REL S/5 Subwoofer

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Equipment report
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Subwoofers
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REL S/5
REL S/5 Subwoofer

If REL Acoustics, the highly regarded subwoofer manufacturer, pulled out of the high-end marketplace tomorrow, never again to manufacture another unit, its place in the audio pantheon would forever be assured. REL has offered superb build-quality and high standards of bass reproduction since the company was founded in 1990. Thankfully for bass fans everywhere, nothing has changed in its latest venture, the S/5, which may be the best-performing midpriced sub REL has offered in its vaunted history. The S/5 goes about its tasks so matter-of-factly, effortlessly, and invisibly that it seems to become another attractive fixture in the room—until you pull it from the system. Then you understand what authentic low bass brings to the party. You also begin to understand the meaning of…addiction.

The REL S/5 is the kingpin of the freshly minted S Series, a line second only to the big Gibraltar subs in the REL lineup. Tipping the scale at seventy pounds, the S/5 is not small, but it isn’t a real-estate hog, either. The S Series enclosures are visually lavish and lavishly inert. Sporting 1 1/8"-thick cabinet walls, my gloss-black sample was superb in fit and finish. The solid T-304 stainless steel grab handles are first cast, then micro-machined, and finally polished in a six-stage process. The polished aluminum trim pieces—such as the footers—elegantly accent its dark good looks.

Inside the S/5 is a new forward-firing 12" alloy-cone woofer. According to John Hunter, REL’s Woofer-in-Chief, this driver’s excursion has been increased to a full two inches, an improvement of a ¼". He also points out that the cone’s moving mass has been reduced almost 60 percent by his reckoning, and that it is “self-quieting,” which is to say, it is so non-resonant that it stops as quickly as it starts. Additionally, there’s a downward-firing 12" passive driver with a unique carbon diaphragm that is similarly stiff and lightweight. REL says that the S/5 uses a simple filter-type that’s quite fast—with about eight milliseconds in group delay—to eliminate the passage of unwanted higher frequencies to the REL driver. Power is also superior to that of its predecessor, the discontinued R-528. The S/5 now uses a NextGen2 550W switching amplifier that can generate up to 873W on hard transients.

Per tradition, REL subs do not use high-pass filters—the main speakers run full-range, full-time. REL’s view is that high-passing the sub/sat looks good on paper, as it allows the main speakers to perform with less stress and more dynamism. But REL also believes that high-pass filtration creates more problems than it solves. Why? Because the main speakers are designed and voiced to operate within a specific range of frequencies, and by cleaving away a portion of that output via a high-pass crossover you are essentially refashioning the speaker into a different, even unpredictable unit never contemplated by its designer. That’s why—at least under their breath—many designers don’t actively embrace third-party subs, high-pass or not. Subwoofers from the same brand are another story. They have purposefully designed drivers and low- and high-pass crossovers to pair with designated models (Revel, among others, comes immediately to mind as a specialist in these matters). In any case, no high-pass filtering for the S/5.

The back panel houses a phase toggle and rotary settings for the low-frequency effects (LFE) level and for volume, plus the tiniest 39-step increments for adjusting the crossover over the range of 30–120Hz. There are dual low-level RCA inputs, plus an LFE input, but the high-level input is and has always been REL’s preferred means of installation. A lengthy Neutrik connector is provided for this purpose. It carries within its jacket four wires for connection to an amplifier’s speaker taps.

REL suggests starting with corner placement, usually on a room diagonal. This not only maximizes room gain but also allows “for the most linear true low bass wavelaunch.” The set-up manual REL provides is quite comprehensive (without being intimidating) about optimizing placement. In my experience, dialing in an REL is a matter of a few easygoing minutes rather than hours of hand-wringing. My advice: Bring a friend for fine adjustments. (Because of the added expense, I hesitate to mention that if you have a “problem” room, setup is easier with two subs, as they work together to smooth and flatten overall room response, and thereby become less of a sonic presence. This was an experience that I enjoyed first-hand with a pair of S/5s, but that’s a story for another time.)

Mood Elevator
There are two sets of criteria that I use to evaluate subwoofers. There’s overall bass quality (extension and musicality), and then there’s integration (the subwoofer’s ability to blend with the main stereo speakers). Net: Does it remain true to the character and voice of the satellites?

In the tight confines of my listening room, the S/5 wasn’t even breathing hard as it extended response into the middle twenty-cycle range. It did so without calling attention to itself—no overhang, perceived box coloration or, to use the sonic slang, “slowness” in its response. In all honesty the S/5 will go even lower, but my room struggled to support 25Hz without the doors rattling and the space over-pressurizing. The S/5 makes short work of large-scale orchestral pieces laden with timpani and bass drum. Every decaying flutter off the skin of these instruments is presented concisely and cleanly, and often in overwhelming detail. Small-scale, low-level cues don’t escape the S/5, either. Towards the end of Jackson Browne’s “Colors of the Sun” from For Everyman, there’s a repeated piano and drum motif that resolves into a deepening bass note that seems to ripple, sustain, and expand as if suspended in space. Each repetition of the motif is heavier and more resonant than the last, until the track begins a long fade. The bass notes hardly exist at all without the help of the S/5. Similarly, during Yes’ “It Can Happen” from 90125, there’s a recurring bass line where the bassist slides his finger down the string, the pitch plunging as if tossed off a cliff. Most speakers by themselves can’t reproduce the full weight of these descending notes convincingly. The S/5 can.