100+ Head-Fier
Pros: Supports multiple BT codecs
Sufficient volume without getting near max
2.5mm "balanced" dual-mono output
EQ interface is quite good
App or HW control
Cons: App has a few bugs (but is still very usable)
Volume changes lag volume adjustments by a second or two.
I bought this to increase the convenience level of my Ety ER4XR. I have previously used (and abused) extensively the Samsung HS3000. What I wanted for my Eties was something like the HS3000, but with more power. The device I received exceeded all expectations.

The app is pretty good. It provides many customizable options, while allowing many to be turned off for those who prefer to keep things simple. It's not without bugs, but I haven't encountered anything serious.

The Ambient Sound feature is interesting, pumping ambient sound into the earphones, eliminating the need to remove good sealing IEMs in some cases, such as to hear an announcement on mass transit.

Being able to control the ES100, not just the source material, from my phone is very convenient.

The EQ supplements the nearly-missing EQ functionality of the iPhone's Music app nicely. The interface is intuitive and easy to use.

Provided the codec is supported at both ends, the ES100 allows the user to force use of a particular BT codec.

Perhaps the most underrated feature is the feature that allow the device to stop taking further charge after the battery reaches 80-90 percent capacity. Completely charged is a very stressful state for lithium ion batteries, so this feature could potentially extend the useful life of the device.

The ES100 does everything I hoped, and more. Most importantly, it allows me to listen with my wired headphones, while using my phone without any cables, without any noticeable SQ deficiencies or unreasonable volume limitations imposed by the amp.


Headphoneus Supremus
Pros: Holy features Batman, esp. with the EarStudio app - 2.5mm Balanced and 3.5mm unbalanced outputs - Battery life - Small size - Price - Pick something
Cons: Tiny, nondescript buttons that are easy to confuse for one another

Today we're checking out the ES100, a Bluetooth receiver from Radsone.

Radsone is a consumer electronics and technology company based out of Seoul, Korea, founded in 2011. Their technology (https://www.radsone.com/technology) is used by some heavy hitters in the industry, like Audio Technica, LG, and Qualcomm, so you know they've got some serious talent under their belt.

We're not here to talk about that though. No, we're here because of the ES100. This little Bluetooth receiver has been lighting up the online forums this past year. This device has garnered a lot of attention from the audio community for it's impressive combination of tech and features offered at a more than reasonable price.

Let's take a closer look.

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I reached out to Radsone to see if they'd be willing to send over a sample of the ES100 for the purposes of review. They said yes, as evidenced by the review you're reading. The thoughts and impressions within this review and my own based on my experiences with the ES100. They do not represent Radsone or any other entity. Should wish to pick one up, and you should if you enjoy Bluetooth devices, you can check it out here; https://www.radsone.com/earstudio. Make sure you scroll to the bottom of the page to ensure you're ordering through an authorized retailer.

If you want a more technical look at this device, I HIGHLY recommend checking out this stellar review from yuriv on Head-fi: https://www.head-fi.org/showcase/radsone-earstudio-es100.23284/reviews

Tested with device firmware version 1.4.2.

Package Contents:

Disregard the condition of the packaging in my pictures. Seems Canada Post had it's way with the ES100 during shipping...
  • ES100 Bluetooth Receiver
  • Micro USB cable
  • Quick start manual

Output RMS Power
- 3.5mm Unbalanced: 1.1 V
- 2.5mm Balanced: 2.2 V

SNR* (1KHz, 20KHz AES17)
- 3.5mm Unbalanced: 109dB (+2.8dBu)
- 2.5mm Balanced: 110dB (+8.8dBu)

Output Impedance
- 0.5~1 ohm

Bluetooth Range
- 10 meters

THD+N* (1KHz, 20KHz AES17)
- 3.5mm Unbalanced: 0.0022%
- 2.5mm Balanced: 0.0014%

- LDAC, aptX-HD, AAC, aptX, SBC

- 14 hours

- https://docs.wixstatic.com/ugd/fb72a4_ca4675b20f6a48cf8da9e504c2f4dddc.pdf

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Build and Ergonomics:

The ES100 is mostly plastic with a very simple, clean design and a professional silver on grey color scheme. Metal is used for the clip on the back, helping out with durability in the long run. The clip's clamping force was fine in my opinion, but I've seen others finding it a little on the weak side. Not an issue I had, but worth noting anyway. Seams between the component parts are quite visible but line up properly without any sloppy gaps, including around the micro-USB, 2.5mm balanced output, and 3.5mm unbalanced output. To the right of the volume rocker on one side is a small grill behind which is the microphone for phone calls and the ambient sound feature. To the left is the 3.5mm output. On the other side of the unit is a rocker button for skipping through tracks, a pause/play button, and the 2.5mm balanced output. The face of the unit looks like a plain grey slab, though when in use you find there is an LED ring hidden beneath. The LED ring performs a number of functions, besides telling you if the device is on or not, using green, red, or blue colorings. I didn't bother to memorize the various notifications, simply because it wasn't necessary. The ES100 is easy to use and works exactly as you would expect.

The buttons used to interact with the ES100 are small and nondescript with limited physical feedback when pressed. I personally found myself routinely pressing the wrong thing, resorting to looking at the device most of the time to adjust volume, or swap tracks. This was even after a month of routine use, though I've gotten used to it by now. If Radsone ever decides to revise the ES100, I would love to see them change up the buttons so that they are easier to tell apart without looking, and provide a more prominent click when pressed. It's a simple quality of life thing. The device is fine to interact with as is, but it could be better with some minor revisions.


The ES100's Bluetooth performance is quite positive. Starting with connection strength, in regular use I didn't have to worry about device placement. It could be in a pocket, clipped to my sleeve or shirt collar, or in my hand and dropouts weren't a worry. It has a 30 foot range which is about standard, and like most devices with that rating can really only achieve it when unobstructed. I liked to use it when connected to my computer or LG G6. Those devices could be left on the living room table, and I would be free to walk nearly anywhere in the apartment without experiencing dropouts. Heading to my office or the front door would put two walls between myself and the device which would lead to stuttering, but the connection would hold. Overall connection strength is quite good.

The ES100 can connect two two devices at a time. It works fine and has remained tied to my LG G6 and Asus FX53V without the need to re-pair throughout the duration of my testing. I'm not sure what Bluetooth codecs my laptop supports, but they're not fantastic as evidenced by the audio delay while watching videos. Connected to my LG G6 over aptX HD or LDAC (defaults to LDAC) there is no delay that I could notice, making for pleasant video

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Sound Quality:

Sound quality, regardless of whether you're using the ES100 over Bluetooth or USB (16bit max via USB on anything but macOS), balanced or unbalanced, is excellent. The two AK4375a DAC/AMP chips from Asahi Kasei provide plenty of driving power along with a warm leaning and smooth but very resolving signature. Some might describe it as an analogue sound. Unlike other products with similar traits, I didn't find the ES100 restricted to earphones with certain signatures. Whether it was being paired with the neutral and very detailed Astrotec Delphinus 5 or smooth and bassy Meze 99 Neo, pairings always sounded great. It's a very versatile product, a quality aided greatly by it's low output impedance.

The ES100 has almost completely replaced my other portable headphone amps (Walnut F1 and Auglamour GR-1). Not only does it sound better regardless of how you're opting to connect to your device, but its also smaller, lighter, and has a vastly longer battery life.

Companion App:

The Earstudio app for Android or iOS gives the ES100 a TON of extra versatility and is an absolute must if you want to get the most out of it.

From the home screen you have a number of options. Swipe right and a menu pops out from the left containing a slew of options, like searching for a device to connect to, LED functions, the manual, factory reset, and much more. Closing that menu, from the main screen you can also select input to change the codec, buffer length, hands-free profiles, output via USB DAC, mess around with Radsone's HD Jitter Cleaner, and even check out measurement graphs showing off the ES100's single tone performance with a variety of cell phones. Under output you can optimize the quality of the sound being pushed out through the 3.5mm and 2.5mm TRRS ports. Under 3.5mm you can select either Normal or High Performance modes. The high performance mode reduces the output impedance by nearly half (~1ohm to ~0.5ohm) resulting in a cleaner sound. Under 2.5mm you can select from Normal or High Voltage modes. The High Voltage mode doesn't change performance and simply doubles the voltage from 3.2v peak-to-peak to 6.4v peak-to-peak allowing you to drive some pretty demanding gear. They even provide an explanation of why balanced is superior, namely it reduces noise ground noise providing a cleaner sound. Going back to the home screen, you can also adjust the analog volume and source volume. Under analog volume you can adjust each channel separately by up to 6dB, set the max volume limit, and even estimate how loud you are listening when using the ES100 as a headphone amp by entering the impedance and sensitivity of your headphones. Cool!

Next up is the equalizer. You're provided a preamp which can be adjusted +12dB or -12dB. Then you have ten sliders for adjusting a variety of frequencies; 31.5, 63, 125, 500, 1k, 2k, 4k, 8k, and 16k. Below that you have 12 distinct preset EQ options like Classical, Jazz, and Bass Reducer, as well as four presets that you can save specific EQ settings too. They can be renamed as well, so you never have to guess which is being used to tame the aggressive treble peak on your HiFiMan RE800.

Next up under Sound Control, you can adjust how aggressively the app will compensate for and remove digital noise via the DCT level. Crossfeed can also be adjusted. Note that these options will be disables if connected via LDAC as they are not supported. Further down you can apply one of four digital filters to the AK4375a DAC, and if you need, play around with the over sampling rate.

Last up is the Ambient Sound feature. This is something I was surprised to see included and not mentioned anywhere on Radsone's site. Most companies brag about such a feature whenever possible. Turning Ambient Sound on uses the ES100's in-built mic to pic up and feed in outside noise so that you can still hear your surroundings. When using this feature outdoors, unless the earphones or headphones I was using were unusually naturally well-isolating, aided further with foam tips, Ambient Sound wasn't as helpful as I was hoping. If the mic sensitivity was left fairly low, it didn't pick up important noises. Increasing the mic's sensitivity enough so that it would pic up sounds a decent distance away also resulted in every little brush and scrape against my clothes to be picked up leading to a very noisy and unpleasant experience. I found it most useful indoors where I could set the ES100 down beside me in a stationary position.

As mentioned before, the app is filled to the brim with features and functionality and it really lets you tailor the ES100 to suit you and your listening behaviours and preferences. I imagine they put a ton of time into it, and it absolutely paid off. Best of all, if you're like me and are still learning the ins and outs of audio terminology and what does what, just click the numerous question marks to the right of most features for well written descriptions of what they do, why they're important, and how to use them. Odd as it is, it one of my favorite parts of the app.

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Final Thoughts:

If you're a fan of high quality, portable audio and have been holding off on getting into wireless due to questionable audio quality, you're safe to dive in with the ES100. If you enjoy cool tech and love messing around with apps and features and fine tuning your audio experience, this is a great product for you. You can tweak until your heart is content. If you are the exact opposite and want something simple and easy to use, forgo the app and run the ES100 as a bare bones Bluetooth receiver. You'll still have an awesome time. This is great product for pretty much anyone. If I were to complain about anything, it would be the tiny, nondescript buttons that can be difficult to tell apart, something that will no longer be an issue once you have used to device for a while.

At only 99.00 USD, the ES100 is beyond being an easy recommendation to any fan of portable audio. I don't say this often, but it lives up to the hype. Great job Radsone. Seriously.

Thanks for reading!

- B9Scrambler
This is the best portable solution on the market in my opinion. Does it all and sounds great.
I haven't tried any of the direct competition, yet, but I can't image they'd be any better. This thing is amazing, lol.


Headphoneus Supremus
Pros: Undoubtable sound improvment, powerfull amping, 2.5mm output, low THD and background noise, excellent imaging, long battery life, infinite features, superb EQ, easy pairing, light and small, USB-OTG Dac, Good value
Cons: Cannot fast fowards-backwards track with the device, too much plastic.
RADSONE ES100 (post-hype?) review:

VALUE: 9/10


How come one of the more sceptical dude about bluetooth technology sound quality became so interested in a Bluetooth device? How is it possible that even if he still don't get intrigued by must BT iem or headphones and don't care to try them, Nymphono was ready to sell an arm (but not its soul) for having the chance to write a review of this Earstudio first creation? Well, for two reason really, one being the hype that never go out of breath and second being the fact sound is processed trough a dual AKM dac before it feed your headphones or iem. Perhaps a third one would be: its not BT earphones and you can use all your favorite one with the ES100. Fourth could be as well that its LG G6 phone sound like soul less crap. ETC!


SO it make lot of reason why I decide to give a try to this wonderfull all-in-one bluetooth receiver. Its hard to understand how such a small portable device can hide that much features as well as having 3.5mm unbalanced and 2.5mm balanced phone out, a mic, usb-otg dac-amp fonction and BT decoding trough 2xAK4375a hifi dac. But thats not all, Earstudio have its own APP to control every features of its device, and this too suprise me alot, its not a basic app that just control volume, in fact it take the ES100 to a next audiophile level by letting him configure every aspect of dac potential. We will talk about this later.

Now lets just begin the review.


SPECS and some features:

Bluetooth DAC/Headphone Amp

LDAC, aptX-HD, AAC, aptX, SBC

14 Hours Playback

USB DAC/Headphone Amp

USB Audio Class 1.0 (48KHz / 16-bit only)

Works as Preamplifier in vehicles

3.5mm output to car AUX

CAR MODE support(auto power on/off)

Proprietary DualDrive Technology

  • Two AK4375a DAC/HPAMP ICs

  • 3.5mm Unbalanced output

  • 2.5mm Balanced output
Proprietary DCT algorithm (on/off option)

  • Eliminate noises in digital sound sources

  • Enhances 16bit into high resolution 24bit
Built-in Analog Volume control

Noise free even with high-sensitivity earphones

Hands-free call with built-in high sensitive microphone

Analog Output Upgrade Technology

Optimized circuit architecture using 2 independent Hi-Fi DACs and Amplifiers

2 selectable operating modes support 2x current or 2x voltage

Capable of driving headphones with high or low impedances

Delivering pure signal without any loss or distortion, and with enough power

AK4375a INFO:
The advanced audio devices have been specifically optimized for portable applications based on AKM’s VELVET SOUND architecture which is established by premium audio devices, realizing high quality sounds for music playback. As an audio device for mobile applications, the AK4375A achieves industry leading level performance of THD+N (-99dB) and 110dB dynamic range with newly developed 32-bit advanced audio DAC and cap-less class G headphone amplifier.
In addition, the AK4375A integrates asynchronous SRCs and crystal oscillator for jitter isolation to prevent degradations of analog characteristics and sound qualities by external clock jitter. It is suitable for audio devices with Hi-Fi function such as smartphones, tablets, portable music players and wireless headphones. The AK4375A is housed in an ultra-small space saving 36-pin CSP package.

Key Features
-1. Stereo High Sound Quality Low Power Advanced 32-bit DAC

- 4 types of Digital Filter for Sound Color Selection

-2. Ground-referenced Class-G Stereo Headphone-Amp

- Output Power: 25mW @ 32Ω, 40mW @ 16Ω, THD+N = 0.1%

- S/(N+D): 99dB

- S/N: 110dB

- Output Noise Level: -119dBV (Analog Volume ≤ -14dB)




This device is not about the look at all, it have a low profile approach in a very small body. Its all plastic with the exception of metal clip. I would have love at least to have metal headphone output of better quality, but it do not change anything for the sound, perhaps the durability tough. So yeah, perhaps too much plastic.

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For the design, its simple and quite intuitive to use, but buttons are very small and there not lot of pression space to feel the click, I would have prefer separate buttons for volume up and down and changing tracks, so it could help to blindly use them. As well, there a light that tell you when device is connected as usb dac (flashing green-red), BT dac (flashing green) or when you shut it down (red) ,the light is not extremely visible wich is perhaps due to plastic being not enough transparent. It’s very subjective whim about how to make ES100 design interface perfect, so its to take with a grain of salt.

Interface is still quite simple, as said, there volume control at one side and tracks control at the other side with starting-shutting button above it. It easily connect to any device and will even connect freely when you open BT of your phone if ES100 is powered on, no need to always struggle with setting, wich is a joy to use.

BATTERY life is very good, going from 8 to 14 hours depending of volume or output you choose, 2.5mm is less power hungry than 3.5 for example.

BT signal distance is about standard but in a very trustable way, in a distance of 12 meter I do not have any connection problem. If I hide myself behind a wall of brick it can interfer with signal...as every BT iem or receiver.

USB DAC work perfectly, its plug and play like everything with ES100, you just never need to struggle about anything. The sound is identical to BT version, but perhaps have a blackest background.



Companion Android / iOS Application

  • Codec selection

  • 2.5mm / 3.5mm output mode selection

  • Battery level status

  • Analog & Digital volume control

  • 10-Band Embedded GEQ control

  • AK4375a DAC filter selection/ Oversampling selection

  • Proprietary DCT level control

  • Cross-feed level control

  • Microphone gain control

  • Ambient mode On/Off
The Earstudio application is a MUST, you can use the device without it and it will be recognize easily by your sound source like a non adroid based DAP with BT, but for a phone it take the ES100 to next level. With this app you can control whole potential of dual dac chips, you can choose type of current output like normal or high performance for 3.5mm so it will give about 1 or 2 times current power, you can use a top of the line EQ that work wonderfully, you can change source and analogue volume, buffer lenght, multipoint pairing, over sampling rate, crossfeed, mic volume and even ambient mode that make you ear outside noise so you can stay alert in urban survival mode. Man, there too much features to explain so its really up to you to discover them and earstudio understand this by explaining every aspect of there features.

Anyway, I will talk about features that I feel can improve sound rendering like.

3.5mm HIGH PERFORMANCE MODE vs 2.5mm Balanced Mode:

For me, the unbalanced way is in High performance mode 99% of the time even with must of my IEM because I feel it give better dynamic and imaging than normal mode.
The opposite happen for balanced mode, I use normal 99% of the time as it give plenty of power and an overall better sound than unbalanced mode, in a very subtle way that will be more hearable at high volume. Wich is overall better clarity and layering with near perfect black background. Don't use High voltage mode with iem, its just too powerfull really, but for high impendance earbuds like the HE150ohm it is quite appreciate.



I sometime play with this and confirm it give very subtle sound difference for the dac Filter, more about attack decay, but its more hearable in balanced mode. For the Oversampling, its very strange but can improve details and texture of lossy files like MP3, anyway, I feel it can stole some air between instruments too. Both are for maniac audiophile really.


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I'm not a big EQ user, because must included with DAP did not work well, but this one take me by suprise and is fun to play with as well. It really can modulate sound rendering precisely and I solve some earbuds and iem sound issue with it, like earbuds that was bass anemic became more bassy without creating distortion or artificial rendering, wich was just incredible really. This EQ is a masterpiece IMO.



Theorically bluetooth signal should sound inferior to direct connection to audio source, but in this case, as it use different high quality dac processing and amp module than stock one on your phone its really a game changer for must of phone but perhaps exceptional one with quad sabre dac like V20 or V30, but even them will not have as much amping power due to powerfull balanced output power of ES100. As well L-DAC is lossless processing for must 48khz 16bit flac music and lower rate one, so, this is litterally an audio revolution.

Balanced Output give the better sound performance by slightly improving resolution and overall clarity due to lower THD and blacker noise floor, but 90% of the time I use unbalanced output for simplicity and versatility as well as because I do not need high amping power form my iem, so impressions are with unbalanced output using 48khz flac and 320kbps mp3.

I will describe overall sound processing of dual AK Dac as extremely well layered, smoothly detailed and wide sounding with lot of extra deepnest to it. It have the capacity of extraction more sound info and give extra excitment to the music you think you know, like if a veil was pulled off wich permit you to perceive whole audio range of your favorite music without it feel artificial or too analytical. As well, I feel it give extra energy and dynamic to the sound, especially mid bass that feel more controled and way less boomy than lot of phone audio, like my G6 or even more my Ipod touch. In some way, if you do not listen to wide music style, perhaps the audio revolution you get will be minimal, but with great quality recording it is an evidence that this bluetooth receiver can transform your music into audiophile experience mustly seen in good quality DAP.

As said, with balanced output it take audio quality to an even more pristine level of clarity and dynamic, so if you have iem with detachable cable, order some 10-30$ balanced cable from Aliexpress ASAP! You will be utterly happy of little extra investment.




The X3II have a dac chip from same Asahi Kasei microdevice japanese maker, but this time its a single premium AK4490, wich can achieve higher resolution specs, but as the ES100 use dual AK4375a with dual amps the game here is change. Anyway, I will just talk about overall soundsignature difference of both device, using same music tracks including 320kbps mp3, but mustly 48 or 96khz flac file. ES100 will be drive trough Bluetooth Ldac from my LG G6 and X3ii directly from audio output at high gain.

What hit me first by comparing these two is how overly smooth sounding is X3ii compared to the more energic ES100, should it be with Monk+, Tinaudio T2 or Takstar PRO82 headphones, the ES100 sound more lively and fowards, wich give more sens of deepness and tigher bass presence. The X3II in other hands have slightly more finess and transparency, but in a wide panoramic approach while the ES100 have space between instrument layering instead of transparent veil.

BASS of X3II feel less impactfull and full bodied, especially in mid bass where the punch is smoothed while the ES100 is a little emphased and have tigh fast approach that never feel hollow even if not with as much decay than X3II.

MIDS are similar here, but again, vocal feel more separate and fowards with the ES100 even if X3II have some extra presence emphasis in this region. ES100 is more detailed and have overall better resolved mids because of extra precise layering.

TREBLE extension of both is good, but because of a smoothed out soundsignature, X3ii feel less detailed even if more sparkly when micro details appear. ES100 have great clairty but do not have long decay in highs presentation, wich permit to have less mixed up soundstage when fast complext tracks with lot of instrument have to be dealt with.

About amping, even if X3II is suppose to be slightly more powerfull, I tend to push volume higher with it to have more sound pressure and compensate its lack of energy and impact.

VS XDUOO X3 (110$) :

The X3 have a more fowards energic sound presentation with an overall better resolution but to the cost of being sometime overly agressive. Bass is thigher and some time too textured and lacking extend after attack where the ES100 is smoother but still fast with more transparent and vast presentation. Mids of ES100 sound wider too, with a hint more smooth natural presence while X3 have greater textured mids with better separation but a lack of fullness in body. Treble extension of both is very good, but I feel the X3 have more focus on it with a blackest background noise floor, but strangely, its the ES100 that have more decay after note impact. In conclusion, I would say ES100 is better suited for bright or sharp iem headphone as it will never create hissing or sibilance while X3 will be more benefic for warm or smooth iem even if he can have great sinergy with near everithing.

VS LG G6 smarthphone :

Firstly, ES100 is way more powerfull and can drive at higher volume whatever you use 3.5mm or 2.5mm balanced output. Amping difference with balanced is extreme. About the sound, G6 feel like an absurd lifeless sounding toy with overcompressed, constraint soundstage, bad layering and imaging, lack of dynamic and details, so when you plug in ES100 to continue same tracks that was playing on stock G6 difference is night and day and you find yourself freely listening to real musicality in a enormous soundstage with great deepness and a lively layering that make sound frequencies fly around you and understand why you need a Radstone ES100 to finally listen to music with your weak anemic sounding smarthphone. The step is so big that I can’t imagine anybody not hearing positive difference unlike when comparaing to good quality DAP wich feel more subtle. It was easy to compare both device using ES100 BT connection as I can listen the same track on G6 without having to change any setup, and yeah, I close my eyes to do ‘’blind testing’’ hehe

Headphones, iem, earbuds Sinergy:


With MONK+:

To me the Monk+ need quite good and clear amping to shine at full potential, and i've been surprise to see the ES100 can drive them perfectly. The monk sound very energic and well layered with the ES100, and it tend to make them even more neutral as the mids feel less fowards. Level of resolution is excellent as well as near supreme black background floor. Perhaps I would love a little more mids colouration this time tough, depending of music style.

With Takstar PRO82:

This is a magnificent sinergy that solve every problem with PRO82 and make it sound more balanced and energic solving its brightness issue that can occur with Xduoo X3 (first gen) and Xduoo X20. Bass became more tigh and well separated, gaining a rounder body too, mids are clearer and less recessed. All in all, we gain a better imaging and layering and loose some highs harsness too.

With Meze 99 Neo:

At 26ohm, the Neo are very easy to drive so ES100 have no problem making them shine. I feel the bass was more tigh even if punch gain in authority, the spacious soundstage was perfectly layered without any harshness, it was a warm but more energic presentation that give Meze extra life and faster presentation than with smoother DAP like X3II. Very engaging sound experience and now i'm curious to know how it could sound with balanced output....need to find a cable ASAP!

With TinAudio T2:

Here, the T2 gain a little much needed mid bass punch as well as hint more rolled off sub without loosing any of its great layering. Soundstage became a little less airy but not in a bad sens as it give more energic agile sound and that with a good clarity and quite black noise floor even if T2 sound more smooth than with ultra clear source like Xduoo X20. For a BT decoding music performance, its outstanding. To note : Using the T2 with 2.5mm balanced output clearly improve clarity and dynamic as well as giving a blacker background, this take me by surprise and i will not go back to unbalanced cable for this iem.



The Radstone ES100 is a phenomenal bluetooth receiver with excellent sound quality, good 3.5 ouput power and powerfull 2.5 balanced output. It have all the features any audiophile could dream of and its battery life is excellent. This take bluetooth sound to the next level with its great dual AK4375a DAC, its DCT technology that transform 16bit into 24bit and L-DAC, Aptx-HD (etc) codec compatibility. Earstudio put lot of work into creating this audio device wich is even more impressive to use with the dedicate application to control it. I really think this is a must have to any phone user that either want better sound quality, more amping for demanding headphones or extra portability that will not drain the phone battery life.
Earstudio is a new comer in audio world and deserve alot of respect, one thing sure, I will follow the evolution of this extremely promising company in the futur. Now that I know bluetooth technology can sound this good, I became interested in something I always been sceptical about and humbly admit BT codec transmission will must certainly achieve high end sound transmission in a very near futur. The hype is far from being finish with the Radsone ES100, and it will surely still be used in years to come.
BIG Applause for Earstudio audio team!!

You can find more reviews and audio related stuffs here:https://nobsaudiophile.wordpress.com/


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Nice and accurate review, thank you.
Does it still relevent today?


100+ Head-Fier
Pros: Built-in 10-band graphic equalizer
Stable Bluetooth connection
Multipoint Bluetooth connections
Latency isn’t too high.
Mic turns any headphone into a Bluetooth headset for making calls.
Mic can be set to let outside sound in.
Analog volume control makes background hiss inaudible.
Analog volume control can make fine volume adjustments (0.5 dB steps).
Low output impedance
2.5 mm jack doubles the voltage output by bridging the amplifiers.
AptX, AAC, and other advanced codecs.
Cons: No parametric equalizer
The crossfeed could be better.
They could have included accessories that make it more convenient to use.
Unless otherwise noted, I’m writing about my experience with firmware version 1.3.2 and iOS control app version 1.7.2 - 1.7.5. I first wrote about my experience with the ES100 and firmware version 1.2.1 in this thread, with some basic audio measurements. I’ve been using the ES100 on and off for the last few months, and I’ve been keeping notes. I put together my observations here.

Sony MH755 with ES100.jpg

Radsone EarStudio ES100 with Sony MH755​

I picked up the Radsone EarStudio ES100 back in May because it gives my portable devices a system-wide equalizer. If iOS and Android had something like Equalizer APO or eqMac2 without having to root or jailbreak, I probably wouldn’t have bought one. It’s the closest thing to an ultra-portable equalizer today. Remember these?

Well, the ES100 is the modern version, except that audio comes in via Bluetooth or USB instead of a line input. But it also does a lot more while being a lot smaller. Besides being a compact graphic EQ, it’s a versatile Bluetooth receiver that you can clip on a belt or even a headphone’s headband. If there are other super compact equalizers out there, Bluetooth or otherwise, I’d like to know about them.

What it is
The EarStudio ES100 is a very small Bluetooth receiver and USB DAC with headphone output. It has an all-plastic exterior that feels cheaply built at first because it’s very light. On the sides are volume up/down, next/previous track controls as well as a play/pause/on/off button. The rest of the controls are in the iOS or Android companion app.

It comes with the standard 3.5mm headphone jack, but there’s also a 2.5mm TRRS output that doubles the output voltage by bridging the amplifiers. On the front is a single ring-shaped status LED, and on one of the short sides is a micro USB port for data and charging.

Bluetooth receiver operation
The ES100’s Bluetooth connection has remained stable in the few months that I’ve had it. It has AptX and AAC, which are good enough for me. The likelihood of hearing offensive lossy compression artifacts is very low, especially with AAC. Other advanced codecs like AptX HD and LDAC are also supported, but low latency AptX LL is missing from the list on the product page.

List of codecs.png

List of supported codecs​

When playing software synthesizers on an iPad, there is considerable lag. I don’t know how well the ES100 will work with some games. For video, the worst Bluetooth audio sync that I’ve heard is in the iOS YouTube app. There are a few audio/video sync test videos on YouTube that give you an idea of how much latency there is. With the ES100, it seems to be a little over 100 ms, which is not as bad as it is on my other Bluetooth devices: it’s in the same ballpark as the Airpods, and much better than my Bose QC35 and Jaybird Freedom. A work-around for iOS is to play the same YouTube video in Safari, where the audio is more in sync. Other iOS apps (like Netflix) fare better than YouTube. In Windows 10 or MacOS, YouTube audio/video is more in sync than in the iOS app.

Buffer length.png

Buffer Length adjustment​

The user has some amount of control over the latency, which can be reduced with a shorter buffer. The tradeoff is in reliability—with a shorter buffer, audio drop-outs are more likely.

The ES100 supports multi-point connections. It can remember several paired devices and connect to two of them simultaneously. It’s convenient because I don’t have to fiddle with the Bluetooth settings on my phone, tablet, or laptop when I want to switch between any two of them.

Another useful feature is the built-in microphone, which allows hands-free phone calls even with headphones that don’t have a built-in mic. The call quality depends on the placement of the ES100. It worked fine when it was clipped to the top of my shirt, but people I talked to said that they could hear me more clearly when I used the Airpods or the Jabra Elite 65t. When the ES100 was clipped to my belt, they said that they couldn’t hear me well at all.

Ambient sound.png

Ambient Sound​

The microphone can also be used to let you hear more of the outside. Radsone calls this feature Ambient Sound, and it comes in handy when you want to be more aware of your surroundings. It’s also convenient when you want to hear people and you don’t want to go through the hassle of removing and reinserting a highly-isolating, deep-insertion IEM like an Etymotic. The track advance button can even be configured to turn Ambient Sound on and off, so you don’t have to whip out your phone and look for the right page in the control app.

USB Audio
The ES100 works as a USB Audio Class 1.0 interface in MacOS and recent Windows 10 updates, so no drivers are needed. The operation is locked at 48 kHz sample rate and 16 bits per sample. In Windows 10, for example, you can’t select any other sample rate or bit depth. All other options are unavailable. This means 16/44.1 CD-quality audio (and any other format) is sample-rate converted to 16/48. The SRC math seems to be working just fine. I didn’t hear any problems playing back 16/44 audio, and my measurements back in May didn’t reveal anything out of the ordinary with 16/44 wav files.

Analog volume control and background noise level

Analog and digital volume controls.png

Analog and Digital Volume Controls​

As you can see from the screenshot above, there are two volume controls. Most of the time, it’s best to keep the digital volume at maximum, and just control everything using the analog volume control. The advantage of doing this: decreasing the analog volume also decreases the background noise coming from the audio jack. This keeps the background hiss low, even inaudible, when using sensitive IEMs. I tested a Logitech UE600vi, which has above average sensitivity even among balanced armature IEMs. With the analog volume at 0 dB, the background hiss is quite loud. But you wouldn’t be listening to music at a crazy level like that with the UE600vi. With pop music, a comfortable level for me is around -36 dB on the analog volume control. It’s higher for classical music—maybe as much as -24 dB for quiet tracks. At that level, I can’t hear any background hiss from the ES100, even with a digital silence wav file.

Noise level in dBV, into 16-ohm load on both channels​

This makes the ES100 only the second Bluetooth device I’ve heard that’s completely silent. (I can’t hear any hiss from my Airpods either.) The physical volume up/down buttons on the ES100 control the analog volume, so it behaves differently in Apple devices than other Bluetooth headphones. In iOS, a Bluetooth device’s physical volume controls normally control the iPhone’s or iPad’s system volume. Not so with the ES100, and that’s a good thing because it gives you fine control: +/- 0.5 dB steps, unlike the very course adjustment in iOS.

Output impedance, distortion under load
When I measured my unit back in May, I found the audio output to be clean enough, even with the dummy load—16 ohms resistive, like the typical dynamic-driver IEM. I also verified the claimed 1-ohm output impedance. Since then, the app seems to have made another feature available: high current mode, which parallels two output stages and cuts the output impedance to 0.5 ohms.

Audio output mode.png

Audio Output Mode​

With a high impedance load, the ES100 starts to clip when the analog volume is around +2 dB. With high current mode and a 16-ohm resistor on each channel, it clips earlier:

High Current, 16-ohm load, +1 dB.png
High Current, 16-ohm load, +1.5 dB.png
High Current, 16-ohm load, +2 dB.png

ES100 playing 0 dBFS 1 kHz sine, 3.5 mm jack, voltage into 16-ohm load on each channel: analog volume control at +1 dB, +1.5 dB, and +2 dB, respectively.​

Here’s how much the output voltage drops when a 16-ohm load is connected to each channel:

Normal, no load, -13 dB.png
Normal, 16-ohm load, -13 dB.png

ES100 playing 0 dBFS sine, 3.5 mm jack, analog volume control at -13 dB: open circuit voltage, voltage into 16-ohm load on each channel, respectively.​

Do the math: www.wolframalpha.com/input/?i=0.198+*+16%2F(R+%2B+16)+%3D+0.192

What’s strange is that I’m getting the same or better results when I leave it on normal mode. It looks like high current mode is on regardless of the setting in the app.

The main feature: the equalizer
With my collection of headphones and IEMs, the ES100 plays with low enough noise and distortion that I don’t have to worry about them. The only concern left is a big one, and it is really where the ES100 distinguishes itself from similar products. Many folks don’t want to admit it—that once you take care of noise, distortion, and lossy compression artifacts, it is the frequency response that determines the sound quality. The behavior in the time domain (e.g., the impulse response, the step response, square waves) is characterized by the system’s magnitude and phase response.

This is why I was looking for an ultra-compact equalizer that can give my mobile devices a system-wide equalizer without rooting or jailbreaking. Here’s a sample of what the ES100’s 10-band EQ can do:


-6 dB at 31.5 Hz, 1 kHz, and 16 kHz


+3 dB at 2 kHz, 4kHz​

This EQ can make many cheap headphones and IEMs sound good. Here’s an example: the Skullcandy Jib plays with low distortion, but its frequency response makes it sound like mud. Have a look: +8 dB at 200 Hz, and +11 dB at 100 Hz, relative to 1 kHz with the response still rising. It’s also missing a lot of information above 10 kHz:

Skullcandy Jib FR.png

Skullcandy Jib frequency response before EQ​

Here’s the result with the ES100’s equalizer:

Skullcandy Jib after EQ.png

Skullcandy Jib response after EQ. 2017 Harman In-Ear Target shown in gray.

Skullcandy Jib EQ.png

EQ for Skullcandy Jib​

The Jib has low enough distortion that it can handle a boost in the treble, and with the sliders shown in the picture, the ES100 gets the Jib’s response close to the 2017 Harman In-Ear target. It’s a good starting point for further adjustments. Me, I prefer less bass and a little bit more above 10 kHz. But even before that, the result already sounds very good IMO—better than many IEMs that cost more than the ES100 itself. This shouldn’t come as a surprise to anyone; for years, people in this forum have been writing about how a carefully-tuned EQ can make dirt cheap IEMs sound like a million bucks.

Skullcandy Jib with ES100.jpg

ES100 with Skullcandy Jib​

Here’s another example—this time with a Sony MH755, a $6 IEM that already sounds very good without EQ:

Sony MH755 sample 2 FR.png

Sony MH755 frequency response before equalization

Sony MH755 after EQ and channel trim.png

Sony MH755 frequency response after EQ. 2017 Harman In-Ear Target shown in gray.

Sony MH755 EQ.png

EQ for Sony MH755​

I have several pairs of MH755 and MH750 IEMs and I chose one that has a little channel imbalance. In the graph of the equalized response above, notice that the left and right channels are more closely matched. The ES100 has a nifty feature that lets you trim each channel, and I used it effectively here:

Channel trim volume -0.5 dB.png

Channel Trim on Device Volume Control page​

The 10-band EQ works best with headphones that already have a smooth response, like the two IEMs above, or when there is a broad peak that lands close to one of the equalizer’s ten center frequencies. It's easy, for example, to give an Etymotic a little more bass. The EQ is more limited when you want to make the adjustment at a frequency that’s far from one of the graphic equalizer’s ten octave-spaced bands. For example, the Bose SoundTrue Ultra has a half-wavelength resonance that’s always at the same frequency because it has the same, repeatable, shallow insertion depth (if you could call it that). On my ears, it’s near 5.5 kHz—far from the ES100 EQ’s 4k or 8k bands.

Even if you could guarantee that the adjustment frequency is correct, the equalizer still can’t handle high-Q resonances, which look like tall, narrow spikes in the frequency response. Here are some examples that can't really be fixed by the ES100's EQ without the help of acoustic methods:

KZ ES4 FR.png

KZ ES4 frequency response

KZ ED16 FR.png

KZ ED 16 frequency response​

These two have the KZ house sound. The older KZ ATE also has that narrow spike near 8 kHz, depending on the insertion depth. For me this peak is not an artifact of measurement because I can clearly hear it in sine sweeps. Music sounds better when I use a parametric EQ to tame the bass and surgically flatten the peak with a narrow biquad filter. The ES100’s graphic equalizer, however, cannot effectively reduce the activation energy for these resonances.

I wish Radsone had included a parametric equalizer with the ES100. Fewer filters bands would be needed and better results can be had for most headphones. If DSP resources are limited, then maybe one could choose to turn off the graphic equalizer to use the parametric EQ.

It’s really a question of priorities. The ES100 has many features that made very little audible difference when I used them—the jitter reducer, the choice of reconstruction filter, the DCT filter, the DAC oversampling rate, and the additional codecs beyond AptX and AAC (although it is nice to have them). The EQ, on the other hand, has a huge impact on the sound. If there is an ES100 Mk.II in the works, my vote is for a more capable EQ, if it is impossible to update the current model’s firmware with one.

The crossfeed is different?
The ES100’s crossfeed has a strange implementation that’s not very effective. It seems to be very different from a Meier or Linkwitz crossfeed. When listening to speakers, each ear can hear a lot of low frequency information from the other channel. Therefore, the crossfeed should be stronger for low frequencies. This is not what I’m hearing from the ES100. Back in May, I got this response from the crossfeed:


RMAA crosstalk measurements with crossfeed off and on.​

Radsone’s implementation uses some inter-aural time difference, or ITD; i.e., the ES100 delays the sound on one channel before feeding it to the other one. I measured 2.5 ms before the crossfeed signal starts. You can figure out how far sound travels in that much time and decide for yourself if they got it right.

So many things that make little audible difference are tweakable on the ES100. So why not something that can easily be heard, like a way to select the crossfeed implementation?

Give me convenience or give me death
Once the new toy syndrome wore off, I took the ES100 out of the house less often, and usually found myself grabbing something more immediate: Airpods, Jabra Elite 65t, Jaybird Freedom, Bose QC35. Their sound isn’t as good, but they’re good enough for enjoying music. Even when the ES100 was already in my pocket, I still went for the Airpods or the Jabras. Just open the case, put them in your ears, and you’re good to go: no cables to unwind, no connectors to plug in, and no power button to turn on. And when you’re done, just put them back in the case.

Here’s one way to make the ES100 more convenient:

ES100 with Philips SHP9500.jpg

ES100 clipped to Philips SHP9500​

I’ve often used the ES100 like this at home. Just turn it on and put on the headphones. Easy. I was lucky that I had a short cable at hand to make it work. The clip doesn’t go around the SHP9500’s headband, but It clamps tightly enough to stay put as long as you don’t shake your head too vigorously.

It’s harder to find a short cable for other headphones:

ES100 with Bose QC25.jpg

Bose QC25 with its cable wrapped around the headband: ugly, but functional. A suitable short cable should work better.​

ES100 with Audio Technica ATH-M40X.jpg

Audio Technica ATH-M40X: none of my cables worked​

A short cable and headphone mounting kit bundled in the box would have made the product more convenient to use. For IEMs, maybe a neckband or behind-the-head kit could work as an optional accessory.

The Radsone EarStudio ES100 is a useful little device. It’s also inexpensive. Audio performance is good enough for almost all listeners: It has low output impedance, it plays back audio with low distortion into realistic loads, its 2.5 mm jack provides double the voltage for insensitive headphones, its analog volume control makes the background hiss inaudible even when using sensitive IEMs, and it supports advanced audio codecs. But the killer feature, the one that improves the sound the most, is its equalizer.

It’s just too bad that they didn’t make it even better by offering a fully parametric EQ as well. The crossfeed could use some help too. Also, a short cable kit to make headphone use easy and convenient would have been a nice addition. Despite these complaints, I know of no other product that does the same things while being so small and affordable. I want to see what they have planned for the next version.

Update: May 11, 2019
This app screenshot might answer some questions about the EQ:
App EQ control settings.png
@abm0 Eh, I replied to the main product page, not the review comments. In any case, you should see the other message. In short, the answer to your question is in the app itself. Look at the screenshot I tacked on at the bottom of my review.
Hello guys Somebody Coul help me posting a link of a short balanced cable? Thanks


100+ Head-Fier
Pros: Separate channel gains
Full work day battery life
Very small and portable
Hardware EQ
AAC / LDAC / aptX
Cons: Crossfeed (preference?)
Incredibly tiny hard to use buttons
Frequent BT disconnects after several weeks
At first I really really really disliked this unit’s sound output and would describe it as precise and yet “lifeless” and “hollow”.

However, after TURNING OFF the crossfeed setting, music like Massive Attack’s Mezzanine and Bjork’s Family or Notget once again sound energetic and live. These songs already have lots of selective crossfeed and keeping the remaining separation sounds soo much better to me.

Now I can say that the output is at least as “fun” to listen to as standard iPhone 6 SE output. It is also more clear/detailed, especially in higher frequencies.

The hardware EQ is ‘cool’ but I leave it off as I trust source and Noble K10U IEMs to take care of managing the sound.

The BT started to frequently disconnect after several weeks of use, and it only has use as a BT receiver so such is disappointing. It seems to disconnect less after being left off / ignored for several days..

I found the ability to adjust the channel gains separately useful as my left ear is less sensitive. Exposing the hardware-based EQ is a nice concept and iOS functioned well-enough. However this does not offset my dislike for the sound output.
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