Facebook Patent | High Compliance Microspeakers For Vibration Mitigation In A Personal Audio Device

Patent: High Compliance Microspeakers For Vibration Mitigation In A Personal Audio Device

Publication Number: 20200304905

Publication Date: 20200924

Applicants: Facebook

Abstract

An audio system includes a speaker configured to emit sound. The speaker is contained in an enclosure, the enclosure forming a front cavity and a rear cavity that are on opposite sides of the speaker. The enclosure includes: at least one output port configured to output a first portion of the sound from the front cavity and at least one rear port configured to output a second portion of the sound from the rear cavity. The second portion of the sound is substantially out of phase with the first portion. The audio system has an equivalent acoustic volume (Vas) greater than ten times a volume of the front cavity and greater than ten times a volume of the rear cavity.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to U.S. Provisional Application No. 62/821,915, filed Mar. 21, 2019, the entire contents of which are hereby incorporated by reference for all purposes as if fully set forth herein.

BACKGROUND

[0002] This disclosure relates generally to speakers for headsets, and more specifically to high compliance microspeakers.

[0003] High performance speakers are an important component for producing high quality audio for consumer electronics devices. As consumer electronics get smaller, lighter, and more wearable, a lot of design constraints (size, weight, power consumption, etc.) are put into the speakers while still hoping to achieve a good audio quality. Hence, a high-performance speaker with small size, light weight, and less power consumption is desired.

SUMMARY

[0004] An audio system includes a speaker configured to emit sound, and at least part of an enclosure containing the speaker. The speaker is a high compliance speaker that includes a transducer with mechanical compliance (Cms) that is high. The transducer may be a diaphragm, also referred to herein as a “membrane,” with a high Cms (e.g., greater than 10 mm/N), according to some embodiments. The speaker may be designed such that it mitigates vibration imparted to a surrounding structure (e.g., a personal audio device) the speaker is mounted to. The enclosure containing the speaker forms a front cavity and a rear cavity that are on opposite sides of the speaker. The enclosure includes at least one output port and at least one rear port. The at least one output port is configured to output a first portion of the sound from the front cavity, and the at least one rear port is configured to output a second portion of the sound from the rear cavity. The second portion of the sound is substantially out of phase with the first portion of the sound. An equivalent acoustic volume (Vas) of the audio system is greater than ten times a volume of the front cavity and greater than ten times a volume of the rear cavity. The audio system may achieve a high Vas, while maintaining a relatively small form factor (e.g. having a physical volume less than 5 cubic centimeters) and weight (e.g. less than 4 grams) of the enclosure and the speaker, by combining a high compliance speaker with the enclosure including the at least one output port and the at least one rear port.

[0005] In some embodiments, the audio system may be part of a personal audio device (e.g., headset). For example, the audio system may be coupled to a frame of a headset. The audio system has a relatively low resonance frequency, which improves the power efficiency of the audio system and reduces unwanted vibrations in structures coupled to the enclosure and the speaker, such as, for example, the frame of the headset.

[0006] The total sound emitted from the audio system may have a dipole configuration, such that the first portion of the sound destructively interferes with the second portion of the sound in the far-field, resulting in low leakage of sound into the far-field, according to some embodiments. As such, the audio system may selectively deliver sound to a user’s ear in the near-field.

[0007] The high compliance speaker, including the high Cms membrane, may have a rectangular shape. The low resonant frequency and improved power efficiency may be due, in part to the shape of the high compliance speaker. In other embodiments, the high compliance speaker may have a different shape. For example, the audio system may include a high compliance speaker with an elliptical shape.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a perspective view of a headset implemented as an eyewear device, in accordance with one or more embodiments.

[0009] FIG. 2A illustrates a front view of a high compliance speaker including a membrane with a mechanical compliance (Cms) that is high, in accordance with one or more embodiments.

[0010] FIG. 2B shows a cross-section along a line I to I’ of the high compliance speaker shown in FIG. 2A, in accordance with one or more embodiments.

[0011] FIG. 3A illustrates an exploded view of an enclosure containing a rectangular high compliance speaker, in accordance with one or more embodiments.

[0012] FIG. 3B shows a rear view of the enclosure shown in FIG. 3A, integrated into a leg portion of a frame of a headset, in accordance with one or more embodiments.

[0013] FIG. 3C shows a front view of the enclosure shown in FIGS. 3A and 3B, integrated into the leg portion of the frame of the headset, in accordance with one or more embodiments.

