Compression driver

Abstract

To provide a compression driver that produces a desirable response.SOLUTION: A compression driver comprises a diaphragm, a phase plug, and a magnet. The diaphragm is connected to a voice coil former 13' along a line 33 forming a closed loop and existing on a plane. The diaphragm and the voice coil former are adapted to reciprocate along an axis. The diaphragm, phase plug, voice coil former are configured to form a compression cavity 9', a surround cavity 11', and a magnet cavity 21'. An abstract surface can be generated by rotating about the axis an abstract line extending from the diaphragm on the line of the closed loop to a convex surface of the phase plug perpendicularly thereto. A plurality of holes 25' are formed in the voice coil former around at least a part of its circumference to connect the compression cavity with the surround cavity. The total area of the holes is substantially the same as the area of the abstract surface.SELECTED DRAWING: Figure 2c

Description

Technical Field

[0001] The present invention relates to the field of compression drivers, and more particularly to a voice coil former of a compression driver and a compression driver incorporating such a voice coil former.

Background Art

[0002] A compression driver is a type of diaphragm loudspeaker that generates sound in a horn loudspeaker. The compression driver is attached to the throat of an acoustic horn. A compression driver generally includes a diaphragm connected to a voice coil driver, and the voice coil driver is placed in a magnetic field usually provided by one or more permanent magnets. When an electric current of an acoustic signal flows through the voice coil, a force is induced, causing the voice coil driver to reciprocate between the poles of the magnet, and the diaphragm vibrates to radiate acoustic waves. The voice coil driver usually includes a voice coil former around which a conductive wire is wound, and the former and the wire coil form an integral article that vibrates integrally. The voice coil former is usually (but not always) cylindrical. The area of the loudspeaker diaphragm is usually significantly larger than the throat aperture of the horn so that the compression driver can provide a high sound pressure. The horn-loaded compression driver is very efficient and has an efficiency about 10 times that of a direct-radiating cone-type loudspeaker. This is used as a midrange and high-frequency tweeter driver in high-power sound reinforcement loudspeakers, as well as in the reflex loudspeakers or folded horn loudspeakers of megaphones and public address systems.

[0003] Compression drivers often use a phase plug that collects the sound radiated by the sound-radiating side of the diaphragm. One common configuration is to use an axially symmetrically curved diaphragm, such as a segment of a sphere, with a phase plug configured to fit the sound-radiating side of the diaphragm (the spherical diaphragm can be adapted to radiate from either its convex or concave surface. In this case, the surface of the phase plug becomes the spherical concave or convex surface respectively). The phase plug usually has a plurality of channels through which the sound radiated by the diaphragm is collected and guided to the horn. Due to the simple spherical geometry, these channels are allowed to be of equal length.

[0004] FIG. 1 shows a partial cross-sectional view of a conventional compression driver 1 to illustrate some of the features related to the present invention. The diaphragm 3 is shaped as part of a sphere and is adapted to radiate sound from its concave surface (downward in the drawing, i.e., in the direction of arrow A). The phase plug 5 has a convex spherical surface adjacent to the diaphragm 3 and channels 7 that penetrate the phase plug 5 to direct sound downward toward a horn (not shown). There is a compression cavity 9 between the surface of the diaphragm 3 and the phase plug 5. The ambient cavity 11 is defined by the outside of the voice coil former 13, the inside of the magnet 15, and the lower side of the outer edge of the diaphragm outside the voice coil former 13. At the top of the magnet 15, there is a magnetic gap 17 between the magnet 15 and the outer surface of the voice coil former 13 (in a different part of the voice coil former 13 around which the voice coil is wound, not shown in FIG. 1 for clarity but shown as reference number 23 in FIGS. 2b, 2c, 4a, and 4b). This opens into a former cavity 19 that extends downward between the outside of the voice coil former 13 and the magnet 15 and leads to the magnet cavity 21.

[0005] In a loudspeaker, ferromagnetic fluid is often used to effectively dissipate heat from the voice coil, resulting in an extended lifespan of the tweeter. By using ferromagnetic fluid in the magnetic gap between the magnet and the voice coil former, a seal is formed that prevents sound from passing through the magnetic gap. This seal typically results in a compression cavity in the form of a spherical cap with a thickness of approximately 0.4 mm between the diaphragm and the phase plug. Sound is radiated into the compression cavity due to the axial movement of the diaphragm and exits the cavity through the channels, which are often annular, in the phase plug. The plurality of channels load the cavity by an amount corresponding to their area, and each channel excites a radial mode in the compression cavity according to its diameter and area. By selecting the correct area and diameter for each channel, it is permissible to bring the total mode excitation closer to zero. The method of achieving this is described in our Patent Document 1.

