Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R27/00—Public address systems
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
  • H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
  • H04R1/34—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by using a single transducer with sound reflecting, diffracting, directing or guiding means
  • H04R1/342—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by using a single transducer with sound reflecting, diffracting, directing or guiding means for microphones
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R3/00—Circuits for transducers, loudspeakers or microphones
  • H04R3/02—Circuits for transducers, loudspeakers or microphones for preventing acoustic reaction, i.e. acoustic oscillatory feedback

Definitions

• the present invention relates to a sound pickup and playback device.
• the present invention has primary application in the field of audio conferencing 1, wherein a recording device and reproducing sound is included in a single set of relatively small dimensions.
• This assembly must be able to be placed easily on a table and operate in any room without the need for acoustic treatment of these premises.
• it can also be used by any number of people gathered in the same room and distributed around the piece of furniture on which the device is placed. To obtain these results, four conditions are sought:
• the device must be associated with two automatic level regulators which ensure that a correct level signal is sent online regardless of the acoustic power collected by the device's microphone (s) depending on the position of the speaker (s) in relation to this microphone (s) and the sending to the speaker (s) of a signal of correct level regardless of the attenuation brought about by the line.
• the sound reproduced by the loudspeaker (s) must be perceived with sufficient listening comfort regardless of the position occupied by the listener (s) in the room.
• the sound collected by the microphone (s) must keep qualities of clarity, sharpness and listening pleasure sufficiently stable whatever the position. of the speaker (s) in relation to the device and whatever the configuration of the room.
• the device must have a good acoustic decoupling between the speaker (s) and the microphone (s) so as to be able to listen to a sufficiently high sound level without causing a LARSEN effect. , but also to send the least possible acoustic echo back to the remote party.
• Currently operational devices are known which satisfy condition 1.
• this type of device does not fulfill conditions 2 (because of the phase shifts of ⁇ radians between speakers, the radiation pattern of the speaker assembly will not be circular in the horizontal plane and will depend significantly on the frequencies emitted) and 3 (because the microphone indifferently picks up direct sounds and indirect reflected sounds, which means that the quality of the sound picked up by the microphone depends too largely on the position of the speaker in the room and the configuration of this room).
• the achievement of the above aim then allows, by orienting one or more loudspeakers in said predetermined direction, fully satisfying condition 3 above, while satisfying conditions 1, 2 and 4 at least as well as the devices of the prior art.
• the invention which is the subject of said French patent application thus proposes a sound pickup method using several sound reception devices, according to which the sound reception devices are arranged substantially in the same plane and they are distributed symmetrically with respect to to a direction of symmetry perpendicular to this plane, a phase shift is applied between the signals originating respectively from different sound reception devices and the signals thus phase shifted are added, so as to substantially cancel the signals relating to any sound wave arriving in phase and with the same intensity on each of the sound receiving devices.
• the incident sounds in the direction of symmetry reach them in phase and with the same intensity. Consequently, due to the applied phase shifts and the addition of the phase-shifted signals, these incident sounds in the direction of symmetry are substantially eliminated after the processing.
• the incident sounds perpendicular to the direction of symmetry reach the various reception devices with phase and / or amplitude differences between these devices. These sounds are therefore preserved and correctly taken into account.
• an even number of sound receiving devices are used which are associated in pairs, the sound receiving devices of each pair being arranged symmetrically with respect to the direction of symmetry, and subtract one from the other the signals coming respectively from the sound reception devices of each pair to add them with a phase shift of 2 ⁇ radians between them.
• the incident sounds in the direction of symmetry, as well as various parasites can be effectively eliminated by a simple subtraction of the signals originating respectively from the reception devices of each pair.
• This subtraction can advantageously be carried out in conjunction with a preamplification by means of a differential preamplifier connected to the output of the reception devices of each pair.
• 2n associated sound reception devices are used in pairs and arranged at regular intervals along a circumference centered on the direction of symmetry, n denoting an integer at least equal to two , and a phase shift of 2 ⁇ radians / 2n is applied between the signals originating respectively from any two adjacent sound reception devices.
