Toroid microphone apparatus
View Patent ↗A video teleconferencing directional microphone includes two microphone elements arranged coincidentally on a vertical axis. The two microphone elements are placed on a supporting surface so that a first microphone element is on the surface, and the second microphone elements are elevated above the supporting surface. The directional microphone also includes filters, an adder assembly, and an equalizer, which are used to shape the directivity pattern of the directional microphone into a toroid sensitivity pattern. The toroid sensitivity pattern increases sensitivity in the direction of a sound source of interest, while simultaneously reduces sensitivity to any sound waves generated by noise sources from certain elevation angles.
1. A toroid microphone comprising:
a first microphone element arranged adjacent to a reflecting surface;
a second microphone element arranged at a predetermined distance (d 2 ) above the first microphone element;
a first filter connected to the first microphone element and having a frequency response H 1 ′(k);
a second filter connected to the first microphone element and having a frequency response H 1 ″(k);
a third filter connected to the second microphone element and having a frequency response H 2 (k); and
an adder configured to combine outputs of the first, second and third filters into a toroid microphone output by adding the outputs of the first and third filters and subtracting the output of the second filter,
wherein the frequency responses of the first, second and third filters combine to generate a toroid directivity pattern for the toroid microphone.
2. The toroid microphone according to claim 1 , wherein the toroid directivity pattern has a minimum sensitivity at elevation angle (θ 1 ).
3. The toroid microphone according to claim 1 , wherein the predetermined distance (d 2 ) is a maximum of one half of a wavelength corresponding to a highest frequency captured by the toroid microphone.
4. The toroid microphone according to claim 1 , wherein the first and second microphone elements are omni directional microphones.
5. The toroid microphone according to claim 1 , wherein each of the first filter, second filter and third filter is a digital filter.
6. The toroid microphone according to claim 1 , wherein each of the second filter and third filter is an amplifier.
7. The toroid microphone according to claim 1 , wherein ω is an angular frequency, c is a speed of sound through air and
k
=
ω
d
2
c
,
H
1
′
(
k
)
=
1
2
(
kd
2
)
2
,
H
1
″
(
k
)
=
β
2
,
H
2
(
k
)
=
β
2
.
8. The toroid microphone according claim 7 , wherein the minimum sensitivity at elevation angle (θ 1 ) corresponds to a value of β 2 , and β 2 ≧1.
9. The toroid microphone according to claim 1 , wherein ω is an angular frequency, c is a speed of sound through air and
k
=
ω
d
2
c
,
H
1
′
(
k
)
=
1
,
H
1
″
(
k
)
=
β
2
2
(
kd
2
)
2
,
H
2
(
k
)
=
β
2
2
(
kd
2
)
2
.
10. The toroid microphone according claim 9 , wherein the minimum sensitivity at elevation angle (θ 1 ) corresponds to a value of β 2 , and β 2 ≧1.
11. A method for creating a toroid directivity pattern for a toroid microphone, comprising:
converting, in a first microphone element, audio waves into corresponding first audio data, the first microphone element being located on are reflective surface;
converting, in a second microphone element, audio waves into a corresponding second audio data, the second microphone element being located a predetermined distance (d 2 ) from the reflective surface;
filtering, in a first filter, the first audio data according to a first frequency response H 1 ′(k);
filtering, in a second filter, the first audio data according to a second frequency response H 1 ″(k);
filtering, in a third filter, the second audio data according to a third frequency response H 2 (k);
adding, in a first adder, outputs of the first and third filters; and
subtracting, in a second adder, the output of the second filter from the output of the first adder to generate a toroid microphone output,
wherein H 1 ′(k), H 1 ″(k) and H 2 (k) combine to generate a toroid directivity pattern for the toroid microphone.
12. The method according to claim 11 , wherein the toroid directivity pattern has a minimum sensitivity at elevation angle (θ 0 ).
13. The method according to claim 11 , wherein the predetermined distance (d 2 ) is a maximum of half of a wavelength corresponding to a highest frequency captured by the toroid microphone.
14. The method according to claim 11 , wherein ω is an angular frequency, c is a speed of sound through air and
k
=
ω
d
2
c
,
H
1
′
(
k
)
=
1
2
(
kd
2
)
2
,
H
1
″
(
k
)
=
β
2
,
H
2
(
k
)
=
β
2
.
15. The method according to claim 14 , wherein the minimum sensitivity at elevation angle (θ 1 ) corresponds to a value of β 2 , and β 2 ≧1.
16. The method according to claim 11 , wherein ω is an angular frequency, c is a speed of sound through air and
k
=
ω
d
2
c
,
H
1
′
(
k
)
=
1
,
H
1
″
(
k
)
=
β
2
2
(
kd
2
)
2
,
H
2
(
k
)
=
β
2
2
(
kd
2
)
2
.
17. A toroid microphone comprising:
a first microphone element disposed on a reflective surface;
a second microphone element disposed at a predetermined distance (d 2 ) above the reflective surface;
a first filter connected to the first microphone element and having a frequency response of H 1 (k)
an adder configured to combine outputs of the first filter and the second microphone element into an adder output; and
an equalizer configured to generate an equalized output in response to the adder output,
wherein a combination of the frequency response of the first filter and the output of the second microphone element generates a toroid directivity pattern for the toroid microphone.
18. The toroid microphone according to claim 17 , wherein the predetermined distance (d 2 ) is a maximum of half of a wavelength corresponding to a highest frequency captured by the toroid microphone.
19. The toroid microphone according to claim 17 , wherein the first and second microphone elements are omni directional microphones.
20. The toroid microphone according to claim 17 , wherein each of the first filter and equalizer is a digital filter.
21. The toroid microphone according to claim 17 , said equalizer has a frequency response H EQ (k), ω is an angular frequency, c is a speed of sound through air and
k
=
ω
d
2
c
,
H
1
(
k
)
=
-
cos
(
kd
2
)
,
H
EQ
(
k
)
=
1
2
[
cos
(
kd
2
cos
θ
0
)
1
-
cos
(
kd
2
)
]
.