[0006] Not all compression drivers use ferromagnetic fluid. In these compression drivers, the compression cavity is also loaded by a narrow channel (i.e., former cavity 19 in FIG. 1) within the magnetic gap between the voice coil and the magnetic pole. The acoustic impedance of the voice coil gap and the former cavity becomes highly irregular due to the air volume in the magnet cavity and the surrounding cavity, resulting in significant Helmholtz-type resonances. Additionally, the surrounding area radiates additional sound through the magnetic gap. Both effects lead to frequency-dependent mode excitation, rendering ineffective the method of minimizing mode excitation. Non-Patent Document 1 concludes that it is impossible to balance, and thus minimize, mode excitation for drivers where the voice coil cavity is at the outer diameter of the compression cavity.

[0007] The sound radiated from the concave side of the diaphragm in the compression cavity exits through the phase plug channel that leads to the outlet where the short flare and horn are connected. However, since the gap between the center pole and the inner diameter of the voice coil acts as an additional outlet, the possibility of suppressing resonance by balancing cavity mode excitation is eliminated (Non-Patent Document 1). The acoustic mass formed by the magnet cavity, the surrounding cavity, and the narrow gap between the coil and the pole coil causes several resonances. Even more complicated, the surrounding radiates to the cavity behind it, and the sound is transmitted through the acoustic filter formed by the mass and compliance. Irregular input to the compression cavity further exacerbates the irregularity of the response.

[0008] Conventional design approaches require sealing the former to contain sound in the compression cavity. This inevitably applies to compression drivers that radiate from the concave side of the diaphragm to which the voice coil is attached.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Non-Patent Documents

[0010]

Non-Patent Document 1

Summary of the Invention

[0011] The present invention is derived from the recognition that advantageous results can be obtained by adopting an alternative approach to the conventional design of compression drivers. That is, the present invention provides a compression driver for connection to the throat of an acoustic horn. The compression driver includes a diaphragm having a concave sound-radiating surface, a phase plug having a convex surface shaped to complementarily match the concave surface of the diaphragm, and a magnet. The diaphragm forms a closed loop and is connected to a voice coil former along a line that lies in a plane. The diaphragm and the former are adapted to reciprocate along an axis. The diaphragm, the phase plug, and the voice coil former together form a compression cavity between the concave surface of the diaphragm and the convex surface of the phase plug, a peripheral cavity defined by the outer surface of the voice coil former, the inner surface of the magnet, and the edge side of the diaphragm outside the voice coil former, and a magnetic gap orthogonal to the axis between the outer and inner portions of the magnet adjacent to the diaphragm. The voice coil former reciprocates through the magnetic gap, and the magnetic gap opens into a voice coil former cavity that extends along the axis away from the magnetic gap. The voice coil former cavity has an outer portion that extends between the outside of the voice coil former and the magnet and an inner portion that extends between the inside of the voice coil former and the phase plug. The voice coil former cavity communicates from the magnetic gap to the magnet cavity. An abstract surface is generated by rotating an abstract line that extends from the diaphragm on the line of the closed loop to the convex surface of the phase plug perpendicular thereto about the axis. A plurality of holes are formed in the voice coil former around at least a part of its circumference to connect the compression cavity to the peripheral cavity and penetrate the voice coil former, and the total area of the plurality of holes is substantially not less than the area of the abstract surface.

[0012] In the case of a circular, curved diaphragm, it will be understood that the abstract surface is conical (i.e., in the shape of a frustum of a cone), and the term "perpendicular thereto" means perpendicular to both curved surfaces when these are complementary shapes. However, if these two surfaces are not exactly the same shape at the junction of the diaphragm and the former, this term means perpendicular only to the convex surface of the phase plug.

[0013] By introducing holes or perforations through the voice coil former with an area similar to that of the cavity cross-section adjacent to the diaphragm, the compression cavity can be expanded, the path through the magnet gap can be bypassed with low impedance, and the excitation of the gap can be significantly reduced. Depending on the shape of the surrounding cavity and the ratio of the surrounding width to the cavity width, it is possible here to suppress the modes in the expanded cavity. The surrounding portion of this expanded cavity adjacent to the coil needs to have a spacing similar to the diaphragm-phase plug spacing. The axial distance between the diaphragm and the phase plug needs to be equal to the displacement of the diaphragm by a nominal displacement amount from the phase plug. The expanded cavity is preferably thinned from this thickness adjacent to the former to a thickness as close to zero as practicable in order to minimize the excitation of the cavity modes. The total area of the holes is preferably the same as the area of the magnetic gap, but the total area of the holes may be 5%, 10%, or 15% larger or smaller than the area of the magnetic gap without significantly affecting the performance.

