Phase plug for compression driver

Abstract

A phase plug for an electrically compressed driver, comprising: a compression chamber formed by an oscillating diaphragm and a boundary surface of a phase plug assembly adjacent to the diaphragm; a single acoustic outlet defined by a terminus of the phase plug assembly; one or more channels traversing the phase plug assembly from the compression chamber to terminate at the acoustic outlet; and a rotational axis defined within an interior of the phase plug assembly extending from the boundary surface of the phase plug assembly at the compression chamber to the acoustic outlet, wherein at least one of the plurality of channels expands in cross-sectional area between a respective inlet at the boundary surface of the phase plug assembly and the terminus at the acoustic outlet while traversing the phase plug, and wherein the at least one interior channel having an expanded cross-section rotates about the rotational axis.

Description

[0001] Cross-reference to related applications

[0002] This U.S. non-provisional patent application claims the benefit and priority of U.S. Provisional Patent Application No. 63 / 426,482, filed November 18, 2022, entitled “Phase Plug for Compression Driver,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The embodiments relate to an electric compression actuator where the geometry of the oscillating diaphragm from the compression chamber adjacent to the diaphragm to the acoustic outlet of the compression actuator requires path length compensation. Specifically, the internal passageway from the compression chamber to the acoustic outlet needs to be lengthened relative to the passageway surrounding the perimeter of the compression chamber. Background Technology

[0004] For over 90 years, audio reproduction and playback have used electroacoustic transducers known as compression drivers. The central feature of a compression driver is an oscillating diaphragm placed at adjacent boundaries and fixed around its perimeter. The diaphragm and boundaries together form a small cavity called a compression chamber. This chamber then leads to an acoustic outlet via one or more channels. The channel between the compression chamber and the acoustic outlet is commonly referred to as a phase plug. The acoustic outlet is then connected to an enlarged mechanical volume from the inlet (throat) to the outlet (mouth). This enlarged mechanical volume is commonly referred to as a horn, waveguide, or acoustic transducer (US4325456A).

[0005] The necessary expansion of the cross-sectional area from the surface of the vibrating diaphragm, through the phase plug to the acoustic outlet, and then to the horn nozzle, is a consequence of physics. Air has greater flexibility (i.e., less stiffness) than any solid diaphragm. This difference in stiffness represents a mismatch in acoustic impedance, which reduces the coupling of energy from the diaphragm to the air near it. To maximize the energy coupling from the diaphragm to the surrounding environment, it is desirable to make the diaphragm's stiffness more closely matched to the air near it. Then, at the horn nozzle, the flexibility of the air should match the flexibility of free space to facilitate sound radiation.

[0006] The smaller the confined air volume, the higher its stiffness. Therefore, a smaller air volume confined to the adjacent resonant diaphragm results in better impedance matching and energy coupling. A lasting method for achieving better energy transfer was patented in 1929 by Thuras's "electric device" (US1707544A). Here, a concave resonant diaphragm of "rigid disc shape" is clamped within a "sound chamber" at its periphery. The diaphragm is then plugged with a "metal plug" that allows acoustic vibrations to propagate from an opening adjacent to the diaphragm to the acoustic outlet. In modern compression actuator terminology, Thuras's metal plug is called a "phase plug."

[0007] Thuras's design aimed to create a closer match between the air near the diaphragm and the diaphragm's stiffness, gradually transitioning to a match with the stiffness of free space. Over time, many improvements have been made to this type of transducer. For example, a compression actuator using a ring-shaped diaphragm was disclosed as early as 1932 (US1845768). A compression actuator with a convex dome diaphragm was disclosed as early as 1934 (US2058555A, US3432002).

[0008] The air in the cavity between the oscillating diaphragm and the boundary of the compression chamber wall exhibits natural resonance, typically within the desired operating frequency range of the compression driver. B. Smith's work on suppressing acoustic cavity modes in a compression chamber bounded by a flat, rigid diaphragm (Reference 1) is a pioneering method for selecting the location where sound should be allowed to travel along the compression chamber from the diaphragm into the phase plug to achieve optimal acoustic response uniformity. Practical compression drivers almost never use flat diaphragms because the additional stiffness of the dome structure tends to suppress unwanted diaphragm resonance. With advancements in computing power, numerical methods are now used to analyze sound propagation from the compression chamber to the acoustic outlet.

