The S/850 is the result of relentless refinement. This progress comes not only from exploring newer, finer materials, but also from the thousands of hours of critical listening our team undertakes each year—experience that transforms raw engineering into musical and theatrical performance of the highest order. With every detail carefully considered, the S/850 delivers a level of power, nuance, and scale that redefines what’s possible in its class.

S/850 drivers now feature lightweight pure carbon-fiber center caps, replacing the solid aluminum moldings of earlier models. These caps reduce moving mass while stiffening the cone, resulting in explosive dynamics and the ability to resolve the quietest passages with delicacy and nuance. Feather-light yet rigid, they extend performance at both extremes—a hallmark of REL design.

Passive Radiator

Supporting this advanced active driver is a newly engineered down-firing passive radiator. Purpose-built to handle the extreme throw distances produced by the S/850’s more powerful amplifier and driver system. Its flat, primary-piston surface—crafted from carbon, glass fibre, and light, stiff closed-cell foam, represents an evolution of prior designs but is now 40% stiffer and significantly lighter. With over 2.4" (60mm) of travel in each direction, it expands dynamics and low-frequency authority, unlocking the full scale and impact of the S/850.

Monoblock Slam, Class D Efficiency

The S/850’s amplifier delivers the slam of massive Class A/B monoblocks while harnessing the efficiency of a modern Class D output stage. Supported by a robust traditional power supply, it produces 850 watts of continuous output and can surge to 1,000 watts during demanding peaks, ensuring ample headroom for both music and theater. Upgraded input filters, equipped with the same thin-film capacitors used in our flagship designs, introduce a new level of transparency and refinement previously unheard of in this class. Together, these advancements create dramatic improvements in clarity, sound staging, and sheer authority—an amplifier that blends brute force with finesse to anchor the performance of the entire Serie S line.

Analog Filtered to Perfection:

We choose analog because it is the only way to achieve truly natural sound. All REL input filters are 100% analog—among the fastest ever offered in a subwoofer. At the core is our renowned High Level Input, which connects directly to the speaker outputs of your main amplifier. This doesn’t draw power; instead, it carries the full sonic signature of your system, allowing REL to blend seamlessly with your speakers—a quality reviewers have praised for decades.

For systems where High Level isn’t possible, our low-level input uses the same analog filter circuit, available via both RCA and XLR connections, to deliver the speed, naturalness, and integration REL is known for. And in theater or dual-use systems, REL uniquely allows High Level and .1/LFE to run together—so music benefits from natural integration, while movies deliver the full impact intended by the mix.

Serie S Line Array

REL’s Line Arrays are revered for producing sound staging and dynamics that rival the world’s finest systems. Designed to grow in pairs, a Line Array can begin with a simple stereo pair, expand with a second, and ultimately rise to three units per channel, delivering floor-to-ceiling authority and scale. 

S/850 now features a precision-milled knurled aluminum adjustment knob integrated into the body rails. This knob allows the bottom subwoofer in a Line Array to achieve perfect level on uneven or soft flooring such as thick-pile carpets or dual-pad installations ensuring a safer, more stable foundation. Purpose-built exclusively for Line Array use, these adjustment knobs enable ideal setup and secure performance without compromise. (Note: 212 Black Label does not include these adjustment knobs.)