Abstract
An electrodynamic compression driver is defined that contains a compression chamber assembly partially bounded by an annular diaphragm. The compression chamber assembly has an annular axisymmetric geometry with a single exit for acoustic radiation. The chamber geometry is further defined such that only the zero-hertz mode of acoustic coupling is supported, allowing the use of a lumped parameter model for analysis of the acoustic coupling of diaphragm and compression chamber. The lumped parameter model is integrated with eigenmode analysis of diaphragm modes and characterization of the cross-coupling between diaphragm and compression chamber. The result is more rapid computation of how to control mechanical modes in the annular diaphragm so that they benefit the compression driver's acoustic output. Embodiments of compression chamber and diaphragms with geometry that facilitate modal control are provided.
Claims
1. An annular, axisymmetric compression chamber comprising: an annular diaphragm; a compliance volume with a singular exit conduit having a perimeter that is partially bounded by the annular diaphragm; wherein the annular diaphragm is electromechanically actuated by a voice coil to produce acoustic vibrations; and wherein a geometry of the annular diaphragm is defined in such a manner as to intentionally exhibit mechanical modes within a frequency range of operation which acoustically couple primarily with a zero acoustic mode of the compression chamber.
2. The compression chamber of claim 1, wherein dimensions of the compression chamber are constrained to suppress acoustic modes of the chamber, other than mode zero, in the range of operating frequency.
3. The compression chamber of claim 1, wherein the annular diaphragm is composed of a material with a largely uniform thickness.
4. The compression chamber of claim 1, wherein the annular diaphragm has a parametrically defined geometric cross-section intended to create mechanical modes of desired amplitude, phase, and frequency distribution.
5. The compression chamber of claim 1, wherein the compression chamber is preferentially integrated within an electrodynamic loudspeaker driver assembly.
6. An annular, axisymmetric compression chamber, comprising: an annular diaphragm; and a compliance volume with singular exit conduit whose perimeter is partially bounded by the annular diaphragm; wherein the annular diaphragm is electromechanically actuated by a voice coil to produce acoustic vibrations; wherein a geometry of the annular diaphragm is defined in such a manner as to intentionally exhibit mechanical modes within a frequency range of operation which acoustically couple primarily with a zero acoustic mode of the compression chamber; and wherein a contribution of the mechanical modes to exit radiation is calculated using a lumped parameter model for both the compression chamber and for the diaphragm.
7. The compression chamber of claim 6, wherein dimensions of the chamber are constrained to suppress acoustic modes of the chamber, other than mode zero, in the range of operating frequency.
8. The compression chamber of claim 6, wherein amplitude, phase, and frequency distribution of the mechanical modes of the annular diaphragm are directly estimated without considering fluid mechanical effects of air contained within the compliance volume on the diaphragm.
9. The compression chamber of claim 6, wherein each mechanical diaphragm mode is analyzed for coupling to the zero acoustic mode of the compression chamber, in order to modulate exit radiation according to the lumped parameter model.
10. The compression chamber of claim 6, wherein mechanical diaphragm modes are analyzed for coupling to movement of the voice coil, in order to modulate exit radiation according to the lumped parameter model.
11. The compression chamber of claim 6, wherein the annular diaphragm is composed of a material with a largely uniform thickness.
12. The compression chamber of claim 6, wherein the annular diaphragm has a parametrically defined geometric cross-section intended to create mechanical modes of desired amplitude, phase, and frequency distribution, as determined from the lumped parameter model.
13. The compression chamber of claim 6, wherein the compression chamber is preferentially integrated within an electrodynamic loudspeaker driver assembly.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts, in which:
[0035] FIG. 1 is a dimetric projection of the cross-section of compression driver with the first and second annular compression chambers. The cross-section geometry of the second annular diaphragm in this assembly has been intentionally modified to create additional mechanical modes.
[0036] FIG. 2 is the same projection as FIG. 1, but with all additional features removed to focus on a single diaphragm, compression chamber, and voice coil.
[0037] FIG. 3 is a cross-section of only the diaphragm geometry shown in FIGS. 1 and 2.
[0038] FIG. 4 is a parameterization of a diaphragm defined symmetrically about the diaphragm peak, with features of the parameterization labeled to correspond with FIG. 3.
[0039] FIG. 5 is another diaphragm embodiment, in the manner of FIG. 3, showing a different configuration of geometric cross-section that results in different mechanical modes in the diaphragm.