[0014] FIG. 4 illustrates a cross-section of an enclosure containing a high compliance speaker, in accordance with one or more embodiments.

[0015] FIG. 5A shows a front view of an enclosure with an offset configuration containing a high compliance speaker, coupled to a leg portion of a frame of a headset, in accordance with one or more embodiments.

[0016] FIG. 5B shows a rear view of the enclosure with the offset configuration shown in FIG. 5A, in accordance with one or more embodiments.

[0017] FIG. 5C shows a cross-section along a line I to I’ of the enclosure 510 shown in FIGS. 5A and 5B, in accordance with one or more embodiments.

[0018] FIG. 6A shows a front view of an enclosure with an offset configuration containing a high compliance speaker, coupled to a leg portion of a frame of a headset, in accordance with one or more embodiments.

[0019] FIG. 6B shows a rear view of the enclosure shown in FIG. 6A, in accordance with one or more embodiments.

[0020] FIG. 6C shows a cross-section along a line I to I’ of the enclosure 610 shown in FIGS. 6A and 6B, in accordance with one or more embodiments.

[0021] FIG. 7 illustrates power efficiency for various sound frequencies for examples of audio systems, in accordance with one or more embodiments.

[0022] FIG. 8 is an example system environment of a headset including an audio system, in accordance with one or more embodiments.

[0023] The figures depict embodiments of the present disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles, or benefits touted, of the disclosure described herein.

DETAILED DESCRIPTION

Overview

[0024] Rectangular speakers used in smartphones or other consumer electronics typically have transducers with mechanical compliance (Cms) that is low (e.g., 4 mm/N or less) for converting electrical energy into sound, where the Cms of the transducer is the reciprocal of the mechanical stiffness of the transducer. These speakers can have poor performance when integrated into virtual reality (VR), augmented reality (AR), and/or mixed reality headsets. For example, conventional speakers with low Cms transducers tend to be heavy, consume high power, produce unwanted vibrations in the headsets, and are incapable of efficiently generating low frequency audio at high sound volumes.

[0025] While speakers with a high Cms transducer are used in some high-performance audio applications, these often have a large form factor and weight. Conventional audio systems using speakers with a small form factor may not provide enough acoustic output for applications such as for use as on-board speakers for headsets, particularly at low frequencies. Additionally, some applications use features unavailable in such conventional audio systems, such as far-field acoustic cancellations, to provide privacy for users. As a result, small form factor speakers with high audio performance, including at low frequencies, are desired.

[0026] An audio system is provided that includes one or more audio assemblies and an audio controller (e.g., controls audio content output by the audio system). The one or more audio assemblies include a speaker. According to some embodiments, the speaker may be a high compliance speaker having a transducer in the form of a high Cms membrane. The audio assembly includes at least some of a speaker enclosure, also referred to herein as an “enclosure.” In some embodiments, the remaining portion of the enclosure is part of a device (e.g., a personal audio device) the audio assembly couples to. A personal audio device is a device worn and/or carried by a user that includes the audio system, and is configured to present audio to a user via the audio system. A personal audio device may be, e.g., a headset, a cellphone, a table, some other device configured to present audio to a user via the audio system, or some combination thereof. In other embodiments the audio assembly include all of the enclosure, and the whole enclosure couples to a device (e.g., a headset). The enclosure contains a high compliance speaker that achieves a higher equivalent acoustic volume (Vas) than comparably sized audio assemblies including a speaker with a lower Cms transducer. In some embodiments, an audio assembly has a small form factor (e.g. having a physical volume less than 5 cubic centimeters) and low weight of the speaker (e.g. less than 2 grams) which is beneficial for applications, such as an audio system for use in a headset. In this example, the high compliance speaker may have a transducer with a Cms greater than 10 N/mm and a Vas greater than 15 cc. The audio assembly may have a Vas greater than ten times the physical volume of an acoustic cavity of the enclosure, according to some embodiments. For example, if an enclosure has a front acoustic cavity with a volume of 1 cubic centimeter (cc), a Vas of the audio system is 10 cc or greater.

