EP0710427A1 - Sound pick-up and reproduction apparatus and use thereof for conference calls - Google Patents

Sound pick-up and reproduction apparatus and use thereof for conference calls

Info

Publication number
EP0710427A1
EP0710427A1 EP94907599A EP94907599A EP0710427A1 EP 0710427 A1 EP0710427 A1 EP 0710427A1 EP 94907599 A EP94907599 A EP 94907599A EP 94907599 A EP94907599 A EP 94907599A EP 0710427 A1 EP0710427 A1 EP 0710427A1
Authority
EP
European Patent Office
Prior art keywords
sound
symmetry
axis
signals
reception devices
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.)
Granted
Application number
EP94907599A
Other languages
German (de)
French (fr)
Other versions
EP0710427B1 (en
Inventor
Philippe Parment
Frederic Zurcher
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Prescom
Original Assignee
Prescom
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Prescom filed Critical Prescom
Publication of EP0710427A1 publication Critical patent/EP0710427A1/en
Application granted granted Critical
Publication of EP0710427B1 publication Critical patent/EP0710427B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R27/00Public address systems
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00Details of transducers, loudspeakers or microphones
    • H04R1/20Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/32Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
    • H04R1/34Arrangements 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
    • H04R1/342Arrangements 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
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00Circuits for transducers, loudspeakers or microphones
    • H04R3/02Circuits 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.

Abstract

A sound pick-up and reproduction apparatus (Aac) which is rotatable about an axis (D) and includes a mounting (1), a sound pick-up device (2) and a sound reproduction device (3) with a convex or planar surface (revolving cone) opposite the sound pick-up device. Said sound reproduction device (3) fits within a revolving cone (B' C A') of which the axis coincides with the axis of symmetry (D), and is directly attached to the mounting (1). The apparatus is useful for conference calls.

