CA1181162A - Conference microphone unit - Google Patents
Conference microphone unitInfo
- Publication number
- CA1181162A CA1181162A CA000398508A CA398508A CA1181162A CA 1181162 A CA1181162 A CA 1181162A CA 000398508 A CA000398508 A CA 000398508A CA 398508 A CA398508 A CA 398508A CA 1181162 A CA1181162 A CA 1181162A
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- Prior art keywords
- axis
- microphone
- null
- bidirectionality
- acousto
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
Abstract
ABSTRACT
A microphone unit particularly suitable for conference applications is provided, wherein an acousto-electric transducer is disposed between two dish-like back-to-back sound collectors, each having a central aperture exposing one side of the transducer, which preferably has a single planar diaphragm.
A microphone unit particularly suitable for conference applications is provided, wherein an acousto-electric transducer is disposed between two dish-like back-to-back sound collectors, each having a central aperture exposing one side of the transducer, which preferably has a single planar diaphragm.
Description
Field of the ~nvention The present invention relates to microphones in general and to directional microphones in particular.
More particularly, the invention rela-tes -to a microphone unit, which is capable of being combined with o-ther such units, and with acous-tic radiators, for conference appli~
cations.
Background and Prior Art An electro-acoustic microphone having a single planar diaphragm in a free field exhibits a nuli-response in the plane of its diaphragm, while having its maximum response along its perpendicular axis of symmetry. Such an ideal device is called a "cosine microphone". At any point between the axis and the plane of the diaphragm, the response is proportional to the cosine of the angle, say ~, that the point is at w.r.t. the axis-centre. The reason for a response null in the plane of the diaphragm, of course, is that sound pressure impinges equally on either side there~f in opposite directions~ thereby not ~o causing movement of the diaphragm, given perfect symmetry in a free field. Practical microphones have relatively small diaphragms. Even sound pressure emanating from a point of maximum response far along the axis is bound to also reach the other side of the diaphragm with some phase shift and thereby cause some cancellation in the response.
It is desirable in many applications -to have good cancella~tion in the plane of the diaphragm, yet to maintain high sensitivity on either side thereof, parti-cularl~ in the vicinity of the axis. Such desirable char-acteris-tics would result in a conference apparatus having a reduced degree of voice switching, thereby enabling more natural two-way communication between two or more parties of conferees. It is also desirable to have a frequency response that is relatively independant of source position (this means quality of response is independent of the tal-ker's position).
:` ~
United States patent No. 4,237,339 issued December 2, 1980 to Bunting et al and assigned to The Post Office, London~ England is an example of *he use to which such bidirectional microphones are put for purposes of audio teleconferencing. The patent discloses an electro-acoustic terminal unit for use in an audio teleconferencing - 20 system comprising a loudspeaker and one or more microphones each having a sens;tiv;ty which is directionally depen-dent and exhibits at least one null or substantially null position. The loudspeaker and microphones are rigidly mounte~ on a boom and the microphones are so located and orientated relative to the loudspeaker that the null pos-ition is directed towards the loudspeaker.
ZJ
In figure 3 of -the above patent to Bunting et al, two "shallow" voice switches (35 and 44 ) are used in order to eliminate undesirable feedbac~ between the loud-speaker 10 and the microphones 12 and 14. The permitted degree of "shallowness" of the voice swi-tching is clearly dependent on the degree of isolat;on provided by the micro-phone.
It is possible to utilize complicated microphones to provide acceptable isolation. For instance, United States patent No. 3,573,399 issued April ~, 1971 to Schroeder et al and assigned to Bell Telephone Laboratories, Incorpora-ted, N.J., U.S.A. discloses the structure of a mic-rophone having toroidal characteristics. The microphone is constructed from a plurality of concentric transducer elements, the outputs of which are combined in accordance with a predetermined formula.
It is, therefore, generally recognized in the field of teleconferencing as desirable to have microphones of sufficient sensitivity to pick-up distance talkers and conferees, while simultaneously providing good direction-ality to lessen pick-up of background noise and rever-beratîon and to prevent feedback with a minimum of voice switching.
