Audio device with low frequency extension filter

Abstract

A filter is provided that can amplify and extend the bass frequency response of a speaker in an audio device. The filter can be space-efficient. The filter can be part of a device that does not necessarily have a large rear cavity and does not necessarily have ports and / or passive radiation. The low-frequency extension filter can, for example, be used with a smaller rear cavity while essentially simulating the acoustic effects of a much larger rear cavity. The low-frequency extension filter can include multiple acoustic paths, such as tubes, which can be wound along a tortuous path and can resemble a labyrinthine design. The tubes can be selected to resonate with a specific predetermined low-frequency channel. For example, these tubes can be approximately a quarter wavelength of the center of the corresponding frequency channel, or even slightly shorter.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 115,532, filed November 18, 2020, the entire contents of which are incorporated herein by reference for all purposes. Background Technology

[0003] Portable audio devices, such as speakerphones and portable speakers (e.g., smart speakers and / or Bluetooth speakers), typically have a small form factor. The small size of these devices can present several challenges.

[0004] For example, generating sufficient bass response in a speaker within a small audio device is a design challenge due to the lack of space to provide a large rear cavity within the device and behind the speaker. While this is sometimes overcome using ports (appropriate openings in the rear cavity) or passive radiators, these ports are not always ideal because they introduce distortion that is not suitable for all use cases. For instance, acoustic echo cancellation (AEC) requires special consideration of ports or passive radiators because they can introduce nonlinearity; their effects may be relatively uncorrelated with the sound source (speaker) in amplitude and phase, thus reducing the effectiveness of AEC in eliminating echoes. On the other hand, AEC is ideal for many use cases, such as speakerphones. Summary of the Invention

[0005] The following overview presents a simplified overview of some features. This overview is not exhaustive and is not intended to identify key or important elements.

[0006] For example, according to some aspects, an apparatus including a low-frequency extension filter can be provided. This filter can increase (and thus effectively extend) the bass response of a speaker in the apparatus without having to occupy a large space within the apparatus. Typically, to provide a large bass response, large rear cavities, ports, and / or passive radiators are used. However, as previously mentioned, ports and passive radiators are not always compatible with the intended use of the apparatus, and large rear cavities are impractical in small form factor devices. Therefore, a low-frequency extension filter is provided that can increase the bass frequency response without requiring a large rear cavity and without requiring ports and / or passive radiators. In practice, the low-frequency extension filter can be used with a smaller rear cavity while essentially simulating the acoustic effects of a much larger (and less feasible) rear cavity. The low-frequency extension filter can include multiple tubes that can be wound along a tortuous path (and can be similar to a labyrinthine design), wherein these tubes are selected to resonate with a specific predetermined low-frequency channel. For example, these tubes can resonate at a quarter wavelength from the center of the corresponding frequency channel (e.g., having a length approximately equal to a quarter wavelength, or even slightly less than a quarter wavelength for the reasons discussed here).

[0007] According to other aspects, an audio device may be provided, comprising a housing forming an internal space, a speaker connected to the housing and configured to emit sound, and a low-frequency filter disposed within the internal space. The low-frequency filter may be configured to filter multiple frequency bands within the stiffness control response domain of the audio device. The low-frequency filter may include multiple acoustic paths. Each of the multiple acoustic paths may include a first end open to the internal space and a closed second end. Each of the multiple acoustic paths may have different lengths corresponding to different frequency bands within the multiple frequency bands of the audio device's stiffness control response domain.

[0008] According to other aspects, an audio device may be provided that includes a low-frequency filter configured to filter within an octave band frequency range below a specific frequency (e.g., below about 500 Hz). The low-frequency filter may include a plurality of acoustic paths. Each of the plurality of acoustic paths may include a first end that is open, such that at least a portion of the acoustic energy received by the low-frequency filter is received at the first end. Each of the plurality of acoustic paths may include a closed second end. Each of the plurality of acoustic paths may include different tortuous acoustic paths and have different lengths corresponding to different frequency bands within a plurality of frequency bands in the octave band range below the specific frequency.

