Stack Audio Auva SW isolation feet
Stack Audio is a British audio firm founded in 2013 in Devon which makes a range of audio accessories including turntable upgrades and streaming filters, today the emphasis is on isolation products. The firm offers a range of supports tailored to specific applications including record mats, speaker supports and in this case subwoofer feet.
A set of four Auva SW feet is priced at £325, these isolators can be either placed under each corner of your subwoofer or screwed into the mounting holes which feature on most subwoofers. My REL HT/1510 Predator is a very high performing home theatre subwoofer packing a 15” carbon reinforced woofer in a sealed cabinet driven by a 1,000W amplifier. The woofer is forward rather than downward firing and the exceptionally well-built cabinet weighs over 45Kg. This is a subwoofer capable of delivering significant levels of shock and awe, imagine receiving incoming howitzer fire while standing in a greenhouse and you get the idea! The REL as standard sits on two support rails along the sides which are bolted to the underside with six M4 bolts.
The Auva SW feet can be ordered with one of a range of fittings, in my case M4 which enabled me to screw mount them into the REL cabinets in place of the usual rails. The Auva SW can also be used with the subwoofer placed directly on top of them. For best results Stack Audio recommends screwing them directly into the subwoofer which permits more efficient energy absorption and transfer.
Particle impact damping
The technical design underpinning the Auva isolation devices is quite different to the air damped springs in the Townshend Audio Seismic supports I use under my main loudspeakers. Stack Audio use a completely different approach, although the design objectives are very similar to those of Townshend Audio – to isolate the equipment from vibration by damping and to also reduce the amount of energy being transmitted into the floor by loudspeakers. To achieve this, they use a compartment filled with small particles to provide what they refer to as ‘particle impact damping’, this is supported by a silicone absorber which is matched to the weight of the component being supported.
The easiest way to appreciate what their technology does is to consider a tennis ball being thrown onto sand. It won’t bounce because the sand particles absorb the kinetic energy of the ball and dissipate it. Powerful subwoofers like my REL produce vast amounts of vibrational energy which is usually transmitted into the floor. This causes the floor to vibrate in sympathy with the subwoofer, especially when it is a timber floor as I have in my listening room. This floor vibration contributes to overblown bass and leads to smearing and overhang of notes which doesn’t affect just the subwoofer itself, but also potentially any other loudspeakers or electronics operating on the same floor.
I am relatively unusual in that I run a two-channel hi-fi which is integral to my larger Dolby Atmos equipped home cinema system. I don’t mind admitting that I am a passionate movie and music lover with a deep appreciation for both mediums, so it has always been important to me to achieve high quality sound for both purposes. At the core of my AV system is the immense Emotiva MR1 surround amplifier, which delivers 100 Watts per channel into all 11.2 channels driven and supports up to 4k video and all modern surround sound formats. This routes signal to the surround speakers and subs and enables me to drive the front left and right channels with my main Naim pre/power amplifier combination for both music and movies.
The REL is currently placed in-between the centre channel speaker on its shot filled Custom Design CS302 support stand and the right front ATC SCM40 which sits on a Townshend Seismic Podium. My main source for 4k Blu-ray, SACD and Blu-ray audio discs is the Cambridge Audio CXUHD, now sadly discontinued but one of the finest 4k Blu-ray players of all time and perhaps the only serious rival to the Panasonic DP-UB9000. The key benefit of the Cambridge CXUHD though is it plays SACD and DVD Audio too, the Panasonic does not.
Listening
I never use my subwoofer to augment two channel audio, so in terms of testing I used a mix of films, live concert Blu-rays and also SACD and Blu-ray audio discs, all of which are guaranteed to give the mighty REL a good workout. I started out by running a few test tracks of both music and film through the system without any supports in place to establish a benchmark. I then replayed the same tracks after placing the REL sub directly on the Auva SW supports, which given it’s a subwoofer that weighs more than most (45kg) is easier said than done!
I began with the 4k Blu-ray release of Top Gun and the scene where Tom Cruise executes a demonstration run through the test range. The sub-bass track on this segment sounded superbly clean and powerful with noticeably less bloom than without the Auva SW feet. It was noticeable too that while the floor was certainly still vibrating, the vibrations were noticeably less apparent than they were with the subwoofer sitting directly on the floor.
I did try to detect whether there was any more definition to the left front and right speaker outputs and I couldn’t. What was particularly interesting was that the dialogue track which is primarily mixed through the centre channel did seem a little more distinct with the Auva SW in place. My deduction from this is that the Townshend Seismic supports were protecting the front left and right speakers from the impact of the subsonic energy being fed into the floor, but the centre channel has no such isolation and so with the Auva SW in place and less energy being transmitted to the floor the centre channel benefitted – interesting.
