U.S. patent number 9,271,069 [Application Number 14/324,835] was granted by the patent office on 2016-02-23 for microphone housing arrangement for an audio conference system.
This patent grant is currently assigned to RevoLabs, Inc. The grantee listed for this patent is Scot T. Armstrong, Klaus Hartung. Invention is credited to Scot T. Armstrong, Klaus Hartung.
United States Patent |
9,271,069 |
Hartung , et al. |
February 23, 2016 |
Microphone housing arrangement for an audio conference system
Abstract
An audio conference system has a plurality of specially designed
microphone housings into each of which a directional microphone is
positioned. Each microphone housing is positioned entirely within
the body of the audio conferencing system, the microphone housings
are strategically positioned at each one of four corners of the
audio conference system body in order to provide maximum exposure
of a microphone to its operating environment, and the interior
structure of the microphone housing is designing to reflect
unwanted energy harmlessly away from the microphone. Each
directional microphone is positioned in the microphone housing such
that the most sensitive node in its polar response pattern is
oriented normal (at right angles) to a line radiating outward from
the center of the system.
Inventors: |
Hartung; Klaus (Hopkinton,
MA), Armstrong; Scot T. (Merrimack, NH) |
Applicant: |
Name |
City |
State |
Country |
Type |
Hartung; Klaus
Armstrong; Scot T. |
Hopkinton
Merrimack |
MA
NH |
US
US |
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|
Assignee: |
RevoLabs, Inc (Sudbury,
MA)
|
Family
ID: |
53680352 |
Appl.
No.: |
14/324,835 |
Filed: |
July 7, 2014 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150215689 A1 |
Jul 30, 2015 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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61931882 |
Jan 27, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04M
1/03 (20130101); H04R 1/342 (20130101); H04M
3/567 (20130101); H04M 3/568 (20130101); H04R
27/00 (20130101) |
Current International
Class: |
H04R
1/02 (20060101); H04M 3/56 (20060101); H04R
1/34 (20060101); H04R 27/00 (20060101) |
Field of
Search: |
;381/332-336,365,182,388 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ni; Suhan
Attorney, Agent or Firm: Schuler; Robert
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit under 35 U.S.C. .sctn.119(e) of
U.S. Provisional Patent Application Ser. No. 61/931,882 entitled
"MICROPHONE HOUSING ARRANGEMENT FOR AN AUDIO CONFERENCE SYSTEM",
filed Jan. 27, 2014, the entire contents of which is incorporated
by reference.
Claims
We claim:
1. An audio conference system, comprising: one or more microphone
housings positioned around a circumference of the audio conference
system, each microphone housing has an acoustic port and an
acoustic reflective surface; and a directional microphone in each
of the one or more microphone housings is oriented such that a ray
passing through a zero degree point in a polar response pattern of
each of the directional microphones is oriented in a horizontal
plane and normal to a horizontal axis that extends from the
directional microphone, through a central point of the audio
conference system to a point located on the opposite side of the
audio conference system housing circumference.
2. The audio conference system of claim 1, further comprising the
microphone housing acoustic port geometry and acoustic reflective
surface geometry is configured to permit a substantially
unobstructed exposure to an acoustic environment with respect to
the polar response pattern of both sides of a transducer comprising
the directional microphone.
3. The audio conference system of claim 2, further comprising the
acoustic reflective surface geometry reflecting acoustic energy
entering the microphone housing away from the directional
microphone.
4. The audio conference system of claim 1, where the polar response
pattern of the directional microphone is a cardioid response
pattern.
5. The microphone housing of claim 1, further comprising the
directional microphone being retained in the microphone housing by
a member that subtends from the acoustic reflective surface.
6. The microphone housing of claim 5, wherein the directional
microphone retaining member displays a minimal profile to acoustic
energy entering the microphone housing.
7. The microphone housing of claim 1, wherein the acoustic port is
substantially open to the surface upon which the audio conference
system rests.
8. The microphone housing of claim 1, wherein the acoustic
reflective surface is substantially arcuate shaped when viewed in a
vertical cross section that is normal to an axis intersecting the
center of and normal to the directional microphone.
9. A method for detecting acoustic energy, comprising: positioning
a directional microphone in a microphone housing located on a
circumference of an audio conference system such that a ray passing
through a zero degree point in a polar response pattern of the
directional microphone is oriented in a horizontal plane and normal
to a horizontal axis that extends from the directional microphone,
through a central point of the audio conference system to a point
located on the opposite side of the audio conference system housing
circumference.
