EP 2 975 863 A1
TEPZZ 97586¥A_T
(19)
(11)
EP 2 975 863 A1
EUROPEAN PATENT APPLICATION
(12)
(43) Date of publication:
(51) Int Cl.:
H04R 5/02 (2006.01)
20.01.2016 Bulletin 2016/03
G10K 11/178 (2006.01)
(21) Application number: 15176936.1
(22) Date of filing: 15.07.2015
(84) Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB
GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO
PL PT RO RS SE SI SK SM TR
Designated Extension States:
BA ME
Designated Validation States:
MA
• GREIG, Nigel
1022 Auckland (NZ)
• DARBONNE, Thomas Allen
Santa Cruz, California 95062 (US)
• POLETTI, Mark
5010 Lower Hutt (NZ)
• DE GUIGNÉ, Johann Frédéric
1050 Auckland (NZ)
(30) Priority: 15.07.2014 NZ 62750814
(74) Representative: Elkiner, Kaya
(71) Applicant: Phitek Systems Limited
Keltie LLP
No.1 London Bridge
London SE1 9BA (GB)
Auckland 1023 (NZ)
(72) Inventors:
• GUL, Hassan Faqir
0600 Auckland (NZ)
(54)
NOISE CANCELLATION SYSTEM
EP 2 975 863 A1
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Systems and methods of active noise cancellation are disclosed, that are for aircraft in-flight entertainment
systems. An input is received from an input device that is processed to produce an output signal. The output signal is
provided to at least one driver which is adapted to transmit the output signal to a user seated in a seat. The output signal
is adapted so that, in use, the user hears a reduced ambient noise when seated in the seat.
Printed by Jouve, 75001 PARIS (FR)
(Cont. next page)
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Description
[0001] The present invention relates to an active noise
cancellation system which uses a microphone which is
detached from a user of the system, and in particular,
but not exclusively, to such a system which is configured
for use in a passenger vehicle such as an aircraft.
tion is not, and should not be taken as, an acknowledgement or any form of suggestion that the prior art forms
part of the common general knowledge in any country.
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Background to the Invention
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[0002] Many aircraft, including most aircraft on long
haul and international routes, provide an inflight entertainment (IFE) system. Such systems provide a combination of audio and video entertainment. Modern IFE systems provide passengers with a variety of audio and visual media options, for example, music channels, games,
movies, and television programmes. Users can be provided with audio or video-on-demand, meaning that each
individual user may select an audio track or audio channel, or an audio-visual programme that they wish to listen
to, or watch, at any given time. This is usually achieved
by each passenger seat in an aircraft environment having
its own visual display unit (usually in the form of an LCD
display) and an appropriate jack for receiving the plug
for a headset which delivers the audio content to the user.
The VDU may be connected to the server directly or
through an intermediary device such as a seat electronics
box.
[0003] Audio from the IFE system is typically delivered
to a user through a headset (the terms "headset" and
"headphone" are used interchangeable herein). However, the noise generated by the aircraft can be distracting
or annoying for the user. Jet engined aircraft tend to generate low frequency noise in and around the 150-200Hz
range. The need to minimise the cost of the headsets
precludes the use of dense sound insulating materials
which would be required to attenuate noise in this frequency range to any significant degree.
[0004] A well-known method of reducing the level of
ambient noise apparent to a headset wearer is the technique known as active noise cancellation or active noise
reduction (ANR). Here, a microphone mounted to the
headset detects the ambient noise. Through suitable signal processing the headset’s drivers are driven to produce an inverted (antiphase) version of the signal. The
ambient noise and the inverted signal cancel each other,
and the user experiences a decrease in the ambient noise
level, particularly at low frequencies.
[0005] While headphones with integrated active noise
cancellation hardware work well, they may be prohibitively expensive to issue to passengers.
[0006] Other headphones have sensing microphones
which supply a signal to active noise cancellation circuitry
provided in the seat i.e. the noise cancellation circuitry
is not included in the headset. This reduces the cost of
the headset, but even these headsets may be prohibitively expensive to issue to passengers.
[0007] The reference to any prior art in this specifica-
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Object of the Invention
[0008] It is an object of the invention to provide an active noise cancellation system, a controller for an active
noise cancellation system and/or a method of generating
an active noise cancellation anti-noise signal which will
overcome or ameliorate problems with active noise cancellation systems at present, or which will at least provide
the public with a useful choice.
[0009] Other objects of the present invention may become apparent from the following description, which is
given by way of example only.
Brief Summary of the Invention
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[0010] In a first aspect the invention may be said to
broadly consist in an active noise cancellation system for
an aircraft In-flight entertainment system, the active noise
cancellation system comprising:
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At least one input device, associated with a seat on
the aircraft, to receive an input representative of an
ambient noise in the vicinity of the seat;
Processing means adapted to process the input to
produce an output signal adapted to reduce the ambient noise in volume associated with the seat;
An output for transmitting an output signal to at least
one driver, the driver adapted to transmit the output
signal to a user, and
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Wherein the output signal is adapted so that, in use, the
user hears a reduced ambient noise when seated in the
seat.
[0011] Preferably at least one driver is associated with
a headset and/or at least one driver or at least one input
device is associated with the seat.
[0012] Preferably in use a position of the user may
change, and wherein the user hears a reduced ambient
noise in a plurality of positions.
[0013] Preferably system comprises a plurality of input
devices, the input devices spatially separated in a substantially planar arrangement.
[0014] Preferably system as claimed in claim 5 wherein
the plurality of input devices are separated around a driver.
[0015] Preferably the output comprises a jack adapted
to form a connected with an audio device.
[0016] Preferably the input means is adapted to receive an input from a plurality of input devices.
[0017] Preferably at least some of the plurality of input
devices are associated with a passenger seat.
[0018] Preferably the output means is adapted to transmit an output to a plurality of output devices.
[0019] Preferably at least one of the plurality of output
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devices is associated with a passenger seat.
[0020] Preferably at least one driver or at least one
input device are attached or attachable to an arm or arms
of a seat headrest, wherein the angle of the diver or microphone is acute with respect to a user of the seat.
[0021] Preferably the passenger seat or headrest has
at least one arm and the at least one of the plurality of
the input and/or output devices is associated with the
arm of the headrest.
[0022] Preferably at least one driver or at least one
input device are attached or attachable to an arm or arms
of a seat headrest, wherein the angle of the diver or microphone is acute with respect to a user of the seat.
