The present disclosure provides a noise cancellation enabled headphone to be worn on or over an ear of a user.
Nowadays a significant number of headphones are equipped with noise cancellation techniques. For example, such noise cancellation techniques are referred to as active noise cancellation or ambient noise cancellation, both abbreviated with ANC. ANC generally makes use of recording ambient noise that is processed by filters for generating an anti-noise signal, which is then combined with a useful audio signal to be played over a speaker of the headphone.
Various ANC approaches make use of feedback, FB, microphones, feed-forward, FF, microphones or a combination of feedback and feed-forward microphones. For FF ANC, the feed-forward (FF) microphone is placed on the outside of the headphone, such that it is acoustically decoupled from the headphones driver.
Some noise cancellation headphones are able to perform an adaptation of the filter of the FF ANC based on an error signal recorded by an error microphone placed inside a volume that is directly acoustically coupled to the eardrum, conventionally close to the front of the headphones driver. However, an optimum performance for the adaptation would be achieved at the location of the eardrum being the desired target for the cancellation. Nevertheless, in a real headphone it is not possible to place a microphone inside an ear canal to monitor a signal at the eardrum.
The present disclosure provides an improved concept for adaptive noise cancellation in a headphone.
The improved concept relates to an adaptive noise cancellation headphone that can refine an anti-noise signal to compensate for changes in headphone acoustics due to variation in headphone fit and due to manufacturing tolerances. For example, such changes in acoustics of a headphone to be worn on or over an ear of a user can occur if a leakage from the ambient environment to the headphone volume being directly acoustically coupled to the eardrum changes.
Specifically the improved concept is based on the insight that a phase relation between a sound path from the ambient environment to the eardrum and a sound path from the speaker or driver to the eardrum does not match a phase relation between a sound path from the ambient environment to the error microphone and a sound path from the speaker or driver to the error microphone. Hence the improved concept proposes to delay the output signal of the headphone driver relative to the error microphone such that ratios resulting from the signals detected at the error microphone more closely represent those at the eardrum reference point (DRP). The delay is achieved by a baffle placed between the speaker and the error microphone. In short, this allows an adaptive noise cancellation system to more accurately monitor the signals at the eardrum which results in a more accurate adaptation and better noise cancellation.
The improved concept is applicable e.g. to circumaural headphones and/or supra-aural headphones. Circumaural headphones (sometimes called full size headphones or over-ear headphones) have circular or ellipsoid ear pads or ear cushions that encompass the ears. Because these headphones completely surround the ear, circumaural headphones can be designed to seal against the head to attenuate external noise. Supra-aural headphones or on-ear headphones have pads that press against the ears, rather than around them. This type of headphone generally tends to have less attenuation of outside noise.
The FF target of a conventional headphone is commonly understood to be represented by the formula:
where AE is the ambient to ear acoustic transfer function, DE is the driver to ear acoustic transfer function and AFFM is the ambient to FF microphone acoustic transfer function. At the error microphone, this becomes:
where AErr is the ambient to error acoustic transfer function and DErr is the driver to error acoustic transfer function. By analyzing the signal paths on a headphone when there is an acoustic leakage under the ear cushion, it can be seen that the key difference between the two FF targets is that the difference in path length between the AE/DE signals relative to the AErr/DErr signals is significant, leading to a significant phase difference in FF targets. Delaying DErr reduces this difference.
Hence, a noise cancellation enabled headphone to be worn on or over an ear of a user according to the improved concept comprises a speaker, a feed-forward microphone predominantly sensing ambient sound and an error microphone being arranged in front of the speaker in a primary direction of sound emission of the speaker. The error microphone is adapted to sensing sound being output from the speaker and ambient sound. The headphone further comprises a baffle arranged between the speaker and the error microphone in the primary direction of sound emission such that the sound being output from the speaker is delayed by the baffle at a location of the error microphone. The headphone is configured to record a feed-forward signal with the feed-forward microphone and an error signal with the error microphone, and to provide the feed-forward signal and the error signal to an adaptive noise cancellation controller.