• the invention object of this patent application proposes a camera and its restitution comprising at least one oriented speaker in a direction of symmetry and means for the outlet, wherein the es sound pickup means comprise a system according to the second object of the invention, with the direction of symmetry of the system identical to the direction of orientation of the loudspeaker.
• a base 1 having a flat surface 20
• a sound pickup device 2 microphones
• a sound reproduction device 3 speaker
• the invention sets itself the aim, while retaining the advantages of the device of the aforementioned French patent application, of overcoming these drawbacks.
• the invention provides to fix the sound reproduction device directly on the flat surface of said base and to provide the part of the reproduction device with its view of the recording device. sound recording of an appropriate form, that is to say a form such that its intersection with any horizontal plane passing through it is a circle.
• it is a convex shape comprised between two limiting shapes: a cone and a hemisphere.
• the sound reproduction device is fixed to the base by means of spacers of small dimensions.
• spacers of small dimensions.
• the subject of the invention is therefore a device for taking and reproducing sound from at least one sound source, intended to be placed on a work surface, of the type comprising a support provided with a flat surface, a taking device of its arranged on this flat surface and a sound reproduction device, said sound pick-up and reproduction devices being arranged one relative to the other so as to present a structure of symmetry about an axis of symmetry orthogonal to said flat surface, characterized in that the sound reproduction device is fixed directly to said flat surface; in that the restitution device fits inside a cone of revolution with an axis coincident with said axis of symmetry; this cone being obtained by drawing a straight line between a first point distant by a first determined length from said axis of symmetry and by a determined height from said work plane and a second point located on said flat surface and distant from said axis of symmetry by a second determined distance, the line segment intersecting said axis of symmetry at the top of the cone, and by rotating this line segment by an angle of revolution equal
• FIG. 2 shows a sectional view of part of the apparatus shown in Figure 1, taken along the plane II-II indicated in Figure 1;
• FIG. 3 shows an overall diagram of the means for processing the sounds picked up by the microphones of the device of Figures 1 and 2;
• FIG. 4 is a diagram explaining the CCITT recommendation P34
• - Figure 5 is an example of an amplitude response versus frequency curve for sound pickup devices according to the aforementioned patent application and the invention, respectively;
• - Figure 6 schematically illustrates an embodiment of an apparatus according to the invention;
• FIG. 7 and 8 schematically illustrate two alternative embodiments of a sound reproduction device incorporated in an apparatus according to the invention
• the apparatus illustrated in these figures comprises a housing 1, a body or sound recording device 2 in which are housed several sound reception devices M1, M2, M3, M4, and a sound reproduction device or element 3 in which a loudspeaker 4 is mounted.
• the body 2 and the element 3 have a general shape of revolution around in a direction of symmetry D.
• the element 3 is mounted on the body 2 which is itself mounted on the housing 1.
• Phonically insulating materials, and / or mechanically damping materials such as 5, can be interposed between the element 3 and the body 2, or even between the body 2 and the upper part of the housing 1.
• the device has a symmetrical structure around the direction D to minimize the effect of mechanical vibrations which can affect the signals produced. by microphones Ml, M2, M3, M4.
• the housing 1 is provided at its lower part with feet 6 of rubber or the like for placing the apparatus on a horizontal surface such as a table.
• the direction of symmetry D is then vertical, which is the general case.
• Electrical circuits 7, 8 are mounted inside the housing 1. These circuits can be connected as shown diagrammatically, at 9, 10 in FIG. 1, to an external audio conference system (not shown) with which the apparatus according to the invention.
• These circuits include an amplification circuit 7 which receives signals from the audio conference system and sends them in amplified form to the loudspeaker 4 so that the latter emits the corresponding sounds, and processing means 8 for processing the signals from the elementary sound reception devices M1, m2, M3, M4, and address them after processing to the audio conference system.
• the amplification circuit 7 can include, to increase listening comfort, an electronic cell for correcting the response curve of the loudspeaker 4, in particular to reinforce the low frequencies and eliminate any resonances or anti-resonances.
• conventional means of echo cancellation are generally mounted between circuits 7 and 8.
