The REL Acoustics S/550 is a high-performance subwoogfer designed to add deep, natural low frequencies to both your music and movie systems. If you are new to high-end audio, think of it as the missing foundation beneath your main speakers. Most speakers do a fine job with midrange and treble, but they often run out of steam at the very bottom. The S/550 fills in that bottom octave so the whole system sounds bigger, more effortless, and more lifelike.
REL positions the S/550 in its Serie S range, which sits above the entry-level models and brings more refined engineering, more power, and a more sophisticated cabinet. It is meant for someone who cares about accurate, musical bass, not just loudness.
What Kind of Subwoofer Is It?
The S/550 is a closed box, active design with a passive radiator. In plain terms, "closed box" means the main cabinet is sealed, which tends to produce tight, controlled bass that starts and stops quickly. "Active" means it has its own built-in amplifier, so it powers itself rather than drawing from your main amplifier. The "passive radiator" is a second driver with no motor of its own that reinforces the deepest notes, giving you extension you would normally only get from a much larger box.
What Does the Active Driver Do?
The active driver is a 10 inch (250mm) forward-firing long-throw alloy cone, and it is the part that actually generates the sound you hear. "Forward-firing" means it points out toward the room. "Long-throw" means the cone can move a long distance in and out, which lets a relatively compact driver move plenty of air for deep, powerful bass. The alloy cone is stiff and light, so it moves precisely without flexing or distorting.
What Is the Passive Radiator For?
The passive radiator is a 12 inch (300mm) down-firing driver that boosts the lowest frequencies without adding electrical power. It works by responding to the pressure changes inside the sealed cabinet created by the active driver. Because it is larger than the active driver and fires toward the floor, it helps the S/550 reach very low notes and couple that energy into your room in a smooth, even way.
Power and Performance
How Powerful Is the Amplifier?
The S/550 uses a Class D amplifier rated at 500 watts (RMS). Class D is a modern amplifier type that is efficient and runs cool, which means more of the power goes into producing bass rather than being wasted as heat. The 500 watt RMS figure is the continuous, honest power rating, so you can trust it to drive that 10 inch driver hard without straining. In daily use, this means clean, confident bass whether you are playing quiet acoustic music or a demanding action movie.
How Deep Does It Go?
The S/550 reaches down to approximately 21 Hz (-6dB in room). To put that in perspective, 21 Hz is near the bottom edge of what humans can hear, and it is the range you feel as much as hear, like the rumble of a pipe organ or a deep cinematic explosion. The "-6dB in room" note is important and honest. It means REL is measuring how the subwoofer actually performs in a real room, not in a lab under ideal conditions, so the number reflects what you will genuinely experience.
Connections
One of the strengths of REL subwoofers is their flexible connection options. The S/550 offers several ways to hook into your system so it works with both stereo music setups and home theater receivers.
What Is the High-Level Speakon Input?
The high-level input uses a Neutrik Speakon connector, and it is REL's signature way of connecting to your amplifier. Instead of taking a separate signal, it connects to the same speaker terminals that feed your main speakers. This lets the subwoofer hear exactly the same signal your speakers do, which helps it blend seamlessly and take on the sonic character of your amplifier. The Speakon plug is a secure, twist-lock connector that will not fall out.
What Is the Low-Level RCA Input?
The low-level RCA input accepts a standard single RCA cable, the same familiar plug used on much home audio gear. This is a simple, direct way to feed the subwoofer a signal, often from a preamplifier or an integrated amplifier that has a dedicated subwoofer output. It is a common alternative when the high-level connection is not convenient.
What Are the .1/LFE and Balanced LFE XLR Inputs?
These two inputs are designed for home theater use. The .1/LFE input takes the dedicated bass channel from an AV receiver or processor, which is the ".1" in a setup like 5.1 or 7.1 surround sound. The balanced LFE XLR input does the same job but uses an XLR connector, a professional-grade plug that resists noise over longer cable runs. Having both gives you flexibility depending on what your receiver offers and how far the subwoofer sits from it.
Can It Connect Wirelessly?
Yes, the S/550 is compatible with the REL AirShip II wireless system, which is available separately. This optional system lets you send the signal to the subwoofer without running a long cable across the room. It is a helpful solution when your subwoofer needs to sit far from your amplifier or in a spot where cables would be awkward to route.
Controls and Setup
What Does the Crossover Control Do?
The continuously variable crossover sets the point where the subwoofer takes over from your main speakers. "Continuously variable" means you can fine-tune it smoothly rather than choosing from a few fixed steps. You adjust it so the subwoofer picks up right where your speakers naturally roll off, creating a smooth handoff with no gap and no overlap in the bass.
What Does the Level Control Do?
The level control, also called gain, sets how loud the subwoofer plays relative to your main speakers. The goal is balance, not maximum volume. You turn it up or down until the bass feels like a natural part of the music rather than a separate thumping source. Once dialed in correctly, you should notice fuller sound without being aware the subwoofer is even there.
What Does the Phase Switch Do?
The phase switch aligns the timing of the subwoofer's output with your main speakers. Depending on where the subwoofer sits, its bass waves can either reinforce or partially cancel the bass from your speakers. Flipping the phase switch and listening for which setting gives fuller, stronger bass ensures the two work together rather than against each other.
Build, Size, and Who It Suits
Why Does REL Build Quality Matter?
REL builds its subwoofers to be precise musical instruments, and that care shows in the S/550. The high gloss black or high gloss white finishes are furniture-grade, so the subwoofer looks at home in a real living space. More importantly, a well-built, rigid cabinet keeps unwanted vibration and coloration out of the sound, so what you hear is clean bass rather than the box rattling along.
How Big and Heavy Is It?
The S/550 measures approximately 17.7 x 14.75 x 18.0 inches (HxWxD) and weighs about 46.3 lb (21 kg). That is a compact footprint that fits neatly beside a cabinet or in a corner, while the substantial weight reflects the solid construction and quality components inside. It is easy to place in most rooms without dominating the space.
Who Is the S/550 For?
The S/550 suits anyone building a serious music or home theater system who wants deep, accurate, musical bass from a compact, beautifully finished subwoofer. Thanks to its high-level, low-level, and LFE connection options, it fits equally well into a two-channel stereo setup and a surround sound system. If you are new to high-end audio and want a foundation that will grow with your system, the S/550 is a confident, well-rounded choice.
