Constant-beamwidth loudspeaker array

• US 20040240697A1
• Filed: 11/04/2003
• Published: 12/02/2004
• Est. Priority Date: 05/27/2003
• Status: Active Grant

• Current Assignee: Harman International Industries Incorporated (Samsung Electronics Co. Ltd.)
• Original Assignee: Harman International Industries Incorporated (Samsung Electronics Co. Ltd.)
• Inventors: Keele, D. Broadus Jr.
• Granted Patent: US 7,826,622 B2
• Time in Patent Office: Days
• US Class Current: 381/336
• CPC Class Codes: H04R 1/403 loud-speakers
• CPC Class Codes: H04R 2430/20 Processing of the output signals of the acoustic transducers of an array for obtaining a desired directivity characteristic H04R2203/12 takes precedence
• CPC Class Codes: H04R 3/12 for distributing signals to two or more loudspeakers specially adapted for hearing aids H04R25/407

Abstract

A loudspeaker is provided for receiving an incoming electrical signal and transmitting an acoustical signal that is directional and has a substantially constant beamwidth over a wide frequency range. The loudspeaker may include a curved mounting plate that has curvature over a range of angles. The loudspeaker may include an array of speaker drivers coupled to the mounting plate. Each speaker driver may be driven by an electrical signal having a respective amplitude that is a function of the speaker driver'"'"'s respective location on the mounting plate. The function may be a Legendre function. Alternatively, the loudspeaker may include a flat mounting plate. In this case, the respective electrical signal driving each speaker may have a phase delay that virtually positions the speaker onto a curved surface.

Claims

1. A loudspeaker system for receiving an incoming electrical signal and generating a sound field, the sound field being directional and having a substantially constant beamwidth across an operational frequency range, the loudspeaker system comprising:

a mounting plate having a curved outer surface, where the outer surface has curvature over a range of angles from −

A to +A in a plane perpendicular to the outer surface; and

an array of speaker drivers coupled to the mounting plate along a linear arc in the plane perpendicular to the outer surface, each speaker driver of the array being coupled at a respective angle A_x that is greater than angle −

A and less than angle +A;

where each speaker driver of the array responds to a driving electrical signal that is derived from the incoming electrical signal so that each speaker driver of the array generates a respective acoustic output having a respective sound pressure level that is a function of the respective angle A_x.

2. The loudspeaker system of claim 1, where the function comprises a Legendre function of the angle A_x for each speaker driver of the array.

3. The loudspeaker system of claim 1, where the function comprises a Legendre function of a cosine of the angle Ax for each speaker driver of the array.

4. The loudspeaker system of claim 1, where the function comprises a multi-term series approximation of a Legendre function of the angle A_x for each speaker driver of the array.

5. The loudspeaker system of claim 1, where the function comprises a multi-term series approximation of a Legendre function of a cosine of the angle Ax for each speaker driver of the array.

6. The loudspeaker system of claim 1, where a normalized angle X for each speaker driver of the array is equal to the absolute value of (A_x/A), and the function is equal to about:

1+0.066 X−

1.8 X²+0.743 X³.

7. The loudspeaker system of claim 1, where the outer surface of the mounting plate has a substantially circular cross-section in the plane perpendicular to the outer surface.

8. The loudspeaker system of claim 1, where the outer surface of the mounting plate has a substantially toroidal cross-section in the plane perpendicular to the outer surface.

9. The loudspeaker system of claim 1, wherein the array of speaker drivers comprises a first array of speaker drivers, and the loudspeaker system further comprises a second array of speaker drivers coupled to the mounting plate over a second range of angles from −

B to +B in a second plane perpendicular to the outer surface, each speaker driver of the second array being coupled at a respective angle B_x that is greater than angle −

B and less than angle +B and responding to a driving electrical signal that is derived from the incoming electrical signal so that each speaker driver of the second array generates a respective acoustic output having a respective sound pressure level that is a function of the respective angle B_x.

10. The loudspeaker system of claim 9, where the second plane is parallel to the plane containing the first array of speaker drivers.

11. The loudspeaker system of claim 9, where the second plane is perpendicular to the plane containing the first array of speaker drivers.

12. The loudspeaker system of claim 1, where each speaker driver of the array includes a movable surface having an area, and the areas of the movable surfaces of the speaker drivers of the array are substantially equal in size.

