Noise Control

Abstract

An earmuff is provided, comprising: a shell; an ear pad attached to the shell and arranged so that the shell and the ear pad together define a cavity having an opening; and an acoustic driver arranged in the cavity. The earmuff also includes a feedforward microphone, a feedback microphone, and an active noise control (ANC) circuit. The active noise control (ANC) circuit is configured to operate the acoustic driver using a feedforward signal provided by the feedforward microphone to attenuate noise having a frequency within a feedforward ANC range, and is configured to operate the acoustic driver using a feedback signal provided by the feedback microphone to attenuate noise having a frequency within a feedback ANC range, the feedforward ANC range having a lower limit of not less than 300 Hz and an upper limit greater than 1.5 kHz, and the feedback ANC range having an upper limit of not more than 1.5 kHz.

Description

Technical Field

[0001] The present invention relates to noise control in an earmuff or a speaker assembly, and more particularly to the implementation of active noise control in an earmuff of a head-mounted air purifier. Background Art

[0002] Air pollution is a growing problem, with various air pollutants causing known or suspected harmful effects on human health. The adverse effects that air pollution may cause depend on the type and concentration of the pollutant and the duration of exposure to polluted air. For example, high levels of air pollution may cause immediate health problems, such as severe cardiovascular and respiratory diseases, while long-term exposure to polluted air may have permanent health effects, such as loss of lung function and decreased lung function and the development of diseases such as asthma, bronchitis, emphysema, and possibly cancer.

[0003] In places where air pollution is particularly severe, many people have recognized the benefits of minimizing exposure to these pollutants and have therefore worn masks that are designed to filter out at least a portion of the pollutants present in the air before they reach the mouth and nose. These masks range from basic dust masks that only filter out relatively large dust particles to more complex air-purifying respirators that require air to pass through filter elements or cartridges. However, because these masks typically cover at least the user's mouth and nose, they can make normal breathing more laborious and can also cause problems with the user's ability to speak to others, making their use in daily life somewhat reluctant despite the potential benefits.

[0004] As a result, various attempts have been made to develop air purifiers that can be worn by a user, but that do not need to cover the user's mouth and nose. For example, there are a variety of designs of wearable air purifiers that are worn around the user's neck and produce a jet of air that is directed upward toward the user's mouth and nose. While these may be more socially acceptable, they are generally less effective at limiting the user's exposure to air pollutants than some of the best performing face-worn filters. This is primarily due to their lack of accuracy in delivering the air jet to the user's mouth and nose, as well as the fact that an unfiltered stream of air can still reach the user's mouth and nose.

[0005] WO2017120992, CN103949017A, KR101796969B1 and CN203852759U all describe head-mounted purifiers that provide alternatives to masks and neck-mounted purifiers. WO2017120992 describes a system in which a separate air filter unit is connected to an air outlet disposed on an arm extending from one of the earphones via a duct. Each of CN103949017A, KR101796969B1 and CN203852759U describes a head-mounted headset in which a fan and a filter are incorporated into at least one earmuff. Among them, only KR101796969B1 considers using active noise control (ANC) to reduce the noise generated by the air supply unit. Specifically, KR101796969B1 states that the earmuffs are provided with a frequency generator that generates a frequency for canceling the noise of the air supply unit, and states that this can be achieved using conventional techniques for reducing noise. However, contrary to this claim, the method of implementing active noise control to attenuate the noise generated by the fan located inside the earmuffs is not simple.

[0006] Active noise control uses destructive interference to attenuate noise. The frequency, amplitude and phase of any undesired sound are identified and another sound of the same frequency and amplitude but opposite phase is created, the “anti-noise” sound, with the goal that this “anti-noise” sound cancels the noise. Inside the headset, the anti-noise signal is combined with the desired audio signal before being output by the audio transducer.

[0007] Active noise control can be implemented using any of the feedforward, feedback, or hybrid systems. In a feedforward system, a reference noise microphone (called a feedforward microphone) is located near the outside of the headset to directly measure the noise from the environment and provide this measurement as an input to a feedforward ANC filter. The feedforward ANC filter then uses the input from the feedforward microphone to generate an anti-noise signal intended to attenuate the measured noise. In a feedback system, an error noise microphone (called a feedback microphone) is located near the user's ear, usually close to an acoustic transducer, to measure the sound heard by the user and provide this measurement as an input to a feedback ANC filter. The feedback ANC filter then compares the input from the feedback microphone with the desired audio source to identify unwanted noise and generates an anti-noise signal intended to attenuate the identified noise. A hybrid system then combines the feedforward and feedback systems together to improve overall noise cancellation performance. In particular, in advanced hybrid systems, the feedforward and feedback systems cannot function completely independently of each other because the noise identified by the feedback system is used to improve the performance of the feedforward ANC filter (ie, used as input for determining the coefficients of the feedforward ANC filter).

[0008] In conventional headphones, active noise control is only required to cancel externally generated noise. However, in head-worn purifiers where the fan is located inside the ear cup, the motor driving the fan and the rush of air entering the headphones also generate noise internally. Conventionally configured ANC systems cannot simultaneously attenuate both external environmental (i.e., exogenous) noise and internally sourced (i.e., endogenous) noise. Summary of the invention

[0009] The object of the present invention is to provide an earmuff and a head-mounted air purifier comprising the earmuff, wherein active noise control is capable of attenuating both external environmental (ie exogenous) noise and internally-sourced (ie endogenous) noise.