10. The method for detecting acoustic energy of claim 9, further
comprising the microphone housing acoustic port geometry and
acoustic reflective surface geometry is configured to permit a
substantially unobstructed exposure to an acoustic environment with
respect to the polar response pattern of both sides of a transducer
comprising the directional microphone.
11. The method for detecting acoustic energy of claim 10, further
comprising the geometry of the acoustic reflective surface reflects
acoustic energy entering the housing away from the directional
microphone.
12. The method for detecting acoustic energy of claim 9, where the
polar response pattern of the directional microphone is a cardioid
response pattern.
13. The method for detecting acoustic energy of claim 9, further
comprising the directional microphone being retained in the
microphone housing by a member that subtends from the acoustic
reflective surface.
14. The method for detecting acoustic energy of claim 13, wherein
the directional microphone retaining member displays a minimal
profile to acoustic energy entering the microphone housing.
15. The method for detecting acoustic energy of claim 9, wherein
the acoustic port is substantially open to the surface upon which
the audio conference system rests.
16. The method for detecting acoustic energy of claim 9, wherein
the acoustic reflective surface is substantially arcuate shaped
when viewed in a vertical cross section that is normal to an axis
intersecting the center of and normal to the directional
microphone.
Description
1. BACKGROUND
A room audio system, such as a conference phone, can be used to
conduct audio meetings between groups of participants that are
remote with respect to each other. These devices allow the meeting
participants to position themselves in a range of positions and
orientations within a conference room or around a conference table
in order to effectively participate in a conference call.
Among other things, conference phones or conference systems
typically integrate loudspeakers into a housing with some number of
microphones. Positioning a loudspeaker proximate to microphones
creates a number of problems with respect to the capture and
processing of audio signals (voice signals) from the local
environment. The proximity of a loudspeaker to a microphone results
in the microphone capturing energy from the loudspeaker (called
acoustic coupling . . . far-end voice) which is then sent back as
an acoustic echo to a far-end audio system where the participants
hear their own voices as echo. This acoustic echo is distracting
and denigrates the quality of an audio conferencing session. While
it is possible to remove a certain amount of this acoustic echo in
a microphone signal (maybe 25-30 db of acoustic echo energy) by
applying acoustic echo cancellation (AEC) methods to the signal,
the resulting audio signal can still include some acoustic echo
energy.
One design technique that is typically used to mitigate the effects
of acoustic coupling between a loudspeaker and microphone is to
place the microphones as far away from the loudspeakers as is
possible, and to position the microphones so that their positive
polar pattern is oriented away (faces away) from the direction of
loudspeaker energy waves. Typically, directional microphones are
employed that exhibit a cardioid polar response pattern, where one
side of the microphone is much less sensitive to acoustic energy
than the other side. Moving microphones away from a loudspeaker and
employing directional microphones further reduces the acoustic
coupling between microphone and a loudspeaker proximate to them. A
range of microphone polar response patterns are illustrated with
reference to FIG. 1. Another advantage to the use of directional
microphones is that they operate to pick up more of the direct
sound waves and less of the reflected sound from the walls and
ceiling than an omni-directional microphone. This makes the voices
sound less reverberant and results in better intelligibility than
with a single or multiple omnidirectional microphones. If
directional microphones are used, typically a switching algorithm
selects the microphone with the highest energy and mutes the
remaining microphones.
Loudspeakers associated with audio conference systems are generally
positioned at a central location with respect to the microphones
comprising the audio system. Additionally, the microphones are
typically located at the end of microphone arms that extend
radially away from the central loudspeaker. The length of these
microphone arms is dictated by the amount of echo return loss
needed to provide a microphone signal that, after being processed,
is relatively free from far-end voice energy. Alternatively, the
entire body of an audio conference system can be extended laterally
from a central loudspeaker location, and one or more microphones
can be positioned at the outside radius or edges of the lateral
body extension.
