Audio apparatus with circularly arranged microphones

An audio apparatus has a housing including a tub-shaped recessed part having an upper surface and a wall surface formed on the upper surface. Microphones are circularly arranged in the vicinity of the wall surface inside the recessed part. Each microphone face toward a center direction of the recessed part and the upper surface so that a sound pick-up directivity is toward the center of the housing. A back side, opposite to the direction having the directivity of each microphone is open acoustically and is directed toward a direction higher than the wall surface of the tub-shaped recessed part.

This application is a U.S. National Phase Application of PCT International Application PCT/JP2009/068166 filed on Oct. 22, 2009, which is based on and claims priority from Japanese Patent Application No. 2008-271545 filed on Oct. 22, 2008, the contents of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to an audio apparatus used for an audio conferencing and, in particular, to an audio apparatus provided with a plurality of microphones.

BACKGROUND ART

When persons discuss with each other on a conference, a sound recorder or an audio conferencing apparatus is mostly placed at a center of conference participants (a center of conference desks, and the like). For example, Patent Literature 1 proposes an audio conferencing apparatus which collects sound of the conference participants existing around the apparatus. In the apparatus as set forth in Patent Literature 1, a recessed part is formed on an upper surface of a disk-shaped housing, and a plurality of microphones are arranged on a bottom surface of the recessed part as viewed from an upper side of the housing. The microphones are arranged on a circle as viewed from the upper side of the housing. Each of the microphones has a unidirectivity and is disposed so that the directivity of the microphone is directed toward a center direction as viewed from the upper side of the housing.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the apparatus of Patent Literature 1, however, a wall surface of the recessed part of the housing exists at a rear side of each microphone (a direction opposite to a direction having a directivity). A unidirectional microphone has a sensitivity toward only its front side by combining a sound reaching from its back side and a sound reaching from its front side (a direction having a directivity) by means of level adjustment and phase adjustment. Thus, if a housing exists at the back side, the sound reaching from the front side reflects just at the back side, and the sensitivity with respect to the front side is lowered. Accordingly, directivity may be lowered.

Thus, an object of the present invention is to provide an audio apparatus which hardly causes a directivity to be lowered even in a case where a plurality of unidirectional microphones, each having a directivity toward a center of a housing of the apparatus, are embedded in a recessed part provided on an upper surface of the housing.

Solution to Problem

An audio apparatus according to an aspect of the invention includes: a housing including a tub-shaped recessed part which is defined by an upper surface and a wall surface formed on the upper surface; a plurality of directional microphones which are arranged in a circle in the vicinity of the wall surface inside the recessed part, each of the microphones having a directivity directed toward a center direction of the recessed part as viewed from an upper side of the housing and toward the upper surface, and a direction opposite to the direction having the directivity of each of the plurality of directional microphones is open acoustically. Namely, a front side of each microphone is directed toward a bottom surface of the recessed part, and its back side is directed toward a direction higher than the wall surface of the tub-shaped recessed part as viewed from a lateral side of the housing. Note that the shape of the recessed part may be in any form only if the side of the upper surface is open acoustically.

In the aspect, the audio apparatus may further include a plurality of speakers which are arranged in a concentric circle larger in radius than the circle on which the plurality of directional microphones are arranged, and disposed toward a radiation direction of the concentric circle as viewed from the upper side of the housing.

In the aspect, the audio apparatus may be configured in that the direction opposite to the direction having the directivity of each of the plurality of directional microphones is open acoustically by covering a part of the recessed part with a mesh steel sheet.

Advantageous Effects of Invention

According to the invention, a directivity is hardly lowered even in a case where a plurality of unidirectional microphones, each having a directivity toward a center of a housing of the apparatus, are embedded in a recessed part provided on an upper surface of the housing.

DESCRIPTION OF EMBODIMENTS

A description is made of a sound conferencing apparatus provided with microphones and speakers as an embodiment related to an audio apparatus of the invention with reference to the drawings.

FIG. 1shows an outer appearance of the sound conferencing apparatus.FIG. 2is a schematic view showing an arrangement of the microphones and the speakers of the sound conferencing apparatus.FIG. 3is a block diagram showing the configuration of the sound conferencing apparatus.

(A) inFIG. 1and (A) inFIG. 2are plan views of the sound conferencing apparatus, and (B) inFIG. 1is its front view. (C) inFIG. 1is a rear view of the sound conferencing apparatus. (B) inFIG. 2is a cross sectional view taken from line A-A shown by (A) inFIG. 2.