[0023] Preferably the plurality of input and/or output
devices are substantially arranged in a row and at least
one of the of the plurality of input and/or output devices
is forward of another of the devices.
[0024] Preferably at least some of the plurality of input
and/or output devices are arranged to span the head of
a user.
[0025] Preferably each of the plurality of input devices
is associated with an output device. Alternatively each
of the plurality of input devices is associated with a plurality or all of the output devices.
[0026] Preferably each of the plurality of input devices
is associated with at least one output device and the input
and output devices are at least partially aligned.
[0027] Preferably the system comprises a output device detector to determine a characteristic of the output
device.
[0028] Preferably at least one of the plurality of output
devices is associated with a set of headphones.
[0029] Preferably at least one of the plurality of output
devices is a driver in a set of headphones.
[0030] Preferably at a plurality of the input devices are
arranged in a group. Preferably the group forms a polygonal arrangement. Wherein each of the input devices is
at a vertex of the polygon. Preferably an output device
is positions at substantially the centre of the group.
[0031] Preferably the active noise cancellation system
is associated with an IFE system.
[0032] Preferably the input device is a microphone.
Preferably the driver is a speaker.
[0033] Preferably the ANC is an analogue system.
[0034] In a second aspect the invention may be said
to broadly consist in an active noise cancellation system
comprising:
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An input means adapted to receive an input from an
input device;
Processing means adapted to process the input to
produce an output adapted to reduce the noise apparent at the input;
An output means and adapted to transmit an output
to at least one driver separated from the input device,
and
[0035]
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ed to allow a change in the separation of the input and
output means and there is a reduction in noise apparent
at the driver.
[0036] Preferably the adaption a plurality of spatially
separated input device allows a change in separation of
the input device and the output means.
[0037] Preferably the input devices are spatially separated in a geometrical arrangement.
[0038] Preferably the input devices are substantially in
a plane.
[0039] Preferably a second output device is associated
with the input device/s.
[0040] In a third aspect the invention may be said to
broadly consist in a method of active noise cancellation
in an In-Flight Entertainment system, the method comprising the steps of:
Receiving an input from an input device associated
with the In-Flight Entertainment system;
Processing the input to produce an output signal
adapted to reduce the ambient noise in a volume
associated with the seat;
Outputting an output signal to at least one driver, the
driver adapted to transmit the output signal to a user,
and
Wherein the output signal is adapted so that, in use,
the user hears a reduced ambient noise when seated
in the seat.
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[0041] Preferably the driver is attachable to a user and
input device is attached to an object.
[0042] Preferably the object is a seat or part of an IFE
system.
[0043] Preferably the spatially separation is by attachment to separate objects.
[0044] Preferably the spatial separation is variable.
[0045] Preferably the method includes the step of varying the separation wherein the output continues to receive a reduced noise.
[0046] In a further aspect the invention may be said to
broadly consist in an active noise cancellation system for
an In-flight entertainment system comprising:
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Wherein the active noise cancellation is adapt-
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An input means adapted to receive an input from an
input device associated with a seat associated with
the IFE system;
Processing means adapted to process the input to
produce an output adapted to reduce the noise apparent at the input;
An output means and adapted to transmit an output
to at least one driver separated from the input device,
and
[0047] Wherein the active noise cancellation is adapted so that, in use, a user of the In-flight entertainment
system hears a reduced apparent noise when seated in
the seat.
[0048] Preferably the driver is in a headset worn by the
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user.
[0049] Preferably the driver is connected to the IFE
system by wired or wireless means.
[0050] Preferably there are a plurality of drivers.
[0051] In a further aspect the invention may be said to
broadly consist in an active noise cancellation system
adapted for a seated user, the system comprising:
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An input means adapted to receive an input from an
input device associated with the seat;
Processing means adapted to process the input to
produce an output adapted to reduce the noise apparent at the input;
An output means adapted to transmit an output to at
least one driver, the driver adapted to provide the
output to the user; and
[0052] Wherein there is a reduction in noise apparent
to the user.
[0053] In a further aspect the invention may be said to
broadly consist in an active noise cancellation system
adapted for a seat for a user, the system comprising:
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An input means adapted to receive an input from an
input device associated with the seat;
Processing means adapted to process the input to
produce an output adapted to reduce the noise apparent at the input;
An output means adapted to transmit an output to at
least one driver, the driver adapted to provide the
output to the user; and
[0054] Wherein there is a reduction in noise apparent
to the user when the user is sat on the seat.
[0055] Preferably the input device is attached, or attachable to the seat. More preferably the input device is
attached, or attachable, a headrest of the seat. Preferably
the input device is a removable attachment for the seat.
Preferably the input device and driver are attached to a
removable attachment for the seat.
[0056] Preferably the reduction in noise is apparent for
the user when a separation between the user and the
seat changes.
[0057] Preferably there are a plurality of input devices
associated with the seat, the input devices spatially separated to reduce the noise apparent to the user when the
space between the user and the seat changes.
[0058] Preferably there driver is worn by the user. Preferably the driver is worn as a headset.
[0059] Alternatively the driver is attached, or attachable to, the seat.
[0060] Preferably a plurality of drivers is associated
with the seat. Preferably at least one driver is attached
or attachable to the seat and at least one driver is attachable to the user.
[0061] In a second aspect the invention may be said
to broadly consist in a seat portion for an active noise
cancellation system, the seat portion comprising:
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An input device for receiving an input;
An driver means associated with the input device
and adapted to transmit an output adapted to reduce
the noise apparent at the input.
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[0062] Preferably the output is adapted to allow a
change in the separation of the input and output means.
[0063] Preferably the seat portion is unitary with, a part
of, attached to or attachable to a seat.
[0064] Preferably the seat is associated with a
processing means, the processing means adapted to receive the input and generate an anti-noise signal for
transmitting to the output.
[0065] Preferably the input device comprises a plurality
of microphones.
[0066] Preferably a plurality of microphones surround
or encircle a driver means.
[0067] Preferably the seat portion comprises a connection means to an IFE system.
[0068] Preferably the seat portion can transmit and/or
receive communication from the IFE system. Preferably
the output can be transmitted to a driver of a headset.
