⌈ STACK AUDIO is a British company founded in 2013 by Theo Stack. The company's first product was the ONSET file player/server. Later, it specialized in upgading Linn LP12 Sondek turntable bases, and sometimes also offered audio file transports and isolators, in which it applied solutions developed for the LP12. ⌋

here is an abundance of ANTI-VIBARTION FEET (cones, or isolators) on the market. They differ in size, weight, technologies applied and purpose, and above all – in price. They have one thing in common: they are used for reducing vibrations of devices and speakers that are placed on them. And, as is well known, vibrations adversely affect sound, inducing triboelectric noise, magnifying electron tube microphonics, and forcing circuits used to control CD and SACD player optics to work harder, not to mention LP playback.

So, to differentiate themselves from this clamor of different voices and to succeed, manufacturers must offer something similar to what is already on the market on the one hand, but different enough to gain recognition on the other hand. Products from Stack Audio, founded and run by Theo Stack (hence the name) meet these requirements.

As we can read on the manufacturer's website:

Stack Audio is a Devon-based British manufacturer of award-winning hi-fi products. Stack Audio has gained reputation with its customers internationally for delivering products of uncompromising build and finish quality with exceptional sound. This has been at the heart of all of our products since incorporation in 2013.

⸜ Our Story, STACKAUDIO.co.uk, accessed: 18.09.2023.

As you can see, the company emphasizes both the workmanship and sound of its products, but also the place where they were made - the UK. This is important, because in this way the production of audio equipment, slowly but hopefully irrevocably, is returning from the Far East to home countries, and outsourcing is being replaced with jobs with a given company. The manufacturer points it out by placing the inscription "Designed and Manufactured in the UK" on the packaging of the tested AUVA EQ isolators, while a lot of major players write, for example: "Designed in USA", but "Manufactured in China".

Stack Audio offers two isolator models, including one in three sizes. However, isolators were not the first product offered by the company.

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| A few simple words with…

JOSH STEPHENSON
Customer Success Manager (CSM)

⸜ THEO STACK (on the right) and JOSH STEPHENSON (on the left) • photo Stack Audio

THEO STACK IS A PASSIONATE hi-fi enthusiast, engineer and entrepreneur (all bolding by the Editor). He believes that combining state-of-the-art (electronic and/or mechanical) engineering with high-quality industrial design results in audio products that improve sound and, just as importantly, are durable and pleasant to use.

Stack Audio's first product was an audiophile music streamer called ONSET. It was proof of the validity of just such an approach to product design and set the direction in which all subsequent Stack Audio products were built, which is removing vibrations and electrical noise which disrupt and mask the music we hear from audio systems.

In 2017, Stack Audio's offer was enriched with a series of Linn LP12 Sondek turntable upgrades, under the common name SERENE. They combined precision engineering with vibration dissipation. Improvements for the LP12 are a specialized, niche part of the hi-fi market, so in 2019 Stack Audio expanded its offerings with a new USB music streamer with a more mainstream look, called LINK. Collaborating with the renowned digital and electronics solutions designer John Westlake, LINK utilized ONSET concept vibration dissipation technologies with an ultra-quiet power supply, clock and digital circuit design. LINK was very well received by both reviewers and customers. It remained in production until 2022.

⸜ A cross-section of the AUVA EQ isolators • photo Stack Audio

At the end of 2021 Theo decided that the future of Stack Audio would be connected with anti vibration products. They were a natural extension of the company's earlier experience with machining aluminum components and its knowledge of vibration absorption technology. Key to the development of AUVA speaker isolators is the use of particle impact damping, also used in the AUVA EQ system isolators. This vibration dissipation technique, rarely seen in the world of hi-fi equipment and audio components, allows speakers to be rigidly supported while absorbing vibrations. The specifics of the AUVA design are the subject of a patent application by Stack Audio.

All our products are manually assembled in Devon from components manufactured by long-term partners in the UK. Looking into the future, Theo Stack intends to grow Stack Audio by continually innovating in the world of hi-fi isolation products. A consistent philosophy of good design, high quality and a focus on noise and vibration absorbing technologies will be part of every product bearing the Stack Audio name. ●

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▌ AUVA EQ

In Removing the vibrations, revealing the music the manufacturer says that understanding how to control vibrations led him to focus on three areas of technology and engineering knowledge. We read that it employs technologies that enable rapid dissipation of vibrations in a more efficient way than simply by using mass to absorb and slowly release them, as well as that precision manufacturing, rigidity and shape are key to making these technologies perform at the highest level.

