Introduction to the VCD Speaker
Introduction to the VCD Speaker
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The high performance of the VCD (Voice Coil Diaphragm) speaker is achieved through the combination of two innovative technologies: the “VCD structure,” which suppresses vibration propagation without relying on increased diaphragm rigidity or specific material properties, and the “VCD magnet plate,” which generates a strong, uniformly directed magnetic field over a wide area.
■VCD Diaphragm Structure
The VCD (Voice Coil Diaphragm) diaphragm may appear similar in form to a planar magnetic diaphragm; however, it adopts a fundamentally different structure in the aspects that directly determine performance.
●High-Density Structure with No Gaps Between Conductors
In the VCD structure, the conductors (voice coils) are arranged at high density without any gaps. This is a distinctive feature unique to VCD.
・Significant reduction of unwanted lateral vibration
Because adjacent coils mutually restrain lateral movement, vibration is effectively confined to the front–back direction. As a result, unwanted vibrations originating from lateral motion are greatly reduced, enabling operation closer to ideal piston motion.
・Suppression of rear-sound leakage
Since there are no gaps between conductors, sound generated on the rear side is less likely to leak to the front. Rear sound inherently involves time delay and reflections that disturb phase and waveform; therefore, suppressing such leakage significantly contributes to improved time-domain characteristics and reduced distortion.
Furthermore, because each conductor is divided into small units and vibration propagation is suppressed, a thicker diaphragm can be adopted, which further enhances the suppression of rear-sound leakage.
・Improved magnetic field utilization efficiency
The high-density arrangement of conductors allows magnetic flux to be utilized more efficiently.
●Ultra-Thin and Flexible Movable Support
The support structure that holds the conductors (movable support) is extremely thin and flexible, allowing each conductor to vibrate independently as a small unit in the front–back direction.
This structure achieves exceptionally high vibration control performance compared with conventional designs.
・Suppression of vibration propagation
Because each conductor operates independently as a small unit, energy is less likely to spread across the entire diaphragm, significantly suppressing unwanted vibration propagation.
・Reduction of breakup modes through suppression of standing waves
Standing waves are less likely to form on the diaphragm surface, resulting in a substantial reduction in breakup vibration.
Thus, the VCD structure represents a diaphragm design that structurally achieves improved time-domain performance.
The “ultra-thin and flexible movable support” is made possible precisely because of the high-density structure with no gaps between conductors. Since adjacent coils mutually support one another, the mechanical load imposed on the support structure is reduced, enabling the realization of an ultra-thin movable support capable of flexible motion.
Furthermore, this high-density arrangement without gaps between conductors itself can only be achieved through the “VCD magnet plate,” which forms a strong, uniformly directed magnetic field over a wide area.
■VCD Magnet Plate
The VCD (Voice Coil Diaphragm) magnet plate adopts a structure composed of multiple small magnets with different magnetization directions. This configuration makes it possible to simultaneously achieve three key requirements within the VCD diaphragm region: (1) high magnetic flux density, (2) a wide-area magnetic field, and (3) a uniform in-plane magnetic field distribution.
The magnetization direction and placement range of each small magnet are optimized through numerical simulation to maximize these characteristics.
●Magnetization Direction that Achieves High Magnetic Flux Density
In this simulation, a cylindrical magnet plate with a diameter of 100 mm and a thickness of 10 mm is modeled, and its central cross section is displayed. In the figure, the X-axis represents the radial direction, and the Y-axis represents the thickness direction of the magnet. The magnet region is shown as a green grid (□).
The VCD diaphragm is positioned 5 mm above the surface of the magnet plate and arranged parallel to it. In the figure, this corresponds to the scale position marked “+5.”
The radial range from 10 mm to 45 mm on the diaphragm is defined as the conductor region (orange line) and is designated as the effective driving area.
The magnetic flux that generates Lorentz force in the conductors of the VCD diaphragm is the component parallel to the diaphragm surface and directed radially. In this document, this component is defined as the “effective magnetic flux component.” In the present analysis, this corresponds to the X-direction component extending from the center toward the outer circumference.
The optimal magnetization direction at each location within the magnet plate was determined as the condition that maximizes the surface-averaged (simple average) value of the effective magnetic flux component within the effective driving area.
The resulting distribution of magnetization directions is indicated by arrows within the magnet region.
This analysis was conducted using three-dimensional finite element method (FEM) simulation under unexcited static magnetic field conditions.