[0009] Those skilled in the art typically use a phase plug comprising several concentric channels, with smaller openings near the diaphragm and larger openings at the acoustic outlet. The location of the channel openings adjacent to the diaphragm is chosen to manage and control the resonance of the compression chamber and / or the diaphragm. Optimizations of the compression actuator have been sought to reduce the coupling of modal resonances, see, for example, US8121330B2 for dome diaphragms. Since resonance cannot be completely avoided, those skilled in the art can reduce the physical dimensions of the compression chamber, diaphragm, and phase plug channels to increase the minimum onset frequency of undesired modal behavior.

[0010] Phase plug channels are typically multiple concentric rings, or a combination of concentric rings and radial slits. The channels through the phase plug can be considered a collection of transmission lines. To avoid additional acoustic resonance caused by the different sound propagation through multiple channels of the phase plug, each path should have similar length and acoustic impedance. For the case of concave diaphragms, providing phase plugs with channels of equal length is mechanically simple and straightforward. The longest path length is naturally in the middle of the diaphragm, and any channel originating near the periphery of the compression chamber from the diaphragm to the acoustic outlet can be extended by a geometry defined around the periphery of the phase plug or by the boundaries between nested components. Therefore, forming a geometry with a longer path length at the periphery of the phase plug eliminates the need to manufacture phase plug assemblies with undercuts or complex internal channels.

[0011] Concave diaphragms present disadvantages when aiming to manufacture the smallest possible compression driver. This is because the diaphragm is driven by an oscillating voice coil moving within the magnetic flux of the magneto structure. Modern compression drivers commonly utilize permanent magnets to generate magnetic flux within the motor. If the phase plug is located inside the voice coil, as in the case of a typical concave dome, then the permanent magnets and flux paths of the motor structure are typically positioned outside the diaphragm and voice coil assembly. This is to obtain sufficient magnetic flux within the motor, especially for voice coils with smaller diameters. Positioning the permanent magnets outside the voice coil diameter increases the overall external dimensions of the motor structure, and thus the overall external dimensions of the compression driver.

[0012] In contrast, the use of a convex diaphragm allows the permanent magnet of the motor to be placed inside the voice coil. With the permanent magnet inside the voice coil, the amount by which the magneto structure extends beyond the outer diameter of the voice coil can be reduced. The result is a smaller overall external size for the compression driver. In applications where the distance between multiple drivers is critical, the smaller compression driver size allows transducers to be positioned closer together. Example applications include acoustic beamforming and the integration of multiple transducers on a single waveguide.

[0013] To accommodate a permanent magnet inside the voice coil in a compact compression driver, the compression chamber and phase plug are now located on one side of the diaphragm, while the magnet is located on the opposite side. Due to this orientation of the diaphragm, magnet, and phase plug, the preferred diaphragm curvature is now convex. This provides physical space for the rigid diaphragm, the permanent magnet, and the shortest possible voice coil assembly. A long voice coil assembly adds extra moving mass, which would otherwise degrade the compression driver output at high frequencies.

[0014] The use of a convex diaphragm alters the nature of the phase plug channel. Unlike a concave diaphragm, where the longest path is located at the center, a convex diaphragm has the shortest path distance to the acoustic outlet at the center. For a concave diaphragm, additional channel length is added to the channel surrounding the phase plug; for a convex diaphragm, additional channel length is required midway between the phase plug and the dome assembly, where the dome is at its highest point. The convex diaphragm results in a phase plug in which the required additional path length becomes a matter of internal geometry.

[0015] The internal geometry introduces complexity into manufacturing:

[0016] Near-net-shape forming technologies (such as 3D printing) can produce these geometries, but they are expensive for many applications;

[0017] Traditional injection molding or die casting technologies have limitations in producing parts with undercut and internal geometry, or require extremely expensive tooling operations;

[0018] Dividing a geometry into segments (e.g., half-models) has limitations regarding what geometry can be considered rotational or symmetrical.

