Patent Application
20160295330
This disclosure relates to an acoustic diaphragm.
Acoustic transducers include a diaphragm that is used to reproduce sound. An ideal diaphragm would be rigid to prevent uncontrolled motions, and would have low mass to minimize starting force requirements and energy storage issues.
All examples and features mentioned below can be combined in any technically possible way.
In one aspect, an acoustic diaphragm includes an expanded paper material with a cellulose-containing layer having more than about 55% by volume voids. In another aspect, an acoustic diaphragm includes an expanded felt material layer comprising synthetic and glass fibers and having more than about 55% by volume voids. In another aspect an acoustic diaphragm comprises an expanded material comprising one or more of: cellulose, synthetic fibers and glass fibers, wherein the expanded material has more than about 55% by volume voids.
Embodiments may include one of the following features, or any combination thereof. The expanded material may have more than about 70% by volume voids, and more specifically may have at least about 97% by volume voids. The expanded material may have a density of from at least about 0.04 g/cc to about 0.7 g/cc. The expanded material may have a density, and the density may vary by location in the diaphragm. For example, the diaphragm may have a generally round shape, and the density may vary by radial location. The expanded material may have an aerial density of from about 0.4 to about 1 kg/m3. The expanded material may have a thickness of from about 0.2 mm to about 10 or 11 mm.
Embodiments may include one of the following features, or any combination thereof. The expanded material may comprise, or may consist of, or may consist essentially of, cellulose and a polymer material. The polymer material may be an acrylic. The acrylic may comprise polyacrylonitrile.
Embodiments may include one of the following features, or any combination thereof. The acoustic diaphragm may further comprise a skin at least partially overlying and fixed to the expanded material, wherein the skin is made from a different material than that of the expanded material. The skin may comprise at least one of a metal layer (e.g., aluminum), a plastic layer, and a thermoset layer. The acoustic diaphragm may further comprise an adhesive material between the skin and the expanded material. The adhesive material may comprise at least one of: a polymer, a thermoset such as epoxy, a low-density polyethylene, a pressure-sensitive adhesive, a carboxylated ethylene/vinyl acetate (EVA) copolymer, a thermoplastic elastomer (TPE), and a styrene-isobutylene-styrene block copolymer. The skin may have a thickness of from about 7 microns to about 250 microns. The material of the acoustic diaphragm of low areal density may have a longitudinal speed of sound of from about 1,500 m/s to about 7,000 m/s. The acoustic diaphragm may further include a damping material on a surface of or impregnated into the expanded material. The expanded material may further comprise one or more of synthetic fibers and glass fibers.
Embodiments may include one of the following features, or any combination thereof. The acoustic diaphragm may further comprise skins at least partially overlying and fixed to both surfaces of the expanded material, wherein the skins are made from a different material than that of the expanded material. The acoustic diaphragm may have opposed surfaces, wherein at least one surface has ribbing. The ribbing may be radial. The acoustic diaphragm may have a generally annular shape. The radial ribbing may extend along at least most of the length of radii of the annulus. The acoustic diaphragm may have a generally frustoconical shape. The acoustic diaphragm may be generally flat. The acoustic diaphragm may have a bending resistance, defined as |E*|*h3, where E* is the complex tensile modulus and h is the thickness of the diaphragm. For diaphragms of equal mass the bending resistance is proportional to the material merit number of |E*|/ρ3, where ρ is density. For diaphragms (preferably for those with areal density between about 0.1 and about 1 kg/m2), |E*|/ρ3 may range from about 30 to about 500 Pa*m9/kg3.
In another aspect, an acoustic diaphragm includes a paper layer having opposed surfaces and a skin at least partially overlying and fixed to at least part of at least one surface of the paper layer, wherein the skin is made from a different material than the paper layer.
Embodiments may include one of the following features, or any combination thereof. The paper layer may comprise an expanded paper material. The expanded paper material may have between about 55% and about 97% by volume voids. The paper layer may have a density of from about 0.04 g/cc to about 0.7 g/cc. The paper layer may have a thickness of from about 0.2 mm to about 10 or 11 mm.