[0069] According to one aspect of the present invention
there is provided an active noise cancellation system
controller comprising:
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first input means for receiving an ambient noise signal from at least one sensing microphone;
second input means for receiving a signal from a
measuring means which is representative of a distance between a reference point and a head of a
user, wherein the reference point is substantially stationary relative to the at least one sensing microphone;
processing means for receiving the signals from the
first and second input means and generating an antinoise signal which will destructively interfere with the
ambient noise detected by the sensing microphone;
and
output means for transmitting the anti-noise signal
to at least one driver;
wherein the processing means varies a property of
the antinoise signal in response to changes in the
signal from the measuring means.
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[0070] Preferably the property comprises one or more
of a phase amplitude, or audio spectrum content so of
the antinoise signal.
[0071] Preferably the controller comprises an input for
receiving an audio signal, wherein the controller superimposes the audio signal with the anti-noise signal and
transmits the combined signal to the output.
[0072] Preferably the audio signal is generated by an
in-flight entertainment (IFE) system.
[0073] Preferably the driver forms part of a headset.
[0074] Preferably the controller comprises means for
adjusting at least one property of the anti-noise signal
dependent on at least one characteristic of the at least
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one driver and/or the headset.
[0075] Preferably the controller comprises an input
means for receiving a signal which is indicative of the at
least one characteristic.
[0076] Preferably the controller adjusts one or more of
a phase, amplitude, or audio spectrum content of the
anti-noise signal in response to a signal received by the
second input means and/or a signal received by the third
input means.
[0077] According to a further aspect of the present invention there is provided a seat for a passenger vehicle,
the seat comprising at least one sensing microphone operable to sense noise and provide a sensed noise signal
to an active noise cancellation system controller.
[0078] Preferably the seat comprises at least two microphones, wherein at least one microphone is provided
on each side of the seat.
[0079] Preferably the active noise cancellation system
controller comprises the controller of the first aspect.
[0080] According to a further aspect of the present invention there is provided an active noise cancellation system comprising:
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a seat comprising at least one sensing microphone
for receiving ambient noise;
a measuring means for measuring or estimating a
distance between a user’s head and a reference
point, wherein the reference point is substantially
fixed with respect to the sensing microphone;
processing means for receiving signals from the
sensing microphone and the measuring means and
generating an anti-noise signal which will destructively interfere with the ambient noise detected by
the sensing microphone; and
output means for transmission of the anti-noise signal to at least one driver;
wherein the processing means varies a property of
the antinoise signal in response to changes in the
signal from the measuring means.
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More preferably the processing means receives the signal from the headset.
[0087] Preferably the processing means uses the distance between the user’s head and the reference point
and/or the at least one characteristic as a variable in determining at least one of a required phase, amplitude, or
audio spectrum content of the anti-noise signal.
[0088] Preferably the measuring means comprises
one of an infra-red proximity sensor or an ultra-sonic
proximity sensor. Alternatively the measuring means
comprises a camera.
[0089] According to a further aspect of the present invention there is provided a method of creating an active
noise cancellation anti-noise signal comprising:
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[0081] Preferably the property is the phase/timing/delay of the antinoise signal.
[0082] Preferably the sensing microphone is positioned at or adjacent a headrest or upper portion of the
seat, and the reference point is at or adjacent the headrest or upper portion of the seat.
[0083] Preferably the processing means receives an
audio signal, wherein the processing means superimposes the audio signal with the anti-noise signal and transmits the combined signal to the output.
[0084] Preferably the audio signal is generated by an
in-flight entertainment (IFE) system.
[0085] Preferably the driver forms part of a headset,
and the processing means adjusts at least one property
of the anti-noise signal dependent on at least one characteristic of the at least one driver and/or the headset.
[0086] Preferably the processing means receives a
signal which is indicative of the at least one characteristic.
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receiving an ambient noise signal at a first location;
dynamically measuring or estimating a distance between the first location and a second location in
which a noise cancellation effect is required;
generating an anti-noise signal; and
outputting the anti-noise signal;
the method further comprising adjusting a property
of the anti-noise signal in response to changes in the
distance between the first and second locations such
that the anti-noise signal is suitable to produce a
noise cancellation effect at the second location.
[0090] Preferably the property is the phase/timing/delay of the antinoise signal.
[0091] According to a further aspect of the present invention there is provided a seat for a passenger vehicle
comprising at least one sensing microphone, at least one
output jack, and connecting means for connecting the at
least one microphone and the output jack to an active
noise cancellation system controller.
[0092] Preferably the controller comprises the controller of the first aspect.
[0093] Preferably the seat further comprises a measuring means for measuring or estimating a distance between a user’s head and a reference point, wherein the
reference point is substantially fixed with respect to the
sensing microphone.
[0094] In a further aspect the invention broadly provides a noise cancellation system comprising:
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an input means for receiving a noise signal from a
sensing microphone associated with a vehicle passenger seat;
an output means for providing an anti-noise signal
to a passenger headset;
a processing means to process the noise signal to
provide the anti-noise signal based a location of the
headset in use.
[0095] In one embodiment the location of the headset
is estimated based on a user’s likely head position in the
seat.
[0096] In another embodiment the location is deter-
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mined or estimated by measurement.
[0097] The invention may also be said broadly to consist in the parts, elements and features referred to or
indicated in the specification of the application, individually or collectively, in any or all combinations of two or
more of said parts, elements or features, and where specific integers are mentioned herein which have known
equivalents in the art to which the invention relates, such
known equivalents are deemed to be incorporated herein
as if individually set forth.
[0098] According to a still further aspect of the present
invention, an active noise cancellation system and/or a
controller for such a system is substantially as herein
described, with reference to the accompanying drawings.
[0099] Further aspects of the invention, which should
be considered in all its novel aspects, will become apparent from the following description given by way of example of possible embodiments of the invention.
Brief Description of the Figures
Figure 13
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Figure 14
10
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Figure 12
Is a diagrammatic side view of an active
noise control system of the present invention installed in an aircraft passenger seat.
is a schematic view of a controller for an
active noise control system of the present
invention.
is a schematic view of an active noise control system of the present invention having
(a) 2 and (b) 4 microphones.
is a schematic view of arrangements of the
seat, headrest and arms.
is a schematic view of an active noise control system of the present invention where
the arms of the headrest are used for (a)
microphones and (b) microphones and
speakers
(Prior Art) is a diagrammatic view of an ANC
system.