As described above, the directional microphones comprising an audio
conference system are typically placed at the distal ends of these
arms with respect to a central audio system location (loudspeaker
position), and the microphones can be placed in a specially
designed microphone housing that maximizes their exposure to a
conference room environment while minimizing their exposure to
loudspeaker energy. Such an audio conference phone arrangement is
illustrated with reference to FIG. 2. As the directional
microphones operate according to a pressure gradient difference
between their front and back (as determined by their polar response
pattern), anything that distorts this pressure gradient (reflected
energy of any type) tends to reduce the directional characteristics
of a microphone. It is critical to the operation of a directional
microphone that the design of this microphone housing and placement
of the microphone within the housing is affected as little as
possible by reflected energy from the housing walls. Consequently,
microphone housings are designed without side wall surfaces and
with a back wall (behind the microphone) that is at least 2.5 cm
away and sloped at an angle away from the microphone so that energy
is reflected upward and away from the microphone.
2. BRIEF DESCRIPTION OF THE DRAWINGS
The present invention can be best understood by reading the
specification with reference to the following figures, in
which:
FIG. 1 illustrates a plurality of microphone polar response
patterns.
FIG. 2 is a drawing showing a prior art conference phone design
with microphone arms.
FIG. 3 is a drawing of a conference phone according to one
embodiment.
FIG. 4 illustrates a perspective view of the conference phone of
FIG. 3 without loudspeaker and microphone housing grills.
FIG. 5 is a drawing of the lower body cavity of the conference
phone showing an embodiment of a microphone housing in vertical
cross-section.
FIG. 6 is a graphical representation of a directional microphone
polar response pattern.
FIG. 7 is a front view of another embodiment of a microphone
housing.
FIG. 8 is a side view of the embodiment of FIG. 7.
DETAILED DESCRIPTION
Although audio conference phones designed with microphone arms and
housings that adequately expose directional microphones to their
operating environment can operate to capture and process very high
quality voice signals, the disadvantage with this type of design is
that it has a relatively large table-top footprint. The smaller
this footprint, the less obtrusive the audio conference system is,
and the more room there is on the table for meeting materials used
by the participants. It is possible to realize an audio
conferencing system with a relatively smaller footprint if the
microphone arms are eliminated from the design, but this requires
that the directional microphones be positioned within the housing
of the audio conference system, which can limit the exposure of the
microphones to the acoustical operating environment in which they
are intended to operate. Limiting a microphones exposure to their
operating environment in this manner can alter the directional
characteristics of the microphone such that they behave more like
an omni-directional microphone, in which case acoustic coupling
with a loudspeaker becomes much more prevalent and they can operate
to capture much more unwanted environmental noise.
An audio conferencing system having a relatively small footprint is
disclosed that does not need microphone arms or a laterally
extended housing to move microphones away from a system
loudspeaker. According to one embodiment, an audio conference
system has a plurality of specially designed microphone housings an
acoustic opening or port and an acoustic reflective surface into
which is placed a directional microphone. Each microphone housing
is positioned to be substantially entirely within an audio
conferencing system housing, and a set of two or more microphone
housings are strategically positioned around the circumference of
the audio conference system in order to provide maximum exposure of
the microphone set as a whole to acoustic environment in which the
audio conference system is operating. Each microphone housing has
an acoustic reflective surface that is designing with a geometry
that reflects unwanted or reflected acoustic energy away from the
microphone, and to provide both sides of a transducer comprising
each directional microphone in the set of microphones with
substantially unobstructed exposure (no acoustical barrier) to the
acoustic environment with respect to a polar response pattern
associated with the directional microphone.
Further, each directional microphone is positioned in a microphone
housing such that a ray extending through the zero degree
(0.degree.) point in the microphone's polar response pattern is
oriented substantially normal (at right angles) to an axis
extending from the microphone through a center point in the audio
conference system to a point on an opposite side of the system
housing. A directional microphone oriented in this manner in such a
specially designed microphone housing exhibits good directional
operating characteristics and the acoustic coupling between the
speaker and microphone is low enough so that the signal can be
easily processed to remove any acoustic echo present.
An audio conference system 300 having a relatively small footprint
according to one embodiment is illustrated with reference to FIG.
3. The audio conference system 300 shown here has a relatively
small footprint when compared to prior art audio conference systems
or phones. This small footprint is at least in part achieved by
eliminating the microphone arms and integrating the microphones
into the audio conference system housing without laterally
extending the system housing. One embodiment of the audio
conference system 300 is illustrated as being cubic in shape with
an upper body housing cavity and a lower body housing cavity. Other
embodiments can assume a round shape or can have more or fewer than
four sides. The upper body housing cavity of system 300 is
comprised of a top surface (below a grill), that can be square and
substantially horizontally oriented, and four substantially
vertical side wall surfaces all of which can be substantially flat.