~8~
Su~mar~ o~ the Invention _ The object of the present invention is -to pro-vide a simple, inexpensive microphone unit which exhibits good sensi-tivity and directionality~
The acousto-electric transducer necessary ~or the present unit can be a simple bidirectional transducer having a single planar diaphragm, such as the now ubi-quitous electret transducers.
The transducer is placed at the junction of two dish-like sound collectors, which are back-to-back with their convex sides. An opening in each dish exposes the diaphragm to its concave side. The total s-tructure exhibits rotational symmetry along the axis perpendicular to the centre of the transducer. And whether the two collectors actually touch or not, is not of primary importance. In-deed, the exact shape of the collectors does not appear to greatly alter the unit characteris-tics. For ins-tance, a collector may be part of a sphere. Or it may be para-bolic.
Due to the symmetry o~ the total unit, the two identical back-to-back collectors do not in-terfere with the signal cancellation effect inherent in the cosine transducer in the plane of its diaphragm. But the collectors p~rform an important function along the axis of maximum response. ~or they reduce the cancellation effect for a sound source at a far point on the axis:
the collector facing the source enhances -the sound pres-sure on its side, while the other collec-tor provides a sound "shadow" -to the other side, thereby improving the transducer output. This improv~ment directly means in-creased acoustic isolation or directionality, achieved with a single structure and a single element transducer.
Thus, the sens~tivity o~ the microphone of the present invention is proportional to collector size, whereas its directionality is practically independent thereof, meaning that the frequency response, i.e. the variation of output with frequency or wavelength, is in-dependent of collector s;ze. Such independence of direc-tionality from frequency response translates into better quality independent of talk~r position. This is of some importance in conferencing and conference telephony.
Accordingly, the present invention provides a microphone unit comprising a bidirectional acousto-elec-tric transducer disposed in proximity to, and between, two dish-like back-to-back sound collectors each having an aperture therein exposing one of two active, opposite surfaces of said acousto-electric transducer, whereby said microphone unit exhibits substantially rotational symmetry around a cen-tral axis of bid;rectionality.
More narrowly, the acousto-electric transducer is of the cosine response type.
More narrowly s-till, each of -the -two opposite surfaces of the transducer being within a substan~ially coex~ensive aperture in the respective collector.
In a preferred embodiment the transducer is an electret microphone.
In another preferred embodiment, two micro-phone units are positioned one above the other, having their axes of bidirectionality at a right angle and both having a common null-axis in the third spatial dimension, thereby yielding a quasi-toroidal directionality pattern.
It is particularly advantageous for conference applications to combine the microphone unit of the present invention with an electro-acoustic transducer placed to substantially symmetrically intersect with the symmetry plane of the microphone unit that is perpendicular to its central axis o~ bidirectionality.
By a variant thereof, two microphone units, one having its axis of bidirectionality perpendicular to -that of the other, and both having a common null-axis in the -third spa-tial dimension, are combined with an elec-tro-acoustic -transducer placed -to substantially symmetrically intersect with the symmetPy plane of each of the two microphone units, each symmetry plane being perpendicular to the central axis of bidirectionality of the respective microphone unit.
Brief Description of the Drawings The present invention will be better understood in describing the preferred embodimen-ts in conjunction with attached drawings, in which:
Fig. 1 schematically illustrates a microphone unit according to the present invention;
- 6a -Pig. 2 schematically illu~trates a microphone unit acco~ding to the present invention wherein truncated parapelic reflec-tors are utiliæed;
Fig. 3 shows a combined microphone unit and a loudspeaker for conference applica-tions;
Fig. 4 shows a combined microphone unit and two loudspeakers for conference applications;
Fig. 5 shows an alternative arrangement using a microphone unit and two loudspeakers for con~erence lQ applications;
Fig. 6 shows an alternative arrangement for a microphone unit and a loudspeaker for conference pur-poses;
Fig. 7 shows an arrangement utilizing -~wo orthogonal microphone units and a loudspeaker for con-ference purposes;
Fig. 8 is a plan view of the general direc-tionality pattern of the two orthogonal microphone units shown in figure 7; and Fig. 9 shows a more detailed palar direction-ality pattern of a microphone unit in the plane of its axes.
