[ian91]

A couple of months ago I started looking into bullet-style IEMs and 'stick' single BA IEMs for the portability and isolation they offer. I wanted to aim for an Etymotic but living in Europe/UK seemed to mean paying a rather high price new and a certain amount of luck on the used market to find the model you want. So to avoid the hassle and disappointment I thought I would look for Chinese equivalents. I came across Yu9 Audio through a serendipitous post on a Facebook group. Looking into things, Yu9 Audio have released a number of sets over the years, historically selling via Taobao and now also selling via an intermediary on AliExpress.

Last year saw the release of their showpiece the U-556 and U-554, two sister models that use a single full-range Sonion BA with a replaceable 2pin cable, the U-556 using a Sonion 2356 and the U-554 using a Sonion 2354. The U-554 being the brighter, diffuse-field tuning and the U-556 a slightly warmer more traditional tuning (see graphs below). The shell and venting system they have developed supposedly reduces harmonic distortion and improves midrange detail and cleans up imaging. Both sets come in at $136 and have a generous assortment of tips and a set of replacement BA filters, filter removal tool and leather hardcase with magnetic closure. I purchased from AE seller here if anyone is interested (it helps if you can read Chinese!). The packaging, box and accessories are hitting well beyond the $136 price point IMO.

FR Graph

U-554 (orange), U-556 (blue), graph provided by manufacturer

Specs (U-556):
20Hz-16kHz
96.5dB/100mV@1kHz
116ohm@1kHz

(get your dongles/DACs/amps out - they both sound bad out of my mobile phone, with a significant tonal imbalance and zero bass extension)
(both are driven well with the Cayin RU6 dongle and Shanling M8 single ended)

Sound Impressions
Comparing to my other single BA set that uses the popular Knowles 29689 driver, the Sonion driver here provides a much more natural attack and decay with similar technical performance. This is a definite benefit for instrumental replay where the 29689 can, despite its incredible resolution, come off as overly clinical with string instruments and percussion demonstrating a somewhat unnatural tightness (this is me niggling here, I still love the 29689). Bass extension on both the U-556 and U-554 extends into the sub frequencies and there is plenty of midbass kick. Treble extension and detail is down-right impressive, with the U-556 being the much more approachable set, offering the more natural extension and decay. Midrange is the focus on both sets. I've not heard better vocals or more accurate instrument replay since coming into the hobby. I don't detect any sibilance on either model but the U-554 is certainly the brighter set and has more air and breath to vocal replay. From a technical standpoint we are limited by the single BA config but they both demonstrate very good L-R separation and imaging is very precise. Soundstage is wide with an out-of-the-head effect but with little forward depth and average layering. Obviously note-weight doesn't compete with that offered by a DD but a physicality is definitely present and drums/woodwind/piano/strings all sound great, especially on the U-556.

U-554 (left), U-556 (right)

Leatherette case, assortment of tips, BA filter tool & filters, cleaning cloth.

U-556 (left), Penon Legend (right)

Other observations:

• Comfort - with my small ears and acutely angled ear canals I still manage to get a deep fit. If you're used to Etymotics these won't be an issue at all. For newbies, be willing to experiment with the tips provided. Getting a good seal and a deep(er) fit than traditional IEMs is important as all Ety heads will tell you. I was initially quite apprehensive about this venture but thankfully fit is not really an issue for me.
• Genres / Library - these work tremendously well with acoustic/jazz/classical/instrumental (the majority of my library). If you listen to electronic/pop/ambient I would recommend the U-556 and if you're after pristine clarity to your vocals, with shimmer and spice from a super-natural treble go for the U-554.
• Sources - do not underpower these (or any other high impedance/low sensitivity BA), they will sound awful and nowhere near the intended FR.
• Portability & isolation - these are light, incredibly light, 4g light. Isolation is unbeaten so train & airplane journeys are fine.
• Pressure build up - the novel venting system that does seem to vent to open air doesn't prevent pressure build up completely. It doesn't stop me from listening but I would recommend equalising every now and then (as you would with other deep fit IEMs) or taking a short break every few hours.

It would be great to see more Head-Fi'ers take the dive on these. Especially those with intimate knowledge of the Etymotic ER series. I would like to know how these stack up. While I'm going to let the honeymoon period settle I already have plans to let many of my other IEMs go. In the age of multi-driver sets this a reminder for me not to overlook simplicity, in this case it's definitely a strength.

 

[Dumbber]

I see that you also have their Yu9 ER4B, how does it compare to these?

Some more useful information I've found from chinese reviews (as I am fluent in the language),
https://zhuanlan.zhihu.com/p/457437534
https://zhuanlan.zhihu.com/p/416552081
Of particular interest is the FR compared to the ER2XR:

Frequency response differences with different tips - Red: foam, Green: Large triple flange, Blue: Small triple flange

Take note that the measurement rig was not specified, but the comparative differences are useful enough. The U556 looks like a hybrid between DF and Harman in its mids and comes with bass between that of the ER2SE and ER2XR. Very interesting.

 

[ian91]

Excellent post. Cheers! I will check the reviews out. Whats in your inventory? Are you thinking of purchasing?

I'll post a deeper comparison this evening when I'm back from work but from memory there is definitely a softer attack and decay to notes on both the U-556 and U-554. I prefer this than the tighter more clinical picture on the Yu9 ER4B. Percussion feels more natural. Both models have greater height to staging but may be slightly narrower compared the Yu9 ER4B. The U-554 does make up for this with the enhanced treble to improve air to things, however.