(Prior Art) is a diagrammatic view of an ANC
system with multiple channels.
shows plotted feedback views of the sound
levels for impingement angles of (a) 0, (b)
45, (c) 90 and (d) 180 degrees at a distance
of 60mm .
shows the feedback field along an axis for
a 2 channel canceller with speaker to microphone distances of 20mm to 120 mm for
impingement angles of (a) 0, (b) 45, (c) 90
and (d) 180 degrees.
shows plotted feedback views as in Fig 8a
for (a) 4 microphones 2 drivers and (b) 4
microphones 4 speakers at 60mm.
shows plotted feedback views as in Fig 8a
and Fig 10 at a distance of 12mm.
are schematic and diagrammatic views of
a controller for an active noise control system using a circular array of microphones
of the present invention.
is a plot view of the loop gain of a controller
using (a) a single speaker and (b) a circular
array for an active noise control system of
the present invention.
shows noise cancellation achieved by a
driver from (a) a low cost headphone, (b) a
better quality headphone and (c) a loudspeaker in the present invention.
Brief Description of Embodiments of the Invention
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[0100]
Figure 1
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[0101] Referring first to Figures 1 and 2, an active noise
cancellation system according to an embodiment of the
present invention is generally referenced by arrow 100.
[0102] The system 100 comprises a seat 1 which is
provided with at least one sensing microphone 2. The
sensing microphone 2 is located on or in the seat, preferably at or adjacent the headrest 3 or upper portion of
the back of the seat 1. The or each sensing microphone
2 is preferably positioned so as to be in the vicinity of the
ears of an average user U of the system 100 when the
user is seated in a normal position. In a preferred embodiment at least one microphone is provided on either
side of the seat. The provision of two or more microphones allows a sound wave to be modelled in three
dimensions, this allowing an improved model of the
acoustic environment, so a more effective anti-noise signal can be generated.
[0103] Preferably the input device, e.g. microphone, is
substantially stationary but the noise cancellation produced by the system is adapted to reduce the ambient
noise at a plurality of positions of a user, and in particular
a user’s head. That is the user’s head will typically move
in a spatial area of the seat and the noise cancellation
should be adapted to reduce the sound in at least a portion of this area. The area (which represents a 3D volume)
may include changes to the horizontal and vertical separation of the microphone and user and/or microphone
and driver. For instance the user may lean forward to
retrieve an item and her head may increase in separation
from the microphone/s location. The area associated with
the seat is preferably a general area which has strong
attenuation in a first area, the attenuation reducing as a
user moves from the area. Preferably the area or volume
includes a range of typical head positions.
[0104] A controller 200 is provided. The controller has
a first input 10 for receiving a signal from the sensing
microphone 2 which is representative of the ambient
noise. A second input 11 may be provided for receiving
a signal from a measuring means 12 which measures or
estimates a distance between the head of the user U and
a reference point R on the seat. The reference point R
is preferably substantially fixed with respect to the one
or more sensing microphones 2, and in some embodiments the reference point R may be coincident with one
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of the sensing microphones 2. Suitable measuring
means 12 are described in more detail herein. In a preferred embodiment multiple microphones, or an array of
are used. Multiple microphones allow separation of the
sound or ambient noise into various directions of arrival.
This provides information about the sound field instead
of a single sensor. In an embodiment microphones may
be present in multiple locations around the user seat, for
instance at the VDU and in the user seat.
[0105] The controller 200 is further provided with an
output means 13 for sending a signal to at least one driver
14. The at least one driver 14 preferably forms part of a
standard headphone set 15 such as is routinely provided
to aircraft passengers.
[0106] In most embodiments the controller 200 includes an IFE input means 16 for receiving an audio signal from the IFE system or directly from a user’s portable
device.
[0107] The controller 200 comprises a suitable processor 201 (which may be digital or analogue, or a combination of both) which generates an anti-noise signal
which, when broadcast by the headphones, will destructively interfere with the sound wave detected by the sensing microphone(s) 2 when that sound wave reaches the
user’s ear. The anti-noise signal is superimposed on any
audio signal received from the IFE input means 16 and
sent to the output 13.
[0108] Figure 3a shows an embodiment of the system.
At least one, and preferably two, transducers 2 such as
microphones are positioned in a portion of the seat 1,
preferably the headrest 3. At least one controller 200,
comprising or associated with a processor 201, which
may be two active noise cancellers, use the driver 14 or
speaker 14 of the headphones to cancel the sound at the
microphones 2. When the listener or user is close to the
microphones 2 the sound at the ears will also be reduced.
The reduction in sound is frequency dependent. In the
case of aircraft reducing low frequencies (i.e. 150-200Hz)
is particularly important as this frequency is generated
by the engines.
[0109] Figure 3b shows an embodiment of the invention where 4 microphones and 2 drivers are used, the
drivers supplied on a headset. Embodiments of the invention may have a plurality of microphones and drivers
(which may equivalently be other suitable input or output
means or connections) to improve cancellation or broaden the range of positions achieving audio cancellation.
The two speaker, four microphone (2S4M) set up of Figure 4 could similarly be arranged with the drivers present
on the headrest 3 of the seat, or elsewhere in the aircraft
or in association with the IFE system.
[0110] Figure 5a shows 4 microphone 2 speaker
(4M2S) and 4 microphone 4 speaker (4S4M) arrangements. In embodiments of the invention, and as shown
in Figure 5 at least some of the microphones and speakers are positioned at a distance from the plane of the seat
back. That is there is a difference in distance from user
U. For example they may be associated with or connect-
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ed to the sides or arms 4 of the headrest 3 which may
be slightly forward of the back of the headrest. This offsets the microphones or drivers by a small distance, such
as 20-100mm forward of the origin (or position of the
backmost microphone or speaker). Figure 5b shows a
system with speakers on both the headset and seat 1.
In a further embodiment there may be no speakers on
the user, e.g. no headset is used.
[0111] Some embodiments may allow reduction in the
delay between headphones and the microphones, for instance placing microphones in the headrest wings may
improve performance by reducing delay. In an embodiment having a single microphone per headphone driver
delay may improve noise cancellation, although this is
dependent on the headphones used and, in part the low
frequency response. The use of microphones and/or drivers in the headrest wings also allows the radiation of
sound out of the headphones to be more symmetric with
microphones in the wings. Having the microphones or
microphone array in the wings of the seat, or otherwise
angled with respect to the seat, allows the microphone
array to be directed towards the ear. This can be important because the ear is where the noise wants to be cancelled. Performance is based on both angle and location
of the microphones and/or drivers. Preferably the microphones are angled within 90 degrees of the drivers, more
preferably less than 45 degrees from the angle of the
drivers and most preferably substantially at the angle, or
the approximate angle, of the drivers. That is, there is a
stronger relation between the headphone drivers and the
microphones. In alternative embodiments the microphones may be in the same plane as the back of the seat
but may be rotated or substantially parallel with respect
to the seat. Preferably the microphones are position away
from the location of a user’s head, so as to avoid blockage
or dampening of any input signal.
