EP0297975B1 - Sound pick-up and reproduction device, particularly for audio conferences - Google Patents

Description

The present invention relates to a device for picking up and reproducing sound in broadband, in particular for ensuring effectively and with high quality in listening comfort, the transmission of words or sounds pronounced by a group of people distributed in a conference room of any geometry and therefore comprising acoustics not specially adapted.

We know that, to ensure good sound capture and reproduction, in particular in a wide frequency band of up to 7 kHz or more, it is generally necessary, either to have a room whose acoustics have been carefully studied so that the sound emitted at any point in this room is reflected at any other point in this room in a substantially homogeneous way, or to multiply the pickup microphones and the speakers for the latter. In both cases, this results in a high cost of the corresponding installations and, if the room is not suitably arranged as regards its dimensions and its interior layout, discomfort for the users who cannot in a any room that becomes available at any given time, organize an impromptu audio conference with several speakers with equivalent listening comfort.

In addition, the multiplication of microphones and loudspeakers inside, in the same room leads to coupling effects in the acoustic transmission between these devices by creating what we in the technique calls for the LARSEN effect, characterized by a particularly unpleasant whistle which appreciably disturbs the atmosphere. In addition, and more generally, it has already been noted that the quality of the sound recording depends directly on the value of the ratio established between the direct acoustic field and the reverberant field picked up by a microphone, this ratio being all the better that in the same space the number of microphones in service is more limited. Likewise, it is known that in the case of an enclosure or a specialized room reserved for an audio conference, with a plurality of microphones suitably distributed geographically and kept open permanently, the looping gain, ie the level of the LARSEN effect between these microphones and the speakers is lower the more the number of these microphones is reduced.

FR-A-2 377 735 describes an apparatus combining a microphone and a loudspeaker for use in a conference room, mounted on a common vertical axis, the loudspeaker being directed upwards. However, in such an arrangement, the microphone used does not make it possible to obtain a significant reduction in the acoustic coupling with the loudspeaker, while simultaneously allowing normal perception of the speakers arranged around the device.

GB-2 008 359 also illustrates a teleconferencing system but in which a single loudspeaker is associated with a plurality of directional microphones each arranged in front of a speaker, these microphones being mounted with a determined spacing and fixed between them by means of a rigid elongated support. In this case, there is no association of a loudspeaker and a single microphone, hence a distribution of the restored sound which is not homogeneous for all the participants.

The present invention relates to a device which takes into account the necessary compromise between the contradictory imperatives stated above, by allowing appreciable omnidirectionality of the recording and reproduction of the sound, while minimizing the number of microphones used, the mounting of these microphones and speakers which are associated with them to restore the received sound, being arranged to best limit looping with each other, by reducing to the lowest level the amount of energy captured by the microphones from the speakers.

The invention also aims to produce a compact assembly, where a microphone and an associated loudspeaker together occupy a minimum volume, the device being able to operate in a wide frequency band, being easy to use, inexpensive and capable of being lent easily to construction adaptations improving its exterior aesthetic appearance.

To this end, the device for picking up and reproducing sound, in particular for audio conference between several speakers distributed in any room, substantially around a central point arranged in the reference plane, in particular around a table, comprising a directional microphone and a loudspeaker, the membrane of which is arranged opposite the microphone, the loudspeaker and the microphone being placed in an orientation substantially perpendicular to the reference plane, the microphone being of the cardioid type and having a directivity s extending perpendicular to the reference plane and omnidirectionality parallel to this plane, the microphone being arranged at the top of the device and the speaker at the bottom, the microphone and the speaker being mounted coaxially inside '' a common support, resting on a base extending parallel to the reference plane or resting on it, is because operates in that an intermediate transverse separation, improving the acoustic decoupling between the microphone and the loudspeaker is provided between the microphone and the loudspeaker, this loudspeaker being associated, in the vicinity of the reference plane, with a cone of revolution forming a reflector of the sound emitted, returning the sound waves coming from the loudspeaker, substantially in the direction of this plane.

Advantageously and according to another characteristic of the invention, the loudspeaker is secured to a support plate, open at its center for the passage of sound towards the reflective cone located under the loudspeaker at a determined distance from it.

