U.S. patent application number 16/857426 was filed with the patent office on 2021-10-28 for wearable audio device magnetometer compensation.
The applicant listed for this patent is Bose Corporation. Invention is credited to Jordan J. Bonner, Stephen J. Maguire.
Application Number | 20210337298 16/857426 |
Document ID | / |
Family ID | 1000005895428 |
Filed Date | 2021-10-28 |
United States Patent
Application |
20210337298 |
Kind Code |
A1 |
Maguire; Stephen J. ; et
al. |
October 28, 2021 |
Wearable Audio Device Magnetometer Compensation
Abstract
A wearable audio device that includes an electro-acoustic
transducer for creating audio output and a magnetometer system
comprising a magnetic field sensor with an output, a temperature
sensor that is configured to determine an internal device
temperature, a processor, and memory. The magnetometer system is
configured to derive from the magnetic field sensor output a
directional heading of the Earth's magnetic field. The magnetometer
system is further configured to compensate the magnetic field
sensor output, wherein the compensation is temperature dependent.
The memory is configured to store temperature-dependent
compensation information. The magnetometer system is further
configured to use the temperature sensor output to retrieve
compensation information from the memory in order to compensate the
magnetic field sensor output at the current temperature.
Inventors: |
Maguire; Stephen J.;
(Grafton, MA) ; Bonner; Jordan J.; (Waltham,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bose Corporation |
Framingham |
MA |
US |
|
|
Family ID: |
1000005895428 |
Appl. No.: |
16/857426 |
Filed: |
April 24, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04R 1/1041 20130101;
H04R 1/32 20130101 |
International
Class: |
H04R 1/10 20060101
H04R001/10; H04R 1/32 20060101 H04R001/32 |
Claims
1. A wearable audio device, comprising: a housing; an
electro-acoustic transducer in the housing for creating audio that
is directed out of the housing, wherein the transducer comprises a
transducer magnet that has a transducer magnetic field; a coupling
magnet in the housing and configured to couple the housing to
another structure, wherein the coupling magnet has a coupling
magnetic field; a magnetometer system in the housing and comprising
a magnetic field sensor that is configured to detect the Earth's
magnetic field and has an output, the magnetometer system
configured to derive from the magnetic field sensor output a
directional heading of the Earth's magnetic field, wherein the
magnetic field sensor is located within both the transducer
magnetic field and the coupling magnetic field such that the
transducer magnetic field and the coupling magnetic field affect
the magnetic field sensor's detection of the Earth's magnetic
field; wherein the magnetometer system is further configured to
compensate the magnetic field sensor output, wherein the
compensation is temperature dependent; a temperature sensor that is
configured to determine an internal temperature in the housing; and
a processor and associated memory in the housing, wherein the
memory is configured to store temperature-dependent magnetometer
system compensation information, and wherein the processor is
configured to use the determined internal housing temperature to
retrieve the compensation information from the memory to compensate
the magnetic field sensor output for temperature.
2. (canceled)
3. The wearable audio device of claim 1, wherein the housing
comprises an earbud body.
4. The wearable audio device of claim 1, wherein the housing is
inside of an eyeglass temple piece.
5. (canceled)
6. The wearable audio device of claim 1, wherein the housing
comprises a portion of an on-ear headphone.
7. The wearable audio device of claim 1, wherein the magnetometer
system is configured to compensate the magnetic field sensor output
when a magnetic field emanating from the wearable audio device is
greater than a threshold level.
8-9. (canceled)
10. The wearable audio device of claim 1, wherein the
temperature-dependent compensation information is determined for a
plurality of wearable audio devices and a composite of these
determinations is stored in the memory.
11. The wearable audio device of claim 1, wherein the
temperature-dependent compensation information is determined
relative to a reference temperature.
12. The wearable audio device of claim 1, wherein the magnetometer
system is configured to compensate the magnetic field sensor output
when the internal housing temperature exceeds a reference
temperature by more than a predetermined amount.
