Patent ID: 12192698

DETAILED DESCRIPTION

Several embodiments are described with reference to the appended drawings are now explained. While numerous details are set forth, it is understood that some embodiments of the invention may be practiced without these details. In other instances, well-known circuits, structures, and techniques have not been shown in detail so as not to obscure the understanding of this description.

FIG.1shows a view of a listening area101with an audio receiver103, a loudspeaker105, and a listener107. The audio receiver103may be coupled to the loudspeaker105to drive individual transducers109in the loudspeaker105to emit various sound beam patterns into the listening area101. In one embodiment, the loudspeaker105may be configured and is to be driven as a loudspeaker array, to generate beam patterns that represent individual channels of a piece of sound program content. For example, the loudspeaker105(as an array) may generate beam patterns that represent front left, front right, and front center channels for a piece of sound program content (e.g., a musical composition or an audio track for a movie). The loudspeaker105has a cabinet111, and the transducers109are housed in a bottom102of the cabinet111and to which a baseplate113is coupled as shown.

FIG.2Ashows a component diagram of the audio receiver103according to one embodiment. The audio receiver103may be any electronic device that is capable of driving one or more transducers109in the loudspeaker105. For example, the audio receiver103may be a desktop computer, a laptop computer, a tablet computer, a home theater receiver, a set-top box, or a smartphone. The audio receiver103may include a hardware processor201and a memory unit203.

The processor201and the memory unit203are generically used here to refer to any suitable combination of programmable data processing components and data storage that conduct the operations needed to implement the various functions and operations of the audio receiver103. The processor201may be an applications processor typically found in a smart phone, while the memory unit203may refer to microelectronic, non-volatile random access memory. An operating system may be stored in the memory unit203along with application programs specific to the various functions of the audio receiver103, which are to be run or executed by the processor201to perform the various functions of the audio receiver103.

The audio receiver103may include one or more audio inputs205for receiving multiple audio signals from an external or remote device. For example, the audio receiver103may receive audio signals as part of a streaming media service from a remote server. Alternatively, the processor201may decode a locally stored music or movie file to obtain the audio signals. The audio signals may represent one or more channels of a piece of sound program content (e.g., a musical composition or an audio track for a movie). For example, a single signal corresponding to a single channel of a piece of multichannel sound program content may be received by an input205of the audio receiver103, and in that case multiple inputs may be needed to receive the multiple channels for the piece of content. In another example, a single signal may correspond to or have encoded therein or multiplexed therein the multiple channels (of the piece of sound program content).

In one embodiment, the audio receiver103may include a digital audio input205A that receives one or more digital audio signals from an external device or a remote device. For example, the audio input205A may be a TOSLINK connector, or it may be a digital wireless interface (e.g., a wireless local area network (WLAN) adapter or a Bluetooth adapter). In one embodiment, the audio receiver103may include an analog audio input205B that receives one or more analog audio signals from an external device. For example, the audio input205B may be a binding post, a Fahnestock clip, or a phono plug that is designed to receive a wire or conduit and a corresponding analog signal.

In one embodiment, the audio receiver103may include an interface207for communicating with the loudspeaker105. The interface207may utilize wired mediums (e.g., conduit or wire) to communicate with the loudspeaker105, as shown inFIG.1. In another embodiment, the interface207may communicate with the loudspeaker105through a wireless connection. For example, the network interface207may utilize one or more wireless protocols and standards for communicating with the loudspeaker105, including the IEEE 802.11 suite of standards, IEEE 802.3, cellular Global System for Mobile Communications (GSM) standards, cellular Code Division Multiple Access (CDMA) standards, Long Term Evolution (LTE) standards, and/or Bluetooth standards.

As shown inFIG.2B, the loudspeaker105may receive transducer drive signals from the audio receiver103through a corresponding interface213. As with the interface207, the interface213may utilize wired protocols and standards and/or one or more wireless protocols and standards, including the IEEE 802.11 suite of standards, IEEE 802.3, cellular Global System for Mobile Communications (GSM) standards, cellular Code Division Multiple Access (CDMA) standards, Long Term Evolution (LTE) standards, and/or Bluetooth standards. In some embodiments, the drive signals are received in digital form, and so in order drive the transducers109, the loudspeaker105in that case may include digital-to-analog converters (DACs)209that are coupled in front of the power amplifiers211, for converting the drive signals into analog form before amplifying them to drive each transducer109.

Although described and shown as being separate from the audio receiver103, in some embodiments, one or more components of the audio receiver103may be integrated in the loudspeaker105. For example, as described below, the loudspeaker105may also include, within its cabinet111, the hardware processor201, the memory unit203, and the one or more audio inputs205.

