GB1587549A - Telephone conferencing apparatus - Google Patents

Description

(54) TELEPHONE CONFERENCING APPARATUS (71) We, NORTHERN TELECOM LIMITED, a company organized under the laws of Canada, of 1600 Dorchester Blvd., West, Montreal, Quebec, Canada, H3H it1., do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a telephone conferencing apparatus and particularly to a unitary loudspeaker/microphone unit which gives adequate sound power output of good quality, is omnidirectional in both transmit and receive modes, and is aesthetically and practically acceptable for telephone conferences or public address uses.

Conventional telephone conference devices have certain disadvantages, depending upon the form of the device. Many have the speaker more obvious than the microphone which creates a human behaviour problem in that users speak to the speaker (which represents the remote party) instead of to the microphone.

This can reduce the level and quality of the speech signal. In some devices the microphone is not omnidirectional and differing signal levels and quality arise as different participants in a room talk. The speaker and/or microphone may be very obvious and create some reaction by talkers.

The present invention provides a telephone apparatus for use in a conference room comprising: a housing; a speaker mounted at the top end of the housing and a microphone mounted at the bottom end of the housing, on a common axis and facing outwards away from each other, the minimum peripheral distances measured from the centre line of the speaker to the centre line of the microphone around the outside of the housing being not less than about 15 inches; an inclined surface surrounding the microphone and extending upwardly and outwardly from the microphone to the periphery of the housing, at an angle of about 30 + about 5 relative to a plane normal to the common axis; means for supporting said housing such that the common axis is vertical with the outer face of the microphone a distance of about inch + .05" from a surface normal to the common axis, the microphone being of the type sensitive to airborne sound only.

The apparatus has omnidirectional capabilities but still has adequate acoustic separation between speaker and microphone and may be designed to be aesthetically pleasing and nonintrusive in a conference.

The speaker and microphone are, in use, on a common vertical axis, the speaker facing upward and the microphone downward. The microphone is at the centre of an inclined surface which avoids or reduces the effects of standing wave and other distortions. The speaker and microphone have omnidirectional capabilities, while at the same time good acoustic separation can be provided. An existing electronic circuit, as used in an existing speakerphone, can be used, mounted in the housing of the apparatus, for connection to a telephone system, and a telephone dial, and other controls, can also be mounted in or on the housing. It is possible to have several of the speaker/microphone units interconnected. With voice switching - which is part of the normal electronic circuit - the unit being addressed will act as the microphone while the other units will be in a loudspeaker condition.

The invention will be readily understood by the following description of certain embodiments by way of example, in conjunction with the accompanying drawings, in which: Figure 1 is a vertical cross-section through one form of apparatus; Figure 2 is a view in the direction of arrow A in Figure 1, with the base plate removed; Figure 3 is a plan view on the loudspeaker end; Figure 4 is a side view, illustrating positioning of control buttons and a telephone dial; Figure 5 is a perspective view of an alternative form of housing.

The apparatus as illustrated in Figures 1 to 4 has a housing 10 forming an enclosure elongate in the vertical direction, as seen in Figures 1 and 4, and having a square cross-section normal to the vertical axes, as seen in Figures 2 and 3. The dimensions of the square crosssection, in the example illustrated, sufficient to house the speaker 11. The top surface 12 of the housing 10 has an aperture 13 over the speaker 11. The speaker works in an enclosed chamber, 14, the chamber being closed at the base by a diaphragm 15.

Attached to the diaphragm 15 is a micro phone housing 16. The microphone housing has an aperture 17 facing downwards and a micro phone 18 is mounted in the aperture, facing downwards. The microphone housing has an inclined surface 19, extending outwardly and upwardly to the housing 10. The angle of the surface 19, relative to the horizontal, is important.

The apparatus can be placed on a flat horizontal surface, with the microphone spaced close to the surface. Thus legs 20 can be used to support the apparatus with the desired clearance between microphone and supporting surface.

