■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 shows a comparison of the ETC (Energy Time Curve) characteristics of each type of tweeter under 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: 10 cm
●Bandwidth: 3 kHz – 96 kHz (Butterworth HPF, 2nd order ×2; no LPF applied)
●Sampling Frequency: 192 kHz
●Normalization: Peak Normalization
●ETC Smoothing: 0.01 ms (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 can be clearly observed that the input energy is highly concentrated and radiated immediately after excitation, with extremely little residual energy thereafter.
・Very rapid decay after the initial peak
The ETC −40 dB decay time is extremely short, with the first crossing at 236 µs and final convergence at 378 µs, indicating that the energy dissipates within a very short time.
・Extremely low residual energy
The energy distribution after the initial response is minimal, showing that temporal energy dispersion is effectively suppressed.
・Minimal late-stage energy storage
Vibrational components in the mid-to-late time region are extremely low, and delayed components caused by reflections or re-radiation are almost nonexistent. These characteristics indicate that diaphragm breakup modes and internal reflections are effectively suppressed, preventing temporal energy dispersion and enabling rapid energy convergence. As a result, this directly contributes to accurate attack reproduction, high sound image clarity, and a transparent spatial presentation.
The VCD approach is not merely an extension of frequency response performance; rather, it is based on a design philosophy that emphasizes precise control of energy in the time domain, achieving both high sound image clarity and natural spatial reproduction at an advanced level.
■AMT-type : Mundorf AMT21CM2.1-C
The AMT (Air Motion Transformer) exhibits a strong initial response; however, periodic residual energy can be observed in the ETC.
・The initial peak is relatively sharp
・Residual energy appears at regular intervals thereafter
・Complete convergence requires a somewhat longer time
These characteristics are considered to result from the presence of multiple vibration modes and internal reflections inherent to the folded diaphragm structure, which cause the energy to be distributed and released over time. In addition, the AMT-specific rear radiation is reflected within the back chamber and re-transmitted through the thin diaphragm, contributing to delayed components that wrap around to the front.
■Dome-type : HiVi TN25
Dome-type tweeters exhibit relatively well-behaved decay characteristics; however, a noticeable energy tail is observed in the mid-time region.
・The initial response is stable
・Residual energy persists around 200–800 µs
・The convergence speed is moderate
These characteristics can be regarded as typical time-domain behavior of conventional dome-type tweeters.
Horn-type : Fostex FT17H
Horn-type tweeters exhibit high initial response efficiency, with energy being clearly radiated immediately after the input. However, in the ETC, a certain amount of residual energy can be observed following the initial peak.
・The initial peak is relatively strong
Due to acoustic loading by the horn, the energy is radiated efficiently and appears clearly immediately after excitation.
・Residual energy is observed after the initial peak
Energy persists for a certain period after the initial response, indicating the presence of temporally delayed components.
・The convergence speed is moderate
These characteristics are considered to result from reflections and propagation paths within the horn, as well as diffraction at the horn mouth, which introduce delayed energy components over time.
As a result, while horn-type tweeters provide high efficiency and a clear initial response, their time-domain behavior can be characterized as exhibiting a typical level of energy convergence.
Full-range type : Fostex FF105WK
Although a full-range unit clearly exhibits energy radiation immediately after input, the ETC shows that residual energy tends to persist over a relatively wide time range.
・he initial peak is clearly observed, but the rise is somewhat gradual
After the initial response, energy remains distributed over time, and multiple delayed components can be identified.
・It is clearly not optimized for high-frequency-only reproduction
・Convergence requires a relatively long time
The time required for the energy to decay to a low level is comparatively long, and rapid convergence is not achieved.
These characteristics are considered to result from diaphragm breakup modes associated with the size and structure of the cone, as well as reflections and re-radiation within the cone and surrounding structures, in addition to acoustic interactions within the cavity, all of which cause energy to be distributed and released over time.
Given its design philosophy of reproducing the full frequency range with a single driver, it can be said that bandwidth reproduction is prioritized over time-domain response.
As a result, while full-range units are capable of wideband reproduction using a single driver, they tend to exhibit energy dispersion and residual energy in the time domain, which can affect the accuracy of attack, the clarity of sound images, and the transparency of spatial reproduction.
■STEP Response (Step Response Waveform)
Next, the STEP response is compared using the official data of the Mundorf AMT21CM2.1-C, which is widely regarded as one of the fastest and best-performing examples, after aligning the conditions of both graphs.
【Initial Rise (Rise Speed and Temporal Concentration)】
The VCD-DT63 exhibits an extremely sharp rise with a very narrow main peak, showing almost no temporal spreading. This indicates that the energy is highly concentrated in time, demonstrating excellent tracking of the input signal.
In contrast, although the Mundorf AMT21CM2.1-C also shows a fast rise, its peak is slightly broader compared to the VCD-DT63, and a small degree of spreading is observed around the initial peak, likely due to structural factors. Therefore, in terms of temporal concentration, the VCD-DT63 is superior.
【First Undershoot (OSR and Damping Behavior)】
The VCD-DT63 exhibits a clearly defined first undershoot that is not excessive, and the subsequent oscillation is rapidly suppressed, indicating that the damping is within an appropriate range. In other words, the design ensures that the energy is effectively settled in the initial stage.