13. (canceled)
14. An eyeglass headphone, comprising: an eyeglass frame with a
temple piece that is constructed and arranged to be positioned
proximate an ear of a wearer; an electro-acoustic transducer in the
temple piece for creating audio output that is directed out of the
temple piece, the electro-acoustic transducer producing a
transducer magnetic field; a coupling magnet in the temple piece
and configured to couple the temple piece to another structure,
wherein the coupling magnet has a coupling magnetic field; a
magnetometer system in the temple piece and comprising a magnetic
field sensor that is configured to detect the Earth's magnetic
field and has an output, the magnetometer system configured to
derive from the magnetic field sensor output a directional heading
of the Earth's magnetic field, wherein the magnetic field sensor is
located within both the transducer magnetic field and the coupling
magnetic field such that the transducer magnetic field and the
coupling a magnetic field affect the magnetic field sensor's
detection of the Earth's magnetic field; a temperature sensor that
is configured to determine a temperature of the eyeglass frames; a
processor and associated memory in the temple piece, the
magnetometer system configured to derive from the magnetic field
sensor output a directional heading of the Earth's magnetic field;
wherein the magnetometer system is further configured to compensate
the magnetic field sensor output to reduce heading errors caused at
least in part by the transducer magnetic field and the coupling
magnetic field, wherein the compensation is temperature dependent;
wherein the memory is configured to store temperature-dependent
compensation information; and wherein the magnetometer system is
further configured to use the temperature sensor output to retrieve
compensation information from the memory to compensate the magnetic
field sensor output for temperature.
15. The eyeglass headphone of claim 14, wherein the
temperature-dependent compensation information is determined for a
plurality of eyeglass headphones and a composite of these
determinations is stored in the memory.
16. The eyeglass headphone of claim 14, wherein the magnetometer
system is configured to compensate the magnetic field sensor output
when the combined transducer magnetic field and the coupling
magnetic field are greater than a threshold level.
17-18. (canceled)
19. The eyeglass headphone of claim 14, wherein the magnetometer
system is configured to compensate the magnetic field sensor output
when the sensed temperature exceeds a reference temperature by more
than a predetermined amount.
20. (canceled)
Description
BACKGROUND
[0001] This disclosure relates to a wearable audio device.
[0002] Wearable audio devices such as audio-enabled eyeglass
headphones and earphones (e.g., earbuds or headphones) can include
orientation tracking systems that use a magnetometer to track
motions of the head and the direction in which the wearer is
facing. Magnetometers need to accurately detect the Earth's
magnetic field. The wearable audio device's electro-acoustic
transducer typically includes a magnet. The wearable audio device
may also include magnet material such as steel. The wearable audio
device can also include a magnet used to dock or park the wearable
audio device to another structure. Since the electro-acoustic
transducer, the magnetometer, steel used to house the transducer
and/or the docking magnet of many wearable audio devices are in
close proximity, the magnetic field of the other magnets and the
magnetic field aberrations caused by steel can inhibit the
magnetometer from accurately sensing the Earth's magnetic
field.
SUMMARY
[0003] All examples and features mentioned below can be combined in
any technically possible way.
[0004] In one aspect, a wearable audio device includes an
electro-acoustic transducer for creating audio output, and a
magnetometer system comprising a magnetic field sensor with an
output. The magnetometer system is configured to derive from the
magnetic field sensor output a directional heading of the Earth's
magnetic field. The magnetometer system is further configured to
compensate the magnetic field sensor output, wherein the
compensation is temperature dependent. The magnetometer system is
further configured to use a temperature in order to compensate the
magnetic field sensor output.
[0005] Some examples include one of the above and/or below
features, or any combination thereof. In some examples the wearable
audio device also includes structure that is constructed and
arranged to be positioned so as to direct the audio output into the
environment adjacent to the wearable audio device. In an example
the structure that is constructed and arranged to be positioned so
as to direct the audio output into the environment adjacent to the
wearable audio device comprises an earbud body. In an example the
structure that is constructed and arranged to be positioned so as
to direct the audio output into the environment adjacent to the
wearable audio device comprises an eyeglass temple. In an example
the electro-acoustic transducer and the magnetometer system are
carried by the eyeglass temple. In an example the electro-acoustic
transducer and the magnetometer system are located inside of the
eyeglass temple. In an example the structure that is constructed
and arranged to be positioned so as to direct the audio output into
the environment adjacent to the wearable audio device comprises a
portion of an on-ear headphone.