In (A) inFIG. 1and (A) inFIG. 2, the right side of the sheet refers to an X direction, the left side refers to a −X direction, the top side refers to a Y direction, and the down side refers to a −Y direction. In (B) inFIG. 1and (B) inFIG. 2, the right side of the sheet refers to the X direction, the left side refers to the −X direction, the top side refers to a Z direction, and the down side refers to a −Z direction. In (C) inFIG. 1, the right side of the sheet refers to the X direction, the left side refers to the −X direction, the top side refers to the −Z direction, and the down side refers to the Z direction.

The sound conferencing apparatus includes a disk-shaped housing1. The housing1includes a dish-shaped lower housing11and an upper housing12engaged with the lower housing11so as to cover an upper surface of the dish-shaped lower housing11. A recessed part13which is recessed in a tub shape is formed on an upper surface of the upper housing12. The recessed part13has a depth (a height of a wall surface) by which microphones can be embedded. A part of the recessed part13excluding the vicinity of the center as viewed from an upper side of the housing1is covered with a mesh steel sheet. InFIG. 2, indication of the mesh steel sheet is omitted. When the mesh steel sheet is removed, a plurality of microphones are exposed.

In (A) inFIG. 1, a display unit14including an LCD and an operation unit15including a plurality of operation buttons are arranged at a front side (−Y direction) of the upper housing12. An input/output interface16such as an audio terminal and a USB terminal is arranged at a rear side (Y direction) of the upper housing12. The display unit14displays various information such as a state of the sound conferencing apparatus. The operation unit15is an interface provided for accepting the user's operation.

Further, the sound conferencing apparatus includes a plurality of unidirectional microphones (sixteen microphones10A to10P in the embodiment) arranged at regular intervals on a circle around a center position of the recessed part13on the recessed part.

The microphones10A to10P are arranged in the vicinity of the wall surface of the recessed part13. The respective microphones10A to10P are arranged at equiangular intervals (about 22.5° intervals in this embodiment) regarding the center position of the housing11as a rotation center as viewed from the upper side of the housing1. Each microphone is arranged so that its sound-collecting direction (a direction having a high directivity) corresponds to a center direction as viewed from the upper side of the housing1. The number of microphones is not limited to sixteen, and may be set arbitrarily in accordance with a specification as necessary.

Four speakers SP1to SP4are arrange on an inclined surface of the lower housing11. The respective speakers SP1to SP4are arranged at equiangular intervals (about 90° intervals in this embodiment) regarding the center position of the housing11as a rotation center as viewed from the upper side of the housing1. Each speaker is arranged so that its sound-emitting direction corresponds to a radiation direction as viewed from the upper side of the housing1. Namely, the sound-emitting direction and the sound-collecting direction of the adjacent speaker and microphone (the speaker SP1and the microphone10A, for instance) are directions opposite to each other as viewed from the upper side of the housing1. The speaker and microphone (the speaker SP3and the microphone10A, for instance) whose sound-emitting and sound collecting directions are the same direction as viewed from the upper side of the housing1are arranged at the positions farthest from each other. Accordingly, the sound fed back from the speaker to the microphone becomes extremely small.

Next, an explanation is made of a sound signal process by the sound conferencing apparatus. As shown inFIG. 3, in addition to the above-configuration, the sound conferencing apparatus includes a control unit20, AMPs (amplifiers)21A to21P, A/D converters22A to22P, a microphone signal processing circuit23, an echo canceller24, a speaker signal processing circuit26, four D/A converters27and four amplifiers28.

Sounds collected by the microphones10A to10P are input to the amplifiers21A to21P. The amplifiers21A to21P amplifies outputs the sounds collected by the microphones10A to10P respectively, and outputs the amplified sounds to the A/D converters22A to22P. The A/D converters22A to22P digitally converts the sound signals amplified by the amplifiers21A to21P, and outputs the digitally-converted sound signals to the microphone signal processing circuit23.

The microphone signal processing circuit23selects and outputs one signal having the highest sound pressure level among the sound signals output from the A/D converters22A to22P. At this time, a process for adding the sounds input from the respective microphones to the sound signal collected by the adjacent microphone may be performed. Addition of the signal collected by the adjacent microphone strengthens the signal in the front direction of the microphone and weakens the signal in directions other than the front direction so as to improve the directivity of the microphone.