Description

"Appareil de prise et de restitution de son, et son application à 1'audio-conférence" "Sound recording and reproducing apparatus, and its application to audio conferencing"
La présente invention concerne un appareil de prise et de restitution de son.The present invention relates to a sound pickup and playback device.
La présente invention a une application principale dans le domaine de l1audio-conférence, dans lequel un dispositif de prise et de restitution de son est compris dans un ensemble unique de dimensions relativement faibles. Cet ensemble doit pouvoir être posé facilement sur une table et fonctionner dans une salle quelconque sans nécessité d'un traitement acoustique de ces locaux. On souhaite qu'il soit utilisable par une personne ayant une grande liberté de mouvement dans un rayon d'au moins 4 m autour du dispositif tout en continuant la conversation avec son interlocuteur dans des conditions de confort d'écoute normales pour les deux interlocuteurs.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. We would like it to be usable by a person with great freedom of movement within a radius of at least 4 m around the device while continuing the conversation with his interlocutor under normal listening comfort conditions for both interlocutors.
De préférence, il peut aussi être utilisé par un nombre quelconque de personnes réunies dans un même local et réparties autour du meuble sur lequel est posé le dispositif. Pour obtenir ces résultats, quatre conditions sont recherchées:Preferably, 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:
1. Le dispositif doit être associé à deux régulateurs automatiques de niveau qui assurent l'envoi en ligne d'un signal de niveau correct quelle que soit la puissance acoustique recueillie par le(s) microphone(s) du dispositif en fonction de la position du(des) locuteur(s) par rapport à ce(s) microphone(s) et l'envoi vers le(s) hauts-parleur(s) d'un signal de niveau correct quel que soit l'affaiblissement apporté par la ligne.1. 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.
2. Le son restitué par le(s) hauts-parleur(s) doit être perçu avec suffisamment de confort d'écoute indépendamment de la position occupée par 1' (les)auditeur(s) dans le local.2. 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.
3. Le son recueilli par le(s) microphone(s) doit garder des qualités de clarté, de netteté et d'agrément d'écoute suffisamment stables quelle que soit la position du(des) locuteur(s) par rapport au dispositif et quelle que soit la configuration du local.3. 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.
4. Le dispositif doit présenter un bon découplage acoustique entre le(s) hauts-parleur(s) et le(s) microphone(s) de manière à pouvoir assurer une écoute d'un niveau sonore suffisamment élevé sans provoquer d'effet LARSEN, mais aussi pour renvoyer le moins possible d'écho acoustique vers l'interlocuteur distant. On connaît actuellement des dispositifs opérationnels satisfaisant la condition 1.4. 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.
Il existe également des dispositifs qui privilégient la condition 4 en utilisant un microphone unique et quatre haut-parleurs orientés selon quatre directions espacées d'un angle de π/2 radians les unes des autres, et attaqués en opposition de phase deux par deux. Ce procédé permet effectivement d'obtenir un couplage faible car le microphone est placé en un point qui est un centre de symétrie par rapport aux haut- parleurs. Comme ces derniers sont attaqués en opposition de phase deux par deux, et à condition qu'ils aient des caractéristiques identiques, le son en provenance des haut-parleurs recueilli par le microphone sera très faible et donc le découplage sera très bon.There are also devices which favor condition 4 by using a single microphone and four loudspeakers oriented in four directions spaced by an angle of π / 2 radians from each other, and attacked in phase opposition two by two. This process effectively makes it possible to obtain a weak coupling because the microphone is placed at a point which is a center of symmetry with respect to the loudspeakers. As these are attacked in phase opposition two by two, and provided that they have identical characteristics, the sound coming from the speakers collected by the microphone will be very weak and therefore the decoupling will be very good.
Mais ce type de dispositif remplit mal les conditions 2 (à cause des déphasages de π radians entre haut-parleurs, le diagramme de rayonnement de 1'ensemble à haut-parleurs ne sera pas circulaire dans le plan horizontal et dépendra notablement des fréquences émises) et 3 (car le microphone capte indifféremment les sons directs et les sons réfléchis indirects, ce qui entraîne que la qualité du son capté par le microphone dépend trop largement de la position du locuteur dans le local et de la configuration de ce local) .But this type of device does not fulfill conditions 2 (because of the phase shifts of π 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).
Dans une demande de brevet français n° 9112125 déposée le 2 octobre 1991, la Demanderesse a proposé un procédé et un appareil de prise de son dont le but principal est de donner lieu à une faible sensibilité aux sons parvenant selon une direction prédéterminée. Un autre but de l'invention objet de cette demande de brevet est que, dans un plan perpendiculaire à la direction prédéterminée, on obtienne une sensibilité variant relativement peu en fonction de la direction d'où proviennent les sons et en fonction des composantes fréquencielles de ces sons.In a French patent application No. 9112125 filed on October 2, 1991, the Applicant has proposed a sound pick-up method and apparatus the main purpose of which is to give rise to low sensitivity to sounds arriving in a predetermined direction. Another object of the invention which is the subject of this patent application is that, in a plane perpendicular to the predetermined direction, a sensitivity varying relatively little is obtained as a function of the direction from which the sounds originate and as a function of the frequency components of these sounds.
Dans le cadre de l'utilisation préférée quoique non limitative de l'invention, objet de cette demande de brevet, à un dispositif d'audio-conférence à prise et restitution de son, la réalisation du but ci-dessus permet alors, en orientant un ou plusieurs haut-parleurs selon ladite direction prédéterminée, de satisfaire pleinement la condition 3 ci-dessus, tout en satisfaisant les conditions 1, 2 et 4 au moins aussi bien que les dispositifs de la technique antérieure.In the context of the preferred, although not limiting, use of the invention, the subject of this patent application, of an audio conference device with sound pickup and reproduction, 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.
L'invention objet de ladite demande de brevet français propose ainsi un procédé de prise de son utilisant plusieurs dispositifs de réception de son, selon lequel on dispose les dispositifs de réception de son sensiblement dans un même plan et on les répartit de façon symétrique par rapport à une direction de symétrie perpendiculaire à ce plan, on applique un déphasage entre les signaux issus respectivement de différents dispositifs de réception de son et on additionne les signaux ainsi déphasés, de façon à annuler sensiblement les signaux relatifs à toute onde sonore parvenant en phase et avec la même intensité sur chacun des dispositifs de réception de son.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.
Grâce à la disposition symétrique des dispositifs de réception de son, les sons incidents suivant la direction de symétrie leur parviennent en phase et avec la même intensité. Par conséquent, du fait des déphasages appliqués et de l'addition des signaux déphasés, ces sons incidents selon la direction de symétrie sont sensiblement éliminés après le traitement. En revanche, les sons incidents perpendiculairement à la direction de symétrie parviennent aux différents dispositifs de réception avec des différences de phase et/ou d'amplitude entre ces dispositifs. Ces sons sont donc conservés et correctement pris en compte.Thanks to the symmetrical arrangement of the sound reception 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. On the other hand, 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.
Selon une version préférée du procédé de cette invention, on utilise un nombre pair de dispositifs de réception de son qu'on associe par paires, les dispositifs de réception de son de chaque paire étant disposés symétriquement par rapport à la direction de symétrie, et on soustrait l'un de l'autre les signaux issus respectivement des dispositifs de réception de son de chaque paire pour les additionner avec un déphasage de 2 π radians entre eux.According to a preferred version of the method of this invention, 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 π radians between them.
Ainsi, les sons incidents suivant la direction de symétrie, ainsi que divers parasites peuvent être éliminés de manière efficace par une simple soustraction des signaux issus respectivement des dispositifs de réception de chaque paire. Cette soustraction peut avantageusement être effectuée conjointement à une préamplification au moyen d'un préamplificateur différentiel relié à la sortie des dispositifs de réception de chaque paire.Thus, 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.
De façon préférée, dans le procédé ci-dessus, on utilise 2n dispositifs de réception de son associés par paires et disposés à intervalles réguliers le long d'une circonférence centrée sur la direction de symétrie, n désignant un nombre entier au moins égal à deux, et on applique un déphasage de 2 π radians/2n entre les signaux issus respectivement de deux dispositifs de réception de son adjacents quelconques. Ces particularités permettent d'obtenir un diagramme de rayonnement régulier dans un plan perpendiculaire à la direction de symétrie. En principe, plus le nombre n de paires de dispositifs de réception de son est élevé, plus le diagramme de rayonnement dans le plan perpendiculaire à la direction de symétrie est homogène. En pratique, on constate qu'avec deux paires de dispositifs de réception, on peut obtenir un excellent compromis entre cette homogénéité et le coût des composants utilisés. La demande de brevet précitée a également pour second objet un système de prise de son conforme audit procédé.Preferably, in the above method, 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 π radians / 2n is applied between the signals originating respectively from any two adjacent sound reception devices. These features make it possible to obtain a regular radiation pattern in a plane perpendicular to the direction of symmetry. In principle, the higher the number n of pairs of sound receiving devices, the more homogeneous the radiation pattern in the plane perpendicular to the direction of symmetry. In practice, it can be seen that with two pairs of reception devices, an excellent compromise can be obtained between this homogeneity and the cost of the components used. The aforementioned patent application also has the second object of a sound recording system conforming to said process.