DETAILED DESCRIPTION
[0040] FIG. 1 shows an overall electrodynamic transducer assembly, or compression driver 10. This exemplary embodiment contains two compression chamber sub-assemblies (16, 18) each bounded by an annular diaphragm assembly (20, 22). The two compression chambers share a central axis of rotation 12. The diaphragms (24, 26) of each compression chamber driven by an electrodynamic voice coil (28, 30) contained in the flux of a magnetic motor assembly (32, 34). The motor assemblies derive their flux from permanent magnets (36, 38) and may include additional shorting rings/caps to minimize inductance and/or inductance modulation. The first compression chamber assembly 16 of the FIG. 1 embodiment has a copper shorting cap 40 on top of its corresponding motor assembly 32. Both compression chambers (16, 18) of FIG. 1 share a common exit 14 for acoustic radiation, but do not share a compression chamber. The impedance mismatch element 42 used to combine the acoustic radiation between the two compression chambers is the subject of U.S. Pat. No. 11,343,608 and U.S. patent application Ser. No. 17/750,526, the entire disclosure of which is incorporated by reference herein.
[0041] The dual compression chamber assemblies of FIG. 1 do not limit embodiments to multiple compression chambers, diaphragms, voice coils, and magnetic motor assemblies; exemplary embodiments can alternatively feature a single compression chamber sub-assembly. The embodiment of FIG. 1 shows multiple annular diaphragms (24, 26) that are not coplanar about their planes of vertical oscillation. This does not limit other configurations where multiple diaphragms are vertically coplanar or where multiple diaphragms otherwise share and bound an annular compression chamber with a singular exit. Throughout all embodiments, the defining aspect of compression chamber construction to enable the methods of simplified computation remains: [0042] Compression chambers with primarily zero-mode acoustic coupling.
[0043] The compression driver of FIG. 1 contains a first diaphragm 24 with no intentional modification of the diaphragm mechanical modes, and a second diaphragm 26 where modal control is used to extend the diaphragm's operating bandwidth. As the additional mechanical modes occur near the maximum frequency of the diaphragm's operation and are acoustically coupled via the compression chamber, they boost the exit radiation at frequencies where the compression chamber sub-assembly 18 would otherwise begin to exhibit reduced acoustic output at the exit 14.
[0044] FIG. 2 presents the view of FIG. 1 but shows only the second compression chamber 18, annular diaphragm assembly 22, diaphragm 26, and voice coil 30 that drives the diaphragm to oscillate. This second diaphragm 26 is the diaphragm whose geometric cross-section has been modified to introduce additional mechanical modes that couple to the exit radiation. The boundaries of the second compression chamber 18 are defined as follows: [0045] 1. The second compression chamber perimeter is bounded on one face by the second annular diaphragm 26, which is oscillated by the voice coil 30 that moves in the magnetic field of the motor assembly (not shown). The diaphragm 26 has the general form of an inverted V, with the voice coil 30 mechanically attached at the peak of the V 44 below the compression chamber 18. [0046] 2. The inside and outside radii of the annular diaphragm assembly 22 are supported by a clamping ring 58. The ring assembly provides centering, mechanical support, and aids in even distribution of the clamping force around the perimeter of compression chamber 18. [0047] 3. Above the second diaphragm 26, one boundary surface of the compression chamber 46 is formed by the inside surface of the rear mechanical housing 48 of the compression driver. Because exit radiation is usually to the interior of the compression driver 14, the face defined by 46 is to the outside of the voice coil 30 radius. In addition to forming the compression chamber, this mechanical housing supports the first compression chamber 16 and acts as a heat sink for heat created by the voice coils (28, 30). [0048] 4. Above the diaphragm 26, the other boundary surface of the second compression chamber 18 is defined by the outside face 50 of the mechanical impedance mismatch element 42. Because exit radiation 14 is usually to the interior of the compression driver, the face defined by 50 is to the inside of the radius of the voice coil 30. [0049] 5. The beginning of the annular axisymmetric exit of the compression chamber 52 is defined via the gap between the inside face 46 of the mechanical housing 48 and the outside face 50 of the impedance mismatch element 42. The compression chamber exit termination 54 couples the acoustic compliance 56 adjacent to the diaphragm 26 to the exit radiation of the compression driver 14 through the body of the impedance mismatch device 42. The fundamental mode vertical oscillation of the diaphragm 26 is often a maximum at the peak of the overall V 44, where the voice coil 30 meets the diaphragm 26. Because of this, the compression chamber exit 52 begins approximately radially centered about the voice coil 30 to allow maximum vertical displacement of the diaphragm peak 44. Additional vertical diaphragm displacement supports more acoustic output at the lowest frequencies of operation.
[0050] The compression chamber of the embodiment in FIG. 2 could be mechanically bounded by other faces and/or assemblies as long as the chamber retains the general zero mode constraint necessary to facilitate calculations.