The adaptive noise cancellation controller is configured to perform feed-forward noise cancellation based on the feed-forward signal filtered with feed-forward filter parameters. The adaptive noise cancellation controller is further configured to adjust the feed-forward filter parameters based on the error signal recorded with the error microphone.
Accordingly, the baffle fulfils the function of delaying the driver to error acoustic transfer function DErr. Hence the error signal recorded with the error microphone with respect to both ambient sound and the sound being output by the speaker better matches the desired target at the user's eardrum.
In particular, the baffle is arranged such that it does not delay the ambient sound being sensed by the error microphone and entering an air volume between the speaker and an ear of a user at an ear cushion of the headphone. The baffle may further be arranged such that neither sound being output from the speaker nor ambient sound entering the air volume between the speaker and an ear of the user at the ear cushion is delayed on its way to the user's eardrum.
In various implementations of the headphone, the baffle for example increases a sound route or acoustic propagation route, e.g. a propagation time or propagation distance, between the speaker and the error microphone, for example compared to a direct sound route between the speaker and the error microphone without the baffle. Accordingly, the delay of the sound being output from the speaker is achieved by the increased sound route of the acoustic signal.
In various implementations the baffle is acoustically opaque, such that the sound being output from the speaker propagates to the error microphone along the baffle. In other words, to reach the microphone, the sound being output from the speaker cannot go through the baffle but has to propagate around the baffle, e.g. along a surface of the baffle.
In some implementations the baffle is an acoustically translucent baffle or an acoustically resistive baffle, such that the sound being output from the speaker propagates to the error microphone along a path of least resistance determined by an acoustic impedance of the baffle. For example, if the baffle is not completely acoustically opaque, then the delay that the baffle produces will be reduced as the impedance of the baffle material is reduced.
In various implementations the error microphone, respectively an area of sound reception of the error microphone, is located in the center of the headphone. This achieves that a variation in the ambient to error acoustic transfer function AErr is minimized if a leakage under the ear cushion comes from different locations.
For example, an area of sound reception of the error microphone is located generally equidistantly with respect to an ear cushion of the headphone, e.g. a circumferential ear cushion. Generally equidistantly for example means that a variation in the distance to the circumference of the ear cushion is minimized.
For example, the area of sound reception is an opening of a cavity in which the error microphone is enclosed. Hence, all sound going to the error microphone has to go through this area of sound reception such that the actual position of the error microphone within the cavity plays no role or only a minor role with respect to the effective sound route or acoustic propagation route to the error microphone. This particularly is effective with respect to the various positions where ambient sound can enter the air volume between the speaker and the ear of the user at the ear cushion.
In various implementations the baffle at least partially covers an active area of sound emission of the speaker. For example, the baffle covers between 30% and 95% of an active area of sound emission of the speaker, e.g. between 50% and 80%.
In various implementations the baffle is located basically centrally in front of an active area of sound emission of the speaker. In such an implementation the error microphone, or at least the area of sound reception of the error microphone, may be located centrally with respect to the baffle.
In various embodiments the active area of sound emission may simply be determined by the diaphragm of the speaker. However, in some implementations the diaphragm of the speaker may be arranged in a cavity or in a housing of the speaker, wherein an outlet of the cavity or the housing determines the active area of sound emission of the speaker. For example, the outlet of the cavity or the housing couples to an ear-canal volume of the user.
In some implementations the error microphone is also used as a feedback (FB) microphone for performing FB noise cancellation. For example, the adaptive noise cancellation controller is further configured to perform FB noise cancellation based on the error signal recorded with the error microphone and filtered with FB filter parameters.
However, due to the delay introduced by the baffle, the upper bandwidth of the FB noise cancellation may be reduced. This may lead to a reduction of FB noise cancellation performance. This will be tolerable in a number of applications due to the improved feed-forward noise cancellation performance.
However, in some implementations the headphone further comprises a feedback microphone being arranged in proximity to the speaker in the primary direction of sound emission and sensing sound being output from the speaker and ambient sound. The headphone is further configured to record a feedback signal with the FB microphone and to provide the feedback signal to the adaptive noise cancellation controller, which is further configured to perform FB noise cancellation based on the feedback signal recorded with the FB microphone and filtered with FB filter parameters.