[0006] Some examples include one of the above and/or below
features, or any combination thereof. In some examples the
magnetometer system further comprises a temperature sensor that is
configured to determine an internal temperature, a processor, and
memory. In an example the memory is configured to store
temperature-dependent compensation information. In an example the
processor is configured to use the determined internal temperature
to retrieve compensation information from the memory. In an example
the temperature-dependent compensation information is determined
for a plurality of wearable audio devices and a composite of these
determinations is stored in the memory. In an example the
temperature-dependent compensation information is determined
relative to a reference temperature.
[0007] Some examples include one of the above and/or below
features, or any combination thereof. In some examples the
magnetometer system is configured to compensate the magnetic field
sensor output when a magnetic field emanating from the wearable
audio device is greater than a threshold level. In an example the
magnetic field emanating from the wearable audio device is at least
in part from one or both of a transducer magnet and a coupling
magnet for coupling the wearable audio device to another
structure.
[0008] Some examples include one of the above and/or below
features, or any combination thereof. In an example the
magnetometer system is configured to compensate the magnetic field
sensor output when the internal temperature exceeds a reference
temperature by more than a predetermined amount. In an example the
magnetometer system is further configured to compensate the
magnetic field sensor output to reduce heading errors, where
heading errors are caused at least in part by at least one of a
magnet of the electro-acoustic transducer, a coupling magnet for
coupling the wearable audio device to another structure, and
magnetic material of the wearable audio device.
[0009] In another aspect an eyeglass headphone includes an
electro-acoustic transducer for creating audio output, the
electro-acoustic transducer producing a stray magnetic field. There
is a temple piece constructed and arranged to be positioned
proximate an ear of a wearer and to direct the audio output into
the environment adjacent to the temple piece. There is also a
magnetometer system carried by the temple piece and comprising a
magnetic field sensor with an output, a temperature sensor that is
configured to determine the device's internal temperature, a
processor, and memory, the magnetometer system configured to derive
from the magnetic field sensor output a directional heading of the
Earth's magnetic field. The magnetometer system is further
configured to compensate the magnetic field sensor output to reduce
heading errors caused at least in part by the stray magnetic field,
wherein the compensation is temperature dependent. The memory is
configured to store temperature-dependent compensation information.
The magnetometer system is further configured to use the
temperature sensor output to retrieve compensation information from
the memory in order to compensate the magnetic field sensor output
at the internal temperature.
[0010] Some examples include one of the above and/or below
features, or any combination thereof. In an example the
temperature-dependent compensation information is determined for a
plurality of wearable audio devices and a composite of these
determinations is stored in the memory. In an example the
magnetometer system is configured to compensate the magnetic field
sensor output when the stray magnetic field is greater than a
threshold level. In an example the stray magnetic field is at least
in part from a transducer magnet.
[0011] Some examples include one of the above and/or below
features, or any combination thereof. In an example the eyeglass
headphones also include a magnetic field from a coupling magnet for
coupling the eyeglass headphones to another structure. In an
example the magnetometer system is configured to compensate the
magnetic field sensor output when the internal temperature exceeds
a reference temperature by more than a predetermined amount. In an
example the stray magnetic field is caused at least in part by at
least one of a magnet of the electro-acoustic transducer and
magnetic material of the electro-acoustic transducer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is perspective view of a headphone.
[0013] FIG. 2 is a partial cross-sectional view of elements of a
headphone.
[0014] FIG. 3 is a schematic diagram of a headphone.
[0015] FIG. 4 is a plot of magnetic field offset vs. temperature
for an internal magnet of a wearable audio device.
[0016] FIG. 5 is a front perspective view of eyeglass
headphones.
[0017] FIG. 6 is a partial cross-sectional schematic view of the
right temple piece of eyeglass headphones.
DETAILED DESCRIPTION
[0018] Some examples of this disclosure describe a type of wearable
audio device that is known as a headphone or earbud. Headphones
generally deliver sound into a closed or partially-closed volume in
the outer ear. Earbuds generally deliver sound directly into the
user's ear canal. Other examples of this disclosure describe a type
of wearable audio device that is known as an open audio device.
Open audio devices have one or more electro-acoustic transducers
(i.e., audio drivers) that are located off of the ear canal
opening. Open audio devices are further described in U.S. Pat. No.
10,397,681, the entire disclosure of which is incorporated herein
by reference for all purposes.
