Metamaterial Loudspeaker Diaphragm

Abstract

A metamaterial loudspeaker diaphragm is disclosed. The diaphragm includes a cone structure having a periodic arrangement of two dissimilar materials, e.g., soft and hard, in an alternating periodic pattern to achieve an anisotropic structure, which results in passive amplification of the sound. The anisotropic cone structure includes a baseline cone material and a different, compatible second material. The cone includes a body having a conical cross-section, an interior side, an exterior side, and concentric circles of material alternating between a soft material and a rigid material. Circumferential grooves disposed within the concentric circles include rigid material. Concentric circles including rigid material line the interior side of the body. Substantially all the soft material of the concentric circles is disposed on the exterior side of the cone. Spokes disposed on the exterior side of the cone extend from a base toward a vertex of the cone.

Claims

1. A speaker cone, comprising: a body including a conical cross-section having a first end including a base, a second end including a vertex, said first end opposite said second end, an interior side, and an exterior side, said interior side opposite said exterior side, said body tapering in circumference from said first end toward said second end.sup.1, said body rigid in a radial direction and alternating soft and hard in a circumferential direction.sup.2; a first plurality of concentric circular regions formed of a soft material and a second plurality of concentric circular regions formed of a rigid material, said concentric circular regions of said first and second plurality of concentric circular regions alternating in arrangement along said body from said first end to said second end such that said first and second plurality of concentric circular regions taper in circumference from the base to the vertex; a circumferential groove disposed within each of said plurality of concentric circles, said circumferential grooves including a rigid material; wherein said concentric circles of said first and second pluralities plurality of concentric circular regions substantially form a cone which extends from a base towards a vertex.

2. (canceled)

3. The speaker cone of claim 1, wherein a concentric circular region of said first plurality of concentric circular regions formed of soft material has a portion thereof which extends into one of said circumferential grooves within a concentric circular region of said second plurality of concentric circular regions formed of rigid material.

4. The speaker cone of claim 3, wherein said second plurality of concentric circular regions formed of rigid material substantially line said interior side of said cone.

5. The speaker cone of claim 4, the second plurality of concentric circular regions formed of rigid material include spokes that extend from said base towards said vertex of said body of said speaker cone, said spokes extending radially inwardly through said body and traversing said second plurality of concentric circular regions.

6. The speaker cone of claim 5, wherein said spokes are on said exterior side of said body and substantially all of said soft material of said first plurality of concentric circles is on said exterior side of said body.

7. The speaker cone of claim 6, wherein said rigid material is harder than said soft material by a factor of at least 1 billion.

8. The speaker cone of claim 7, wherein said soft material is meta material silicone.

9. The speaker cone of claim 8, wherein said soft material comprises at least 60% of material of said first and second plurality of concentric circular regions of said speaker cone.

10. (canceled)

11. A speaker cone, comprising: a body including a conical cross-section having a first end including a base, a second end including a vertex, said first end opposite said second end, an interior side, and an exterior side, said interior side opposite said exterior side, said body tapering in circumference from said first end toward said second end and including a layered construction in the radial direction, the layered construction including a first plurality of circumferential layers of soft material extending circumferentially around the body and a second plurality of circumferential layers of rigid material extending circumferentially around the body, the soft material being a different material from the rigid material, said first plurality of circumferential layers of soft material and said second plurality of circumferential layers of rigid material alternating in arrangement along said body from said first end to said second end such that said rigid material extends radially from said base toward said vertex of said body of said speaker cone.

12. The speaker cone of claim 11, wherein said soft material and said rigid material are soft and rigid relative to one another by a factor of at least 1 billion.

13. The speaker cone of claim 12, wherein said interior side of said speaker cone is substantially all rigid material.

14. The speaker cone of claim 13, wherein in said circumferential direction substantially all the material forming said speaker cone is soft material.

15. The speaker cone of claim 11, further comprising radially extending spokes disposed on said exterior side of said body, said spokes extending radially inwardly through said body and traversing said second plurality of concentric circular regions wherein said alternating circumferential layers of said soft material and said rigid material are supported by said radially extending spokes.

16. The speaker cone of claim 11, further comprising circumferentially extending grooves disposed in said rigid material of said second plurality of circumferential layers, said circumferentially extending grooves holding at least some of said soft material of said first plurality of circumferential layers to at least some of the rigid material of the said second plurality of circumferential layers.