[0010] According to a first aspect of the present invention, an earmuff is provided, the earmuff comprising: a shell; an ear pad attached to the shell and arranged so that the shell and the ear pad together define a cavity having an opening; and an acoustic driver arranged in the cavity. The earmuff also comprises: a feedforward microphone (i.e., a reference noise microphone) carried by the shell and acoustically coupled to the environment outside the shell; a feedback microphone (i.e., an error noise microphone) arranged in the cavity; and an active noise control (ANC) circuit. The active noise control (ANC) circuit is configured to operate the acoustic driver using a feedforward signal provided by the feedforward microphone to attenuate noise having a frequency within a feedforward ANC range, and is configured to operate the acoustic driver using a feedback signal provided by the feedback microphone to attenuate noise having a frequency within a feedback ANC range, the feedforward ANC range having a lower limit of at least (i.e., not less than) 300 Hz and an upper limit greater than 1.5 kHz, and the feedback ANC range having an upper limit not greater than 1.5 kHz.

[0011] In conventional headphones, feedforward ANC systems are typically configured to attenuate noise with frequencies below 2kHz, particularly noise in the range of 40Hz to 1.5kHz, while conventional feedback ANC systems are typically configured to attenuate noise with frequencies in the range of 20Hz to 500Hz. In contrast, the inventors have discovered that, although the motor within a head-mounted air purifier can be configured so that the fundamental frequency of the motor noise is attenuated by a conventionally configured feedback ANC system, the attenuation of additional endogenous noise (e.g., higher harmonics of motor noise, air impact noise, etc.) requires a feedforward ANC system whose source is applied in a completely different manner than conventional ANC headphones.

[0012] The active noise control circuit may include a feedforward filter configured to receive the feedforward signal as an input and to generate a feedforward filter output that causes the acoustic driver to attenuate noise having a frequency within the feedforward ANC range.

[0013] The lower limit of the feed-forward ANC range may be at least (i.e., not less than) 350 Hz. The lower limit of the feed-forward ANC range may be approximately 500 Hz. The upper limit of the feed-forward ANC range may be at least (i.e., not less than) 2 kHz. The upper limit of the feed-forward ANC range may be approximately 2 kHz. The lower limit of the feed-forward ANC range may be approximately 500 Hz, and the upper limit may be approximately 2 kHz.

[0014] The active noise control circuit may include a feedback filter configured to receive the feedback signal as an input and generate a feedback filter output that causes the acoustic driver to attenuate noise having a frequency within the feedback ANC range.

[0015] The upper limit of the feedback ANC range may be about 500 Hz. The lower limit of the feedback ANC range may be at least (ie, not less than) 20 Hz, and may be about 50 Hz. The lower limit of the feedback ANC range may be about 50 Hz, and the upper limit may be about 500 Hz.

[0016] The earmuff may further comprise a motor-driven impeller disposed within the housing, wherein the motor-driven impeller is arranged to generate an airflow through the housing. The earmuff may further comprise a control circuit, the control circuit being arranged to control the rotational speed of the motor-driven impeller such that the maximum rotational speed of the motor-driven impeller is 9000 to 18,000 RPM. The control circuit may be arranged to control the rotational speed of the motor-driven impeller such that the maximum rotational speed of the motor-driven impeller is 10,000 to 14,000 RPM, and preferably 10,000 to 12,000 RPM.

[0017] The housing may include an air inlet through which airflow can be drawn into the housing by the motor-driven impeller, and an air outlet for exhausting the airflow from the housing. The earmuff may also include a filter assembly arranged within the housing, wherein the motor-driven impeller is arranged to generate airflow through the filter assembly. The air outlet of the housing may be downstream of the filter assembly.

[0018] According to a second aspect of the present invention, there is provided an earmuff, comprising: a shell; an ear pad attached to the shell and arranged so that the shell and the ear pad together define a cavity having an opening; and an acoustic driver arranged in the cavity. The earmuff also includes a feedback microphone (i.e., an error noise microphone) disposed in the cavity; a feedforward microphone (i.e., a reference noise microphone) carried by the shell and acoustically coupled to the environment outside the shell; and an active noise control circuit. The active noise control circuit is configured to operate the acoustic driver to attenuate noise having a frequency within a feedback ANC range using a feedback signal provided by the feedback microphone, and is also configured to operate the acoustic driver to attenuate noise having a frequency within a feedforward ANC range using a feedforward signal provided by the feedforward microphone, wherein the feedback ANC range does not overlap with the feedforward ANC range.

[0019] Conventional hybrid ANC systems use both feedforward ANC systems and feedback ANC systems to process low-frequency noise (e.g., 100-500Hz), so that they are intentionally configured to overlap the attenuation provided by the feedforward ANC system and the feedback ANC system. On the contrary, the inventors found that although the motor in the head-mounted air purifier can be configured so that the fundamental frequency of the motor noise can be attenuated by the conventionally configured feedback ANC system, the feedforward ANC system should target higher frequency air impact noise and overtones of motor noise. In addition, the response of the feedforward ANC system should not result in undesirable endogenous noise amplification. Therefore, in such a system, it is desirable to configure the feedback ANC system and the feedforward ANC system so that their responses do not overlap.

[0020] The active noise control circuit may include a feed-back filter configured to receive the feed-back signal as an input and generate a feed-back filter output, the feed-back filter output causing the acoustic driver to attenuate noise having a frequency within the feed-back ANC range. The active noise control circuit may also include a feed-forward filter configured to receive the feed-forward signal as an input and generate a feed-forward filter output causing the acoustic driver to attenuate noise having a frequency within the feed-forward ANC range.

