Abstract: An electret transducer for producing a directional response, electret foil (92) and a backplate (94) with the actual air gap thickness therebetween varying in accordance with a predetermined relationship. The sensitivity of the electret transducer varies inversely as the actual air gap thickness. In one embodiment the actual air gap thickness is realized by a plurality of posts (90) having heights varying according to the aforesaid relationship. In another embodiment, the actual air gap thickness is realized by varying the thickness of the aforesaid backplate.

Abstract: An electret transducer for producting a highly directional response characteristic comprises a backplate (18) and, superimposed thereon, an electrostatically charged electret foil (10). The electrostatic charge varies according to a predetermined relationship. The sensitivity of the electret transducer, at any point thereon, is directly proportional to the electrostatic charge on the electret foil at that point.

Abstract: A directional electret transducer comprises an electret foil and a metalized backplate the effective air gap thickness therebetween varying according to a predetermined relationship. The sensitivity of the electret transducer is directly proportional to the effective air gap thickness. The effective air gap thickness is realized in three ways: first, a plurality of equal diameter holes are drilled to varying depths in the aforesaid backplate; second, a plurality of holes of varying diameters are drilled through the aforesaid backplate; third, a plurality of equal diameter holes are drilled through the aforesaid backplate, the density of the holes varying. In each of the aforesaid three ways, the variation is according to the predetermined relationship.

Abstract: An electret transducer comprises an electrostatically charged electret foil (10) superimposed directly over a selectively metalized rough surface (16) of a backplate (18). Selective metalization is realized by depositing a thin metal layer (20), the contour of which is defined by a predetermined relationship, over the rough surface (16). The sensitivity of the electret transducer at any point thereon is directly proportional to the width of the metal layer on the backplate. The response characteristic of the electret transducer comprises a main lobe and a plurality of sidelobes below a preselected threshold.

Abstract: An acoustic transducer for producing highly directional characteristics comprises a metalized backplate (130) facing the flat surface (134) of an electrostatically charged electret foil (132). The thickness of the electret foil varies along the length thereof according to a predetermined relationship. The sensitivity of the electret transducer varies directly with the thickness of the electret foil.

Abstract: Highly directional response patterns can be obtained by connecting microphones or loudspeakers with tubular coupling path structures. The coupling paths comprise a plurality of elements (110,111 . . . 157) arranged in pairs (110,111; 112,113; . . . 156,157) so that for every element (110) below a center line (102) there is an element (111) above the line. Furthermore, the relationship between the element pairs is nonlinear. The desired directional response comprises one main lobe and a plurality of substantially smaller lobes below a determinable threshold value. The elements may be a bundle of tubes (90) or a plurality of apertures (110,111, . . . 157) in a single tube (100).

Abstract: A directional array of acoustic transducers is disclosed. The acoustic transducers are arranged colinearly and in pairs symmetrically about a center line of the directional array. The distances of the acoustic transducers on either side of the center line of the array are neither linear nor monotonic. These distances are calculated using a recursive far field response formula which effectively reduces sidelobe magnitudes to a desired design amplitude envelope. The response produced is highly directional, comprising one main lobe and a plurality of sidelobes each less than the desired design envelope, which is substantially lower than the main lobe but of arbitrary (e.g., stepped) shape.