Damper and loudspeaker using the same

The present disclosure provides a damper. The damper has alternating ridges and furrows thereon and has a through hole defined at a center of the damper. The ridges and furrows are concentric. The damper includes a matrix and at least one carbon nanotube structure disposed in the matrix. The present disclosure also provides a loudspeaker using the damper.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 200910190386.6, filed on Sep. 18, 2009, in the China Intellectual Property Office, the contents of which are hereby incorporated by reference. This application is related to commonly-assigned application entitled, “DAMPER AND LOUDSPEAKER USING THE SAME”, filed (Jun. 28, 2010 (U.S. Ser. No. 12/824,399).

BACKGROUND

1. Technical Field

The present disclosure relates to a damper based on carbon nanotubes, and a loudspeaker using the same.

2. Description of Related Art

A loudspeaker is an acoustic device transforming received electric signals into sounds. The electric signals have enough power to make the sounds audible to humans. There are different types of loudspeakers that can be categorized by their working principle, such as electro-dynamic loudspeakers, electromagnetic loudspeakers, electrostatic loudspeakers and piezoelectric loudspeakers. Among the various types, electro-dynamic loudspeakers have simple structures, good sound quality, and low cost, thus it is most widely used.

Electro-dynamic loudspeakers typically include a diaphragm, a bobbin, a voice coil, a damper, a magnet, and a frame. The voice coil is an electrical conductor, and is placed in the magnetic field of the magnet. By applying an electrical current to the voice coil, a mechanical vibration of the diaphragm is produced due to the interaction between the electromagnetic field produced by the voice coil and the magnetic field of the magnets to produce sound waves.

To evaluate the loudspeaker, a sound volume is a decisive factor. The sound volume of the loudspeaker relates to the input power of the electric signals and the conversion efficiency of the energy (e.g., the conversion efficiency of the electrical to sound). The larger the input power, the larger the conversion efficiency of the energy and sound volume of the loudspeaker. However, when the input power is increased to certain levels, the damper and diaphragm could deform or even break, thereby causing audible distortion. Therefore, the strength of the elements in the loudspeaker affect a rated power of the loudspeaker. The rated power is the highest input power the loudspeaker can produce sound without the audible distortion. Additionally, the lighter the weight of the elements in the loudspeaker, such as the weight of the damper and the weight per unit area of the diaphragm, the smaller the energy required for vibrating the diaphragm, and the higher the energy conversion efficiency of the loudspeaker, and sound volume produced by the same input power. Thus, the strength and the weight of the damper are important factors affecting the sound volume of the loudspeaker. The weight of the damper is related to a thickness and a density thereof. Accordingly, the higher the specific strength (e.g., strength-to-density ratio), the thinner the damper of the loudspeaker, and the higher the sound volume of the loudspeaker.

However, in prior art, the damper is usually made of pure cotton or blended fabric. The rated power of conventional loudspeakers is difficult to increase because of the conventional material of the damper. In general, the rated power of a small sized loudspeaker is only 0.3 watt (W) to 0.5 W. A larger bobbin thickness to achieve a larger specific strength, results in a greater damper weight. Thereby, it is hard to improve the energy conversion efficiency of the loudspeaker. Therefore, to increase the rated power and the energy conversion efficiency of the loudspeaker and to increase sound volume, the improvement of the loudspeaker is focusing on increasing the specific strength and the decreasing of the weight of the damper.

What is needed, therefore, is a damper with high specific strength and light weight and a loudspeaker using the same.

DETAILED DESCRIPTION

Referring toFIGS. 1,2and3, a damper100of a first embodiment is illustrated. A shape and a size of the damper100can be selected according to need.

The damper100can be corrugated with a plurality of ridges and furrows (not labeled) defined in the damper100. The ridges and the furrows can be concentric. In the present embodiment, the damper100is a corrugated round sheet having alternating circular ridges and furrows. The thickness of the damper100can be about 1 micrometer to about 2 millimeters. A through hole101can be defined at a center of the round sheet. A size and shape of the through hole101correspond to a size and shape of a bobbin of a loudspeaker using the damper100. When the bobbin and the damper100are assembled together, the bobbin can easily extend through the through hole101of the damper100. The damper100can be made by a hot pressing method.

A plurality of wires (not shown) can be fixed on a surface of the damper100by adhesive. The wires can be used to supply a current to a voice coil of the loudspeaker using the damper100. A tensile force produced during a mechanical vibration of the damper100can be alleviated to prevent the wires and the voice coil from breaking connection.