In contrast, the Mundorf AMT21CM2.1-C shows a relatively shallow and gentle undershoot; however, small-amplitude ripples tend to persist for a longer duration afterward. While the initial response is smooth, this indicates that energy remains in the later stage.
【Post-Rise Ripple and Convergence (after 0.2 ms)】
The VCD-DT63 reaches settling time at approximately 360 µs, and the residual vibration thereafter is extremely small, rapidly approaching the background noise level. This indicates a response with outstanding temporal cleanliness.
In contrast, the Mundorf AMT21CM2.1-C exhibits small-amplitude ripples that persist for more than 1 ms, with a tendency for periodic residual oscillations to be observed. This is considered to be caused by the characteristic rear radiation of the AMT, which is reflected within the back chamber and re-transmitted through the thin diaphragm, wrapping around to the front.
【Overall Waveform Characteristics (Design Philosophy)】
Examining the overall behavior of the STEP response, the VCD-DT63 releases its energy within an extremely short time and exhibits rapid decay without in-plane propagation of vibration. Its STEP response is fully consistent with the ETC, clearly indicating a design philosophy that prioritizes time-domain performance.
In contrast, although the Mundorf AMT21CM2.1-C shows very high performance in the initial response, its structure inevitably involves energy storage and back-and-forth motion. As a result, its STEP response exhibits behavior consistent with the periodic residual components observed in the ETC, and can be characterized as a design that prioritizes high efficiency, high SPL capability, and wide bandwidth.
【Perceptual Implications (as inferred from the STEP Response)】
From the STEP response, the VCD-DT63 suggests a perceptual tendency characterized by an extremely clear onset, with consonants and transient attacks reproduced with minimal smearing. The sound image is rendered with sharp contours, and the spatial presentation remains clear with little sense of haze.
In contrast, the Mundorf AMT21CM2.1-C provides a strong sense of loudness and energy due to its high efficiency, offering a sense of ease in reproduction and maintaining stable performance even at high sound pressure levels. However, the presence of small-amplitude residual vibrations in the later stage may be perceived as slight smearing or added reverberant tail during the overlap of fine signals and in the decay process.
【Overall Evaluation (Limited to the STEP Response)】
The Mundorf AMT21CM2.1-C exhibits one of the highest levels of transient performance among commercially available tweeters; however, in the STEP response, the VCD-DT63 demonstrates superior performance in both the sharpness of the initial response and the speed of subsequent convergence.
This indicates that the VCD structure fundamentally suppresses unnecessary energy storage in the time domain.
■Impulse Response (Impulse Response Waveform)
Furthermore, the Impulse Response is also compared using the official data of the Mundorf AMT21CM2.1-C, after aligning the conditions of both graphs.
【Main Peak (Initial Response and Temporal Concentration)】
The VCD-DT63 exhibits an extremely narrow and sharp initial peak, with energy highly concentrated near t = 0. In addition, almost no sluggishness is observed in the rise.
In contrast, although the Mundorf AMT21CM2.1-C shows a high peak, a slight broadening is observed, indicating that the VCD-DT63 is superior in terms of temporal concentration.
【Behavior Immediately After the Main Peak (Undershoot and Initial Damping)】
The VCD-DT63 exhibits a clearly defined undershoot, yet converges rapidly within a short time, releasing its energy in the initial stage.
In contrast, the Mundorf AMT21CM2.1-C shows a relatively gentle undershoot, but small-amplitude residuals persist for a longer duration, indicating energy retention in the later stage.
【Post-Rise Ringing / Convergence (after 0.2 ms)】
The VCD-DT63 effectively converges after approximately 0.2–0.3 ms, with almost no periodic ringing observed.
In contrast, the Mundorf AMT21CM2.1-C exhibits small but regular periodic components that persist for more than 1 ms. This is considered to be caused by rear radiation inherent to the AMT structure, which is reflected within the back chamber and re-transmitted through the thin diaphragm to the front.
【Design Philosophy as Reflected in the Overall Waveform】
The VCD-DT63 concentrates and radiates energy within a very short time and decays immediately; its Impulse Response, ETC, and STEP Response are mutually consistent, indicating a design that prioritizes time-domain performance.
In contrast, the Mundorf AMT21CM2.1-C achieves a very high level of initial response, but due to its structure, time-domain residuals cannot be completely avoided. This reflects a design philosophy that prioritizes high efficiency, high SPL capability, and wide bandwidth.
【Perceptual Implications (as inferred from the Impulse Response)】
The VCD-DT63 excels in clarity of onset, separation of consonants and transient attacks, sharp definition of image contours, and resistance to spatial haze.
The Mundorf AMT21CM2.1-C offers a strong sense of energy and weight, along with headroom due to its high efficiency and stable performance at high sound pressure levels.
【Overall Evaluation (Limited to the Impulse Response)】
The Mundorf AMT21CM2.1-C exhibits top-tier performance and an excellent impulse response among commercially available tweeters; however, structural limitations become evident in the time domain, whereas the VCD-DT63 demonstrates superior temporal concentration and convergence.