• the four microphones Ml, M2, M3, M4 are distributed symmetrically with respect to the direction of symmetry D, which is perpendicular to the plane of Figure 2. These four microphones are located on a circumference 13 parallel to P and centered on the direction of symmetry D. These four microphones are associated in pairs, respectively Ml, M3 and M2, M4, the microphones of each pair being arranged symmetrically with respect to the direction of symmetry D, and the two pairs microphones being arranged along two radial lines 14, 15 forming between them a right angle. Each of the microphones Ml, M2, M3, M4 is housed in a respective cavity 12 machined in the body 2. This body 2 is metallic, for example made of brass.
• an axial bore 16 in the direction of symmetry D, and it further comprises four radial bores 17, each extending between the axial bore 16 and one of the four cavities 12.
• the axial bore 16 serves the passage of the connecting wires (not shown) of the loudspeaker 4 to the amplification circuit 7, with a corresponding bore 18 provided at the base of 1 • element 3.
• the axial bore 16 and the four radial bores 17 are used for passage of the connection wires (not shown) of the microphones Ml, M2, M3, M4, to the processing means 8 located in the housing 1.
• the four microphones M1, M2, M3, M4 are advantageously of the condenser type, and have a small dimension (for example a cylindrical shape with a diameter of 6 mm, and a height of 4.5 mm). It is known that, for a given production series, such microphones have substantially the same response curve, with an offset between them not exceeding 3 to 4 decibels. For the realization of the device, it is therefore easy to sort four microphones having response curves identical to a predetermined tolerance (for example 0.5 decibel).
• the body 2 is mounted on a flat metal plate 20, parallel to the plane P of the microphones and constituting the upper face of the housing 1.
• the cylindrical body 2 has an axial cylindrical extension 21, of smaller diameter which rests on this flat plate 20 and which defines a spacing 22 between the flat plate 20 and the surface 23 of the body 2 which is parallel to the plane P, and on which the machined cavities open 12.
• the extension 21 of the body 2 provides a certain acoustic insulation between the microphones Ml , M2, M3, M4 vis-à-vis the sounds arriving in a plane perpendicular to the direction of symmetry D. As can be seen in FIG.
• the cavities 12 have an axial height greater than the height of the cylinders of the microphones Ml , M2, M3, M4, and the latter are pressed into their respective cavities 12 so as to leave a gap 24 between the side of each microphone facing the plate 20 and the surface 23 defining the bor d of the cavities 12.
• each cavity 12 extends into a part 25 of smaller diameter which defines a shoulder against which the rear face of the microphone rests, and into which the radial bore opens. 17, thus giving space for the connection wires not shown.
• the element 3 mounted above the body 2 forms a resonance box for the loudspeaker 4.
• the loudspeaker 4 is mounted in the element 3 in the direction of symmetry D, and oriented in this direction of symmetry D , opposite the plane P where the microphones Ml, M2, M3, M4 are located.
• the membrane 29 of the speaker 4 which has a shape of revolution around an axis, is arranged in the element 3 so that this axis coincides with the direction of symmetry D of the device, the edge outside 30 of this membrane 29 being located in a plane perpendicular to the direction of symmetry D.
• this outer edge 30 of memLrane 29 is typically located between 100 and 150 mm above the horizontal surface on which the device is placed.
• a protective grid 32 is mounted at the top of the element 3 to protect the membrane 29 of the loudspeaker 4.
• the outer peripheral surface 33 of the element 3 has a concave curvature and is tangentially connected to the outer peripheral surface of the body 2, this outer peripheral surface of the body 2 being a cylinder defined by generatrices substantially parallel to the direction of symmetry D.
• each device elementary reception is composed of several microphones and not of a single microphone as shown in FIG. 2 (the microphones M1 to M4 respectively). The output signals from these microphones are added in phase.
• Said French patent application also provides means for processing signals from sound reception devices arranged to apply a phase shift equal to 2 ⁇ radians / n (or 2 radians / m in the last variant mentioned above) between the signals from respectively from any two adjacent sound reception devices and for adding the signals thus phase-shifted so as to obtain a substantially uniform and undiminished reception of signals relating to the components parallel to the plane P, whatever the direction of the waves, and a reception substantially null of the signals relating to the components parallel to the line of symmetry D of the captured acoustic waves.
