The AUVA SWs were comprehensively tested on REL subs throughout our R&D phase.
Why REL Advise Against Subwoofer Isolation
REL Acoustics advise against isolation platforms, and their reasoning is solid. As John Hunter explains, REL tune the height of every subwoofer precisely so “the notes release perfectly”, and raising the cabinet a couple of inches on a platform decouples it from the floor, reducing deep bass, increasing upper bass, and leaving a sound that’s “very light”. For the products he’s describing, that’s good advice.
It’s advice we largely agree with. REL’s subwoofers are excellent; we used a REL unit during our own development and listening tests, and the concerns in that video are real. They apply to platforms, and just as much to typical isolation feet: most are soft rubber or Sorbothane, sit the cabinet at whatever height they happen to be, and can’t be tuned to the subwoofer’s mass. Different shape, same problems.
The AUVA SW was designed around those exact concerns. It’s a set of feet that adjust to match the height of REL’s stock feet exactly. Inside, a compliant element tuned specifically for subwoofer loads allows controlled movement, while a rigid braced outer shell keeps the cabinet firmly supported and timing intact. Nothing raised, nothing loose, nothing untuned. The question that remains isn’t whether REL’s concerns are valid; it’s what your floor is actually doing.
What the Advice Assumes About Your Floor
REL’s view is that the sub’s energy should “mechanically couple out into the room” through the floor, and that isolation traps that energy inside the sub. It’s worth unpacking what that means in practice. The bass you hear comes from the driver moving air, not from the cabinet shaking the floorboards. When energy couples into the floor, the building becomes a transducer nobody designed or tuned: out of time with the driver, out of your control, and different in every house. Keeping that energy out of the structure isn’t losing it; it’s keeping it where the driver put it.
The advice also works best when the floor is a neutral, stable foundation. In real listening rooms:
- Suspended timber floors flex and store energy, with resonances that can extend into the sub-bass region, directly overlapping the subwoofer’s operating range
- Concrete floors transmit structure-borne vibration and reflect low-frequency energy back into the cabinet, increasing mechanical feedback
- Carpets introduce inconsistent coupling
When you couple a subwoofer to a floor like this, the floor becomes part of the subwoofer, but not in any controlled way. Energy is stored and re-radiated by the structure, producing smeared low-frequency detail, delayed energy release, and one-note, boomy bass. The energy REL intend to pressurise the room is instead being dumped into the building.
REL acknowledge this themselves: in the same explanation, they note that in an apartment, preventing bleed-through to the floor below may require decoupling. The floor isn’t always your friend; the only real question is how often that’s true, and what to do about it.
Where REL Are Right
Two of REL’s concerns are well founded, and most isolation products fail on both:
Bad isolation makes bass worse. A soft, tall platform under a massive moving energy engine is exactly the “wobbly platform” REL describe, and soft isolation feet are the same compromise in a smaller package. Foam, rubber, springs: underdamped, untuned to the subwoofer’s mass, they lose weight, impact, and timing, and shift the cabinet height as the load compresses them. Spikes maintain stability but couple vibration straight into the structure. Neither dissipates energy; both just redirect it.
Height matters. Subwoofers are tuned with a specific driver-to-floor distance, and REL’s own T/x series is a perfect example, with a passive radiator firing straight down at the floor. That gap directly influences loading and output at the lowest frequencies. Raise the cabinet two inches on a platform, or sit it on feet that can’t match the original height, and you’ve changed the tuning. REL are right to call that out.
These aren’t reasons to avoid isolation; they’re the design brief for doing it properly.
How the AUVA SW Addresses Both Concerns
Tuned, controlled compliance, not soft absorption. A compliant element tuned specifically for subwoofer loads decouples the cabinet from the floor, with movement limited and controlled rather than free. A rigid, braced outer shell keeps the subwoofer firmly supported, preserving timing and transient response. Particle impact damping then converts the vibration into heat; the energy isn’t absorbed or redirected; it’s dissipated.
Height is preserved. The AUVA SW is height-adjustable from 39.8mm to 52mm, so the intended acoustic geometry is maintained:
- REL T/ Series stock feet: 44mm
- REL S/ Series stock feet: 50mm
- REL Carbon Range stock feet: 50mm
Every one of these sits within the AUVA SW’s adjustment range, so the geometry REL tuned for is preserved exactly.