[0027] Using an audio assembly with high Vas, small form factor, and a low weight speaker for use in a headset is advantageous. In order to provide a comfortable user experience, the audio assembly may be integrated or coupled into a portion of a frame of a headset, according to some embodiments. Specifically, the enclosure may be integrated into a leg portion of the frame. In some embodiments, the enclosure is integrated into a temple portion of a leg portion of the frame, the temple portion corresponding to a temple region on a user’s head. The audio assembly has a small form factor and weight, which may result in a more comfortable experience for the user of the headset with the audio assembly integrated into the temple portion of the frame, without sacrificing audio quality and/or audio volume.

[0028] Embodiments of the present disclosure may include or be implemented in conjunction with an artificial reality system. Artificial reality is a form of reality that has been adjusted in some manner before presentation to a user, which may include, e.g., a virtual reality (VR), an augmented reality (AR), a mixed reality (MR), a hybrid reality, or some combination and/or derivatives thereof. In some embodiments, the headset including the audio system is configured for use in an artificial reality system. Artificial reality content may include completely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, haptic feedback, or some combination thereof, and any of which may be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional effect to the viewer). Additionally, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, e.g., create content in an artificial reality and/or are otherwise used in (e.g., perform activities in) an artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a headset connected to a host computer system, a standalone headset, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

[0029] FIG. 1 is a perspective view of a headset 100 implemented as an eyewear device, in accordance with one or more embodiments. In some embodiments, the eyewear device is a near eye display (NED). In general, the headset 100 may be worn on the face of a user such that content (e.g., media content) is presented using a display assembly and/or an audio system. However, the headset 100 may also be used such that media content is presented to a user in a different manner. Examples of media content presented by the headset 100 include one or more images, video, audio, or some combination thereof. The headset 100 includes a frame 105, and may include, among other components, a display assembly including one or more display elements 110, a depth camera assembly (DCA), an audio system, and a position sensor 115. While FIG. 1 illustrates the components of the headset 100 in example locations on the headset 100, the components may be located elsewhere on the headset 100, on a peripheral device paired with the headset 100, or some combination thereof. Similarly, there may be more or fewer components on the headset 100 than what is shown in FIG. 1.

[0030] The frame 105 holds the other components of the headset 100. The frame 105 includes a front part that holds the one or more display elements 110 and end pieces (e.g., temples) to attach to a head of the user. The front part of the frame 105 bridges the top of a nose of the user. The length of the end pieces may be adjustable (e.g., adjustable temple length) to fit different users. The end pieces may also include a portion that curls behind the ear of the user (e.g., temple tip, ear piece). The end piece may also be referred to herein as a “leg portion of the frame.”

[0031] The one or more display elements 110 provide light to a user wearing the headset 100. As illustrated the headset includes a display element 110 for each eye of a user. In some embodiments, a display element 110 generates image light that is provided to an eyebox of the headset 100. The eyebox is a location in space that an eye of user occupies while wearing the headset 100. For example, a display element 110 may be a waveguide display. A waveguide display includes a light source (e.g., a two-dimensional source, one or more line sources, one or more point sources, etc.) and one or more waveguides. Light from the light source is in-coupled into the one or more waveguides which outputs the light in a manner such that there is pupil replication in an eyebox of the headset 100. In-coupling and/or outcoupling of light from the one or more waveguides may be done using one or more diffraction gratings. In some embodiments, the waveguide display includes a scanning element (e.g., waveguide, mirror, etc.) that scans light from the light source as it is in-coupled into the one or more waveguides. Note that in some embodiments, one or both of the display elements 110 are opaque and do not transmit light from a local area around the headset 100. The local area is the area surrounding the headset 100. For example, the local area may be a room that a user wearing the headset 100 is inside, or the user wearing the headset 100 may be outside and the local area is an outside area. In this context, the headset 100 generates VR content. Alternatively, in some embodiments, one or both of the display elements 110 are at least partially transparent, such that light from the local area may be combined with light from the one or more display elements to produce AR and/or MR content.

[0032] In some embodiments, a display element 110 does not generate image light, and instead is a lens that transmits light from the local area to the eyebox. For example, one or both of the display elements 110 may be a lens without correction (non-prescription) or a prescription lens (e.g., single vision, bifocal and trifocal, or progressive) to help correct for defects in a user’s eyesight. In some embodiments, the display element 110 may be polarized and/or tinted to protect the user’s eyes from the sun.

[0033] Note that in some embodiments, the display element 110 may include an additional optics block (not shown). The optics block may include one or more optical elements (e.g., lens, Fresnel lens, etc.) that direct light from the display element 110 to the eyebox. The optics block may, e.g., correct for aberrations in some or all of the image content, magnify some or all of the image, or some combination thereof.