The peripheral portion of the top surface is defined by an upper
circumferential edge and one or more loudspeakers can be mounted on
the top surface of the upper body cavity of the audio conference
system. These loudspeakers are oriented in an upward direction
behind the speaker grill. The top surface area need be only large
enough to accommodate the number of loudspeakers comprising the
system and in this regard the size of the loudspeakers directly
impacts the footprint of the audio conference system. The lower
body cavity of the audio conference system provides a physical
barrier between the loudspeakers in the upper body cavity, serves
as an enclosure for electronics associated with the audio
conferencing system and supports separate housings for each of four
directional microphones. Each microphone is positioned in a
microphone housing that is located behind a microphone grill which
is composed of a suitable acoustically transparent material. While
the audio conference system described with reference to FIG. 3 has
four microphone housings positioned at each of the four corners of
the system, the system can, depending upon the system shape or
other considerations, be implemented with fewer than four
microphone housings.
The microphone housings are positioned proximate to a lower
circumferential edge of the lower body cavity. The location of the
housings (and therefore the microphones) positions them a maximum
distance from the loudspeakers, which has the effect of minimizing
the acoustic coupling between the loudspeaker and the microphones.
However, the directional characteristics (polar response pattern)
of a microphone can be distorted if it is placed into a microphone
housing that is not designed to reflect unwanted acoustic energy
away from the microphone. This distortion can be manifested by the
microphone exhibiting characteristics that are more
omni-directional than directional in nature. If the microphone
behaves in an omni-directional manner, it is likely to capture
unwanted environmental acoustic energy (noise, speaker
reflection/refraction, etc.) in addition to voice signals, and this
unwanted energy can denigrate both the operation of a microphone
selection algorithm and an acoustic echo cancellation function. The
audio conference system 300 of FIG. 3 can be either a room audio
system or it can be an audio conference system, but for the purpose
of this description, is referred to here as audio system 300.
FIG. 4 shows the audio system 300 of FIG. 3 with the loudspeaker
grill and one microphone grill removed. According to this
embodiment, each one of four directional microphones is positioned
in a separate microphone housing. Each microphone housing is
substantially triangular in shape when viewed in horizontal cross
section, the entire front area or acoustic port comprising the
microphone housing is open to the local acoustic environment, and
this acoustic port comprises a portion of the area that would
otherwise comprise portions of two lower cavity side walls. The
microphone housing acoustic port is circumscribed by a top external
edge, two side edges A and B, and a bottom external edge
(optional). The bottom area of the acoustic port comprising the
microphone housing is substantially open to a surface (i.e.,
conference table top) upon which the audio system 300 rests, and a
comprising substantially a entire interior surface of the
microphone housing is specially designed to both reflect unwanted
environmental acoustic energy away from a directional microphone
and to not be an acoustical barrier between the microphone and the
acoustical environment that attenuates a polar response pattern
associated with the microphone. A directional microphone is shown
positioned in a central location within the microphone housing, and
it is oriented, as previously described, such that the ray
extending from the microphone to the zero degree (0.degree.) point
in the microphone's polar response pattern is oriented normal (at
right angles) to an axis-A extending from the microphone through a
center point in the audio conference system to a point on an
opposite side of the system housing. This microphone housing design
in combination with the microphone orientation within the housing
maximizes the microphones exposure to its acoustic operating
environment, and at the same time preserves its directional
operating characteristics by minimizing its exposure to reflected
acoustic energy. The operating characteristics of a directional
microphone positioned in such a microphone house are illustrated
with reference to FIG. 6.
FIG. 6 is a graphical representation of a polar response pattern
associated with the directional microphone in the microphone
housing described with reference to FIG. 4. Microphone sensitivity
measurements are shown on the graph for frequencies at 250, 500,
1000, 2000, 4000 and 8000 hertz. While there is some loss of
microphone sensitivity at the 8000 hertz frequency, there is no
substantial loss of sensitivity at the lower frequencies in the
polar direction of interest.