[0019] Therefore, a novel design is desired to manufacture a path length extension channel as an internal geometry phase plug for use with compression actuators having convex diaphragm assemblies, or in other applications requiring an internal path length extension. Summary of the Invention

[0020] We propose a novel phase plug design that can be manufactured using conventional die-making methods or other near-net-shape forming methods. The new design offers:

[0021] • The phase plug inlet position is flexibly positioned adjacent to the diaphragm within the compression chamber;

[0022] • Path length adjustment for each internal acoustic channel;

[0023] • Control of the amplification rate of each channel, thereby controlling the acoustic impedance;

[0024] • The physical shape of the acoustic outlet is compatible with existing designs;

[0025] • The shape of the acoustic wavefront is compatible with existing designs.

[0026] Unlike existing designs, the new phase plug offers applications where the path length through the interior of the phase plug is increased to match the path length of any surrounding phase plug channel. Example applications include compression drivers with convex diaphragms and the conversion of circular sound sources to produce linear sound sources.

[0027] For example, a phase plug is provided for an electric compression actuator, comprising: a compression chamber formed by an oscillating diaphragm and a boundary surface of the phase plug assembly adjacent to the diaphragm; a single acoustic outlet defined by a terminal of the phase plug assembly; one or more channels traversing the compression chamber through the phase plug assembly to terminate at the acoustic outlet; and a rotation axis defined within the interior of the phase plug assembly extending from the boundary surface of the phase plug assembly at the compression chamber to the acoustic outlet, wherein at least one of the plurality of channels, while traversing the phase plug, expands the cross-sectional area between a corresponding inlet at the boundary surface of the phase plug assembly and a terminal at the acoustic outlet, and wherein at least one of the internal channels having the expanded cross-section rotates about the rotation axis.

[0028] According to an exemplary embodiment, the rotation axis of the diaphragm coincides with the rotation axis of the phase plug assembly.

[0029] In another exemplary embodiment, the axis of rotation of the diaphragm does not coincide with the axis of rotation of the phase plug assembly.

[0030] In one embodiment, the enlarged internal channel rotates relative to the axis of rotation in a spiral, conic spiral, or helical manner.

[0031] According to an exemplary embodiment, the multiple channels are distributed in a rotationally symmetrical manner around the axis of rotation.

[0032] In another embodiment, the multiple channels around the axis of rotation are not distributed in a rotationally symmetric manner.

[0033] According to an exemplary embodiment, the outermost channel is rotationally symmetric about the rotation axis.

[0034] According to an exemplary embodiment, one or more internal channels are disposed radially inside the outermost channel, each internal channel having a cross-sectional area that expands in the direction toward the acoustic outlet, and each internal channel rotating relative to the axis of rotation in a spiral, conical, or helical manner.

[0035] In another exemplary embodiment, the phase plug assembly includes an outermost component having an inner wall, an intermediate component having an outer surface and a hollow interior, and a third nested component having an outer surface, wherein a channel is formed at the inner wall of the hollow interior.

[0036] In yet another embodiment, the intermediate component is housed within the outermost component to define an outermost channel between the inner wall of the outermost component and the outer surface of the intermediate component.

[0037] Advantageously, the third nested member can be accommodated within the hollow interior of the intermediate member to define one or more internal channels between the outer surface of the third nested member and the channels of the inner wall of the intermediate member. In a preferred embodiment, the length of the outermost channel is equal to the length of each of the one or more internal channels. Attached Figure Description

[0038] For a more complete understanding of this disclosure, reference is now made to the following brief and detailed description taken in conjunction with the accompanying drawings, wherein like reference numerals denote like parts, wherein:

[0039] Figure 1 This is a cross-sectional view of a physical embodiment of a compression driver 8 with a new phase plug assembly 18.

[0040] Figure 2 Is with Figure 1 A similar cross-sectional view, but with some features removed to focus on the details of the phase plug 18 between the diaphragm 14 and the compression chamber 16 to the acoustic outlet 20.

[0041] Figure 3 This is an exploded view of the nested components (38, 40, 42) of the phase plug assembly 18 in this embodiment. Detailed Implementation

[0042] Figure 1 It is a cross-section taken through the middle of the embodiment of the compression driver 8, listing the main features, including: magnet 9, magneto 10, voice coil 12, convex diaphragm 14, compression chamber 16, phase plug assembly 18, acoustic outlet 20, and rotation axis 22 of diaphragm 14 and phase plug 18.

