■Minimize the Front Surface Area
The front structure of a loudspeaker is designed to radiate sound, but at the same time it can also become a source of unwanted reflections. Therefore, minimizing the frontal surface area is important for achieving high sound quality and natural soundstage reproduction. 

The frontal surface area of a loudspeaker is one of the factors that significantly influence both sound quality and soundstage reproduction.
Its effects can be broadly considered in the following two aspects:
1) The influence of the diaphragm area of the speaker unit
2) The influence of the size of the unit itself and the baffle used to mount the unit

Regarding item 1), the diaphragm area has the characteristic that directivity becomes stronger as the area increases. Since directivity is an important factor that greatly influences soundstage reproduction, this point will be discussed in another section.
Here, the discussion focuses mainly on item 2), namely the influence of the size of the unit itself and the baffle.

■Baffle Area and Edge Reflections
When a large surface area exists on the front side of a loudspeaker, time delays caused by edge reflections occur.
Sound radiated from the speaker follows the process:
Radiation from the speaker → Propagation along the baffle surface → Arrival at the baffle edge → Diffraction at the edge → Re-radiation as a secondary sound source

Through this process, the sound is re-radiated with a time delay.
In impulse response and ETC characteristics, this reflected sound appears as a small reflection component.
Furthermore, the larger the frontal surface area becomes, the greater the delay time of this reflected sound.

■Conventional Loudspeaker Design
In conventional loudspeaker design, there has also been an approach that utilizes the baffle area.
This is because a larger surface area can strengthen forward radiation, sometimes making the sound image appear clearer.
However, this method adjusts sound characteristics by relying on elements other than the speaker unit itself, and therefore has both advantages and disadvantages.
In particular, as the performance of the speaker unit improves, the influence of these side effects tends to become relatively more significant.

■Evaluation of the Effects on Sound Quality 

To evaluate the effect of a baffle placed in front of the tweeter on its time-domain characteristics, a comparison was conducted with and without a paper baffle.
The measurement results of the Impulse Response, ETC (Energy Time Curve), and Step Response are shown in the figure below. 

To evaluate the effect of a baffle placed in front of the tweeter on its time-domain characteristics, a comparison was conducted with and without a paper baffle.
The measurement results of the Impulse Response, ETC (Energy Time Curve), and Step Response are shown in the figure below. 

When a baffle with an outer diameter of 100 mm is placed in front, no significant change is observed in the initial response; however, the delayed energy after 100 µs increases, indicating a tendency for reduced convergence in the time domain. 

■Characteristics of the Impulse Response
In the initial response region of 0–60 µs, the red (without baffle) and green (with paper baffle) curves are nearly identical, indicating no significant change in the intrinsic transient characteristics of the unit.
This suggests that the influence of the baffle does not affect the driving or damping systems, but is primarily due to the external sound field, and that the unit’s original initial response (direct sound) is preserved.

In the second peak region of 60–120 µs, particularly around 70–110 µs, the red curve is slightly larger, while the green curve is relatively suppressed. Although the response with the baffle may appear better at first glance, this difference is considered to result from temporal dispersion of energy caused by reflections from the front baffle and diffraction near its edges. In other words, the red curve represents a response with temporally concentrated energy, whereas the green curve reflects a response in which energy is dispersed due to the superposition of reflected components.

Furthermore, in the 180–250 µs region, a clear increase is observed in the green curve, which is considered to be a delayed component caused by reflections from the front baffle.
This delay corresponds to approximately 200 µs, which translates to about 68 mm in terms of sound propagation distance. This is on the same order as the baffle radius (approximately 50 mm), indicating consistency with a reflection path originating from the baffle.

These differences in time-domain characteristics may have the following effects on sound quality:
・Red (without baffle): The sound image has clear contours, fast rise, and clean decay, resulting in a tight and well-defined spatial impression.
・Green (with baffle) : Due to increased temporal dispersion and delayed components, the sound image becomes slightly enlarged, high-frequency details (e.g., hi-hats) become somewhat blurred, and although the soundstage appears wider, the focus tends to be slightly softened. 