[0014] As described above, the length of the surrounding cavity in the axial direction may be substantially the same as the length of the compression cavity in the axial direction, but the length of the surrounding cavity may be 5%, 10%, or 15% larger or smaller than the length of the compression cavity.

[0015] Preferably, the length of the peripheral cavity in the axial direction decreases as the peripheral cavity extends outward in a direction orthogonal to the axis from the voice coil former. This minimizes the excitation of the cavity mode.

[0016] The plurality of holes may extend axially by a distance sufficient for at least some of the holes to fit within the voice coil cavity. By extending these holes a short distance into the voice coil gap, it is permissible to achieve an ideal area that causes the compression cavity and the peripheral cavity to behave as one cavity. The peripheral cavity must be narrow enough to allow all the holes to be within the voice coil cavity when the voice coil former reciprocates.

[0017] A hollow channel may be provided such that the magnet cavity communicates directly with the throat of the horn. For example, by closing the magnet cavity and adding a plurality of holes to allow sound to be transmitted through the gap to the throat, the magnet gap becomes another exit channel for the sound. In this case, it is preferable to match the flare rate of the other channel of the phase plug. This approach is similar to the use of the gap as a phase correction channel in U.S. Patent No. 5,117,462, but has the advantage that it can pass the iron material of the driver rather than air in the channel extending from the magnetic gap.

[0018] The channel may have an inlet disposed in the compression cavity and an outlet disposed in the throat of the horn, and the inlet is located at a node point of a selected mode in the compression cavity. The compression driver may further include a molding that can be disposed within the peripheral cavity. This molding is effective in modifying the axial range of the peripheral cavity adjacent to the magnetic gap and / or in changing the radial area of the peripheral cavity to decrease in the outward direction.

[0019] The present invention may be combined with the features described in UK Patent Application Publication No. _______, our co-pending patent application, which gives axial mechanical compliance to a voice coil driver as a means of adapting the frequency response of a loudspeaker. In a compression driver, a vibrating diaphragm is attached to a voice coil driver, which is normally placed in a magnetic field obtained by one or more permanent magnets. By passing an alternating current through the voice coil, a force is induced, causing the voice coil driver to move back and forth, the diaphragm to vibrate, and acoustic waves to be radiated. The voice coil driver includes a voice coil former around which a conductive wire is wound, the former and the wire coil forming an integral article that vibrates as a unit. The voice coil former is usually (but not always) cylindrical. In applications where mass is important and space is limited, the voice coil former is made of materials such as titanium or Nomex® (Nomex is a trademark of DuPont Safety & Construction, Inc., of Delaware, USA). A titanium voice coil former is usually formed from a flat strip of material that is rolled into a cylinder. Normally, the axial ends of the rolled strip are not joined, leaving an axial thin gap extending along the length of the voice coil former, and the circumferential forces across this gap cannot be balanced by symmetry. As a result, the "hoop" stiffness acting on the circumferential forces due to axial symmetry is significantly reduced near the gap in the former.

[0020] Our co-pending UK Patent Application Publication No. _______ discloses a configuration for introducing mechanical axial compliance into a voice coil former, which is particularly (but not exclusively) for loudspeakers where mass is critical and / or space is limited, and is relatively simple, easy to manufacture and easily "tunable". This describes a voice coil former formed by a roll, considering a voice coil former having a narrow axial gap extending along the length of the voice coil former, which is a mechanically axially compliant configuration that is relatively easy to tune. A compression driver typically provided with a 6 dB / octave low-pass filter at 2 to 3 kHz by mass can benefit from introducing resonance. In many cases, the output level at the upper part of the response is lower than desired, and introducing resonance by making the former axially compliant results in a desirable response.

[0021] A relatively simple mechanical compliance configuration can be obtained by utilizing the effect of a cantilever that is relatively easily calculated, and by using a cantilever of a predetermined configuration, a voice coil driver can be formed in which the overall performance is significantly improved compared to a conventional system.

[0022] A voice coil former for a compression driver may have a row of at least two axially spaced holes that extend circumferentially about an axis or at least partially circumferentially. By rotating adjacent rows relative to each other, adjacent holes overlap circumferentially, and an arcuate spar disposed circumferentially about the voice coil former is formed between the holes. Each arcuate spar is adapted to flex axially in a cantilever fashion in response to the voice coil former being driven axially to permit a change in the axial length of the voice coil former. The overlap of adjacent holes in adjacent rows can be such that the length of the arcuate spar is at least 25% of the circumferential length of the adjacent holes. One or more of these at least two rows of holes may include or be added to holes that penetrate a voice coil former having an area similar to an abstract surface. In addition to the holes that penetrate a voice coil former having an area similar to an abstract surface, if there are one or more rows of holes, these one or more rows of holes are preferably axially disposed within the voice coil cavity.