[0021] The earmuffs may be configured as any one of circum-aural earmuffs and supra-aural earmuffs, and are preferably configured as circum-aural earmuffs.

[0022] According to a third aspect of the present invention, there is provided a head mounted device comprising a head mounted component and an earmuff as defined in any one of the first and second aspects, wherein the earmuff is attached to the head mounted component and is arranged to be worn on an ear of a user.

[0023] The head mounted device may further include another earmuff, the other earmuff being arranged to be worn on the other ear of the user. The other earmuff may be as defined in any one of the first aspect and the second aspect. The head mounted device may include a headband, the headband being arranged to be worn on the head of the user. Then, the earmuff may be mounted on a first end of the headband, and the other earmuff may be mounted on an opposite second end of the headband.

[0024] According to another aspect, an active noise control (ANC) circuit is also provided, the active noise control (ANC) circuit being configured to receive a feedforward signal and use the feedforward signal to generate instructions for an acoustic driver to attenuate noise having a frequency within a feedforward ANC range, the feedforward ANC range having a lower limit of at least (i.e., not less than) 300 Hz and an upper limit greater than 1.5 kHz. The active noise control (ANC) circuit may be configured to receive the feedforward signal from a feedforward microphone. The active noise control (ANC) circuit may be configured to send instructions to the acoustic driver.

[0025] According to another aspect, a method of implementing active noise control (ANC) is also provided. The method includes receiving a feedforward signal from a feedforward microphone and using the feedforward signal to generate instructions for an acoustic driver to attenuate noise having a frequency within a feedforward ANC range, the feedforward ANC range having a lower limit of at least (i.e., not less than) 300 Hz and an upper limit greater than 1.5 kHz. The method may also include sending the instructions to the acoustic driver.

[0026] According to another aspect, an active noise control (ANC) circuit is also provided, which is configured to receive a feedback signal and a feedforward signal. The active noise control (ANC) circuit is also configured to use the feedback signal to generate instructions for the acoustic driver to attenuate noise with a frequency within the feedback ANC range, and to use the feedforward signal to generate instructions for the acoustic driver to attenuate noise with a frequency within the feedforward ANC range, wherein the active noise control (ANC) circuit is configured so that the feedback ANC range does not overlap with the feedforward ANC range. The active noise control (ANC) circuit may be configured to receive a feedback signal from a feedback microphone. The active noise control (ANC) circuit may be configured to receive a feedforward signal from a feedforward microphone. The active noise control (ANC) circuit may be configured to send instructions to the acoustic driver.

[0027] According to yet another aspect, a method for implementing active noise control (ANC) is also provided. The method includes receiving a feedback signal and a feedforward signal, using the feedback signal to generate instructions for an acoustic driver to attenuate noise having a frequency within a feedback ANC range, and using the feedforward signal to generate instructions for an acoustic driver to attenuate noise having a frequency within the feedforward ANC range, wherein the feedback ANC range does not overlap with the feedforward ANC range. The method may also include receiving a feedback signal from a feedback microphone. The method may also include receiving a feedforward signal from a feedforward microphone. The method may also include sending instructions to an acoustic driver. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0029] Figure 1a is a front perspective view of an embodiment of a head-mounted air purifier as described herein;

[0030] Figure 1b yes Figure 1a A front view of a head-mounted air purifier;

[0031] Figure 2a yes Figure 1a A side view of an earmuff of a head-mounted air purifier;

[0032] Figure 2b yes Figure 2a A perspective view of the earmuffs;

[0033] Figure 3a yes Figure 2a a cross-sectional view of a speaker assembly;

[0034] Figure 3b yes Figure 2a Another cross-sectional view of the speaker assembly;

[0035] Figure 4a is a graph showing sound measurements made on a head-worn purifier such as described herein without any active noise control;

[0036] Figure 4b is a graph showing sound measurements made on a head-worn purifier such as described herein with mixed active noise control;

[0037] Figure 4c is a graph comparing the attenuation achieved by hybrid active noise control of internally originated noise with the attenuation achieved by hybrid active noise control of externally originated noise;

[0038] Figure 5ais a graph showing sound measurements made on a head-worn purifier such as described herein without any active noise control;

[0039] Figure 5b is a graph showing sound measurements made on a head-worn purifier such as described herein with only feed-back active noise control;

[0040] Figure 5c is a graph comparing the attenuation achieved by only feed-back active noise control of internally originated noise to the attenuation achieved by only feed-back active noise control of externally originated noise; and

[0041] Figure 6 is a graph illustrating an example of a response provided by a hybrid active noise control configured in accordance with the present invention. DETAILED DESCRIPTION

[0042] The earmuffs and head-mounted air purifiers including the earmuffs will now be described, wherein active noise control is capable of attenuating both external ambient (i.e., exogenous) noise and internal source (i.e., endogenous) noise. As used herein, the term "air purifier" refers to a device or system capable of removing impurities from the air and releasing a supply of purified or filtered air. The term "head-mounted" is used herein to define an item capable of or suitable for being worn on a user's head.