As shown inFIG.1, the loudspeaker105houses multiple transducers109in a speaker cabinet111, which may be aligned in a ring formation relative to each other, to form a loudspeaker array. In particular, the cabinet111as shown is cylindrical; however, in other embodiments, the cabinet111may be in any shape, including a polyhedron, a frustum, a cone, a pyramid, a triangular prism, a hexagonal prism, a sphere, a frusto-conical shape, or any other similar shape. The cabinet111may be at least partially hollow, and may also allow the mounting of transducers109on its inside surface or on its outside surface. The cabinet111may be made of any suitable material, including metals, metal alloys, plastic polymers, or some combination thereof.

As shown inFIG.1andFIG.2B, the loudspeaker105may include a number of transducers109. The transducers109may be any combination of full-range drivers, mid-range drivers, subwoofers, woofers, and tweeters. Each of the transducers109may have a diaphragm or cone that is connected to a rigid basket or frame via a flexible suspension that constrains a coil of wire (e.g., a voice coil) that is attached to the diaphragm to move axially through a generally cylindrical magnetic gap. When an electrical audio signal is applied to the voice coil, a magnetic field is created by the electric current in the voice coil, making it a variable electromagnet. The coil and the transducers'109magnetic system interact, generating a mechanical force that causes the coil (and thus, the attached cone) to move back and forth, thereby reproducing sound under the control of the applied electrical audio signal coming from an audio source, such as the audio receiver103. Although electromagnetic dynamic loudspeaker drivers are described for use as the transducers109, those skilled in the art will recognize that other types of loudspeaker drivers, such as piezoelectric, planar electromagnetic and electrostatic drivers are possible.

Each transducer109may be individually and separately driven to produce sound in response to separate and discrete audio signals received from an audio source (e.g., the audio receiver103). By having knowledge of the alignment of the transducers109, and allowing the transducers109to be individually and separately driven according to different parameters and settings (including relative delays and relative energy levels), the loudspeaker105may be arranged and driven as an array, to produce numerous directivity or beam patterns that accurately represent each channel of a piece of sound program content output by the audio receiver103. For example, in one embodiment, the loudspeaker105may be arranged and driven as an array, to produce one or more of the directivity patterns shown inFIG.3. Simultaneous directivity patterns produced by the loudspeaker105may not only differ in shape, but may also differ in direction. For example, different directivity patterns may be pointed in different directions in the listening area101. The transducer drive signals needed to produce the desired directivity patterns may be generated by the processor201(seeFIG.2A) executing a beamforming process.

Although a system has been described above in relation to a number of transducers109that may be arranged and driven as part of a loudspeaker array, the system may also work with only a single transducer (housed in a cabinet111). Thus, while at times the description below refers to the loudspeaker105as being configured and driven as an array, in some embodiments a non-array loudspeaker may be configured or used in a similar fashion described herein.

As shown and described above, the loudspeaker105may include a single ring of transducers109arranged to be driven as an array. In one embodiment, each of the transducers109in the ring of transducers109may be of the same type or model, e.g., replicates. The ring of transducers109may be oriented to emit sound “outward” from the ring, and may be aligned along (or lying in) a horizontal plane such that each of the transducers109is vertically equidistant from the tabletop, or from a top plane of a baseplate113of the loudspeaker105. By including a single ring of transducers109aligned along a horizontal plane, vertical control of sound emitted by the loudspeaker105may be limited. For example, through adjustment of beamforming parameters and settings for corresponding transducers109, sound emitted by the ring of transducers109may be controlled in the horizontal direction. This control may allow generation of the directivity patterns shown inFIG.3along a horizontal plane or axis. However, by lacking multiple stacked rings of transducers109this directional control of sound may be limited to this horizontal plane. Accordingly, sound waves produced by the loudspeaker105in the vertical direction (perpendicular to this horizontal axis or plane) may expand outwards without limit.

For example, as shown inFIG.4, sound emitted by the transducers109may be spread vertically with minimal limitation. In this scenario, the head or ears of the listener107are located approximately one meter and at a twenty-degree angle relative to the ring of transducers109in the loudspeaker105. The spread of sound from the loudspeaker105may include sound emitted 1) downward and onto a tabletop on which the loudspeaker105has been placed and 2) directly at the listener107. The sound emitted towards the tabletop will be reflected off the surface of the tabletop and towards the listener107. Accordingly, both reflected and direct sound from the loudspeaker105may be sensed by the listener107. Since the reflected path is indirect and consequently longer than the direct path in this example, a comb filtering effect may be detected or perceived by the listener107. A comb filtering effect may be defined as the creation of peaks and troughs in frequency response that are caused when signals that are identical but have phase differences are summed. An undesirably colored sound can result from the summing of these signals. For example,FIG.5shows a logarithmic sound pressure versus frequency graph for sound detected at one meter and at twenty degrees relative to the loudspeaker105(i.e., the position of the listener107as shown inFIG.4). A set of bumps or peaks and notches or troughs illustrative of this comb filtering effect may be observed in the graph shown inFIG.5. The bumps may correspond to frequencies where the reflected sounds are in-phase with the direct sounds while the notches may correspond to frequencies where the reflected sounds are out-of-phase with the direct sounds.