[0043] Figure 2 The embodiment details between the compression chamber 16 and the acoustic outlet 20 are highlighted. The compression chamber 16 is defined by the boundary surface 24 of the diaphragm 14 and the phase plug assembly 18. This embodiment provides the following features:

[0044] • Channels (26, 28, 30, 32, 34, 36) begin at compression chamber 16, pass through phase plug assembly 18, and are defined from the surface 24 of phase plug 18 (opposite to diaphragm 14) to acoustic outlet 20.

[0045] • A peripheral channel 26 surrounds the outside of the phase plug assembly 18, starting from the boundary surface 24 of the phase plug 18 facing the compression chamber 16.

[0046] • Channels (28-36) rotate around the central axis 22 of phase plug 18 to ensure that the path length at acoustic outlet 20 is substantially equal to the length of the surrounding channels 26.

[0047] • The acoustic impedance of all channels (26-36) is controlled by selecting the area expansion rate of the phase plug assembly 18 from the compression chamber 16 to the outlet 20.

[0048] • The acoustic outlet 20 is circular, which is a common construction for compression drives.

[0049] • By changing the path length of the internal channels (28-36) relative to the peripheral channels 26, the shape of the acoustic wavefront at the outlet 20 can be defined as a plane wave or a wavefront with some curvature.

[0050] This embodiment is manufactured using conventional injection molding technology, rather than other near-net-shape forming technologies. To enable the molding process, this embodiment has internal channels (28-36) of equal length symmetrically distributed around a rotation axis 22. Due to these geometric choices, the internal mold sliding assembly used to generate the rotating channels (28-36) can be pulled out and rotated out of the mold in a corkscrew manner.

[0051] The embodiments described herein provide six channels (26-36) from the opposite face of the diaphragm 14 to the acoustic outlet 20. The outermost channel 26 is rotationally symmetrical about the axis 22 of the phase plug and the diaphragm. The five inner channels (28-36) take the form of an enlarged cross-sectional area rotating about the axis 22 of the phase plug in a spiral manner. In this embodiment, all five inner channels (28-36) rotate in the same manner and are distributed in a rotationally symmetrical manner about the axis of rotation 22.

[0052] Figure 3 This is an exploded view showing how the nested components (38, 40, 42) are assembled to form the phase plug assembly 18 and its channels (26-36). The inner wall 44 of the outermost component 38 forms... Figure 2 The outer wall boundary of the peripheral channel 26. Similarly, the inner wall 46 of the intermediate component 40 forms the outer wall boundary of the five internal rotating channels (28-36). Finally, the inner wall boundaries of the five channels (28-36) are defined by the outer surface 48 of the third nested component 42. The components (38, 40, 42) are concentrically assembled to form Figure 1 The entire phase plug assembly 18 is produced using conventional molding techniques. The result is a phase plug with a complex internal geometry.

[0053] The outermost component 38 is an annular member, and its shape and size are configured to accommodate the intermediate component 40 within the outermost component 38. The intermediate component 40 is a truncated conical element, and when the intermediate component 40 is disposed within the outermost component 38, its outer surface, together with the inner wall 44 of the outermost component 38, defines an internal channel 26. The intermediate component 40 has multiple openings at its narrow end of the truncated cone. The intermediate component 40 has a hollow interior that opens at the wider end of the truncated cone and is defined by an inner wall 46, wherein the hollow interior is configured to accommodate a third nested component 42. The inner wall 46 includes multiple channels leading to the hollow interior, and when the third nested component 42 is disposed within the hollow interior of the intermediate component 40, these channels, together with the outer surface 48 of the third nested component 42, form a spiraling internal channel 28-36. The multiple channels extend to the openings at the narrow end of the intermediate component 40 such that the internal channel 28-36 formed by the inserted third nested component 42 also extends to the openings. The third nesting member 42 is a solid element in the shape of a truncated cone, which is received within the hollow interior of the intermediate member 40 by friction fit and / or fixed by adhesive. The third nesting member 42 may include a mating portion at its narrow end to facilitate connection to the intermediate member 40 at a corresponding mating portion located within the hollow interior of the intermediate member 40. For example, in Figures 1-2 This engagement between the third nested component 42 and the intermediate component 40 can be seen in the image.

