GB2138283A - Conference table - Google Patents

Abstract

Directional, preferably differential, microphones (11) at the back of the V-shape table point to respective speaker positions disposed at the front of the table substantially in line with the microphones (11). The microphones serve as selective sound pick-ups for receiving each speaker's speech and also for determining which one of the various possible speakers is actually speaking. A grating (26), e.g. of metal and with a fabric covering (25), and having longitudinal and cross bars (28,27), is disposed a short distance in front of the microphones between the microphones and the speaker positions. The grating provides a useful degree of "blinkering" to make the microphones relatively less sensitive to off-axis speakers than they would be without the grating. <IMAGE>

Description

SPECIFICATION Teleconference table The present invention relates to equipment for teleconference rooms enabling voice interchanges between distant groups of people, with simultaneous indication of the distant speaker, which indication may be performed, for example, in an audio conference simply by lighting a lamp designating said distant speaker, or else in a video conference by displaying a moving image of the distant speaker on a television screen. The invention relates more particularlyto teleconference tables used in such rooms, said tables providing selective sound pick-ups for the various possible local speakers enabling the actual local speaker to be automatically identified for indication to the distant participants.

Tables for audio-only conferencing are generally hexagonal in shape, as described in French patent nO 2 358 800, in order to receive the various possible local speakers around their periphery with one speaker per side of the table. They have a central portion, likewise hexagonal in shape, standing proud of the table top with omnidirectionalmicrophone-containing blocks facing each speaker position backed up against the central portion and fixed thereto. Each block has a reflecting paraboloidal cavity which is open towards the speaker position corresponding to the block and in which the microphone is held at the focus of the paraboloid and pointing towards the apex thereof.This disposition ensures that each of the microphones is insensitive to speakers other than the speaker in the corresponding position, thereby enabling the local speaker to be automatically identified on the basis of the output signals from the microphones. A number representative of the local speaker may then, for example, be transmitted to the far end. For reasons of appearance, the openings to the cavities in the blocks housing the microphones are covered in cloth which hides the microphones.

This type of table having speaker positions distributed around a hexagon is not suitable forvideoconferencing which generally uses elongate tables with all the local speakers received on the same side to facilitate taking individual camera shots of each speaker. Such tables have unidirectional microphones disposed at the back of the horizontal table top and pointing towards respective speaker positions at the front of the table. These microphones are fully visible, are highly directional (usually being differential microphones), and are much more sensitive to sounds made by their respective speakers than to sounds made by more distant speakers, thus enabling the local speaker to be automatically identified as in the previous case.In the present case this identification is used to select the camera taking a shot of the actual local speaker from a plurality of cameras taking shots of respective possible local speakers.

For reasons of appearance, as for tables of the preceding type, it would be desirable to hide the - microphones, or at least to make them less visible.

The Applicants have observed that although appearance can be improved by using a longitudinal strip of cloth or other highly sound-permeable fabric to cover the front of the microphones between the users and microphones, and possibly to cover the rear of the microphones as well, this nevertheless has the drawback of considerably reducing the directivity of the sound pick-up.

Preferred embodiments of the present invention improve the directivity of sound pick-up as provided at a teleconference table by directional microphones, and thus, in particular, make problems of appearance and problems of acoustics compatible with each other.

The present invention provides a conference table having directional microphones disposed substantially at the back of the table, each microphone facing a respective speaker position for selectively picking up sound from the speaker in that position, wherein the table includes a grating disposed close to the microphones, substantially along the line defined by the microphones, and interposed between the microphones and the speaker positions.

Preferably the table includes a housing which is substantially transparent to sound and in which said microphones are housed, said housing having a wall facing said speaker positions and including said grating.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure I is a front view of a teleconference table in accordance with the invention; Figures 2 and 3 are respectively a top view and a bottom view of the Figure 1 teleconference table; Figure 4 is a section on a larger scale on a line IV-IV of Figure 2; Figure 5 shows a detail marked V in Figure 4 to a still larger scale; Figures 6 and 7 are two top view of portions of a table element, respectively marked VI and VII in Figure 2; and Figure 8 is a polar diagram showing advantages provided by a teleconference table in accordance with the invention.