[0023] The arcuate spar forms a structural link that transmits force between the portion of the former around which the voice coil is wound and the portion of the former attached to the diaphragm. The spar flexes like a spring, and the resulting restoring force upon deflection causes the configuration to behave as a spring linking the coil and the diaphragm, similar to a corrugation in the former. Aligning the spar circumferentially increases the flexibility compared to an axial spar.

[0024] The spurs are manufactured by creating a plurality of perforations in the former. This is by removing material from the former. A portion of the former is linked to another portion of the former joined to the diaphragm via a circumferential array of deflecting spurs. By varying the length, axial depth, position, orientation, or number of the spurs, the axial compliance can vary over a wide range, allowing the desired axial compliance to be achieved. The length of the spur may be 30%, 35%, or 40% of the circumferential length of the adjacent hole. The longer the spur, the more it can bend under a given axial load and the more compliance can be introduced into the voice coil former. The overlap should be less than 50%. Otherwise, consecutive slots will merge with each other and create a clean cut in the former. It is preferred that the maximum overlap is 40% so that the circumferential dimension of the axial extending portion between adjacent holes is sufficiently rigid. Depending on the type of material to be removed, the manufacturing method can be press tool forming, laser cutting, precision photoetching, high-precision microjet water cutting, plasma cutting, or micro milling. Further, these spurs can be varied (e.g., in position, size, shape, or orientation) to easily compensate for various circumferential effects resulting from the axial gap in which the former is formed by the roll and / or to vary the axial rigidity at different points around the former. Generally, the longer the spur, the larger the manufacturing tolerance to achieve an acceptable variation in responsiveness. This allows for the economical manufacture of the voice coil former.

[0025] The holes / perforations may extend circumferentially, or at least a portion thereof may extend circumferentially, or may have a portion with at least a circumferential orientation component about the axis, and arcuate spurs are formed along at least a portion of each hole. In this case, a row of holes provides spurs that give the required axial compliance to the former. The circumferential row of holes extending about the axis may be one, two, or any number, and the holes are oriented and / or shaped to form arcuate spurs adapted to flex in a cantilever fashion.

[0026] There are two circumferential rows of holes extending about the axis and axially spaced apart such that the voice coil former forms arcuate spurs between adjacent rows of holes. A configuration with such two rows of holes is easy to manufacture and provides spurs that give a given axial mechanical compliance that can be calculated relatively easily using finite element method (FEM) analysis. Also, this arrangement is most easily tuned to accommodate non-axisymmetry (the presence of an axial gap) or to give an axial compliance that is itself non-axisymmetric.

[0027] A plurality of holes axially disposed between the compression cavity and the surrounding cavity may provide air venting. Here, at least some of the plurality of holes or perforations are axially disposed within the voice coil cavity, and at least some of these may be filled with either a sound-absorbing damping material that attenuates the air flow through the perforations or a material more flexible than the material of which the voice coil bobbin is made, and / or, depending on the particular application, at least some of the plurality of perforations may be covered with a flexible material that does not allow air to pass through (and is more flexible than the material of which the voice coil former is made).

[0028] The plurality of holes may be substantially the same shape, which ensures that all the spurs are similar, simplifies manufacturing, and makes the calculation of the axial compliance effect of the spurs relatively easy. Alternatively, the holes may be of different shapes. This can be useful for tuning the axial compliance in the circumferential direction and / or for distinguishing between holes that allow air flow and acoustic communication between the compression cavity and the surrounding cavity and holes that may or may not allow air flow and acoustic communication between the outer and inner portions of the voice coil former cavity within the voice coil cavity.

[0029] The plurality of holes may be substantially the same size, which ensures that all the spurs are similar, simplifies manufacturing, and makes the calculation of the axial compliance effect of the spurs relatively easy. Alternatively, the plurality of holes may be of different sizes and / or different circumferential lengths, which can be useful for tuning the axial compliance in the circumferential direction.

[0030] The plurality of holes may be circumferentially spaced apart by substantially the same distance in the circumferential direction and / or axially spaced apart, which ensures that all the spurs are similar, simplifies manufacturing, and makes the calculation of the axial compliance effect of the spurs relatively easy. Alternatively, the plurality of holes may be spaced apart by different distances, which can be useful for tuning the axial compliance in the circumferential direction.

[0031] The plurality of holes may be similarly oriented, which ensures that all the spurs are similar, simplifies manufacturing, and makes the calculation of the axial compliance effect of the spurs relatively easy. Alternatively, the plurality of holes may be of different orientations, which can be useful for adjusting the axial compliance in the circumferential direction.

Brief Description of the Drawings

[0032] The present invention will now be described by way of example with reference to the following accompanying drawings.