[0034] The DCA determines depth information for a portion of a local area surrounding the headset 100. The DCA includes one or more imaging devices 120 and a DCA controller (not shown in FIG. 1), and may also include an illuminator 125. In some embodiments, the illuminator 125 illuminates a portion of the local area with light. The light may be, e.g., structured light (e.g., dot pattern, bars, etc.) in the infrared (IR), IR flash for time-of-flight, etc. In some embodiments, the one or more imaging devices 120 capture images of the portion of the local area that include the light from the illuminator 125. As illustrated, FIG. 1 shows a single illuminator 125 and two imaging devices 120. In alternate embodiments, there is no illuminator 125 and at least two imaging devices 120.

[0035] The DCA controller computes depth information for the portion of the local area using the captured images and one or more depth determination techniques. The depth determination technique may be, e.g., direct time-of-flight (ToF) depth sensing, indirect ToF depth sensing, structured light, passive stereo analysis, active stereo analysis (uses texture added to the scene by light from the illuminator 125), some other technique to determine depth of a scene, or some combination thereof.

[0036] The audio system provides audio content. The audio system includes a sensor array, a speaker array, and an audio controller 130. However, in other embodiments, the audio system may include different and/or additional components. Similarly, in some cases, functionality described with reference to the components of the audio system can be distributed among the components in a different manner than is described here. For example, some or all of the functions of the controller may be performed by a remote server.

[0037] The speaker array presents sound to user. The speaker array includes one or more audio assemblies. As shown in FIG. 1, the audio system of the headset 100 includes two audio assemblies, with one audio assembly corresponding to a left ear of the user and another audio assembly corresponding to a right ear of the user. Each audio assembly includes a high compliance speaker and at least a portion of an enclosure. For example, as shown in FIG. 1, the audio system of the headset 100 includes an audio assembly coupled to a right side of the frame 105, including the high compliance speaker 135a and a portion of the enclosure 140a, corresponding to the right ear of the user and another audio assembly coupled to a left side of the frame 105, including the high compliance speaker 135b and a portion of the enclosure 140b, corresponding to the left ear of the user. Each of the high compliance speakers 135a and 135b (collectively, the high compliance speakers 135) is contained in a respective one of the enclosures 140a and 140b (collectively, the enclosures 140). In some embodiments, the audio system also includes an array of tissue transducers (e.g., a bone conduction transducer or a cartilage conduction transducer). Although the high compliance speakers 135 are shown enclosed in the frame 105, the high compliance speakers 135 may be exterior to the frame 105. In some embodiments, instead of individual speakers for each ear, the headset 100 includes a speaker array comprising multiple speakers integrated into the frame 105 to improve directionality of presented audio content. The tissue transducer couples to the head of the user and directly vibrates tissue (e.g., bone or cartilage) of the user to generate sound. The number and/or locations of high compliance speakers 135 may be different from what is shown in FIG. 1.

[0038] In FIG. 1, each of the enclosures 140 is shown integrated into a leg portion of the frame 105, but an enclosure may be coupled to the frame in a different configuration, according to some embodiments. Each of the enclosures 140 includes an output port 150 coupled to a front cavity of the respective enclosure and two rear ports 155 coupled to a rear cavity of the enclosure. In other embodiments, an enclosure may include more than one output port and one or more rear ports. In some embodiments, at least one of the rear ports is a resistive port configured to dampen the second portion of sound emitted from the rear cavity of the enclosure 140. The resistive port may smoothen the frequency response of the respective enclosure, in addition to providing dust protection for the respective high compliance speaker. The resistive port may have the form of a mesh film or fabric covering an opening defined in the respective enclosure, according to some embodiments. In other embodiments, at least one of the rear ports is an open port that does not dampen the second portion of the sound. In other embodiments, one or both of the enclosures 140 includes a plurality of rear ports that are a combination of resistive ports and open ports. The high compliance speaker emits sound, in response to an electronic audio signal received from the controller 120, according to some embodiments. The controller 120 may provide and transmit instructions for the audio system to present audio content to the user. The output port 150 is configured to output a first portion of the sound from the front cavity of the enclosure 140, and the two rear ports 155 are configured to output a second portion of the sound from the rear cavity of the enclosure 140.