Continuing to refer to FIG. 4, the acoustic reflective surface
comprising substantially the entire interior surface of the
microphone housing is comprised of a back wall or surface portion
that transitions vertically upward to a curved surface portion
which continues to a top surface portion. This reflective surface
can extend in a straight line from side A of the microphone housing
to side B of the microphone housing, and it can extend from the top
external edge of the microphone housing to the rear or back bottom
edge of the microphone housing. The microphone housing acoustic
reflective surface, according to this embodiment, is substantially
parallel over its entire surface area with respect to an axis B
(which comprises the ray associated with the microphone polar
response pattern and an extension of the ray 180.degree. in the
opposite direction) and the surface is straight when viewed in
horizontal cross section from one side (side A) of the microphone
housing to the other side (side B). Further, this reflective
surface is specially designed such that its profile is curved when
viewed in vertical cross section (see FIG. 5) from the top external
edge to the bottom back edge of the microphone housing. According
to the embodiment illustrated in FIG. 5, the vertical cross
sectional profile of the acoustic reflective surface is
substantially straight from point C, at the bottom back edge, to
point D, which is located at approximately the midpoint of the back
surface portion of the housing. Above the midpoint in the back
surface, the profile assumes a curved or arcuate shape having a
radius that is selected to reflect unwanted environmental acoustic
energy away from the directional microphone. This curve can extend
to the top external edge of the microphone housing or nearly to the
top external edge of the housing at a point labeled E.
As described earlier, and as shown in FIG. 4, substantially the
entire bottom area of the microphone housing is open to the surface
upon which the audio system is resting, and this bottom area can
have a bottom/front microphone grill support member (optional) that
extends laterally from and horizontal to the two bottom edges of
the corresponding lower cavity side walls. While the embodiment
described here with reference to FIG. 5 has a bottom grill member,
it should be understood that this grill member is not an essential
to the operation of this invention. The purpose of this opening is
to provide an egress from the housing for acoustic energy reflected
downward by the acoustic reflective surface.
As illustrated in FIGS. 4 and 5, the directional microphone is
placed at an optimal position and orientation within the microphone
housing to capture direct (unreflected) acoustic energy (voice)
generated by meeting participants. The directional microphone is
connected to a microphone retaining member that subtends from the
top portion of the acoustic reflective surface comprising the
microphone housing. The microphone retaining member is composed of
a flexible, rubber-like material that has the property of absorbing
vibrations so that they are not transmitted from the acoustic
reflective surface to the microphone. The microphone retainer
member has a window that functions to permit acoustic energy that
enters the housing to pass through without being reflected from the
retainer. The purpose of the retainer member design is to hold the
directional microphone in position within the housing while having
a minimal surface area from which acoustic energy can reflect.
The horizontal and vertical cross sectional profiles of the
acoustic reflective surface are not limited to the embodiment
described with reference to FIGS. 4 and 5. Depending upon the need
to reflect more acoustic energy away from the microphone and/or to
expand a microphones exposure to acoustic environment (in order to
increase higher frequency sound fidelity), other embodiments of a
microphone housing acoustical port and reflective surface can
exhibit a more complex geometry. According to an embodiment of a
microphone housing illustrated in FIGS. 7 and 8, a vertical cross
section of an acoustic reflective surface that is normal to an axis
z running through the center of a microphone positioned in the
housing is arcuate in shape from a left to a right side edge of the
waveguide. A measured radial dimension or distance of the acoustic
reflective surface in a vertical cross section located proximal to
the microphone is relatively smaller than a measured radial
dimension or distance of the acoustic reflective surface in a
vertical cross section located at right and left edges of the
acoustic reflective surface as shown in FIGS. 7 and 8. The measured
radial dimension of the waveguide surface can increase either
linearly or non-linearly from the point proximal to the microphone
to either of the right or left distal ends or edges of the acoustic
reflective surface.
The forgoing description, for purposes of explanation, used
specific nomenclature to provide a thorough understanding of the
invention. However, it will be apparent to one skilled in the art
that specific details are not required in order to practice the
invention. Thus, the forgoing descriptions of specific embodiments
of the invention are presented for purposes of illustration and
description. They are not intended to be exhaustive or to limit the
invention to the precise forms disclosed; obviously, many
modifications and variations are possible in view of the above
teachings. The embodiments were chosen and described in order to
best explain the principles of the invention and its practical
applications, they thereby enable others skilled in the art to best
utilize the invention and various embodiments with various
modifications as are suited to the particular use contemplated. It
is intended that the following claims and their equivalents define
the scope of the invention.
* * * * *