These bumps and notches may move with elevation or angle (degree) change, as path length differences between direct and reflected sound changes rapidly based on movement of the listener107. For example, the listener107may stand up such that the listener107is at a thirty-degree angle or elevation relative to the loudspeaker105as shown inFIG.6instead of a twenty-degree elevation as shown inFIG.4. The sound pressure vs. frequency as measured at the thirty-degree angle (elevation) is shown inFIG.7. It can be seen that the bumps and notches in the sound pressure versus frequency behavior move with changing elevation, and this is illustrated in the contour graph ofFIG.8which shows the comb filtering effect ofFIGS.5and7as witnessed from different angles. The regions with darker shading represent high SPL (bumps), while the regions with lighter shading represent low SPL (notches). The bumps and notches shift over frequency, as the listener107changes angles/location relative to the loudspeaker105. Accordingly, as the listener107moves in the vertical direction relative to the loudspeaker105, the perception of sound for this listener107changes. This lack of consistency in sound during movement of the listener107, or at different elevations, may be undesirable.

As described above, comb filtering effects are triggered by phase differences between reflected and direct sounds caused by the longer distance the reflected sounds must travel enroute to the listener107. To reduce audio coloration perceptible to the listener107based on comb filtering, the distance between reflected sounds and direct sounds may be shortened. For example, the ring of transducers109may be oriented such that sound emitted by the transducers109travels a shorter or even minimal distance, before reflection on the tabletop or another reflective surface. This reduced distance will result in a shorter delay between direct and reflected sounds, which consequently will lead to more consistent sound at locations/angles the listener107is most likely to be situated. Techniques for minimizing the difference between reflected and direct paths from the transducers109will be described in greater detail below by way of example.

FIG.9Ashows a loudspeaker105in which an integrated transducer109has been moved closer to the bottom of the cabinet111than its top, in comparison to the transducer109in the loudspeaker105shown inFIG.4. In one embodiment, the transducer109may be located proximate to a baseplate113that is fixed to a bottom end of the cabinet111of the loudspeaker105. The baseplate113may be a solid flat structure that is sized to provide stability to the loudspeaker105while the loudspeaker105is seated on a table or on another surface (e.g., a floor), so that the cabinet111can remain upright. In some embodiments, the baseplate113may be sized to receive sounds emitted by the transducer109such that sounds may be reflected off of the baseplate113. For example, as shown inFIG.9A, sound directed downward by the transducer109may be reflected off of the baseplate113instead of off of the tabletop on which the loudspeaker105is resting. The baseplate113may be described as being coupled to a bottom102of the cabinet111, e.g., directly to its bottom end, and may extend outward beyond a vertical projection of the outermost point of a sidewall of the cabinet. Although shown as larger in diameter than the cabinet111, in some embodiments, the base-plate113may be the same diameter of the cabinet111. In these embodiments, the bottom102of the cabinet111may curve or cut inwards (e.g., until it reaches the baseplate113) and the transducers109may be located in this curved or cutout section of the bottom102of the cabinet111such as shown inFIG.1.

In some embodiments, an absorptive material901, such as foam, may be placed around the baseplate113, or around the transducers109. For example, as shown inFIG.9C, a slot903may be formed in the cabinet111, between the transducer109and the baseplate113. The absorptive material901within the slot903may reduce the amount of sound that has been reflected off of the baseplate113in a direction opposite the listener107(and that would otherwise then be reflected off of the cabinet111back towards the listener107). In some embodiments, the slot903may encircle the cabinet111around the base of the cabinet111and may be tuned to provide a resonance in a particular frequency range to further reduce sound reflections. In some embodiments, the slot903may form a resonator coated with the absorptive material901designed to dampen sounds in a particular frequency range to further eliminate sound reflections off the cabinet111.

In one embodiment, as seen inFIGS.9D,9E, a screen905may be placed below the transducers109. In this embodiment, the screen905may be a perforated mesh (e.g., a metal, metal alloy, or plastic) that functions as a low-pass filter for sound emitted by the transducers109. In particular, and as best seen inFIG.9D, the screen905may create a cavity907(similar to the slot903depicted inFIG.9C) underneath the cabinet111between the baseplate113and the transducers109. High-frequency sounds emitted by the transducers109and which reflect off the cabinet111may be attenuated by the screen905and prevented from passing into the listening area101. In one embodiment, the porosity of the screen905may be adjusted to limit the frequencies that may be free to enter the listening area101.