[0009] According to other aspects, an audio device may be provided, comprising a housing forming an internal space, a speaker connected to the housing and configured to emit sound, and a low-frequency filter disposed within the internal space. The low-frequency filter may be configured to filter multiple frequency bands below a transition point frequency, at which the quality control response domain of the audio device begins. The low-frequency filter may include multiple acoustic paths. Each of the multiple acoustic paths may include a first end open to the internal space and a closed second end. Each of the multiple acoustic paths may have different lengths corresponding to different frequency bands among the multiple frequency bands below the transition point frequency, at which the quality control response domain of the audio device begins.

[0010] These and other features, as well as their potential advantages, are described in more detail below. Attached Figure Description

[0011] Some features are shown in the accompanying drawings by way of example rather than limitation. Similar numbers in the drawings denote similar elements.

[0012] Figure 1 This is a side view of an example device including a speaker, microphone, and low-frequency spread filter.

[0013] Figure 2 yes Figure 1 A top view of the device.

[0014] Figures 3 to 7 This is a top view of an example low-frequency spread filter.

[0015] Figure 8 This is a side view of another example device including a speaker, microphone, and low-frequency spread filter.

[0016] Figure 9 It is a graph showing an example of the analog internal impedance versus frequency relationship of a filtered audio device (which includes a low-frequency spread filter) and a comparable unfiltered device (which does not include a low-frequency spread filter).

[0017] Figure 10 It is a graph showing an example of the sound pressure level versus frequency relationship of a filtered audio device (which includes a low-frequency spread filter) and a comparable unfiltered device (which does not include a low-frequency spread filter).

[0018] Figure 11 This is a graph showing the example loudspeaker displacement response in both the stiffness control domain and the mass control domain.

[0019] Figure 12 This is a graph showing the displacement response of an example loudspeaker superimposed with an example filtered octave.

[0020] Figure 13This is a block diagram illustrating an example configuration of a computing device that can be used to implement at least a portion of any of the devices described herein, such as controller 106. Detailed Implementation

[0021] The accompanying drawings, which form part of this document, illustrate examples of this disclosure. It should be understood that the examples shown in the drawings and / or discussed herein are non-exclusive, and other examples of how this disclosure may be practiced exist.

[0022] Figure 1 This is a side view of the example device 100, and Figure 2 This is a top view of device 100. Device 100 shown includes a speaker driver 103 and a microphone 107, although device 100 may include multiple drivers and / or multiple microphones, and alternatively may not include microphones at all. Device 100 may also include a housing 101 (which may also be the body of device 100) that holds the driver 103 and microphone 107 in a fixed position, and may partially or completely enclose a controller 106 electrically connected to the driver 103 and microphone 107. Housing 101 may also partially or completely enclose the structure of what will be referred to herein as a low-frequency spread filter 104 and will be described in further detail below.

[0023] Controller 106 can control the operation of device 100, including the operation of driver 103 and / or microphone 107. For example, controller 106 can receive electrical signals generated by microphone 107 in response to (and representing) sound detected by microphone 107, and process those received electrical signals in any desired manner, such as by storing data representing the detected sound in memory, or by transmitting communication representing the detected sound to a location outside device 100. Controller 106 may also include circuitry for generating signals representing sound emitted by driver 103. For example, controller 106 can receive electrical signals from a location outside device 100 and cause driver 103 to emit sound based on those signals. Such communication outside device 100 can be performed via one or more wired connections (such as a USB connection) and / or via wireless connections such as Wi-Fi or cellular communication. In the latter case, controller 106 may include a wireless communication module, such as a Wi-Fi communication module, a cellular network communication module, and / or a Bluetooth communication module. Controller 106 may be implemented as, for example, a computing device that executes stored instructions, and / or hardwired circuitry that may or may not execute stored instructions.

[0024] Although the driver 103 can be directed to primarily direct sound from the device 101 outwards (e.g., in...), Figure 1While the driver 103 radiates sound generally in the upward direction, it can also radiate sound into a rear-enclosed cavity 102 defined by the housing 101, at least in the rearward direction. Drivers without a rear cavity (e.g., free-air drivers) typically radiate sound inefficiently because the driver radiates uniformly in both the forward and rearward directions, resulting in a sum of zero in the far field. The housing behind the driver typically sets the radiation conditions, and the size of the rear cavity surrounded by the housing affects the air stiffness behind the driver. To optimize the driver's forward radiation, the enclosed cavity 102 can then be adapted to collect and contain rearward sound radiated from the inward-facing (rearward) portion of the driver 103 into the housing 101. By capturing the rearward-radiated sound, the enclosed cavity 102 ideally has a geometry that appropriately sets the rearward air stiffness and damping experienced by the system at a critical point, such that sound radiates primarily only (or at least mostly) from the exposed (front) surface of the driver. However, as mentioned above, it can be difficult to fit a cavity with the desired geometry (e.g., size and / or shape) into a portable audio device.