Embodiments may include one of the following features, or any combination thereof. The skin may comprise at least one of: a metal layer (e.g., aluminum), a plastic layer, and a thermoset layer (e.g., cured polyurethane). The acoustic diaphragm may further comprise an adhesive material between the skin and the paper layer. The adhesive material may comprise at least one of: a polymer, a thermoset such as epoxy, a low-density polyethylene, a pressure-sensitive adhesive, a carboxylated ethylene/vinyl acetate (EVA) copolymer, a thermoplastic elastomer (TPE), and a styrene-isobutylene-styrene block copolymer. The skin may have a thickness of from about 7 microns to about 250 microns. The acoustic diaphragm may further comprise skins at least partially overlying and fixed to both surfaces of the paper layer, wherein the skins are made from a different material than the paper layer. The acoustic diaphragm may further include a damping material on a surface of or impregnated into expanded material layer. The paper layer may further comprise one or more of synthetic fibers and glass fibers. The paper layer may comprise an expanded paper material, which may have between about 55% and about 97% voids.
In another aspect, the disclosure includes expanded paper consisting essentially of cellulose and polymer, where the expanded paper has more than about 55% by volume voids and preferably has at least about 70% voids, and more preferably about 97% voids.
In another aspect, a method of manufacturing expanded material includes creating a suspension consisting essentially of cellulose fibers (for expanded paper diaphragms) or plastic and glass fibers (for synthetic expanded diaphragms). There are particles of a physical blowing agent, and a liquid suspension medium. Each particle of blowing agent comprises a volatile substance encapsulated in a polymer shell. The suspension is felted for molding under conditions such that the resulting expanded material has more than about 55% by volume voids.
In another aspect an acoustic diaphragm assembly includes a diaphragm comprising a cellulose-containing material and having opposed surfaces, and a voice coil electrical lead that is at least partially embedded in the diaphragm.
Embodiments may include one of the following features, or any combination thereof. The diaphragm may comprise a plurality of layers, and at least two of the layers may be coupled together, for example with an adhesive material that may also be a damping material. The electrical lead may be coated at least in part with the adhesive material. A portion of the electrical lead may be located between the two layers that are coupled together. In one example, the layers comprise a cellulose-containing layer and a skin at least partially overlying and fixed by an adhesive to the cellulose-containing layer, wherein the skin is made from a different material than the cellulose-containing layer, and wherein a portion of the electrical lead is located between the cellulose-containing layer and the skin. The cellulose-containing layer may comprise expanded cellulose-containing paper material that has more than about 55% by volume voids.
Embodiments may include one of the following features, or any combination thereof. The skin may comprise at least one of: a metal layer, a plastic layer, and a thermoset layer. The adhesive material may comprise a damping material. A skin may have a thickness of from about 7 microns to about 250 microns. The cellulose-containing layer may have a density between about 0.04 g/cc and about 0.7 g/cc.
Embodiments may include one of the following features, or any combination thereof. A portion of the electrical lead may not be embedded in the diaphragm, and that portion may be crimped. The diaphragm may comprise at least one of: an expanded cellulose-containing paper material and an expanded synthetic paper material.
In another aspect, an acoustic diaphragm assembly includes a diaphragm comprising at least one of: an expanded cellulose-containing paper material and an expanded synthetic paper material, and one or more skins at least partially overlying and fixed to the expanded material by an adhesive material, wherein a skin is made from a different material than the expanded material. There is a voice coil electrical lead that is at least partially disposed within the diaphragm between the expanded material and the skin.
Embodiments may include one of the following features, or any combination thereof. The skin may comprise at least one of: a metal layer, a plastic layer, and a thermoset layer. The skin may have a thickness of from about 7 microns to about 250 microns. The expanded material may have more than about 70% by volume voids and a density between about 0.04 g/cc and about 0.7 g/cc. The expanded paper material may comprise synthetic fibers and glass fibers.
In another aspect, an acoustic diaphragm assembly includes a diaphragm comprising an expanded paper material, wherein the expanded paper material has more than about 70% by volume voids, and a density between about 0.04 glee and about 0.7 g/cc, and a voice coil electrical lead that is at least partially disposed within the expanded paper material.
Embodiments may include one of the following features, or any combination thereof. The expanded paper material may comprise at least one of: expanded cellulose-containing paper material and expanded synthetic paper material. The diaphragm may comprise a plurality of layers, and at least two of the layers may be coupled together with a damping material. The layers may comprise a cellulose-containing layer and a skin at least partially overlying and fixed by an adhesive to the cellulose-containing layer, wherein the skin is made from a different material than the cellulose-containing layer, and wherein a portion of the electrical lead is located between the cellulose-containing layer and the skin. A portion of the electrical lead may be located between the two layers that are coupled together. The expanded paper material may comprise synthetic fibers and glass fibers.