Suivant un troisième objet, l'invention objet de cette demande de brevet propose un appareil de prise et de restitution de son comprenant au moins un haut-parleur orienté suivant une direction de symétrie et des moyens de prise de son, dans lequel l'es moyens de prise de son comprennent un système conforme au second objet de l'invention, avec la direction de symétrie du système identique à la direction d'orientation du haut-parleur.According to a third object, 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.
Cet appareil est utilisable pour des audio¬ conférences et remplit de façon très satisfaisante les critères 1 à 4 énumérés au début de la présente description et donc satisfait aux buts fixés. La figure 1, qui sera détaillée ultérieurement, représente un tel appareil.This device can be used for audio-conferences and satisfies very satisfactorily the criteria 1 to 4 listed at the beginning of this description and therefore meets the set goals. Figure 1, which will be detailed later, shows such an apparatus.
Il comprend trois parties principales un socle 1 présentant une surface plane 20, un dispositif de prise de son 2 (microphones) et un dispositif de restitution de son 3 (haut-parleur) .It comprises three main parts, a base 1 having a flat surface 20, a sound pickup device 2 (microphones) and a sound reproduction device 3 (loudspeaker).
L'expérience a montré cependant qu'il était difficile de maîtriser et de minimiser de manière reproductible le couplage mécanique entre les dispositifs de prise de son 2 et de restitution de son 3, dans la configuration de l'appareil conforme à la demande précitée.Experience has shown, however, that it is difficult to master and reproducibly minimize the mechanical coupling between the sound pickup 2 and sound reproduction devices 3, in the configuration of the device according to the aforementioned request.
D'autre part, l'expérience a permis de constater également dans certaines conditions d'utilisation des irrégularités dans la courbe de réponse en amplitude fonction de la fréquence de la prise de son.On the other hand, experience has also shown under certain conditions of use irregularities in the amplitude response curve as a function of the frequency of the sound recording.
L'invention se fixe pour but, tout en conservant les avantages du dispositif de la demande de brevet français précitée, de pallier ces inconvénients. Pour ce faire, l'invention prévoit de fixer le dispositif de restitution de son directement sur la surface plane dudit socle et de doter la partie du dispositif de restitution de son vue du dispositif de prise de son d'une forme appropriée, c'est-à-dire une forme telle que son intersection avec un plan horizontal quelconque la traversant soit un cercle.The invention sets itself the aim, while retaining the advantages of the device of the aforementioned French patent application, of overcoming these drawbacks. To do this, 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.
Dans une variante préférée, il s'agit d'une forme convexe comprise entre deux formes limites: un cône et une demi-sphère.In a preferred variant, it is a convex shape comprised between two limiting shapes: a cone and a hemisphere.
Toujours dans une variante préférée, le dispositif de restitution de son est fixé sur le socle par l'intermédiaire d'entretoise de faibles dimensions. Avantageusement, on dispose quatre entretoises, régulièrement espacées de π/4 radians.Still in a preferred variant, the sound reproduction device is fixed to the base by means of spacers of small dimensions. Advantageously, there are four spacers, regularly spaced by π / 4 radians.
L'invention a donc pour objet un appareil de prise et de restitution de son d'au moins une source sonore, destiné à être posé sur un plan de travail, du type comprenant un support muni d'une surface plane, un dispositif de prise de son disposé sur cette surface plane et un dispositif de restitution de son, lesdits dispositifs de prise et de restitution de son étant disposés 1 'un par rapport à 1'autre de manière à présenter une structure de symétrie autour d'un axe de symétrie orthogonal à ladite surface plane, caractérisé en ce que le dispositif de restitution de son est fixé directement sur ladite surface plane; en ce que le dispositif de restitution s'inscrit à l'intérieur d'un cône de révolution d'axe confondu avec ledit axe de symétrie; ce cône étant obtenu en traçant un segment de droite entre un premier point distant d'une première longueur déterminée dudit axe de symétrie et d'une hauteur déterminée dudit plan de travail et un second point situé sur ladite surface plane et distant dudit axe de symétrie d'une seconde distance déterminée, le segment de droite coupant ledit axe de symétrie au sommet du cône, et en faisant tourner ce segment de droite d'un angle de révolution égal à 2 π radians; et en ce que la surface dudit dispositif de restitution de son en regard dudit dispositif de prise de son est dotée d'une forme comprise entre une demi-sphère et un cône. L'invention sera mieux comprise et d'autres caractéristiques et avantages apparaîtront à la lecture de la description qui suit en regard des figures annexées et parmi lesquelles: - la figure 1 représente une vue en coupe axiale d'un appareil conforme à la demande de brevet français n° 9112125;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 to 2 π radians; and in that the surface of said sound reproduction device opposite said sound recording device is provided with a shape comprised between a hemisphere and a cone. The invention will be better understood and other characteristics and advantages will appear on reading the description which follows with reference to the appended figures and among which: FIG. 1 represents a view in axial section of an apparatus in accordance with the request of French patent no. 9112125;
- la figure 2 représente une vue en coupe d'une partie de l'appareil représenté à la figure 1, prise selon le plan II-II indiqué sur la figure 1;- Figure 2 shows a sectional view of part of the apparatus shown in Figure 1, taken along the plane II-II indicated in Figure 1;
- la figure 3 représente un schéma d'ensemble des moyens de traitement des sons captés par les microphones de l'appareil des figures 1 et 2;- Figure 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;
- la figure 4 est un schéma explicitant la recommandation P34 du CCITT;- Figure 4 is a diagram explaining the CCITT recommendation P34;
- la figure 5 est un exemple de courbe de réponse en amplitude en fonction de la fréquence pour des dispositifs de prise de son conformes à la demande de brevet précité et à l'invention, respectivement; - la figure 6 illustre schématiquement un exemple de réalisation d'un appareil selon l'invention;- 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;
- les figures 7 et 8 illustrent schématiquement deux variantes de réalisation d'un dispositif de restitution de son incorporé dans un appareil conforme à l'invention;- Figures 7 and 8 schematically illustrate two alternative embodiments of a sound reproduction device incorporated in an apparatus according to the invention;
- la figure 9 illustre des dispositions spécifiques à l'invention.- Figure 9 illustrates specific provisions of the invention.
On va tout d'abord rappeler les principales caractéristiques du dispositif objet de la demande précitée, ce dans la mesure où elles ont une incidence sur la présente invention.We will first of all recall the main characteristics of the device which is the subject of the above-mentioned application, to the extent that they have an impact on the present invention.
On va se référer aux figures 1 et 2. L'appareil illustré sur ces figures comporte un boîtier 1, un corps ou dispositif de prise de son 2 dans lequel sont logés plusieurs dispositifs de réception de son Ml, M2, M3, M4, et un dispositif de restitution de son ou élément 3 dans lequel est monté un haut-parleur 4. Le corps 2 et 1'élément 3 ont une forme générale de révolution autour d'une direction de symétrie D. L'élément 3 est monté sur le corps 2 qui est lui-même monté sur le boîtier 1. Des matériaux isolants phoniquement, et/ou amortissants mécaniquement tels que 5, peuvent être interposés entre l'élément 3 et le corps 2, ou encore entre le corps 2 et la partie supérieure du boîtier 1. De façon générale, l'appareil a une structure symétrique autour de la direction D pour minimiser l'effet des vibrations mécaniques qui peuvent affecter les signaux produits par les microphones Ml, M2, M3 , M4.Reference will be made to FIGS. 1 and 2. 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. In general, 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.
Le boîtier 1 est muni à sa partie inférieure de pieds 6 en caoutchouc ou analogue pour poser l'appareil sur une surface horizontale telle qu'une table. La direction de symétrie D est alors verticale, ce qui est le cas général. Des circuits électriques 7, 8 sont montés à l'intérieur du boîtier 1. Ces circuits peuvent être raccordés comme indiqué schématiquement, en 9, 10 à la figure 1, à un système d'audio-conférence extérieur non représenté avec lequel fonctionne l'appareil selon l'invention. Ces circuits comprennent un circuit d'amplification 7 qui reçoit des signaux issus du système d'audio-conférence et les adresse sous forme amplifiée au haut-parleur 4 pour que celui-ci émette les sons correspondants, et des moyens de traitement 8 pour traiter les signaux issus des dispositifs élémentaires de réception de son Ml, m2, M3, M4, et les adresse après traitement au système d*audio-conférence. De façon connue, le circuit d'amplification 7 peut inclure, pour augmenter le confort d'écoute, une cellule électronique de correction de la courbe de réponse du haut-parleur 4, notamment pour renforcer les fréquences graves et supprimer d'éventuelles résonances ou anti-résonances. En outre, des moyens classiques d'annulation d'écho sont généralement montés entre les circuits 7 et 8. Dans l'exemple représenté, il y a quatre dispositifs élémentaires de réception de son, constitués chacun par un microphone unique Ml, M2 , M3 , M4. Ces quatre microphones Ml, M2 , M3 , M4 sont tous disposés dans un même plan horizontal P perpendiculaire à la direction de symétrie D.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. In a known manner, 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. In addition, conventional means of echo cancellation are generally mounted between circuits 7 and 8. In the example shown, there are four elementary sound reception devices, each consisting of a single microphone Ml, M2, M3 , M4. These four microphones Ml, M2, M3, M4 are all arranged in the same horizontal plane P perpendicular to the direction of symmetry D.