• differential amplifiers and cascade phase shifters are used to perform these functions.
• FIG. 3 schematically represents an exemplary embodiment of the means 8 for processing the signals from the microphones Ml, M2, M3, M4.
• These processing means comprise on the one hand two differential preamplifiers A13, A24 of inputs El to E4, supplying the respective signals S13 and S14, and two phase shift channels D13, D24 for applying a phase shift between the signals originating respectively from different microphones of outputs SD13 and SD14, and on the other hand an adder circuit 40 provided for summing the phase-shifted signals coming from the phase-shifting channels D13, D24.
• a circuit 41 which formats the signals with a view to their transmission to the external audio conference system (not shown) and provides an output signal VS.
• the phase shifts applied and the addition carried out are such that the signals relating to any sound wave arriving in phase and with the same intensity on each of the microphones Ml, M2, M3, M4 are substantially canceled at the output of the circuit. adder 40.
• the sounds emitted by the loudspeaker 4 and reflected by the horizontal ceiling located above the device reach the four microphones in the direction of symmetry D and have, taking into account the symmetrical arrangement of the microphones, an identical phase and intensity on each of the microphones. Consequently, these reflected signals are advantageously eliminated from the output signal from the processing circuit 8.
• the symmetrical structure of the sound pick-up system ensures that the mechanical vibrations of the device will reach each of the microphones identically. Therefore, the effect of these vibrations on the microphones is also eliminated from the output signal from the processing circuit 8.
• a differential preamplifier A13 (respectively A24) has two inputs El, E3 (respectively E2, E4) each connected to one of the microphones Ml, M3 (respectively M2, M4) of a pair of microphones arranged in diametrically opposite position relative to the direction of symmetry D.
• the differential preamplifiers A13, A24 carry out a preamplification of the output signals of the microphones, eliminate certain parasites present in these output signals. In this combination, therefore, the contributions of the sounds reaching the microphones in the direction of symmetry D and the effects of symmetrical mechanical vibrations are eliminated.
• the sounds emitted by speakers are thus taken into account satisfactorily whatever the position of these speakers relative to the device, while the echoes of the speaker are noticeably eliminated.
• the arrangement of the microphones Ml, M2, M3, M4 in the body 2 (FIG. 1) and the presence of the pressure zones between this body 2 (FIG. 1) and the metal plate 20 (FIG. 1) reflecting the sound waves. largely eliminate indirect echoes from microphones.
• FIG. 4 schematically illustrates some features of this recommendation.
• An artificial Bart mouth is used to test the reception of an Aac audio conference device, for example a device of the type described in relation to FIG. 1.
• This Aac device is placed on a plane, for example a table. Ta used for audio conference.
• the Bart artificial mouth is placed vertically and at a height h from the edge of the table Ta.
• the angle a is therefore equal to ⁇ / 2 radians.
• the edge of the table is at a distance 1 2 from the Aac device and the artificial mouth Bart at a distance 1, from the Aac device.
• the conditions for obtaining the curve C1 is as follows: - unissued curve raised in a room not acoustically treated;
• the curve C1 has a "hole” with a depth of approximately 12 dB and a width of the order of 100 Hz for a frequency usually included in the frequency interval ranging from 2000 Hz to approximately 2500 Hz. In the present case, the central frequency of the irregularity is approximately 2.2 kHz.
• the curve typically has a growth of 3 dB per octave with undulations of the order of + 2 dB depending on the specific responses of each microphone and the quality of their pairing. This growth of 3 dB per octave is recommended by recommendation P34.
• the invention while retaining the advantages of the device described in relation to Figure 1, aims to overcome the two faults which have just been recalled. To do this, if we refer again to Figure 1, we will move the device 3 away from the device 2. But to keep the whole a compact appearance, this distance must remain as small as possible. To more specifically remedy the first defect, the device 3 will be fixed directly no longer on the device 2, with or without the intermediary of an insulating material 5, but directly on the surface of the plane 20.