Detailecl Description of -the Preferred Embodiments Figure 1 of the drawings shows a basic mi.cro-phone unit 10 of the present invention. The unit 10 com-prises two dish-like collectors 11 and 12, each having a surface of an electret transducer 13 exposed through a coopera-ting aperture therein. Ideally, the outside sur-faces of the transducer 13 are each coplanar with the in-side surface of therespective collector 11 and 12. Shown schematically is the diaphragm 14 of the transducer 13, t~e plane o~ ~hich is perpendicular to the plane of the drawing and is the null-plane, or plane of minimum sen-sitivity, of the total unit 10. Axis A is the axis of maxi~um sensitivity, the sensitivity or response of the unit 10 declining with the decrease in the angle with the plane of the diaphragm 14, Thus, for practical purposes a rotational angleo~defines a dead-zone of the microphone unit 10. The angle ~ is in the vicinity of thirty deg-rees, and the response on the surface of the dead-zone is an average of - 14dB from the maximum response along the axis A by a collector width W of five inches. The average response of - 14dB does not vary appreciably with frequency, and remains within ~ldB from 300 Hz ~o 3,000 Hz.
Such frequency range is approxi~ately the standard band-width of a telephone channel, The collectors 11 and 12 may be made of a wide choice of materials such as plastic, plexiglass, me-tal and -the like, and the transducer 13 is simply glued to the edges of the apertures in the collec-tors 11 and 12, which themselves are glued together at their junction by a compatible glue~ Of course, other methods of assembly, such as riveting are possible.
The collectors in ~igure 1 are shown to be 1~ spherical, or almost spherical. In figure 2, however, the collectors 15 and 16 are parabolic surfaces truncated some distance from the apex in order to permit placing of the transducer 13 at or close to the parabolic focus of both reflectors 15 and 18. A planar insert 17 closes the opening and accomodates the transducer 13 in a suitable aperture.
The unit shown in figure ~ ~xhibits somewhat higher direc-tionality so that the dead-zone angle ~ is somewhat lar-ger than the angle c~ in figure 1, given the same width W of the collectors 11, 12 and i5, 16. Both the micro-phone unit 10 and that of figure 2 are rotationally sym-metrical with respect to the axis A.
Figure 3 shows a conference device comprising the microphone unit 10 and a loudspeaker 18 placed in a suitable enclosure 19 on a conference table ~0. The loudspeaker 18 radiates upwardly, and the conference participants sit along the long sides of the table 20.
In this arrangement no conference participants may sit along the narrow sides of the table 20, which are largely in the dead-zone~
Figure 4 shows a more preferred arrangement than that in figure 3, because two loudspeakers 21 and 22 are radiating one to either side of the conference table 20.
In this arrangement it is mandatory that the loudspeakers be driven in-phase and be identical. Moreover, they must be posi-tioned sy~metrically on either side of the null-plane of the unit 10 within the dead-zone of the unit 10.
This arrangement is preferred over the previous one~
~ because of the higher "treblc" content of the sound reaching the conference participants when the lol-dspeakers 21 and 22 are facing them.
' - . .
In the embodiment of figure 5, the unit 10 is placed on the top of the conference table 20, while two loudspeakers, or loudspeaker rows, 23 and 24 are piaced as shown under the ta~le 20 facing the conference participants Any feedback from the loudspeakers 23 and 24 to the unit 10., if the loudspeakers 23 and 24 are operating in phase, would shown under the table 20 partially facing the conference participants. Any feedback from the loudspeakers 23 and 24 to the unit 10, if the loudspeakers 23 and 24 are operat-ing in phase, would cancel in the unit 10 ar,d produce minimal net feedback, given good symmetry.
.
Figure 6 shows a loudspeaker 25 suspended from a point above the unit 10, which is placed on the conference table 20. This arrangement gives good quality probably due to the treble frequencies from the loudspeaker 25 bouncing off the table 20 top to the participants on either side of the -table 20.