An output signal of the microphone signal processing circuit23is input to the echo canceller24. An output signal of the echo canceller24is output to another apparatus via the input/output interface16. The input/output interface16outputs a sound signal input from another apparatus to the echo canceller24. The echo canceller24estimates a feedback component reaching from the speakers SP1to SP4to the microphones10A to10P and subtracts the estimated feedback component from the output signal of the microphone signal processing circuit23.

The output signal of the echo canceller24(a sound signal input from the other apparatus) is output to the speaker signal processing circuit26. The speaker signal processing circuit26divides the sound signal input from the echo canceller24in four ways and outputs the divided signals. At this time, the phases of the respective sound signals may be shifted. Phase-shift of the respective sound signals evades causing only the low-frequency component to be emphasized. Thus, the conference participants existing around the apparatus can clearly catch the sounds emitted from the speakers which exist closest to themselves.

The four-way sound signals output from the speaker signal processing circuit26are input to the four D/A converters27respectively, and converted into the respective analog sound signals. The four-way analog sound signals are amplified by the four amplifiers28respectively, and emitted from the respective speakers SP1to SP4.

In the sound conferencing apparatus according to the embodiment, here, the direction (rear side) opposite to the direction having the directivity of each of the plurality of directional microphones arranged on the upper surface of the recessed part13is open acoustically. Since the microphones10A to10P are disposed in the vicinity of the wall surface of the recessed part13, the reflection at the wall surface of the sound reaching from the front side (the direction having the directivity) may cause the directivity to be lowered. For this reason, as shown by (B) inFIG. 2, the front side of each microphone is directed toward a side of a bottom surface of the recessed part13, and its back side is directed toward a direction higher than the wall surface of the tub-shaped recessed part as viewed from a lateral side of the housing. Although, as mentioned above, each microphone is covered with the mesh steel sheet, it is open acoustically because the mesh steel sheet has little sound insulating properties and little sound absorbability.

FIG. 4is an enlarged view showing the arrangement of the microphone. InFIG. 4, although an explanation is made of the microphone10A on behalf of the microphones, other microphones have the same configuration and function. Since the conference participants exist around the sound conferencing apparatus, the sound reaches the microphone10A from obliquely-above as viewed from the lateral side of the housing. In an example of the figure, sound A (as a noise, mainly) from the X, Z direction and sound B (as speech sound of the conference participant) from the −X, Z direction reach the microphone10A.

Since the microphone10A is a unidirectional microphone, the sound A is hardly collected. That is, the sound A is cancelled as a result of combining a sound signal collected at the rear side of the microphone10A and a fed-back sound signal collected at the front side of the microphone10A. On the other hand, the sound B is collected at the front side of the microphone10A directly or by reflection on the upper surface of the recessed part13. Here, since the rear side of the microphone10A is open acoustically, the sound B is hardly collected from the rear side, and is not also reflected toward the front side. Accordingly, the microphone10A has a sensitivity only at its front side, and the directivity cannot be lowered (i.e., the unidirectivity is secured).

Further, since the microphone10A is equivalent to be placed in a position extremely close to the upper surface of the recessed part13, the sound-collecting sensitivity with respect to the front side is further improved due to the boundary effect.

The sound conferencing apparatus according to the embodiment is configured so that the sound-emitting direction and the sound-collecting direction of the adjacent speaker and microphone (the speaker SP1and the microphone10A, for instance) are directions opposite to each other, and therefore, the fed back sound from the speaker to the microphone is extremely small structurally. Further, since the unidirectivity of each microphone is secured due to the arrangement configuration, the fed back sound becomes small furthermore.

AlthoughFIG. 4shows an example in which the microphone10A is arranged at an angle of about forty-five degrees, the arrangement angle is not limited to this angle. The microphone10A may be arranged at any angle only if its rear side is open acoustically.

The embodiment shows an example in which a part of the recessed part13is covered with a mesh steel sheet in order to open the back side of the microphone acoustically, but the invention is not limited thereto. For example, the rear side of the microphone may be physically and completely open without providing the mesh steel sheet, or a hole may be formed in a part of the wall surface corresponding to the back side of the microphone, or the like.

In the invention, the configuration of the speakers is not essential. The sound conferencing apparatus can collect the speech sounds in all directions at high S/N ratio even if the sound of the conference is recorded only using the microphones.