examiner(s): SCHREYER, STAFFORD
• Application Number:
  US06/212,089
• Time in Patent Office: 1,105 Days
• Field of Search: 179/115.5 R, 179/115, 179/181, 181/159, 181/163, 181/166, 181/172
• US Class Current: 381/423
• CPC Class Codes: H04R 7/12 Non-planar diaphragms or cones
• CPC Class Codes: H04R 9/06 Loudspeakers

Abstract

The electro-acoustical transducer comprises a membrane flexible or rigid before assembling, the front portion of which has an aperture with a half-angle α. In order to obtain sound waves in phase at any listening point, the front portion is the site of vibrations which are responsible for sound emission and are transmitted in the membrane material with a velocity V_m approximating V₀ /cos α, where V₀ is the velocity of sound in air. The membrane is rigidly attached to the transducer chassis and is tensioned under a tensile stress between 5 and 20 KN, in order to the vibrations be bending transverse waves, the vibrational energy of which is totally transferred to air in form of sound waves before reaching the larger end of the membrane. The mechanical-acoustical output is close to unity and the overall energy output lies between 50 and 80%. The displacement of the rear portion of the membrane into airgap of motor is in the macro-deformation field. The membrane may be cone or dihedron-shaped.

Claims

1. An electro-acoustical transducer comprising:

a motor for imparting vibrations to a shaped membrane;

a shaped membrane in the form of a dihedron constituting the site of vibrations responsible for sound transmission, said dihedron having a predetermined half angle α

to transmit said vibrations from said membrane at a velocity V_m being approximately equal to V₀ /cos α

where V₀ is a velocity of sound in air;

said membrane having two side edges, a front end and a rear end, the front end constituting the two front surfaces of the dihedron, the rear end constituting the rear surfaces of the dihedron, and the side edges adapted for secure attachment to the chassis at the rear of the membrane;

a chassis having front and rear portions constituting the supporting structure for said motor and said membrane;

an air gap defined between the intersecting planar surface of the dihedron which constitutes the rear end of said membrane and the moving portion of said motor, and the stationary portion of said motor which is spaced from said membrane which is fixed by said chassis with the membrane centered in said air gap;

said chassis centering said air gap which is located at the center of said membrane along a plane of symmetry passing through the vertex of the dihedron along the fold of the dihedron and adjacent said motor whereby the plane of symmetry bisects the angle of the dihedron to provide the predetermined angle α and

permits the placement of a stress tensioning means to apply stress to the front of the membrane from a position behind the membrane and attached to the rear portion of said chassis;

securing means on the front portion of said chassis between the front end of said membrane and the rear portion of said chassis for securing the membrane to the chassis;

said securing means including a stress-tensioning means connected between the front part of said membrane and the rear portion of said chassis to apply a tensile stress to the front of said membrane whereby after said membrane is inserted into said chassis with the bolt of the dihedron in proper relation to said air gap and motor, said stress tensioning means lies along the plane of symmetry extending through the vertex of the dihedron through to the back portion of said chassis and the tensile stress provides membrane vibrations in the form of bending transverse waves having the velocity V_m, said tensile stress applying means also preventing reflection of sound waves from the back end of the membrane.

2. An electro-acoustical transducer as claimed in claim 1 wherein said tensile stress applying means is in the form of a corrugated sheet which lies in the plane of symmetry of the dihedron.

3. An electro-acoustical transducer as claimed in claim 2 wherein said motor comprises poles which constitute a planar boundary surface of the motor adjacent said air gap and wherein a front edge of said tension applying means is inserted adjacent the pole of said motor and the air gap to secure said membrane under tension at the front edge to form bending transverse waves of velocity V_m.

4. An electro-acoustical transducer as claimed in claim 3 wherein said dihedron has two identical rectangular or square plane surfaces.

5. An electro-acoustical transducer as claimed in claim 3 wherein said tensile stress applying means is introduced behind the rear end of said membrane whichis in the air gap and adjacent the pole, by forcible insertion of said rear end into said air gap while assuring that the membrane is centered in relation to the air gap and that the tensile stress applying means lies along the plane of symmetry of the dihedron.

6. An electro-acoustical transducer as claimed in claim 5 wherein the tensile stress applying means tensions said membrane to a value of 5 to 20 k N.