According to another characteristic also, the spacing between the loudspeaker and the reflective cone is determined by vertical spacers providing a plurality of lateral passages for the sound returned by the reflective cone, parallel to the reference plane. Advantageously, the passages between the spacers are closed by a layer of sound-transparent protective foam.

According to yet another characteristic of the device considered, the microphone is arranged in the axis of the loudspeaker at the top of the support, and is held vertically in the latter by a block of material made of compact acoustic foam, resting on the intermediate transverse separation.

Preferably, the microphone is mounted in a cavity formed inside a foam cover, transparent to sound, disposed at the upper part of the support and covering the microphone.

Finally, and in a particular embodiment of the device of the invention, the electrical connection wires of the microphone and the loudspeaker are connected to a connection connector, mounted in the base for connection to electronic amplification assemblies, filtering and adaptation, necessary for its operation. Advantageously, these electronic assemblies include a gain variation circuit and / or suppression of acoustic echoes.

Other characteristics of a sound pickup and restitution device, established according to the invention, will become more apparent from the following description of an exemplary embodiment, given by way of non-limiting example, with reference to the attached drawing. in which the single figure is a schematic view in axial section of the device considered.

In the example shown in this diagram, the reference 1 designates the envisaged device, comprising in particular a microphone 2, preferably of the type with cardioid directivity, mounted vertically at the upper part of the assembly. This microphone 2, itself known in the art but whose assembly and mode of implementation constitute in combination with the other provisions of the proposed system, the object of the present invention, is in particular arranged so that the acoustic waves coming in a determined direction from any point in a horizontal plane, induce vibrations in phase in the membrane (not shown) of the microphone. The microphone 2 is held in a vertical position inside a block of compact acoustic foam 3, immobilized in a support 4, comprising a cylindrical body 5 at the top of which the block 3 is mounted. The microphone 2 is housed, above the block 3, in a chamber 6, delimited inside a foam cover 7, made of a material transparent to sound and covering the assembly, protecting it from the external environment. The block 3 also rests inside the body 5, on a transverse separation member, constituted by a plate 8 extending horizontally.

According to the invention, there is mounted inside the support 4, opposite the microphone 2 in the same vertical direction, a speaker 9 whose membrane is directed downwards. This loudspeaker 9 can be of a type known per se, in particular electrodynamic or electrostatic and is secured to a support plate 10, pierced in its center in order to facilitate the emission downwards of the sound reproduced by the speaker. The support plate 10 is supported by means of vertical spacers 11 by a lower support base 12. The spacers 11 laterally delimit passages, closed by a cylinder 13 of foam transparent to sound. In addition, in order to facilitate the reflection of the sounds emitted vertically by the loudspeaker 9, the device according to the invention comprises a part 14 of conical shape mounted on the top of the base 12 substantially in the common axis of the microphone 2 and the speaker 9, the cone 14 thus allowing the sound returned by the speaker to undergo an appropriate deflection, to escape through the layer of foam 13, substantially in the plane horizontal. The support 12 is usually placed on a table or the like which thus constitutes a reference plane.

The equipment of the device is completed by a connector 15 mounted inside the base 12 and to which electrical conductors, respectively 16 and 17 are connected, making it possible to connect the microphone 2 on the one hand, the speaker on the other part, to one or more electronic assemblies (not shown), advantageously arranged under the table which receives the device 1. These electronic assemblies make it possible in particular to ensure amplification, filtering and adjustment of the sound level, or even elimination parasitic echoes, with control of the gain variation according to the conditions of use.

A particularly simple device is thus produced, making it possible for a group of speakers distributed around the table and on the central part of which the device rests, to take and reproduce the sound in a very wide frequency band, possibly ranging, or even exceed 7 kHz, omnidirectionality in the plane of the pickup table and the sound reproduction being optimally ensured. Simultaneously, the mounting opposite the other of the microphone and the loudspeaker, provides an effective acoustic decoupling between these two devices, by eliminating any possible parasitic effects.