13. The loudspeaker system of claim 1, where the driving electrical signal includes a plurality of driving electrical signals and the incoming electrical signal is a speaker-level signal that is selectively attenuated to produce the plurality of driving electrical signals.

14. The loudspeaker system of claim 1, where the incoming electrical signal is a speaker-level signal, the driving electrical signal is about equal to the incoming electrical signal, and each of the speaker drivers of the array has an impedance that is a function of the speaker driver'"'"'s respective angle A_x.

15. The loudspeaker system of claim 1, further including a plurality of sound amplifiers, each sound amplifier of the plurality associated with one speaker driver of the array, where the driving electrical signal includes a plurality of driving electrical signals and each sound amplifier receives the incoming electrical signal and amplifies the incoming electrical signal as a function of the one associated speaker driver'"'"'s respective angle A_x to provide one of the driving electrical signals of the plurality to the associated one speaker driver.

16. The loudspeaker system of claim 1, further including a plurality of sound amplifiers, each sound amplifier of the plurality associated with one or more speaker drivers of the array, where the driving electrical signal includes a plurality of driving electrical signals and each sound amplifier receives the incoming electrical signal and amplifies the incoming electrical signal as a function of the one or more associated speaker drivers'"'"' respective angles A_x to provide one of the driving electrical signals of the plurality to the associated one or more speaker drivers.

17. The loudspeaker system of claim 1, where the speaker drivers of the array are about equally spaced apart from each other.

18. The loudspeaker system of claim 1, where the array includes at least three speaker drivers.

19. The loudspeaker system of claim 1, where the array includes at least five speaker drivers.

20. A loudspeaker system for receiving an electrical signal and generating a sound field, the sound field being directional and having a substantially constant beamwidth across an operational frequency range, comprising:

a mounting plate having an outer surface that is curved between a first end and a second end; and

an array of speaker drivers coupled to the mounting plate in a linear arc between the first end and the second end;

where the speaker drivers of the array are about equally spaced apart from each other, and each speaker driver of the array responds to a driving electrical signal that is derived from the incoming electrical signal so that each speaker driver of the array generates a respective acoustic output having a respective sound pressure level that is a function of the speaker driver'"'"'s location on the mounting plate.

21. The loudspeaker system of claim 20, where the array of speaker drivers is a two-dimensional array.

22. The loudspeaker system of claim 20, where the function comprises a Legendre function.

23. The loudspeaker system of claim 20, where the function comprises a multi-term series approximation of a Legendre function.

24. The loudspeaker system of claim 20, where the outer surface of the mounting plate has a substantially circular cross-section in a plane perpendicular to the outer surface.

25. The loudspeaker system of claim 20, where the outer surface of the mounting plate has a substantially toroidal cross-section in a plane perpendicular to the outer surface.

26. The loudspeaker system of claim 20, where the driving electrical signal includes a plurality of driving electrical signals and the incoming electrical signal is a speaker-level signal that is attenuated to produce the plurality of driving electrical signals.

27. The loudspeaker system of claim 20, where the incoming electrical signal is a speaker-level signal, the driving electrical signal is about equal to the incoming electrical signal, and each of the speaker drivers of the array has an impedance that is a function of the speaker driver'"'"'s respective location on the mounting plate.

28. The loudspeaker system of claim 20, further including a plurality of sound amplifiers, each sound amplifier of the plurality associated with one speaker driver of the array, where the driving electrical signal includes a plurality of driving electrical signals and each sound amplifier receives the incoming electrical signal and amplifies the incoming electrical signal as a function of the one associated speaker driver'"'"'s respective location on the mounting plate to provide one of the driving electrical signals of the plurality to the associated one speaker driver.

29. The loudspeaker system of claim 20, further including a plurality of sound amplifiers, each sound amplifier of the plurality associated with a plurality of speaker drivers of the array, where the driving electrical signal includes a plurality of driving electrical signals and each sound amplifier receives the incoming electrical signal and amplifies the incoming electrical signal as a function of the respective locations on the mounting plate of the associated plurality of speaker drivers to provide one of the driving electrical signals of the plurality of driving electrical signals to the associated plurality of speaker drivers.