Comme on le voit à la figure 2, les quatre microphones Ml, M2, M3, M4 sont répartis symétriquement par rapport à la direction de symétrie D, qui est perpendiculaire au plan de la figure 2. Ces quatre microphones sont situés sur une circonférence 13 parallèle au P et centrée sur la direction de symétrie D. Ces quatre microphones sont associés par paires, respectivement Ml, M3 et M2, M4, les microphones de chaque paire étant disposés symétriquement par rapport à la direction de symétrie D, et les deux paires de microphones étant disposées suivant deux lignes radiales 14, 15 formant entre elles un angle droit. Chacun des microphones Ml, M2, M3, M4 est logé dans une cavité respective 12 usinée dans le corps 2. Ce corps 2 est métallique, par exemple en laiton. Il est traversé par un alésage axial 16 suivant la direction de symétrie D, et il comporte en outre quatre alésages radiaux 17, s'étendant chacun entre l'alésage axial 16 et l'une des quatre cavités 12. L'alésage axial 16 sert au passage des fils de raccordement (non représentés) du haut-parleur 4 au circuit d'amplification 7, avec un alésage correspondant 18 prévu à la base de 1élément 3. L'alésage axial 16 et les quatre alésages radiaux 17 servent au passage des fils de raccordement (non représentés) des microphones Ml, M2, M3, M4, aux moyens de traitement 8 situés dans le boîtier 1.As seen in Figure 2, 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. It is traversed by 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.
Les quatre microphones Ml, M2, M3, M4 sont avantageusement du type à condensateur, et ont une petite dimension (par exemple une forme cylindrique de diamètre 6 mm, et de hauteur 4,5 mm) . On sait que, pour une série de fabrication donnée, de tels microphones présentent sensiblement la même courbe de réponse, avec un décalage entre elles ne dépassant pas 3 à 4 décibels. Pour la réalisation de l'appareil, on peut donc facilement trier quatre microphones ayant des courbes de réponse identiques à une tolérance prédéterminée près (par exemple 0,5 décibel).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).
Le corps 2 est monté sur une plaque métallique plane 20, parallèle au plan P des microphones et constituant la face supérieure du boîtier 1. Le corps cylindrique 2 comporte un prolongement cylindrique axial 21, de plus petit diamètre qui s'appuie sur cette plaque plane 20 et qui définit un écartement 22 entre la plaque plane 20 et la surface 23 du corps 2 qui est parallèle au plan P, et sur laquelle débouchent les cavités usinées 12. Le prolongement 21 du corps 2 fournit une certaine isolation acoustique entre les microphones Ml, M2, M3, M4 vis-à-vis des sons parvenant dans un plan perpendiculaire à la direction de symétrie D. Comme on le voit à la figure 1, les cavités 12 ont une hauteur axiale supérieure à la hauteur des cylindres des microphones Ml, M2, M3, M4, et ces derniers sont enfoncés dans leurs cavités respectives 12 de façon à laisser un intervalle 24 entre le côté de chaque microphone faisant face à la plaque 20 et la surface 23 définissant le bord des cavités 12.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. 1, 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.
A l'arrière du microphone Ml, M2, M3, M4, chaque cavité 12 se prolonge en une partie 25 de diamètre plus faible qui définit un épaulement contre lequel s'appuie la face arrière du microphone, et dans laquelle débouche 1'alésage radial 17, donnant ainsi un espace pour les fils de raccordement non représentés.At the rear of the microphone M1, M2, M3, M4, 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.
L'élément 3 monté au-dessus du corps 2 forme une caisse de résonance pour le haut-parleur 4. Le haut- parleur 4 est monté dans l'élément 3 sur la direction de symétrie D, et orienté suivant cette direction de symétrie D, à l'opposé du plan P où sont situés les microphones Ml, M2, M3, M4. Ceci signifie que la membrane 29 du haut-parleur 4, qui a une forme de révolution autour d'un axe, est disposée dans l'élément 3 de façon que cet axe coïncide avec la direction de symétrie D de l'appareil, le bord extérieur 30 de cette membrane 29 étant situé dans un plan perpendiculaire à la direction de symétrie D. Pour une application à l'audio conférence, ce bord extérieur 30 de la memLrane 29 se situe typiquement entre 100 et 150 mm au-dessus de la surface horizontale sur laquelle est posé l'appareil. Une grille de protection 32 est montée à la partie supérieure de l'élément 3 pour protéger la membrane 29 du haut-parleur 4.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. This means that 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. For an application to audio conference, 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.
La surface périphérique extérieure 33 de 1 'élément 3 présente une courbure concave et se raccorde tangentiellement à la surface périphérique extérieure du corps 2, cette surface périphérique extérieure du corps 2 étant un cylindre défini par des génératrices sensiblement parallèles à la direction de symétrie D.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.
Au lieu de quatre microphones, on peut utiliser un nombre de microphones n supérieur à deux, toujours disposés à intervalles réguliers, sur une circonférence centrée par rapport à ladite direction de symétrie D. Dans une variante particulière de réalisation (non illustrée) , chaque dispositif élémentaire de réception est composé de plusieurs microphones et non pas d'un microphone unique comme représenté sur la figure 2 (respectivement les microphones Ml à M4) . Les signaux de sortie de ces microphones sont additionnés en phase. Dans une variante de réalisation préférée, on utilise des dispositifs élémentaires de réception de son en nombre pair, soit m = 2 n, avec m supérieur à trois. Ladite demande de brevet français prévoit aussi des moyens de traitement de signaux issus des dispositifs de réception de son agencés pour appliquer un déphasage égal à 2 π radians/n (ou 2 radians/m dans la dernière variante de réalisation précitée) entre les signaux issus respectivement de deux dispositifs de réception de son adjacents quelconques et pour additionner les signaux ainsi déphasés de façon à obtenir une réception sensiblement uniforme et non affaiblie de signaux relatifs aux composantes parallèles au plan P, quelle que soit la direction des ondes, et une réception sensiblement nulle des signaux relatifs aux composantes parallèles à la droite de symétrie D des ondes acoustiques captées.Instead of four microphones, it is possible to use a number of microphones n greater than two, always arranged at regular intervals, on a circumference centered with respect to said direction of symmetry D. In a particular variant of embodiment (not illustrated), 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. In a preferred embodiment, elementary sound reception devices are used in an even number, ie m = 2 n, with m greater than three. Said French patent application also provides means for processing signals from sound reception devices arranged to apply a phase shift equal to 2 π 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.
De façon pratique, on utilise des amplificateurs différentiels et des déphaseurs en cascade pour réaliser ces fonctions.In practical terms, differential amplifiers and cascade phase shifters are used to perform these functions.
La figure 3 représente schématiquement un exemple de réalisation des moyens de traitement 8 des signaux issus des microphones Ml, M2, M3, M4. Ces moyens de traitement comprennent d'une part deux préamplificateurs différentiels A13, A24 d'entrées El à E4, fournissant les signaux respectifs S13 et S14, et deux canaux déphaseurs D13, D24 pour appliquer un déphasage entre les signaux issus respectivement de différents microphones de sorties SD13 et SD14, et d'autre part un circuit additionneur 40 prévu pour faire la somme des signaux déphasés issus des canaux déphaseurs D13, D24. A la sortie ST du circuit additionneur 40 est monté un circuit 41 qui met en forme les signaux en vue de leur transmission vers le système d'audio-conférence extérieur (non représenté) et fournit un signal de sortie VS. Conformément à l'invention, les déphasages appliqués et l'addition effectuée sont tels que les signaux relatifs à toute onde sonore parvenant en phase et avec la même intensité sur chacun des microphones Ml, M2, M3, M4 soient sensiblement annulés en sortie du circuit additionneur 40. En particulier, lorsque 1'appareil est posé horizontalement sur une table, les sons émis par le haut-parleur 4 et réfléchis par le plafond horizontal situé au-dessus de l'appareil parviennent vers les quatre microphones selon la direction de symétrie D et présentent, compte tenu de la disposition symétrique des microphones, une phase et une intensité identiques sur chacun des microphones. Par conséquent, ces signaux réfléchis sont avantageusement éliminés du signal de sortie du circuit de traitement 8. En outre, la structure symétrique du système de prise de son assure que les vibrations mécaniques de 1'appareil parviendront de manière identique à chacun des microphones. Par conséquent, l'effet de ces vibrations sur les microphones est également éliminé du signal de sortie du circuit de traitement 8.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. At the output ST of the adder circuit 40 is mounted 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. In accordance with the invention, 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. In particular, when the device is placed horizontally on a table, 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. In addition, 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.