[0033]

Figure 1

Figure 2a

Figure 2b

Figure 2c

Figure 2d

Figure 3

Figure 4a

Figure 4b

Figure 4c

Figure 5a

Figure 5b

Figure 6a

Figure 6b

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0034] The configuration of the prior art shown in FIG. 1 is as described above.

[0035] FIG. 2a shows an embodiment of a compression driver 1' according to the present invention, which has a spherical curved diaphragm 3' driven by a cylindrical voice coil former 13' having a plurality of holes 25' arranged around its circumference. The diaphragm 3' is adapted to radiate acoustic waves in the direction of arrow A from its concave surface towards a horn (not shown) in a conventional manner.

[0036] Figures 2b and 2c show only one physical entity. That is, a part of the voice coil former 13' from FIG. 1 is shown together with the hole 25' passing through it and a part of the voice coil 23. In FIG. 2c, only a schematic of these physical features is shown. The other features shown in FIGS. 2b and 2c are mainly volumes or acoustic paths that allow the passage of acoustic waves and are defined by a plurality of physical components of the compression driver. These physical components have been omitted from FIG. 2b for the purpose of clearly explaining the present invention (these physical components are the diaphragm, phase plug, and magnet shown in FIG. 1). These hollow volumes are the compression cavity 9', the ambient cavity 11', the voice coil cavity 19', and the magnet cavity 21'. The hole 25' is arranged so as to allow the ambient cavity 11' and the compression cavity 9' to freely communicate when the compression cavity 9' is at its maximum volume (that is, when the diaphragm is at its maximum positive extension and the voice coil former 13' is displaced maximally upward in the drawing).

[0037] Referring now to FIG. 2c, the dotted line 33 indicates the shortest distance between the diaphragm and the phase plug on the radial line 31 (to be described later in relation to FIG. 2d). In the case of the spherical curved diaphragm and phase plug of FIG. 2a, the line 33 is perpendicular to both the concave sound radiating surface of the former and the convex surface of the other. When the line 33 is rotated 360° about the axis A of the compression driver, an abstract conical surface in the form of a frustum of a cone is generated. The total area of all the holes 25' in the voice coil former 13' is substantially the same as the area of the abstract conical surface (that is, the curved surface of the frustum of a cone). This configuration effectively expands the compression cavity by providing an alternative acoustic path (through the holes in the voice coil former and the voice coil cavity to the magnet cavity). Thereby, the acoustic excitation in the gap is significantly reduced.

[0038] Figure 2d shows the compression driver diaphragm 3’ and the voice coil former 13’ of Figure 2a. The voice coil former 13’ is similar to the diaphragm assembly disclosed in our European Patent No. 2952014 / US Patent No. 9467782, except for the holes 25’ (detailed below with reference to Figures 5a and 5b). The diaphragm 3’ has an inner spherical portion 27 and an outer annular portion 29, and the transition between the spherical portion and the annular portion is indicated by a radial line 31 (a circle in the illustrated configuration). The diaphragm 3’ and the voice coil former 13’ are manufactured separately and joined together on the concave side of the diaphragm along the line of the radial line 31 to form an integral article or an integrally molded product. A conductive voice coil 23 (only part shown) is wound around the outer peripheral surface of the voice coil former. There are a plurality of holes 25’ extending circumferentially around the voice coil former 13’ between the voice coil 23 and the radial line 31.

[0039] Figure 3 shows a compression driver 1’ having a different diaphragm assembly 3”. Here, the two rows of slot-shaped holes 25’ in the voice coil former 3’ of Figure 2d are replaced by a single row of circular holes 25” in the former 13”. Also in this case, the total area of all the holes is the same as the area of the abstract conical surface. Different from the holes in Figures 2a, 2b, 2c, and 2d, the holes in Figure 3 do not provide axial mechanical compliance (compression and extension). Axial compliance will be described later with reference to Figures 5a and 5b.

[0040] Figures 4a and 4b are views of a compression driver 1” that differs from Figure 2a in two respects. First, a plurality of channels 37 are provided that pass through the phase plug 5 from the inlet 41 to the outlet 43 such that the magnet cavity 21” communicates directly with the throat T of the phase plug 5. Second, a molding 39 (see Figures 4b and 4c) is provided to fit within the ambient cavity (11 in Figure 1, 11’ in Figure 2c). The molding 39 forms a cavity that is an extension of the voice coil cavity 19”. The magnet cavity 21” is still shown in the drawing but is here isolated from the acoustic path. Figure 4c shows only two physical things. That is, a portion of the voice coil former 13’ from Figure 2a is shown together with the hole 25’ passing through it, a portion of the voice coil 23, and the molding 39. In Figure 4c, these physical features are shown only schematically. The other features shown in Figure 4c are mainly volumes or acoustic paths that allow the passage of acoustic waves and are defined by the plurality of physical components of the compression driver. These physical components have been omitted from Figure 2b to clearly illustrate these two aspects of the invention (these physical components are the diaphragm, phase plug, and magnet shown in Figure 1).