[0043] As used herein, the term "earphone" refers to a pair of small loudspeakers or speakers connected by a headband, which is designed to be worn on or around the user's head. Typically, the speaker is provided by an electroacoustic transducer, which converts an electrical signal into a corresponding sound. Circular earphones are generally referred to as full-size or circumaural earphones, which have an ear pad shaped as a closed loop shape (e.g., circular, oval, etc.) so that it covers the entire ear. Since these earphones completely surround the ear, the circum-ear earphones can be designed to be completely sealed against the head to reduce external noise. On-ear headphones (commonly referred to as in-ear headphones) have ear pads that are pressed against the ear rather than around the ear. This type of earphone will usually be smaller and lighter than circum-ear headphones, thereby having little attenuation of external noise.

[0044] Figure 1a and 1b 1 is an external view of an embodiment of a head-mounted air purifier 1000. The head-mounted air purifier 1000 includes a pair of generally cylindrical earmuffs or speaker assemblies 1100a, 1100b connected by an arched headband 1200, and a nozzle 1300 extending between the two earmuffs 1100a, 1100b and connected to the two earmuffs 1100a, 1100b at opposite ends. Then, Figure 2a Shows Figure 1a and 1bA side view of the earmuff 1100 of the air purifier 1000, and Figure 3b Shows Figure 1a and 1b A perspective view of the earmuff 1100 of the air purifier 1000. Then, Figure 3a and 3b is through Figure 3a An alternative cross-sectional view of the earmuff 1100 is shown.

[0045] Each earmuff 1100 includes a shell 1101 and an ear pad 1102 attached to the shell 1101, wherein the shell 1101 and the ear pad 1102 together define a cavity 1103 having an opening 1104. A speaker or acoustic driver unit 1105 is then attached to the shell 1101 so that it is placed in the cavity 1103. A feedforward microphone (i.e., reference noise microphone) 1106 is then mounted to the shell 1101 so that it is acoustically coupled to the environment outside the shell 1101. An active noise control (ANC) circuit 1107 is then connected to the feedforward microphone 1106 and the acoustic driver 1105. The ANC circuit 1107 is configured to operate the acoustic driver 1105 using a feedforward signal provided by the feedforward microphone 1106 to attenuate noise having a frequency within a feedforward ANC range / interval, wherein the feedforward ANC range has a lower limit / minimum value of at least (i.e., not less than) 300 Hz and an upper limit / maximum value of at most (i.e., not greater than) 1.5 kHz. Specifically, the ANC circuit 1107 includes a feedforward filter configured to receive the feedforward signal as an input and generate a feedforward filter output that causes the acoustic driver 1105 to attenuate noise having a frequency within the feedforward ANC range / interval.

[0046] The lower limit of the feedforward ANC range is at least 300 Hz, preferably the lower limit is at least (i.e., not less than) 350 Hz, and more preferably about 500 Hz. In addition, the upper limit of the feedforward ANC range is greater than 1.5 kHz, preferably the upper limit of the feedforward ANC range is at least 2 kHz, and more preferably about 2 kHz. In a preferred embodiment, the lower limit of the feedforward ANC range is about 500 Hz and the upper limit is about 2 kHz.

[0047] In a more preferred embodiment, the ANC circuit 1107 is configured to operate the acoustic driver 1105 using the feedforward signal provided by the feedforward microphone 1106 to achieve one or more of at least 5 dB of attenuation at 2 kHz, at least 10 dB of attenuation between 350 Hz and 1.5 kHz, and at least 15 dB of attenuation between 500 Hz and 1 kHz.

[0048] Each earmuff 1100 also includes a feedback microphone (i.e., error noise microphone) 1108 disposed within the cavity 1103, adjacent to the acoustic driver 1105. Thus, the ANC circuit 1107 is also configured to operate the acoustic driver 1105 using a feedback signal provided by the feedback microphone 1108 to attenuate noise having a frequency within a feedback ANC range / interval, the feedback ANC range / interval having an upper limit / maximum value of at most 1.5 kHz. Specifically, the ANC circuit 1107 includes a feedback filter configured to receive the feedback signal as an input and generate a feedback filter output that causes the acoustic driver 1105 to attenuate noise having a frequency within the feedback ANC range.

[0049] Although the upper limit of the feed-back ANC range is at most 1.5kHz, it is preferred that the upper limit is about 500Hz. In addition, it is also preferred that the lower limit / minimum value of the feed-back ANC range is at least 20Hz, and more preferably about 50Hz. In a preferred embodiment, the lower limit of the feed-back ANC range is about 50Hz and the upper limit is about 500Hz.

[0050] Therefore, in a preferred embodiment, the ANC circuit 1107 is also configured to operate the acoustic driver 1105 using the feedback signal provided by the feedback microphone 1108 to achieve one or more of at least 5 dB attenuation between 50 Hz and 500 Hz, at least 15 dB attenuation between 100 Hz and 300 Hz, and at least 25 dB attenuation between 150 Hz and 250 Hz.

[0051] Each earmuff 1100 further comprises a motor-driven impeller 1109 disposed within the housing 1101, the motor-driven impeller 1109 being arranged to generate an airflow through the housing 1101. Thus, the housing 1101 is provided with an air inlet 1110, through which an airflow can be drawn into the housing 1101 by the motor-driven impeller 1109, and an air outlet 1111 for exhausting the airflow from the housing 1101. A filter assembly 1112 is also disposed within the housing 1101, such that the airflow generated by the motor-driven impeller 1109 passes through the filter assembly 1112, and such that the airflow exhausted from the earmuff 1100 is filtered / purified by the filter assembly 1112. Thus, the filter assembly 1112 is located downstream of the air inlet 1110 of the housing 1101 (i.e., with respect to the airflow generated by the impeller 1109) and upstream of the air outlet 1111. In the illustrated embodiment, the filter assembly 1112 is also located upstream with respect to the motor-driven impeller 1109.

