Teleconference microphone arrays

• US 4,311,874 A
• Filed: 12/17/1979
• Issued: 01/19/1982
• Est. Priority Date: 12/17/1979
• Status: Expired due to Term

• Current Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Original Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Inventors: Wallace, Robert L. Jr.
• Primary Examiner(s): Konick, Bernard
• Assistant Examiner(s): POPEK, JOSEPH A
• Application Number:
  US06/104,375
• Time in Patent Office: 764 Days
• Field of Search: 179/1 CN, 179/1 DM, 179/121 D, 179/1 HF, 179/1 VC, 179/1 P, 179/18 BC, 179/1 AT, 343/742, 181/125
• US Class Current: 381/87
• CPC Class Codes: B06B 1/085 using multiple elements, e.g. arrays
• CPC Class Codes: H04R 1/406 microphones

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.

Claims

1. A microphone array comprising a plurality of microphone elements arranged in a colinear array

CHARACTERIZED IN THAT

the spacings between adjacent pairs of said elements is nonuniform, and

the distance between any of said elements and the center of said array is given by the application of the recursive formulae:

space="preserve" listing-type="equation">D'"'"'.sub.i =D.sub.i -Δ

D.sub.i

space="preserve" listing-type="equation">Δ

D.sub.i =-2KR/(2π

SinJ)Sin(2π

D.sub.i SinJ),

where,

R=response of said array,

K=Δ

R/R, desired fractional change in response,

Δ

R=desired change in response,

J=angle between arriving incident sound and the normal to said array,

D_i =initial distance of the i^ith element from the center of said array, and

D'"'"'_i =final distance of the i^ith element from the center of said array.

2. The microphone array according to claim 1 further

CHARACTERIZED IN THAT

the elements of said array are displaced symmetrically around the center line of said array.

3. The microphone array according to claim 2

CHARACTERIZED BY

a support structure, and

means for mounting said microphone elements in said structure to support said microphones.

4. The microphone array according to claim 3

CHARACTERIZED IN THAT

said structure is self-supporting.

5. The microphone array according to claim 3 further

CHARACTERIZED IN THAT

said structure is mounted on a wall.

6. The microphone array according to claim 3 further

CHARACTERIZED BY

means for suspending said structure from a ceiling so that the array is parallel to said ceiling.

7. The microphone array according to claim 1 further

CHARACTERIZED IN THAT

said elements comprise omnidirectional electret microphones.

8. An array comprising a plurality of acoustic transducers arranged colinearly

CHARACTERIZED IN THAT

the spacings between said acoustic transducers and the center of said array are monuniform, such that said array produces a response pattern with one main lobe of a given amplitude and a plurality of sidelobes having a preselected envelope with lesser amplitudes.

9. The array according to claim 8 further

CHARACTERIZED IN THAT

said colinear arrangement comprises a plurality of pairs of acoustic transducers placed symmetrically about said center of said arrangement.

10. The array according to claim 8 further

CHARACTERIZED IN THAT

said spacings of said acoustic transducers from said center of said array are determined by the following formulae:

space="preserve" listing-type="equation">R=(2/Σ

Ai)Σ

A.sub.i Cos(2π

D.sub.1 SinJ),

space="preserve" listing-type="equation">Δ

R=P/Σ

A.sub.i (2π

SinJ).sup.2,

space="preserve" listing-type="equation">P=KRΣ

A.sub.i /(2π

SinJ).sup.2,

and

space="preserve" listing-type="equation">Δ

D.sub.i =-2KR/2π

SinJ)Sin(2π

D.sub.i SinJ),

where,

space="preserve" listing-type="equation">D.sub.i '"'"'=D.sub.i -Δ

D.sub.i

R=response of said array,

A_i =sensitivity of the i^th transducer of said plurality of transducers,

D_i =distance of the i^th pair of said transducers from the center of said array,

J=angle between arriving incident sound and the normal to said array,

Δ

R=desired change in response,

P=constant of proportionality,

K=Δ

R/R, desired fractional change in response,

D_i '"'"'=final distance of the i^th pair from the center of said array.

11. A colinear arrangement of 28 microphones of substantially equal sensitivities

CHARACTERIZED IN THAT

pairs of said microphones are located symmetrically about a center line of the arrangement, and the distances, in wavelengths, from the center line to members of each pair is given by:

D₁ =±

0.0677, D₂ =±

0.2260, D₃ =±

0.4308, D₄ =±

0.6426, D₅ =±

0.8231, D₆ =±

0.9767, D₇ =±

1.1443, D₈ =±

1.3881, D₉ =±

1.6663, D₁₀ =±

1.8687, D₁₁ =±

2.0697, D₁₂ =±

2.5321, D₁₃ =±

2.8251, and D₁₄ =±

3.5000.

12. A colinear arrangement of 56 microphones of substantially equal sensitivities

CHARACTERIZED IN THAT

pairs of said microphones being located symmetrically about a center line of the arrangement, and

the distances, in wavelengths, from the center line of each number of said pairs being given by:

D₁ =±

0.0823, D₂ =±

0.2459, D₃ =±

0.4076, D₄ =±

0.5684, D₅ =±

0.7312, D₆ =±

0.8982, D₇ =±

1.0685, D₈ =±

1.2391, D₉ =±

1.4087, D₁₀ =±

1.5798, D₁₁ =±

1.7565, D₁₂ =±

1.9405, D₁₃ =±

1.289, D₁₄ =±

2.3185, D₁₅ =±

2.5108, D₁₆ =±

2.7117, D₁₇ =±

2.9257, D₁₈ =±

3.1493, D₁₉ =±

3.3772, D₂₀ =±

3.6155, D₂₁ =±

3.8786, D₂₂ =±

4.1651, D₂₃ =±

4.4633, D₂₄ =±

4.8000, D₂₅ =±

5.2023, D₂₆ =±

5.6453, D₂₇ =±

6.2611, and D₂₈ =±

7.0000.