[0051] FIG. 3 shows only the diaphragm 26 from FIG. 2 in cross-section. Removing the voice coil 30 and clamping ring assembly 58 provides clarity on the geometric cross-section of the diaphragm. Both the inner and outer circumferences (64, 66) of the diaphragm 26 are retained mechanically at their perimeter, and do not experience a vertical displacement during oscillation. Control of the geometric cross-section results in creation and/or manipulation of mechanical modes in the diaphragm. The inverted V-shaped diaphragm geometry has additional substructure in the form of a pair of steps (60, 62) placed on either side of the diaphragm peak 44 where the voice coil 30 attaches. Steps are a useful modification of the base diaphragm cross-section due to straightforward parameterization, mechanical formability, minimal increase in diaphragm mass, and retention of nearly uniform cross section in the diaphragm material. Mechanically, the steps (60, 62) behave as areas of additional local stiffness in the diaphragm's cross-section.
[0052] FIG. 4 details parameterization of a diaphragm cross-section defined symmetrically about the diaphragm's overall V shape. Parameterization includes definitions of the radius 68 of the diaphragm with respect to the peak of the V 44, as well as the locations of the inner edge 70, peak 72, and outer edge 74 of the step 60. Corresponding diaphragm heights at the diaphragm peak 76 and across 78 the step 60 are defined. Diaphragm thickness 80 and width of clamped region 82 are also required. The other inner step geometry 62 is then a consequence of mirror symmetry about 44. Depending on the method of calculating eigenmodes in the diaphragm 26, other material parameters are defined. Potential parameters include Young's modulus, Poisson's ratio, loss tangent, density, and any parameters for material anisotropy.
[0053] The symmetric parameterization about 44 defined in FIG. 4 should not be construed to limit any other approach for defining the geometry of the annular diaphragm. There are numerous methods, variables, and coordinate systems that could be used to define the diaphragm surface. For instance, the entire diaphragm surface 26 could be point by point parameterized in 3D space or defined radially about the central axis of rotation of the diaphragm 12. Numerical methods and/or closed form solutions for diaphragm modal behavior can inform the choice of parameterization. Parametrization that retains rotational symmetry about the central axis of diaphragm rotation 12 may provide a more computationally efficient simulation of mechanical modes.
[0054] FIG. 5 provides an additional embodiment of an exemplary annular diaphragm 84 with asymmetry of position of the diaphragm peak 86. Additionally, this embodiment has asymmetry in quantity and location of steps (88, 90, 92) with respect to the diaphragm peak 86. The areas of clamping (94, 96) may also have their own independent dimensions. The additional steps and/or asymmetry are utilized to: generate additional modes; damp new or existing modes; influence effectiveness of acoustic coupling to the compression chamber; modify mode location along the diaphragm; influence mode amplitude; change mode shape; control mode bandwidth.
[0055] Diaphragm mechanical modes, other than the fundamental mode, become a key consideration as frequency increases. In turn those mechanical modes have varying degrees of coupling to the acoustic compliance within the compression chamber that is adjacent to the diaphragm. To increase the acoustic output of the compression chamber assembly via modal control of the diaphragm requires both generating mechanical modes and ensuring that they couple acoustically in an advantageous way at the compression chamber exit. In mechanical systems, generation of one desirable mode can spur other less desirable modes. To best improve the acoustic performance, it is desirable to minimize the acoustic coupling of any unwanted diaphragm modes. Determining the interplay of introducing desirable diaphragm modes, and then controlling the coupling of secondary modes that may also result, is the driving force behind the methods herein. Practical development of compression drivers that utilize mechanical modes in a way that improves the exit radiation requires rapid analysis of the overall acoustic radiation. The disclosed achieves analysis in a more expedient manner than full simulation. The result is compression drivers with improved acoustic performance.
[0056] Various embodiments of the present invention are described herein with reference to the related drawings. Alternative embodiments can be devised without departing from the scope of this invention. It is noted that various connections and positional relationships (e.g., over, below, adjacent, etc.) are set forth between elements in the description and in the drawings. These connections and/or positional relationships, unless specified otherwise, can be direct or indirect, and the present invention is not intended to be limiting in this respect. Accordingly, a coupling of entities can refer to either a direct or an indirect coupling, and a positional relationship between entities can be a direct or indirect positional relationship.
[0057] 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 advantageous over other embodiments or designs. The terms at least one and one or more are understood to include any integer number greater than or equal to one, i.e. one, two, three, four, etc. The terms a plurality are understood to include any integer number greater than or equal to two, i.e. two, three, four, five, etc. Terms such as connected to, affixed to, etc., can include both an indirect connection and a direct connection.
[0058] The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.