Figure 1 shows a teleconference table seen from behind, looking in the direction of arrow F1 in Figure 2, while Figures 2 and 3 show the same table seen from above and from below.

These three Figures 1 to 3 show the general disposition of the teleconference table. The table is elongate in form, and more preceisely, it is in the form of a V having its arms widely spread apart at an obtuse angle. The speakers sit in front of the table, i.e., along the outside of the two arms of the V, and the table is rounded where the two arms meet.

Looking at Figures 1 to 3, it can be seen that the table comprises a main table top 1 which is substantially horizontal and which defines the V shape. At the back of the table top 1 there is a raised shelf 2 which is also substantially horizontal and in the form of a V with arms parallel to the arms of the V shape of the table top. Each end of the table top is supported by an end leg 3, each of its intermediate portions is supported by an intermediate leg 4, and its central portion where the two arms of the V meet is supported by a central leg 5. The end legs 3 and the intermediate legs 4 which are only partially visible in Figure 1 are generally C-shaped with a middle portion located near the back of the table top 1 acting as a vertical leg and with the side portions running along the ground or floor and along the underside of the table top 1.Each top side portion has cross pieces such as 13 on the legs 3 or 14 on the legs 4 on which the table top is supported and to which it is fixed.

The central leg 5 is generally C-shaped similar to the legs 3 and 4, and includes a tube 6 which is visible in Figure 1 only. The portions of the C-shaped leg 5 serve the same functions as the corresponding portions of the legs 3 and 4, and its side portions supporting the table top is fitted with cross pieces 15 for this purpose. The vertical tube 6 is mounted at the back of the central portion of the C-shaped leg 5.

It serves as a sheath for electrical conductors feeding the electrical equipment in the table and for providing connections between said equipment and other equipment not in the table. One end ofthetube 6 meets the ground or the floor via a flexible coupling 7, and it other end opens out at table top level at the back of the internal join between the two arms of the table top V.

Finally, a piece of trim 16 is mounted at each end of the table, at right angles to the table 1 and the shelf 2 to hide the bare edges thereof.

Still with reference to Figures 1 to 3, but also, and more particularly, with reference to Figures 4 and 5, it can be seen that the shelf 2 is located at the back of the table top 1 behind the table legs, and is associated with a front strip 8 and a back strip 9 which, together with the shelf 2, constitute a nearly closed housing 10 in which the microphones 11 are mounted (not shown in Figure 3 for the sake of clarity).

The teleconference table is thus equipped with two angle strips 17 and 18 referred to as link strips.

These link strips are of L-shaped section and are mounted at the back of the table substantially level with the table top 1. Figure 3 in particular, together with Figures 4 and 5 show that these strips run along the length of respective ones of the arms of the V-shaped table, between the back edge of the table top 1 and the front edge of the shelf 2. Figure 3 and Figures 4 and 5 show that each of these strips, eg.

the strip 17 abuts against the vertical portion of one of the intermediate legs 4, and is fixed to cross pieces 14' provided for the purpose. Each of the strips also has one end fixed to a cross piece 13' provided on the end legs 3, and its other end fixed to the central leg 5. The two strips are interconnected at the join between the arms of the V either by being fixed to cross pieces 15' mounted on the central leg 5 in correspondance with each of the strips or else by connection to a plate which goes round the tube 6 of the central leg.

As can be seen in Figures 4 and 5, the shelf 2 is supported on brackets 19 which are fixed to the angle strips such as 17. The support brackets 19 are in the shape of upsidedown Ls with the free ends of their vertical arms being bent over at rightangles for better positioning and retention. The shelf 2 is fixed to the horizontal arms of the support brackets 19.