However, the type of the supporting surface can affect the microphone. For example, if placed on a hard surface, such as a wood surface as in a table, the microphone will be effective. However if placed on a carpeted floor, or on a cloth surface of a table, the sensitivity of the microphone will be reduced especially at high frequencies. To make the apparatus independent of supporting surface, a hard base member 21 can be provided, attached by the legs 20, for example. The provision of the base 21 makes the unit suitable for any kind of vertical mounting, for example on the floor, on a table, or on a horizontal supporting surface on a wall or on a ceiling. The sensitivity will not be affected, nor will the omnidirectional capability, but when it is vertically mounted adjacent a wall surface it will receive sound from only 1800.

The size of speaker can be varied, but it has been found that a 6" speaker gives adequate sound power output and acceptable quality.

With a smaller speaker, base tones are lost and output sound power is less.

There are various parameters which should be taken into account when the apparatus is designed. There must be sufficient acoustic separation between the speaker 11 and the microphone 18. It has been found that this can-be obtained by making the minimum peripheral distance between the speaker centre line and the microphone centre line not less than IS" - that is the distance as indicated by the chain dotted line and arrows 25 in Figure 1. This distance can be reduced slightly, but the desired level of acoustic separation starts to be reduced, if the distance is much less than about IS". The distance between the outer face, or input, of the microphone and the support surface - the distance "d" in Figure 1 - should be approximately 1/2", and the angle of the inclined surface 19 relative to the support surface - a in Figure 1 - should be approximately 300.

The physical separation - the minimum distance from the speaker centre line to the microphone centre line around the casing, is of course a function of the width of the housing and the height. It is possible to make the housing tall and thin or short and fat. There is no objection to increasing this distance but it is a matter of aesthetic appeal and also of being unobtrusive that provides some determination.

For example, if stood on a table in a conference, with participants sitting around the table, it is desirable that the housing does not interfere with eye contact between participants.

Also if made too thin then some local enlargement for the speaker will be necessary.

The mounting of the speaker and microphone on a common vertical axis is advantageous in that acoustic separation is symmetrical about the housing. Also, a very important feature, with the speaker facing upwards it is omnidirectional, and similarly with the microphone facing downwards it is also omnidirectional. This avoids the need for multiple speakers and/or multiple microphones, or alternatively the occurrence of directional sensitivity variations which can occur with other forms of conference apparatus.

With a downward facing microphone facing a hard surface and the microphone mounted in a flat surface, strong resonances occur at the entrance to the microphone, due to standing waves. By inclining the surface surrounding the microphone, the formation of such resonances is avoided. This means that the apparatus itself does not add to the resonances of the room in which the apparatus is used and a substantially uniform frequency response of the microphone results. The inclination of the surface can vary, an optimum of about 30 having been obtained. However, this can be varied + 5 quite readily. The inclined surface 19 is preferably flat but can be slightly curved, with the introduction of some undesirable frequency irregularities.

As stated, the vertical distance between the microphone entrance and the surface opposite the microphone, be it the base 21, when provided, or a table top or the like if base 21 is not provided, is important. A distance of about .5" + 10% gives acceptable results, the efficiency of the microphone decreasing rapidly as the distance varies from the above. Outside these limits the microphone frequency response will not be uniform to an extent which is acceptable.

The minumum physical separation distance is preferably, and not less than, about 15".

Reduction of this dimension will increase acoustic feedback from speaker to microphone.

This distance is important because low frequencies, for example below 1000 Hz, can diffract easily around obstacles. With increase in frequency, the increase in speaker directionality, as well as the effect of the "shadow" of the housing in the microphone areas, make up for the increase of microphone sensitivity with frequency as is the case with telephone transmitters. Therefore a substantially constant value of acoustic separation is obtained and the acoustic stability of the unit becomes independent of frequency.

While in Figures 1 and 3, an open aperture is shown over the speaker this will normally be closed by a grille or screen to avoid damage to the speaker.