[0025] One way to implement a rear cavity is by including resonant tubes that force sound from the rear of the driver to travel along a specific acoustic path within the housing. In some cases, the rear cavity can be completely sealed (without any acoustically apparent opening). In other cases, the rear cavity may have one or more openings, referred to as ports. In still other cases, the rear cavity may have a passive radiator that bends in response to acoustic energy, thereby dynamically changing the acoustic response of the rear cavity over time in a desired manner.

[0026] If the geometry is well-designed (e.g., flared inlet and / or damped cavity), a closed-tube quarter-wave resonator (a tube with an open near-end / source end and a closed far-end) can produce a minimized (e.g., zero) impedance condition at a specific frequency, as well as reduced impedance in a small band around that frequency. Using a series of these quarter-wave resonators in overlapping or nearly overlapping frequency bands can produce sealed conditions approaching the free-air behavior of the driver in a specific frequency region. This has the potential benefit of extending effective low-frequency radiation due to the efficient removal of air stiffness from the closed (e.g., sealed) cavity at specific frequencies specified by the individual resonators. The resonators can be tuned to a range of frequencies below the characteristic frequencies of the first-stage driver / housing system to potentially improve the low-frequency radiation efficiency of the system. This can also effectively reduce the required cavity volume for a given driver's frequency response.

[0027] To implement multiple such resonators, the low-frequency spread filter 104 may include multiple tubes through which sound from the driver 103 can pass. At least a portion of each tube (also referred to herein as a channel) may follow a tortuous path to reduce the volume required to hold the tube. One such tube in Figure 1 The example is represented by element 109. Sound from driver 103 can pass through enclosed cavity 102, downward into the central cavity 105 of low-frequency extension filter 104, and into one or more of its tubes. As will be described in more detail, these tubes can be configured to amplify (e.g., generate additional resonance) certain low-frequency sounds radiated from driver 103, thereby effectively extending the bass response of driver 103. Low-frequency extension filter 104 allows device 100 to have a smaller enclosed cavity 102. This is because when sound enters the tubes and reflects within them, the sound therein may resonate in the same way as in a much larger conventional enclosed cavity.

[0028] Figure 2 A low-frequency spread filter 104 with a main body is shown, which, when viewed from above, may be generally circular (e.g., disc-shaped). However, this is merely an example; the low-frequency spread filter 104 may alternatively have a main body of any other shape, such as rectangular, elliptical, cubic, or any other geometric or non-geometric two- or three-dimensional shape. Furthermore, when viewed from the side, the low-frequency spread filter 104 may or may not have a substantially flat profile. For example, Figure 1 A low-frequency spread filter 104 with an outer circumferential portion 108 is shown, which is curved upward at an angle to follow the contour of the outer bottom of a housing 101. This bending capability allows the low-frequency spread filter 104 to be more easily fitted into a housing 101 of any shape and can be used to reduce limitations on the shape and / or size of the housing 101. Typically, the shape of the low-frequency spread filter 105 can be designed to fit into the housing 101 in a manner that allows the housing 101 to have a desired size and shape, for example, allowing the housing 101 to be part of a portable (e.g., handheld) audio device. The tubes within the low-frequency spread filter 105 can be wired as needed to fit within the body shape of the low-frequency spread filter 105. Furthermore, the number and length of the tubes, as well as their cross-sectional area, can be designed based on the number of desired corresponding frequency bands to be filtered, their center frequencies, and other design factors. Therefore, the low-frequency spread filter 105 can have an overall shape that is generally independent of the geometry of the tube in which it is wired, and can be designed to be fitted into the housing 101, provided that the body of the low-frequency spread filter 105 is large enough to accommodate the tube.