The surround factor
Music came next and the excellent 20th anniversary SACD 5.1 surround mix of Dire Straits’ Brothers in Arms. The original recording was in its day one of the most iconic demo discs at hi-fi shows, to the point where many audiophiles grew tired of hearing it! This 5.1 mix done at British Grove Studios (Mark Knopfler’s own studio) under his direct supervision does make the old familiar recording seem fresh again. I was impressed with the way the REL HT/1510 Predator reproduced John Illsley’s taut and precise bass playing with and without the Auva SW in place, however it was when I played the drum intro to Money for Nothing that I could really hear how much more delineated each drum strike sounded with the Auva SW feet under the sub. The effect on clarity wasn’t subtle at all.
I’ve written before that as you upgrade audio equipment whether source, amps or speakers what you gain is mostly greater separation of instruments, as if you’re getting closer to hearing the original master recording. It becomes much easier to hear every different element of the mix. That’s precisely what these Stack Audio devices did under the subwoofer in my system – improved articulation and clarity, making it easier to follow basslines, drums or other deep bass effects in movies.
Too many subwoofers offer uncontrolled and boomy bass, this absolutely isn’t the case with the REL Predator, it is sublimely tuneful and taut, and explains why I have been using REL subwoofers at home as my reference for over 30 years. However even a subwoofer as taut and controlled as mine benefits significantly from being damped and isolated from the supporting surface by feet like the Auva SW.
The 2023 Blu-ray Dolby Atmos mix of Dark Side of the Moon further reinforced the point. Yes, you will hear less room resonance because the floor is no longer being driven, so bass synths for example don’t shake the floor in the same way, but then you realize that what you’re hearing without the Auva SW is distortion. Fit the Auva SW supports and this distortion is replaced with far greater note articulation, more drum slam and superior timing.
Abbey Road
I concluded with the simply jaw dropping Dolby Atmos mix of the Beatles’ Abbey Road from their Super Deluxe CD/Blu-ray box set. IMHO this is one of the greatest albums ever made, the second half might just be the finest 22 minutes of popular music ever laid down on tape. The fabulous Atmos mix adds so much immersion to the experience bringing every nuance of the record into far clearer focus. Dolby Atmos music isn’t about whizzing sound effects around the room or indeed placing you in with the band, it’s about increasing the space, bringing out all the detail and delineating each of the elements of the music far more clearly.
It’s exactly what high end audio does, but I believe that Atmos makes that level of extreme fidelity available to everyone. It frankly amazes me that high end audio firms across the planet haven’t jumped to offer HDMI output on their streamers to enable Tidal replay of Dolby Atmos tracks, because once you have experienced what Atmos is capable of, I believe it represents one of the biggest leaps in sound quality in the past fifty years. Whenever you go and see live music, even if it’s just a four-piece band, you are hearing sound that is bouncing all around the room from all directions – this is exactly what Atmos replicates far more effectively than any stereo pair system can.
With the Auva SW feet under the sub, Ringo’s drumming took on far more definition and shape, notes started and stopped with far greater precision and the detail of his technique was more clearly revealed. This of course applied to every instrument passing through the subwoofer – electric bass and deeper notes on the piano included. The heavy bass intro on Sun King for example was just gloriously fruity, rich and tuneful.
Conclusion
The Auva SW feet impressed me greatly with the way they improved bass note shape and definition and also reduced in room resonance spread through the floor. This is comparable to effective room treatment in terms of the magnitude of improvement on offer and thus comes highly recommended. It’s also a beautifully engineered product which very effectively meets its aims at a reasonable price, all subwoofer users should give the Auva SW supports a try.
Pros
Significant sonic improvements: A substantial increase in bass articulation, clarity, and note definition. It makes it easier to follow complex basslines and individual drum strikes.
Reduced distortion and bloom: By isolating the subwoofer from the floor, the Auva SW feet remove ‘smearing’ and ‘overhang,’ replacing uncontrolled vibrations with greater ‘slam’ and superior timing.
Effective vibration damping: The ‘particle impact damping’ technology (using a compartment of small particles and silicone) successfully reduces the amount of energy transmitted into the floor, particularly beneficial for timber/wood floors.
Secondary benefits to other speakers: By reducing floor vibrations, the Auva SW indirectly improved the performance of non-isolated components (like the centre channel speaker), leading to clearer dialogue.
Versatile mounting: They can be used as ‘sit-on’ feet or screwed directly into the subwoofer’s mounting holes. The company also provides adapters (e.g., M4 adapters for REL subs) to ensure a proper fit.
Build quality: A beautifully engineered product from a reputable British firm.
Value for money: The £325 price point is reasonable given the magnitude of the improvement, comparing the effect to professional room treatment.
Cons
Physical setup challenges: For heavy subwoofers (like the 45kg REL Predator), installing the feet is easier said than done.
Potential loss of ‘room shake: Because the floor is no longer being ‘driven’ by the subwoofer, users may notice less physical floor-shaking. While the reviewer identifies this shake as distortion, some users who enjoy the tactile sensation of a vibrating floor might initially miss it.
Specific fitment issues: While the company provides adapters, the standard fittings are M6. Users with non-standard mounting holes may need to ensure they have the correct adapters before installation.