The use of a microphone which is sensitive to airborne sound only enables the speaker and microphone to be in a common housing. Such a microphone is insensitive to mechanical vibrations of its housing, the surface of which it is mounted, etc. A suitable microphone is an electret microphone. This provides a simple and economic solution to the problem of solidborne acoustic feedback through the housing.

The configuration, substantailly as illustrated, and with the physical characteristics given above, provides an acoustic separation in excess of 20 decibels. This provides stable acoustic operation of the apparatus with a switch loss (a usual technique to avoid howling, in speaker-phones) of no more than 50 decibels.

This makes the effect of voice-switching almost unnoticable In long subscriber loops there is ecessive attenuation toward the high end of the telephone frequency range above 1000 Hz. A resonator 26 attached at the microphone inlet boosts this high end of the frequency range, giving a crisper sound, a high intelligibility of speech signals and an improved chance for talker recognition. The resonator 26 is a flat disc with a peripheral rim, and having apertures 27 in the disc portion. The apertures can be slots, holes or other formations.

The apparatus can be used in various ways.

Thus it can be wired into an existing speakerphone set, using the circuitry of the set. It can be used as a combined conferencing and public address system in that each unit can have its own circuitry contained within the housing and the various units interconnected. The unit nearest to whoever is talking at a particular time will be voice-switched to a microphone regime, while the remaining units will be in a speaker regime, ensuring everyone can hear what is said.

Controls can be provided and, for example volume and/or tone controls can be provided.

The unit can be directly wired into the telephone system, without an intervening speakerphone unit. In such a case the speakerphone circuitry is mounted within the housing, as indicated in chain-dotted outline at 28, in Figures 1 to 4. The dial 29 can be mounted in one side, together with various control buttons 30 and control knobs 31.

While the apparatus has been illustrated, and described as being of square cross-section, when viewed on the top or bottom, other crosssections can be provided. Thus cylindrical housings, and multisided housings such as hexagons and octagons can be used. Figure 5 is a perspective view of a unit having a cylindrical housing 35. In the particular example illustrated, the outer casing extends right the way down to encompass the microphone housing.

The microphone is surrounded by an inclined surface in the same manner as in the previously described example, the inclined surface being conical. A perforated section 36 of the housing 35 surrounds the microphone section.

WHAT WE CLAIM IS: 1. A telephone apparatus for use in a conference room comprising: a housing; a speaker mounted at the top end of the housing and a microphone mounted at the bottom end of the housing, on a common axis and facing outwards away from each other, the minimum peripheral distance measured from the centre line of the speaker to the centre line of the microphone around the outside of the housing being not less than about 15 inches; an inclined surface surrounding the microphone and extending upwardly and outwardly from the microphone to the periphery of the housing, at an angle of about 30 + about 5 relative to a plane normal to the common axis; means for supporting said housing such that the common axis is vertical with the outer of the microphone a distance of about inch + .05" from a surface normal to the common axis, the microphone being of the type sensitive to airborne sound only 2. Apparatus as claimed in Claim 1, includ- ing a base member attached to the housing, a surface of the base member forming the surface opposed to the microphone.

3. Apparatus as claimed in Claim 2, the housing including an outer casing extending to the base member, and apertures in the casing in the portion surrounding the microphone.

4. Apparatus as claimed in Claim 1,2 or 3, including a resonator attached to the inlet of the microphone, to boost the high end of the frequency range thereof.

4. Apparatus as claimed in Claim 1, 2 or 3, including a resonator attached to the inlet of the microphone, to boost the high end of the frequency range thereof.

5. Apparatus as claimed in any one of the preceding claims, including electrical control members in the housing.

6. Apparatus as claimed in any one of the preceding claims, including electrical circuit means mounted in the housing.

7. Apparatus as claimed in Claim 6, the electrical circuit means comprising telephone circuit means, and a telephone dial mounted on the housing.