In one embodiment, the vertical distance D between a center of the diaphragm of the transducer109and a reflective surface (e.g., the top of the baseplate113) may be between 8.0 mm and 13.0 mm as shown inFIG.9B. For example, in some embodiments, the distance D may be 8.5 mm, while in other embodiments the distance D may be 11.5 mm (or anywhere in between 8.5 mm-11.5 mm). In other embodiments, the distance D may be between 4.0 mm and 20.0 mm. As shown inFIGS.9A and9B, by being located proximate (i.e., a distance D) from the surface upon which sound is reflected (e.g., the baseplate113, or in other cases a tabletop or floor surface itself such as where no baseplate113is provided), the loudspeaker105may exhibit a reduced length of its reflected sound path. This reduced reflected sound path consequently reduces the difference between the lengths of the reflected sound path and the direct sound path, for sound originating from a transducer109integrated within the cabinet111, e.g., the difference, reflected sound path distance—direct sound path distance, approaches zero). This minimization or at least reduction in difference between the length of the reflected and direct paths may result in a more consistent sound (e.g., a consistent frequency response or amplitude response) as shown in the graphs ofFIG.10AandFIG.10B. In particular, the bumps and notches in bothFIG.10AandFIG.10Bhave decreased in magnitude and moved considerably to the right and closer to the bounds of human perception (e.g., certain bumps and notches have moved above 10 kHz). Thus, comb filtering effects as perceived by the listener107may be reduced.

Although discussed above and shown inFIGS.9A-9Cfor a single transducer109, in some embodiments each transducer109in a ring formation of multiple transducers109(e.g., an array of transducers) may be similarly arranged, along the side or face of the cabinet111. In those embodiments, the ring of transducers109may be aligned along or lie within a horizontal plane as described above.

In some embodiments, the distance D or the range of values used for the distance D may be selected based on the radius of the corresponding transducer109(e.g., the radius of the diaphragm of the transducer109) or the range of frequencies used for the transducer109. In particular, high frequency sounds may be more susceptible to comb filtering caused by reflections. Accordingly, a transducer109producing higher frequencies may need a smaller distance D, in order to more stringently reduce its reflections (in comparison to a transducer109that produces lower frequency sounds.) For example,FIG.11Ashows a multi-way loudspeaker105with a first transducer109A used/designed for a first set of frequencies, a second transducer109B used/designed for a second set of frequencies, and a third transducer109C used/designed for a third set of frequencies. For instance, the first transducer109A may be used/designed for high frequency content (e.g., 5 kHz-10 kHz), the second transducer109B may be used/designed for mid frequency content (e.g., 1 kHz-5 kHz), and the third transducer109C may be used/designed for low frequency content (e.g., 100 Hz-1 kHz). These frequency ranges for each of the transducers109A,109B, and109C may be enforced using a set of filters integrated within the loudspeaker105. Since the wavelengths for sound waves produced by the first transducer109A are smaller than wavelengths of sound waves produced by the transducers109B and109C, the distance DAassociated with the transducer109A may be smaller than the distances DBand DC, associated with the transducers109B and109C, respectively (e.g., the transducers109B and109C may be located farther from a reflective surface on which the loudspeaker105is resting, without notches associated with comb filtering falling within their bandwidth of operation). Accordingly, the distance D between transducers109and a reflective surface needed to reduce comb filtering effects may be based on the size/diameter of the transducers109and/or the frequencies intended to be reproduced by the transducers109.

Despite being shown with a single transducer109A,109B, and109C, the multi-way loudspeaker105shown inFIG.11Amay include rings of each of the transducers109A,109B, and109C. Each ring of the transducers109A,109B, and109C may be aligned in separate horizontal planes.

Further, although shown inFIG.11Aas including three different types of transducers109A,109B, and109C (i.e., a 3-way loudspeaker105), in other embodiments the loudspeaker105may include any number of different types of transducers109. In particular, the loudspeaker105may be an N-way array as shown inFIG.11B, where N is an integer that is greater than or equal to one. Similar toFIG.11A, in this embodiment shown inFIG.11B, the distances DA-DN, associated with each ring of transducers109A-109N may be based on the size/diameter of the transducers109A-109N and/or the frequencies intended to be reproduced by the transducers109A-109N.

Although achieving a small distance D (i.e., a value within a range described above) between the center of the transducers109and a reflective surface may be achievable for transducers109with smaller radii by moving the transducers109closer to a reflective surface (i.e., arranging transducers109along the cabinet111to be closer to the baseplate113), as transducers109increase in size the ability to achieve values for the distance D within prescribed ranges may be difficult or impossible. For example, it would be impossible to achieve a threshold value for D by simply moving a transducer109in the vertical direction along the face of the cabinet111closer to the reflective surface when the radius of the transducer109is greater than the threshold value for D (e.g., the threshold value is 12.0 mm and the radius of the transducer109is 13.0 mm). In these situations, additional degrees of freedom of movement may be employed to achieve the threshold value for D as described below.