The names of all Stack Audio isolator models begin with the acronym AUVA (AUdio Vibration Absorber) - this is the first of these techniques. Originally developed for Linn LP12 Sondek turntables, it uses a phenomenon called "particle impact damping." It was carried out with the help of many tiny particles, including tungsten ones, placed in a closed chamber in several layers. They aim to convert vibration energy into heat through friction and collisions between these elements. The idea is also for heat to be lost immediately, rather than with a delay. Let me remind you that similar techniques are used by Acoustic Revive (more → HERE).

The second technique is called AVDC (Audio Vibration Dissipation Compound). The manufacturer says it's a thin membrane of visco-elastic foam placed between two layers of metal and uses it in selected products. And finally, there is PRS (Precision, Rigidity and Shape), which is rather a description of a method of manufacturing rather than a technique as such. This is because the manufacturer believes that only super-precise manufacturing and application of the above techniques lead to valuable changes.

The company now offers three versions of isolators designed to support speakers or stands. The AUVA EQ is designed to support audio equipment and the EQ in its name is not derived from EQualizer, but from EQuipment. The isolators use the AUVA technology and combine it with the CSA (Custom Silicone Absorber) module. These are small rollers, 28 mm in height and ϕ 50 mm in diameter, made of precision-milled aluminum coated with scratch-resistant paint.

The upper part of the isolator houses the particles in which heat is lost, and the lower, unscrewed one is a "dome" made of silicone. It is glued to a metal plate fused to a screw which can be used to adjust the height of the AUVA EQ (the level of the device). The silicone dome comes in three different degrees of susceptibility, so you can adjust the isolators to the weight of the device in question (the given weight applies to one isolator):

• CSA 1: 0-4 kg,
• CSA 2: 4-10 kg,
• CSA 3: 10-15 kg.

The isolators are sold in sets, three or four pieces each, and are housed in nice simple boxes that vividly resemble the ones offered by the Polish company Divine Acoustics.

▌ THE LISTENING SESSION

˻ THE WAY WE LISTENED ˺ Stack Audio's isolators were tested in the "High Fidelity" reference system. I always test such devices in my system in the same way – under the signal source, sometimes assisted by other devices. This time I tested them under the Ayon Audio CD-35 HF SACD player.

I move the player during a test, so its connections must be flexible. I use Crystal Cable Absolute Dream interconnects for that purpose, and the player is powered by the Harmonix X-DC350M2R Improved-Version cable. The comparison consisted in listening to the same fragment of a track (2 min) on the Divine Audio Galileo reference feet and transferring it to the tested isolators. The reference and tested feet/isolators stood on the upper carbon shelves of the Finite Elemente Pagode Edition Mk II rack.

I also devoted a separate listening session to using the AUVA EQ isolators under the Planar 3 50th Anniversary Edition.

» ALBUMS USED IN THE TEST ⸜ a selection

⸜ RED HOT CHILLI PEPPERS, Californication, Warner Bros. Records 9362 47386 2, CD (1999).
⸜ THE OSCAR PETERSON TRIO, We Get Request, Verve/Lasting Impression Music LIM K2HD 032, K2HD Mastering, „24 Gold Direct-from-Master Edition UDM”, Master CD-R (1964/2009).
⸜ JOHNY CASH, My Mother’s Hymn Book, American Recordings ‎B0002362-02, CD (2004).
⸜ ANDRZEJ KURYLEWICZ QUINTET, Go Right, Polskie Nagrania „Muza”/Warner Music Poland 4648809, „Polish Jazz | vol. 0”, Master CD-R (1963/2016).

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ONE OF THE PROBLEMS THAT ARE MOST DIFFICULT TO OVERCOME in audio is getting good sound out of heavily, almost maximally compressed discs. In a studio, a compressor is one of the most important devices that always helps to arrange sound when it is properly used. The best mastering specialists talk about a maximum of 3 dB, sometimes only increased by another one or two dB.

In the real world, almost all rock and pop records are very compressed, some to the maximum. This is also how the album Californication by RED HOT CHILLI PEPPERS was prepared. The material for it was recorded under the supervision of Rick Rubin on two 24-track Ampex 124 analog tape recorders, and then ripped into a DAW system (more → HERE). It is an album that is often given as an example of massacring sound with compression.

