UNIDIRECTIONAL MICROPHONES

• US 3,715,500 A
• Filed: 07/21/1971
• Issued: 02/06/1973
• Est. Priority Date: 07/21/1971
• Status: Expired due to Term

• Current Assignee: Gerhard Martin Sessler, James Edward West
• Original Assignee: Gerhard Martin Sessler, James Edward West
• Inventors: Sessler, Gerhard Martin, West, James Edward
• Primary Examiner(s): Blakeslee, Ralph D.
• Assistant Examiner(s): Leaheey, Jon Bradford
• Application Number:
  US05/164,507
• Time in Patent Office: 566 Days
• Field of Search: 179/121D,1DM,121R,111E
• US Class Current: 381/191
• CPC Class Codes: H04R 1/38 in which sound waves act upon both sides of a diaphragm and incorporating acoustic phase-shifting means, e.g. pressure-gradient microphone

Abstract

A second-order unidirectional microphone is constructed with two pairs of acoustic tubes arranged to sample a sound field at four different points on a straight line. Acoustic signals from two diametrically opposed tubes, one short and one long, are summed in a first cavity and signals from two other opposed tubes, one short and one long, are summed in another cavity. Signals developed in the two cavities are differentially combined by an electret or other transducer interposed between the cavities. Necessary signal delay is provided directly by differences in tube lengths.

Claims

1. A unidirectional microphone, which comprises, first and second selectively dimensioned acoustic chambers, electroacoustic means positioned to separate said chambers for differentially converting acoustic signals in said chambers into electrical signals, first and second acoustic tubes of first and second lengths, respectively, mated into said first chamber and extending outward therefrom to sample a sound field at first and second points on a straight line, and third and fourth acoustic tubes of said first and second lengths, respectively, mated into said second chamber and extending outward therefrom to sample said sound field at third and fourth points on said straight line, the sampling end of said first tube and the sampling end of said fourth tube being spaced apart from one another on said straight line by the same distance as the sampling end of said second tube and the sampling end of said third tube are spaced apart on said straight line, and the sampling ends of said first and said second tubes being spaced farther apart from one another than the sampling ends of said third and said fourth tubes.

2. A unidirectional microphone as defined in claim 1, wherein, said electroacoustic means comprises a foil-electret transducer.

3. A unidirectional microphone as defined in claim 1, wherein, said tubes of said first length are selected to be longer than the tubes of said second length by a length related to the spacing on said straight line between the sampling point of one of said first length tubes feeding said first chamber and one of said second length tubes feeding said second chamber.

4. A unidirectional microphone as defined in claim 3, wherein, the ratio of the difference in length between said tubes of said first and second lengths to the spacing on said straight line between the sampling point of that of said first length tubes feeding said first chamber and one of said second length second tubes feeding said second chamber is unity.

5. A directional electrostatic transducer, which comprises, first and second selectively dimensioned cylindrical acoustic cavities, transducer means separating said cavities for differentially converting acoustic signals supplied to said cavities into electrical signals, two acoustic tubes of first and second lengths opening, respectively, into said first and second cavities and extending outward therefrom to sample a sound field at first points separated from one another by a selected distance on a straight line parallel to a diameter of said cavity, and two acoustic tubes of said first and second lengths opening, respectively, into said second and first cavities and extending outward therefrom to sample said sound field at second points separated from one another by said selected distance and diametrically opposed to said first points on said line, the sampling ends of said tubes opening into said first cavity being spaced farther from one another than the sampling ends of said tubes opening into said second cavity.

6. A directional transducer as defined in claim 5, wherein, said electrostatic transducer means comprises, a foil-electret transducer supported between said cavities in a plane perpendicular to an axis thereof.

7. A unidirectional second-order gradient microphone, which comprises, first and second selectively dimensioned acoustic cavities, transducer means intermediate said chambers for differentially converting acoustic signals in said cavities into electrical signals, two acoustic tubes of first and second lengths opening, respectively, into said first and second cavities and extending outward therefrom in a first direction to samplE a sound field at points on a straight line separated from one another by a selected distance, and two acoustic tubes of said first and second lengths opening, respectively, into said second and first cavities and extending outward therefrom in a second direction opposite to said first direction to sample said sound field at points on said straight line separated from one another by said selected distance.

8. A second-order gradient microphone, as defined in claim 7, wherein, all of said tubes are equipped with means for damping acoustic resonances.

9. A second-order gradient microphone, as defined in claim 7, wherein, said cavities are proportioned to be resonant at the lower end of the frequency range to be accommodated by said microphone.