[0019] The term headphone is often used to refer to a device that
typically fits around, on, or in an ear and that radiates acoustic
energy directly or indirectly into the ear. Headphones are
sometimes referred to as earphones, earpieces, headsets, earbuds,
or sport headphones, and can be wired or wireless. A headphone
includes an electro-acoustic transducer (driver) to transduce
electrical audio signals to acoustic energy. The acoustic driver
may or may not be housed in an earcup. A headphone may be a single
stand-alone unit or one of a pair of headphones (each including at
least one acoustic driver), one for each ear. A headphone may be
connected mechanically to another headphone, for example by a
headband and/or by leads that conduct audio signals to an acoustic
driver in the headphone. A headphone may include components for
wirelessly receiving audio signals. A headphone may include
components of an active noise reduction (ANR) system. Headphones
may also include other functionality, such as a microphone.
[0020] In an around the ear or on the ear or off the ear headphone,
the headphone may include a headband or other support structure and
at least one housing or other structure that contains a transducer
and is arranged to sit on or over or proximate an ear of the user.
The headband can be collapsible or foldable, and can be made of
multiple parts. Some headbands include a slider, which may be
positioned internal to the headband, that provides for any desired
translation of the housing. Some headphones include a yoke
pivotably mounted to the headband, with the housing pivotally
mounted to the yoke, to provide for any desired rotation of the
housing.
[0021] An open audio device includes but is not limited to an
off-ear headphone, i.e., a device that has one or more
electro-acoustic transducers that are coupled to the head or ear
(typically by a support structure) but do not occlude the ear canal
opening. In an example the open audio device is an off-ear
headphone comprising audio eyeglasses, but that is not a limitation
of the disclosure as the electro-acoustic transducer and the
magnetometer system can be used in any device that is configured to
deliver sound to or proximate one or both ears of the wearer where
there are typically but not necessarily no ear cups. The wearable
audio systems contemplated herein may include a variety of devices
that include an over-the-ear hook, such as a wireless headset,
hearing aid, eyeglasses, a protective hard hat, and other open ear
audio devices.
[0022] One or more of the devices, systems and methods described
herein, in various examples and combinations, may be used in a wide
variety of wearable audio devices in various form factors,
including but not limited to headphones and various other types of
head, shoulder or body-worn acoustic devices (e.g., audio
eyeglasses or other head-mounted audio devices) that include one
more electro-acoustic transducers to produce sound, with or without
contacting the ears of a user. It should be noted that although
specific implementations of wearable audio devices primarily
serving the purpose of acoustically outputting audio are presented
with some degree of detail, such presentations of specific
implementations are intended to facilitate understanding through
provisions of examples and should not be taken as limiting either
the scope of the disclosure or the scope of the claim coverage.
[0023] Many wearable audio devices are powered by batteries that
must be periodically charged. Battery charging can be accomplished
using a charger that may be built into a case that is also
configured to store the wearable audio devices when they aren't in
use. The charger can alternatively be carried by another structure
such as a separate battery charging device. In order for the
wearable audio device batteries to properly charge, the wearable
audio device must be brought into close proximity to the battery
charger, which requires the wearable audio device to be "docked" to
the battery charger. Docking of wearable audio devices to a charger
is often accomplished using magnetic attraction of the wearable
audio device to the correct location of the charger. A docking
magnet, located in the wearable audio device such that it is
attracted to a magnet or magnetic material in the charger, can be
used to help properly locate and orient the wearable audio device
in the charger.
[0024] Wearable audio devices, in particular earbuds, may also be
configured to allow the left and right earbuds to be held or
"parked" together when not in use. Earbuds can also be configured
to be parked to another structure, such as a neckband. Parking of
earbuds is often accomplished with a parking or coupling magnet in
the earbud, where the parking or coupling magnet is located such
that it is at or very close to the surface of the earbud.
[0025] Wearable audio devices can include one or both of a docking
magnet and a parking magnet. Wearable audio devices many times
include other magnetic devices or materials, for example the
transducer magnet of an electro-acoustic transducer, ferrite cores
(which may be used in filters, for example), magnetic reed
switches, and steel or other magnetic materials. These magnetic
devices and materials can cause stray magnetic fields and magnetic
field perturbations at the location of the magnetometer or other
magnetic field sensor that is used in determining heading
information. In an earphone with an electro-acoustic transducer
magnet and a magnetometer that is located close to the transducer,
the transducer's magnetic field can overwhelm the magnetometer and
prevent it from properly detecting the strength of the Earth's
magnetic field. Magnetometers typically operate in a stable
operational range only if they are compensated for any stray fields
or field perturbations.