[0112] Figure 4 shows a series of embodiments for the
system having speakers 14 and/or transducers 2 arranged on a seat. Preferably they are on the head of the
seat or headrest, or a part of the seat nearest the user’s
head. In some embodiments there may be speakers 2
at multiple levels to allow users of different heights. Figure
4B shows the change in depth of the seat allowing arms
or wings 4 to be closer to the User. In particular the arms
4 may be angled which enables the speakers 2 to be
angled to match the headphones and/or ears of the user.
Figure 4c shows that multiple transducers 2 may be
placed on the seat. In a further embodiment shown in
Figures 4D and 4E the head of the seat or a part thereof
may be removable 3a. This allows a quick change or
replacement of the system connected to the seat. An
embodiment may have the input and/or output means as
an attachment to, or connected portion of the seat or
headrest. In other embodiments the electronic components or input devices may be replaceable in portions of
the seat, or may be unitary with the seat.
[0113] Figure 6 shows a representation of an ANC system where a cancellation signal is obtained from a mi-
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crophone 2 or similar input device. The controller
X(w)aims to provide sufficient noise cancellation while
maintaining stability of the feedback loop. Typically X(w)
consists of a gain, g, in series with a loop filter, L(w),
which aims to reduce the gain sufficiently to prevent the
system going unstable at high frequencies. For the system of Figure 6 a transfer function (STF) can be calculated to show the frequency dependence of attenuation:
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[0114] Where H is the transfer function of the amplifier
and loudspeaker transfer functions plus the acoustic
transfer function to the microphone, X is the signal and
β represents the transduction factor from sound pressure
to microphone output voltage. The pressure at the microphone is equal to the original sound pressure, plus a
cancelling field generated by the loudspeaker which is in
anti-phase to the incident field. For large loop gains the
pressure is exactly cancelled. In practice the level of cancellation is limited by the risk of instability which is governed by the open-loop transfer function. For the reproduction of music at the microphone position, the STF is
ideally flat.
[0115] Figure 7 shows the system of figure 6 extended
to multiple channels where some cross-coupling between the channels has been considered. The system
assumes that there is a separate controller - each consisting of a gain, gn, and loop filter L(w) - per channel
however in alternative embodiments multiple channels
may be combined or connected. If the number of loudspeakers and microphones differ there must be a relationship, for instance shown in a matrix K, which maps
M microphone signals into N loudspeaker signals. For N
= M, K may be the identity matrix. For M > N, and even
numbers of transducers, the simplest approach is to sum
two or more microphones to one speaker. However in
some cases microphones may be combined in more
complicated patterns, such as linking microphones on
the same side of the seat.
[0116] In order for the anti-noise signal to effectively
cancel the ambient noise, its phase (relative to the ambient noise signal) must be correct when it reaches the
user’s U ear. This is relatively easy to achieve if the user
U has their head pressed against the seat 1 such that
their ears are in close proximity to the microphone(s) 2.
However, if the U user leans forward, such that the distance between the user’s ears and the sensing microphone 2 is a significant proportion of the wavelength of
the ambient noise, then the phase of the anti-noise signal
may be incorrect, and the noise cancelling effect may be
reduced. In extreme cases the anti-noise signal may constructively interfere with the ambient noise, causing an
increase in the perceived background noise at some frequencies. This may be particularly problematic with noise
at the higher frequency/shorter wavelength end of the
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relevant spectrum. An approach as described with an
analogue system which does not have to account for the
phase shift as it reduces sound pressure at the or each
microphone or sound input device. In embodiments of
the invention the phase shift between the microphone
and driver or headset is not compensated for directly but
is reduced by controlling the distance, or imperfect cancellation is achieved.
[0117] In order to mitigate the deterioration in noise
cancelling effect experienced when the user U moves
their head away from the seat, the system 100 is provided
with measuring means 12 as mentioned above.
[0118] In one embodiment the measuring means 12
comprises a camera 17, for example a "webcam" type
camera which may be provided as part of a prior art IFE
screen 18. The controller 200 (and/or a separate processor) may determine the distance between the head of
the user U and the reference point R by calculating the
proportion of the camera’s field of view which is filled by
the user’s head. An increase in the proportion of the field
of view filled indicates a movement of the head toward
the camera, and therefore an increase in the distance
between the user’s head and the microphone(s) 2.
[0119] In an alternative embodiment the seat 1 may be
provided with a proximity sensor, for example an infrared proximity sensor (not shown) or an ultra-sonic proximity sensor. The sensor may be located at or adjacent
the headrest 3 or upper portion of the back of the seat 1.
In some embodiments the proximity sensor may be located in the rear surface of the seat in front of the user.
In one embodiment the sensor may be integrated into
the IFE screen provided at the back of the seat in front
of the user.
[0120] The processor 201 uses the information from
the measuring means 12 to adjust and/or generate the
anti-noise signal. In one embodiment the processor uses
the information to provide or adjust one or more of the
phase, amplitudes or audio spectrum content of the antinoise signal, to allow for the distance and/or relative position between the microphone and the user’s head.
[0121] In an embodiment of the invention the head
movement is allowed for by the use of multiple microphones. Head movement can produce significant variations in the open loop transfer function, affecting the loop
gain and phase shift (group delay). This may be possible
by the use of multiple microphones arranged geometrically, or otherwise, around a centre point. Preferably the
arrangement or array of microphones has an equal spacing between each of the microphones and a central point;
alternatively there may be equal spacing between each
of the microphones. Preferably a transducer or driver is
positioned substantially at the centre point. That is, multiple microphones are used (for each headphone channel) and variations in the loop transfer function are reduced. One possible embodiment is to use a circular (or
forming the points of a polygon) array of microphones. If
a driver is associated with the microphones this may be
positioned substantially at the centre of the array. For
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example the speaker may be positioned within the perimeter formed by the microphones. However some variability in this may be workable because as the speaker
moves away from the centre, the distance to some microphones increases but the distance to others decreases, compensating for any loss of effect.