[0052] Each earmuff 1100 further comprises a motor control circuit 1107, which is arranged to control the rotational speed of the motor 1113 driving the impeller 1109 so that the maximum rotational speed of the impeller 1109 is between 9000 RPM and 18,000 RPM, preferably between 10,000 and 14,000 RPM, and more preferably between 10,000 and 12,000 RPM. As described below, it has been found that these rotational speed ranges result in a fundamental frequency of motor noise that can be attenuated by a conventionally configured feed-back ANC system, thereby increasing the degree to which noise generated by the motor 1113 and / or the impeller 1109 can be cancelled.

[0053] As shown, the housing 1101 comprises: a speaker chassis 1114 on which the acoustic driver unit 1105 is mounted; and a generally frustoconical speaker cover 1115, which is mounted on the speaker chassis 1111 above the acoustic driver unit 1105. The speaker chassis 1114 comprises a generally circular base 1114a surrounded by a cylindrical side wall 1114b. The air outlet 1111 of the housing is then defined by a hole formed in the cylindrical side wall 1114b. The earmuff 1100 is also provided with a hollow, rigid outlet duct 1130 extending from the housing 1101 and arranged to connect the air outlet 1111 of the earmuff 1100 to the air inlet of the nozzle 1300.

[0054] The central portion of the base 1114a of the speaker chassis provides a driver support plate 1111c on which the acoustic driver unit 1105 can be located. Then, a speaker cover 1115 of a generally truncated cone shape is mounted on the speaker chassis 1114 over the entire driver support plate 1114c so that the acoustic driver unit 1105 is covered by the speaker cover 1115. The driver support plate 1114c of the speaker chassis 1114 is provided with an array of holes to allow the sound generated by the acoustic driver unit 1105 to pass through the speaker chassis 1114 into the cavity 1103 surrounded by the ear pad 1102. In addition, the driver support plate 1114c is angled or tilted relative to the peripheral portion of the base 1114a of the speaker chassis 1111. The angle or tilt of the driver support plate 1114c is selected so that when the head-mounted air purifier 1000 is worn on the head of the user with the earmuffs 1100 located above the ears of the user, the acoustic driver unit 1105 is substantially parallel to the ears. For example, in the illustrated embodiment, the angle of the driver support plate 1114c relative to the outer peripheral portion of the base 1114a is 10 to 15 degrees.

[0055] The feed-back microphone 1108 is disposed within the cavity 1103, adjacent to the acoustic transducer 1105, so as to pick up the sound reaching the user so that any unwanted noise can be identified. Specifically, the feed-back microphone 1108 is mounted on the speaker chassis 1114 between the acoustic transducer 1105 and the opening 1104 of the cavity 1103. The feed-back microphone 1108 is arranged to provide data to the ANC circuit 1107. The ANC circuit 1107 is provided by one or more processors that implement feed-forward and feed-back ANC filters and provide their outputs to an audio control circuit that is configured to control the audio transducer 1105.

[0056] In the illustrated embodiment, the ANC circuitry, the motor control circuitry and the audio control circuitry are provided by a single circuit board 1107 which is disposed on or mounted to a peripheral portion of the speaker chassis 1114. Thus, when the acoustic driver unit 1105 is mounted to the driver support plate 1114c, the control circuitry 1107 thus at least partially surrounds the acoustic driver unit 1105 (i.e., is arranged outside / around the periphery of the acoustic driver unit 1105).

[0057] A generally frustoconical impeller housing 1116 containing both the impeller 1109 and the motor 1113 is then placed over the speaker cover 1115 so that the acoustic driver unit 1105 is nested within a recess or cavity defined by the back / rear portion of the impeller housing 1116. The impeller housing 1116 comprises a generally frustoconical impeller casing 1117 surrounding the impeller 1109 and the motor 1113, and an annular volute 1118 fluidly connected to the base of the impeller casing 1117 and arranged to receive air exhausted from the impeller casing 1117. The impeller casing 1117 is provided with an air inlet 1119 through which air is drawn in by the impeller 1109, and an air outlet 1120 through which air is released from the impeller casing 1117 into the annular volute 1118. The air inlet 1119 of the impeller housing 1117 is provided by a hole / opening at the small diameter end of the impeller housing 1117 , while the air outlet 1120 is provided by an annular slot formed around the large diameter end or base of the impeller housing 1117 .

[0058] The annular volute 1118 includes a spiral (i.e., gradually widening) duct that is arranged to receive air exhausted from the impeller housing 1117 and direct the air to the air outlet 1121 of the volute 1118. The air outlet 1121 of the volute 1118 is then fluidly connected to the air outlet 1111 of the speaker assembly 1100. As used herein, the term "volute" refers to a spiral funnel that receives fluid pumped by the impeller and increases in area as it approaches the exhaust port. Thus, the air outlet 1121 of the volute 1118 provides an efficient and quiet means for collecting air exhausted from the circumferential annular groove that forms the air outlet 1120 of the impeller housing 1117.

[0059] In the illustrated embodiment, the impeller 1109 is a mixed flow impeller having a generally conical or truncated conical shape. The impeller 1109 is hollow so that the rear / back side of the impeller 1109 defines a generally truncated conical recess. The motor 1113 is then nested / arranged in the recess. Preferably, the impeller 1109 is a semi-open / semi-closed mixed flow impeller, i.e., only having a rear shroud 1122. The rear shroud 1133 of the impeller 1109 then defines a recess, and the motor 1113 is nested / arranged in the recess 1132.