[0026] Wearable audio devices include an electro-acoustic
transducer for creating audio output. For wearable audio devices
that are configured to determine a directional heading of the
Earth's magnetic field there is also a magnetometer system that
includes a magnetic field sensor. The magnetometer system is
configured to derive from the magnetic field sensor output a
directional heading of the Earth's magnetic field. Magnetometer
systems are typically enabled to compensate the magnetic field
sensor output for offsets due to changes in stray magnetic fields,
nearby magnetic materials, and ambient temperature changes.
Compensation helps reduce heading errors, particularly in cases
where there are stray magnetic fields and/or magnetic materials
(such as iron) that are close enough to the magnetometer to affect
its sensitivity to the Earth's magnetic field. Compensation can
interrupt operation of the directional heading system and thus
cause inconvenience for the user. Accordingly, reducing the
frequency of magnetometer compensation and reducing the offsets
that need to be compensated for will enable better heading accuracy
and fewer and shorter compensation-based interruptions to the
heading system.
[0027] The compensation of some magnetometers is temperature
dependent. In such cases the wearable audio device has the ability
to determine the wearable audio device's internal temperature. In
an example the internal temperature is determined using a
temperature sensor. The wearable audio device can also include a
processor, and associated memory. The memory can be configured to
store temperature-dependent compensation information. In an example
the magnetometer system is configured to use the wearable audio
device's internal temperature to retrieve compensation information
from the memory, in order to compensate for changes in the device's
internal stray magnetic fields caused by changes to the device's
internal temperature.
[0028] FIG. 1 is a perspective view of a wireless in-ear headphone
or earbud, 10. An earbud is only one non-limiting example of the
subject audio device. Other examples are described elsewhere
herein. Earbud 10 includes body or housing 12 that houses the
active components of the earbud. Portion 14 is coupled to body 12
and is pliable so that it can be inserted into the entrance of the
ear canal. Sound is delivered through opening 15. Retaining loop 16
is constructed and arranged to be positioned in the outer ear, for
example in the antihelix, to help retain the earbud in the ear.
Earbuds are well known in the field (e.g., as disclosed in U.S.
Pat. No. 9,854,345, the disclosure of which is incorporated herein
by reference), and so certain details of the earbud are not further
described herein. An earbud 10 is an example of a wearable audio
device according to this disclosure, but is not limiting of the
scope of the disclosure as other types of wearable audio devices
can include a magnetometer that needs to be compensated.
[0029] FIG. 2 is a partial cross-sectional view of only certain
elements of an earphone or earbud 20 that are useful to a better
understanding of the present disclosure. Earbud 20 comprises
housing 21 that encloses electro-acoustic transducer 30. Some or
all of housing 21 can be made of steel or another magnetic
material. Housing 21 comprises front housing portion 50 and rear
housing portions 60 and 62. Transducer 30 has diaphragm 32 that is
driven in order to create sound pressure in front cavity 52. Sound
pressure is directed out of front housing portion 50 via opening
54. An earbud, such as shown by earbud 10 in FIG. 1, typically
includes a pliable tip (not shown) that is engaged with neck 51 of
housing portion 50, to help direct the sound into the ear canal.
Earbud housing 21 further comprises a rear enclosure made from rear
housing portions 60 and 62, and grille 64. Note that the details of
earbud 20 are exemplary of aspects of earphones and are not
limiting of the scope of this disclosure, as the present
magnetometer compensation can be used in varied types and designs
of earphones and other wearable audio devices.
[0030] Transducer 30 further comprises magnetic structure 34.
Magnetic structure 34 comprises transducer magnet 38 and magnetic
material that functions to confine and guide the magnetic field
from magnet 38, so that the field properly interacts with coil 33
to drive diaphragm 32, as is well known in the electro-acoustic
transducer field. The magnetic material comprises cup 36 and front
plate 35, both of which are preferably made from a material with
relatively high magnetic susceptibility, also as is known in the
field. Transducer printed circuit board (PCB) 40 carries electrical
and electronic components (not shown) that are involved in driving
the transducer. Pads 41 and 42 are locations where wires (not
shown) can be coupled to PCB 40.