[0122] Figure 12a shows the transfer function can be
calculated from an ideal point source speaker positioned
a distance d away from a circular array, and at a distance
y off-axis. An average array response can be calculated
as
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where H(f) is the transfer function to each microphone.
Figure 12b shows a possible arrangement of microphones 2 around the speaker 14.
[0123] The loop gain and group delay for a single microphone, at a distance of 60 mm from the on-axis speaker, are substantially constant across the frequency spectrum Fig 13a. The gain varies with the reciprocal of the
speaker to microphone distance d producing a variation
of around 8 dB and the corresponding group delay is the
propagation delay time, which varies over 0.3 ms. That
is there is a measureable change in loop gain and group
delay with horizontal head movement. Figure 13b shows
the loop gain for a circular array of 5 microphones at a
radius of 100 mm, and the same on-axis distance of 60
mm. At low frequencies, the loop gain variation for offaxis distances up to 100 mm is negligible and the gain
drops by around 2dB for the 150mm off-axis case, where
the speaker is outside the microphone array radius. That
is there is essentially no variation in loop gain if the speaker remains within the microphone array radius and the
system is less susceptible to loss of effect when a user’s
head moves sideways.
[0124] A similar effect occurs in the corresponding
group delay with negligible variation at low frequencies
when the loudspeaker is off-axis distance but within the
microphone array. The average group delay (345 ms) is
larger than for the single microphone with no off-axis shift
(176ms), but shows little variation. This means that a stable loop gain can be set which will allow a noise canceller
to provide a more consistent level of cancellation.
[0125] In one embodiment head/headset position can
be measured or estimated using the capacitance. Since
a human head has a significantly different dielectric loss
from that of air, linear changes in capacitance correlate
to head proximity.
[0126] The sound pressures at the microphones need
to be considered for waves approaching from different
directions, for instance angles of incidence 0, 45, 90 and
180 degrees relative to user U. The effect on the approach angle of the noise signal may determine how the
noise cancellation should vary along the aircraft or how
a system can be adapted to attenuate signals from mul-
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tiple directions. Different drivers 14 in headphones 14 or
speakers 14 can also react differently to a noise signal.
For instance an electrodynamic loudspeaker (which may
be modelled by including a second order high-pass filter
in the feedback loop may have poor noise cancellation
at low frequencies. This is because the speakers are unable to radiate significant sound at this frequency.
[0127] Figure 8 shows the performance of an ANC system for a 2 microphone, 2 driver system. Looking first at
Fig. 8a the feedback field for 0 degrees incidence (i.e.
the field travels from the right to the left of the images)
shows attenuation of around 10 dB behind the microphones. This occurs because the loudspeakers generate
a field propagating along the negative x-axis to cancel
the pressure at the microphones, and the cancelling field
travels beyond the microphone and continues to cancel
the noise at points beyond the microphones also. Figures
8b, c and d show the variation in performance as the
noise wave is varied. The relative positions of the noise
source, the microphones 2 and the drivers 14 may improve performance by creating a desired feedback field
based on knowledge of the noise.
[0128] The sound field along the x-axis is shown in
Figure 9 for driver to microphone distances of 20mm to
120 mm. These reflect the changing positions of a user’s
head when using the system. The position of the speakers is denoted by a square, which is where the centre of
the listener’s head would be, in each case the microphone is located at 0 on the x axis. In each case a maximum attenuation is achieved for a microphone to headset distance of between 60 and 100 mm. The effectiveness of the attenuation also depends on the angle at
which the noise is arriving. The maximum attenuation at
different angles is approximately: 5 dB maximum for 0
degrees incidence, 6 dB for 45 degrees and is 15 dB for
90 and 180 degrees.
[0129] A limiting feature for large distances is that the
performance degrades because the loop transfer function matrix has large delays and the loop gain must be
reduced to maintain stability, reducing the cancellation.
That is the delay between the driver changing its output
and the output being received by the microphone becomes too large to make an accurate estimate of the
noise cancellation required. The controller may have systems to attempt to reduce, or have knowledge about this
delay, for instance by obtaining a measurement of the
approximate distance of the microphone and the driver
and compensating for this. This compensation may be a
phase delay or gain control. The compensation may use
the direction of the sound, as detected by the multiple
microphones, to adjust the signal dependent on the angle
of arrival of the ambient noise. This may be implemented
by a calibration stage in which a required set-up is measured. A limiting feature for small distances, such as the
cancellation for the 0 degrees incidence at 20mm) is that
the spherical divergence of the cancelling field is reduced
when the speaker is further away. This allows the cancelling field to appear more planar at the microphone and
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attenuate the noise more effectively. Similar behaviour
is seen for the 180 degree case, where there is greater
cancellation for positive x value, which is downstream
from the canceller for this incident direction. The speakers or transducer 14 may be placed at a distance d behind
the seat back to ensure the minimum distance is met. In
use the presence of the head of a user will alter the response behaviour at medium to high frequencies which
makes these less relevant to consider.
[0130] Figure 10 shoes the effect of transducer 2 and
driver 14 arrangements. Figure 10a and 10b show the
feedback field for the 2S4M and 4S4M arrangements respectively. The area over which cancellation occurs is
increased by the use of four microphones and the region
of cancellation is slightly increased using four speakers.
This means that there may be more opportunity for a user
to move their head and maintain a reasonable level of
noise cancellation where more speakers are used. This
is because the additional speakers contribute to the cancellation of the sound at the microphones and therefore
the output of the speakers to obtain noise cancellation
can be reduced. The effect of the noise cancellation also
changes with distance between the speakers and the
microphone as shown in Figures 12 which shows a separation of 120mm for systems of 8a, and 10a and 10b).
The increased distance requires large microphone amplitudes to cancel the noise. In embodiments of the system the distance of the head may be measured this measurement may help to compensate for the required increase in amplitude.
[0131] In some embodiments the controller 200 may
further comprise a further input for receiving information
regarding one or more characteristics of the driver(s) 14
and/or headphones 15 which are being used. Such characteristics may comprise information regarding the electrical impedance of the drivers 14, the acoustic impedance of the headphones 15, the frequency response of
the drivers, acoustic volume over the ear, or any other
characteristic of the headphones and/or drivers which
affects properties of the anti-noise signal required and/or
the headphone’s ability to generate the required antinoise signal.
[0132] In one embodiment one or more characteristics
may be detected electrically and/or electronically. For example, in one embodiment the impedance of the headphone drivers may be detected electronically.
