Microphone array with high directivity

• US 6,526,147 B1
• Filed: 11/12/1998
• Issued: 02/25/2003
• Est. Priority Date: 11/12/1998
• Status: Expired due to Fees

• Current Assignee: GN Netcom A/S (GN Store Nord A/S)
• Original Assignee: GN Netcom A/S (GN Store Nord A/S)
• Inventors: Rung, Martin
• Primary Examiner(s): Nguyen, Duc
• Assistant Examiner(s): LAO, LUNSEE
• Application Number:
  US09/191,208
• Time in Patent Office: 1,566 Days
• Field of Search: 381/92, 381/122, 381/111-117, 381/26, 381/91, 381/356, 381/147, 381/148, 381/151
• US Class Current: 381/92
• CPC Class Codes: H04R 3/005 for combining the signals of two or more microphones specially adapted for hearing aids H04R25/407

Abstract

Microphone array which comprises a multiple of microphones which are arranged in an elongated element or housing, in which the individual microphones in the microphone array are arranged in pairs. The individual microphones in each pair are disposed on each their side of a centerline for the microphone array, where the signals from the microphones are summated in the formation of the output signal from the microphone array. The microphones on each side of the centerline of the microphone array are disposed with non-equidistant spacing between them, and low-pass filters are coupled between each microphone and a summation link, in that the microphones associated with one and the same pair are connected to low-pass filters having the same cut-off frequency. The cut-off frequency for the low-pass filters is different for each pair of microphones, in that the cut-off frequency is lowest for that pair of microphones which lie furthest away from the centerline, and is higher the closer the pair of microphones lies to the centerline. The microphone array is arranged in such a manner that the distances between the microphones and the cut-off frequencies for the low-pass filters are mutually adjusted in relation to one another.

Claims

1. A microphone array comprising:

multiple individual microphones arranged in pairs and disposed in an elongated housing, the individual microphones in each pair are disposed on opposing sides of a centerline of the microphone array and the microphones on opposing sides of the centerline are positioned at different distances from the centerline;

a summation link for summing signals from the microphones to form an output signal of the microphone array; and

low pass filters operatively coupled between the microphones and the summation link, wherein associated microphone pairs are connected to low-pass filters having identical cut-off frequencies and the cut-off frequencies are different for each microphone pair, and further wherein cut-off frequencies of low-pass filters associated with microphone pairs disposed distant from the centerline are lower than cut-off frequencies of low pass filters associated with microphone pairs disposed proximate the centerline, wherein cut-off frequencies for low-pass filters associated with microphone pairs mutually correspond to distances between microphone pairs and the centerline of the microphone array.

2. The microphone array according to claim 1, wherein the microphone array has a constant directivity up to an upper frequency, and the cut-off frequency is a function of a distance of a microphone pair from the centerline of the microphone array and the distance is a function of the wavelength of the upper frequency to which there is constant directivity.

3. The microphone array according to claim 2, wherein a microphone in a microphone pair is arranged at distances Y relative to the wavelength L₀ from the centerline of the microphone array as follows:

Y₁₊=0.33 L₀, Y₁₋

=0.33 L₀,

Y₂₊=1.03 L₀, Y₂₋

=1.03 L₀,

Y₃₊=1.85 L₀, Y₃₋

=1.85 L₀,

Y₄₊=2.89 L₀, Y₄₋

=2.89 L₀;

and the cut-off frequencies f_c for low pass filters associated with microphones in microphone pairs are as follows;

f_c1+=1.10 f_c f_c1−

=1.10 f_c,

f_c2+=0.80 f_c, f_c2−

=0.80 f_c,

f_c3+=0.45 f_c, f_c3−

=0.45 f_c,

f_c4+=0.04 f_c, f_c4−

=0.04 f_c.

4. The microphone array according to claim 2, wherein the upper frequency is 5000 Hz and corresponds to a wavelength of 68.4 mm, and that the distances Y from the centerline of the microphone array to a microphone in a microphone pair is as follows:

Y₁₊=22.3 mm, Y₁₋

=−

22.3 mm,

Y₂₊=70.3 mm, Y₂₋

=−

70.3 mm,

Y₃₊=126 mm, Y₃₋

=−

126 mm,

Y₄₊=198 mm, Y₄₋

=−

198 mm;

and the cut-off frequencies f_c for low pass filters associated with microphones in the microphone pairs are as follows;

f_c1+=5500 Hz, f_c1−

=5500 Hz,

f_c2+=4000 Hz, f_c2−

=4000 Hz,

f_c3+=2300 Hz, f_c3−

=2300 Hz,

f_c4+=200 Hz, f_c4−

=200 Hz.

5. The microphone array according to claim 2, wherein the low-pass filters are 3rd-order low-pass filters phase-corrected with 2nd-order all-pass filters by means of analog electronics.

6. The microphone array according to claim 1, wherein the microphones in the microphone array are the same type.

7. The microphone array according to claim 1, wherein the microphones are disposed in the elongated housing facing out towards one side of the housing, and an indicator is disposed in the one side of the housing, wherein the indicator informs a user that the user is in a main lobe area of the microphone array.

8. The microphone array according to claim 7, wherein the indicator is a light source disposed in a recess in the housing, wherein the recess in the housing limits distribution of light from the light source to an angular area corresponding to the main lobe area of the microphone array.