Hidizs ST2 PRO Nebula 

A Compact Innovation for Ultra-Mobile Audio

Pros:

• Innovative DAC Cable: The ES9281AC PRO-powered cable delivers excellent audio performance while doubling as a portable DAC.

• Impressive Sound Tuning: A slightly tweaked Harman curve offers a fun, engaging, and versatile sound profile.

• VR Gaming Star: Excels in spatial audio and imaging, creating an immersive gaming experience.

• Ultra-Portability: Combines the convenience of a dongle and IEM cable into a compact, lightweight package.

Cons:

• Midbass Decay: Slightly loose midbass can bleed into the lower mids, adding warmth but reducing precision.

• Midrange Detailing: Mids feel slightly recessed and lack layering or microdetail for analytical listening.

The Hidizs ST2 PRO Nebula is a bold step forward in the IEM space, blending the simplicity of a single dynamic driver with the power of a high-performance DAC cable. At first glance, it may look like just another Type-C IEM package, but a closer look reveals a game-changing feature: the cable itself doubles as a fully-fledged DAC. Powered by the ES9281AC PRO chip (found in full sized dac devices like the Astell&Kern AK-HB1 and Fiio KA1), the ST2 PRO delivers an impressive 70mW of power, proving that big things do come in small packages, and i do believe this is the next innovative step to the ultra portable setup.

Whats in the box? here is a quick unboxing video:


Here’s what you get:

ST2 PRO IEMs

USB-C DAC Digital 0.78mm 2Pin Earphone Cable

Three pairs of silicone eartips

USB-C to USB-A adapter

Leather Hidizs pouch bag

Warranty card

Product quality certificate

Design & Build Quality

The ST2 PRO Nebula’s design strikes a balance between form and function. The cable showcases an aluminum alloy USB connector, with transparent windows on either side to reveal the internal PCB. A small LED indicator provides real-time feedback on audio sampling rates—red for PCM (44.1-48kHz) and blue for PCM (88.2-384kHz) or native DSD playback.

The in-line controls and splitter are similarly crafted from aluminum alloy for that extra durability. While the earphone connectors are unfortunately plastic, the build overall feels good for the price point.

The cable measures 1.2 meters and is made from high-purity oxygen-free copper wires wrapped in a textile material for enhanced flexibility and durability. It’s soft, lightweight (just 16 grams), and resists microphonics well. However, it does feel a bit delicate—something to consider if you’re rough with your gear.

Color options include a sleek silver-gray and a striking black-blue, both of which complement the minimalistic yet modern aesthetic.

This sound impression is based on using the ST2 Nebula IEM, but I've also paired the cable with various other IEMs, including planar drivers. It’s incredibly impressive how well the cable handles planars, delivering generous volume with plenty of headroom to spare. I’m genuinely impressed with how effectively the ES9281AC PRO chip is implemented here. The level of detail, clarity, and power packed into such a small device is quite surprising.

I’ve tried a lot of DSP cables, but none come close to the performance of the ST2. If there’s a next iteration of this cable, I’d love to see a more premium version with thicker cables and metal connectors—it would make an already impressive product even better.

For some reason, my graph measurements don’t seem to fully reflect the actual sound of the ST2. When measuring the ST2 IEM with the DAC cable, the graph shows a subbass roll-off that’s not present in real listening. Similarly, when using a regular cable, the graph shows a noticeable peak in the upper treble, which isn’t accurate based on what I hear. It’s a reminder that graphs can be helpful, but they don’t always tell the whole story.

Hidizs has tuned the ST2 PRO Nebula to a slightly tweaked Harman curve, creating a sound profile that's fun, engaging, and surprisingly versatile. One area where this tuning truly shines is gaming. For me, the ST2 PRO feels tailor-made for immersive gameplay. Paired with my MetaQuest 2 VR goggles, it delivers exceptional spatial audio performance. The 3D soundscape is impressively detailed, with precise imaging that places every sound exactly where it should be. It wraps you in a fully immersive audio environment, making every gaming session feel incredibly lifelike and engaging.