[0060] The impeller housing 1116 is then supported / suspended within the housing 1101 by a plurality of resilient supports 1123, which reduce the transmission of vibrations from the impeller housing 1116 to the speaker housing 1101. To this end, each of the plurality of resilient supports 1123 comprises a resilient material, such as an elastomer or rubber material. In the illustrated embodiment, the only direct connection between the speaker housing 1101 and the impeller housing 1116 is provided by the resilient supports 1123.

[0061] The filter assembly 1112 is then mounted to the speaker chassis 1114 such that the filter assembly 1112 is positioned upstream of the impeller 1109 and is arranged to nest above the impeller housing 1116. The filter assembly 1112 includes a filter seat 1124 that supports one or more filter elements 1125, 1126. In the illustrated embodiment, the filter assembly 1112 includes both a particle filter element 1125 and a chemical filter element 1126, wherein the particle filter element 1125 is located upstream relative to the chemical filter element 1126.

[0062] The filter seat 1124 is provided with a plurality of apertures 1127 which allow air to pass from the front surface of the filter seat 1124 to the rear / back surface of the filter seat 1124 which is arranged to support the filter elements 1125, 1126 over the plurality of apertures 1127. The filter seat 1124 then further defines an air passage or channel 1128 between the rear / back surface of the filter seat 1124 and the air inlet 1119 of the impeller housing 1116, the air passage or channel 1139 being arranged to direct the air to the air inlet 1119 of the impeller housing 1116. The air passage 1128 is provided by a cavity defined between the rear / back surface of the filter seat 1124 and the front surface of the impeller housing 1116. Thus, the air must first pass through the filter elements 1125, 1126 before passing through the apertures 1127 in the filter seat 1124 and into the air passage 1128 leading to the air inlet 1119 of the impeller housing 1116.

[0063] In the illustrated embodiment, the filter seat 1124 is mounted to the speaker chassis 1114 and is located above the impeller housing 1117, wherein the impeller housing 1117 is partially disposed within a volume defined by the back of the filter seat 1124. In particular, the filter seat 1124 includes a generally frustoconical peripheral portion and a generally cylindrical central portion. The generally frustoconical peripheral portion of the filter seat 1124 is provided with a plurality of holes 1127 and is arranged to support one or more generally frustoconical filter elements 1125, 1126 above the plurality of holes 1127. The impeller housing 1117 is then at least partially disposed within the generally cylindrical central portion of the filter seat 1124. In particular, the air inlet 1119 of the impeller housing 1117 is disposed within a volume defined by the back of the cylindrical central portion of the filter seat 1124.

[0064] The housing 1101 also includes an outer cover 1129 mounted on the speaker chassis 1114. The outer cover 1129 is arranged to fit over (and thus generally conform to) the filter assembly 1112 and is provided with an array of holes that allow air to pass through the outer cover 1129 and thus define an air inlet of the outer cover 1129. The size of these holes is determined to prevent larger particles from passing through to reach the filter assembly 1112 and blocking or otherwise damaging the filter elements 1125, 1126. Alternatively, to allow air to pass, the outer cover 1129 may include one or more grilles or meshes mounted within windows in the outer cover 1129. It will also be clear that alternative patterns of arrays are contemplated within the scope of the present invention.

[0065] The outer cover 1129 is releasably attached to the speaker chassis 1114 so as to cover the filter assembly 1112. For example, the outer cover 1129 can be attached to the speaker chassis 1114 using mating threads provided on the outer cover 1129 and the speaker chassis 1114 and / or using some snap-fit ​​mechanism. When mounted on the speaker chassis 1114, the outer cover 1129 protects the filter elements 1125, 1126 from damage, such as during transportation, and also provides a visually attractive outer surface covering the filter assembly 1112, which is consistent with the overall appearance of the purifier 1000.

[0066] In the illustrated embodiment, the outer cover 1129 is configured as a hollow truncated cone with an open end. The open large diameter end of the outer cover 1129 is arranged to fit over the outer periphery of the large diameter end of the filter assembly 1112, while the open small diameter end of the outer cover 1129 is arranged to fit over both the outer periphery of the small diameter end of the filter assembly 1112 and the substantially cylindrical central portion of the filter seat 1124. Therefore, the circular front surface 1124a of the substantially cylindrical central portion of the filter seat 1124 is exposed within the open small diameter end of the outer cover 1129, thereby forming a portion of the outer surface of the speaker assembly 1100. Preferably, the circular front surface 1124a of the filter seat 1124 is transparent, thereby forming a window through which a user can see the rotation of the impeller 1109 through the air inlet 1119 of the impeller housing 1116. This allows the user to visually check the speed of the impeller 1109 and confirm that the impeller 1109 is working properly.

[0067] The feedforward microphone 1106 is disposed adjacent to the outer surface of the housing 1101, toward the exterior of the earmuff 1100. In particular, the feedforward microphone 1106 is mounted on the inner surface of the circular front surface 1124a of the filter seat 1124. The feedforward microphone 1106 is arranged to provide data to the ANC circuit 1107, which is then configured to implement active noise cancellation (ANC) when controlling the acoustic driver unit 1105.