[0041] By adding Channel 37, it is allowed that sound is transmitted through the magnetic gap 17", and the magnetic gap 17" becomes another acoustic outlet channel. It is preferable to match the flare rate of the path through the channel with the flare rate of the other phase plug channels 7". This means that the volume and / or shape of the magnet cavity 21", as well as the volume of Channel 37, are adjusted to match the flare rate of the flow path through all of the other phase plug channels 7" (as can be seen from the drawings, the magnet cavity 21" in Figure 4c is made shorter axially than the magnet cavity in Figure 2a and is shaped such that the area decreases towards the inlet 41 to each channel). In this case, the acoustic wave generated by the diaphragm travels so as to descend through both parts of the voice coil former cavity 19" (the outer part extending between the outside of the voice coil former 13' and the magnet 15, and the inner part extending between the inside of the voice coil former 13' and the phase plug 5). In practice, the radius of the inner part of the voice coil ranges from about 0.15 mm to about 0.25 mm, and the radius of the outer part of the voice coil cavity ranges from about 0.25 mm to about 0.35 mm. This approach is similar to the use of the gap as a phase correction channel in U.S. Patent No. 5,117,462, but has the advantages of allowing the magnetic flux to pass through iron rather than air in the channel extending from the magnetic gap, and allowing the compression driver to emit an increased amount of HF acoustic energy. The channel outlet 43 may be arranged on the node or alternately on both axial sides of the node to allow a simple modal balance, and may also be made larger or smaller according to the requirements of the application (such that the channel tapers).

[0042] The molding 39 has two distinct functions that can be incorporated in combination or separately in all embodiments. That is, making the axial length of the peripheral cavity (11 in FIG. 1) adjacent to the magnetic gap (17 in FIG. 1) the same length as the radius of the magnetic gap, and reducing the peripheral cavity in a gentle tapered shape to provide uniform excitation of the acoustic pressure across the diaphragm surface. In some applications, the magnet cavity may be the same as the area of the voice coil cavity.

[0043] FIG. 5a shows a voice coil former 2a similar to that of FIGS. 2a - 2c in that it has two rows 4a, 4b of axially spaced holes 6. Each hole 6 has the shape of a slot formed by two semi - circles joined by a straight edge, and the straight edge extends circumferentially. In this example, the former is made of titanium with a thickness of 0.025 mm, rolled into a cylindrical shape with an approximate diameter of 34 mm, and there are 28 holes / slots in each row. Each slot is approximately 2.2 mm long, 0.2 mm wide, with a radius of 0.1 mm at each end, and is approximately 1.1 mm spaced from the next slot in the row. As clearly shown in FIG. 4b, there is an axially extending portion 8 between adjacent holes 6 in each row, and the rows 4a, 4b rotate relative to each other such that each axially extending portion 8 aligns with the center of the nearest slot. This forms circumferentially extending spurs 10 on both sides of each axially extending portion 8 between the ends of the slots in the two overlapping rows (multiple spurs 10 are also shown in FIG. 5a in a darker shading. However, these do not show the spurs that extend to the rounded ends of the holes in the actual case shown in FIG. 5b for the sake of clarity). Since each spur is formed on the surface of the cylinder, it is arc - shaped. In the illustrated embodiment, there are a total of 56 circumferential spurs (2 spurs per slot). Each spur has a circumferential length of 0.7 mm and an axial depth (i.e., the axial distance between the two rows 4a, 4b (the vertical direction in the drawing)) of 0.3 mm. The overlap (i.e., the length of each circumferentially extending arc - shaped spur) is, in this case, approximately 27% of the circumferential length of each hole. By varying the size of the plurality of slots, their circumferential spacing, and / or the distance between rows, it is possible to vary the axial compliance of this configuration to suit specific requirements / applications. This axial compliance can be calculated relatively easily.

[0044] Figure 6a is similar to that of Figure 5a, but shows an enlarged portion of the former 2a with holes of different shapes. If the sides of the perforations adjacent to the spurs are maintained constant / linear, the shape of the holes has little effect on the rigidity of the spurs. In this example, the "D"-shaped perforations exhibit almost exactly the same behavior as the race-track shaped holes of Figures 4a and 4b. Adjacent holes in adjacent rows overlap such that the length of the arcuate spur is approximately about 27% of the circumferential length of the adjacent holes. The holes may be of any shape (e.g., semi-circular, semi-ovoid, semi-elliptical) as long as the shape of the perforation edges forming the circumferential spurs remains substantially constant / linear.