[0029] Figure 3A more detailed top view of the low-frequency spread filter 104 is shown. It is clear from the figure that the low-frequency spread filter 104 can be arranged as a plurality of circumferential walls 302 centered on a central cavity 105. Furthermore, there can be a plurality of radially extending (or otherwise outwardly extending) walls 301 extending between the central cavity 105 and the outer circumference (or other outer boundary) of the low-frequency spread filter 104. Together, the walls can form multiple segments, such as segments labeled A, B, C, D, E, F, G, and H, each typically shaped as a pie slice (an angular segment of a disk), but not necessarily limited to the extent of a pie "slice". In the example shown, segment A is typically located between radial walls 301HA and 301AB, segment B is typically located between radial walls 301AB and 301BC, segment C is typically located between radial walls 301BC and 301CD, segment D is typically located between radial walls 301CD and 301DE, segment E is typically located between radial walls 301DE and 301EF, segment F is typically located between radial walls 301EF and 301FG, segment G is typically located between radial walls 301FG and 301GH, and segment H is typically located between radial walls 301GH and 301HA.

[0030] As will be explained further below, each of these segments can correspond to a specific tube, and each tube can correspond to a specific resonant frequency band. This is because each segment can utilize a different tube length tuned to one of the resonant frequency bands. In the example shown, there are eight corresponding resonant frequency bands (each corresponding to a different one of the eight tubes). However, the low-frequency spread filter 104 can be configured to have any number of segments, and therefore any number of corresponding resonant frequency bands. To tune a tube to a specific frequency band, the tube (which may be open at only one end) can have a length approximately one-quarter of the wavelength of the center frequency of the band. However, as will be described further below, by designing the tube to utilize the viscous loss characteristics of the tube wall, the length of each tube can be less than one-quarter of the wavelength. This shorter tube length allows the low-frequency spread filter 104 to be smaller than in other cases, and / or allows the tubes therein to be tuned to lower frequencies than in other cases using the same tube length, without the need for designing appropriate tube wall absorption.

[0031] from Figure 3It can also be seen that the central cavity 105 laterally opens to multiple openings, such as opening 302. In the example shown, there are four such smaller lateral openings; however, any number of lateral openings may be present as needed. Each lateral opening may open to one, two, or more tubes 109. In the example shown, each lateral opening opens to two different tubes, such that each pair of tubes shares the lateral opening from the central cavity 105. Sound from the driver 103 may enter the central cavity 105 and then into the lateral openings, as indicated by the four arrows in the central cavity 105. Alternatively, in this eight-band example, there may be eight separate, non-co-located lateral openings, one for each segment.

[0032] For each segment, the corresponding tube can be wound back and forth (e.g., along a tortuous path) to generally assemble (though not necessarily completely) within one segment of the pie-shaped slice. For example, Figure 4 One tube in tube 401 corresponding to segment A is shown, highlighted to make it easier to distinguish from the other tubes and segments of the low-frequency spread filter 104. Note that tube 401 is not necessarily entirely contained within the segment represented as segment A, and extends outward at an angle from the pie-shaped region as needed to accommodate the desired length of tube 401 (beyond the radial wall 301AB).

[0033] Figure 5 Another example of tube 501 corresponding to segment B is shown, with emphasis placed on the tube again to make it easier to distinguish it from the other tubes and segments of the low-frequency spread filter 104. In this example, tube 501 is contained within a disc-shaped segment defined between radial walls 301AB and 301BC.

[0034] Figure 6 Another example of tube 601 corresponding to segment C is shown, with emphasis placed on the tube again to make it easier to distinguish it from the other tubes and segments of the low-frequency spread filter 104. In this example, tube 601 is also contained within the disc-shaped segment defined between radial walls 301BC and 301CD.

[0035] Figure 7 Another example of tube 701 corresponding to segment D is shown, with emphasis placed on the tube again to make it easier to distinguish it from the other tubes and segments of the low-frequency spread filter 104. In this example, tube 701 is generally contained within the pie-shaped segment defined between radial walls 301CD and 301DE, and also extends partially beyond radial wall 301CD.