Bass
The subbass on the ST2 PRO Nebula is generous, it deep and resonates delivering a satisfying rumble that adds depth and weight to tracks, particularly in genres like electronic, hip-hop, or cinematic scores. It’s the kind of subbass that makes you feel the music, not just hear it. The midbass follows up with a punchy, impactful presence, though its slower decay can sometimes bleed into the lower mids. Interestingly, this bass bleed doesn’t detract from the overall experience; instead, it adds warmth and body to the midrange, creating a cohesive and inviting sound signature. This characteristic works especially well for gaming, where impactful and immersive bass can heighten the experience.

Midrange
The midrange is slightly recessed, which might leave vocals and instruments positioned a step back in the mix compared to the bass and treble. Despite this, the mids maintain a natural timbre and tonal accuracy, which helps them feel lifelike and engaging. The clarity is respectable, though the midrange lacks the intricate layering or microdetails that more analytical listeners might crave. However, its smooth and warm presentation makes it well-suited for casual listening, particularly with vocals and acoustic tracks that benefit from its organic tonality.

Treble
The treble performance is a standout feature of the ST2 PRO Nebula. Energetic and well-extended, the highs bring a sense of air and sparkle to the overall sound signature. This added clarity balances out the warmth from the bass, ensuring that the sound never feels overly dark or congested. The treble's extension also contributes to uncovering fine details in the music, enhancing the perception of resolution across the frequency spectrum. Importantly, it avoids harshness or sibilance, making it suitable for long listening sessions without fatigue. The treble’s liveliness adds refinement and helps tie the entire sound signature together, making it dynamic and engaging for various listening scenarios.

The soundstage is average in width and depth, providing a focused, intimate listening experience rather than an expansive one. Imaging is precise, making it easy to pick out instruments and positions in the mix.

Resolution & Dynamics

For its price, the ST2 PRO Nebula punches above its weight in resolution. It captures subtle details and nuances in listening to music and in gaming, making it a capable performer for music and even in VR gaming. You’ll hear microdetails in recordings and soundscapes that you might miss with lesser gear. Dynamics are equally strong, effortlessly transitioning between quiet and loud passages with ease.

DAC Cable Performance:

The integrated DAC cable is where the ST2 PRO truly shines. Equipped with the ES9281AC PRO chip, the cable delivers enough power to drive even demanding planar IEMs without breaking a sweat. It handles volume adjustments smoothly, with plenty of headroom to spare.

What’s impressive is the level of portability this DAC cable brings. It bridges the gap between traditional USB dongles and standard IEM cables, offering the same performance as many dongles while remaining far more compact. For ultra-mobile audiophile setups this is a game-changer.

While the ST2 PRO Nebula excels in many areas, there’s room for refinement:

Bass Control: The midbass decay could be tighter to avoid occasional bleeding into the mids.

Midrange Detailing: While pleasant, the mids could use more layering and resolution to appeal to analytical listeners.

Build Durability: The lightweight cable, while flexible and comfortable, feels slightly delicate. A thicker, more premium version would be a welcome addition—even at a higher price point.

Final Thoughts:

The Hidizs ST2 PRO Nebula showcases just how far compact audio solutions have come. It’s a versatile IEM that combines great sound with innovative DAC technology, all in a package that’s as portable as it is powerful. Personally, I’d choose this kind of ultra-portable setup over a full-sized USB dongle DAC any day. Plus, I’ve finally found a use for that included Hidizs leather pouch—it’s perfect for carrying this setup around.

For an IEM that delivers stellar sound quality, impressive DAC capabilities, and unmatched portability, the Hidizs ST2 PRO Nebula is a tough contender to beat at its price.

Link: https://www.kickstarter.com/project...efining-hi-res-audio-with-usb-c-dac-earphones