[0045] Figure 6b shows a part of another voice coil former 2'. This is similar to that of Figure 5b, but has holes of the same size and shape in three rows 4a, 4b, 4c, with a greater degree of circumferential overlap between the holes in adjacent rows (and a longer circumferentially extending arcuate spur), which is approximately 33% of the circumferential length of the holes. This results in a greater axial compliance in the voice coil former than in the configuration of Figure 5.

[0046] FIG. 7 is an enlarged view of a part of the voice coil former of FIG. 1 (wherein, here, the overlap between the perforations is such that the length of the arcuate spurs is approximately 25% of the circumferential length of the adjacent perforations), and this time shows the axial gap 12 extending along the former. By ensuring that the gap 12 is present between the slots and preferably equidistant, and bisecting the axial extension 8 of one of the multiple rows 4a and the slots 6' of the other of the multiple rows 4b, a former with deflected spurs can be designed such that there is little variation in the local axial rigidity around the circumference of the former. If necessary, the length and thickness of the spurs adjacent to the gap of the former may be adjusted to correct for the reduction in rigidity due to the change in the geometric shape.

[0047] In FIG. 8, the improved response below 1.7 kHz is due to the modified cavity, and the improved response above 5 kHz is due to the flexible former design shown in FIGS. 4 and the patent application. In this example, the phase plug has not been modified from the original design and the surrounding cavity ring has not been used. By reducing the volume of the surrounding cavity and adjusting the position and area of the phase plug channels to minimize the mode excitation of the compression cavity, the response is further improved.

[0048] Of course, it should be understood that many variations can be made to the above-described embodiments without departing from the scope of the present invention. For example, although the present invention is described herein mainly with reference to a cylindrical voice coil (in the form of a substantially planar ring having a central hole), the present invention is equally applicable to non-circular configurations such as voice coils having an oval, elliptical, or racetrack shape (figure-eight, or rounded-corner triangle / square / polygon), or to any shape having a central hole that is symmetric in one or two orthogonal directions existing in a general plane perpendicular to the voice coil axis. It should be understood that in any such non-circular configuration, the shape of the abstract surface does not become the shape of a frustum. Although the diaphragm is described herein as spherical, the present invention is also applicable to curved non-spherical diaphragms such as elliptical, parabolic, or hyperbolic. In any of the illustrated embodiments, a damping material may be provided in some or all of the plurality of holes, and / or a flexible material that does not allow air to pass through may be provided to cover the inner or outer surface of any of the plurality of holes disposed within the voice coil cavity. All of the described embodiments of the voice coil former and / or diaphragm are of titanium, but may also be formed from thermosetting or polyimide composite materials. The holes connecting the compression cavity to the ambient cavity may be configured to provide a flexure arc-shaped spur that adds axial mechanical compliance (as in FIGS. 2, 4, 5, and 6), or may be configured only for connecting the compression cavity to the ambient cavity (as in FIG. 3). In the latter case, the only configuration of the described holes is a single row of circular holes shown in FIG. 3, but holes of different shapes (square, diamond, oval, elliptical, or racetrack shape (figure-eight, or rounded-corner triangle / square / polygon)) may be used, and / or these holes may be regularly arranged in one row, two rows, or more rows, and / or in a matrix and / or irregularly. However, if there is still a spur that can flex in the axial component to provide axial compliance, the spur may have side portions of any shape and / or may be inclined away from the circumferential direction.

[0049] If different variations or alternative configurations are described above, it should be understood that embodiments of the present invention can incorporate such variations and / or alternatives in any combination for different applications and can combine the features of different embodiments to form further embodiments. For example, the holes in each circumferential row may all include holes of the same size, shape, and orientation, and any of these features may vary within a row. Additionally or alternatively, the holes or perforations in a row may be regularly spaced or irregularly spaced, and in either case, the holes or perforations may be of the same length or different lengths. Any or all of these combinations may be similarly applied to voice coil formers having three or more rows of holes and / or perforations. The phase plug channels and moldings described with reference to FIG. 4c may be used separately in multiple embodiments of the present invention and need not be used in combination. If axial mechanical compliance is required, two or more rows of perforations providing a flexed arcuate spur such as in FIGS. 2, 4, 5, and 6 may be disposed within the voice coil cavity, while one, two, or more circumferential rows of holes penetrating the voice coil former may be provided to connect the compression cavity to the surrounding cavity. These holes may also be of the type of perforation (such as in FIGS. 2, 4, 5, and 6) that adds axial mechanical compliance, or may be of other types (such as in FIG. 3). Briefly, all of the variations described in this and the previous paragraph may be incorporated in any combination in any of the embodiments described in detail herein, and all possible combinations are not described for the sake of brevity, but these are all understandable to those skilled in the art.