[0036] exist Figures 4 to 7Each of the tubes 401, 501, 601, and 701 highlighted in the text has a different length corresponding to a different frequency band. The same applies to the remaining four tubes corresponding to cross section EH. To determine the tube length, an initial calculation can involve one-quarter of the wavelength of the frequency occupied in free air. The equation is: length = c / (4f), where c is, for example, approximately 343 m / s at 20 degrees Celsius, and f is the center frequency of the frequency band (in Hertz). However, this calculation may not consider certain factors that might affect the ideal tube length. For example, the tubes may each have a certain cross-sectional area that is small enough relative to their length that the viscous loss on the inner wall surface of the tube may be significant. If the cross-sectional area is small enough relative to the length of the tube, the length of the tube required for optimal resonance can be slightly less than one-quarter of the wavelength.

[0037] In one example embodiment, the tube of the low-frequency spread filter 104 has a rectangular cross-sectional shape consisting of four vertical 5mm walls (thus resulting in a cross-sectional area of ​​25 square millimeters per tube), and the tube length is calculated for the following frequencies, taking into account viscous losses:

[0038] Table 1 - Example frequencies and corresponding tube lengths

[0039]

[0040]

[0041] The logic for assembling eight channels (approximately 3.56 m in length in this example) within the region of the low-frequency spread filter 104 involves an iterative design process. For example, generating... Figure 3 The iterative design process for the specific low-frequency extension filter 104 shown (which has a circular layout and uses a 5mm × 5mm tube) may include dividing a representative circle with a diameter of approximately 105mm into eight segments, each segment occupying the same angular width (in this example, each segment has an angular width of 22.5 degrees). This circle can be further subdivided into sixteen 5mm-wide circumferential channels (each channel extending around the circle at a different distance from its center). These channels can then be selectively opened to form channels along a meandering path, for example, mimicking the serpentine manner of, for example, a traditional Greek labyrinth. Finally, a top surface can be placed over the channels to form the tube. The resulting tube can be empty (e.g., naturally filled with ambient air without any other material) to allow acoustic energy not to be absorbed by the tube in an undesirable manner. At this point, the purpose of the low-frequency extension filter 104 may be to improve efficiency (and reduce internal acoustic impedance) at frequencies of a specific design, particularly in the low-frequency region, rather than to absorb energy at those frequencies.

[0042] The geometry of the low-frequency extended filter 104 can be developed using design and manufacturing software such as NX, and then imported into physical modeling software such as COMSOL to determine the air resonant frequency using acoustic modules and eigenfrequency solvers. The physical implementation of the design can be performed using a 3D printer, for example, with conventional 3D printing materials such as plastic or other materials. After tuning the lengths of the individual channels, the final geometry can be formed. Using this process, the inventors have developed a solution for the above-mentioned... Figure 3 The eigenfrequencies calculated for the specific example geometry shown are as follows:

[0043] 130.14694986593182+12.109782043560736i Hz

[0044] 144.06801486379595+12.254009097819758i Hz

[0045] 171.3592263830207+13.023017255005177i Hz

[0046] 188.29581560770052+13.411817789644426i Hz

[0047] 210.76477769185323+13.117674703946287i Hz

[0048] 229.00717584342897+12.795806806436937i Hz

[0049] 229.3793865576183+13.272769199959392i Hz

[0050] 263.23715375734133+13.193887679345387i Hz

[0051] The tube length used for a given implementation will ultimately depend on the tube's cross-sectional area, the material used to manufacture the tube, and the desired frequency band. Interestingly, the tube length can be shortened with a smaller tube cross-sectional area (potentially allowing the low-frequency spread filter 104 to be even smaller and / or making it easier to lay out the tube path), although this relationship only applies to the point where the cross-sectional area becomes too small to effectively receive acoustic energy due to the increased acoustic impedance of the tube. Furthermore, the tube layout may appear different between implementations when the low-frequency spread filter 104 has different shapes or sizes.