17. The speaker cone of claim 1, wherein said first plurality of concentric circular regions formed of a soft material and said second plurality of concentric circular regions formed of a rigid material include substantially the same width.sup.3.

18. The speaker cone of claim 1, wherein said soft material of said first plurality of concentric circular regions includes an elastic modulus of 1.3×10.sup.4 and density of 500 Kg/m.sup.3 and said rigid material of said second plurality of concentric circular regions includes an elastic modulus of 574×10.sup.10 and a density of 1550 Kg/m.sup.34.

19. The speaker cone of claim 11, wherein said first plurality of circumferential layers of soft material and said second plurality of circumferential layers of rigid material include substantially the same width.

20. The speaker cone of claim 11, wherein said soft material of said first plurality of circumferential layers includes an elastic modulus of 1.3×10.sup.4 and density of 500 Kg/m.sup.3 and said rigid material of said second plurality of circumferential layers includes an elastic modulus of 574×10.sup.10 and a density of 1550 Kg/m.sup.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1A shows a schematic view of the structure of the metamaterial loudspeaker diaphragm according to one embodiment of the present disclosure.

[0032] FIG. 1B shows a schematic view of the structural elastic domain of the metamaterial loudspeaker diaphragm according to one embodiment of the present disclosure.

[0033] FIG. 2 shows a schematic view of the metamaterial loudspeaker diaphragm, illustrating the cone divided into concentric rings according to one embodiment of the present disclosure.

[0034] FIG. 3 shows a perspective view of the metamaterial loudspeaker diaphragm, illustrating the cone divided into concentric rings with baseline material according to one embodiment of the present disclosure.

[0035] FIG. 4 shows a schematic view of the metamaterial loudspeaker diaphragm, illustrating the spokes of the concentric rings with baseline material according to one embodiment of the present disclosure.

[0036] FIG. 5 shows a perspective view of the metamaterial loudspeaker diaphragm, illustrating the cone divided into concentric rings which alternate with baseline material and silicone material according to one embodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE DISCLOSED TECHNOLOGY

[0037] The present disclosed technology provides a metamaterial loudspeaker diaphragm including a cone structure providing passive sound enhancement of sound. The metamaterial cone structure employs a periodic arrangement of two dissimilar materials in an alternating periodic pattern to achieve an anisotropic structure, which results in passive amplification of the sound. The anisotropic cone structure can be achieved by using a variety of different materials, starting with the baseline cone material and selecting a different, compatible/suitable second material. The structural integrity and vibration resonance of the cone is retained in this new anisotropic material. The radial elastic properties of the new structure are still about the same as the baseline cone structure, whereas the azimuthal/circumferential properties of the cone structure would have changed in the resulting anisotropic structure. Thus, sound emanating from a speaker will improve until the first resonance frequency due to the lower longitudinal wave speed in the azimuthal direction. Above the first resonance frequency, anisotropic structure design will still be effective with larger enhanced structural resonances which can be damped. The sound from the speaker is radiated at all frequencies.

[0038] FIG. 1A shows a schematic view of the structure of the metamaterial loudspeaker diaphragm according to one embodiment of the present disclosure. FIG. 1A illustrates the concept of anisotropy using a periodic arrangement of multilayer structure with the incident wave in the r-direction. Each layer is composed of isotropic and homogenous materials with mass density ρA and ρB and bulk modulus κA and κB. The thickness of each layer is much smaller than the wavelength so the whole stack can be treated as a single anisotropic material using effective medium theory. The homogenized density tensor and bulk modulus can be expressed as

[00001]${\rho }_r=\frac{{\rho }_A+{\mathrm{\eta \rho }}_B}{1+\eta },\frac{1}{{\rho }_{\theta }}=\frac{1}{1+\eta }\left(\frac{1}{{\rho }_A}+\frac{\eta }{{\rho }_B}\right)$$\frac{1}{K}=\frac{1}{1+\eta }\left(\frac{1}{K_A}+\frac{\eta }{K_B}\right)$

where η=d.sub.B/d.sub.A is the ratio of thicknesses for the B and A layers, ρ.sub.rΛρ.sub.θ are the radius and angular components of the effective anisotropic density tensors respectively, and κ is the effective bulk modulus.

