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Fostex’s proprietary RP (Regular Phase) Technology full-range planar diaphragm driver has undergone continuous evolution since its inception in 1974, now spanning over 50 years. Compared to conventional dynamic drivers, the RP driver enables uniform and regular phase drive across the entire diaphragm.It achieves precise rise and fall times across all frequency bands, delivering sharp resolution, wide dynamic range, and excellent transient response with low distortion. This enables accurate, uncolored sound reproduction of the input signal. Consequently, it is utilized as the driver unit in professional recording studio monitor headphones, and the RP series has earned recognition in studios worldwide.

Among its history, the third-generation RP driver installed in the T50RP, born in 2001, achieved a dramatic evolution. This involved changing from the previous circular diaphragm to a square diaphragm and replacing the magnet with a more powerful bar-shaped neodymium magnet.This third generation solidified its position as a monitor headphone, set the standard for competitors using planar diaphragms, and became the driving force behind the current trend.

Though the third-generation RP driver served for nearly 20 years, its final application was in the T60RP, featuring a wood housing specifically optimized for listening. Then, in 2024, the fourth-generation RP driver was completed, building upon the third generation with further refinements.The fourth generation features a newly designed printed coil pattern to expand and homogenize the diaphragm’s vibrating area, while also increasing the number of magnets. Components within the magnetic circuit were also overhauled to optimize magnetic flux distribution and suppress unwanted diaphragm resonance. This results in sharper rise and fall response, improved sensitivity, smoother frequency response, and markedly superior transient performance.

The first model announced to feature the fourth-generation RP driver was the T50RPmk4. However, the T60RPmk2 was also born, incorporating the fourth-generation RP driver into the popular T60RP for listening purposes, along with various improvements such as switching to detachable cables with connectors on both sides. It is highly regarded as a reasonably priced yet high-quality model within the increasingly expensive market of planar magnetic headphones designed for listening.Based on this T60RPmk2, the T60RPmk2ai was crafted as the first domestically produced model in the T60RP series. It incorporates the same Awa indigo finish and solid hard maple wood housing found in the flagship TH1000RPmk2 and TH1100RPmk2.

The housing of the T60RPmk2, changed from solid black walnut to the harder solid hard maple also used in guitars, continues to employ a semi-open design. Its finish incorporates dyeing with Awa indigo by skilled artisans, minimizing the finish’s impact on sound to achieve a natural, moderately tight sound without coloring.The housing’s presence, blending the subdued hue of Awa indigo with the beauty of hard maple grain, and its timeless, elegant finish represent a high-quality presentation inherited from the flagship model, satisfying the desire to own it.

The internal wiring from the RP driver to the connector within the housing has been upgraded to 7N-grade high-purity OFC, the same material used in our higher-end models. Although the distance is minimal, using higher-purity copper wire at the final point of signal input to the driver is expected to reduce transmission loss and improve sound quality, resulting in a particularly clear, uncolored sound with excellent openness.

Additionally, the ear pads now come standard with Toray’s Ultrasuede® ear pads, previously an optional accessory. They provide a soft, premium feel that minimizes heat buildup, while the low-rebound cushioning and around-ear design ensure comfort even during extended wear. Furthermore, they deliver smooth, high-quality sound across the entire frequency range.

The detachable cable using a dual-output configuration with a 3.5mm 2-pole connector is also carried over from the T60RPmk2.In addition to the optional balanced cable ET-RP4.4BL2Y with a 4.4mm balanced plug, the detachable TH1000RPmk2/TH1100RPmk2, which also uses the same 2-pole 3.5mm connector, comes standard with the unbalanced ET-TH2.0UB2Y/ET-TH4.4BL2Y, which uses the same grade of conductor as the internal wiring.

Compared to the T60RPmk2, the T60RPmk2ai features a stiffer housing and high-purity internal wiring. This results in a tighter soundstage, greater transparency, and an overall evolution towards a refreshingly crisp sound with excellent airiness.Experience the crisp attack of the rhythm section and the natural gradation of reverberation. This is not a tendency towards thinness; instead, orchestras are rendered with rich, expansive melodies from the wind and string sections, while the low end delivers a solid, full-bodied presence. The resonance of percussion instruments meticulously captures the nuances of the drumhead, creating a brilliant harmony alongside the wet, lustrous quality of strings with excellent harmonic sustain.

Furthermore, the jazz horn section possesses a thick, stable body, and the refreshing quality of the reverberation stands out, including the soft touch of cymbals and piano. The balance between the smooth string movement and the resilient body resonance of the double bass is exquisite, creating an extremely pleasant sound. Vocals are lustrous and expansive, with the movement of the mouth clearly expressed.For rock recordings, the rhythm section faithfully conveys the kick drum’s dense, fat impact, while electric guitar riffs are rendered with tenacious brilliance.

Finally, I swapped to the optional ET-TH2.0UB2Y cable, which uses the same 7N-grade high-purity OFC conductor as the internal wiring, to verify the sound when unified with 7N-grade components.Compared to the standard high-purity OFC conductor cable included, the sound exhibited better separation and higher transparency, with improved spatial imaging. The precision of reverberation and tonal gradation also improved, delivering a sound with excellent separation and depth while maintaining sound image density.

The wet, lustrous quality of string instruments, the natural richness of woodwinds, and the sudden emergence of a truly lifelike soundstage—all are elevated to a level of expression far surpassing standard cables. This achieves both excellent forward presence and a refreshingly open, spacious sound. Alongside its fatigue-free, refined, and flowing texture rendering, it offers a glimpse of the high-resolution, natural spatial expression that hints at the “RP lineage”—a lineage long praised even as monitor headphones.

■Listening Samples
〇Andrea Battistoni conducting the Tokyo Philharmonic Orchestra: Mahler: Symphony No. 5 ~ “First Movement”
〇 ‘Pure2-Ultimate Cool Japan Jazz-‘ ~ “Unreachable Love”
〇 Suara “Kimi ga Tame” 11.2MHz Recording
〇 Chō “The Calling”
〇 TOTO ‘TAMBU’ ~ “Gift Of Faith”

T60RPmk2kai Product Page

Profile

Takashi Iwai

Born in Nagano Prefecture in 1977. He began avidly reading audio magazines in junior high school and started building his own vacuum tube amplifiers during high school. He also awakened to the appeal of music. After attending a specialized school for sound engineering, he found employment at a recording studio in Tokyo. Following a stint working at a game company, he gained opportunities to write for audio magazines.He writes audio reviews for publications such as MJ・Radio and Experiment, Stereo, PROSOUND, Audio Accessory, and analog, drawing on his experience in the environments where music is created.