[0052] The inventors also simulated a final housing including a low-frequency spread filter 104 and a comparable unfiltered housing, and then compared it with internal impedance measurements of the two housings. These impedance measurements show the resistance or air stiffness of the corresponding housing at a specific frequency. Figure 9 The graph shows a comparison of two impedances, illustrating the impedance versus frequency relationship between a filtered cavity (i.e., including the low-frequency spread filter 104) and an unfiltered cavity (i.e., excluding the low-frequency spread filter 104) using the same driver. Figure 9 As shown, the impedance of the filtered cavity is significantly lower than that of the unfiltered cavity, particularly for the aforementioned eight frequency bands. This should correspond to an increased sensitivity within this frequency range. Therefore, the low-frequency extension filter 104 can act as a low-pass rainbow filter, where it reduces the impedance of each of the defined low-frequency bands by decreasing the air stiffness in these bands, resulting in an increase in the acoustic output of the corresponding driver in these bands. The trade-off is that the filtered impedance in this example increases at higher frequencies (e.g., starting from approximately 330 Hz) compared to the unfiltered impedance, and then uniforms again at even higher frequencies (e.g., above 450 Hz). This behavior can also be seen in the frequency response of two separate housings with the same driver, which... Figure 10 The graph shown for this specific implementation illustrates the relationship between sound pressure level (dB SPL) and frequency (Hz) for both the filtered and unfiltered versions of the housing.

[0053] The example above uses eight low-frequency bands ranging from approximately 140 Hz to approximately 280 Hz. However, the low-frequency extension filter 104 can alternatively be tuned to other numbers of low-frequency bands within other low-frequency band ranges. For example, the low-frequency extension filter 104 can be tuned to a band ranging from 100 Hz to 500 Hz, or to any sub-range within that range. The wider the total frequency range over which a given number of bands extend, the less overlap (if any) the bands can have with each other, resulting in a more uneven frequency response in the low-frequency range. However, this can be offset by increasing the number of bands (and similarly increasing the number of corresponding tubes / segments in the low-frequency extension filter 104, i.e., the number of bands to which the low-frequency extension filter 104 is tuned).

[0054] The low-frequency extended filter 104 is tuned to a frequency band that is within a frequency range where the upper end of the frequency range is below (and in some cases, just below and / or reaches) a transition point where the system response is dominated by a stiffness-controlled response at lower frequencies and by a mass-controlled response at relatively higher frequencies. These two types of response domains refer to how the air-moving portion of the driver (e.g., the speaker cone or other diaphragm) moves according to the driving frequency. When the driving frequency is below the resonant frequency, the air-moving portion typically displaces itself by approximately the same amount within the driving frequency range. As the frequency increases slightly, the displacement can gradually increase to a certain point. This domain of driver operation is called the stiffness-controlled response domain because at lower frequencies, the air-moving portion of the driver moves slowly enough that its stiffness (e.g., based on how the air-moving portion is connected to the fixed portion of the driver and / or based on any bending that the air-moving portion must undergo during displacement) rather than inertia governs how far the air-moving portion displaces. In the stiffness control response domain, the displacement response of the actuator (and the corresponding acoustic energy emitted from the actuator, for example, as indicated by its frequency response in this domain) generally depends on the size of the actuator housing and the mechanical stiffness of the air-moving parts (e.g., the cone and the suspension system for the cone).

[0055] On the other hand, when the driving frequency is above the resonant frequency, the displacement of the air-moving part typically decreases to zero as the frequency increases. This region of actuator operation is called the mass control response region because at higher frequencies, the inertia of the air-moving part becomes significant and limits how far it can displace within a relatively short time period (e.g., the cycle of the frequency). In the mass control response region, the displacement response of the actuator (and the corresponding acoustic energy emitted from the actuator, e.g., as indicated by the frequency response in this region) is generally independent of the dimensions of the actuator housing.

[0056] There exists a rather sharp transition point between the two domains, where displacement begins to increase in the stiffness-controlled domain as the frequency approaches the transition point. Then, after passing the transition point and as the frequency continues to increase, the displacement begins to decrease as the effect of inertia becomes increasingly significant. The transition point can ideally be modeled using the following equation:

[0057]

[0058] Where ω0 is the undamped natural (resonant) frequency response of the system, s is the stiffness of the air-moving part, and m is the mass of the air-moving part. Figure 11 The figure shows an example graph illustrating this behavior, where the transition point between the two domains is represented by a vertical dashed line at the normalized frequency ω / ω0, where ω is the driving frequency.