The device can be particularly reduced in its size, the volume of the assembly not exceeding 10 dm³ for a maximum height of approximately 35 cm. The weight of the device can be reduced, under normal operating conditions, to less than 2.5 kg, the directivity of the assembly, however, making it possible to ensure an audio conference with great listening comfort, even with a number high speakers distributed around the table and away from the center of it by a distance between and 1 and 5 m.

The device, thanks to its central position in the middle of the table, at substantially equal distances from all the speakers allows in all cases an omnidirectional reception of the sound emitted by the different speakers towards the microphone; in the same way, the sound reproduced by the loudspeaker is returned by the reflective cone substantially at the level of the plane of the table, or even slightly above the latter, allowing perfect listening by all users. The mounting of the microphone and the loudspeaker opposite each other in the same vertical direction also limits to the maximum the coupling of the sound to reception and to retransmission, the device being able to be used in a band of frequency which can extend to the vicinity or beyond 7 kHz, without requiring, in the circuit of the loudspeaker, any system of pre-accentuation of the treble which makes it possible to reduce in particularly sensitive conditions the price and the size of the device.

The angle at the top of the reflective cone is determined by construction according to the conditions of use of the device. Advantageously, this angle is chosen to be 112 °. The transverse separation plate, mounted between the microphone and the loudspeaker improves the separation between microphone and loudspeaker, by further reducing their acoustic coupling, while the omnidirectionality of the sound recording remains maintained in the reference plane, by allowing it to retain its full effectiveness.

Of course and as follows from the above, it goes without saying that the device considered is not exclusively limited to the embodiment more specifically described and shown above which was given only by way of 'example; on the contrary, it embraces all its variants.

Claims (7)

1. An apparatus for picking up and reproducing sound, particularly for audio conference purposes involving a plurality of speakers distributed over any room, substantially around a central point disposed in a reference plane, particularly around a table, comprising a directional microphone (2) and a loudspeaker (9) the diaphragm of which is disposed opposite the microphone, the loudspeaker and the microphone being placed according to an orientation substantially at right-angles to the reference plane, the microphone being of the cardioid type and having a directivity which extends at right-angles to the reference plane and an omni-directionality parallel with this plane, the said microphone being disposed in the upper part of the apparatus and the loudspeaker in the lower part, the microphone (2) and the loudspeaker (9) being mounted coaxially within a common support (4), resting on a base (12) extending parallel with or bearing on the reference plane, characterised in that an intermediate transverse separation (8) improving acoustic de-coupling between the microphone and the loudspeaker, is provided between the microphone (2) and the loudspeaker (9) within the support (4), the loudspeaker (9) being, in the vicinity of the reference plane, associated with a cone of revolution (14) forming a reflector of emitted sound, returning the sound waves emanating from the loudspeaker substantially in the direction of this plane.
2. An apparatus according to Claim 1, characterised in that the loudspeaker (9) is rigid with a supporting plate (10) open in the centre to allow sound to pass in the direction of the reflector cone situated underneath and at a specific distance from the loudspeaker.
3. An apparatus according to one of Claims 1 or 2, characterised in that the spacing between the loudspeaker (9) and the reflector cone (14) is determined by vertical partitions (11) defining a plurality of lateral passages for the sound returned by the reflector cone parallel with the reference plane.
4. An apparatus according to Claim 3, characterised in that the passages between the partitions (11) are occluded by a layer of protective foam (13) which is transparent to sound.
5. An apparatus according to any one of Claims 1 to 4, characterised in that the microphone (2) is disposed in the axis of the loudspeaker (9) in the upper part of the support (4) and is maintained vertically within this latter by a block (3) of compact acoustic foam material supported on the intermediate transverse separator (8).
6. An apparatus according to any one of Claims 1 to 5, characterised in that the microphone (2) is mounted in a cavity (6) disposed inside a cover (7) of sound transparent foam, disposed in the upper part of the support (4) and fitting over the microphone.
7. An apparatus according to any one of Claims 1 to 6, characterised in that the electrical connecting wires (16, 17) of the microphone (2) and of the loudspeaker (9) are connected to a junction box (15) mounted in the base (12) for connection to electronic amplifying, filtering and adaptation assemblies required for its operation.

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