[0039] In some embodiments, each of the output ports 150 faces an interior of the frame 105. The interior is a direction facing a head of the user wearing the headset 100. In this case, the two rear ports 155 faces an exterior of the frame 105. The exterior is the direction facing away from the head of the user wearing the headset 100.

[0040] The audio assembly, including the high compliance speakers 135, may achieve a high Vas, relative to the actual size or weight of the audio assembly, without excessive electrical power consumption, resulting in high efficiency audio performance. This is advantageous for audio systems used in headsets, where the audio assembly may need to fit in a relatively small space. Thus, the audio assemblies, as shown for example in FIG. 1, may satisfy the design requirements for a variety of headset configurations without sacrificing audio performance and/or audio volume. In comparison to other audio systems of comparable size and weight, the audio system may generate sounds at a higher sound volume with the same or less electrical power input, according to some embodiments. For instance, using the same electrical power input, the audio system may generate sounds at a higher sound volume than a comparably sized audio system that does not include an embodiment of the enclosure 140 and an embodiment of the high compliance speaker 135, according to some embodiments.

[0041] The audio system may also be included in or integrated with devices other than a headset, according to some embodiments. For example, the audio system may be integrated with a mobile device, or any other application requiring a small, light-weight speaker with relatively efficient audio performance.

[0042] The sensor array detects sounds within the local area of the headset 100. The sensor array includes a plurality of acoustic sensors 145. An acoustic sensor 145 captures sounds emitted from one or more sound sources in the local area (e.g., a room). Each acoustic sensor is configured to detect sound and convert the detected sound into an electronic format (analog or digital). The acoustic sensors 145 may be acoustic wave sensors, microphones, sound transducers, or similar sensors that are suitable for detecting sounds.

[0043] In some embodiments, one or more acoustic sensors 145 may be placed in an ear canal of each ear (e.g., acting as binaural microphones). In some embodiments, the acoustic sensors 145 may be placed on an exterior surface of the headset 100, placed on an interior surface of the headset 100, separate from the headset 100 (e.g., part of some other device), or some combination thereof. The number and/or locations of acoustic sensors 145 may be different from what is shown in FIG. 1. For example, the number of acoustic detection locations may be increased to increase the amount of audio information collected and the sensitivity and/or accuracy of the information. The acoustic detection locations may be oriented such that the microphone is able to detect sounds in a wide range of directions surrounding the user wearing the headset 100.

[0044] The audio controller 130 processes information from the sensor array that describes sounds detected by the sensor array. The audio controller 130 may comprise a processor and a computer-readable storage medium. The audio controller 130 may be configured to generate direction of arrival (DOA) estimates, generate acoustic transfer functions (e.g., array transfer functions and/or head-related transfer functions), track the location of sound sources, form beams in the direction of sound sources, classify sound sources, generate sound filters for the high compliance speakers 135,* or some combination thereof*

[0045] The position sensor 115 generates one or more measurement signals in response to motion of the headset 100. The position sensor 115 may be located on a portion of the frame 105 of the headset 100. The position sensor 115 may include an inertial measurement unit (IMU). Examples of position sensor 115 include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, a type of sensor used for error correction of the IMU, or some combination thereof. The position sensor 115 may be located external to the IMU, internal to the IMU, or some combination thereof.

[0046] In some embodiments, the headset 100 may provide for simultaneous localization and mapping (SLAM) for a position of the headset 100 and updating of a model of the local area. For example, the headset 100 may include a passive camera assembly (PCA) that generates color image data. The PCA may include one or more RGB cameras that capture images of some or all of the local area. In some embodiments, some or all of the imaging devices 120 of the DCA may also function as the PCA. The images captured by the PCA and the depth information determined by the DCA may be used to determine parameters of the local area, generate a model of the local area, update a model of the local area, or some combination thereof. Furthermore, the position sensor 115 tracks the position (e.g., location and pose) of the headset 100 within the room. Additional details regarding the components of the headset 100 are discussed below in connection with FIG. 8.

[0047] Some embodiments of the headset 100 and audio system have different components than those described here. For example, the enclosure 140 may include a different configuration of ports, for example, with a different number, shape, type, and/or size of ports. The example of the audio system shown in FIG. 1 includes two enclosures 140, each enclosure containing a high compliance speaker, corresponding to a left and right ear for presenting stereo sound. In some embodiments the audio system comprises speaker array including a plurality of enclosures 140 (e.g. more than two) coupled to the frame 105 of the headset 100. In this case, each enclosure contains one or more high compliance speakers. Similarly, in some cases, functions can be distributed among the components in a different manner than is described here. Additionally, the dimensions or shapes of the components may be different.

