Comparison with Conventional Designs
Comparison with Conventional Designs
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Here, comparisons with conventional designs are conducted primarily using tweeters as the main subject. In addition, full-range speakers and headphones are also included in the comparison based on their time-domain characteristics (Impulse, ETC, and STEP) within the tweeter frequency range.
Differences in sound quality and soundstage reproduction among various designs are determined by the amount of components that appear after the direct sound (delayed sound) and the speed at which they decay.
By unifying the comparison bandwidth, it becomes possible to directly compare the occurrence of delayed sound under the same conditions across different designs.
Furthermore, in the high-frequency range, time resolution is high, and delayed sound can be observed most clearly in Impulse, ETC, and STEP responses. Therefore, differences in time-domain characteristics among various designs can be evaluated most directly. In particular, time-domain behavior in the high-frequency range directly determines soundstage reproduction, including image definition, localization, and spatial clarity, making its evaluation extremely important in sound quality assessment.
Therefore, comparisons are conducted based on Impulse, ETC, and STEP responses in the high-frequency range, using the amount of delayed sound and its decay characteristics as the primary evaluation criteria.
AMT (Air Motion Transformer) is a tweeter principle proposed by Oskar Heil in the 1960s and is characterized by a diaphragm folded in an accordion-like structure.
In this section, measurements were conducted on two representative AMT products: the Mundorf AMT21CM2.1-C, regarded as a high-performance model of this type, and the AMT2-4 manufactured by the U.S. speaker parts manufacturer Dayton Audio. Their characteristics are described based on these measurements.
At first glance, the planar magnetic drive system may appear similar to the VCD (Voice Coil Diaphragm) method, as both employ a structure that drives the entire vibrating surface. However, their actual physical behavior differs significantly, resulting in fundamentally different characteristics and sound quality. These differences can be clearly observed in the Impulse, ETC, and STEP responses, and manifest audibly as variations in transient attack, decay behavior, and resolution.
Planar magnetic drive systems are rarely used for tweeter applications in loudspeakers. In this study, measurements were conducted using the planar magnetic headphone OPPO PM-3, and its impulse response, ETC, and step response were analyzed.
Based on these results, the characteristics of planar magnetic drive systems in the tweeter frequency range are clarified.
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