In some embodiments, the orientation of the transducers109in the loudspeaker105may be adjusted to further reduce the distance D between the transducer109and the reflective surface, reduce the reflected sound path, and consequently reduce the difference between the reflected and direct sound paths. For example,FIG.12shows a side view of a loudspeaker105according to one embodiment. Similar to the loudspeaker105ofFIG.9, the loudspeaker105shown inFIG.12includes a ring of transducers109situated in or around the bottom of the cabinet111and near the baseplate113. The ring of transducers109may encircle the circumference of the cabinet111(or may be coaxial with the circumference), with equal spacing between each adjacent pairs of transducers109as shown in the overhead cutaway view inFIG.13.

In the example loudspeaker105shown inFIG.12, the transducers109are located proximate to the baseplate113, by being mounted in the bottom102of the cabinet111. The bottom in this example is frusto conical as shown having a sidewall that joins an upper base and a lower base, and wherein the upper base is larger than the lower base and the base plate113is coupled to the lower base as shown. Each of the transducers109in this case may be described as being mounted within a respective opening in the sidewall such that its diaphragm is essentially outside the cabinet111, or is at least plainly visible along a line of sight, from outside of the cabinet111. Note the indicated distance D being the vertical distance from the center of the diaphragm, e.g., the center of its outer surface, down to the top of the baseplate113. The sidewall (of the bottom102) has a number of openings formed therein that are arranged in a ring formation and in which the transducers109have been mounted, respectively. As was noted above in relation toFIGS.9A and9B, by positioning the transducers109close to a surface upon which sound from the transducers109is reflected, e.g., by minimizing the distance D while restricting the angle theta.

Referring toFIG.14B, the angle theta may be defined as depicted in that figure, namely as the angle between (1) a plane of the diaphragm of the transducer109, such as a plane in which a perimeter of the diaphragm lies, and (2) the tabletop surface, or if a baseplate113is used then a horizontal plane that touches the top of the base plate113. The angle theta of each of the transducers109may be restricted to a specified range, so that the difference between the path of reflected sounds and the path of direct sounds may be reduced, in comparison to the upright arrangement of the transducer109shown inFIG.14A. A transducer109that is not angled downward is shown inFIG.14A, where it may be described as being upright or “directly facing” the listener107, defining an angle theta of at least ninety degrees, and a distance D, between the center of the transducer109and a reflective surface below, e.g., a tabletop or the top of the baseplate113. As shown inFIG.14B, angling the transducer109downward at an acute angle theta (Θ) results in a distance D2between the center of the transducer109and a reflective surface, where D2<D1. Accordingly, by rotating (tilting or pivoting) the transducer109“forward” and about its bottommost point, so that its diaphragm is more directed to the reflective surface, the distance D between the center of the transducer109and the reflective surface decreases (because the bottommost edge of the diaphragm remains fixed betweenFIG.14AandFIG.14B, e.g., as close as possible to the reflective surface). As noted above, this reduction in D results in a reduction in the difference between the direct and reflected sounds paths and a consequent reduction in audio coloration caused by comb filtering. The reduction in the reflected sound path may be seen inFIG.14C, where the solid line from the non-rotated transducer109is longer than the dashed line from the transducer109that is tilted by an angle theta, Θ. Thus, to further reduce the distance D (e.g., the distance between the center of the transducer109and either the baseplate113or other reflective surface underneath the cabinet111) and consequently reduce the reflected path, the transducer109may be angled downward toward the baseplate113as explained above and also as shown inFIG.12.

As described above, the distance D is a vertical distance between the diaphragm of each of the transducers109and a reflective surface (e.g., the baseplate113). In some embodiments, this distance D may be measured from the center of the diaphragm to the reflective surface. Although shown with both protruding diaphragms and flat diaphragms, in some embodiments inverted diaphragms may be used. In these embodiments, the distance D may be measured from the center of the inverted diaphragm, or from the center as it has been projected onto a plane of the diaphragm along a normal to the plane, where the diaphragm plane may be a plane in which the perimeter of the diaphragm lies. Another plane associated with the transducer may be a plane that is defined by the front face of the transducer109(irrespective of the inverted curvature of its diaphragm).

Although tilting or rotating the transducers109may result in a reduced distance D and a corresponding reduction in the reflected sound path, over rotation of the transducers109toward the reflective surface may result in separate unwanted effects. In particular, rotating the transducers109past a threshold value may result in a resonance caused by reflecting sounds off the reflective surface or the cabinet111and back toward the transducer109. Accordingly, a lower bound for rotation may be employed to ensure an unwanted resonance is not experienced. For example, the transducers109may be rotated or tilted between 30.0° and 50.0° (e.g., Θ as defined above inFIG.14Bmay be between 30.0° and 50.0°). In one embodiment, the transducers109may be rotated between 37.5° and 42.5° (e.g., Θ may be between 37.5° and 42.5°). In other embodiments, the transducers109may be rotated between 39.0° and 41.0°. The angle theta of rotation of the transducers109may be based on a desired or threshold distance D for the transducers109.