[0031] Magnetometer system 72 in this non-limiting example is
mounted on PCB 70. Magnetometer system 72 includes a magnetic field
sensor such as a magnetometer that is arranged to sense the
strength of magnetic fields at the location of the magnetometer, as
is known in the field. Magnetometer system 72 is configured to
detect the Earth's magnetic field. The output of the magnetic field
sensor of magnetometer system 72 can be used to determine the
direction in which the wearer's head is pointed, as described in
U.S. Patent Application Publication 2019/0246235, published on Aug.
8, 2019, the entire disclosure of which is incorporated herein by
reference for all purposes.
[0032] Since the magnetic field sensor of magnetometer system 72 is
relatively close to transducer magnet 38, the transducer's magnetic
field can affect the ability of the magnetic field sensor to
properly detect the Earth's magnetic field. Parking magnet 74 is in
this non-limiting example located just inside of grill 64. It
should be understood that a parking magnet is generally located
inside of or at least close to (adjacent) the inside surface of
earphone housing 21 at a location where it can act to help park the
earphone to another structure, such as another earphone housing.
Magnet 74 could alternatively be a coupling or docking magnet,
which would generally be located inside of or at the inside surface
of housing 21 at a location where it can act to help dock or couple
the earphone to a battery charger. One possible location of a
coupling magnet would be somewhere on the interior of front housing
portion 50 inside the front cavity 52. In some examples magnet 74
is also located such that its magnetic field can affect the ability
of the magnetic field sensor to properly detect the Earth's
magnetic field.
[0033] FIG. 3 is a schematic diagram of in-ear headphone 102,
illustrating in part a coupling or parking magnet 106. The
described components are located in earbud body 100. Battery 114
provides power to powered components. Processor and associated
memory 112 is used, in part, to drive transducer 104. Processor 112
is also used to determine the wearer's look direction, in part
using the output of the magnetic field sensor of the combined
magnetic field sensor and inertial measurement unit (IMU)
functional block 108. It should be understood that earphones will
have more components and can have different components than those
shown in FIG. 3. Some earphones include a magnet other than the
transducer magnet. This other magnet is represented in this
non-limiting example by coupling or parking magnet 106. Coupling or
parking magnet 106 can be used to couple or park earphone 100 to
another structure. As one non-limiting example, magnet 106 can be
used to "dock" an earbud to a battery charger. As another
non-limiting example, magnet 106 can be used to park an earbud to
another structure, such as a neckband or another earbud. Other uses
of coupling and/or parking magnets are known in the field and are
included within the scope of the present disclosure. All of the
magnets in earbud body 100 of earphone 102 create magnetic fields
that can adversely impact the accuracy of the sensing of the
Earth's magnetic field by sensor 108, as described above.
[0034] An effect that stray magnetic fields and materials that
perturb the Earth's magnetic field have on the magnetic field
sensor of magnetometer system 72 can be compensated for using
compensation routines that are known in the technical field. Such
compensation routines can entail a complex, lengthy process that
might involve user action, such as moving the magnetometer. The
need for compensation has a temperature dependency. Accordingly, as
the ambient temperature changes the magnetometer might need to be
compensated more frequently because its internal stray fields are
changing significantly. As an example, a person wearing a wearable
audio device such as audio eyeglasses may step out of a warm
building into a cold environment. Or, the wearable audio device may
absorb strong sunlight, which can heat up the device's internal
magnets and cause temperature-dependent changes to their magnetic
fields. Wearable audio device temperature changes will cause
changes to the device's internal stray magnetic fields, leading to
potential errors in directional headings determined by the
magnetometer system until the magnetometer is compensated, which
might take some time.
[0035] The present wearable audio device is configured to use the
wearable device temperature in order to address the negative
consequences of magnetometer compensation. In an example the
wearable device internal temperature is determined using a
temperature sensor that is part of the wearable audio device. In an
example the wearable audio device includes an IMU with a gyroscope
and/or accelerometer. The IMU is involved in the heading
determination, as is known in the technical field. Some IMUs
include a temperature sensor, which can be used to determine the
internal temperature. In an example the wearable audio device is
enabled to access the ambient temperature from a temperature sensor
of the wearable audio device or from another device or system, or
from the cloud. For example if the wearable audio device
communicates with a smartphone, the wearable audio device might
derive the temperature from the smartphone, or from another source
via the smartphone. In an example the wearable audio device's
internal temperature can be inferred from the ambient
temperature.