~ n figure 7 is shown an arrangement similar -to that in figure 6, except that two microphone units lOa and - lOb are placed on the table 20 top orthogonal to each other. This way, by summing the outputs from the unit`s lOa and lOb, a quasi-toroidal pattern is obtained with its axis of symmetry vertical to table 20. This quasi-toroidal pa-ttern is shown in a plan view in figure 8. The two axes of maximum sensi-tivity of the units lOa and lOb are perpendicular and parallel to the plane of the table 20. At ~5~ from either of these two àxes, the output of each of the units ~Oa and lOb is 3dB below maximum~ but because the outputs of the units lOa and lOb are summed the total response of the combined units lOa and lOb is again maximum along the ~0 45 directions. Thus, the pattern is close to being tor-oidal, and the total response or sensitivity is almost constant at any angle in the horizontal plane, dependent - only on the distance from the units lOa and lOb. This is a desirable condition for conference applications.
~h~.16~
The arrangement shown in figure 7 is particularly suitable for a conference room with a hard ceiling and sound-absorbing walls, whereby the sound level of the loud-speaker is enhanced, while acous-tic feedback is reduced.
Figure 9 shows a typical response of a single microphone unit 10 in one quadrant of -the plane of the axis A. As may be seen3 the response declines from its maximum (OdB~ oh the axis A to its minimum in the plane of the dia-phragm of some - 20dB. The important feature is the rela-tive constancy of the response irrespective of frequency.
The three plots at 300, 1000 and 3000 H~ are almost coin-cident, indicating the aforement;oned independence of response quality from the talker's position.
More particularly, the invention rela-tes -to a microphone unit, which is capable of being combined with o-ther such units, and with acous-tic radiators, for conference appli~
cations.
Background and Prior Art An electro-acoustic microphone having a single planar diaphragm in a free field exhibits a nuli-response in the plane of its diaphragm, while having its maximum response along its perpendicular axis of symmetry. Such an ideal device is called a "cosine microphone". At any point between the axis and the plane of the diaphragm, the response is proportional to the cosine of the angle, say ~, that the point is at w.r.t. the axis-centre. The reason for a response null in the plane of the diaphragm, of course, is that sound pressure impinges equally on either side there~f in opposite directions~ thereby not ~o causing movement of the diaphragm, given perfect symmetry in a free field. Practical microphones have relatively small diaphragms. Even sound pressure emanating from a point of maximum response far along the axis is bound to also reach the other side of the diaphragm with some phase shift and thereby cause some cancellation in the response.
It is desirable in many applications -to have good cancella~tion in the plane of the diaphragm, yet to maintain high sensitivity on either side thereof, parti-cularl~ in the vicinity of the axis. Such desirable char-acteris-tics would result in a conference apparatus having a reduced degree of voice switching, thereby enabling more natural two-way communication between two or more parties of conferees. It is also desirable to have a frequency response that is relatively independant of source position (this means quality of response is independent of the tal-ker's position).
:` ~
United States patent No. 4,237,339 issued December 2, 1980 to Bunting et al and assigned to The Post Office, London~ England is an example of *he use to which such bidirectional microphones are put for purposes of audio teleconferencing. The patent discloses an electro-acoustic terminal unit for use in an audio teleconferencing - 20 system comprising a loudspeaker and one or more microphones each having a sens;tiv;ty which is directionally depen-dent and exhibits at least one null or substantially null position. The loudspeaker and microphones are rigidly mounte~ on a boom and the microphones are so located and orientated relative to the loudspeaker that the null pos-ition is directed towards the loudspeaker.
ZJ
In figure 3 of -the above patent to Bunting et al, two "shallow" voice switches (35 and 44 ) are used in order to eliminate undesirable feedbac~ between the loud-speaker 10 and the microphones 12 and 14. The permitted degree of "shallowness" of the voice swi-tching is clearly dependent on the degree of isolat;on provided by the micro-phone.
It is possible to utilize complicated microphones to provide acceptable isolation. For instance, United States patent No. 3,573,399 issued April ~, 1971 to Schroeder et al and assigned to Bell Telephone Laboratories, Incorpora-ted, N.J., U.S.A. discloses the structure of a mic-rophone having toroidal characteristics. The microphone is constructed from a plurality of concentric transducer elements, the outputs of which are combined in accordance with a predetermined formula.
It is, therefore, generally recognized in the field of teleconferencing as desirable to have microphones of sufficient sensitivity to pick-up distance talkers and conferees, while simultaneously providing good direction-ality to lessen pick-up of background noise and rever-beratîon and to prevent feedback with a minimum of voice switching.