Still with reference to Figures 4 and 5, it can be seen that the link strips, such as the illustrated link strip 17, also serve to hold the microphones 11 in position in their housing 10. Each microphone 11 is rotatably mounted on a stand 20 which has a fixing tab 21 fixed to the corresponding strip 17 or 18. The microphones are thus suitably held at the back of the table with their sound-sensitive front portions 22 above and behind the table top 1 and pointing towards the front of the table.

When thus positioned along the back edge of the table inside the housing 10 and inclined relative to the table top 1, the microphones define respective positions for different speakers at the front of the table opposite each microphone. The microphones 11 are chosen to be highly directional, and are advantageously differential microphones.

The microphones 11 are hidden by the strips 9 and 8 which respectively close the back of the housing 10 and the front thereof facing the speakers.

The front strip 8 comprises a rigid grating 26 in accordance with the invention, and having an outer band 25 of fabric, eg. cloth, stretched thereover. The grating 26 runs along the length of the table substantially along the line defined by the sensitive front portions 22 of the microphones 11, and advantageously, as shown, perpendicularly to the axis of each microphone, ie. to their directions of maximum free field sensitivity which correspond approximately to the directions in which the bodies of the microphones are pointing. The grating 26 is placed a little way in front of the microphones 11, a few centimeters from their sensitive front faces 22. The grating is essentially constituted by cross bars 27 held relative to one another by longitudinal bars 28.

It is preferably made of metal.

The grating 26 is folded over the top of the microphones to constitute a substantially horizontal flat 29 level with the shelf 2. Two longitudinal strength members 30 and 31 run along respective longitudinal edges of the grating, holdig the cross bars in place and strengthening the longitudinal edges of the grating. Another longitudinal strength member 32 provides rigidity along the ridge of the fold.

The strength members 30 and 31 also facilitate mounting the grating 26 between the table top 1 and the shelf 2. The two edges of the grating are simply placed in recesses 33 and 34 provided respectively in the table top 1 and in the shelf 2, with the grating being held in place by the mere fact of placing the longitudinal edges of the grating into abutment against the walls of said recesses.

The back strip 9 is essentially constituted by a band of fabric, eg. cloth 36, which is simply stretched over a rigid structure 37 defining the shape of the back cover and transparent to sound. The back cover strip 9 is fixed to the angle strip 17 (or 18) which is partially enclosed thereby, and also to the shelf 2 or to its support brackets 19.

The housing 10 is nearly closed, being open only beneath the front portion of the microphones which can thus be seen only from underneath the table.

Figures 6 and 7 are views of portions of the grating 26 of the front strip 8, and correspond respectively to the portions referenced VI and VII in Figure 2.

It can clearly be seen that the grating comprises an assembly of cross bars 27 and of longitudinal bars 28 which are of circular section. The bars are welded together where they meet. It can also be seen that the ends of the cross bars 27 are welded to the flat strength members 30 and 31 and that the ridge running along the longitudinal fold in the grating is strengthened by a preferably thicker bar 32.

In Figure 6, the microphone emplacements behind the grating are marked by windows such as 40 and defined in the grating 26 by removing just enough links from the mesh thereof for the corresponding microphones to be received therein. These windows serve to prevent possible shocks to the grating being directly applied to the microphones.

Looking at Figure 2 it can be seen that the front strip 8 is advantageously made of two symmetrical portions 8a and 8b which are assembled on the teleconferencing table so as to leave a space between them at the join of the two arms of the V in which a manual control panel 50 is located for general control of the many possible equipments which there may be in a teleconference room external to the table itself. It thus follows that the grating 26 is made in two parts such as the part 26a shown in Figure 7, which fit against a lip 51 on the above-mentioned control panel 50, and which are thus strengthened by a flat end cross bar referenced 35.

Tests performed by the Applicants on a teleconferencing table have demonstrated that using a grating such as described above in association with a front band of fabric 8 largely compensates for the loss of directivity associated with the use of differential microphones in conjunction with fabric on its own. These tests have shown that satisfactory microphone operating conditions during teleconferencing are obtained by using a metal grating 26 having cross bars and long bars of 2 mm or 2.5 mm diameter defining a grating have a mesh size of 15 mm by 15 mm or 25 mm by 15 mm, or else by using bars of 2.5 mm diameter defining a mesh size of 50 mm by 30 mm.