High Compliance Speaker

[0048] FIG. 2A illustrates a front view of a high compliance speaker 210 including a membrane with a Cms that is high, in accordance with one or more embodiments. The high compliance speaker 210 is an embodiment of the high compliance speaker 135. The high compliance speaker 210 has a rectangular shape, corresponding to a rectangular prism, according to some embodiments. In the example shown in FIG. 2A, a surface of the high Cms membrane 220 also has an approximately rectangular shape. In further embodiments, the high Cms membrane 220 has an approximate 2D shape corresponding to a rectangle with rounded corners, as shown in FIG. 2A. In other embodiments, the high compliance speaker 210 and the high Cms membrane 220 may have other shapes than what is shown in FIGS. 2A and 2B.

[0049] The rectangular shape of the high compliance speaker 210 may satisfy various design requirements. For example, the high compliance speaker 210 may be used in a temple region of a leg of a headset (e.g., eyeglass form factor), as shown in FIG. 1. As such, a rectangular shape may be desired for the high compliance speaker 210, to conform to the shape of the temple region.

[0050] In other embodiments, the high Cms membrane 220 has an elliptical shape. In further embodiments, the body of the high compliance speaker 210 also has a shape corresponding to an ellipse, such as a shape approximating an elliptical prism. Using an elliptical shape of the high Cms membrane 220 may make it easier to suppress undesired resonant modes of the high compliance speaker 210, while still maintaining a shape that is effective for designs that require non-circular speakers, according to some embodiments. In other embodiments, the high compliance speaker 210 and the high Cms membrane 220 has other shapes, to match design requirements for various applications of the audio system. In other embodiments, the high compliance speaker 210 may have a different overall shape from the high Cms membrane 220. For example, the high compliance speaker may have a rectangular shape 210, while the high Cms membrane 220 has an elliptical shape. The high compliance speaker 210 and the high Cms membrane 220 each may have shapes other than a rectangular shape or an elliptical shape, according to some embodiments.

[0051] Additionally, the high compliance speaker 210 may has a small size suitable for various design requirements, such as for integration with a headset. In some embodiments, the high compliance speaker 210 is a speaker with a total area of the high Cms membrane 220 being less than 200 square millimeters. The high Cms membrane 220 may have a different size, according to some embodiments.

[0052] FIG. 2B shows a cross-section along a line I to I’ of the high compliance speaker 210 shown in FIG. 2A, in accordance with one or more embodiments. The high compliance speaker 210 includes components not shown in FIG. 2B, such as electrical circuit elements, according to some embodiments. In response to receiving an electrical audio signal, the high compliance speaker 210 actuates the high Cms membrane 220, generating an acoustic wave (i.e. the emitted sound) corresponding to the received electrical audio signal. The actuated Cms membrane 220 may be displaced, as depicted in FIG. 2B, according to some embodiments. A high Cms membrane (e.g., a membrane having a Cms greater than 10 mm/N) has a greater displacement of the membrane than a low Cms membrane, in response to an electrical audio signal. In some embodiments, the high Cms membrane 220 has a lower stiffness than a membrane with a low Cms, such that the amount of energy necessary to displace the high Cms membrane 220 is lower than that of a low Cms membrane. Also, the high CMS membrane 220 may generally have larger displacement amplitudes of the high Cms membrane 220 than a speaker of the same size with a low Cms membrane. The audio system including the high compliance speaker 210, coupled with the enclosure 140, according to some embodiments, may have a high Vas, relative to the size of the enclosure 140.

[0053] The high compliance speaker 210, due in part to the low stiffness of the high Cms membrane 220, may have a low resonant frequency, relative to speakers of the same size that have a low Cms membrane, according to some embodiments. Lower resonant frequencies enable the audio system to have a larger bandwidth and improved performance at low frequencies, than audio systems with higher resonant frequencies. In some embodiments, the high compliance speaker 210 has a resonant frequency of the fundamental node that is less than 200 Hz. In other embodiments, the high compliance speaker 210 has a resonant frequency of the fundamental node that is in the range of 100-200 Hz.