And isolation works in both directions. The same barrier that keeps the sub’s energy out of the floor keeps the floor’s energy out of the sub. Footfall, household vibration, and, most relevantly, the energy your main speakers drive into the floor all travel back up through a coupled cabinet’s feet. Decoupled, the subwoofer responds only to its own signal, not to whatever the floor happens to be carrying. That’s a benefit coupling can’t offer, however well the height is tuned.
Customer Feedback: REL T/9x Subwoofer with AUVA SW Isolation Feet – Paul G.
“The results were impressiveβ¦sublime even. The bass is now clearer, tighter, and easier to follow, but as often with subwoofers, the mid-range and treble have also benefited from snapping into tighter focus.
Also, as far as Iβm concerned, the Stack feet look better than the rather large silver REL feet that Iβve replaced. Good news all around!β
Critic Feedback: Hans Beekhuyzen – REL T5
“The AUVA SWs’ impact on overall sound quality is anything but subtle. And if you like to play loud, your neighbours might appreciate them too.”
The Bottom Line
REL’s advice is good advice about isolation as it’s usually done; soft platforms and untuned, height-mismatched feet genuinely do the damage they describe. The AUVA SW takes those concerns as its starting point: height-matched, rigid, and tuned to subwoofer loads, it keeps everything REL engineered into the cabinet, and stops the floor from working against it.
With height maintained, stability preserved, and vibration actively dissipated, you get tighter, faster bass, better pitch definition, and cleaner integration with your main speakers. Bass becomes easier to follow, not just easier to feel.
Every set is covered by our 60-day money-back guarantee.
Frequently Asked Questions
Do AUVA SW isolation feet work with REL subwoofers? Yes. The AUVA SW adjusts from 39.8mm to 52mm, covering REL’s stock foot heights exactly: T/ Series (44mm), S/ Series (50mm), and Carbon Range (50mm). The subwoofer sits at the precise height REL tuned it for.
Will isolating my REL subwoofer reduce deep bass? Not if height is matched and the isolation is rigid and tuned to the load. REL’s warning applies to tall, soft platforms and untuned compliant feet, which genuinely can thin out deep bass. Independent REW measurements with the AUVA SW show the dominant change is reduced structural decay between 40 and 80Hz, not reduced output.
What height are REL’s stock feet? T/ Series: 44mm. S/ Series: 50mm. Carbon Range: 50mm. All within the AUVA SW’s adjustment range.
What CSA/Fixing does my REL require?
| Range | Model | Weight | Thread | AUVA SW CSA |
|---|---|---|---|---|
| Series T/x | Tzero MKIII | 6.8kg (15 lbs) | M8-1.25 | CSA 1 |
| T/5x | 14.3kg (31.5 lbs) | M8-1.25 | CSA 1 | |
| T/7x | 17.5kg (38.5 lbs) | M8-1.25 | CSA 2 | |
| T/9x | 20.6kg (45.5 lbs) | M6 | CSA 2 | |
| T/9x SE | 20.6kg (45.5 lbs) | M6 | CSA 2 | |
| Series T/i | T/5i | 14.0kg (30.9 lbs) | M6 | CSA 1 |
| T/7i | 16.7kg (36.8 lbs) | M6 | CSA 2 | |
| T/9i | 18.5kg (40.8 lbs) | M8-1.25 | CSA 2 | |
| Classic | Classic 98 | 18.1kg (40 lbs) | M6-1.0 | CSA 2 |
| Series S | S/2 | 21.5kg (47.4 lbs) | M8-1.25 | CSA 2 |
| S/3 | 27.5kg (60.6 lbs) | M8-1.25 | CSA 3 | |
| S/5 SHO | 31.7kg (70 lbs) | M4-0.75 | CSA 3 | |
| S/510 | 31.7kg (70 lbs) | M4-0.75 | CSA 3 | |
| S/812 | 34.0kg (75 lbs) | M4-0.75 | CSA 4 | |
| Carbon Special | 38.7kg (85.3 lbs) | M4-0.75 | CSA 4 | |
| Carbon Special Black Label | 44.5kg (98 lbs) | M4-0.75 | CSA 5 | |
| Reference | No.31 | 52.0kg (114.5 lbs) | M4-0.75 | CSA 6 |
Learn more about the AUVA SW: https://www.stackaudio.co.uk/auva-sw
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