[0039] The disclosed loudspeaker cone moves as a rigid body, due to in-plane waves, at low frequencies where, longitudinal waves dominate loudspeaker vibrations. As the excitation frequency increases, the transverse velocity of the cone surface becomes non-uniform, since the amplitude of the vibration increases towards the base of the cone, where bending waves can propagate. At high enough frequencies the whole cone is dominated by bending waves. The longitudinal wave speed is given by

[00002]$C_L=\sqrt{\frac{Y}{P}},$

where, Y is the Young's modulus and ρ is density of the material. The preliminary guideline that the high impedance of the loudspeaker diaphragm (i.e., higher than acoustic impedance) restricts sound radiation at low frequencies indicates the prominent role of longitudinal wave speed of sound in the diaphragm material.

[0040] At low frequencies, the loudspeaker is usually assumed to be a rigid piston and the cone will move as a rigid body. However, the cone itself is not rigid at high frequencies and should be modeled as a flexible system. For example, at 100 Hz the cone moves almost as a rigid body, and the amplitude of motion in the azimuthal (or circumferential direction, θ, is much greater than that in the radial direction, r. The dynamic behavior at a given position along the cone depends on whether the excitation is above or below the ring frequency at this location. The ring frequency is given by

f.sub.R=C.sub.L/2πR

where R is the distance between the cone and cone axis measured perpendicular to the cone meridian. Since the ring frequency varies along the length of the cone the dynamic behavior of the cone depends on whether the frequency is in one of three regions, namely, longitudinal, longitudinal/bending, and/or bending.

[0041] Since isotropic materials used for loudspeaker cone construction have same elastic properties in radial and circumferential (r, θ) directions, longitudinal wave speeds are equally high in both directions in the material. For example, longitudinal wave speed in carbon fiber epoxy material (E=574×10.sup.9 and density of 1550 Kg/m.sup.3) is about 19240 m/s, which is much higher than speed of sound (343 m/s). Since isotropic materials used in loudspeaker cone can range from PVC and polypropylene to Beryllium and more exotic materials with extremely high Young's modulus, other material is needed which has exceptionally low elastic modulus and/or low speed of sound. Accordingly, the present disclosure employs acoustic metamaterials with exceptionally low sound speeds, as low as 60 m/s with accompanying low Young's modulus. Such acoustic metamaterials are composed of soft, porous silicone rubbers.

[0042] The control of sound wave propagation in metamaterials is of primary importance in the present disclosure. Highly compressible air-filled pores may strongly soften the material, mostly by decreasing the longitudinal modulus Y, which leads to a decrease of the longitudinal sound speed C.sub.L. Soft porous silicone rubbers have been demonstrated to exhibit extremely low sound speeds of tens of m/s for these dense materials, even for low porosities of the order of a few percent. By controlling both the porosity and the elastic characteristics of the matrix allows for a full control over the acoustic index in materials.

[0043] As stated above, a periodic arrangement of multi-layered structure using two different properties can result in an anisotropic structure. If two layers have drastically different properties than vastly different properties can be achieved in two directions, e.g., longitudinal and transverse directions. For example, in one embodiment of the present disclosure, a carbon fiber epoxy glass sheet (elastic modulus of 574×10.sup.9 and density of 1550 Kg/m.sup.3) with soft silicon layers (with elastic modulus of 1.3×10.sup.4 and density of 500 Kg/m.sup.3) is used for the multi-layer period arrangement and results in an anisotropic material with an effective bulk modulus of κ=1.1987×10.sup.09 and Y.sub.θ=2.6×10.sup.4 and densities ρ.sub.r=1030 Kg/m.sup.3 and ρ.sub.θ=756 Kg/m.sup.3. These anisotropic elastic properties are effectively used for the loudspeaker cone structure to enhance sound radiation.

[0044] Referring now to FIGS. 2-5, simultaneously, FIG. 2 shows a schematic view of the metamaterial loudspeaker diaphragm, illustrating the cone divided into concentric rings according to one embodiment of the present disclosure. FIG. 3 shows a perspective view of the metamaterial loudspeaker diaphragm, illustrating the cone divided into concentric rings with baseline material according to one embodiment of the present disclosure. FIG. 4 shows a schematic view of the metamaterial loudspeaker diaphragm, illustrating the spokes of the concentric rings with baseline material according to one embodiment of the present disclosure. FIG. 5 shows a perspective view of the metamaterial loudspeaker diaphragm, illustrating the cone divided into concentric rings which alternate with baseline material and silicone material according to one embodiment of the present disclosure.