[0133] In another embodiment the headphone plug
may have a physical characteristic or configuration which
is representative of headphones having one or more
characteristics, and the headphone jack may send a signal to the controller 200 depending on the plug configuration or characteristic.
[0134] In one embodiment this may be the shape/type
of pins, or a measurement of headset characteristics
such as impedance. Passive or active components may
be provided in the headset or jack (such as a resistor
and/or capacitor) to facilitate identification.
[0135] In one embodiment global settings in the IFE
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may be varied to allow for different drivers. Furthermore,
another party such as a headphone manufacturer/supplier) could send updated settings to Airlines for different
batches of headphones, or at least different models of
headphones.
[0136] In another embodiment a user may calibrate the
system 100 to suit the characteristics of the headset 15.
For example, the controller 200 may be operatively connected to an IFE touch screen 18 and may display a
virtual slider on the screen. In a calibration mode, the
user U may be instructed to slide the virtual slider until
the perceived noise cancelling effect is maximised.
Changing the position of the virtual slider may, for example, affect the phase/delay or the amplitude or audio
spectrum content of the anti-noise signal generated by
the controller 200.
[0137] In an embodiment the system identifies microphone parameters to improve performance. This may be
obtained from the impulse responses of the headphones
or drivers. For example low cost headphones typically
have peaks at around 100 Hz and by peaks of over 20dB
at 2 and 3kHz, respectively. Better quality headphones
typically have a flatter response, showing a more gradual
rise of around 20 dB above 1 kHz and an extended bass
response below 100 Hz. The flatter response results in
more equal treatment of each frequency. Some headphones have holes on the outside, presumably to allow
sound to escape from the rear of the driver diaphragm.
This tends to produce a dipole response which is characterised by a reduced exterior sound level, particularly
at low frequencies. Therefore it may be useful to cover
the holes to reduce the radiation from the rear of the
drivers.
[0138] The controller 200 may be provided in any one
of a number of positions within the aircraft. In one embodiment the controller 200 may be integrated into the
IFE screen. In another embodiment the controller may
be located within the base of the seat. In a further embodiment the controller 200 may be integrated into a central IFE controller which may for example be present as
a crew IFE controller.
[0139] A limitation to the attenuation provided by the
system is the requirement to ensure stability of the microphone 2 and driver 14 systems. Stability avoids loud
sounds reaching the ears of the user. This may be
achieved by examining the eigenvalues of the system.
The eigenvalue loci should not encircle the point to ensure so the system is stable. The determinant should
encircle the origin, to further confirm that the feedback
system is stable.
[0140] In an embodiment a second or higher-order
controllers is used. In other embodiments digital controllers may allow additional inputs to be included from the
IFE system or other components.
[0141] High order controllers can be designed using
techniques such as H∞ optimization and techniques well
known in the art of controller design. In some circumstances a low-order controller may be advantageous be-
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cause it does not require such a stable plant. In the embodiment described instabilities in the plant can be created as head position alters. This can cause instability
with high-order controller. Significant variations in the
plant with high order controllers will rapidly produce instability.
[0142] A higher-order controller may produce good
performance if there is robustness to changing plant conditions included. Second-order controllers are commonly
used in analogue noise control and are used in applications such as practical cancellers and analogue active
headsets. A second order phase lag filter suitable for use
in noise cancellation has the normalised transfer function
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[0143] For a given plant, the parameters of this equation, together with the overall loop gain, can be optimised
to maximise cancellation. However, given the plant is
highly variable, it would probably require a digital
processing system to track the head position and control
the five parameters precisely to produce something approaching optimum performance. This would require digital control of the analogue filter, or the direct implementation of a digital controller, which would introduce additional delay in to the feedback loop. It is more practical
to consider a simpler second order controller which has
less parameters. A possible alternative is described by
the equation:
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which has a gain of one at DC and a gain of β2 = (1x)2/(1+α)2 at high frequencies. The controller has two
parameters which govern its performance. A second order controller may have a faster roll-off and be able to
maintain a higher loop gain between 100 Hz and 1 kHz.
This means that a higher suppression of noise can be
produced in this frequency range.
[0144] Figure 14 shows noise cancellation for a variety
of headphones and drivers. Noise cancellation is very
poor with a null of around 5 dB at 200 Hz and an average
cancellation of around 2 dB up to 400 Hz for both covered
and uncovered holes for the low cost headphones of Figure 14a. Using better quality headphones increased the
cancellation to between 5 and 15 dB for frequencies between 100 and 200 Hz, and the cancellation extends up
to 2 kHz as shown in Figure 14b. The performance can
be improved because the better quality headphones
have larger drivers with greater volume velocities. Figure
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14c shows a driver associated with the seat, and preferably the headrest and more preferably the arms of the
headrest. This enables the passenger to have noise cancellation with no headphones or for improvement to the
noise cancellation of the headphones. For instance a
Tymphany P830983 2 inch full range driver could be
used.
[0145] The microphones may be placed directly in front
of, or nearby the driver or in an arrangement around the
driver, Figure 12b. The effect of moving the microphones
further away from the centre of the driver is to shift the
region of cancellation. For instance centralised microphones create a broad region of cancellation from about
200 to 800 Hz, whereas a wider arrangement moves the
null to approximately 400 Hz and extending up to 1 kHz.
The movement may also increase the depth of the null.
The effectiveness of arrangement geometries will depend on the noise spectrum to be cancelled. That is, by
moving the microphones further apart a higher frequency
of cancellation may be achieved. Increasing the spacing
of distance of the microphones also shifts the bandwidth
of the cancellation frequencies. As described above the
geometry will also affect the ability for the head to move.
[0146] The higher quality headphones were more able
to provide noise cancellation, although all headphones
had reasonable low-frequency responses in the ear canal. It is likely that this occurs because in order to cancel
sound at the external microphones, the loudspeakers
must be able to produce reasonable low-frequency responses outside the ear canal. This is more likely to be
possible using drivers with large volume velocities at low
frequencies, which requires larger driver size and excursions. Similarly low-cost microphones may have a low
frequency response that rolls off below 200 Hz. This
means that the loop controller has to provide greater attenuation at high frequencies to maintain stability. It may
be useful to include a low frequency boost to compensate
for this roll-off in the processor. That is, if the characteristic of the microphone or speaker is known the processor
can ameliorate this, possibly by boosting the low frequency effect in the knowledge that this will not be transmitted
as effectively. In embodiments of the invention the low
frequency noise, below 300 Hz, may be enhanced because the high frequencies are more strongly filtered and
controlled. In some embodiments the invention may include a low-frequency gain control means or controller
adapted to attenuate the low frequencies more strongly,
or to focus on the attenuation of low frequencies.
