The REL Acoustics S/850 is an active powered subwoofer from REL's high performance S line, built to add deep, natural bass to both music and home theater systems. In plain terms, a subwoofer is a specialized speaker that handles only the lowest sounds, the ones you often feel as much as hear. Your main speakers do a fine job with voices and instruments, but they usually run out of steam at the very bottom of the musical range. The S/850 fills in that missing foundation. The word "active" means it has its own built-in amplifier, so it powers itself rather than drawing power from your main amplifier or receiver.
Where does it fit in a hi-fi or home theater setup?
The S/850 sits alongside your existing speakers and connects to your amplifier, receiver, or processor to reproduce the lowest frequencies in your music and movies. Think of it as the anchor of your system. In a stereo music setup, it deepens and enriches the sound so instruments feel fuller and more lifelike. In a home theater, it delivers the rumble of explosions, the weight of a film score, and the sense of scale that makes a movie feel real. It works quietly in the background, blending with your speakers so you notice better sound rather than an obvious source of bass.
The Driver System: How the S/850 Makes Bass
What does the 12 inch forward-firing active driver do?
The 12 inch forward-firing active driver is the main speaker cone that pushes air to create the bass you hear, and it points forward from the front of the cabinet. "Long-throw" means the cone is designed to move a long distance in and out, which lets it move a large volume of air. Moving more air is exactly what you need to produce deep, powerful low notes without strain. Twelve inches refers to the diameter of the cone; a larger cone can shift more air more easily, which helps with the effortless, room-filling quality of good bass.
What is the 12 inch down-firing passive radiator?
The 12 inch down-firing passive radiator is a second cone, mounted to fire toward the floor, that has no amplifier or motor of its own. Instead, it is driven by the air pressure created inside the cabinet when the active driver moves. As the powered driver pushes and pulls, the changing pressure inside the sealed box makes the passive radiator move too, adding extra low-end output and reinforcing the deepest notes. This approach lets a compact cabinet produce bass that would otherwise require a much larger box, giving you deep extension without a huge footprint.
Power and Amplification
What kind of amplifier is inside the S/850?
The S/850 uses a Class A/B amplifier, a well established amplifier design known for smooth, musical sound. Different amplifier types handle power in different ways, and Class A/B is a classic approach that many listeners associate with a natural, refined character. For you day to day, the important thing is that the amplifier is matched to the drivers by REL, so the whole subwoofer is tuned as one unit. You do not need to worry about pairing it with a separate bass amplifier; it is complete and ready to perform.
Connections: How You Hook It Up
What is the high-level Speakon input for?
The high-level Speakon input is REL's signature connection, and it lets the subwoofer take its signal from the same output that feeds your main speakers. This is a REL hallmark because it allows the subwoofer to hear exactly what your amplifier is sending to your speakers, which helps the bass blend seamlessly with the rest of the music. The Speakon connector is a secure, twist-lock plug that stays firmly in place. For music listening especially, this connection is often the one REL owners prefer for the most integrated, coherent sound.
What are the low-level RCA inputs (L/R)?
The low-level RCA inputs are a pair of standard connectors, one for the left channel and one for the right, that accept a line-level signal from a preamplifier or receiver. RCA cables are the familiar round plugs used throughout home audio. This is a simple, common way to connect the subwoofer if your system provides a preamp or subwoofer output rather than a speaker-level signal. It gives you flexibility to match whatever gear you already own.
What is the .1/LFE input?
The .1/LFE input is designed for home theater, where it receives the dedicated low-frequency effects channel from an AV receiver or processor. In surround sound, the ".1" in a format like 5.1 refers to that separate bass channel packed with movie effects. When you plug into this input, your receiver takes charge of directing bass to the subwoofer, which is exactly how home theater systems expect to work. It makes setup with an AV receiver straightforward.
What is the balanced LFE XLR input?
The balanced LFE XLR input is another home theater connection that uses a balanced XLR cable for the low-frequency effects signal. XLR is a professional style connector, and balanced cables are good at rejecting electrical noise, which is helpful over longer cable runs. If your processor offers a balanced subwoofer output, this input lets you take advantage of it for a clean, quiet signal path.
Controls: Dialing It In
What does the continuously variable crossover do?
The continuously variable crossover sets the point where the subwoofer takes over from your main speakers, and being continuously variable means you can fine tune it smoothly rather than in fixed steps. Set it too high and the bass can sound thick or boomy; set it too low and you may leave a gap. The smooth adjustment lets you find the exact handoff point that matches your speakers and room so the transition sounds seamless.
What does the gain and level control do?
The gain, or level, control adjusts how loud the subwoofer plays relative to your main speakers. The goal is balance: you want the bass to feel like a natural part of the music, not a separate thumping presence. This control lets you turn the subwoofer up or down until it blends in properly, and you can revisit it as your tastes or your room change.
What does the phase control do?
The phase control aligns the timing of the subwoofer's output with your main speakers so their sound waves work together instead of canceling each other out. When phase is set wrong, bass can sound thin because the subwoofer and speakers are partly fighting one another. Adjusting phase until the bass sounds fullest at your listening seat ensures they reinforce each other for solid, well defined low end.
Wireless, Build, and Finish
Can the S/850 be used wirelessly?
Yes, the S/850 is compatible with the REL AirShip II and HT-Air MKII wireless systems, which are sold separately. These add-on systems let you send the signal to the subwoofer without running a long cable across the room. This is handy when the best spot for bass is far from your main system, giving you placement freedom without wires along the floor.
Why does REL Acoustics build quality matter?
REL Acoustics build quality matters because a subwoofer's cabinet and finish directly affect how clean and controlled the bass sounds. A well made, rigid cabinet resists unwanted vibration, so you hear the music rather than the box. The S/850 comes in high-gloss black or high-gloss white, both attractive finishes that suit a living room, and includes isolation feet that decouple the subwoofer from the floor to reduce unwanted resonance. This care shows REL builds these to last and to perform.
Who is the S/850 best suited to?
The S/850 suits a listener who wants serious, high quality bass for both music and movies and values flexible connection options. With its Speakon, RCA, .1/LFE, and balanced XLR inputs, it fits stereo systems and home theaters alike. If you are new to high-end audio and ready to hear what a properly integrated subwoofer adds, the S/850 is a capable, well built choice that grows with your system.
