■What Is a VCD (Voice Coil Diaphragm) Speaker?
Hanada Speaker Laboratory conducts research and development on an entirely new loudspeaker architecture—the VCD (Voice Coil Diaphragm) speaker—with the objective of overcoming the fundamental limitations inherently associated with conventional diaphragm structures.
The VCD speaker proposes a mechanically highly rational Voice Coil Diaphragm (VCD) structure that suppresses the propagation of vibration itself, without relying on increased diaphragm rigidity or specific material properties.
Conventional loudspeaker design has primarily evolved with emphasis on steady-state metrics such as frequency response and distortion characteristics. However, actual auditory perception is strongly governed by time-domain behavior, including impulse response and energy decay.
In VCD technology, unwanted breakup modes and residual energy storage are fundamentally suppressed, resulting in transient behavior that approaches the characteristics of an ideal impulse waveform. The VCD speaker represents the world’s first loudspeaker concept to propose a new benchmark in transient reproduction.
This website presents an introduction to the VCD speaker and publishes the research outcomes of VCD technology in an objective and reproducible manner, with particular focus on Impulse, ETC, and Step response characteristics.
■Vibration does not propagate.
Therefore, the sound does not become blurred.
A structure that prevents vibration propagation changes sound quality at a fundamental level.
The only mechanical structure capable of simultaneously satisfying the seemingly contradictory requirements of “maintaining stable shape” while “preventing the spread of vibration” fundamentally liberates loudspeaker design from the structural limitation of breakup vibration.
As a result, transient response approaches the ideal impulse with remarkable accuracy, and sound becomes extraordinarily precise—from its initial rise, through its decay, to complete extinction.
The graph below compares the ETC (Energy Time Curve) characteristics of tweeters based on different operating principles, all measured under strictly identical conditions.
【Measurement Conditions 】 This comparison is conducted under conditions that prioritize accuracy over visual clarity.As a result, the data presented here most faithfully reflects the true time-domain response characteristics of each system.
●Acoustic Measurement Software: REW (Room EQ Wizard)
●Analysis Items: Impulse Response / ETC
●Measurement Distance: 2 cm (near-field measurement) ※Room reflections and spatial factors are eliminated in order to evaluate the intrinsic characteristics of the driver itself.
●Bandwidth: 3 kHz – 96 kHz (Butterworth HPF, 2nd order ×2; no LPF applied)
●Sampling Frequency: 192 kHz
●Normalization: Peak Normalization
●ETC Smoothing: None (common to all configurations)
ETC is a metric derived from the impulse response and represents how the energy of the input sound decays over time.
The faster unwanted energy settles, the less blurring occurs in the sound image, resulting in clearer localization and more precise spatial reproduction.
Differences in sound quality and soundstage reproduction are determined by the amount of sound arriving later than the direct sound (delayed sound).
In the ETC, the energy components appearing after the direct sound correspond to sound arriving later (delayed sound).
■VCD-type : Hanada Speaker Laboratory VCD-DT63
It is clearly observed that acoustic energy is concentrated and radiated immediately after excitation, with extremely little residual energy remaining thereafter.
・The decay following the initial peak is exceptionally fast.
ETC −30 dB：230 µs (Even high-performance AMT tweeters typically reach 300–400 µs; this value is effectively at the theoretical limit.)
ETC −40 dB：420 µs (Even high-performance AMT tweeters typically require 500–650 µs; this represents an extraordinarily short value, only several tens of microseconds above the ideal.)
・Unwanted residual energy is extremely low.
・Energy storage in the later time region is minimized.
These results indicate that breakup vibration on the diaphragm and internal reflections are effectively suppressed, preventing temporal dispersion of energy and allowing it to settle within a very short time span.
Such characteristics are directly linked to the accuracy of sound onset, the clarity of sound imaging, and the transparency of spatial reproduction.
Rather than focusing solely on high-frequency extension, the VCD system is based on a design philosophy that emphasizes precise control of sound in the time domain, achieving exceptional image clarity and natural spatial expression.
■AMT-type : Dayton Audio AMT2-4
The AMT system exhibits a strong initial response; however, periodic residual energy can be observed in the ETC.
・The initial peak is relatively sharp.
・Subsequently, energy remains at regular intervals.
・Complete settling requires a slightly longer time.
This is considered to be an effect in which rear radiation characteristic of AMT designs reflects within the back chamber and re-transmits through the thin diaphragm, wrapping around to the front.
■Dome-type : HiVi TN25
The dome-type tweeter exhibits a relatively well-behaved decay characteristic; however, a trailing of energy can be observed in the mid-time region.
・The initial response is stable.
・Residual energy persists in the region of approximately 200–800 µs.
・The settling speed is average.
Overall, this can be regarded as a typical time-domain response characteristic of conventional dome-type tweeters.
Horn-type : Fostex FT17H
While horn-type tweeters offer high efficiency, the ETC shows a tendency toward longer energy retention.
・Energy persists even after the initial peak.
・The decay slope is relatively gentle.
・時Temporal dispersion is comparatively large.
Full-range type : Fostex FF105WK
The full-range type shows a tendency toward greater residual energy.
・Energy remains over a wide time range even after the initial peak.
・It is clearly not a design dedicated to high-frequency reproduction.
・Time-domain settling is the slowest among the compared types.
By design, a single driver reproducing the entire frequency range prioritizes bandwidth coverage over time-domain response, and this characteristic is reflected in the observed behavior.
■Step Response Waveform
Next, we compare the step response waveform with the official data of the Mundorf AMT21CM2.1-C, which is widely regarded as a representative example of one of the fastest and best step responses currently achievable.
The Mundorf AMT21CM2.1-C exhibits top-class transient performance among commercially available tweeters; however, in the step response, the VCD-DT63 demonstrates clear superiority in both the sharpness of the initial response and the speed of subsequent settling.
This indicates that the VCD structure fundamentally suppresses unnecessary energy storage in the time domain.
■Impulse Response Waveform
Additionally, we also compare the impulse response waveform with the official data of the Mundorf AMT21CM2.1-C.
The Mundorf AMT21CM2.1-C exhibits top-tier performance and impulse response among commercially available tweeters; however, in the time domain, structural limitations become apparent, while the VCD-DT63 demonstrates superior temporal energy concentration and settling behavior.