The damper100includes at least one carbon nanotube structure104and a matrix102. The carbon nanotube structures104can be located in the matrix102. The matrix102and the at least one carbon nanotube structure104comprises a composite structure. The carbon nanotube structure104can be layer-shaped. If the damper100includes a plurality of carbon nanotube structures104and a matrix102, the plurality of the carbon nanotube structures104can be stacked or spaced apart from each other. The matrix102can be a polymer film, a paper, a metal film, or metal sheet. For example, the matrix102can be a polyimide film, a polyester film, or an aluminum film. In the present embodiment, the damper100includes a matrix102of polyimide film and only one carbon nanotube structure104located therein. The polyimide film has a small density (only 1.35 g/cm3) to lighten and improve a specific strength of the damper100.

Disposing the carbon nanotube structure104into the matrix102depends on the material of the matrix102. In one embodiment, the matrix102is a liquid-state polymer, and a method for disposing the carbon nanotube structure104into the liquid-state polymer includes:

step (a1): dipping the carbon nanotube structure104into the liquid-state polymer bath; and

step (b1): removing the carbon nanotube structure104from the liquid-state polymer bath after the carbon nanotube structure104has been soaked by the liquid-state polymer.

In one embodiment, the matrix102is a solid-state polymer, and a method for disposing the carbon nanotube structure104into the solid-state polymer includes:

step (a2): covering at least one surface of the carbon nanotube structure104with the solid-state polymer;

step (b2): treating the carbon nanotube structure104and the solid-state polymer by a hot pressing method to form a composite structure; and

step (c2): cooling the composite structure.

In one embodiment, the material of the matrix102is a metal deposited on at least one surface of the carbon nanotube structure104by physical vapor deposition. The carbon nanotube structure104includes a plurality of carbon nanotubes and has a plurality of gaps formed by the carbon nanotubes. Therefore, the matrix102can be filled in the gaps or cover the surfaces of the carbon nanotubes of the carbon nanotube structure104. In the composite structure, the carbon nanotube structure104and the matrix102are firmly combined together.

If the matrix102is a polymer, when disposing the carbon nanotube structure104into the matrix102, the temperature of the matrix102is about 20° C. to about 50° C. higher than a glass transition temperature of the matrix102, and lower than a decomposition temperature of the matrix102. The pressure applied to the matrix102in the hot pressing method, is in a range from about three atmospheric pressures to about ten atmospheric pressures.

The method for making the damper100has no restriction. In one embodiment, the composite structure comprising the matrix102and the carbon nanotube structure104is corrugated to form a damper preform having a plurality of concentric and alternating ridges and furrows, and a through hole101is formed in a centre of the damper perform thereafter to obtain the damper100.

The surfaces of the carbon nanotube structure104can be coated by an enhancement layer. The material of the enhancement layer can be metal, diamond, boron carbide, or ceramics. The enhancement layer can improve the bonding force of the matrix102and the carbon nanotube structure104. The material of the enhancement layer is compatible with the material of the matrix102. The material of the enhancement layer can be the same as the material of the matrix102. For example, the material of the matrix102and the enhancement layer is metal.

In one embodiment, the carbon nanotube structure104comprises at least one carbon nanotube film. If the carbon nanotube structure104comprises a plurality of carbon nanotube films, the plurality of carbon nanotube films can be stacked. The carbon nanotube film comprises a plurality of carbon nanotubes. The plurality of carbon nanotubes in the carbon nanotube film can be single-walled, double-walled, and/or multi-walled carbon nanotubes. The diameters of the single-walled carbon nanotubes can range from about 0.5 nanometers to about 50 nanometers. The diameters of the double-walled carbon nanotubes can range from about 1 nanometer to about 50 nanometers. The diameters of the multi-walled carbon nanotubes can range from about 1.5 nanometers to about 50 nanometers.

The carbon nanotube film can be a freestanding film. The carbon nanotube film includes a plurality of carbon nanotubes distributed uniformly and attracted by van der Waals attractive force therebetween. The carbon nanotubes in the carbon nanotube film can be orderly or disorderly aligned. The orderly aligned carbon nanotubes are arranged in a consistently systematic manner, e.g., most of the carbon nanotubes are arranged approximately along a same direction or have two or more sections within each of which the most of the carbon nanotubes are arranged approximately along a same direction (different sections can have different directions). The disorderly aligned carbon nanotubes are arranged along many different directions, such that the number of carbon nanotubes arranged along each different direction can be almost the same (e.g. uniformly disordered); and/or entangled with each other. Specifically, the carbon nanotube film can be a drawn carbon nanotube film, a flocculated carbon nanotube film, a pressed carbon nanotube film, or a carbon nanotube film formed by spraying, coating, or deposition.

