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Overview
The T50RPmk4CL is the latest closed-back model of the RP technology headphones that have been adopted by professional music studios worldwide, continuing to evolve for over 50 years since their inception. The T50RPmk4, equipped with the 4th generation RP driver featuring Fostex's uniquely developed and manufactured planar magnetic driver, has been arranged as a long-awaited closed-back type. It achieves dense sound monitoring that suppresses environmental sound leakage during vocal and instrument studio recording and mixing, and can be used as a closed-back headphone with the accurate sound reproduction characteristic of RP drivers.
The closed-back housing is based on the semi-open T50RPmk4 housing, with careful sound insulation of each ventilation part and meticulous sound balance tuning. By ensuring sound isolation, it enables more concentrated monitoring of the dense original sound. Additionally, since the internal shape of the housing is identical between the T50RPmk4CL and T50RPmk4, you can choose either the closed-back or semi-open type according to your work and environment from recording to mixing without worrying about sound differences.
The RP technology planar magnetic driver, which has been continuously improved with proprietary technology for 50 years, has undergone significant enhancements in its 4th generation. To expand and uniformize the vibration area of the planar diaphragm, the magnets sandwiching the diaphragm have been increased, and the printed coil pattern has been redesigned. Additionally, by renewing the magnetic circuit components and optimizing magnetic flux distribution, unwanted resonance of the diaphragm is suppressed, achieving sharp response in sound attack and decay. The 4th generation driver, developed by fully incorporating various technologies cultivated over the years, simultaneously achieves improved sensitivity, smooth frequency characteristics for easier monitoring, and excellent transient response. By enabling accurate and delicate reproduction from deep bass to high frequencies, it further enhances the accurate positioning and sound field reproduction capabilities compared to previous models. As before, consistent quality is ensured through integrated manufacturing at the company’s own factory.
Both the left and right housings are equipped with connectors for the supplied cable, so that the cable can be connected to either the left or right depending on the usage environment. In addition, by making the left and right housings symmetrical, the difference in sound characteristics, usually caused by differing internal structures between sides, has been eliminated. The connector is equipped with a 4-pole 3.5mm connector, which supports balanced connections, increasing ease of use and versatility. The cable uses high-quality OFC conductors.
Features
• For Audiophiles, Musicians, Creators
• Planar Magnetic Driver
• Proprietary Regular Phase Technology
• Closed-Back Earcups, Flat & Clear Sound
• Improved Magnetic Circuit
• Sensitivity of 97 dB
• Frequency Response of 10 Hz to 40 kHz
• Symmetrical Housing
• Detachable 3.5mm TRRS to TRS Cable
What's In The Box?
• Fostex AMS-T50RPMK4-CL Premium Closed-Back RP Headphones
• Detachable 3.5mm TRRS to TRS Cable
• 3.5mm to 1/4" TRS Adapter
• Limited 1-Year Manufacturer Warranty
Generating expert take…
Fostex emerged in 1973 as the branded consumer and professional division of Foster Electric Co., Ltd., a Japanese loudspeaker manufacturer founded in 1949. Established to bring Foster's high-quality speaker components directly to dealers and customers, Fostex quickly gained international recognition through innovative products like the T20RP headphones and 6301 studio monitors. The brand's foundation rests on Foster's position as one of the world's largest OEM loudspeaker developers, employing tens of thousands across multiple countries and manufacturing millions of speaker units monthly.
The company built its reputation across three interconnected product categories: professional studio equipment, consumer headphones, and powered monitor speakers. Fostex became particularly renowned for pioneering RP (Regular Phase) technology, which delivers clear sound with high sensitivity and wide dynamic range—a signature that defines their headphones, microphones, and speaker designs. Beginning in 1978, the brand expanded into professional speaker development, eventually introducing the PM series of powered monitors and establishing itself as a trusted choice for recording studios, broadcast facilities, and serious home listeners.
Fostex occupies a distinctive middle ground in the audio market: neither ultra-premium boutique nor mass-market consumer, but rather a respected specialist brand with deep professional credentials. Their products appeal to recording engineers, studio owners, and discerning hi-fi enthusiasts who prioritize accuracy and reliability over luxury positioning. The 6301B monitor remains an industry standard after decades in production, while the T20RP headphones maintain popularity among studio professionals—testament to Fostex's enduring reputation for sonic integrity and engineering excellence.
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