FIG.15Ashows a logarithmic sound pressure versus frequency graph for sound detected at a position (of the listener107) along a direct path that is one meter away from the loudspeaker105, and twenty degrees upward from the horizontal—seeFIG.4. In particular, the graph ofFIG.15Arepresents sound emitted by the loudspeaker105shown inFIG.12with a degree of rotation theta of the transducers109at 45°. In this graph, sound levels are relatively consistent within the audible range (i.e., 20 Hz to 10 kHz). Similarly, the contour graph of FIG. for a single transducer109shows relative consistency in the vertical direction, for most angles at which the listener107would be located. For instance, a linear response is shown in the contour graph ofFIG.15Bfor a vertical position of the listener107being 0° (the listener107is seated directly in front of the loudspeaker105) and for a vertical position between 45° and 60° (the listener107is standing up near the loudspeaker105). In particular, notches in this counter graph have been mostly moved outside the audible range, or they have been moved to vertical angles where the listener107is not likely to be located (e.g., the listener107would not likely be standing directly above the loudspeaker105, at the vertical angle of 90°).

As noted above, rotating the transducers109achieves a lower distance D between the center of the transducers109and a reflective surface (e.g., the baseplate113). In some embodiments, the degree of rotation or the range of rotation may be set based on the set of frequencies and the size or diameter of the transducers109. For example, larger transducers109may produce sound waves with larger wavelengths. Accordingly, the distance D needed to mitigate comb filtering for these larger transducers109may be longer than the distance D needed to mitigate comb filtering for smaller transducers109. Since the distance D is longer for these larger transducers109in comparison to smaller transducers109, the corresponding angle Θ at which the transducers are tilted, as needed to achieve this longer distance D, may be larger (less tilting or rotation is needed), in order avoid over-rotation (or over-tilting). Accordingly, the angle of rotation Θ for a transducer109may be selected based on the diaphragm size or diameter of the transducers109and the set of frequencies desired to be output by the transducer109.

As described above, positioning and angling the transducers109along the face of the cabinet111of the loudspeaker105may reduce a reflective sound path distance, reduce a difference between a reflective sound path and a direct sound path, and consequently reduce comb filtering effects. In some embodiments, horns may be utilized to further reduce comb filtering. In such embodiments, a horn enables the point at which sound escapes from (an opening in) the cabinet111of the loudspeaker105(and then moves along respective direct and reflective paths toward the listener107) to be adjusted. In particular, the point of release of sound from the cabinet111and into the listening area101may be configured during manufacture of the loudspeaker105to be proximate to a reflective surface (e.g., the baseplate113). Several different horn configurations will be described below. Each of these configurations may allow use of larger transducers109(e.g., larger diameter diaphragms), or a greater number or a fewer transducers109, while still reducing comb filtering effects and maintaining a small cabinet111for the loudspeaker105.

FIG.16Ashows a cutaway side view of the cabinet111of the loudspeaker105having a horn115and no baseplate113.FIG.16Bshows an elevation or perspective view of the loudspeaker105ofFIG.16Aconfigured as, and to be driven as, an array having multiple transducers109arranged in a ring formation. In this example, the transducer109is mounted or located further inside or within the cabinet111(rather than within an opening in the sidewall of the cabinet111), and a horn115is provided to acoustically connect the diaphragm of the transducer109to a sound output opening117of the cabinet111. In contrast to the embodiment ofFIG.9Dwhere the transducer109is mounted within an opening in the sidewall of the cabinet111and is visible from the outside, there is no “line of sight” to the transducer109inFIGS.16A,16Bfrom outside of the cabinet111. The horn115extends downward from the transducer109, to the opening117, which is formed in the sloped sidewall of the bottom102of the cabinet111which lies on a tabletop or floor. In this example, the bottom102is frusto conical. The horn115directs sound from the transducer109to an inside surface of the sidewall of the cabinet111where the opening117is located, at which point the sound is then released into the listening area through the opening117. As shown, although the transducer may still be closer to the bottom end of the cabinet111than at top end, the transducer109is in a raised position (above the bottom end) in contrast to the embodiment ofFIG.12. Nevertheless, sound emitted by the transducer109can still be released from the cabinet111at a point that is “proximate” or close enough to the reflective surface underneath. That is because the sound is released from an opening117which itself is positioned in close proximity to the baseplate113. In some embodiments, the opening117may be positioned and oriented to achieve the same vertical distance D that was described above in connection with the embodiments ofFIGS.9B,12,14B(in which the distance D was being measured between the diaphragm and the reflective surface below the cabinet111.) For the horn embodiment here, the predefined vertical distance D (from the center of the opening117vertically down to the tabletop or floor on which the cabinet111is resting) may be for example between 8.0 millimeters and 13.0 millimeters. In the case of the horn embodiment here, the distance D may be achieved in part by inclining the opening117(analogous to the rotation or tilt angle theta ofFIG.14B), for example, appropriately defining the angle or slope of the sidewall of the frusto-conical bottom102(of the cabinet111) in which the opening117is formed.