[0059] As previously described, the low-frequency spread filter 104 can be tuned to a frequency range in which the upper end of the frequency range is below (and in some cases, just below and / or reaches) the transition point between the stiffness control response domain and the mass control response domain. For example, the frequency range in which multiple bands lie can be within an octave frequency range ending at or just below the transition point. Selecting such a frequency range below the transition point can reduce or even minimize harmonic-based distortion at the next higher octave, which will be in the mass control response domain. Because the low-frequency spread filter 104 will be tuned in this manner in this case, the low-frequency spread filter 104 tuned in this case can be expected to reduce or even minimize the air stiffness experienced by the system without significantly affecting the system's mass control response (which dominates the response in the next higher octave). Figure 12 An example of such tuned octaves is shown, labeled "Filtered Octaves". Although not explicitly shown in the figure, multiple tuned bands (those shown in Table 1 above) will lie within the filtered octaves or other tuned frequency ranges. For the example in Table 1, the filtered octaves are octaves from 140 Hz to 280 Hz.

[0060] Referring to the example pipe length in Table 1 above, where the cross-sectional area is, for example, 25 mm (e.g., 5 mm × 5 mm²), the ratio of pipe length to cross-sectional area will be approximately 12.3 mm. -1 (307.142857mm / 25mm 2 (approximately 24.6 mm) -1 (614.285714mm / 25mm 2 Within the range of ), however, other ratios can be used, such as within 10mm. -1 Up to 30mm -1 Any ratio within the range, or a ratio below or above that range. In the case of octave filtering, the ratio of the low-frequency extended filter 104 is expected to be in the range from R to approximately 2*R, where R is a smaller ratio (e.g., 12.3 mm). -1 And 2*R is twice that ratio (e.g., 24.6mm). -1 Furthermore, as previously mentioned, the inlet of each tube (e.g., the opening at the circumference of the central cavity 105) can be opened to a larger cross-sectional area to increase the acoustic energy transfer into and out of these tubes and reduce the sudden acoustic impedance transition at the tube inlet.

[0061] Figure 8Another example of the device 100 is shown, except that two low-frequency spread filters 104 (104a and 104b) are stacked, one on top of the other. The two low-frequency spread filters 104 can be tuned differently, thus allowing for more tuning frequency channels. For example, low-frequency spread filter 104a can be tuned to a first set of frequency channels, while low-frequency spread filter 104b can be tuned to a different second set of frequency channels.

[0062] Figure 13 An example block diagram of controller 106 is shown. Controller 106 may be implemented as, for example, a computing device that executes stored instructions, and / or a hard-wired circuit that may or may not execute the stored instructions. In the example shown, controller 106 may include or be connected to any of the following: one or more processors 2201, memory 2202 (which may include one or more computer-readable media such as memory), external interface 2203 (which may be or be connected to a communication module such as previously described), user interface 2204, microphone driver circuitry 2206 configured to receive audio information signals from one or more microphones (such as microphones 107, 107a and / or 107b) of device 101, one or more digital signal processors 2207 and / or speaker driver circuitry 2208, the one or more digital signal processors being configured to implement any digital signal processing of device 100, such as AEC and / or LF boost, and the speaker driver circuitry being configured to provide audio signals to one or more drivers of device 101 (e.g., speaker 103) and cause one or more drivers to produce sound.

[0063] One or more processors 2201 may be configured to execute instructions stored in memory 2202. When executed by one or more processors 2201, these instructions may cause controller 106 (and thus device 100) to perform any functions described herein performed by controller 106 and / or device 100.

[0064] Power may be suitably supplied to controller 106, driver 103, microphones 107, 107a and / or any other element of device 100. Although not explicitly shown, any example device 100 described and illustrated herein may include an internal battery and / or an external power supply connection.

[0065] Although some of the accompanying drawings show examples of device 100 with specific features such as a particular housing shape, one or more low-frequency extension filters, one or more speaker drivers, one or more microphones, wiring, and / or controllers, which may not be present in other drawings, their absence in a particular drawing does not imply that those features are not present in those examples. Any example of device 100 described and illustrated herein may include any of these and other features described herein in any combination or subcombination. For example, while a particular housing 101 shape is shown in a particular example of device 100, any example of device 100 may use any housing shape.