 ■Characteristics of the ETC (Energy Time Curve)
In the initial response region (0–100 µs), the red (without baffle) and green (with paper baffle) curves are generally consistent, indicating no significant difference in the energy distribution of the direct sound.
This suggests that the initial radiation characteristics of the unit are maintained regardless of the presence of the baffle.

In contrast, beyond 100 µs, a clear difference emerges between the two. In particular, in the 150–400 µs range, the green curve shows slower decay and maintains a higher energy level compared to the red curve.
This difference is considered to result from reflected components from the front-mounted paper baffle being superimposed with a time delay.
Furthermore, the increase in energy observed around approximately 200 µs corresponds to the delayed component identified in the impulse response, and is consistent with contributions from front-side reflections.

 This delay corresponds to a propagation distance on the order of several tens of millimeters in terms of sound velocity, which aligns with the dimensions of the baffle, suggesting that it is primarily caused by front reflection paths.
As a result, under the condition with the baffle, the temporal convergence of energy is delayed and time dispersion is increased.

■Characteristics of the Step Response
In the initial rise region (0–100 µs), the red and green curves are nearly identical, indicating no difference in the initial response speed of the unit or in the rise characteristics of the direct sound.
This suggests that the presence of the baffle does not affect the driving or damping characteristics.

In the subsequent 100–400 µs region, the green curve exhibits a slightly larger response amplitude than the red curve, and the time required for convergence is longer.
This is interpreted as the result of delayed reflected components from the front baffle being superimposed, thereby emphasizing secondary responses in the step response.
Furthermore, the delayed component around approximately 200 µs observed in the impulse and ETC is also manifested in the step response as a swelling and delayed convergence, indicating consistency among the three results.

Thus, under the condition with the baffle, the temporal distribution of energy becomes broader, and the convergence of the response tends to be more gradual.

■Physical Interpretation Integrating Impulse, ETC, and Step Metrics
Based on the above results, the following points can be summarized:
・The initial response (direct sound component) is nearly identical under both conditions, indicating no significant change in the intrinsic reproduction characteristics of the unit.
・The differences between the two conditions appear primarily as the addition of delayed components (front-side reflections).
・Diffraction is considered a secondary factor, while the primary cause is front reflection.
・The influence of the baffle consistently appears across Impulse, ETC, and Step responses as an increase in temporal dispersion.

These differences in time-domain characteristics may manifest as the following perceptual differences:
・Without baffle: The sound image has clear contours, fast rise, and clean decay.
・With baffle: Due to the addition of delayed components caused by front reflections, the sound image becomes slightly more diffuse and the spatial spread increases, while the focus tends to become slightly softer.

In general, these effects may appear as a reduction in temporal resolution (i.e., an increase in perceived “smearing”), and may be perceived as the following changes:
・The contours of the sound image become slightly less distinct.
・Fine localization and spatial detail are reduced.
・High-frequency sharpness tends to decrease.

A similar comparison was conducted for the HiVi TN25 to evaluate the effect of a baffle placed in front of the tweeter on its time-domain characteristics, comparing conditions with and without a paper baffle.
The measurement results of the Impulse Response, ETC (Energy Time Curve), and Step Response are shown in the figure below. 

Furthermore, the measurement results of the Impulse Response, ETC (Energy Time Curve), and Step Response for the VCD-DT63 and HiVi TN25, with and without the paper baffle, are overlaid and presented. 

■Characteristics of the HiVi TN25 
Similar to the VCD-DT63, the installation of a front baffle results in increased delayed energy and slower decay in the Impulse, ETC, and Step responses.
This indicates that the influence of front-side reflections is not specific to a particular driver type, but is a general phenomenon.

However, compared to the VCD-DT63, the differences observed in the TN25 do not appear as distinct delayed peaks, but rather as delayed components distributed toward later times.
It should be noted that this does not imply that the response is newly extended further into later times, but instead indicates that the energy is distributed over a broader time range.
This behavior is considered to result from the inherently greater time dispersion of dome-type tweeters, in which reflected components are more likely to be superimposed on the existing response.
As a result, while the physical effect of the baffle is common to both cases, its manifestation differs depending on the intrinsic time-domain characteristics of the unit.