Acoustune HS2000MX SHO MKII & MKIII In-ear Monitors Review

Cheryl Tan is charmed by these unique, premium-priced modular in-ear monitors…
Acoustune
HS2000MX SHO MKII & MKIII In Ear Monitors
Price: MKII - JPY¥ 250,000, MKIII - JPY¥ 412,500
Chambers - from JPY¥ 92,400 to JPY¥ 270,600
Acoustune may not be as well known as some other head-fi brands out there, but this Japanese company offers some highly innovative products nonetheless. Back in 2021 it launched the first version of its HS2000MX SHO, a highly unusual in-ear monitor that let users switch-out the acoustic chamber and driver. This is made possible by the manufacturer’s unique Acoustune Capsule Technology, which separates the transducer assembly from the housing.
ACT allows for the acoustic chamber and driver to be removed by undoing a screw on the housing of the in-ear monitor – in other words, the entire chamber can be popped out. The company sells a variety of chambers, each with different materials that subtly tweak the sound signature. Every one so far has come with a single 10mm dynamic driver that uses a polymer biomaterial called Myrinx for the diaphragm, although the two drivers in the MKII and MKIII models come with a thin beryllium film for the diaphragm, for higher rigidity.
While the first HS2000MX SHO used CNC-machined Duralumin for the chamber, the brand has released other chambers in materials such as brass, copper and silver, with interesting baffle materials like wood and stone. StereoNET managed to get our hands on the ACT06 and ACT07 chambers thanks to our friends at Zeppelin & Co, which are made with nickel silver and sport white jade and jadeite baffle plates respectively. We’ll talk more about how they change the sound later on.
We also procured the newer HS2000MX SHO MKII and MKIII IEMs that were released in February 2023 and February 2024 respectively. Although it seems as if there might be big differences between the two, the biggest changes are in the colours for the mechanical housing and acoustic chamber material. The MKII comes in a striking grey and red colourway with gold accents in the screws – I prefer this as it offers a nice pop of vibrancy. The MKIII comes in black and silver, although people will only be able to see the shiny silver when in the ear.
UP CLOSE
The MKII has the ACT05 chamber, which is made out of CNC-machined Oxygen Free Copper (OFC), while the MKIII has the newest ACT07 chamber that uses CNC-machined pure silver. Of course, these chamber materials also affect the sound, and we will expand more on that later.
There is also a difference in the cables provided. The older MKII comes with the ARS100 cable, a 16-core hybrid cable that uses silver-plated OFC and ultra-fine OFC wires. The newer MKIII has the ARX500 8-core cable that uses high purity OFC. Both use the Pentaconn Ear connector and the ARX500 comes with the ability to switch between a 3.5mm 3-pole unbalanced plug and a 4.4mm 5-pole balanced plug. The workmanship on both cables is very well done, although I’m partial to the ARX500 because the unbraided Japanese PVC cable sheath is smooth, not microphonic and has little cable memory.
One quirk of Acoustune’s products is that its IEMs might not fit everybody’s ears, due to the unique shape of the shell. The fit is very different from something you might expect, with a shallow insertion that does the product no favours. Due to the use of aluminium and metal for the shell and chamber, the HS2000MX models are all rather heavy, which means that if a listener’s ears don’t allow for a good fit, the IEM is more prone to dropping out. It’s essential to get a good, long demo at an audio shop to better gauge the fit.
In order to swap the chambers, the eartips have to be pulled off, then the faceplate lid can be unscrewed and swung open. The chamber is then easily pulled or pushed out, and a new chamber can be inserted. There are two pins on the chambers that need to be aligned with a rail on the inside of the shell for the chamber to be slid into place, and L and R are engraved right next to the pins so that the chambers won’t be mistakenly placed into the wrong side.
THE LISTENING
Our focus is on how the different chamber modules sound, so let’s start with the ACT05 that comes in the HS2000MX SHO MKII model. Made with copper, the acoustic chamber is relatively heavy at 6.3g per side and comes in a high-shine finish. The use of copper here imparts a gorgeous warmth to the sound with more of a focus on the bass regions. There’s a little boost in the low bass which provides decent impact without crossing the line into boomy, muddy bass. The bottom end is pleasantly full-bodied, while the mids take a slight step back in the mix. Despite that, there’s still a good amount of detail.
Treble is slightly tapered back, so it is a comfortable listening experience for those who are sensitive to sibilance and harshness. There’s plenty of energy and accuracy, and the soundstage is wide with excellent spatial imaging. Listening to Feel Good Inc. by Gorillaz was a delight, with the iconic bass line having a little more heft. Little details that might be missed like the distorted guitar were still crisp and clear.
As for ACT06, which uses nickel silver and a natural white jade baffle plate, it comes with a 10mm Myrinx SS driver. It’s a little lighter at 5g per side, and comes in a matt, blasted finish that’s more resilient to scratches compared to the glossy ones. The sound signature of this chamber is a little unusual, with Acoustune claiming it provides a hard sound, which is a little confusing. Vocals are stronger and more full-bodied, and there’s a subtle thickness to the sound. Midband and treble are smooth and gentle, without sharpness or too much brightness. It’s relatively neutral with next-to-no colouration of the sound, and details are brought out nicely.
The ACT07 is quite similar to the ACT06, with a nickel silver casing paired with an artificial jadeite baffle plate and the same 10mm Myrinx SS driver. The overall sound signature is also neutral with no added warmth or coolness, although it does feel sharper and crisper. This helps to bring out the edge in vocals and higher-pitched instruments, particularly female vocals and wind instruments like flutes. There’s also a bit more energy, which makes for a more fun listening experience if you’re not keen on a laid-back sound. Both chambers have a decent enough soundstage with wide with accurate imaging, although that ‘hard’ sound makes it feel a little less airy.
The newest ACT47 chamber that comes with the HS2000MX SHO MKIII is the most expensive to date, thanks to its pure silver chamber. It’s also the heaviest at 6.5g per side, which means it’s a harder trying to get the HS2000MX MKIII to stay securely in the ear because of the extra weight. The sound signature for this chamber leans towards the cooler side. Treble is extended but not harsh or shrill, and the chamber offers plenty of resolution and detail. For people who value a clean sound with good timbre and dynamics, this is ideal. The soundstage is decently wide, which is helped by the airiness and brightness from the chamber.
THE VERDICT
The ability to swap out chambers to get different sound signatures, offers so much flexibility and potential for in-ear monitor fans. So if you feel like bass-heavy music one day, then switch to the Acoustune ACT05. And if you’re in the mood for some classical the next, the Acoustune ACT47 works beautifully. You don’t even have to purchase separate IEMs, since you can just swap out the chambers – which are more affordable than buying multiple flagship in-ear monitors. So Acoustune is certainly onto something here, and hopefully we’ll see more products with this modular concept come to market soon.
For more information visit Acoustune

Cheryl Tan
After diving down the custom IEMs rabbit hole since she was 18, Cheryl has embarked on a long journey trying out as many audio products as possible ever since. She’s still waiting for the day a company can create a pair of true wireless earbuds that sound just as good as wired earphones.
Posted in: Applause Awards | 2025 | Headphones | In Ear Monitors | Headphones
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