Highly expanded, low density, cellulose (e.g., paper)-based and synthetic fiber-based foams are light and stiff, and thus are well suited for use in acoustic diaphragms. Their stiffness can be enhanced with thin coatings (skins) of stiff materials on some or all of one or both faces of the diaphragm. Damping can be enhanced by the use of highly damped materials between the foam and the skin, or by integrating (e.g., impregnating) the damping materials into the foam. The foam diaphragms can be produced in various shapes, including flat diaphragms and shallow cones. Further, the foams can be created with variable thickness, to produce acoustic transducers with tailored performance.
A loudspeaker 10, shown in
Acoustic diaphragm 25,
The expanded cellulose-containing paper material may also include a polymer material such as an acrylic, though other polymers may be used. Polyacrylonitrile is one preferred acrylic material, though others may be used. The expanded paper material may be fabricated by mixing cellulose fibers, particles of a physical blowing agent such as described herein, and a liquid suspension medium such as water, to form a suspension, and then felting the suspension and molding the felted suspension under conditions that cause the blowing agent to form voids, resulting in an expanded paper material that has more than about 55% by volume voids. An example of a prior art normal (i.e., not expanded) paper, and an expanded paper made in the described fashion, are shown in
To fabricate an expanded paper diaphragm, cellulose, synthetic, and/or glass fibers may first be mixed with a liquid suspension medium, such as water. A physical blowing agent (such as those described herein) having a liquid material encapsulated in polymer shells, may be added to the mixture. The mixture is then deposited onto a die or tool placed on top of a screen using a felting tube. The die or tool may have the desired shape of the diaphragm to be formed. For example, the die or tool may have grooves or indentations, and may be a generally flat or generally conical shape (though other shapes may be used). Following deposition of the mixture onto the die or tool, a vacuum is applied to the mixture from the bottom of the felting machine through the screen. The vacuum pulls the mixture onto the die and removes most of the water from the mixture, leaving only a wet felt comprising cellulose, synthetic and/or glass fibers and the blowing agent, if used, on the die. If the die contains grooves or indentations, the vacuum pulls the mixture into those grooves or indentations, thus forming a diaphragm having variable areal density. Next, the wet material is inserted into a press, and heat and/or pressure are applied to mold the diaphragm. While in the press, the water steam evaporates and the material dries. If a blowing agent is used, the blowing agent expands, thus forming the expanded paper material.
The expanded synthetic paper material does not contain cellulose. It typically includes synthetic fibers and glass, and potentially other components. An unexpanded synthetic paper material that includes components used in the present synthetic paper expanded material is disclosed in U.S. Pat. No. 8,172,035, the disclosure of which is incorporated herein by reference in its entirety.
The polymer material may be present in the cellulose-containing expanded paper material from the residual shells of the blowing agent. In one example the blowing agent comprises a liquid (such as pentane and other low boiling hydrocarbons) that gasifies and greatly expands under the molding conditions (i.e., with application of pressure and temperature), where that liquid material is carried in polymer capsules or shells. The polymer may be an acrylonitrile homopolymer or copolymer. Other polymers may be used for the blowing agent shell. Once the molding operation is complete, the polyacrylonitrile (or other polymer from the blowing agent shell) remains in the expanded paper. In this example, then, the expanded paper consists essentially of only (or consists only of) cellulose and the polyacrylonitrile (or other residual polymer from the blowing agent capsules). In other examples the expanded paper comprises cellulose and a polymer.
The stiffness of diaphragm 25,
In an alternative example the acoustic diaphragm may comprise a paper layer rather than an expanded material layer. Desired stiffness is achieved in this case by using one or two skins made of a different material than the underlying paper layer. The skins may for example be of one or more of the types described herein.
The subject acoustic diaphragm can take any desired shape. The diaphragm can, for example, be flat or generally flat, or not. It can be generally cone shaped (e.g., frustoconical), and have a desired height to diameter ratio (i.e., aspect ratio). It can be annular, oval, square or rectangular, or have other shapes or peripheral configurations. The shape will normally be dictated by the requirements of the acoustic transducer in which the diaphragm is to be used. Examples of shapes include flat diaphragm 40,
The diaphragm can include ribbing that can change the stiffness profile. The ribbing can be integrally formed in the expanded material layer, and on one or both surfaces of the diaphragm, or the ribbing can be in one or both skins when skins are present. For a diaphragm that is generally round such as diaphragm 50,
Integral ribbing is illustrated in cellulose-containing layer 60,
When present, the skin(s) can be coupled to a surface of the expanded material layer in a desired fashion. One preferred manner is to use a material that acts like an adhesive between the expanded material layer and the skin. Such materials may include a soft polymer resin such as polyethylene, or a thermoset such as epoxy, for example. The adhesive may also act as a damping agent that helps to damp unwanted vibrations of the diaphragm. Low-density polyethylene, various pressure-sensitive adhesives (PSAs) such as carboxylated acrylics, carboxylated ethylene/vinyl acetate (EVA) copolymer, and thermoplastic elastomers (TPEs), such as styrene-isobutylene-styrene block copolymers can be used as damping adhesives. The adhesive can be applied to the outer surface of the expanded material layer, or one surface of the skin, and then the skin can be applied to the expanded material layer. The skins can be applied via insert molding, or can be applied post-molding.