[0068] like Figure 1bAs shown, the first open end of the nozzle 1300 is connected to a rigid outlet duct 1130 extending from the housing 1101 of the first speaker assembly 1100a. Then, the nozzle 1300 extends away from the first earmuff 1100a and is in an arcuate shape, so that the opposite second open end 1302 of the nozzle 1300 is connected to the rigid outlet duct 1130 extending from the housing 1101 of the second earmuff 1100b. The nozzle 1300 is arranged so that when the user wears the purifier 1000 with the first earmuff 1100a on the first ear of the user and the second earmuff 1100b on the second ear of the user, the nozzle 1300 can extend from one side to the other side around the user's face and in front of the user's mouth. In particular, the nozzle 1300 extends from around the user's chin, from one adjacent cheek to another adjacent cheek, without contacting the user's mouth, nose or surrounding facial area. Therefore, it is preferred that at least a portion of the nozzle 1300 is formed of a transparent or partially transparent material so that the user's mouth is visible through the nozzle 1300, thereby avoiding limiting the user's ability to speak clearly to others. For example, the central portion of the nozzle can be made of a flexible transparent plastic such as polyurethane, while the two end portions can each be made of a hard, transparent plastic, such as polyethylene terephthalate glycol (PETG). Alternatively, the entire nozzle 1300 can be formed of a single transparent or partially transparent material.

[0069] The nozzle 1300 is provided with an air outlet 1301 for releasing / delivering filtered air to a user. For example, the air outlet 1301 of the nozzle 1300 may include an array of holes formed in a portion of the nozzle 1300, the holes extending from an internal passage defined by the nozzle 1300 to an outer surface of the nozzle 1300. Alternatively, the air outlet 1301 of the nozzle 1300 may include one or more grilles or meshes mounted within a window in the nozzle 1300.

[0070] In use, the purifier 1000 is worn by a user, wherein the first earmuff 1100a is over the first ear of the user and the second earmuff 1100b is over the second ear of the user, so that the nozzle 1300 can extend from one ear to the other ear around the face of the user and over at least the mouth of the user. In each earmuff 1100a, 1100b, the rotation of the impeller 1109 driven by the motor 1113 will cause an airflow through the impeller housing 1116, and the impeller housing 1108 draws air into the speaker assembly 1100 through the holes in the outer cover 1129. Then, the air flow will pass through the filter elements 1125, 1126 disposed between the outer cover 1129 and the filter seat 1124, thereby filtering and / or purifying the airflow. The resulting filtered airflow will then pass through an aperture 1127 provided in the frustoconical portion of the filter seat 1124 into an air passage 1129 provided by the space between the opposing surfaces of the impeller housing 1116 and the filter seat 1124, which then directs the airflow to an air inlet 1119 of the impeller housing 1116. The impeller 1109 will then force the filtered airflow out through an annular slot providing an air outlet 1120 of the impeller housing 1117 and into a volute 1118 of the impeller housing 1116. The volute 1118 then directs the filtered airflow through an air outlet 1111 of the speaker assembly 1101, through a rigid outlet duct extending from the housing 1101, and into the nozzle 1300 through an air inlet provided by one of the open ends of the nozzle 1300.

[0071] Example

[0072] The head-mounted purifier as described above was measured using an artificial head measurement system equipped with a microphone.

[0073] Figure 4a shows measurements taken with the motor on and without any ANC applied, while Figure 4b shows a measurement taken with the motor on and hybrid ANC applied. Then, Figure 4c shows the attenuation achieved by hybrid ANC of internally originated noise due to motor turning on (i.e., Figure 4a and 4b The difference between the measured values ​​of ) and the attenuation achieved by hybrid ANC for externally originated noise (i.e., produced by performing a frequency sweep using an external speaker) are compared. From this graph it can be seen that the hybrid ANC provides better attenuation for externally originated noise than for internally originated noise at a frequency of 150Hz.

[0074] These measurements were repeated using only the feed-back ANC. Figure 5a shows measurements taken with the motor on and without any ANC applied, while Figure 5bMeasurements taken with the motor on and feedback-only ANC applied are shown. Then, Figure 4c shows the attenuation achieved by feed-back-only ANC of the internally originated noise due to motor turn-on (i.e., Figure 5a and 5b ) compared to the attenuation achieved by feed-back-only ANC of externally originated noise (i.e., produced by performing a frequency sweep using an external speaker). From this graph, it can be seen that the feed-back-only ANC provides almost the same degree of attenuation of externally originated noise as it does of internally originated noise caused by motor turn-on.

[0075] From these results, it can be determined that the feedforward ANC does not achieve any further attenuation of the internally originated noise caused by the motor being turned on, because the amount of motor noise propagating from the outer surface of the earmuff is too low to add to the noise inside the earmuff. Therefore, the inventors recognized that the feedback source of the hybrid ANC system should be targeted at the fundamental frequency (first-order harmonic) of the motor noise, and recognized that the feedforward source can be tuned to handle higher frequency noise such as the sixth-order harmonic of the motor noise and the wider air impact noise without amplifying the motor noise. Applying this approach to the example of a head-mounted purifier as described above shows that by appropriately tuning the feedback portion of the hybrid ANC system, an attenuation of approximately 20 dB at a frequency of approximately 150 Hz can be achieved, and it is shown that this is sufficient to suppress the fundamental frequency (first-order harmonic) of the motor noise, while the feedforward portion of the hybrid ANC system can be tuned separately to attenuate noise up to 10 dB or more in the 500 Hz to 2 kHz band. Figure 6 An example of a response provided by a hybrid ANC system configured in this manner is shown.