~8~
Su~mar~ o~ the Invention _ The object of the present invention is -to pro-vide a simple, inexpensive microphone unit which exhibits good sensi-tivity and directionality~
The acousto-electric transducer necessary ~or the present unit can be a simple bidirectional transducer having a single planar diaphragm, such as the now ubi-quitous electret transducers.
The transducer is placed at the junction of two dish-like sound collectors, which are back-to-back with their convex sides. An opening in each dish exposes the diaphragm to its concave side. The total s-tructure exhibits rotational symmetry along the axis perpendicular to the centre of the transducer. And whether the two collectors actually touch or not, is not of primary importance. In-deed, the exact shape of the collectors does not appear to greatly alter the unit characteris-tics. For ins-tance, a collector may be part of a sphere. Or it may be para-bolic.
Due to the symmetry o~ the total unit, the two identical back-to-back collectors do not in-terfere with the signal cancellation effect inherent in the cosine transducer in the plane of its diaphragm. But the collectors p~rform an important function along the axis of maximum response. ~or they reduce the cancellation effect for a sound source at a far point on the axis:
the collector facing the source enhances -the sound pres-sure on its side, while the other collec-tor provides a sound "shadow" -to the other side, thereby improving the transducer output. This improv~ment directly means in-creased acoustic isolation or directionality, achieved with a single structure and a single element transducer.
Thus, the sens~tivity o~ the microphone of the present invention is proportional to collector size, whereas its directionality is practically independent thereof, meaning that the frequency response, i.e. the variation of output with frequency or wavelength, is in-dependent of collector s;ze. Such independence of direc-tionality from frequency response translates into better quality independent of talk~r position. This is of some importance in conferencing and conference telephony.
Accordingly, the present invention provides a microphone unit comprising a bidirectional acousto-elec-tric transducer disposed in proximity to, and between, two dish-like back-to-back sound collectors each having an aperture therein exposing one of two active, opposite surfaces of said acousto-electric transducer, whereby said microphone unit exhibits substantially rotational symmetry around a cen-tral axis of bid;rectionality.
More narrowly, the acousto-electric transducer is of the cosine response type.
More narrowly s-till, each of -the -two opposite surfaces of the transducer being within a substan~ially coex~ensive aperture in the respective collector.
In a preferred embodiment the transducer is an electret microphone.
In another preferred embodiment, two micro-phone units are positioned one above the other, having their axes of bidirectionality at a right angle and both having a common null-axis in the third spatial dimension, thereby yielding a quasi-toroidal directionality pattern.
It is particularly advantageous for conference applications to combine the microphone unit of the present invention with an electro-acoustic transducer placed to substantially symmetrically intersect with the symmetry plane of the microphone unit that is perpendicular to its central axis o~ bidirectionality.
By a variant thereof, two microphone units, one having its axis of bidirectionality perpendicular to -that of the other, and both having a common null-axis in the -third spa-tial dimension, are combined with an elec-tro-acoustic -transducer placed -to substantially symmetrically intersect with the symmetPy plane of each of the two microphone units, each symmetry plane being perpendicular to the central axis of bidirectionality of the respective microphone unit.
Brief Description of the Drawings The present invention will be better understood in describing the preferred embodimen-ts in conjunction with attached drawings, in which:
Fig. 1 schematically illustrates a microphone unit according to the present invention;
- 6a -Pig. 2 schematically illu~trates a microphone unit acco~ding to the present invention wherein truncated parapelic reflec-tors are utiliæed;
Fig. 3 shows a combined microphone unit and a loudspeaker for conference applica-tions;
Fig. 4 shows a combined microphone unit and two loudspeakers for conference applications;
Fig. 5 shows an alternative arrangement using a microphone unit and two loudspeakers for con~erence lQ applications;
Fig. 6 shows an alternative arrangement for a microphone unit and a loudspeaker for conference pur-poses;
Fig. 7 shows an arrangement utilizing -~wo orthogonal microphone units and a loudspeaker for con-ference purposes;
Fig. 8 is a plan view of the general direc-tionality pattern of the two orthogonal microphone units shown in figure 7; and Fig. 9 shows a more detailed palar direction-ality pattern of a microphone unit in the plane of its axes.