Desired acoustic response of a diaphragm can at least in part also be accomplished by varying the thickness of the diaphragm across its dimensions. A non-limiting example is shown in
Maximizing the first modal frequency of a diaphragm of fixed dimensions and minimizing its mass may be achieved by maximizing the material merit number of |E*|/ρ3, where E* is the complex tensile modulus and ρ is density. It has been found that materials characterized by |E*|/ρ3 of from about 30 to about 500 Pa*m9/kg3 provide for efficient diaphragms with better frequency response than a material with a lower |E*|/ρ3. High value of |E*|/ρ3 is equivalent to a high value of bulk longitudinal speed of sound, the square root of the ratio of |E*|/ρ, and a low value of areal density in the completed diaphragm. It has been found that diaphragm materials of this disclosure (with low areal densities between about 0.4 and about 1 kg/m2 and particularly those with one or two skins) should have a longitudinal speed of sound that is generally in the range of from about 1,500 meters per second (m/s) to about 7,000 m/s.
A molding process that allows for different thicknesses and densities of the cellulose-containing layer is schematically depicted in
Table 1 presents data for some of the materials used in the present diaphragms, and for diaphragms made from prior art materials. Table 2 presents data for certain components of the acoustic diaphragms that fall under the principles of the present disclosure. Several acoustic diaphragms with expanded paper material that comprises cellulose (with and without skins), and paper diaphragms with skins, were fabricated and tested for certain properties. Some of the test data is presented in Table 3.
In these tables, in the compositions the amounts are given by weight percent. Also, BA stands for a blowing agent (which in one non-limiting example is Advancell EMH 204 from Sekisui), glass is EC-11-3-SP glass fibers from JSA Valmiera Glass, PAN is fibrillated acrylic fiber as disclosed in U.S. Pat. No. 8,172,035 (the disclosure of which is incorporated herein in its entirety), Pliogrip is a polyurethane structural adhesive available from Ashland Chemical, and PP is polypropylene fibrids as disclosed in U.S. Pat. No. 8,172,035. The glass can be short cut e-glass fibers as disclosed in U.S. Pat. No. 8,172,035, Lyocell is reconstituted cellulose fiber from EFT, SIBS is SIBStar from Kaneka Corporation (styrene-isobutylene-styrene triblock copolymer thermoplastic elastomer), Al is aluminum foil, either close to 100% Al (like alloy 1100, ‘commercially pure’), or an alloy with ˜5% Mg (composition like alloy 5056), and the beaten pulps are beaten pulps that may be of the types as disclosed in U.S. Pat. No. 8,172,035. Further, the variable tan δ is a measure of damping, i.e., the ratio of the loss modulus (E″, the imaginary part of the complex dynamic tensile modulus, E*=E′+i*E″) and the storage modulus (E′, the real part of the complex dynamic tensile modulus). δ=arctan E″/E′ is the phase lag between stress and strain, and tan δ=E″/E′. The higher it is, the more damped the material is. The materials used in these tables are merely exemplary; other materials may be used to construct diaphragms according to the principles described herein.
On-axis sound pressure level of acoustic transducers, built with the diaphragms of the present disclosure, was measured. Sound output was measured at 1 m in front of the transducer, at IV. Several examples are presented in the plots of
The data and figures establish that the acoustic diaphragms produced according to the principles herein are stiff and damped.
Acoustic transducers with a voice coil have an electrical lead that runs from the voice coil to the control electronics. This lead is often either a thin wire, or a flat conductor or “ribbon.” Tinsel leads are bulkier and more difficult to fixture, and flying lead-outs may create a buzz. The wire or ribbon can be difficult to handle and terminate during the transducer assembly process where the lead needs to be terminated at the voice coil and to a remote structure. The leads may be embedded in or disposed within the expanded composite diaphragm itself, that may (or may not) comprise stiff surface skins. In the present acoustic transducer assembly 100,
Acoustic transducer assembly 112,
A number of implementations have been described. Nevertheless, it will be understood that additional modifications may be made without departing from the scope of the inventive concepts described herein, and, accordingly, other embodiments are within the scope of the following claims.