[0066] More generally, although examples have been described above, the features and / or steps of those examples can be combined, divided, omitted, rearranged, modified, and / or expanded in any desired manner. Various changes, modifications, and improvements will readily occur to those skilled in the art. Although not expressly stated herein, such changes, modifications, and improvements are intended to be part of this specification and are intended to be within the spirit and scope of this disclosure. Therefore, the foregoing description is merely exemplary and not restrictive.

Claims

1. An audio device, comprising: An outer casing that forms an internal space; A speaker, which is connected to the housing and configured to emit sound; and A low-frequency filter, disposed within the internal space and configured to filter multiple frequency bands within the stiffness control response domain of the audio device, the low-frequency filter comprising multiple acoustic paths and a cavity, wherein: The sound enters the plurality of acoustic pathways through the cavity; Each of the plurality of acoustic pathways is arranged in a section surrounding the cavity, and includes a first end open to the interior space and a closed second end; and Each of the plurality of acoustic paths has a different length corresponding to a different frequency band among the plurality of frequency bands within the stiffness control response domain of the audio device.

2. The audio device of claim 1, wherein the plurality of acoustic paths are configured to reduce air stiffness within the plurality of frequency bands.

3. The audio device of claim 1, wherein each of the plurality of acoustic paths is filled only with air.

4. The audio device of claim 1, wherein each of the plurality of acoustic paths comprises a tube.

5. The audio device according to claim 1, wherein the internal space is an enclosed internal space.

6. The audio device of claim 1, wherein the first end of each of the plurality of acoustic paths includes a flare.

7. The audio device of claim 1, wherein the first end of each of two of the plurality of acoustic paths shares an opening leading to the interior space.

8. The audio device of claim 1, wherein each of the plurality of acoustic paths has a depth of 10 mm. -1 up to 30 mm -1 The ratio of length to cross-sectional area within the specified range.

9. The audio device of claim 1, wherein each of the plurality of acoustic paths has a depth of 12.3 mm. -1 up to 24.6 mm -1 The ratio of length to cross-sectional area within the specified range.

10. The audio device of claim 1, wherein at least some of the plurality of frequency bands overlap.

11. An audio device including a low-frequency filter configured to filter in a frequency range below 500 Hz, the low-frequency filter comprising: Multiple acoustic pathways and cavities, Each of the plurality of acoustic pathways is arranged in a section surrounding the cavity and includes a first end that is open, such that at least a portion of the acoustic energy received by the low-frequency filter is received at the first end through the cavity. Each of the plurality of acoustic pathways includes a closed second end, and At least some of the plurality of acoustic paths include different tortuous acoustic paths and have different lengths corresponding to different frequency bands in the plurality of frequency bands within the frequency range.

12. The audio device of claim 11, wherein each of the plurality of acoustic paths is filled only with air.

13. The audio device of claim 11, wherein the first ends of two of the plurality of acoustic paths share an opening.

14. The audio device of claim 11, wherein the low-frequency filter includes a portion that bends at the outer periphery of the body and includes at least a portion of one or more of the plurality of acoustic pathways.

15. The audio device of claim 11, wherein the frequency range is below 280 Hz.

16. An audio device, comprising: An outer casing that forms an internal space; A speaker, which is connected to the housing and configured to emit sound; and A low-frequency filter, disposed within the internal space and configured to filter multiple frequency bands below the transition point frequency, wherein the quality control response domain of the audio device begins at the transition point frequency, the low-frequency filter comprising multiple acoustic paths and a cavity, wherein: The sound enters the plurality of acoustic pathways through the cavity; Each of the plurality of acoustic pathways is arranged in a section surrounding the cavity and includes a first end open to the interior space and a closed second end; and Each of the plurality of acoustic paths has a different length corresponding to a different frequency band among the plurality of frequency bands below the transition point frequency, and the quality control response domain of the audio device begins at the transition point frequency.

17. The audio device of claim 16, wherein the plurality of acoustic paths are configured to reduce air stiffness within the plurality of frequency bands.

18. The audio device of claim 16, wherein each of the plurality of acoustic paths is filled only with air.

19. The audio device of claim 16, wherein the internal space is an enclosed internal space.

20. The audio device of claim 16, wherein each of the plurality of acoustic paths has a depth of 10 mm. -1 up to 30 mm -1 The ratio of length to cross-sectional area within the specified range.

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