The drawn film can be drawn from a carbon nanotube array. Examples of the drawn carbon nanotube film are taught by U.S. Pat. No. 7,045,108 to Jiang et al., and WO 2007015710 to Zhang et al. The drawn carbon nanotube film includes a plurality of carbon nanotubes arranged substantially parallel to a surface of the drawn carbon nanotube film. A large number of the carbon nanotubes in the drawn carbon nanotube film can be oriented along a preferred orientation, meaning that a large number of the carbon nanotubes in the drawn carbon nanotube film are arranged substantially along the same direction. An end of one carbon nanotube is joined to another end of an adjacent carbon nanotube arranged substantially along the same direction by van der Waals attractive force. The drawn carbon nanotube film is capable of forming a freestanding structure. The successive carbon nanotubes joined end to end by van der Waals attractive force realizes the freestanding structure of the drawn carbon nanotube film. An SEM image of the drawn carbon nanotube film is shown inFIG. 3.

Some variations can occur in the orientation of the carbon nanotubes in the drawn carbon nanotube film. Microscopically, the carbon nanotubes oriented substantially along the same direction may not be perfectly aligned in a straight line, and some curve portions may exist. It can be understood that a contact between some carbon nanotubes located substantially side by side and oriented along the same direction cannot be totally excluded.

More specifically, the drawn carbon nanotube film can include a plurality of successively oriented carbon nanotube segments joined end-to-end by van der Waals attractive force therebetween. Each carbon nanotube segment includes a plurality of carbon nanotubes substantially parallel to each other, and joined by van der Waals attractive force therebetween. The carbon nanotube segments can vary in width, thickness, uniformity, and shape. The carbon nanotubes in the drawn carbon nanotube film are also substantially oriented along a preferred orientation. A thickness of the drawn carbon nanotube film can range from about 0.5 nm to about 100 μm. A width of the drawn carbon nanotube film relates to the carbon nanotube array from which the drawn carbon nanotube film is drawn. When the carbon nanotube structure104consist of the drawn carbon nanotube film, and a thickness of the carbon nanotube structure104can be relatively small (e.g., smaller than 10 μm), the carbon nanotube structure104can have a good transparency, and the transmittance of the light can reach about 90%. The transparent carbon nanotube structure104can be used to make a transparent damper100with the transparent base102.

The carbon nanotube structure104can include at least two stacked drawn carbon nanotube films. An angle between the aligned directions of the carbon nanotubes in two adjacent carbon nanotube films can range from about 0 degrees to about 90 degrees)(0°≦α≦90°). Spaces are defined between two adjacent and side-by-side carbon nanotubes in the drawn carbon nanotube film. If the angle between the aligned directions of the carbon nanotubes in adjacent carbon nanotube films is larger than 0 degrees, the carbon nanotubes define a microporous structure. The carbon nanotube structure104in one embodiment employing these films will define a plurality of micropores. A diameter of the micropores can be smaller than 10 μm. Stacking the carbon nanotube films will add to the structural integrity of the carbon nanotube structure104.

The flocculated carbon nanotube film can include a plurality of long, curved, disordered carbon nanotubes entangled with each other. A length of the carbon nanotubes can be larger than about 10 μm. In one embodiment, the length of the carbon nanotubes is in a range from about 200 μm to about 900 μm. Further, the flocculated carbon nanotube film can be isotropic. Adjacent carbon nanotubes are acted upon by van der Waals attractive force to obtain an entangled structure with micropores defined therein. The flocculated carbon nanotube film is very porous. The sizes of the micropores can be less than 10 μm. In one embodiment, the sizes of the micropores are in a range from about 1 nm to about 10 μm. Further, because the carbon nanotubes in the carbon nanotube structure104are entangled with each other, the carbon nanotube structure104employing the flocculated carbon nanotube film has excellent durability, and can be fashioned into desired shapes with a low risk to the integrity of the carbon nanotube structure104. The flocculated carbon nanotube film is freestanding because the carbon nanotubes are entangled and adhered together by van der Waals attractive force therebetween. The thickness of the flocculated carbon nanotube film can range from about 1 micrometer (μm) to about 1 millimeter (mm). In one embodiment, the thickness of the flocculated carbon nanotube film is about 100 μm.