And indeed, the album listened to on a system that is slightly better than one used in a car sounds uncomfortable at times. On the other hand, however, I assume Rubin had a purpose in doing so – and this is, after all, the man who has given us records by Johnny Cash, Adele, U2, Black Sabbath or Metallica's "black" album. He's a producer who knows what he's doing. In the case of RHCP, he was concerned, it seems to me, with giving the whole album a monumental expression and density, bringing the instruments and the vocalist closer to the listener.

When I moved the Ayon player from the reference feet to the Stack Audio isolators, everything I wrote about was clear: what we have here is powerful compression, the sound is big and, finally, despite the low resolution, we get quite a lot of information. The British isolators showed this very nicely. As it turns out, this element brings a lot of selectivity as well as purity to the sound, allowing it to emerge from the surroundings and showing it clearly.

A similar effect can also be achieved by placing devices or speakers on spikes. Personally, I am not a fan of this type of products, but I know that in some applications they can work out. However, if used incorrectly, they lead to sound sharpening and slimming it down. Sound is cleaner, more selective, but also has less "flesh" in it. The tested isolators play just as selectively as elements with point blade support, but without brightening the sound.

The filling is also very good, because when two guitars entered in the title track of Californication, they had nice mass and filling with the AUVA EQ. The sound as a whole was a bit farther away than with the Galileo feet, but it was not, I repeat, diminished. It's just that the apparent sound sources were located a bit further away from me, behind the line connecting the speakers. This will appeal to all those who find strong and "tangible" sound overwhelming or tiring.

Perhaps this is because the sound obtained with the help of the British isolators is warm in a way. It is not warm directly, but it is more about soft delivery of sound attack and filling the sound. Although the message is selective and the individual instruments can be clearly identified, the music sounds pleasant and is easily "absorbed", just like in the opening track of THE OSCAR PETERSON TRIO's album We Get Request. I have it in a version and release that is incredibly resolving and open. The AUVA EQs have not dulled it, as they allow wide bandwidth playing of music, but they also slightly smoothed it.

I am writing this, comparing them with four times more expensive counterparts, so the differences should be clear – otherwise it would not be worth overpaying. However, such a comparison demonstrated that the tested isolators show sound as a whole, as a single event, softening the attack a bit, gently warming the treble and upper midrange, although all within the limits of good taste.

That is why JOHNY CASH's album My Mother’s Hymn Book sounded so good and coherent. Recorded by the mentioned Rubin with the use of two AKG microphones onto a digital ADAT tape recorder, it is an absolutely minimalist release (more → HERE). The British isolators gave the musical message exactly the mood I would expect from this type of recordings: calm, pleasant, but also a bit lofty.

While somewhat withdrawing the foreground, the AUVA EQ do not forget about sound filling and dynamics. Both these elements produce a substantial volume of sound, while maintaining the original proportions. The sound is not as resolving as with the Divine Acoustics feet, or the Pro Audio Bono Ceramic 70 Uni-Foot that I also use. Both Polish sets more strongly differentiate details, nuances, more accurately reflect the size of sound sources. However, this is not sound devoid of detail either, as it is accompanied by very good selectivity.

▌ Conclusions

I WOULD NOT, HOWEVER, attach that much importance to it, especially considering the price of the AUVA EQ isolators. And this is because they draw you into their world. It is a world shown in a pleasant, dense way, but without blurring the details. I would even say that the isolators show a lot of details indeed, and this is due to very good selectivity.

Therefore, they should be appreciated by those of you who don't want to add weight or "dope" anything in sound, but want a clearer picture of the performers and find a clear picture of an instrument more important than ultimate resolution. Compared to feet fitted by companies to their equipment, Theo Stack's isolators are a revelation. Even compared to the best designs of this type I know, they don't fall behind as much as the price difference would suggest.

Therefore, I encourage you to try them out in your own system under all devices, first with CD and file players. The isolators are small, so they "disappear" under the device and thus we will not have the impression that it "hangs" in the air. The Lumin T3 file player, which originally has very low feet, looked especially cool on them. But the Ayon player also matched up nicely with them. They are well made and bring a lot of good into sound. And they are really reasonably priced, which shows that you don't have to outsource production to distant countries to make it work. ●

THIS TEST HAS BEEN DESIGNED ACCORDING TO THE GUIDELINES adopted by the Association of International Audiophile Publications, an international audio press association concerned with ethical and professional standards in our industry, of which HIGH FIDELITY is a founding member. More about the association and its constituent titles → HERE.

→ www.AIAP-online.org