Loudspeakers

Integrating an active sub-bass speaker with a stereo floorstander that already quotes a frequency range extending down to 30Hz or so – give or take several dB – thanks to sizeable bass drivers that already manage to move a significant amount of air around the room, is something that divides opinion among the hi-fi cognoscente. Despite the number of active sub-bass speaker systems being introduced into many new loudspeaker lines, the benefits are more readily associated with multi-channel installations for home cinema enthusiasts, while the idea of adding a dedicated sub-bass speaker to a traditional stereo setup is at odds with many audiophile principles.

It’s certainly the case that sub-bass systems or subwoofers used to be far better suited to explosive action movie effects, and too often lacked the speed and timing to deliver the kind of sensitivity and rhythmic engagement that music listeners prize above all else. But in my odd-shaped listening room, the introduction of a sub-bass unit has often rewarded with marked sonic benefits.

At £1,800, the S/510 is the most affordable of REL’s three-strong, mid-level Serie S range, aimed at elevating higher-end systems in medium-to-large-sized rooms. The series also includes the larger S/812 (£2,300) and twin-active 212SE (£3,500). The S/510 replaces the slightly lower-priced S/3 SHO sub-bass speaker that was previously integrated into my system and has a beefed-up sealed cabinet with nicely designed chrome handles on the sides to help manoeuvre its near-32kg heft into position. Despite the increased weight, the cabinet dimensions are actually smaller than the model that was previously in situ. It comes with a black fabric grille to cover the 250mm forward-firing, ultra-lightweight driver that has been upgraded with carbon fibre bracing strategically positioned on the back to strengthen and stiffen the ContinuousCast alloy cone to enable it to handle the increased 500W power output from the upgraded, built-in NextGen3 Class D amplifier. Personally, I prefer the look with the speaker grilles removed, which shows off the REL branding emblazoned across the front of the cone and ties in with the solid piece of aluminium embedded into the top of the cabinet.

Available in a choice of black or white finishes, the attractive lustre is achieved by a process consisting of up to 12 coats of paint, resulting in an eye-catching high gloss finish. The feet usually found at the four corners are replaced by two rails either side of the downward-firing passive radiator. The rails improve overall stability and have the affect of making the cabinet appear to float a few centimetres above the floor. They also facilitate sub-bass line arrays – where up to three units can be stacked on top of one another to give a floor-to-ceiling perspective, should you wish.

Controls and connections around the back will be familiar to owners of older REL subs, adding both a high-level Neutrik Speakon locking input and output as well as low-level stereo RCAs and LFE ins and outs on both single RCAs and XLRs. Integration controls provide high and low-level input adjustment as well as LFE, variable crossover control, reversible phase and there’s a standby mode for when the speaker isn’t in use.

Given that I have auditioned several active sub-bass systems in my room previously, the manual installation procedure feels pretty straightforward with just minimal adjustments required to get the unit singing with my Dynaudio X38 floorstander. There’s no handset or app control, but there is a new wireless 5.8GHz transmission system called AirShip available for an extra £300. For this review, though, I opt for the supplied 10m interconnect fitted with a Neutrik Speakon connector and, following the instruction manual, carefully hook up the wired end to the loudspeaker terminals at the rear of my amplifier and plug the connector into the high-level input on the S/510.

Sound quality
Boasting new filtering that promises a more musical performance with the sub’s high and low-level inputs, the S/510 gets off to a captivating start placed just behind the plane and to the side of the left loudspeaker, firing diagonally down the length of room to the listening position. Billie Eilish’s Bad Guy shows off the capabilities of the S/510 instantly, delivering the track’s sustained bassline with enough power and depth to get passersby looking through the listening room window intrigued to see what’s going on inside. It’s not the subtlest of tracks, but effectively demonstrates the REL’s potent capabilities at delivering plenty of high energy while managing to sound effortlessly musical at the same time.

It’s an admirable skill that’s further demonstrated by Mark Ronson’s Don’t Leave Me Lonely from the Late Night Feelings album. The track has a hooky beat that sees the REL hit a comfortable stride, delivering bouncy bass notes that can be felt as much as heard and sees this ‘go-to’ listening test track grow substantially in scale.

Vocals appear to grow in stature too, and snap firmly into the space between the floorstanding speakers. The Dynaudios image well, but the addition of the S/510 turns Elbow’s Gentle Storm into an almost holographic performance with a greater sense of front-to-back depth. What I notice more than before is the amount of acoustic space that’s on display as Guy Garvey’s vocals decay amidst the percussive backing, adding a greater sense of hi-fi believability.

The double bass on Easy Money by Rickie Lee Jones has extra gravitas even at late-night listening levels. Nils Frahm’s atmospheric piano on Some appears to lay the acoustical space out before me, while Hans Zimmer’s Time makes an almost emotional connection, thanks to the extra bass perspective the REL brings.

Conclusion
The S/510 digs deep and has the power and speed to delight with up tempo tracks and a subtlety that heightens engagement when the music demands. It’s inclusion adds scale and makes listening fun, which is really what it’s all about after all. LD    

DETAILS
Product: REL Acoustics S/510
Price: £1,800
Origin: UK
Type: Active sub-bass system
Weight: 31.7kg
Dimensions: (WxHxD) 400 x 410 x 464mm

FEATURES
● 1x 250mm long-throw aluminium cone driver
● 1x 300mm super-progressive passive radiator
● Quoted power output: 500W RMS