[0147] In an embodiment of the system the processor
or controller may comprise an analogue ANC system
comprising four channels, each operating as a stereo
pair with a stereo master gain control. Each channel could
have an individual second-order loop filter with adjustable
cut-off frequency and high-frequency attenuation. Amplification of the signal can be provided by a TDA7266P 3
Watt power amplifier which provides two bridge mode
outputs. An output, for example to standard stereo headphones may be achieved by wiring a pair of channels as
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a single-ended output. It should be noted that an IFE
system may be different from the system described, as
it may interface with the IFE server. The various system
components could be interchanged with other electronic
devices or components having the same effect without
leaving the scope of the invention. In other embodiments
the processor may be a microprocessor, FPGA or logic
device capable of being programmed or receiving instructions.
[0148] Although a general amplifier has been discussed a person skilled in the art of amplifier design
would recognize that a number of amplifiers may be suitable. Amplifiers may be used to reduce undesirable cross
talk effects, e.g. by use of separate processor sections
or chips. In an embodiment a class D amplifier may be
used to reduce power usage. The power rating of the
amplifier is related to the sound pressure level that must
be cancelled; and so high sound levels may require high
power ratings, particularly when using loudspeakers.
[0149] The processor or processing means may be associated with, or be part of, the IFE system and the
processing may be completed by the IFE system in some
embodiments. In embodiments the IFE system may allow
connection between microphones and or speakers arranged on the user’s seat or other seats or elsewhere on
the aircraft. For instance the system may have speakers
arranged on the headrest for the seat and a seat behind
the seat.
[0150] In embodiments of the invention the phase error
of the signal or ANC control may be reduced or minimized
by ensuring that a minimum of high-pass filters is used
in the controller and that their cut-off frequencies are well
below 20 Hz. The phase error is likely to be the various
high pass filters in the system. A driver typically has a
second order high pass response which produces 180
phase shift at low frequencies. The electronic high pass
filters and drivers thus introduce significant phase deviations at low frequencies. A further means of minimizing
the phase error is to add further high-pass filters; each
of which introduces a 90 degree phase shift at low frequencies. Using the right number of additional filters
should ensure that the combined effect of the driver and
high pass filters is to maintain a desired phase (e.g. 180
degree loop phase). That is the number of filters, and
phase change of the filters, alone, or including other effects, may be sufficiently close to 180 degree loop phase.
[0151] People skilled in the art will appreciate that the
apparatus or features described may be associated with
the IFE system in various ways. The association may be
by spatial closeness, or connection or connectability, attachment or the ability to be removably attached to the
system.
[0152] Those skilled in the art will appreciate that the
present invention provides a system and method for providing a user with the benefits of active noise cancellation
which can be used with inexpensive passive headphones. The invention has been described using an analogue control scheme. A person skilled in the art will
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appreciate that a similar scheme could be modified for a
digital controller implementation.
[0153] Unless the context clearly requires otherwise,
throughout the description and the claims, the words
"comprise", "comprising", and the like, are to be construed in an inclusive sense as opposed to an exclusive
or exhaustive sense, that is to say, in the sense of "including, but not limited to".
[0154] Where in the foregoing description, reference
has been made to specific components or integers of the
invention having known equivalents, then such equivalents are herein incorporated as if individually set forth.
’Headset’ herein includes an earphone or in-ear device.
Although this invention has been described by way of
example and with reference to possible embodiments
thereof, it is to be understood that modifications or improvements may be made thereto without departing from
the spirit or scope of the invention.
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Claims
1.
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At least one input device, associated with a seat
on the aircraft, to receive an input representative
of an ambient noise in the vicinity of the seat;
Processing means adapted to process the input
to produce an output signal adapted to reduce
the ambient noise in volume associated with the
seat;
An output for transmitting an output signal to at
least one driver, the driver adapted to transmit
the output signal to a user, and
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Wherein the output signal is adapted so that, in use,
the user hears a reduced ambient noise when seated
in the seat.
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2.
A system as claimed in claim 1 wherein at least one
driver is associated with a headset and/or at least
one driver or at least one input device is associated
with the seat.
3.
A system as claimed in either one of claims 1 or 2
wherein, in use, a position of the user may change,
and wherein the user hears a reduced ambient noise
in a plurality of positions.
4.
A system as claimed in claim 2 wherein at least one
driver or at least one input device are attached or
attachable to an arm or arms of a seat headrest,
wherein the angle of the diver or microphone is acute
with respect to a user of the seat.
5.
A system as claimed in any one of claims 1 to 4
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An active noise cancellation system for an aircraft
In-flight entertainment system, the active noise cancellation system comprising:
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comprising a plurality of input devices, the input devices spatially separated in a substantially planar arrangement.
6.
A system as claimed in claim 5 wherein the plurality
of input devices are separated around a driver.
7.
A system as claimed in either on of claims 5 or 6
wherein the plurality of input devices are arranged
on the vertices in a polygon.
8.
A system as claimed in any one of claims 1 to 7
wherein output comprises a jack adapted to form a
connected with an audio device.
9.
A system as claimed in any one of claims 1 to 8
wherein the input device and driver are separated.
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10. A system as claimed in any one of claims 1 to 9
comprising a measuring means for determining the
separation of the driver from the input device.
11. A system as claimed in any one of claims 1 to 10
wherein the input device is a microphone and/or the
driver is a speaker.
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12. A system as claimed in any one of claims 1 to 11
wherein the output signal is combined with an audio
signal from the IFE system.
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13. An aircraft seat adapted for use with a system as
claimed in any one of claims 1 to 12, the seat comprising at least one input device and/ or at least one
driver.
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14. A method of active noise cancellation in an In-Flight
Entertainment system, the method comprising the
steps of:
Receiving an input from an input device associated with the In-Flight Entertainment system;
Processing the input to produce an output signal
adapted to reduce the ambient noise in a volume
associated with the seat;
Outputting an output signal to at least one driver,
the driver adapted to transmit the output signal
to a user, and
Wherein the output signal is adapted so that, in use,
the user hears a reduced ambient noise when seated
in the seat.
15. A method as claimed in claim 14 further comprising
the step of automatically adjusting the output signal
as the separation between the user and the input
device changes.
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