[0036] The three axis magnetometer is involved in determining the
compass heading for the direction that the user is facing. This is
complicated by the fact that there can be significant magnetic
field biases on the magnetometer axes. Such biases can originate in
the wearable device itself. If the temperature were constant, then
these internal biases would not change. In order to determine the
compass direction the user is facing, the system must compensate
for these static biases by offsetting the absolute axis reading by
these static biases. As the device temperature begins to change the
biases of internal origin also change. Typically, when the biases
change by some threshold amount, the system will trigger a dynamic
re-compensation in order to compute new biases to be used for axis
offset. The system does this because it assumes that the magnetic
bias in the environment has changed.
[0037] In the present compensation technique, internal bias changes
due to internal temperature changes are predetermined. Then the
system takes these bias changes into account (i.e., it compensates
for them) in its determinations of compass direction. A result is
that the system does not need to conduct a dynamic re-compensation
as frequently. Thus, the frequency of and the need for user
interaction concerning dynamic compensation events for the
magnetometer can be lessened. In an example the predetermined
temperature-dependent internal bias changes are stored in a memory
that is accessible by the processor of the magnetometer system. The
magnetometer system can then use the device temperature to retrieve
the bias change information for the current internal device
temperature, or the processor can be used to interpolate the stored
information based on the current temperature and the temperature
values that are associated with the stored compensation
information. The magnetometer system can be compensated when the
temperature changes, using the retrieved information. In an example
the temperature-related compensation can occur when the internal
device temperature changes by at least a threshold amount from the
temperature recorded at its last compensation and its present
internal device temperature.
[0038] In an example the temperature-dependent compensation
information is determined relative to a reference temperature. In
an example the magnetometer system is configured to compensate the
magnetometer when the internal device temperature exceeds a
reference temperature by more than a threshold. In an example one
or more wearable audio systems can be exposed to various
temperatures under controlled conditions, for example in a factory
or in a lab. Appropriate compensation-related information can be
measured and stored in the device memory. In an example such
information is determined for a number of ostensibly identical
wearable audio devices and a composite (such as an average) of this
information is stored in the memories of the devices. Or such
information can be made available from another device (such as a
smartphone) that is in communication with the wearable audio
device.
[0039] By automatically compensating the magnetometer as the
temperature changes, the accuracy of the directional heading
determined by the magnetometer system is expected to increase. Also
magnetometer recalibration events should be less frequent since the
directional heading will remain closer to being correct.
[0040] FIG. 4 is an exemplary plot of the magnetic field offset (in
micro Tesla) vs. temperature (in degrees C.) for an internal magnet
of a wearable audio device. This illustrates the temperature
dependency of the magnetic field of a magnet (such as the permanent
magnet of an electro-acoustic transducer) of the type that might be
used in a wearable audio device. If this field is a stray field
that has an effect on the magnetometer, as the temperature of the
magnet changes the strength of the stray field changes. As
described above, the change in the stray field can detrimentally
impact the determination of compass direction by the magnetometer
system. If the data plotted in FIG. 4 is stored and used by the
system, the changes in stray fields can be accounted for without
the need to dynamically compensate the magnetometer.
[0041] One or more of the above described systems and methods, in
various examples and combinations, may be used in a wide variety of
audio systems, including wearable audio devices in various form
factors. Unless specified otherwise, the term wearable audio
device, as used in this document, includes headphones and various
other types of personal audio devices such as head, shoulder or
body-worn acoustic devices (e.g., audio eyeglasses or other
head-mounted audio devices) that include one more acoustic
transducers to receive and/or produce sound, with or without
contacting the ears of a user. It should be noted that although
specific implementations of wearable audio devices primarily
serving the purpose of acoustically outputting audio are presented
with some degree of detail, such presentations of specific
implementations are intended to facilitate understanding through
provisions of examples and should not be taken as limiting either
the scope of disclosure or the scope of claim coverage.
[0042] Off-ear headphones produce sound using an acoustic driver
that is spaced from the ear. Such headphones should ideally deliver
high-quality sound to the ears at desired volumes, without spilling
too much sound to the environment. Eyeglass headphones can be
accomplished with one or more drivers built into the eyeglass
frame. Sound can be emitted from openings or vents in the eyeglass
frame. If one vent is close to an ear and another vent is farther
from the ear, quality sound can be delivered to the ear with
minimal spillage. An eyeglass headphone is disclosed in U.S. Pat.