8. Apparatus substantially as described herein with reference to Figures 1 to 4 of the accompanying drawings.

9. Apparatus substantially as described herein with reference to Figure 5 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. the speaker. The use of a microphone which is sensitive to airborne sound only enables the speaker and microphone to be in a common housing. Such a microphone is insensitive to mechanical vibrations of its housing, the surface of which it is mounted, etc. A suitable microphone is an electret microphone. This provides a simple and economic solution to the problem of solidborne acoustic feedback through the housing. The configuration, substantailly as illustrated, and with the physical characteristics given above, provides an acoustic separation in excess of 20 decibels. This provides stable acoustic operation of the apparatus with a switch loss (a usual technique to avoid howling, in speaker-phones) of no more than 50 decibels. This makes the effect of voice-switching almost unnoticable In long subscriber loops there is ecessive attenuation toward the high end of the telephone frequency range above 1000 Hz. A resonator 26 attached at the microphone inlet boosts this high end of the frequency range, giving a crisper sound, a high intelligibility of speech signals and an improved chance for talker recognition. The resonator 26 is a flat disc with a peripheral rim, and having apertures 27 in the disc portion. The apertures can be slots, holes or other formations. The apparatus can be used in various ways. Thus it can be wired into an existing speakerphone set, using the circuitry of the set. It can be used as a combined conferencing and public address system in that each unit can have its own circuitry contained within the housing and the various units interconnected. The unit nearest to whoever is talking at a particular time will be voice-switched to a microphone regime, while the remaining units will be in a speaker regime, ensuring everyone can hear what is said. Controls can be provided and, for example volume and/or tone controls can be provided. The unit can be directly wired into the telephone system, without an intervening speakerphone unit. In such a case the speakerphone circuitry is mounted within the housing, as indicated in chain-dotted outline at 28, in Figures 1 to 4. The dial 29 can be mounted in one side, together with various control buttons 30 and control knobs 31. While the apparatus has been illustrated, and described as being of square cross-section, when viewed on the top or bottom, other crosssections can be provided. Thus cylindrical housings, and multisided housings such as hexagons and octagons can be used. Figure 5 is a perspective view of a unit having a cylindrical housing 35. In the particular example illustrated, the outer casing extends right the way down to encompass the microphone housing. The microphone is surrounded by an inclined surface in the same manner as in the previously described example, the inclined surface being conical. A perforated section 36 of the housing 35 surrounds the microphone section. WHAT WE CLAIM IS:

1. A telephone apparatus for use in a conference room comprising: a housing; a speaker mounted at the top end of the housing and a microphone mounted at the bottom end of the housing, on a common axis and facing outwards away from each other, the minimum peripheral distance measured from the centre line of the speaker to the centre line of the microphone around the outside of the housing being not less than about 15 inches; an inclined surface surrounding the microphone and extending upwardly and outwardly from the microphone to the periphery of the housing, at an angle of about 30 + about 5 relative to a plane normal to the common axis; means for supporting said housing such that the common axis is vertical with the outer of the microphone a distance of about inch + .05" from a surface normal to the common axis, the microphone being of the type sensitive to airborne sound only

2. Apparatus as claimed in Claim 1, includ- ing a base member attached to the housing, a surface of the base member forming the surface opposed to the microphone.

3. Apparatus as claimed in Claim 2, the housing including an outer casing extending to the base member, and apertures in the casing in the portion surrounding the microphone.

4. Apparatus as claimed in Claim 1,2 or 3, including a resonator attached to the inlet of the microphone, to boost the high end of the frequency range thereof.

4. Apparatus as claimed in Claim 1, 2 or 3, including a resonator attached to the inlet of the microphone, to boost the high end of the frequency range thereof.

5. Apparatus as claimed in any one of the preceding claims, including electrical control members in the housing.

6. Apparatus as claimed in any one of the preceding claims, including electrical circuit means mounted in the housing.

7. Apparatus as claimed in Claim 6, the electrical circuit means comprising telephone circuit means, and a telephone dial mounted on the housing.

8. Apparatus substantially as described herein with reference to Figures 1 to 4 of the accompanying drawings.

9. Apparatus substantially as described herein with reference to Figure 5 of the accompanying drawings.