●Magnetic Flux Distribution of the VCD Magnet Plate
This simulation illustrates the magnetic flux distribution of the magnet plate designed for the VCD tweeter. The magnet region is displayed as a green grid (□). A cylindrical opening is provided at the center of the magnet plate; however, this serves as a structural feature for diaphragm mounting and is not a sound passage.
The VCD diaphragm is positioned 0.75 mm above the surface of the magnet plate and arranged parallel to it. In the figure, this corresponds to the scale position marked “0.” In this tweeter, the radial range from 4 mm to 12.5 mm on the diaphragm (indicated by the orange line) is defined as the effective driving area, within which the conductors are placed.
The direction of magnetic flux in space is represented by lines whose lengths are proportional to the magnitude of the magnetic flux density.
Among the magnetic flux components that generate Lorentz force in the conductors of the VCD diaphragm, the effective magnetic flux component is defined as the radial component within the plane of the diaphragm. In this figure, the distribution of this component at the diaphragm position is evaluated.
The graph shown at the bottom of the figure presents the magnitude of the effective magnetic flux component at the diaphragm position along the radial direction.
The small magnets that constitute the magnet plate are designed so that the effective magnetic flux component is as uniform as possible within the effective driving area (indicated by the orange line). The primary design conditions for achieving this are as follows:
1.The magnetization direction and placement range of the small magnets for efficiently maximizing the effective magnetic flux component while achieving wide-area distribution
2.The position and dimensions of the sound passage openings provided between the small magnets (with consideration for uniformity of the effective magnetic flux component)
3.The overall assembly feasibility and structural rationality of the magnet plate
This analysis was conducted using three-dimensional finite element method (FEM) simulation under unexcited static magnetic field conditions.
This simulation illustrates the magnetic flux distribution assuming a conventional magnet arrangement, using the same total magnet volume as the VCD tweeter magnet plate for comparison.
The configuration consists of a cylindrical magnet with an outer diameter of 11 mm and a thickness of 7 mm placed at the center, and a ring-shaped magnet with an outer diameter of 40 mm, an inner diameter of 22 mm, and a thickness of 7 mm positioned around it.
The analysis was conducted in the same manner as for the VCD tweeter magnet plate, using three-dimensional finite element method (FEM) simulation under unexcited static magnetic field conditions. The direction of magnetic flux in space is represented by lines whose lengths are proportional to the magnitude of the magnetic flux density.
The graph shown at the bottom of the figure plots the effective magnetic flux component (the radial component within the diaphragm plane) along the radial direction at a position 0.75 mm above the surface of the magnet plate (corresponding to the scale position “0” in the figure).
When the radial range of 4–12.5 mm on the diaphragm (indicated by the orange line) is defined as the effective driving area and the conductors are placed within this region, the graph exhibits large fluctuations, confirming significant variation in driving force. The magnetic flux density within the effective driving area is also low, and its simple average differs by approximately a factor of 1.5 compared with the VCD magnet plate.
Under such a conventional configuration, achieving an effective magnetic flux component equivalent to that of the VCD tweeter magnet plate cannot be realized simply by increasing the magnet volume. This is because magnets must inevitably be placed at positions distant from the effective driving area. Even in practical trials where the magnet volume was significantly increased under the constraint of rear-side placement behind the diaphragm, an equivalent effective magnetic flux component could not be obtained.
Furthermore, even when the effective magnetic flux component was small, it was not possible to achieve the uniform distribution within the effective driving area that is realized by the VCD magnet plate.
■ Conclusion: VCD Technology — Redefining the Driving Principle
VCD technology is not an incremental improvement along the conventional path.
It is a new loudspeaker architecture born from a fundamental redesign that integrates the diaphragm and magnetic circuit as a unified system and reexamines the driving principle itself.
The VCD structure prevents vibration from propagating across the diaphragm surface and structurally blocks rear-side sound. It is based on the concept of radiating sound directly from the driving source rather than from the entire diaphragm surface.
Complementing this is the VCD magnet plate, which efficiently concentrates only the magnetic flux required for driving.
By integrating these two elements, VCD simultaneously achieves characteristics that have traditionally been difficult to reconcile: rapid rise time, fast decay, high driving efficiency, and suppression of unwanted vibration.
It is not merely a matter of increasing rigidity or adding more magnet material.
It is about fundamentally optimizing the way vibration propagates and magnetic flux flows.
The sound that emerges from this approach exhibits exceptional clarity, combining response speed with a sense of stillness, as if the motion of the driving source were directly manifested in space.
VCD is a technology intended to redefine conventional assumptions in loudspeaker design.
It represents a new approach — transforming sound through structure.
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