Hence, while the presence of the baffle results in a delay for the sound output by the speaker the error microphone, no delay is effected at the position of the FB microphone. Proximity of the FB microphone to the speaker means that at least an area of sound reception of the FB microphone is so close to the speaker, respectively the area of sound emission of the speaker, that little or no delay exists between sound emission and sound reception.
The adaptive noise cancellation controller may be external to the headphone, e.g. within a mobile device, to which the headphone is connected, or may be comprised by the headphone.
In all of the embodiments described above, ANC can be performed both with digital and/or analog filters. All of the audio systems may include feedback ANC as well. Processing and recording of the various signals is preferably performed in the digital domain.
The improved concept will be described in more detail in the following with the aid of drawings. Elements having the same or similar function bear the same reference numerals throughout the drawings. Hence their description is not necessarily repeated in following drawings.
In the drawings:
The headphone comprises a speaker SP that is shown schematically only with an indication of a coil and an area of sound emission of the speaker SP, e.g. a diaphragm or an opening or housing of the speaker SP, in which the diaphragm is arranged.
The headphone is equipped as a noise cancellation enabled headphone and cooperates with an adaptive noise cancellation controller ANCC and a feed-forward microphone FF_MIC predominantly sensing ambient sound. To this end, the feed-forward microphone FF_MIC is placed in the body BDY facing away from the headphone, respectively towards any ambient sounds. The adaptive noise cancellation controller ANCC is configured to perform feed-forward noise cancellation based on a feed-forward signal recorded with the feed-forward microphone FF_MIC and filtered with feed-forward filter parameters. As is well known in the art, the filtered signal is output via the speaker SP to cancel out or at least compensate for ambient sounds reaching the user's ear with an anti-noise signal. In the present example, the adaptive noise cancellation controller ANCC is comprised by the headphone. However, in other implementations, the adaptive noise cancellation controller ANCC may be external to the headphone, e.g. within a mobile device, to which the headphone is connected.
The feed-forward noise cancellation works by matching an electronic filter, defined by the feed-forward filter parameters, to an acoustic target response that compensates principally for the headphone's passive attenuation and the speaker response.
With changing conditions, in particular changing seal conditions, this target response changes such that it becomes desirable to adjust the feed-forward filter parameters to account for the changed conditions. To this end, the headphone comprises an error microphone ERR_MIC that is arranged in front of the speaker SP in a primary direction of sound emission of the speaker. As can be seen in the drawing, this means that the error microphone ERR_MIC is placed somewhere between the speaker and the user's ear being formed by the outer ear, an ear channel EC and the eardrum ED that defines the drum reference point (DRP). The error microphone ERR_MIC is adapted to sense sound being output from the speaker and ambient sound. An error signal recorded with the error microphone ERR_MIC is used for adjusting the feed-forward filter parameters.
The FF target of a conventional headphone is commonly understood to be represented by the formula:
where AE is the ambient to ear acoustic transfer function between an ambient sound source and the user's eardrum ED, DE is the driver to ear acoustic transfer function between the speaker SP and the user's eardrum ED, and AFFM is the ambient to FF microphone acoustic transfer function between the ambient sound source and the FF microphone FF_MIC.
At the error microphone ERR_MIC, this becomes:
where AErr is the ambient to error acoustic transfer function between the ambient sound source and the error microphone ERR_MIC, and DErr is the driver to error acoustic transfer function between the speaker SP and the error microphone ERR_MIC.
By analyzing the signal paths in a conventional headphone when there is an acoustic leakage under the ear cushion, it can be seen that the key difference between the two FF targets is that the difference in path length between the AE/DE signals relative to the AErr/DErr signals is significant, leading to a significant phase difference in FF targets.
However, the headphone according to the improved concept further comprises a baffle BAF arranged between the speaker SP and the error microphone ERR_MIC in the primary direction of sound emission, such that the sound being output from the speaker SP is delayed by the baffle BAF at a location of the error microphone ERR_MIC.
While in conventional headphones, where such baffle BAF is not present, a sound path from the speaker to the error microphone is quite short, the sound path from the speaker SP to the error microphone ERR_MIC with the baffle BAF is longer, thereby decreasing the phase difference between AErr and DErr, such that it better matches the ideal conditions at the eardrum ED between AE and DE.