The horn115and the opening117may be formed in various sizes to accommodate sound produced by the transducers109. In one embodiment, multiple transducers109in the loudspeaker105may be similarly configured with corresponding horns115and openings117in the cabinet111, together configured, and to be driven as, an array. The sound from each transducer109is released from the cabinet111at a prescribed distance D from the reflective surface below the cabinet111(e.g., a tabletop or a floor on which the cabinet111is resting, or a baseplate113). This distance D may be measured from the center of the opening117(vertically downward) to the reflective surface. Since sound is thus being emitted proximate to the baseplate113, reflected sound may travel along a path similar to that of direct sound as described above. In particular, since sound only travels a short distance from the opening117before being reflected, the difference in the reflected and direct sound paths may be small, which results in a reduction in comb filtering effects perceptible to the listener107. For example, the contour graph ofFIG.17corresponding to the loudspeaker105shown inFIGS.16A and16Bshows a smooth and consistent level difference across frequencies and vertical angles (which are angles that define the possible vertical positions of the listener107), in comparison to the comb filtering effect shown inFIG.8.

FIG.18shows a cutaway view of the cabinet111of the loudspeaker105, according to another horn embodiment. In this example, the transducers109are mounted to or through the sidewall of the cabinet111, but are pointed inward (rather than outward as in the embodiment ofFIG.9D, for example. In other words, the forward faces of their diaphragms are facing into the cabinet111. Corresponding horns115are acoustically coupled to the front faces of diaphragms of the transducers109, respectively, and extend downward along respective curves to corresponding openings117. In this embodiment, although the transducers109are facing a first direction, the curvature of the horns115A allow sound to be emitted from the openings117, which are aimed to emit sound into the listening area101in a second direction (different than the first direction). The openings117of the cabinet111in this embodiment may be positioned and oriented the same as described above in connection with the horn embodiments ofFIGS.16A,16B. Additionally, a phase plug119may be added into the acoustic path between the transducer109and its respective opening117, as shown, so as to redirect high frequency sounds to avoid reflections and cancellations. The contour graph ofFIG.19corresponding to the loudspeaker105ofFIG.18shows a smooth and consistent level difference across frequencies and vertical listening positions (vertical direction angles), in comparison to the undesirable comb filtering effects shown inFIG.8.

FIG.20shows a cutaway view of the cabinet111of the loudspeaker105, according to yet another embodiment. In this example, the transducers109are also mounted within the cabinet111but they are pointed downwards (rather than sideways as in the embodiment ofFIG.18in which the transducers109may be mounted to the sidewall of the cabinet111). This arrangement may enable the use of horns115that are shorter than those in the embodiment ofFIG.18. As shown in the contour graph ofFIG.21, the shorter horns115may contribute to a smoother response by this embodiment, in comparison to the other embodiments that also use horns115(described above.) In one embodiment, the length of the horns115may be between 20.0 mm and 45.0 mm. The openings117of the cabinet111in this embodiment may also be formed in the sloped sidewall of the frusto-conical bottom102of the cabinet111, and may be positioned and oriented the same as described above in connection with the horn embodiments ofFIGS.16A,16Bto achieve a smaller distance D relative to the reflective surface, e.g., the top surface of the baseplate113.

FIG.22shows a cutaway view of the cabinet111in the loudspeaker105, according to yet another embodiment. In this example, each of the transducers109is mounted within the cabinet111, e.g., similar toFIG.20, but the horn115(which directs sound emitted from its respective transducer109to its respective opening117) is longer and narrower than inFIG.20. In some embodiments, a combination of one or more Helmholtz resonators121may be used for each respective transducer109(e.g., an 800 Hz resonator, a 3 kHz resonator, or both) along with phase plugs119. The resonators121may be aligned along the horn115or just outside the opening117, for absorbing sound and reducing reflections. As shown in the contour graph ofFIG.23, the longer, narrower horns115of this embodiment, together with 800 Hz and 3 kHz Helmholtz resonators121may result in a smooth frequency response (at various angles in the vertical direction).