The pressed carbon nanotube film can be a freestanding carbon nanotube film formed by pressing a carbon nanotube array down on the substrate. The carbon nanotubes in the pressed carbon nanotube film are arranged along a same direction or along different directions. The carbon nanotubes in the pressed carbon nanotube film can rest upon each other. Adjacent carbon nanotubes are attracted to each other and are combined by van der Waals attractive force. An angle between a primary alignment direction of the carbon nanotubes and a surface of the pressed carbon nanotube film is about 0 degrees to about 15 degrees. The greater the pressure applied, the smaller the angle obtained. If the carbon nanotubes in the pressed carbon nanotube film are arranged along different directions, the carbon nanotube structure104can be isotropic. Here, “isotropic” means the carbon nanotube film has properties identical in all directions substantially parallel to a surface of the carbon nanotube film. A thickness of the pressed carbon nanotube film ranges from about 0.5 nanometers (nm) to about 1 mm. A length of the carbon nanotubes can be larger than 50 μm. Clearances can exist in the carbon nanotube array, therefore, micropores exist in the pressed carbon nanotube film and are defined by the adjacent carbon nanotubes. An example of pressed carbon nanotube film is taught by US20080299031A1 to Liu et al.

Referring toFIG. 4, a damper200of a second embodiment is provided. The damper200is a corrugated round sheet having radially alternating concentric circular ridges and circular furrows. The damper200has a through hole201. The damper200includes a matrix202and a carbon nanotube structure204located in the matrix202.

The structure of the second embodiment of the damper200is similar to the structure of the first embodiment of the damper100, except that the carbon nanotube structure204in the damper200comprises at least one linear carbon nanotube structure. If the carbon nanotube structure204comprises a single linear carbon nanotube structure, the single linear carbon nanotube structure can be folded or can be wound to form a plane structure. If the carbon nanotube structure204comprises a plurality of linear carbon nanotube structures, the plurality of linear carbon nanotube structures can be substantially parallel to each other, crossed with each other or woven together to form a plane structure. The plane structure and the matrix202comprise a composite structure. Specifically, the plurality of linear carbon nanotube structure can first be formed to a planar shaped structure, and then composited with the matrix202by a hot pressing method to form a composite structure.

The linear carbon nanotube structure comprises at least one carbon nanotube wire. The diameter of the carbon nanotube wire is in a range from about 0.5 nanometers to about 1 millimeter. If the linear carbon nanotube structure includes a plurality of carbon nanotube wires, the carbon nanotube wires can be substantially parallel to each other to form a bundle-like structure or twisted with each other to form a twisted structure. The bundle-like structure and the twisted structure are two kinds of linear carbon nanotube structures.

The carbon nanotube wire can be untwisted or twisted. Treating the drawn carbon nanotube film with a volatile organic solvent can obtain the untwisted carbon nanotube wire. In one embodiment, the organic solvent is applied to soak the entire surface of the drawn carbon nanotube film. During the soaking, adjacent substantially parallel carbon nanotubes in the drawn carbon nanotube film will bundle together, due to the surface tension of the organic solvent as it volatilizes, and thus, the drawn carbon nanotube film will be shrunk into an untwisted carbon nanotube wire. The untwisted carbon nanotube wire includes a plurality of carbon nanotubes substantially oriented along a same direction (i.e., a direction along the length direction of the untwisted carbon nanotube wire). The carbon nanotubes are substantially parallel to the axis of the untwisted carbon nanotube wire. In one embodiment, the untwisted carbon nanotube wire includes a plurality of successive carbon nanotubes joined end to end by van der Waals attractive force therebetween. The length of the untwisted carbon nanotube wire can be arbitrarily set as desired. A diameter of the untwisted carbon nanotube wire ranges from about 0.5 nm to about 100 μm. An example of the untwisted carbon nanotube wire is taught by US Patent Application Publication US 2007/0166223 to Jiang et al.

The twisted carbon nanotube wire can be obtained by twisting a drawn carbon nanotube film using a mechanical force to turn the two ends of the drawn carbon nanotube film in opposite directions. The twisted carbon nanotube wire includes a plurality of carbon nanotubes helically oriented around an axial direction of the twisted carbon nanotube wire. In one embodiment, the twisted carbon nanotube wire includes a plurality of successive carbon nanotubes joined end to end by van der Waals attractive force therebetween. The length of the carbon nanotube wire can be set as desired. A diameter of the twisted carbon nanotube wire can range from about 0.5 nm to about 100 μm.

The carbon nanotube structure204also can include a carbon nanotube hybrid wire structure (not shown). The carbon nanotube hybrid wire structure can include a bundle-like structure formed by the at least one carbon nanotube wire and at least one base wire substantially parallel to each other, or a twisted structure formed by the at least one carbon nanotube wire and the at least one base wire twisted with each other. The carbon nanotube hybrid structure can include at least one linear carbon nanotube structure and at least one base wire substantially parallel to each other, crossed with each other, or woven together. A material of the base wire can be the same as that of the matrix202. The base wire can have an excellent specific strength and a low density. Further, the base wire can also have a high temperature resistance property. In one embodiment, the base wire can be resistant to a temperature larger than about 250° C. For example, the base wire can be fiberglass or carbon fibre.