30. A loudspeaker system for receiving an electrical signal and generating a sound field, the sound field being directional and having a substantially constant beamwidth across an operational frequency range, comprising:

a mounting plate having a planar outer surface; and

an array of speaker drivers coupled to the mounting plate in a line, where each speaker driver of the array is coupled to the mounting plate at a respective angle A_x measured from a point on an axis running through the center of the mounting plate and perpendicular to the mounting plate;

where each speaker driver is powered by a respective driving electrical signal that has a respective attenuation level that is a function of the speaker driver'"'"'s respective angle A_x, and a respective phase delay.

31. The loudspeaker system of claim 30, where the respective attenuation level is derived from a Legendre function of the speaker driver'"'"'s respective angle A_x.

32. The loudspeaker system of claim 30, where the respective level is derived from a Legendre function of a cosine of the speaker driver'"'"'s respective angle Ax.

33. The loudspeaker system of claim 30, where the respective attenuation level is derived from a series approximation of a Legendre function of the speaker driver'"'"'s respective angle A_x.

34. The loudspeaker system of claim 30, where the respective attenuation level is derived from a series approximation of a Legendre function of a cosine of the speaker driver'"'"'s respective angle Ax.

35. The loudspeaker system of claim 30, where the respective phase delay is derived from the speaker driver'"'"'s respective angle A_x.

36. The loudspeaker system of claim 30, including a second array of speaker drivers coupled to the mounting plate in a second line.

37. The loudspeaker system of claim 30, wherein the array of speaker drivers includes a first array of speaker drivers coupled to the mounting plate in a first line, and the loudspeaker system further comprises a second array of speaker drivers coupled to the mounting plate in a second line that is parallel to the first line.

38. The loudspeaker system of claim 30, further including a plurality of sound amplifiers, each sound amplifier of the plurality associated with a speaker driver of the array, where the driving electrical signal includes a plurality of driving electrical signals and each sound amplifier receives the incoming electrical signal and amplifies the incoming electrical signal as a function of the associated speaker driver'"'"'s respective angles A_x to provide one of the driving electrical signals of the plurality to the associated speaker driver.

39. The loudspeaker system of claim 30, further including a plurality of signal processors, each signal processor of the plurality associated with a speaker driver of the array, where each signal processor receives the incoming electrical signal and phase delays the incoming electrical signal as a function of the associated speaker driver'"'"'s respective angle A_x.

40. A loudspeaker system for receiving an electrical signal and generating a sound field, the sound field being directional and having a substantially constant beamwidth across an operational frequency range, the loudspeaker system comprising:

a mounting plate having a curved outer surface, where the outer surface has curvature over a range of angles from −

A to +A in a plane perpendicular to the outer surface;

an array of speaker drivers coupled to the mounting plate, where each speaker driver of the array is coupled to the mounting plate along a linear arc in the plane at a respective angle A_x that is greater than angle −

A and less than angle +A;

a plurality of sub-arrays of speaker drivers of the array of speaker drivers, where each sub-array includes a subset of the array of speaker drivers; and

where each speaker driver of each sub-array responds to a driving electrical signal that is derived from the incoming electrical signal so that each speaker driver of each sub-array generates a respective acoustic output having a respective sound pressure level that is a function of the respective angles A_x of the speaker drivers of the sub-array.

41. The loudspeaker system of claim 40, where the function comprises a Legendre function of the respective angles A_x for one or more of the speaker drivers of the sub-array.

42. The loudspeaker system of claim 40, where the function comprises a Legendre function of a cosine of the respective angles A_x for one or more of the speaker drivers of the sub-array.

43. The loudspeaker system of claim 40, where the function comprises a series approximation of a Legendre function of a cosine of one or more of the respective angles A_x for the speaker drivers of the sub-array.

44. The loudspeaker system of claim 40, where the incoming electrical signal is a speaker-level signal, and each of the respective driving electrical signals is passively attenuated.

45. The loudspeaker system of claim 40, further including a plurality of sound amplifiers, where each sound amplifier receives the incoming electrical signal and provides a driving electrical signal for one of the sub-arrays.

46. The loudspeaker system of claim 40, where each of the sub-arrays includes at least two speaker drivers of the array of speaker drivers.

47. The loudspeaker system of claim 40, where the driving electrical signal includes a plurality of driving electrical signals and the incoming electrical signal is a speaker-level signal that is attenuated to produce the plurality of driving electrical signals.

48. The loudspeaker system of claim 40, where the incoming electrical signal is a speaker-level signal, the driving electrical signal is about equal to the incoming electrical signal, and each of the speaker drivers of each sub-array comprises an impedance that is a function of the respective angles A_x of the speaker drivers of the sub-array.