[0045] In conjunction, FIGS. 2-5 show anisotropic cone structures realized by using periodic arrangement of alternating layers of differing materials. FIG. 2 shows the anisotropic metamaterial loudspeaker diaphragm 10 comprising a loudspeaker cone 12 divided into concentric circles 14. FIG. 3 shows alternate concentric circles of baseline material 16, such as carbon fiber epoxy or fiberglass. The concentric circles of the second material 17, such as soft porous silicon, are shown in FIG. 5. In embodiments, the hard material includes an elastic modulus of 574×10.sup.10 and a density of 1550 Kg/m.sup.3), while the soft material includes an elastic modulus of 1.3×10.sup.4 and density of 500 Kg/m.sup.3. To achieve continuous flexural rigidity, several spokes 18 around the cone 12 are retained to be made of the baseline material.

[0046] In embodiments of the disclosed technology, the metamaterial loudspeaker diaphragm 10 includes the speaker cone 12 having a body 20 having a conical cross-section which radially decreases from a larger circle to a smaller circle which, if continued past said smaller circle would reach a vertex. The body 20 includes an interior side 20A and an exterior side (not shown). The body 20 may be rigid in a radial direction and alternatingly soft and hard in a circumferential direction.

[0047] The plurality of concentric circles 14 of material alternate between a soft material and a rigid material. The concentric circles comprise circumferential grooves disposed within each of the concentric circles 14. The circumferential grooves include, or are filled with, soft material. In some embodiments, the concentric circles 14 that include soft material have a portion which extends into one of the circumferential grooves of a concentric circle that includes rigid material. The concentric circles 14 that include rigid material substantially line the interior side 20A. Substantially all the soft material of the concentric circles 14 may be disposed on the exterior side. The hard material is harder than the soft material by a factor of at least 1 billion. In embodiments, the soft material is preferably silicone and may comprise at least 60% of all of the material that makes up the concentric circles 14.

[0048] The spokes 18 extend from a base of the cone 12 (not shown) toward a vertex of the cone 12 (not shown). The spokes 18 may be disposed on an exterior side of the speaker cone 12. Substantially all the soft material of the concentric circles 14 may be disposed on the exterior side.

[0049] In other embodiments, the speaker cone 12 may include alternating circumferential layers of soft material and hard material, wherein the hard material extends radially from a base toward a vertex of the cone 12.

[0050] In order to build the anisotropic metamaterial loudspeaker diaphragm 10 of the present disclosure, a two-layer construction may be desired. The construction process may start with a cone made of baseline material of appropriate thickness. The base and alternate layers are thus made of the baseline material (e.g., carbon fiberglass epoxy or other suitable material). The alternate layers of soft silicone material, as shown in FIG. 5, are filled into concentric circles cut or drilled in the baseline disc to a depth of about 60 to 80%, leaving the remaining thickness of facing of baseline material.

[0051] Using meta material layers, anisotropy of elastic properties of the entire loudspeaker diaphragm can be controlled (or tailored) according to the required frequency characteristics of the radiated sound field.

[0052] At lower frequencies, the process may be more complex, as outer part of the diaphragm may be more involved in sound radiation than inner dome. This may cause re-distribution of meta material rings as per design requirements.

[0053] The effective parameters of such layered system can also be tuned by selecting proper parameters for A and B, and/or by changing the η, where η=d.sub.B/d.sub.A is ratio of thicknesses for the B and A layers (FIG. 1).

[0054] The concentric ring structure can also be made of materials with graded elasticity which will effectively lead to the desired anisotropy of the loudspeaker cone, for example, in the case of a low frequency sub-woofer.

[0055] Finally, one can optimize and arrive at a meta material diaphragm design which can meet requirements for elastic modulus and density in orthotropic directions.

[0056] Alternatively, the metamaterial cone may be made involving fabrication steps suitable for particular manufacturing processes.

[0057] The present technology can be carried out with one or more of the embodiments described. The drawings show embodiments with the understanding that the present description is to be considered an exemplification of the principles and is not intended to be exhaustive or to limit the disclosure to the details of construction. The arrangements of the components are set forth in the following description or illustrated in the drawings.

[0058] While the disclosed technology has been taught with specific reference to the above embodiments, a person having ordinary skill in the art will recognize that changes can be made in form and detail without departing from the spirit and the scope of the disclosed technology. The described embodiments are to be considered in all respects only as illustrative and not restrictive. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope. Combinations of any of the methods, systems, and devices described herein-above are also contemplated and within the scope of the disclosed technology.