While the sound of the speaker is delayed by the baffle at the location of the error microphone ERR_MIC, the baffle BAF preferably does not delay the ambient sound being sensed by the error microphone ERR_MIC that has entered the air volume between the speaker SP and the ear of the user at the ear cushion ECU.
Accordingly, the baffle BAF may increase the sound route or acoustic propagation route between the speaker SP and the error microphone ERR_MIC, in particular compared to a direct sound route or acoustic propagation route between the speaker SP and the error microphone ERR_MIC without the baffle BAF being present. The exact implementation of the mounting of the error microphone ERR_MIC is not shown in the schematic view used here. However, the position of the error microphone ERR_MIC shown in
As can be seen in
The positioning of the error microphone ERR_MIC can also consider a likelihood of positions where ambient sound enters the air volume inside the ear cushion ECU under leaky conditions. For example, if it is more likely that ambient sound enters the air volume inside the ear cushion ECU from the bottom side, as is shown in
In various implementations, the baffle BAF at least partially covers an active area of sound emission of the speaker SP, as is shown in the implementation of
Referring now to
For example, if the error microphone ERR_MIC is mounted centrally, then the central baffle mounting may be better as with one side open the driver signal from the speaker SP already follows the path of least resistance, so opening the other side will not make the delay any shorter but will improve the driver-to-ear response DE. If the baffle BAF is mounted as in
Referring now to
The upper diagram a) of
In the middle diagram b) of
The bottom diagram c) of
Referring back to
In various other implementations the baffle BAF may be an acoustically translucent baffle or an acoustically resistive baffle, which do not fully block sound going through the baffle but provide an acoustic resistance still contributing to a delay of the respective sound. This effects that the sound being output from the speaker SP propagates to the error microphone ERR_MIC along a path of least resistance determined by an acoustic impedance of the baffle BAF. For example, if the baffle is not completely acoustically opaque, then the delay that the baffle produces will be reduced as the impedance of the material of the baffle is reduced.
The arrangement of the headphone in
Referring now to
Referring now to
While in the shown implementations of the headphone, the headphone is depicted as an over-ear headphone or circumaural headphone, the improved concept employing the baffle BAF can also be used with the headphone being implemented as an on-ear headphone or supra-aural headphone, in particular where ear cushions provide a seal between an air volume between the headphone's speaker and the user's ear.
If the baffle BAF covers the speaker SP, at least partially, this may affect the speaker driver's response. To this end, different distancing of the baffle BAF from the speaker or the area of sound emission of the speaker SP can be considered. Furthermore, as mentioned above, using for example an acoustically resistive baffle instead of a completely acoustically opaque baffle can also be considered.
Furthermore, the baffle BAF in front of the speaker SP may reduce room in a front air volume for the pinna. To this end, the speaker may be moved back a little to increase the room. However, it will be appreciated that there are many alternative arrangements for the error microphone ERR_MIC, speaker SP and baffle BAF that all delay the sound being output from the speaker at the location of the error microphone ERR_MIC.
It will be appreciated that the disclosure is not limited to the disclosed embodiments and to what has been particularly shown and described hereinabove. Rather, features recited in separate dependent claims or in the description may advantageously be combined. Furthermore, the scope of the disclosure includes those variations and modifications, which will be apparent to those skilled in the art and fall within the spirit of the appended claims. The term “comprising”, insofar it was used in the claims or in the description, does not exclude other elements or steps of a corresponding feature or procedure. In case that the terms “a” or “an” were used in conjunction with features, they do not exclude a plurality of such features. Moreover, any reference signs in the claims should not be construed as limiting the scope.
Number | Date | Country | Kind |
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10 2020 133 139.8 | Dec 2020 | DE | national |
The present application is the national stage entry of International Patent Application No. PCT/EP2021/082483, filed on Nov. 22, 2021, and published as WO 2022/122361 A1 on Jun. 16, 2022, which claims priority to German Application No. 10 2020 133 139.8, filed on Dec. 11, 2020, the disclosures of all of which are incorporated by reference herein in their entireties.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2021/082483 | 11/22/2021 | WO |