• FIG. 6 schematically illustrates a device for taking and restoring its Aac according to the invention.
• the sound recording device 2 may be identical to that described in relation to FIGS. 1 and 2 or to its possible variants which have been indicated. It is the same for the housing 1, the plane 20, and the electrical processing and amplification circuits (respectively 7 and 8) contained in the housing 1. These circuits could naturally be arranged outside of this housing 1, but the arrangement inside the housing 1 has the advantage of reducing the length of the connections between the amplification circuits and the loudspeaker, on the one hand; and the processing circuits 7 and the microphones M1 to M4, on the other hand.
• the sound reproduction device 3 is no longer mechanically coupled to the sound recording device
• the device 3 is fixed directly to the housing 1, preferably near the edges of the plane 20, using spacers or the like, four in number Etl to Et4 (in the example illustrated) and regularly spaced.
• the spacer Et2 is not visible. In the present case, the spacing between spacers is ⁇ / 4 radians.
• the shape of the spacers Etl to Et4 can be any: round, oval, triangular, etc. However, the largest dimension must remain small, typically in a range of 10 to 17 mm. This dimension, as well as the material will be chosen according to the weight and dimensions of the device 3, on the one hand, and to avoid any parasitic vibrations on the other hand.
• a number equal to three or four is an acceptable compromise.
• the means of fixing these spacers Etl to Et4, on the one hand, to the device 3 and, on the other hand, to the housing 1, is chosen from known conventional means: screwing, etc.
• the part of the device 3 is "seen" from the device 2 in an appropriate shape, in this case the lower surface 33 of the device 3.
• This is preferably convex but can be between a cone and a hemisphere, which constitute the two extreme forms.
• ⁇ radians that is to say a degenerate shape which tends towards a plane.
• Figures 7 and 8 illustrate the two extreme cases: conical (figure 7) and spherical (figure 8)
• the sound source artificial or human
• the sound source is at a height h from the plane of the table Ta or any other plane on which is placed the device for taking and restoring its Aac and at a distance 12 (projection onto the plane Ta) of the edge of the housing 1.
• FIG. 9 explains what are the conditions to which the arrangement must subscribe in the space of the device 3.
• the spacers Et1 to Et4 have not been shown.
• the devices 3 and 2 will be arranged in such a way that the recommendation P34 defined by the CCITT is respected.
• the sound pickup device 2 is also identical to that used in the device shown in FIG. 1. The same is true of the electronic circuits 7 and 8.
• the transducer ( speaker 4) is identical to that previously used.
• Other measurements, carried out by the Applicant, repeatedly on several devices produced in accordance with the teachings of the invention, have shown that the mechanical vibrations due, essentially in the apparatus of FIG., at the mechanical range between the device 2 and 3, was negligible, but negligible. It follows that, even if each of the microphones picks up a non-homogeneous fraction, in amplitude and in phase, the differences due to this non-homogeneity no longer entail an appreciable dysfunction of the sound pickup device 2.

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• Health & Medical Sciences (AREA)
• Otolaryngology (AREA)
• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• General Health & Medical Sciences (AREA)
• Obtaining Desirable Characteristics In Audible-Bandwidth Transducers (AREA)
• Details Of Audible-Bandwidth Transducers (AREA)
• Fittings On The Vehicle Exterior For Carrying Loads, And Devices For Holding Or Mounting Articles (AREA)

Applications Claiming Priority (3)

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• 1993
  • 1993-03-19 FR FR9303216A patent/FR2702918B1/fr not_active Expired - Fee Related
• 1994
  • 1994-02-18 WO PCT/FR1994/000188 patent/WO1994022277A1/fr active IP Right Grant
  • 1994-02-18 EP EP94907599A patent/EP0710427B1/de not_active Expired - Lifetime
  • 1994-02-18 DE DE69402322T patent/DE69402322T2/de not_active Expired - Fee Related
  • 1994-02-18 AU AU61111/94A patent/AU6111194A/en not_active Abandoned
  • 1994-02-18 ES ES94907599T patent/ES2100052T3/es not_active Expired - Lifetime

Non-Patent Citations (1)

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