FIG.24shows a cutaway or cross-section view taken of a combination transducer109and its phase plug119, in the cabinet111of the loudspeaker105, according to another embodiment. In this embodiment, the phase plug119is placed adjacent to its respective transducer109, and each such combination transducer109and phase plug119may be located entirely within (inward of the sidewall of) the cabinet111as shown. In one embodiment, a shielding device2401that is coupled to the outside surface of the cabinet111or also to the baseplate113may hold the phase plug119in position against its transducer109. The shielding device2401may extend around the perimeter or circumference of the cabinet111, forming a ring that serves to hold all of the phase plugs119of all of the transducers109(e.g., in the case of a loudspeaker array). The phase plug119may be formed as several fins2403that extend from a center hub2405. The fins2403may guide sound (through the spaces between adjacent ones of the fins2403) from the diaphragm of the corresponding transducer109to an aperture2407formed in the shielding device2401. Accordingly, the phase plug119may be shaped to surround the transducer109, including a diaphragm of the transducer109as shown, such that sound may be channeled from the transducers109to the aperture2407. By also guiding the sound from the transducers109to the openings117, respectively, the phase plugs119of this embodiment are also able to place the effective sound radiation area of the transducers109closer to the reflective surface (e.g., the baseplate113, or a tabletop on which the loudspeaker105is resting). As noted above, by positioning the sound radiation area or sound-radiating surface of the transducers109closer to a reflective surface, the loudspeaker105in this embodiment may reduce the difference between reflective and direct sound paths, which in turn may reduce comb filtering effects.

Turning now toFIG.25in this embodiment, the loudspeaker105has a partition2501. The partition2501may made of a rigid material (e.g., a metal, metal alloy, or plastic) and extends from the outside surface of the cabinet111over the bottom102of the cabinet111, to partially block the transducers109—seeFIG.12which shows an example of the bottom102of the cabinet111and the transducers109therein, which would be blocked by the partition2501ofFIG.25. The partition2501in this example is a simple cylinder (extending straight downward) but it could alternatively have a different curved shape, e.g., wavy like a skirt or curtain, to encircle the cabinet111and partially block each of the transducers109. In one embodiment, the partition2501may include a number of holes2503formed in its curved sidewall as shown which may be sized to allow the passage of various desired frequencies of sound. For example, one group or subset of the holes2503which are located farthest from the baseplate113may be sized to allow the passage of low-frequency sounds (e.g., 100 Hz-1 kHz) while another group or subset of holes2503that lies below the low-frequency holes may be sized to allow the passage of mid-frequency sounds (e.g., 1 kHz-5 kHz). In this embodiment, high-frequency sounds may pass between a gap2505created between the bottom end of the partition2501and the baseplate113. Accordingly, high-frequency content is pushed closer to the baseplate113by restricting this content to the gap2505. This movement of high-frequency content closer to the baseplate113(i.e., the point of reflection) reduces the reflected sound path and consequently reduces the perceptibility of comb filtering for high-frequency content, which as noted above, is particularly susceptible to this form of audio coloration.

Turning now toFIGS.26A,26B, these illustrate the use of acoustic dividers2601in a multi-way version, or in an array version, of the loudspeaker105, in accordance with yet another embodiment of the invention. The divider2601may be a flat piece that forms a wall joining the bottom102of the cabinet111to the baseplate113, as best seen in the side view ofFIG.26B. The divider2601begins at the transducer109and extends outward lengthwise, e.g., until a horizontal length given by the radius r, which extends from a center of the cabinet (through which a vertical longitudinal axis of the cabinet111runs—seeFIG.26B). The divider2601need not reach the vertical boundary defined by the outermost sidewall of the cabinet111, as shown. A pair of adjacent dividers2601on either side of a transducer109may, together with the surface of the bottom102of the cabinet111and the top surface of the baseplate, act like a horn for the transducer109.

As explained above, the loudspeakers105described herein when configured and driven as an array provide improved performance over traditional arrays. In particular, the loudspeakers105provided here reduce comb filtering effects perceived by the listener107by either 1) moving transducers109closer to a reflective surface (e.g., the baseplate113, or a tabletop) through vertical or rotational adjustments of the transducers109or 2) guiding sound produced by the transducers109to be released into the listening area101proximate to a reflective surface through the use of horns115and openings117that are the prescribed distance from the reflective surface. The reduction of this distance between the reflective surface and the point at which sound emitted by the transducers109is released into the listening area101consequently reduces the reflective path of sound and reduces comb filtering effects caused by reflected sounds that are delayed relative to the direct sound. Accordingly, the loudspeakers105shown and described may be placed on reflective surfaces without severe audio coloration caused by reflected sounds.

As also described above, use of an array of transducers109arranged in a ring may assist in providing horizontal control of sound produced by the loudspeaker105. In particular, sound produced by the loudspeaker105may assist in forming well-defined sound beams in a horizontal plane. This horizontal control, combined with the improved vertical control (as evidenced by the contour graphs shown in the figures) provided by the positioning of the transducers109in close proximity to the sound reflective surface underneath the cabinet111, allows the loudspeaker105to offer multi-axis control of sound. However, although described above in relation to a number of transducers109, in some embodiments a single transducer109may be used in the cabinet111. In these embodiments, it is understood that the loudspeaker105would be a one-way or multi-way loudspeaker, instead of an array. The loudspeaker105that has a single transducer109may still provide vertical control of sound through careful placement and orientation of the transducer109as described above.

While certain embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that the invention is not limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those of ordinary skill in the art. The description is thus to be regarded as illustrative instead of limiting.