[0054] Although the components in the phase plug 18 and diaphragm 14 of this embodiment are rotationally symmetric about a common axis 22, this embodiment should not be construed as preventing deviations from a design that is rotationally symmetric to each other, nor should it prevent coincident axes of rotation. Deviations in alignment and symmetry are useful for distributing or damping modal behavior within the compression chamber 16 or phase plug 18. Furthermore, although the path lengths and acoustic impedances of the internal channels in this embodiment are matched for each channel (26-36), this should not be construed as preventing deviations from these matched choices. Additionally, by example, the disclosed embodiment includes five internal channels (28-36) having equal path lengths, volumes, and enlarged geometries. Other embodiments may include more or fewer than five internal channels. Furthermore, path lengths, volumes, and / or geometries may vary depending on the internal channels.

[0055] Various embodiments of the invention have been described herein with reference to the accompanying drawings. Alternative embodiments may be designed without departing from the scope of the invention. It should be noted that various connections and positional relationships (e.g., above, below, adjacent, etc.) are illustrated between the elements in the specification and drawings. Unless otherwise stated, these connections and / or positional relationships may be direct or indirect, and the invention is not intended to be limited in this respect. Thus, coupling of entities can refer to direct or indirect coupling, and positional relationships between entities can be direct or indirect positional relationships.

[0056] The term "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or superior to other embodiments or designs. The terms "at least one" and "one or more" are understood to include any integer greater than or equal to 1, i.e., 1, 2, 3, 4, etc. The term "multiple" is understood to include any integer greater than or equal to 2, i.e., 2, 3, 4, 5, etc. Terms such as "connected to" and "attached to" can include both indirect "connection" and direct "connection."

[0057] The description of various embodiments of the present invention is given for illustrative purposes and is not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles of the embodiments, their practical application, or technical improvements to technologies found in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

[0058] References

[0059] Reference 1: BHSmith, “An Investigation of the Air Chamber of Horn Type Loudspeakers”, Journal of the Acoustical Society of America, March 1953, Vol. 25, No. 2, pp. 305-312.

Claims

1. A phase plug for an electric compression drive, comprising: a. A compression chamber formed by a boundary surface adjacent to the dome-shaped oscillating diaphragm and phase plug assembly, the boundary surface having a shape complementary to the convex surface of the diaphragm; b. A single acoustic outlet, defined by the terminal of the phase plug assembly; c. Both the internal acoustic channel and the outermost acoustic channel originate from the inlet at the compression chamber, traverse the phase plug assembly, and reach their terminals at the acoustic outlet; and d. A rotation axis, defined within the interior of the phase plug assembly, extends from the boundary surface of the phase plug assembly located in the compression chamber to the acoustic outlet; e. Wherein the inner acoustic channel and the outermost acoustic channel, while traversing the phase plug, increase in cross-sectional area between their respective inlets at the boundary surface of the phase plug assembly and their terminals at the acoustic outlet; and f. wherein the internal acoustic channel is rotationally symmetrical about the axis of rotation in a manner that is spiral, conical, or helical relative to the axis of rotation; g. wherein the outermost acoustic channel is rotationally symmetrical about the axis of rotation and radially disposed outside the inner acoustic channel; h. Each of the inner acoustic channels, defined by the total distance of the path along the channel from the boundary surface of the phase plug to the acoustic outlet, has a length equal to that of the outermost acoustic channel; i. The entrances to the internal acoustic channel and the outermost acoustic channel are configured according to the mode of the compression chamber to reduce the resonance of the compression chamber; j. The acoustic impedance formed at the ends of the inner acoustic channel and the outermost acoustic channel is controlled by selecting the expansion rate of the cross-sectional area of ​​the inner acoustic channel and the outermost acoustic channel; and k. The phase plug is axially symmetrical with respect to the axis of rotation.

2. The phase plug according to claim 1, wherein, The phase plug assembly includes an outermost component with an inner wall, an intermediate component with an outer surface and a hollow interior, and a third nested component with an outer surface, wherein a channel is formed on the inner wall of the hollow interior.

3. The phase plug according to claim 2, wherein, The intermediate component is housed within the outermost component to define the outermost acoustic channel between the inner wall of the outermost component and the outer surface of the intermediate component.

4. The phase plug according to claim 3, wherein, The third nested component is housed within the hollow interior of the intermediate component to define one or more internal acoustic channels between the outer surface of the third nested component and the channel of the inner wall of the hollow interior of the intermediate component.

5. The phase plug according to claim 1, wherein, The internal acoustic channel includes multiple channels.

6. The phase plug according to claim 5, wherein, The multiple channels include five channels.

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