No. 10,555,071, issued on Feb. 4, 2020, the entire disclosure of
which is incorporated herein by reference for all purposes.
[0043] FIG. 5 is a front, perspective view of eyeglass headphones
120, which are another non-limiting example of an audio device with
a magnetic field sensor that could be affected by the stray fields
and field perturbations caused by the magnet/magnetic material of
the transducer or other structure of eyeglass headphones 120. In
this non-limiting example there is an eyeglass bridge 134 that is
constructed and arranged to sit on the nose, with lenses 136 and
138 in front of the eyes. Right temple piece 122 is coupled to
bridge 134 and extends over the right ear. Left temple piece 132 is
coupled to bridge 134 and extends over the left ear. Each temple
piece carries a loudspeaker (not shown). The right loudspeaker is
carried in section 124 of temple piece 122. Visible in this view
are rear high-frequency loudspeaker dipole opening 126, rear
low-frequency dipole opening 130, and rear resonance damping
opening 128. In another example there are only two sound-emitting
openings, one that emits front side acoustic radiation and one that
emits rear side acoustic radiation. Any or all of the openings can
be covered by a screen. The screen covering opening 128 is
preferably resistive to accomplish waveguide resonance damping.
Note that in this example the left temple piece 132 has a
transducer and sound-emitting opening arrangement that is the same
as that disclosed herein for the right temple piece.
[0044] FIG. 6 is a schematic cross-section of a temple piece 156 of
eyeglass headphones 150. Eyeglass headphones 150 are another
non-limiting example of an audio device with a magnetometer system,
as described above. Electro-acoustic transducer 160 is located in
housing 174 with front cavity 170. Transducer 160 has a transducer
magnet (not shown in this view) that produces a magnetic field.
Housing 174 is located such that an acoustic outlet 172 of housing
174 is arranged to direct sound such that the sound can be received
by ear canal 152 of the wearer's ear E. Magnetic field sensor and
IMU 180 is carried by temple piece 156; sensor and IMU 180 may or
may not be located in housing 174. Control, amplification, power
and wireless communications (e.g. BLE) module 162 is also carried
by the eyeglass headphones 150, and may or may not be carried by
temple piece 156.
[0045] Elements of FIGS. 3 and 6 are shown and described as
discrete elements in a block diagram. These may be implemented as
one or more of analog circuitry or digital circuitry.
Alternatively, or additionally, they may be implemented with one or
more microprocessors executing software instructions. The software
instructions can include digital signal processing instructions.
Operations may be performed by analog circuitry or by a
microprocessor executing software that performs the equivalent of
the analog operation. Signal lines may be implemented as discrete
analog or digital signal lines, as a discrete digital signal line
with appropriate signal processing that is able to process separate
signals, and/or as elements of a wireless communication system.
[0046] When processes are represented or implied in the block
diagram, the steps may be performed by one element or a plurality
of elements. The steps may be performed together or at different
times. The elements that perform the activities may be physically
the same or proximate one another, or may be physically separate.
One element may perform the actions of more than one block. Audio
signals may be encoded or not, and may be transmitted in either
digital or analog form. Conventional audio signal processing
equipment and operations are in some cases omitted from the
drawing.
[0047] Examples of the systems and methods described herein
comprise computer components and computer-implemented steps that
will be apparent to those skilled in the art. For example, it
should be understood by one of skill in the art that the
computer-implemented steps may be stored as computer-executable
instructions on a computer-readable medium such as, for example,
floppy disks, hard disks, optical disks, Flash ROMS, nonvolatile
ROM, and RAM. Furthermore, it should be understood by one of skill
in the art that the computer-executable instructions may be
executed on a variety of processors such as, for example,
microprocessors, digital signal processors, gate arrays, etc. For
ease of exposition, not every step or element of the systems and
methods described above is described herein as part of a computer
system, but those skilled in the art will recognize that each step
or element may have a corresponding computer system or software
component. Such computer system and/or software components are
therefore enabled by describing their corresponding steps or
elements (that is, their functionality), and are within the scope
of the disclosure.
[0048] A number of implementations have been described.
Nevertheless, it will be understood that additional modifications
may be made without departing from the scope of the inventive
concepts described herein, and, accordingly, other examples are
within the scope of the following claims.
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