13. A colinear arrangement of 100 microphones of substantially equal sensitivities

CHARACTERIZED IN THAT

pairs of said microphones being located symmetrically about a center line of the arrangement, and

the distances, in wavelengths, from the center line of each member of said pairs being given by:

D₁ =±

0.0786, D₂ =±

0.2360, D₃ =±

0.3936, D₄ =±

0.5516, D₅ =±

0.7100, D₆ =±

0.8689, D₇ =±

1.0283, D₈ =±

1.1882, D₉ =±

1.3488, D₁₀ =±

1.5100, D₁₁ =±

1.6719, D₁₂ =±

1.8348, D₁₃ =±

1.9985, D₁₄ =±

2.1634, D₁₅ =±

2.3296, D₁₆ =±

2.4973, D₁₇ =±

2.6668, D₁₈ =±

2.8381, D₁₉ =±

3.0114, D₂₀ =±

3.1866, D₂₁ =±

3.3636, D₂₂ =±

3.5426, D₂₃ =±

3.7239, D₂₄ =±

3.9079, D₂₅ =±

4.0950, D₂₆ =±

4.2857, D₂₇ =±

4.4801, D₂₈ =±

4.6788, D₂₉ =±

4.8816, D₃₀ =±

5.0889, D₃₁ =±

5.3006, D₃₂ =±

5.5172, D₃₃ =±

5.7395, D₃₄ =±

5.9688, D₃₅ =±

6.2064, D₃₆ =±

6.4536, D₃₇ =±

6.7109, D₃₈ =±

6.9783, D₃₉ =±

7.2564, D₄₀ =±

7.5470, D₄₁ =±

7.8540, D₄₂ =±

8.1831, D₄₃ =±

8.5398, D₄₄ =±

8.9274, D₄₅ =±

9.3474, D₄₆ =±

9.8084, D₄₇ =±

10.3423, D₄₈ =±

11.0091, D₄₉ =±

11.8083, and D.sub. 50 =±

12.5000.

14. In a telephone station system, an array of acoustic transducers to be utilized as a transmitter

CHARACTERIZED BY

said acoustic transducers being arranged in pairs symmetrically about a central point of the array, and

the distances, in wavelengths, from the center to each member of said pairs being given by

D₁ =±

0.0677, D₂ =±

0.2260, D₃ =±

0.4308, D₄ =±

0.6426, D₅ =±

0.8231, D₆ =±

0.9767, D₇ =±

1.1443, D₈ =±

1.8881, D₉ =±

1.6663, D₁₀ =±

1.8687, D₁₁ =±

2.0697, D₁₂ =±

2.5321, D₁₃ =±

2.8251, and D₁₄ =±

3.5000.

15. An acoustic array of variably spaced microphone elements

CHARACTERIZED IN THAT

each of said microphones is spaced from the center of said array by a distance D_i where D_i is determined by the recursive formula:

space="preserve" listing-type="equation">D.sub.i =D.sub.i '"'"'-2KRSin(2π

D.sub.i '"'"'SinJ)

in which

D_i '"'"'=spacing derived from the previous iteration.

J=angle of response, varied over 360 degrees for each iteration.

R=array response at angle J.

K=% change in response R due to last change in spacing.

16. A conference microphone array having disc-shaped response pattern

CHARACTERIZED BY

a plurality of microphone elements disposed colinearly at nonuniform distances from the center line of said array, and

said distances being determined by successively adjusting arbitrary initial distances so as to provide sidelobes in said response pattern having at least two regions of substantially different amplitudes.

17. A conference microphone array having disc-shaped response pattern

CHARACTERIZED BY

a plurality of microphone elements disposed colinearly at nonuniform distances from the center line of said array, and

said distances being determined by successively perturbating initial distances using far field response criteria to reduce sidelobe amplitudes below a preselected maximum arbitrarily shaped envelope.

18. A colinear arrangement of 28 microphones of substantially equal sensitivities

CHARACTERIZED IN THAT

pairs of said microphones are located symmetrically about a center line of the arrangement, and the distances, in wavelengths, from the center line to members of each pair is given by:

D₁ =±

0.0850, D₂ =±

0.2514, D₃ =±

0.4097, D₄ =±

0.5689, D₅ =±

0.7476, D₆ =±

0.9491, D₇ =±

1.1513, D₈ =±

1.3413, D₉ =±

1.5385, D₁₀ =±

1.8412, D₁₁ =±

2.0280, D₁₂ =±

2.3379, D₁₃ =±

2.7751, D₁₄ =±

3.5000.

19. A colinear arrangement of 28 microphones of substantially equal sensitivities

CHARACTERIZED IN THAT

pairs of said microphones are located symmetrically about a center line of the arrangement, and the distances, in wavelengths, from the center line to members of each pair is given by:

D₁ =±

0.0804, D₂ =±

0.2580, D₃ =±

0.4601, D₄ =±

0.6579, D₅ =±

0.8372, D₆ =±

1.0129, D₇ =±

1.2205, D₈ =±

1.4691, D₉ =±

1.7076, D₁₀ =±

1.9268, D₁₁ =±

2.1986, D₁₂ =±

2.5974, D₁₃ =±

2.9634, D₁₄ =±

3.5000.