Dans l'exemple représenté à la figure 3, un préamplificateur différentiel A13 (respectivement A24) comporte deux entrées El, E3 (respectivement E2, E4) reliées chacune à l'un des microphones Ml, M3 (respectivement M2, M4) d'une paire de microphones disposés en position diamétralement opposée par rapport à la direction de symétrie D. Les préamplificateurs différentiels A13, A24 effectuent une préamplification des signaux de sortie des microphones, éliminent certains parasites présents dans ces signaux de sortie. Dans cette combinaison sont donc éliminés les contributions des sons parvenant aux microphones suivant la direction de symétrie D et les effets des vibrations mécaniques symétriques. Dans l'application préférée de l'appareil à 1'audio-conférence, les sons émis par des locuteurs sont ainsi pris en compte de façon satisfaisante quelle que soit la position de ces locuteurs par rapport à l'appareil, tandis que les échos du haut-parleur sont sensiblement éliminés. En outre, la disposition des microphones Ml, M2, M3, M4 dans le corps 2 (figure 1) et la présence des zones de pression entre ce corps 2 (figure 1) et la plaque métallique 20 (figure 1) réfléchissant les ondes sonores éliminent en grande partie les échos indirects parvenant aux microphones.In the example shown in FIG. 3, 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. In the preferred application of the device to audio conference, 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. In addition, 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.
Ces dispositions sont entièrement conservées dans le cadre de la présente invention.These provisions are entirely preserved in the context of the present invention.
Grâce aux dispositions structurelles telles que décrites en relation avec les figures 1 et 2 et aux dispositions concernant les circuits de traitement 8 qui viennent d'être rappelées en relation avec la figure 3, l'appareil de prise et de restitution de son remplit de façon très satisfaisante les critères l à 4 du préambule de la présente description.Thanks to the structural arrangements as described in relation to FIGS. 1 and 2 and to the arrangements concerning the processing circuits 8 which have just been recalled in connection with FIG. 3, the apparatus for taking and restoring its sound fills in a manner very satisfactory criteria l to 4 of the preamble of this description.
Cependant, comme il a été indiqué, l'expérience a montré qu'il était difficile de maîtriser et de minimiser de manière reproductible le couplage mécanique entre le dispositif de prise de son 2 (figure 1) et le dispositif de restitution 3. De façon plus précise, si on se reporte de nouveau au dispositif de la figure 1, il est difficile d'obtenir que chaque microphone (Ml à M4 dans 1 'exemple illustré) reçoive la même vibration mécanique en amplitude et en phase, même si on utilise un matériau isolant 5.However, as indicated, experience has shown that it is difficult to control and reproducibly minimize the mechanical coupling between the sound pickup device 2 (Figure 1) and the playback device 3. More specifically, if we refer again to the device of Figure 1, it is difficult to obtain that each microphone (Ml to M4 in 1 example illustrated) receives the same mechanical vibration in amplitude and phase, even if an insulating material is used 5.
D'autre part, dans certaines conditions d'utilisation, l'expérience a montré également que la courbe de réponse en fréquence de la prise de son présentait des irrégularités. En particulier, ces conditions existent généralement si on se place dans le cadre de la recommandation P34 du CCITT.On the other hand, under certain conditions of use, experience has also shown that the frequency response curve of the sound recording exhibits irregularities. In particular, these conditions generally exist if one falls within the framework of CCITT recommendation P34.
La figure 4 illustre schématiquement quelques caractéristiques de cette recommandation. On utilise une bouche artificielle Bart pour tester la réception d'un appareil d*audio-conférence Aac, par exemple un appareil du type de celui décrit en relation avec la figure 1. Cet appareil Aac est posé sur un plan, par exemple une table Ta utilisée pour 1 'audio-conférence. La bouche artificielle Bart est disposée à la verticale et à une hauteur h du bord de la table Ta. L'angle a est donc égal à π/2 radians. Le bord de la table est à une distance 12 de l'appareil Aac et la bouche artificielle Bart à la distance 1, de l'appareil Aac. Dans ces conditions, les valeurs respectives de ces paramètres sont: h = 300 mm 1*^ = 500 mm 12 = 400 mm Dans les conditions de mesure précitées, on obtient avec le dispositif de la figure 1 une courbe C-, de réponse d'amplitude en fréquence typique illustrée par la figure 5. L'axe vertical gradué en dB, représente l'amplitude AS du signal VS (figure 3) en fonction de la fréquence F portée sur l'axe horizontal.Figure 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 π / 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. Under these conditions, the respective values of these parameters are: h = 300 mm 1 * ^ = 500 mm 1 2 = 400 mm Under the aforementioned measurement conditions, we obtain with the device of FIG. 1 a curve C-, of response typical frequency amplitude illustrated by FIG. 5. The vertical axis graduated in dB represents the amplitude AS of the signal VS (FIG. 3) as a function of the frequency F carried on the horizontal axis.
Plus précisément, les conditions d'obtention de la courbe Cl est la suivante: - courbe non i issée relevée dans une pièce non traitée acoustiquemerrc;More specifically, the conditions for obtaining the curve C1 is as follows: - unissued curve raised in a room not acoustically treated;
- réalisation d'une transformée de Fourrier rapide sur une réponse impulsionnelle limitée à un intervalle de temps de 10 ms pour éliminer les accidents dus à des réflexions lointaines sur les murs et le plafond de la pièce.- realization of a fast Fourier transform on an impulse response limited to a time interval of 10 ms to eliminate accidents due to distant reflections on the walls and the ceiling of the room.
La courbe Cl présente un "trou" d'une profondeur de 12 dB environ et d'une largeur de l'ordre de 100 Hz pour une fréquence comprise habituellement dans l'intervalle de fréquence allant de 2000 Hz à 2500 Hz environ. Dans le cas présent, la fréquence centrale de l'irrégularité est de 2,2 KHz environ. La courbe présente typiquement une croissance de 3 dB par octave avec des ondulations de l'ordre de + 2 dB dépendant des réponses propres de chaque microphone et de la qualité de leur appairage. Cette croissance de 3 dB par octave est préconisée par la recommandation P34.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.
On a tracé une droite C3 de pente 3 dB par octave qui s'approche de l'allure qu'aurait la courbe Cl parfaitement "lissée", ce dans un but de faciliter la lecture de celle-ci et les comparaisons avec la courbe C2 qui sera décrite ultérieurement.We have drawn a straight line C3 with a slope of 3 dB per octave which approaches the shape that the perfectly smoothed curve C1 would have, in order to facilitate its reading and comparison with curve C2 which will be described later.
On doit naturellement comprendre que le détail de cette courbe Cl dépend de la nature et des caractéristiques des microphones Ml à M4, de la configuration de la table Ta, de la position angulaire du dispositif de prise de son par rapport à la source Bart, de la pression atmosphérique, etc... Cette courbe n'est donnée qu'à titre de meilleure illustration du phénomène parasite constaté.It should naturally be understood that the detail of this curve Cl depends on the nature and the characteristics of the microphones Ml to M4, on the configuration of the table Ta, on the angular position of the sound pickup device relative to the source Bart, on atmospheric pressure, etc. This curve is given only as a better illustration of the parasitic phenomenon observed.
L'invention tout en conservant les avantages du dispositif décrit en relation avec la figure 1, vise à pallier les deux défauts qui viennent d'être rappelés. Pour ce faire, si on se reporte à nouveau à la figure 1, on va éloigner le dispositif 3 du dispositif 2. Mais pour conserver à l'ensemble un aspect compact, il faut que cet éloignement reste le plus faible possible. Pour pallier plus spécifiquement le premier défaut, on va fixer directement le dispositif 3 non plus sur le dispositif 2, avec ou sans l'intermédiaire d'un matériau isolant 5, mais directement sur la surface du plan 20.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.
Dans une variante préférée on le fixe à l'aide d'entretoises, près du bord extérieur de ce plan 20.In a preferred variant, it is fixed using spacers, near the outer edge of this plane 20.
Pour pallier plus spécifiquement le second défaut, on dote la partie du dispositif 3 qui est en "vue" du dispositif 2, c'est-à-dire dans l'exemple illustré sur la figure 1, la partie inférieure surface 33, d'une forme appropriée qui va être explicitée dans ce qui suit.To more specifically remedy the second defect, we endow the part of the device 3 which is in "view" of the device 2, that is to say in the example illustrated in FIG. 1, the lower surface part 33, of an appropriate form which will be explained in the following.
La figure 6 illustre schématiquement un appareil de prise et de restitution de son Aac conforme à 1*invention.FIG. 6 schematically illustrates a device for taking and restoring its Aac according to the invention.
A l'exception des dispositions spécifiques à l'invention, les autres dispositions qui ont été décrites en relation avec les figures 1 à 3 sont conservées et ne seront redécrites qu'en tant que de besoin.With the exception of the provisions specific to the invention, the other provisions which have been described in relation to FIGS. 1 to 3 are retained and will only be re-described as necessary.
En particulier le dispositif de prise de son 2 peut être identique à celui décrit en relation avec les figures 1 et 2 ou à ses variantes possibles qui ont été signalées. Il en est de même pour le boîtier 1, le plan 20, et les circuits électriques de traitement et d'amplification (respectivement 7 et 8) contenus dans le boîtier 1. Ces circuits pourraient naturellement être disposés en dehors de ce boîtier 1, mais la disposition à l'intérieur du boîtier 1 présente l'avantage de réduire la longueur des connexions entre les circuits d'amplification et le haut-parleur, d'une part; et les circuits de traitement 7 et les microphones Ml à M4, d'autre part.In particular, 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.
