Fostex T50RPmk4CL Closed-Back Studio Monitor Headphones with 4th Generation RP Driver

The Fostex T50RPmk4CL is the long-awaited closed-back version of Fostex’s renowned RP technology headphones, a series trusted by professional music studios worldwide for over 50 years. Building on the success of the semi-open T50RPmk4, this new model incorporates the 4th generation RP planar magnetic driver, developed and manufactured exclusively by Fostex, now housed in a fully sealed design.

This closed-back construction minimizes environmental sound leakage, making it ideal for vocal and instrument recording, as well as critical mixing and monitoring tasks. The T50RPmk4CL offers the same highly accurate sound reproduction that RP drivers are known for now with the added benefit of superior isolation.

T50RPmk4 Series Unified Housing Design

The T50RPmk4CL’s closed-back housing is based on the semi-open T50RPmk4, with meticulous sealing of all ventilation areas and precise sound balance tuning. This design ensures excellent isolation, allowing engineers and musicians to focus on the original sound with greater clarity.

Since the internal housing shape is identical between the T50RPmk4CL and T50RPmk4, users can switch between closed-back and semi-open models without experiencing tonal discrepancies making it easier to choose the best type for specific recording or mixing situations.

4th Generation RP Planar Magnetic Driver

The latest evolution of Fostex’s proprietary RP (Regular Phase) technology represents 50 years of refinement. For the 4th generation, several improvements were made:

Expanded vibration area of the planar diaphragm.

Redesigned printed coil pattern for more uniform performance.

Increased magnets sandwiching the diaphragm for improved magnetic control.

Optimized magnetic circuit components for smoother magnetic flux distribution.

These upgrades suppress unwanted diaphragm resonance, delivering sharper attack and decay, higher sensitivity, smoother frequency characteristics, and excellent transient response. The result is precise, detailed reproduction from deep bass to shimmering highs, with enhanced spatial positioning and sound field accuracy.

As with all RP drivers, quality and consistency are maintained through integrated manufacturing at Fostex’s own facilities.

Symmetrical Housing & Flexible Cable Connection

Both left and right earcups feature identical internal structures and cable connectors, allowing the cable to be connected to either side without affecting sound quality. This symmetrical housing eliminates typical left/right tonal differences found in many headphones.

The connectors use a 4-pole 3.5 mm jack, supporting both unbalanced and balanced connections for greater versatility. The supplied cable features high-quality OFC conductors for optimal signal transfer. An optional 4.4 mm balanced cable (ET-RP4.4BL) is also available.

Comfort & Earpad Design

The T50RPmk4CL uses thicker, low-resilience around-ear earpads for a secure yet comfortable fit, even during long studio sessions. The introduction of Ultrasuede® material adds a premium touch, enhancing comfort and durability.

The angled earpad design helps improve perceived sound staging, creating a more immersive listening experience while maintaining the closed-back isolation benefits.

Product Specifications:

Type: Closed-back, Dynamic

Driver: RP Planar Magnetic

Impedance: 28 Ω

Sensitivity: 97 dB/mW

Maximum Input Power: 3,000 mW

Frequency Response: 10 Hz - 40,000 Hz

Weight: Approx. 330 g (excluding cable)

Cable: Detachable 2 m OFC cable (3.5 mm, 4-pole to 3.5 mm, 3-pole)

Connectors: 3.5 mm (4-pole) with 6.3 mm adapter

Optional Cable: 4.4 mm Balanced Cable (ET-RP4.4BL)

Accessories: 2 m unbalanced cable, 6.3 mm conversion adapter, safety precautions