1. Technical Field
The invention, in its several embodiments, pertains to loudspeaker cones and more particularly to composite loudspeaker cones.
2. State of the Art
A loudspeaker cone may be described as an acoustical piston that, when in vibratory operation, increases and decreases air pressure over its surface as part of the role of a loudspeaker working as a transducer turning electrical signals into a recreation of the original sound represented by the electrical signals. A loudspeaker may be characterized as having a particular piston range where, within such a range, the sound pressure over the entire surface of the cone is in phase. When a cone enters a breakup mode, part of the cone moves one direction while another part of the cone moves in the opposite direction. In moving up the frequency range, the first occurrence of this bending or resonant behavior may be termed the first breakup mode of the cone, and the frequency range preceding the first breakup mode may be termed the “pistonic” range of the cone. Above the first breakup mode, the phase coherency necessary to support fully faithful stereophonic reproduction is difficult to maintain and is a source of distortion of the original sound.
Loudspeaker cones may be made from non-resonant material, i.e., materials that exhibit well-damped characteristics, in order to suppress lower frequency breakup modes and/or extend the pistonic frequency range. The type, location, and geometry of the non-resonant material of a loudspeaker cone, while extending the pistonic region, may adversely suppress percussive sounds. Accordingly, there exists a need for a loudspeaker cone having a wide pistonic region, i.e., a high frequency first breakup mode, that does not overly dampen the reproduction of percussive sounds.
A mechanical property that may be used to characterize a material for a composite loudspeaker is the density of the material, where less dense materials tend to act with less inertia and as such are more responsive to fluctuation in the magnetic field to which a voice coil is subjected. A second mechanical property that may be used to characterize a material for a composite loudspeaker is the Young's modulus (E) that can be determined by dividing the tensile stress of a material by the tensile strain of the material. Some materials, such as wood and carbon, have a Young's modulus that will change depending on which direction the force is applied, that is, they are anisotropic. When some materials are composites of two or more ingredients, they may exhibit a “grain” or similar mechanical structure indicative of being anisotropic. As a result, these anisotropic materials exhibit different mechanical properties based on the direction of the load. For example, a carbon fiber is stiffer, i.e., has a higher Young's modulus, when loaded parallel to, i.e., along the grain of, the fibers than when loaded perpendicular to the grain.