Detailecl Description of -the Preferred Embodiments Figure 1 of the drawings shows a basic mi.cro-phone unit 10 of the present invention. The unit 10 com-prises two dish-like collectors 11 and 12, each having a surface of an electret transducer 13 exposed through a coopera-ting aperture therein. Ideally, the outside sur-faces of the transducer 13 are each coplanar with the in-side surface of therespective collector 11 and 12. Shown schematically is the diaphragm 14 of the transducer 13, t~e plane o~ ~hich is perpendicular to the plane of the drawing and is the null-plane, or plane of minimum sen-sitivity, of the total unit 10. Axis A is the axis of maxi~um sensitivity, the sensitivity or response of the unit 10 declining with the decrease in the angle with the plane of the diaphragm 14, Thus, for practical purposes a rotational angleo~defines a dead-zone of the microphone unit 10. The angle ~ is in the vicinity of thirty deg-rees, and the response on the surface of the dead-zone is an average of - 14dB from the maximum response along the axis A by a collector width W of five inches. The average response of - 14dB does not vary appreciably with frequency, and remains within ~ldB from 300 Hz ~o 3,000 Hz.
Such frequency range is approxi~ately the standard band-width of a telephone channel, The collectors 11 and 12 may be made of a wide choice of materials such as plastic, plexiglass, me-tal and -the like, and the transducer 13 is simply glued to the edges of the apertures in the collec-tors 11 and 12, which themselves are glued together at their junction by a compatible glue~ Of course, other methods of assembly, such as riveting are possible.
The collectors in ~igure 1 are shown to be 1~ spherical, or almost spherical. In figure 2, however, the collectors 15 and 16 are parabolic surfaces truncated some distance from the apex in order to permit placing of the transducer 13 at or close to the parabolic focus of both reflectors 15 and 18. A planar insert 17 closes the opening and accomodates the transducer 13 in a suitable aperture.
The unit shown in figure ~ ~xhibits somewhat higher direc-tionality so that the dead-zone angle ~ is somewhat lar-ger than the angle c~ in figure 1, given the same width W of the collectors 11, 12 and i5, 16. Both the micro-phone unit 10 and that of figure 2 are rotationally sym-metrical with respect to the axis A.
Figure 3 shows a conference device comprising the microphone unit 10 and a loudspeaker 18 placed in a suitable enclosure 19 on a conference table ~0. The loudspeaker 18 radiates upwardly, and the conference participants sit along the long sides of the table 20.
In this arrangement no conference participants may sit along the narrow sides of the table 20, which are largely in the dead-zone~
Figure 4 shows a more preferred arrangement than that in figure 3, because two loudspeakers 21 and 22 are radiating one to either side of the conference table 20.
In this arrangement it is mandatory that the loudspeakers be driven in-phase and be identical. Moreover, they must be posi-tioned sy~metrically on either side of the null-plane of the unit 10 within the dead-zone of the unit 10.
This arrangement is preferred over the previous one~
~ because of the higher "treblc" content of the sound reaching the conference participants when the lol-dspeakers 21 and 22 are facing them.
' - . .
In the embodiment of figure 5, the unit 10 is placed on the top of the conference table 20, while two loudspeakers, or loudspeaker rows, 23 and 24 are piaced as shown under the ta~le 20 facing the conference participants Any feedback from the loudspeakers 23 and 24 to the unit 10., if the loudspeakers 23 and 24 are operating in phase, would shown under the table 20 partially facing the conference participants. Any feedback from the loudspeakers 23 and 24 to the unit 10, if the loudspeakers 23 and 24 are operat-ing in phase, would cancel in the unit 10 ar,d produce minimal net feedback, given good symmetry.
.
Figure 6 shows a loudspeaker 25 suspended from a point above the unit 10, which is placed on the conference table 20. This arrangement gives good quality probably due to the treble frequencies from the loudspeaker 25 bouncing off the table 20 top to the participants on either side of the -table 20.
~ n figure 7 is shown an arrangement similar -to that in figure 6, except that two microphone units lOa and - lOb are placed on the table 20 top orthogonal to each other. This way, by summing the outputs from the unit`s lOa and lOb, a quasi-toroidal pattern is obtained with its axis of symmetry vertical to table 20. This quasi-toroidal pa-ttern is shown in a plan view in figure 8. The two axes of maximum sensi-tivity of the units lOa and lOb are perpendicular and parallel to the plane of the table 20. At ~5~ from either of these two àxes, the output of each of the units ~Oa and lOb is 3dB below maximum~ but because the outputs of the units lOa and lOb are summed the total response of the combined units lOa and lOb is again maximum along the ~0 45 directions. Thus, the pattern is close to being tor-oidal, and the total response or sensitivity is almost constant at any angle in the horizontal plane, dependent - only on the distance from the units lOa and lOb. This is a desirable condition for conference applications.
~h~.16~
The arrangement shown in figure 7 is particularly suitable for a conference room with a hard ceiling and sound-absorbing walls, whereby the sound level of the loud-speaker is enhanced, while acous-tic feedback is reduced.
Figure 9 shows a typical response of a single microphone unit 10 in one quadrant of -the plane of the axis A. As may be seen3 the response declines from its maximum (OdB~ oh the axis A to its minimum in the plane of the dia-phragm of some - 20dB. The important feature is the rela-tive constancy of the response irrespective of frequency.
The three plots at 300, 1000 and 3000 H~ are almost coin-cident, indicating the aforement;oned independence of response quality from the talker's position.
Claims (9)
1. A microphone unit comprising a bidirectional acousto-electric transducer of the cosine-response type disposed in proximity to, and between, two dish-like back-to-back sound collectors each having an aperture therein exposing one of two active, opposite surfaces of said acousto-electric transducer, whereby said microphone unit exhibits substantially rotational symmetry around a central axis of bidirectionality.
2. The microphone unit of Claim 1, each of said two opposite surfaces of said acousto-electric transducer being within a therewith substantially coextensive aperture in the respective one of said two dish-like back-to-back sound collectors.
3. Two microphone units as claimed in claim 1 or 2, one having its axis of bidirectionality perpendicular to that of the other, and both having a common null-axis in the third spatial dimension.
4. The microphone unit of claim 1 or 2, said acousto-electric transducer being an electret microphone.
5. Two microphone units as claimed in claim 1 or 2, one having its axis of bidirectionality perpendicular to that of the other, and both having a common null-axis in the third spatial dimension, and the acousto-electric transducer in each of said two microphone units being an electret micro-phone having a single planar diaphragm perpendicular to the central axis of bidirectionality.
6. The microphone unit of Claim 1 or 2, in com-binaition with an electro-acoustic transducer disposed to substantially symmetrically intersect a null-plane of said microphone unit.
7. Two microphone units as claimed in Claim 1 or 2, one having its axis of bidirectionality perpendicular to that of the other, and both having a common null-axis in the third spatial dimension, said common null-axis being the intersection of two null-planes of said two microphone units, in combination with an electro-acoustic transducer disposed substantially symmetrically along said common null-axis.
8. The microphone unit of Claim 1 or 2, in com-bination with an electro-acoustic transducer disposed to substantially symmetrically intersect a null-plane, and said acousto-electric transducer being an electret microphone having a single planar diaphragm perpendicular to said central axis of bidirectionality.
9. Two microphone units as claimed in Claim 1 or 2, one having its axis of bidirectionality perpendicular to that of the other, and both having a common null-axis in the third spatial dimension, said common null-axis being the intersection of two null-planes of said two microphone units, in combination with an electro-acoustic transducer disposed substantially symmetrically along said common null-axis, and the acousto-electric transducer being an electret microphone having a single planar diaphragm perpendicular to said central axis of bidirectionality.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000398508A CA1181162A (en) | 1982-03-16 | 1982-03-16 | Conference microphone unit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000398508A CA1181162A (en) | 1982-03-16 | 1982-03-16 | Conference microphone unit |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1181162A true CA1181162A (en) | 1985-01-15 |
Family
ID=4122317
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000398508A Expired CA1181162A (en) | 1982-03-16 | 1982-03-16 | Conference microphone unit |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1181162A (en) |
-
1982
- 1982-03-16 CA CA000398508A patent/CA1181162A/en not_active Expired
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