On conserve naturellement la symétrique de révolution autour de l'axe D.We naturally keep the symmetric of revolution around the axis D.
Les éléments de la figure 6 identiques ou similaires à ceux de la figure 1 portent la même référence et ne seront également redécrits qu'en cas de besoin.The elements of Figure 6 identical or similar to those of Figure 1 bear the same reference and will also be rewritten only when necessary.
Selon une des caractéristiques importantes de l'invention, le dispositif de restitution de son 3 n'est plus couplé mécaniquement au dispositif de prise de sonAccording to one of the important characteristics of the invention, the sound reproduction device 3 is no longer mechanically coupled to the sound recording device
2. Dans la variante de réalisation préférée illustrée par la figure 6, le dispositif 3 est fixé directement au boîtier 1, de préférence près des bords du plan 20, à l'aide d'entretoises ou d'éléments analogues, au nombre de quatre Etl à Et4 (dans l'exemple illustré) et régulièrement espacées. Sur la figure 6, l'entretoise Et2 n'est pas visible. Dans le cas présent, l'espacement entre entretoises est de π/4 radians.2. In the preferred embodiment illustrated in FIG. 6, 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. In FIG. 6, the spacer Et2 is not visible. In the present case, the spacing between spacers is π / 4 radians.
En coupe horizontale, la forme des entretoises Etl à Et4 peut être quelconque: ronde, ovale, triangulaire, etc... Cependant la dimension la plus importante doit rester faible, typiquement comprise dans une gamme de 10 à 17 mm. Cette dimension, ainsi que la matière seront choisies en fonction du poids et des dimensions du dispositif 3, d'une part, et pour éviter toutes vibrations parasites d'autre part.In horizontal section, 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.
Le nombre de ces entretoises n'est pas critique non plus mais il paraît difficile de descendre en dessous de trois pour assurer une stabilité et une rigidité minimale à l'ensemble. A l'opposé, leur nombre ne peut croître indéfiniment car elles doivent être "transparentes" aux ondes sonores. Du moins l'effet d'écran doit être négligeable.The number of these spacers is not critical either but it seems difficult to descend below three to ensure stability and minimum rigidity to the assembly. Conversely, their number cannot grow indefinitely because they must be "transparent" to sound waves. At least the screen effect must be negligible.
Un nombre égal à trois ou quatre est un compromis acceptable.A number equal to three or four is an acceptable compromise.
Le moyen de fixation de ces entretoises Etl à Et4, d'une part, au dispositif 3 et, d'autre part, au boîtier 1, est choisi parmi les moyens classiques connus: vissage, etc. Selon une autre caractéristique importante de l'invention, on dote la partie du dispositif 3 en "vue" du dispositif 2 d'une forme appropriée, en l'occurrence la surface inférieure 33 du dispositif 3. Celle-ci est de préférence convexe mais peut être comprise entre un cône et une demi-sphère, qui constituent les deux formes extrêmes. Dans le cas d'un cône, on doit éliminer le cas limite pour lequel l'angle au sommet est égal à π radians, c'est-à-dire une forme dégénérée qui tend vers un plan. En effet, dans ce cas, il existe un risque qu'il se développe des ondes stationnaires entre le plan 20 et la surface 33.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. According to another important characteristic of the invention, 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. In the case of a cone, we must eliminate the borderline case for which the apex angle is equal to π radians, that is to say a degenerate shape which tends towards a plane. In fact, in this case, there is a risk that standing waves will develop between the plane 20 and the surface 33.
Les figures 7 et 8 illustrent les deux cas extrêmes: forme conique (figure 7) et sphérique (figureFigures 7 and 8 illustrate the two extreme cases: conical (figure 7) and spherical (figure
8) . Outre les formes intermédiaires, on peut imaginer des formes combinant ces deux aspects, par exemple une forme conique, dans la partie inférieure de la surface 33 se transforme en forme convexe dans la partie supérieure. Le choix précis d'une forme, parmi celles possibles, sera guidé plus par des considérations pratiques (simplicité de réalisation par exemple) ou esthétique que par des raisons purement techniques. En outre, il est le plus souvent requis de conserver un aspect compact à l'appareil comme il a été indiqué. La partie inférieure du dispositif 3 doit donc être disposée le plus près possible du dispositif 2. Cependant un rapprochement trop important du dispositif de restitution de son 3 du dispositif de prise de son 2 est incompatible avec le but que se fixe l'invention car l'expérimentation a montré que la courbe de réponse d'amplitude en fréquence présenterait à nouveau des irrégularités.8). In addition to the intermediate shapes, one can imagine shapes combining these two aspects, for example a conical shape, in the lower part of the surface 33 is transformed into a convex shape in the upper part. The precise choice of a form, among those possible, will be guided more by practical considerations (simplicity of realization for example) or esthetic than by purely technical reasons. In addition, it is most often required to keep a compact appearance to the device as indicated. The lower part of the device 3 must therefore be placed as close as possible to the device 2. However, bringing the sound reproduction device 3 too close to the sound recording device 2 is incompatible with the aim which the invention sets for itself. Experimentation has shown that the frequency amplitude response curve will again show irregularities.
On suppose que la source sonore, artificielle ou humaine, est à une hauteur h du plan de la table Ta ou de tout autre plan sur lequel est disposé l'appareil de prise et de restitution de son Aac et à une distance 12 (projection sur le plan Ta) du bord du boîtier 1.It is assumed that the sound source, artificial or human, 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.
La figure 9 explicite quelles sont les conditions auxquelles devra souscrire la disposition dans l'espace du dispositif 3. Sur cette figure on n'a pas représenté les entretoises Etl à Et4. FIG. 9 explains what are the conditions to which the arrangement must subscribe in the space of the device 3. In this figure, the spacers Et1 to Et4 have not been shown.
position que le dispositif 3 sera le plus proche du dispositif de prise de son 2 tout en satisfaisant aux conditions précédemment énoncées.position that the device 3 will be closest to the sound pickup device 2 while meeting the conditions set out above.
Egalement dans une variante de réalisation préférée, on agencera les dispositifs 3 et 2 de telle manière que la recommandation P34 définie par le CCITT soit respectée.Also in a preferred embodiment, the devices 3 and 2 will be arranged in such a way that the recommendation P34 defined by the CCITT is respected.
Dans ces conditions 12 = 400 mm et h = 300 mm La valeur de x, inférieure à la circonférence du boîtier 1, est typiquement de l'ordre de 140 mm, cette valeur n'étant cependant pas limitative de l'invention. On définit donc un cercle sur la surface 20, de rayon égal à x/2 et centrée sur l'axe D. Avec les dispositions adoptées dans le cadre de l'invention, on a retracé la courbe C2 de réponse d'amplitude en fonction de la fréquence, dans les mêmes conditions que précédemment pour le dispositif de la figure 1. On peut comparer, en se reportant à nouveau à la figure 5, la nouvelle courbe obtenue C2 à la courbe primitive Cl.Under these conditions 1 2 = 400 mm and h = 300 mm The value of x, less than the circumference of the housing 1, is typically of the order of 140 mm, this value however not being limiting of the invention. A circle is therefore defined on the surface 20, of radius equal to x / 2 and centered on the axis D. With the arrangements adopted in the context of the invention, the curve C2 of amplitude response as a function has been traced of the frequency, under the same conditions as previously for the device of FIG. 1. One can compare, by referring again to FIG. 5, the new curve obtained C2 with the primitive curve Cl.
On voit aisément si elle présente encore une irrégularité pour une fréquence centrée sur 2,2 KHz, environ, celle-ci est de bien plus faible amplitude, de l'ordre de -4 à -5 dB (dans l'exemple illustré) par rapport à la courbe "lissée" C3 et de très faible largeur.It is easy to see if it still has an irregularity for a frequency centered on 2.2 KHz, approximately, this is much lower amplitude, of the order of -4 to -5 dB (in the example illustrated) by compared to the "smoothed" curve C3 and of very small width.
Le dispositif de prise de son 2 est par ailleurs identique à celui utilisé dans l'appareil représenté sur la figure 1. Il en est de même des circuits électroniques 7 et 8. En outre dans le dispositif de restitution de son 3, le transducteur (haut-parleur 4) est identique à celui précédemment utilisé. D'autres mesures, effectuées par la Demanderesse, de façon répétitive sur plusieurs appareils réalisés conformément aux enseignements de l'invention, ont montré que les vibrations mécaniques dues, essentiellement dans l'appareil de la figure ., au c '-plage mécanique entre le dispositif 2 et 3 , étaient déso_ ,.*ais négligeables. Il s'ensuit que, même si chacun des microphones en capte une fraction non homogène, en amplitude et en phase, les différences dues à cette non-homogénéité n'entraînent plus un dysfonctionnement appréciable du dispositif de prise de son 2.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. In addition, in the sound reproduction device 3, 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.
L'invention n'est pas limitée aux exemples de réalisation précisément décrits en relation notamment avec les figures 6 à 9. On doit bien comprendre, en particulier que les exemples numériques n'ont été donnés que pour mieux illustrer l'invention et ne sont en aucun cas limitatifs de sa portée. The invention is not limited to the embodiments precisely described in relation in particular to FIGS. 6 to 9. It should be understood, in particular that the numerical examples have been given only to better illustrate the invention and are not in no way limiting its scope.