A third embodiment of a damper300is illustrated inFIG. 5. The damper300comprises a matrix302and at least two carbon nanotube structures304located in the matrix302to form a composite structure. A through hole301is defined in a center of the damper300.

The structure of the damper300is similar to the structure of the damper100in the first embodiment, except that the damper300comprises at least two stacked carbon nanotube structures304spaced apart from each other. The carbon nanotube structure304can be at least one carbon nanotube film described in the first embodiment, or the plurality of linear carbon nanotube structures described in the second embodiment. The method for making the carbon nanotube structure can include a plurality of hot pressing steps or only one step.

The at least two carbon nanotube structures304can be stacked, substantially parallel, or coplanar with each other. In the matrix, the two carbon nanotube structures304can be spaced apart from each other or kept close to each other. In one embodiment, the damper300comprises two stacked carbon nanotube structures304spaced apart, and the matrix is a liquid-state polymer. The method for making the damper300includes, step A, locating the two carbon nanotube structure304into the liquid-state polymer, and step B, solidifying the liquid-state polymer after the liquid-state polymer soaks the carbon nanotube structures304. The carbon nanotube structure and the liquid-state polymer can be vacuumized before step B so that the air in the carbon nanotube structure304and the liquid-state polymer can be removed and the liquid-state polymer soaks into the gaps between the carbon nanotubes of the carbon nanotube structure304adequately.

Referring toFIGS. 6 and 7, a loudspeaker10of one embodiment includes a frame110, a magnetic circuit120, a voice coil130, a bobbin140, a diaphragm150, and a damper100.

The frame110is mounted on an upper side of the magnetic circuit120. The voice coil130is received in the magnetic circuit120and wound on the bobbin140. An outer rim of the diaphragm150is fixed to an inner rim of the frame110, and an inner rim of the diaphragm150is fixed to an outer rim of the bobbin140placed in a magnetic gap125of the magnetic circuit120.

The frame110can be a truncated cone with an opening on one end and includes a hollow cavity112and a bottom113. The hollow cavity112receives the diaphragm150and the damper100. The bottom113has a center hole111to accommodate a center pole124of the magnetic circuit120. The bottom113of the frame110is fixed to the magnetic circuit120.

The magnetic circuit120includes a lower plate121having the center pole124, an upper plate122, and a magnet123sandwiched by the lower plate121and the upper plate122. The upper plate122and the magnet123can be both substantially circular, and define a cylindrical space in the magnetic circuit120. The center pole124is received in the space and extends through the center hole111. The magnetic gap125is formed between the center pole124and the magnet123. The magnetic circuit120is fixed on the bottom113at the upper plate122.

The voice coil130is a driving member of the loudspeaker10. The voice coil130is made of conducting wire. When electric signals are inputted to the voice coil130, a magnetic field is formed by the voice coil130that varies with variations in the electric signals. The interaction of the magnetic field of the voice coil130and the magnetic circuit120induces the voice coil130to vibrate.

The bobbin140is light in weight and has a hollow structure. The center pole124is disposed in the hollow structure and spaced from the bobbin140. When the voice coil130vibrates, the bobbin140and the diaphragm150also vibrate with the voice coil130to produce pressure waves heard as sound.

The diaphragm150has a funnel configuration and is a sound producing member of the loudspeaker10. The diaphragm150can have a conical shape if used in a large loudspeaker10. If the loudspeaker10is small, the diaphragm150can have a round or rectangular planar shape.

The diaphragm150is held mechanically by the damper100. The damper100is fixed to the frame110and the bobbin140. The damper100allows the voice coil130to freely move up and down but not left and right, so that the loudspeaker10can have good mechanical strength and a good electroacoustical characteristic. The damper100can also be of the second and third embodiments of the damper200,300.

An external input terminal can be attached to the frame110. A dust cap (not shown) can be fixed over and above a joint portion of the diaphragm150and the bobbin140.

It is to be understood that, the loudspeaker10is not limited to the above-described structure. Any loudspeaker of any size and shape using the present damper100,200,300is in the scope of the present disclosure.

It is to be understood that the above-described embodiments are intended to illustrate rather than limit the disclosure. Any elements described in accordance with any embodiments is understood that they can be used in addition or substituted in other embodiments. Embodiments can also be used together. Variations may be made to the embodiments without departing from the spirit of the disclosure. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure.