HIDIZS ST2 PRO NEBULA: Practicality and Adaptable Audio Solution

Nebulae are enormous clouds composed of gases and dust in the cosmos which were tenuous and diffused in nature and this interstellar phenomena are the results of either newly-formed stars or due to after effects of a supernovae.

HIDIZS is one of the audio companies that releasing some interesting products in the audio market with the likes of S9 PRO, AP80 PRO X and their best product, the MP145 which is considered one of the best or probably still the top-honcho of planar magnetic IEM at under $200/£140. But now we have another intriguing product from them and this one is cost at an affordable price.

This is HIDIZS ST2 PRO NEBULA, this one is quite a unique product that HIDIZS released at the last quarter of 2024 as it doesn't use a standard connector analogue termination plug but rather a newer form of connectivity which is now a norm to all devices, The USB Type-C. And it has single driver configuration on its ear pieces that the majority of current entry-level sets in the audio market have this kind of driver set-up.

The ST2 PRO NEBULA uses a 10mm dual magnetic chambered dynamic driver with a composite diaphragm consisting of PU (Polyurethane) and PEEK (Polyether Ether Ketone) which are both thermoplastic but offer different properties. With the flexibility and rigidity of a PU along with the low density and high mechanical strength of the PEEK, it gives a diaphragm even more responsive and less distortion to deliver a high resolution sound , a broader response range with deeper bass, clear mids and detailed highs.

The driver then encapsulated in an imported hypoallergenic resin shell structure that was ergonomically-designed that ensures good fitting and comfortable wear for longer listening sessions. It utilises a proven 0.78mm bi-pin connector as its interlocking mechanism, in which you replace the stock cable with a standard one with analogue termination plug.

Regarding its wearability, as I mentioned a while ago that the outline of its shell structure was meticulously designed to be ergonomic to all ear sizes, and it rests well into my Asian-size lugholes without any discomfort. It offers an excellent passive noise isolation that is able to block some unwanted external noises from the outside surroundings.

As for its stock cable, this one is rather a rarity among other IEMs as it doesn't use the analogue termination plug like 3.5mm single-ended or 4.4mm balanced but rather a USB type-C which is the standard of all modern devices. The USB-C itself has a Hi-Fi DAC chip which is a proven flagship SOC model from ESS, the ES9281AC PRO which is also used on other Hi-Fi devices like Questyle M15s, Audirect Team 1 amplifier and A&K AH HB1. This audio chip is a high performance USB DAC which has 32-bit with 2-channels with a proprietary SABRE headphone amp that ensures high quality faithfully reproduced sound quality.

The overall structure of the cable is a 2-core high purity oxygen-free copper and it was coated with a fabric-like insulator. It also has in-line control and a high definition microphone to receive calls or transmitting voice over messages in video gaming.

This one also has a LED light to determine sample rate status. Here are some information of its colour coding modes:

RED: PCM 44.1 - 48kHz

BLUE: PCM 88.2 -384kHz & DSD 64-128

On its product packaging, while it was packed in a square packaging box, like a usual HIDIZS product, it was well-accessorised as it was furnished with quantifying amounts of inclusions inside.

Here are the following contents that we could find inside of its packaging box:

• Pair of ST2 PRO IEM transducers
• Stock cable
• Three (3) of balanced bore silicone ear tips in different standard sizes.
• USB-C to USB-A Adapter
• Leatherette carrying pouch
• Paperwork like warranty card and Q.C. stub

Since this is based on the performance of the audio chip with a support of DSP decoding, this DAC IC will simply decode and transmit audio transmission with zero latency, enough to deliver an almost accurate audio reproduction with a full-range frequency response. This one is universally compatible with most known modern devices like Android phones, iPhones (the ones with USB type-C), PC, iMacs, tablets and laptops.

In terms of software support, This one is universally compatible with major operating systems either in mobile or desktop options like Android, iOS, Windows, MacOS, Linux and Harmony OS. This one can deliver a total of 70 mW + 70mW at 32 ohms of audio signal output.

When it comes to tonal profile, this set has a V-shaped sound signature in a stock tuning format. This one is quite coloured sounding as it has more elevation on low and high frequencies on its overall sound.

LOWS/BASS:

The initial impression that I noticed is that it has a noticeable sub-bass presence on its overall bass quality but the mid bass appears to have an adequate texture which is crucial to the tonal colour of certain bass-centric instruments and low octave male vocals. In general, it delivers a punchy, impactful and rumbly bass response albeit there are some instances of bass bleed that smudge across the lower midrange.

As I perceivably felt the reverberations and rumble that were generated from sub bass-focused instruments like drum machines, synthesisers and double basses, its mid bass texture is enough to give a substantial note weight on bass-clef instruments and deep male vocals. Bass guitars have weight and sombre sound while double-basses have that broadness with raspiness of its sound and  bass kick drums sound full and sonorous on every stroke. As for male vocals, basses have dense and reverberant voices while bass-baritones have a plush and a bit dusky sound from their vocals.

MIDRANGE:

The midrange presentation of this one is definitely in a scooped state in which I noticed that some vocals and instruments are quite behind of its overall sound. But it doesn't sound lean as it has a warm to add more density on a certain note weight on instruments and vocals but there some caveats in which I also noticed that it sounds bit veiled (soft or too smooth) and less detailed in some tracks even this one is tuned to have a bit energetically-tuned midrange.

On male vocals, baritones sound warm and smooth while tenors have brassy with a hint of metallic sound, and countertenors have a fiery and “coppery” sound with a bit of spiciness. As for female vocals, contraltos have strong and husky sound from their chesty vocals, mezzo-sopranos have a fiery sound on their vocals but sometimes it sounds too velvety in my liking particularly on Andrea Corr’s vocals. And then sopranos, they have these silky and gleaming sounds on their vocals which somewhat make them a bit of an all rounder for all sopranos types but on a less refined side.

When it comes to instruments, on strings, guitars sound a bit crisp and a tad bright on every plucking on its note strings, violins have these sweet and sensuous sounds of every bowstroke, and cellos sound sonorous and cantabile. The woodwind instruments like concert flutes, piccolos, clarinets and saxophones, concert flutes sound mellow and brilliant, piccolos sound light and intense, clarinets have mellow and melodic sound, and saxophones have that brilliant and expressive sound. As for brasses like trumpets, trombones and horns, they sound brilliant, sinister and full respectively. Then the percussive ones, snares have a hard and a bit boomy sound, tom-toms have warm and resonant sound, field drums sound a bit boomy and sombre, and the last one, kettledrums have this deep and resonant sound on every stroke. The pianos appear to have a balanced tone as it sounds sweet, warm and full.

HIGHS/TREBLE:

The treble response of this one is quite bright with some shimmer and energy as it gives that sense of crisp and clarity on vocals and instruments, although I noticed that this set has a bit metallic and shrillness on its overall treble sound quality.

For a single dynamic driver, it has a good airy extension with some intensity of its sparkle that certainly affects the tonal colour of some instruments. Cymbals sound bright while the hi-hats have a short sizzling tone on their chick-y sound, celestas have a silvery sound and glockenspiel sound shimmering.

SOUNDSTAGE, IMAGING AND OTHER TECHNICALITIES:

The ST2 PRO NEBULA seems to project just an average-size sound field in which it gives me an intimate head room within my aural perception. It has a middling lateral span on its width, good height reach and an immersive depth.

On its stereo imaging, this one is rather unusual as it has this concave-like stereo presentation in which I was able to pinpoint some of the placements of the vocals and instruments in a perceived sonic spatiality. But my main gripe on this technical aspect was that its layering is quite mediocre but at least, it has decent separation. I’m taking some consideration on recommending this one to do some playback on some complex multi-instrumental genres like orchestra and jazz as this set is somewhat struggling on those genres.

It has an excellent coherency of its driver performance as it was able to perform broad and responsive transients that it was able to deliver a fast bass response and clear sound without any noticeable distortion at all.  As for its resolution capability, I still consider it as average despite that emphasis on upper midrange and some parts of the presence section of the treble region as it is less resolving in my opinion. Its micro-detail capability is less capable of extracting some nuances and subtleties from a sonic background from an audio track but at least, it has a solid macro-dynamics in which I can perceive the variety of loudness.

PEER COMPARISONS:

TANCHJIM TANYA DSP

• This one also has a single dynamic driver with a circular metal shell structure but unlike the ST2 PRO, it doesn't have detachable cable but rather it was fixed on the earpieces.
• This is also powered and processed with DSP chip but the said chip only offers a limited sampling rate up to 96kHz in PCM format, native DSD format doesn't have sampling support on this one.
• It can be used on any device with a USB type-C port as long as it supports USB Audio.
• It is universally supported across major OSes either its a mobile or desktop one.
• The tonal profile of this one has a U-shaped sound signature which aligns with a Harman-ish type of sound as it has rumbly and tighter bass response, a bit recesses yet more balanced midrange presentation with enough treble energy.
• It has very similar technical capabilities with the ST2 PRO from soundstage size up to the resolution capabilities.
• This one is way cheaper than ST2 PRO.

HIBY XENO

• While this one is in the same category with ST2 PRO, it has a rather unusual driver configuration and also an implementation of audio chips as this one has MEMS driver aside from dynamic driver although it has a non-detachable cable on its peculiarly designed 3D-moulded resin shell.
• Another unique implementation of this unit was its dual DAC set-up of different brands and models in which work in tandem to decode high resolution audio at high sample rate.
• It has a control console for play/pause, volume control and tonal presets.
• XENO universally supports major OSes in the market from Android OS up to MacOS.
• Since it has 3 tonal presets, Flat mode has a balanced-neutral sound while the Dynamic mode has a more coloured, U-shaped sound profile, and then the Gaming/Cinematic mode has a more V-shaped sound profile.
• Depends on the tonal presets, but the Gaming/Cinematic mode has the widest perceived soundstage and it is quite more resolving among them.

As the current state of today’s current technology as we are now veering towards wireless connectivity that most modern devices like smartphones are now dropping the final vestiges of analogue technology that traces back from the late 19th century, the 3.5mm headphone jack. And now only the USB type-C ports are now the only viable option as wireless audio capability is still inferior compared to the wired, analogue audio. Given how adaptive the HIDIZS is in the current audio market as they continue to be as innovative as they can and the ST2 PRO is the result of their research and development.

With a plug and play as its main core of the product along with the implementation of an old flagship USB DAC chip that works as it main DSP to deliver a good sound quality, this will be a good option for both audio enthusiasts and also for casual users as operating this device will be beneficial for them to use.

HIDIZS ST2 PRO NEBULA is now available at HIDIZS' official store and also you can support them on the kickstarter campaign for this device. (Non-affiliated links guaranteed)

OFFICIAL STORE:

https://www.hidizs.net/products/hidizs-st2-nebula-2-in-1-high-performance-dac-usb-c-hifi-digital-in-ear-earphones

KICKSTARTER:

https://www.kickstarter.com/projects/hidizs/st2-nebula-redefining-hi-res-audio-with-usb-c-dac-earphones

SPECIFICATION:

MODEL: HIDIZS ST2 PRO

IMPEDANCE: 32Ω

SENSITIVITY: 108dB

FREQUENCY RESPONSE: 20Hz – 40KHz

CABLE LENGTH: 1.2m

PIN TYPE: 0.78 2-PIN CONNECTOR

PLUG TYPE: 3.5mm

DRIVER UNIT(S):  (1) DYNAMIC DRIVER

PROS:

● Lightweight yet solidly structured resin shell chassis.

● Finally, with a detachable cable feature as I encountered models from other brands that are usually fixed on the earpieces.

● Comfortable to wear without any discomfort and wear fatigue.

● It has a substantial amount of inclusions inside of its packaging box.

● Flagship-grade USB DAC from ESS.

● Better than average stock cable.

● DSD decoding supports up to DSD128 for serious audiophiles.

● MQA unfolding capability for MQA format lovers.

● A fun and engaging tuning that casual listeners and audio enthusiasts that prefers more coloured tonality

● Impactful and rumbly bass response 

● Good for tracking on low octave male vocals like bass and bass-baritone ones as they have that deep resonating voices that this set is able to deliver.

● Almost correct timbre and tonality on bass-clef instruments. 

● Warm and smooth midrange presentation.

● An energetic and bright treble presentation.

● Good driver coherency performance.

CONS:

● Too coloured sounding for uncompromising neutral heads.

● Instances of bass smearing

● Recessed midrange presentation

● Some tonal colour oddities particular on vocals like countertenors and mezzo-sopranos.

● Occurrences of tinny, metallic and a tad piercing sound on its midrange up to treble regions.

● Noticeable limitations on the majority of its technical capabilities

● Not the most resolving in terms of resolution capabilities, the fact that it was a bit brightly-tuned.

TESTING TRACKS: ( * = 16-bit FLAC, ** = 24-bit FLAC, *'* = MQA, '*' = DSD, *'= .WAV)

Alison Krauss -When You Say Nothing At All *

Jade Wiedlin - Blue Kiss**

Led Zeppelin - When The Levee Breaks **

Mountain - Mississippi Queen *

Queen - Killer Queen **

Guns N' Roses - Patience *'*

Eric Clapton - Tears in Heaven '*'

Sergio Mendes- Never Gonna Let You Go '*'

Pearl Jam - Daughter **

Roselia - Hidamari Rhodonite *

Assassin - Fight (To Stop The Tyranny)*

Celtic Frost- Visual Aggression *

New Order - Blue Monday *

The Corrs- What Can I do (unplugged version) *

Jimi Hendrix Experience - Voodoo Child *

The Madness- Buggy Trousers *

Metallica - Motorbreath **

Mariah Carey- Always Be My Baby *

Destiny's Child - Say My Name *

Malice Mizer- Au Revoir *

Mozart - Lacrimosa *

New York Philharmonic Orchestra - Dvorak- Symphony 9 " From the New World." *

Eva Cassidy - Fields of Gold (Sting cover)*

Michael Jackson - Give In To Me *

Exciter - Violence and Force *

Diana Krall - Stop This World **

Debbie Gibson - Foolish Beat *'*

The Sisters of Mercy – Lucretia My Reflection**

Suzanne Vega – Luka **

Lauren Christy – Steep *

Ottoman Mehter - Hucum Marsi *

Diana Damrau - Mozart: Die Zauberflöte*

P.S.

I am not affiliated to HIDIZS nor receive monetary incentives and financial gains as they provide me a review unit for an exchange of factual and sincere feedback from yours truly.

Once again, I would like to send my gratitude to BELLA JUAN for providing this review unit. I truly appreciate their generosity and trust towards me and other reviewers.