Claims

REVENDICATIONS
1. Appareil de prise et de restitution (Aac) de son d'au moins une source sonore (SB, SA) , destiné à être posé sur un plan de travail (Ta) du type comprenant un support (1) muni d'une surface plane (20) , un dispositif de prise de son (2) disposé sur cette surface plane (20) et un dispositif de restitution de son (3) , lesdits dispositifs de prise et de restitution de son étant disposés l'un par rapport à l'autre de manière à présenter une structure de symétrie autour d'un axe de symétrie (D) orthogonal à ladite surface plane (20) , caractérisé en ce que le dispositif de restitution de son est fixé directement sur ladite surface plane (20) ; en ce que le dispositif de restitution (3) s'inscrit à l'intérieur d'un cône de révolution d'axe confondu avec ledit axe de symétrie (D) ; ce cône étant obtenu en traçant un segment de droite (B'B) entre un premier point (B') distant d'une première longueur déterminée dudit axe de symétrie (D) et d'une hauteur déterminée (h) dudit plan de travail (Ta) et un second point (B) situé sur ladite surface plane (20) et distant dudit axe de symétrie d'une seconde distance déterminée (x/2) , le segment de droite (BB1) coupant ledit axe de symétrie (D) au sommet du cône (C) , et en faisant tourner ce segment de droite (B'B) d'un angle de révolution égal à 2 ÎΓ radians; et en ce que la surface (33) dudit dispositif de restitution de son (3) en regard dudit dispositif de prise de son (2) est dotée d'une forme comprise entre une demi-sphère (figure 8) et un cône (figure 7) . 1. Apparatus for taking and restoring (Aac) sound from at least one sound source (SB, SA), intended to be placed on a work surface (Ta) of the type comprising a support (1) provided with a flat surface (20), a sound pickup device (2) disposed on this flat surface (20) and a sound reproduction device (3), said sound pickup and reproduction devices being arranged one relative to the other to the other so as to present a structure of symmetry about an axis of symmetry (D) orthogonal to said flat surface (20), characterized in that the sound reproduction device is fixed directly to said flat surface (20 ); in that the restitution device (3) fits inside a cone of revolution with an axis coincident with said axis of symmetry (D); this cone being obtained by tracing a line segment (B'B) between a first point (B ') distant by a first determined length of said axis of symmetry (D) and by a determined height (h) of said work plane (Ta) and a second point (B) located on said planar surface (20) and distant from said axis of symmetry by a second determined distance (x / 2), the line segment (BB 1 ) intersecting said axis of symmetry ( D) at the top of the cone (C), and by rotating this line segment (B'B) by an angle of revolution equal to 2 ÎΓ radians; and in that the surface (33) of said sound reproduction device (3) facing said sound pickup device (2) has a shape comprised between a hemisphere (FIG. 8) and a cone (FIG. 7).
2. Appareil selon la revendication 1, caractérisé en ce que ledit dispositif de restitution de son (3) est fixé à ladite surface plane (20) par l'intermédiaire d'entretoises (Etl à Et4) équiréparties.2. Apparatus according to claim 1, characterized in that said sound reproduction device (3) is fixed to said flat surface (20) by means of spacers (Etl to Et4) distributed equally.
3. Appareil selon la revendication 2, caractérisé en ce que le nombre d'entretoises (Etl à Et4) est égal à quatre.3. Apparatus according to claim 2, characterized in that the number of spacers (Etl to Et4) is equal to four.
4. Appareil selon l'une quelconque des revendications 1 à 3 , caractérisé en ce que ledit support étant inscrit dans une structure de révolution constituée par un cylindre d'axe confondu avec ledit axe de symétrie (D) , de rayon r, la première distance déterminée 1 est définie comme suit: 1 = 400 mm + r, la hauteur (h) est égale à 300 mm et la seconde distance déterminée (x/2) sensiblement égale à 70 mm.4. Apparatus according to any one of claims 1 to 3, characterized in that said support being inscribed in a structure of revolution constituted by a cylinder of axis coincident with said axis of symmetry (D), of radius r, the first determined distance 1 is defined as follows: 1 = 400 mm + r, the height (h) is equal to 300 mm and the second determined distance (x / 2) substantially equal to 70 mm.
5. Appareil selon l'une quelconque des revendications 1 à 4, caractérisé en ce que la surface (33) dudit dispositif de restitution de son (3) en regard dudit dispositif de prise de son (2) est dotée d'une forme convexe.5. Apparatus according to any one of claims 1 to 4, characterized in that the surface (33) of said sound reproduction device (3) facing said sound pickup device (2) has a convex shape .
6. Appareil selon l'une quelconque des revendications 1 à 4, caractérisé en ce que la surface (33) dudit dispositif de restitution de son (3) en regard dudit dispositif de prise de son (2) est un cône (figure 7) d'angle au sommet inférieur à π radians.6. Apparatus according to any one of claims 1 to 4, characterized in that the surface (33) of said sound reproduction device (3) facing said sound pickup device (2) is a cone (Figure 7) vertex angle less than π radians.
7. Appareil selon l'une quelconque des revendications 1 à 6, caractérisé en ce que le dispositif de restitution de son (3) comprend au moins un haut- parleur (4), en ce qu'il comprend une face active (31) destinée à rayonner les ondes acoustiques et en ce que la direction moyenne de rayonnement est confondue avec ledit axe de révolution (D) , dans une direction opposée à ladite surface (33) en regard avec le dispositif de restitution de son (2) .7. Apparatus according to any one of claims 1 to 6, characterized in that the sound reproduction device (3) comprises at least one loudspeaker (4), in that it comprises an active face (31) intended to radiate the acoustic waves and in that the mean direction of radiation coincides with said axis of revolution (D), in a direction opposite to said surface (33) opposite with the sound reproduction device (2).
8. Appareil selon l'une quelconque des revendications 1 à 7, caractérisé en ce que ledit dispositif de prise de son (2) comprend plusieurs dispositifs élémentaires de réception de son (Ml à M4) en nombre n supérieur à deux, et des moyens de traitement8. Apparatus according to any one of claims 1 to 7, characterized in that said sound pickup device (2) comprises several elementary sound reception devices (Ml to M4) in number n greater than two, and means treatment
(8) pour traiter les signaux issus des dispositifs de réception de son, en ce que les dispositifs élémentaires de réception de son (Ml à M4) sont disposés dans un même plan (P) , perpendiculaire audit axe de symétrie (D) , à intervalles réguliers, sur une circonférence (13) centrée par rapport audit axe de symétrie (D) , en ce que lesdits moyens de traitement (8) sont agencés pour appliquer un déphasage égal à 2 π/n radians entre les signaux issus respectivement de deux dispositifs de réception élémentaires de son adjacents quelconques et pour additionner les signaux ainsi déphasés de façon à obtenir une réception sensiblement uniforme et non affaiblie de signaux relatifs aux composantes parallèles au plan (P) quelle que soit la direction des ondes et une réception sensiblement nulle des signaux relatifs aux composantes parallèles à la droite de symétrie (D) , des ondes acoustiques captées. (8) for processing the signals from the sound reception devices, in that the elementary sound reception devices (Ml to M4) are arranged in the same plane (P), perpendicular to said axis of symmetry (D), regular intervals, on a circumference (13) centered with respect to said axis of symmetry (D), in that said processing means (8) are arranged to apply a phase shift equal to 2 π / n radians between the signals from respectively of any two elementary reception devices of any adjacent sound and for adding the signals thus phase shifted so as to obtain a substantially uniform reception and not weakened of signals relating to the components parallel to the plane (P) whatever the direction of the waves and a reception substantially zero of the signals relating to the components parallel to the line of symmetry (D), of the acoustic waves picked up.
9. Appareil selon la revendication 8, caractérisé en ce que chaque dispositif élémentaire de réception de son comprend un microphone unique (Ml à M4) .9. Apparatus according to claim 8, characterized in that each elementary sound reception device comprises a single microphone (Ml to M4).
10. Appareil selon la revendication 8, caractérisé en ce que chaque dispositif élémentaire de réception de son est composé de plusieurs microphones, et en ce que les moyens de traitement (8) sont agencés pour additionner en phase les signaux issus respectivement des microphones composant chaque dispositif élémentaire de réception de son pour établir le signal de sortie de ce dispositif de réception de son.10. Apparatus according to claim 8, characterized in that each elementary sound reception device is composed of several microphones, and in that the processing means (8) are arranged to add in phase the signals originating respectively from the microphones composing each basic sound receiving device for establishing the output signal of this sound receiving device.
11. Appareil selon l'une quelconque des revendications 8 à 10, caractérisé en ce que lesdits dispositifs élémentaires de réception de son (Ml à M4) sont en nombre pair m = 2n supérieur à trois, en ce qu'ils sont associés deux à deux, en n paires, en ce que les dispositifs élémentaires de réception de son de chacune desdites paires sont disposés symétriquement par rapport à ladite direction de symétrie (D) , en ce que les moyens de traitement (8) sont agencés pour que les signaux issus respectivement des dispositifs de réception de chaque paire soient soustraits l'un de l'autre pour les additionner avec un déphasage de 2 π radians entre eux, en ce qu'un déphasage est appliqué sur chaque signal (S13, S14) issu d'une paire pour obtenir un déphasage de 2 π/m radians entre les signaux issus respectivement de deux paires de dispositifs de réception de son adjacents quelconques et en ce que les signaux ainsi déphasés sont additionnés. 11. Apparatus according to any one of claims 8 to 10, characterized in that said elementary sound reception devices (Ml to M4) are in even number m = 2n greater than three, in that they are associated two to two, in n pairs, in that the elementary sound reception devices of each of said pairs are arranged symmetrically with respect to said direction of symmetry (D), in that the processing means (8) are arranged so that the signals respectively from the reception devices of each pair are subtracted from each other to add them with a phase shift of 2 π radians between them, in that a phase shift is applied to each signal (S13, S14) from a pair to obtain a phase shift of 2 π / m radians between the signals originating respectively from two pairs of any adjacent sound reception devices and in that the signals thus phase shifted are added.
12. Application à 1'audio-conférence d'un appareil de prise et de restitution de son (Aac) selon l'une quelconque des revendications 1 à 11. 12. Application to audio conference of a sound pickup and restitution device (Aac) according to any one of claims 1 to 11.
EP94907599A 1993-03-19 1994-02-18 Sound pick-up and reproduction apparatus and use thereof for conference calls Expired - Lifetime EP0710427B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FR9303216 1993-03-19
FR9303216A FR2702918B1 (en) 1993-03-19 1993-03-19 Sound recording and reproducing apparatus, and its application to audio conference.
PCT/FR1994/000188 WO1994022277A1 (en) 1993-03-19 1994-02-18 Sound pick-up and reproduction apparatus and use thereof for conference calls