[0076] It should be understood that the above-mentioned various items can be used alone or in combination with other items shown in the drawings or described in the specification, and that items mentioned in the same paragraph or in the same drawings as each other do not need to be used in combination with each other. In addition, the expression "means" can be replaced by the desired actuator or system or device. In addition, any reference to "including" or "comprising" is not intended to be limiting in any way, and the reader should interpret the description and claims accordingly.

[0077] In addition, although the present invention has been described according to the preferred embodiments described above, it should be understood that these embodiments are illustrative only. In view of this disclosure, those skilled in the art will be able to make modifications and substitutions, which are considered to fall within the scope of the appended claims. For example, in the above-mentioned embodiment, the head-mounted air purifier includes an earphone system in which two speaker assemblies are arranged on opposite ends of the headband. However, the head-mounted air purifier can equally include any head wearable item that can be used to support a first speaker assembly above a first ear of a user and a second speaker assembly above a second ear of the user. For example, the head-mounted air purifier can include any type of headwear such as a hat or a helmet, including a helmet and a helmet, a bicycle helmet, a motorcycle helmet, etc.

[0078] In addition, although in the above embodiment, both speaker assemblies include motor-driven impellers and filter assemblies, and then both speaker assemblies provide filtered / purified air to the nozzle, it is possible that only one of the two speaker assemblies includes a motor-driven impeller and filter assembly, so that only one speaker assembly provides filtered / purified air to the nozzle. However, this arrangement will not be as effective as the arrangement of the above embodiment.

Claims

1. An earmuff, comprising: case; an ear pad attached to the housing and arranged so that the housing and the ear pad together define a cavity having an opening; an acoustic driver disposed within the cavity; a feedforward microphone carried by the housing and acoustically coupled to an environment external to the housing; A feed-back microphone is disposed in the cavity; a motor-driven impeller disposed within the housing and between the feedforward microphone and the feedback microphone, the motor-driven impeller being arranged to generate an airflow through the housing, the housing comprising an air inlet through which airflow can be drawn into the housing by the motor-driven impeller, and an air outlet for exhausting the airflow from the housing; and An active noise control (ANC) circuit configured to operate an acoustic driver using a feedforward signal provided by a feedforward microphone to attenuate noise having a frequency within a feedforward ANC range, and configured to operate an acoustic driver using a feedback signal provided by a feedback microphone to attenuate noise having a frequency within a feedback ANC range, wherein the feedforward ANC range has a lower limit of not less than 300 Hz and an upper limit of greater than 1.5 kHz, and the feedback ANC range has an upper limit of not more than 500 Hz.

2. The earmuff according to claim 1, wherein: The active noise control circuit includes a feedforward filter configured to receive the feedforward signal as an input and to generate a feedforward filter output that causes the acoustic driver to attenuate noise having a frequency within the feedforward ANC range.

3. The earmuff according to claim 1, wherein: The lower limit of the feedforward ANC range is not less than 350 Hz.

4. The earmuff according to claim 1, wherein: The lower limit of the feed-forward ANC range is 500 Hz.

5. The earmuff according to claim 1, wherein: The upper limit of the feedforward ANC range is not less than 2 kHz.

6. The earmuff according to claim 1, wherein: The upper limit of the feed-forward ANC range is 2kHz.

7. The earmuff according to claim 1, wherein: The lower limit of the feed-forward ANC range is 500 Hz, and the upper limit is 2 kHz.

8. The earmuff according to claim 1, wherein: The active noise control circuit includes a feedback filter configured to receive the feedback signal as an input and generate a feedback filter output that causes the acoustic driver to attenuate noise having a frequency within the feedback ANC range.

9. The earmuff according to claim 1, wherein: The upper limit of the feedback ANC range is 500 Hz.

10. The earmuff according to claim 1, wherein: The lower limit of the feedback ANC range is not less than 20 Hz.

11. The earmuff according to claim 1, wherein: The lower limit of the feedback ANC range is 50 Hz.

12. The earmuff of claim 1, further comprising a control circuit arranged to control the rotational speed of the motor driven impeller such that the maximum rotational speed of the motor driven impeller is 9000 to 18,000 RPM.

13. The earmuff according to claim 12, wherein: The control circuit is arranged to control the rotational speed of the motor driven impeller so that the maximum rotational speed of the motor driven impeller is 10,000 to 14,000 RPM.

14. The earmuff according to claim 1, wherein: The housing comprises an air inlet through which air flow can be drawn into the housing by the motor-driven impeller, and an air outlet for exhausting the air flow from the housing.

15. The earmuff of claim 14, further comprising a filter assembly disposed within the housing, wherein: The motor driven impeller is arranged to generate air flow through the filter assembly.

16. The earmuff according to claim 15, wherein: The air outlet of the housing is downstream of the filter assembly.

17. A head mounted device comprising: Headgear; as well as An earmuff according to any one of claims 1-16, wherein the earmuff is attached to the headgear and is arranged to be worn over the ear of a user.

18. The head mounted device of claim 17, further comprising another earmuff arranged to be worn over another ear of the user.

19. The head mounted device according to claim 18, wherein: The other earmuff is as claimed in claim 1.

20. The head mounted device of claim 18, wherein: The headgear comprises a headband arranged to be worn on a user's head, and the earmuff is mounted on a first end of the headband and the other earmuff is mounted on an opposite second end of the headband.

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