[0050] Those skilled in the art will understand that, in this specification, when attributes, advantages, and / or applications are described in relation to only one embodiment, these attributes, advantages, and applications apply equally to other embodiments that share the same or similar features as the described one embodiment, even if not explicitly stated in this specification for reasons of brevity.

Claims

1. 1. A compression driver for connection to a throat of an acoustic horn, comprising: The compression driver includes a diaphragm having a concave sound radiating surface, a phase plug having a convex surface shaped to complement the concave surface of the diaphragm, and a magnet; the diaphragm is connected to a voice coil former along a line that lies in a plane forming a closed loop; the diaphragm and former are adapted to reciprocate along an axis; The diaphragm, phase plug, and voice coil former together form a compression cavity between the concave surface of the diaphragm and the convex surface of the phase plug; a peripheral cavity defined by an outer surface of the voice coil former, an inner surface of the magnet, and an edge side of the diaphragm outside the voice coil former; a magnetic gap perpendicular to the axis between an outer portion and an inner portion of the magnet adjacent the diaphragm; configured to form the voice coil former reciprocates through the magnetic gap, the magnetic gap opening into a voice coil former cavity extending along the axis away from the magnetic gap; the voice coil former cavity has an outer portion extending between an outer side of the voice coil former and the magnet, and an inner portion extending between an inner side of the voice coil former and the phase plug, The voice coil former cavity extends from the magnetic gap to the magnetic cavity; an abstract surface can be generated by rotating an abstract line extending from the diaphragm on the line of the closed loop to the convex surface of the phase plug perpendicular thereto, about the axis; a plurality of holes are formed in the voice coil former about at least a portion of its circumference and extend through the voice coil former to connect the compression cavity to the ambient cavity; A compression driver, wherein a total area of ​​the plurality of holes is substantially greater than or equal to an area of ​​the abstract surface.

2. The compression driver of claim 1 , wherein a length of the peripheral cavity in the axial direction is substantially the same as a length of the compression cavity in the axial direction.

3. 3. A compression driver as claimed in claim 1 or 2, wherein a length of the peripheral cavity in the axial direction decreases as the peripheral cavity extends outwardly from the voice coil former in a direction perpendicular to the axis.

4. 4. A compression driver as claimed in claim 1, 2 or 3, wherein the plurality of holes extend axially a sufficient distance such that at least a portion of the plurality of holes are contained within the voice coil cavity.

5. 5. A compression driver as claimed in claim 1, wherein a plurality of channels are provided such that the magnet cavity communicates directly with the throat of the horn.

6. 6. The compression driver of claim 5, wherein the channel has an inlet disposed in the compression cavity and an outlet disposed in the throat of the horn, the inlet being located at a nodal point of a selected mode in the compression cavity.

7. 7. A compression driver as claimed in any one of claims 1 to 6, further comprising a molding positionable within the peripheral cavity, the molding being effective to modify an axial extent of the peripheral cavity adjacent the magnetic gap and / or to vary a radial area of ​​the peripheral cavity decreasing in an outward direction.

8. 8. A voice coil former for a compression driver as claimed in any one of claims 1 to 7, wherein the voice coil former is configured to provide at least one row of arcuate spars arranged circumferentially around the voice coil bobbin, each arcuate spar adapted to flex axially in a cantilever manner in response to the voice coil bobbin being axially actuated to permit a change in the axial length of the voice coil bobbin.

9. 8. The voice coil former of claim 7, wherein at least two axially spaced rows of holes extending circumferentially or at least partially circumferentially about the axis are present, adjacent rows being rotated relative to one another such that adjacent holes overlap circumferentially to form arcuate spars circumferentially disposed about the voice coil former between the adjacent holes, each arcuate spar adapted to flex axially in a cantilever manner in response to the voice coil bobbin being axially actuated to permit a change in axial length of the voice coil former, and adjacent holes in adjacent rows overlap such that a length of the arcuate spar is at least 25% of a circumferential length of the adjacent holes.

10. 9. The voice coil former of claim 8, wherein the overlap between adjacent holes in adjacent rows is such that the length of the arcuate spar is at least 30%, or at least 35%, or at least 40% of the circumferential length of the adjacent holes.

11. 10. The voice coil former according to claim 7, wherein the plurality of holes are substantially the same shape.

12. 11. The voice coil former of claim 7, wherein the holes are substantially the same size.

13. 11. The voice coil former of claim 7, wherein the holes are spaced circumferentially and / or axially at substantially the same distance apart.

14. A compression driver comprising the voice coil former according to any one of claims 7 to 12.

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