However, the choice of these dimensions is not critical. The size of grating depends on a compromise between the percentage of the grating area which is reflective (which should be as small as possible), and the "blinkering" provided by the grating presenting a more effective obstacle to off-axis sounds than to sound from the speaker located directly in front of each microphone (which should be as large as possible).

Tests performed by the Applicants are illustrated in the polar radiation diagram of Figure 8 showing the level of the amplified electrical signal from the output of a microphone situated in the middle of one of the arms of the V. In Figure 8 the microphone is situated at the origin 0 of the diagram. The output signal is delivered in response to white acoustic noise emitted at constant level from an artificial mouth moved round the microphone at a distance of about one meter. The level was measured using a psophometric voltmeter having an integrating filter to take account of the characteristics of the ear and giving relative value reading edpressed dBmOp.

In Figure 8, the curve L1 represents the output signal from the microphone under test when a band of fabric is associated with the set of microphones mounted in a teleconferencing table while the curve L2 represents the output signal signal from the same microphone when a grating in accordance with the invention is associated with the set of microphones.

The grating was made of metal, had a 25 mm by 15 mm mesh and was covered in fabric. The letters A, B, and C plus the subscript of the associated curve mark points corresponding to the signal delivered by the microphone as excited by the artificial mouth in question when situated in the following positions relative to the microphone: firstly at an angular position denoted as O", ie. substantially occupying the position of the speaker assigned to the microphone; and otherwise at angular positions +45 and -45", ie. substantially occupying the positions of the speakers assigned to the nearest microphones on either side of the microphone under test.

Since the point A2 is very close to the point A1, it can be seen from these curves that adding a grating in accordance with the invention attenuates the delivered O direction signal by very little. In contrast, is can also be seen by comparing the points B2 and B1 or C2 and C1, that the signaldelivered by the microphone is considerably attenuated by the presence of a grating in accordance the invention. This is shown up by the points B2 and C2 since their respective angular positions of +45 correspond in practice to comfortable, but not excessive positioning of speakers other than the speaker placed directly in front of the microphone, but who are still relatively close to the microphone. Similar results are obtained for speakers at angular positions close to the +45 mentioned.

The presence of a grating thus reinforces the directivity of sound pick-up without greatly affecting sensitivity in the O direction. Thus, in practice, the grating provides a satisfactory compromise between these two parameters (sensitivity and directivity) for improving the quality of teleconference interchanges.

The invention is not limited to the particular embodiment which has just been described. In particular, a grating without any fabric could be placed between the microphones and the various possible speakers. Also, the cross bars of the grating used could be other than circular in section, eg. they could be flat bars.

Claims (9)

1. A conference table having directional microphones disposed substantially at the back of the table, each microphone facing a respective speaker position for selectively picking up sound from the speaker in that position, wherein the table includes a grating disposed close to the microphones, substantially along the line defined by the microphones, and interposed between the microphones and the speak er positions.

2. A conference table according to claim 1, including a housing which is substantially transparent to sound, the housing enclosing said microphones and having a wall facing said speaker positions and including said grating.

3. A conference table according to claim 2, wherein said housing is at least partially defined by said grating covered in fabric.

4. A conference table according to claims 1,2 or 3, wherein said grating has a longitudinal fold defining an upper flat which is substantially horizontal above said microphones.

5. A conference table according to any preceding claim, wherein said grating is made of metal.

6. A conference table according to any preceding claim, wherein said grating includes windows opposite respective ones of said microphones and of dimensions at least equal to the dimensions of the microphones' sensitive front faces.

7. A conference table according to any preceding claim, wherein said grating is disposed substantially perpendicular to the axis of each of said microphones.

8. A conference table as claimed in any preceding claim wherein the grating is defined by cross bars.

9. A conference table substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.