Publications (2)

Publication Number Publication Date
EP0710427A1 true EP0710427A1 (en) 1996-05-08
EP0710427B1 EP0710427B1 (en) 1997-03-26

Family

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Application Number Title Priority Date Filing Date
EP94907599A Expired - Lifetime EP0710427B1 (en) 1993-03-19 1994-02-18 Sound pick-up and reproduction apparatus and use thereof for conference calls

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EP (1) EP0710427B1 (en)
AU (1) AU6111194A (en)
DE (1) DE69402322T2 (en)
ES (1) ES2100052T3 (en)
FR (1) FR2702918B1 (en)
WO (1) WO1994022277A1 (en)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2743685B1 (en) * 1996-01-17 1998-02-20 Prescom Sarl SOUND-TAKING APPARATUS AND SOUND-TAKING AND SOUND-MAKING APPARATUS
WO1999046956A1 (en) * 1998-03-09 1999-09-16 Brian Turnbull Radial pickup microphone enclosure
DE102013219636A1 (en) * 2013-09-27 2015-04-02 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. DEVICE AND METHOD FOR TRANSFERRING A SOUND SIGNAL

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Publication number Priority date Publication date Assignee Title
FR2358800A1 (en) * 1976-07-16 1978-02-10 Pontet Robert Sound pick=up for telephone conference - has omnidirectional microphone at focal point of parabolic recess of plaster or fibre glass block
CA1050154A (en) * 1977-01-14 1979-03-06 Conrad D. Lafrance Telephone conferencing apparatus
FR2617660B1 (en) * 1987-06-30 1990-06-08 Larvor Rene SOUND RECORDING AND RESTITUTION DEVICE, PARTICULARLY FOR AUDIO-CONFERENCES
FR2670351B1 (en) * 1990-12-05 1997-04-30 France Etat SOUND RECORDING AND RESTITUTING APPARATUS.
FR2682251B1 (en) * 1991-10-02 1997-04-25 Prescom Sarl SOUND RECORDING METHOD AND SYSTEM, AND SOUND RECORDING AND RESTITUTING APPARATUS.

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9422277A1 *

Also Published As

Publication number Publication date
FR2702918A1 (en) 1994-09-23
DE69402322T2 (en) 1997-10-23
FR2702918B1 (en) 1995-05-12
DE69402322D1 (en) 1997-04-30
WO1994022277A1 (en) 1994-09-29
AU6111194A (en) 1994-10-11
ES2100052T3 (en) 1997-06-01
EP0710427B1 (en) 1997-03-26

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