49. The loudspeaker system of claim 40, where the outer surface of the mounting plate has a substantially circular cross-section in the plane.

50. A method of constructing a loudspeaker system for receiving an incoming electrical signal and transmitting an acoustical signal, the acoustical signal being directional and having a substantially constant beamwidth across an operational frequency range, the method comprising:

selecting a coverage angle for a loudspeaker system to exhibit constant-beamwidth operation over;

fabricating a mounting plate having an outer surface and a curvature measured from a point on a line perpendicular to and running though the center of the outer surface, where the curvature has an angle that is about equal to the coverage angle;

mounting an array of speaker drivers in a linear arc to a mounting plate, where each speaker driver of the array is mounted at a respective angle A_x measured from the line, a first speaker driver of the array is mounted at a largest respective angle A_x, and a second speaker driver of the array is mounted at a smallest respective angle A_x and separated from the first speaker driver by a distance D;

determining a respective attenuation level for each speaker driver, where the respective attenuation level for the speaker driver is a function of the respective angle A_x for the speaker driver; and

fabricating a circuit that provides each speaker driver with a respective driving signal, where the respective driving signal is a function of the incoming electrical signal that is attenuated by the respective attenuation level for the speaker driver.

51. The method of claim 50, comprising:

selecting a lower-operational frequency over which the loudspeaker system exhibits constant-beamwidth operation for the coverage angle; and

determining a linear dimension of the mounting plate that is equal to approximately 2.5×

10⁴ meters-degs-Hz divided by the coverage angle in degrees and further divided by the lower-operational frequency;

where fabricating the mounting plate includes fabricating the mounting plate so that the distance D is about equal to the linear dimension.

52. The method of claim 50, comprising:

selecting an upper-operational frequency over which the loudspeaker system exhibits constant-beamwidth operation for the coverage angle; and

determining a center-to-center spacing that is equal to about one wavelength of the upper-operational frequency;

where each speaker driver includes a planar center in a plane tangential to the outer surface, and mounting the array of speaker drivers to the mounting plate includes mounting the array of speaker drivers so that the planer centers of adjacent speaker drivers of the array are spaced apart by the center-to-center spacing.

53. The method of claim 50, where each speaker driver'"'"'s respective attenuation level is derived from a Legendre function of a cosine of the angle Ax for the speaker driver.

54. The method of claim 50, where each speaker driver'"'"'s respective attenuation level is derived from a series approximation of a Legendre function of a cosine of the angle Ax for the respective speaker driver.

55. A loudspeaker system, the loudspeaker system comprising:

an input terminal that receives an incoming electrical signal;

a mounting plate having a curved outer surface, where the outer surface has curvature over a range of angles from −

A to +A in a plane perpendicular to the outer surface;

a circuit coupled to the input terminal that includes an array of speaker drivers, where the array of speaker drivers is coupled to the mounting plate along a linear arc in the plane perpendicular to the outer surface, each speaker driver of the array being coupled at a respective angle A_x that is greater than angle −

A and less than angle +A;

where the circuit is biased so that each speaker driver of the array receives a driving electrical signal based on the incoming electrical signal that causes the respective speaker driver to generate a respective acoustic output having a respective sound pressure level that is a function of the respective angle A_x for the respective speaker driver, and the respective acoustic outputs from the array combine to form a directional sound field having a substantially constant beamwidth across an operational frequency range.

56. The loudspeaker system of claim 55, where the function comprises a Legendre function of the angle A_x for each speaker driver of the array.

57. The loudspeaker system of claim 55, where the function comprises a Legendre function of a cosine of the angle Ax for each speaker driver of the array.

58. The loudspeaker system of claim 55, where the function comprises a multi-term series approximation of a Legendre function of the angle A_x for each speaker driver of the array.

59. The loudspeaker system of claim 55, where the function comprises a multi-term series approximation of a Legendre function of a cosine of the angle A_x for each speaker driver of the array.

60. The loudspeaker system of claim 55, where a normalized angle X for each speaker driver of the array is equal to the absolute value of (A_x/A), and the function is equal to about:

1+0.066 X−

1.8 X²+0. 743 X³.

61. The loudspeaker system of claim 55, where a normalized angle X for each speaker driver of the array is equal to the absolute value of (A_x/A), and the function is equal to about:

1+0.0561 X−

1.3017 X²+0.457 X³.