Hardware Reviews

Stack Audio Smooth-LAN for clean streaming

Stack Audio Smooth-LAN network filter review https://the-ear.net

Stack Audio Smooth-LAN network Filter

LAN/Ethernet filters are becoming the latest ‘must-have’ for our networked audio systems, and many have been launched over the last few years. The first I became aware of was the ENO from Network Acoustics, which greatly impressed me when I reviewed it a couple of years ago. Since then, I have tested products from English Electric and CAD, which, whilst following different design paths, attempt to improve the sound of our music by reducing network noise. Having read many positive things about Stack Audio’s product range, I was keen to test the company’s recently launched Smooth-LAN. At £240, this filter is priced significantly lower than some of the competition yet Stack audio claims the Smooth-LAN not only filters out network noise but also galvanically isolates the signal between the two components connected to either side of it, which should prevent further noise from spoiling our music.

What’s in the box?

Firstly, unlike many of its similar brethren, Smooth-LAN’s gubbins are housed inside an aluminium case rather than the plastic alternatives we often see elsewhere. Stack Audio says that while plastic cases are often used to help prevent case interaction with internal magnetic fields, the filter can be susceptible to external interference from vibrations, which the strong aluminium case helps to prevent. The company claims that the compartmentalised design includes EMI-absorbing material that provides shielding from external and internal electromagnetic interference.

The case encloses six isolation circuits, which are shielded from each other. Twenty screws ensure this case is tightly secured, which helps eliminate gaps between the shielded packets. The theory here is that such gaps may amplify specific frequency ranges, which degrades performance. The risk of crosstalk is said to be vastly reduced by grounding each circuit on the PCB to the case.

Stack Audio Smooth-LAN network filter review https://the-ear.net

Using such a filter does mean adding an ethernet cable to the network path of course. When I reviewed the English Electric EE1 filter, I found that upgrading the supplied cable brought significant performance gains. The Smooth-LAN comes with a short piece of gold-plated, oxygen-free copper cable. Stack Audio’s website states this is a CAT 7 cable, although the plugs on my sample are marked as CAT 8. The company suggest connecting the Smooth LAN between your switch and streamer in the first instance, then perhaps experimenting by placing it closer to the router. I have found whilst testing other filters that using a second filter and positioning it between router and switch can be beneficial. Stack Audio offers a 30-day returns policy, making experiments with additional filters risk-free.

Music and pictures

As my main system was set up on an SFP network rather than Ethernet, I first tried the Smooth-LAN between my Melco S100 Switch and BT TV box. I experienced considerable benefits from using the EE1 in this position, and the Smooth-LAN proved this was not a one-off. My TV box is fed via a cheap wall-wart type PSU, so it is undoubtedly a noisy piece of kit. As with the EE1, TV pictures via the Smooth-LAN were cleaner and sharper, benefiting darker scenes considerably. I felt the TV audio performance here suited my system better than via the EE1, which, in this location, slightly emphasised the leading edges of sound effects and music, which could get uncomfortable at times. As was the case with the EE1,  the Smooth-LAN did enhance dynamics, and as usual when you reduce unwanted noise, the sound escaped the speakers more convincingly. Impressively, the Smooth-LAN achieved such improvements without adding its own character.

Stack Audio Smooth-LAN network filter review https://the-ear.net

Although my main network audio system now operates over an SFP fibre optic network. My router feeds into an ADOT SFP fibre converter. So the next step was to place the Smooth-LAN between the two, as previous experience has shown filtering here to be effective. Doing so produced a bit of a ‘wow’ moment. I picked a couple of recently released albums from Qobuz and listened before and after adding the Smooth-LAN. The first track that I tried was Slash’s Orgy of the Damned, featuring Billy Gibbons. Without the filter this sounded flat, edgy and two-dimensional despite the 24/96 resolution. With the Smooth-LAN in the circuit, whilst the compressed nature of the recording was still evident, there was now some degree of dimensionality and a nasty edge to the guitars was vastly reduced. The lower noise floor made it easier to hear the reverb to the guitars, and the music had more body to it. The drum kit now had some space around it, and the cymbals had a degree of air and delicacy around them that was previously missing. The bass guitar had more of a growl to it and was much easier to follow, which powered the track along and showed the band were having fun.

A noteworthy piece I found on Qobuz was a fine recording from Karin Kai Nagano in 24/192 of a piece I was previously unfamiliar with; Mozart and Poulenc’s Double and Triple Piano Concertos. I breathed a contented sigh as the music flowed over me. It sounded good before I introduced the Smooth-LAN, but with it, the music possessed a more natural sense of flow. The violins had more body and texture, and the recorded acoustic was more faithfully rendered.

Stack Audio Smooth-LAN network filter review https://the-ear.net

The Smooth-LAN proved equally effective in feeding my Chord 2Go/Hugo2 directly from the router. For this part of the test, I used the Sendy Peacock headphones reviewed earlier this year. I find that the timing improves with the Chord combo when you feed it with a cleaner network signal, and that was the case here. The same relaxed qualities noted in my main system were evident, but with no loss of drive or dynamics; indeed, the opposite was true when the music demanded it. Streaming from my Melco server over the network to the Chord 2Go/Hugo2, I selected Bob Marley’s Lively Up Yourself (Natty Dread 24/96 download) in the hope that it would allow me to say it ‘livened’ it up. Although this was not really the case with this lazy reggae classic, it certainly opened up the track, giving the bass line space to breathe and bringing the guitars to the front right of the soundstage and the keyboards to the front left, which had previously sounded somewhat muddy. GoGo Penguin’s Raven (A Humdrum Star 24/88) did liven up, however – the bass line sounded more defined, faster and easier to follow, and the keyboards cleaner and more dynamic. These two tracks show that the Smooth-LAN follows the demands of the music played through it.

Trialling a few alternatives to the supplied LAN cable proved a worthwhile exercise. Out of the various cables I have at my disposal, the Audioquest Vodka proved the best match, bringing a palpable sense of scale to the soundstage and additional power to the lower frequencies.

Stack Audio Smooth-LAN network filter review https://the-ear.net


Having left the Smooth-LAN in my system for some weeks, its noise-killing abilities have enhanced my enjoyment of all types of music. I love that it does so without drawing attention to itself by accentuating the high-frequencies or leading edges, which certain competitors do. Despite having experienced several products that claim to reduce network noise, I am still surprised at just how much more relaxed the best examples can make my system sound. I certainly put the Smooth-LAN in that category. Although it is the lowest-priced unit I have tried so far, it is also one of the most effective. If you have a high-quality, wired network streaming system for music and video, then Stack Audio’s 30-day, no-quibble money-back guarantee makes a purchase of this clever device the proverbial no-brainer.


Type: network noise reduction device
Connections: RJ45 in- & outputs
Size HxWxD: 21.5 x 104 x 40mm
Weight: 200g
Ethernet cable length: 250mm
Warranty: 2 years

Price when tested:
Manufacturer Details:

Stack Audio
T +44(0)1626 24 9005


ethernet filter


Chris Baillie

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