[0054] Additionally, the high compliance speaker 210 has improved power efficiency over other speakers when enclosed in an embodiment of the enclosure 140. Compared to comparably sized speakers that either use a low Cms membrane and/or have an enclosure with a rear cavity that is sealed (e.g. omitting a rear port in the enclosure), the proportion of electrical energy that is converted into sound energy is higher in the high compliance speaker 210. This is due in part to the reduction in unwanted vibrations in the audio system and in devices and/or structures coupled to the audio system. For example, the acceleration of unwanted vibrations caused by the audio system may be 10 times lower than acceleration caused by speaker systems of the same size, using a low compliance speaker or using an enclosure without the features of the enclosure 140. The unwanted vibrations may occur in the speaker itself, the enclosure, structures coupled to the audio system (e.g. a frame of a headset), and some combination thereof.

[0055] To produce sounds, the high-compliance speaker 210 can be actuated by relatively small electromagnetic force which further minimizes the structural vibration of structures coupled to the audio system (e.g., a frame of artificial reality glasses and headsets). According to some embodiments, a force ratio of the high compliance speaker 210 may be less than 0.1. The force ratio is equal to the amount of applied force required to displace a membrane of a speaker by 0.3 mm divided by a reference force value, where the reference force is 0.33 N. In some embodiments, an acceleration ratio of the high compliance speaker may be less than 0.1. The acceleration ratio is equal to the amount of acceleration a membrane of a speaker undergoes in order to be displaced by 0.3 mm divided by a reference acceleration, where the reference acceleration is 0.000183 m/s.sup.2.

[0056] Additionally, the power consumption for the high compliance speaker 210 is a fraction of typical rectangular speakers, such as those found in smartphones. For applications such as speakers for headsets and/or glasses, vibration reduction is strongly desired to eliminate the unwanted tactility sensed by users.

[0057] The high compliance speaker 210 has a reduced weight which reduces the overall weight of headsets that include the audio system. In some embodiments, the weight of the high compliance speaker is 2 grams or less. In comparison to typical rectangular speakers found in smartphones, the weight of two of the high compliance speakers 210 (corresponding to a left and right speaker for audio sound) may be about 17% lighter. In some embodiments, the high compliance speaker 210 has a height dimension in the range of 10-11 mm, a length dimension in the range of 18-20 mm, and a depth dimension in a range of 2-4 mm. In some embodiments, the weight of two of the high compliance speakers 210 totals less than 4 grams (each weighing less than 2 grams).

Speaker Enclosure

[0058] FIG. 3A illustrates an exploded view 300 of an enclosure 310 containing a rectangular high compliance speaker 320, in accordance with one or more embodiments. The rectangular high compliance speaker 320 is an embodiment of the high compliance speaker 210. The enclosure 140 is an embodiment of the enclosure 310. The enclosure 310 is integrated into a leg portion of a frame 330 of a headset. The leg portion of the frame 330 may be part of an embodiment of the headset 100.

[0059] The enclosure 310 forms a front cavity and a rear cavity that are on opposite sides of the rectangular high compliance speaker 320. A front portion of the enclosure 340 includes an output port 350 configured to output a first portion of sound emitted from the rectangular high compliance speaker 320 from the front cavity. In some embodiments, the front portion of the enclosure 340 includes a plurality of output ports. A rear portion of the enclosure 360 includes one or more rear ports configured to output a second portion of emitted sound from the rear cavity. As illustrated, the rear portion of the enclosure 360 includes two rear ports 370a and 370b (collectively, the rear ports 370).

[0060] A rear portion of the enclosure 360, including the two rear ports 370, is a part of the frame of the headset, such that the leg portion of the frame 330 and the rear portion of the enclosure 360 form one continuous body. In other embodiments, the front portion of the enclosure 340 is a part of the frame of the headset. In the example shown in FIG. 3A, the front portion of the enclosure 340, including the output port 350, is a separate part that can be separated from and reattached to the rear portion of the enclosure 360. In alternate embodiments, the rear portion of the enclosure 360 and the front portion of the enclosure 340 are distinct components that can be separated from each other and reattached. Additionally, in FIGS. 3A-3C, the enclosure 310 is shown with the one output port 350 and the two rear ports 370, but the number and configuration of output ports and rear ports may be different, according to some embodiments.

[0061] The rectangular high compliance speaker 320 may be contained by the enclosure 310 integrated into the leg portion of the frame 320, in a way that is optimal for the space and size constraints of the frame. The shape of a high compliance speaker in the audio system may be configured to optimize the audio performance of the audio system, for the size and space constraints of the frame of the headset.

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