I can't grumble at any of the 3 models, they all offer something different but the form factor, fit and timbre make the U models the winner for me. I prefer the U-554 over the U-556 for most of my music so far. Its ultra revealing but quite smooth at the same time. Images seem more defined in space with a crystalline sound approaching the more exacting Yu9 ER4B.

Tip changes and insertion depth are at play here for sure. You can soften the U-554 treble region with foams/thicker silicone (and insertion depth) while still retaining the added dimensionality the model offers.

I was so enamoured with the Yu9 ER4B I've purchased a second with a detachable cable in the interests of longevity

 

[-rowan-]

Great impressions, @ian91!

I ordered the Yu9 ER4B last week… look forward to comparing it with my Ety ER4B when it arrives.

I was thinking I might try the U-556 next if I like what I hear, but your review is making it a tough choice.

Also found a U-554 review on the same site, which compares it briefly with the ER4B (which one, I’m not entirely sure from the translation). If it behaves anything like the Ety 4B, I’d venture that you were feeding yours with more power.
https://zhuanlan.zhihu.com/p/463499864

 

[ian91]

Thanks!

Reallllllyyy interested to see how you like the ER4B.

The U-554 is an exciting listen and more akin to the ER4B. What was pushing you in the direction of the U-556?

 

[-rowan-]

What was pushing you in the direction of the U-556?

I’m… not sure anymore actually lol. It might have looked like the more natural-sounding one. But we know that graphs don’t necessarily tell the whole story.

 

[ian91]

I’m… not sure anymore actually lol. It might have looked like the more natural-sounding one. But we know that graphs don’t necessarily tell the whole story.

I think there's a fair argument in this. The U-556 does sound more 'natural' but there's quite a bit of room to control the U-554 with tip choice and if you're coming from the ER4B you might find the U-556 lacking the revealing clarity. It's a tough one! Only time will tell which one I end up using more often. I imagine my daily carry will be U-556 and then evenings of focused listening with the U-554.

 

[-rowan-]

I think there's a fair argument in this. The U-556 does sound more 'natural' but there's quite a bit of room to control the U-554 with tip choice and if you're coming from the ER4B you might find the U-556 lacking the revealing clarity. It's a tough one! Only time will tell which one I end up using more often. I imagine my daily carry will be U-556 and then evenings of focused listening with the U-554.

Makes sense - I had the ER4XR and ER4SR for a period and ended up selling the XR (much to the delight of the buyer) so it might well go the same way here.

 

[Charlyro222]

Interesting Iems

 

[Dumbber]

Excellent post. Cheers! I will check the reviews out. Whats in your inventory? Are you thinking of purchasing?

I'll post a deeper comparison this evening when I'm back from work but from memory there is definitely a softer attack and decay to notes on both the U-556 and U-554. I prefer this than the tighter more clinical picture on the Yu9 ER4B. Percussion feels more natural. Both models have greater height to staging but may be slightly narrower compared the Yu9 ER4B. The U-554 does make up for this with the enhanced treble to improve air to things, however.

I can't grumble at any of the 3 models, they all offer something different but the form factor, fit and timbre make the U models the winner for me. I prefer the U-554 over the U-556 for most of my music so far. Its ultra revealing but quite smooth at the same time. Images seem more defined in space with a crystalline sound approaching the more exacting Yu9 ER4B.

Tip changes and insertion depth are at play here for sure. You can soften the U-554 treble region with foams/thicker silicone (and insertion depth) while still retaining the added dimensionality the model offers.

I was so enamoured with the Yu9 ER4B I've purchased a second with a detachable cable in the interests of longevity

I'm new to the hobby. In terms of IEMs I currently own the 7Hz Timeless and the unfortunately revised QKZ VK4. I have an Etymotic Ety Kids coming soon that I got for $15 to have a taste of the tuning and fit, before I splurge on either other Etymotics or one of these new IEMs from Yu9. If the manufacturer's graphs are to be believed, and extrapolating from the measurements I posted, the Ety Kids would likely have a similar tuning to the U556 due to its increased brightness compared to the ER2SE.

I am just afraid the U554 might be too fatiguing for me considering it has 3-5dB more upper mids/treble compared to the U556, so hopefully I'll be able to gauge what I really prefer from this.

 

[G777]

The mids tuning of the U556 seems very close to my ER3SE, which I would consider to be essentially the perfect tuning for the midrange. Any more upper mids would make it sound too shouty and fatiguing.

Looks like the U556 has a bit more bass and treble, which is similar to how I EQ my ER3SE. Might be the perfect upgrade

 

[ian91]

I am just afraid the U554 might be too fatiguing for me considering it has 3-5dB more upper mids/treble compared to the U556, so hopefully I'll be able to gauge what I really prefer from this.

For anyone who is unsure what their tolerance is I would say go for the U-556. It's a much safer choice and is a great all-rounder. For those who've already sampled brighter Ety tunings and who are confident with fit, achievable insertion depth and have a reasonable selection of tips I would probably say go for the U-554.

Looks like the U556 has a bit more bass and treble, which is similar to how I EQ my ER3SE. Might be the perfect upgrade

The bass has great nuance and the whole presentation is spacious, detailed and dynamic when you give it power. I'm listening to Monolake currently and all the subtleties to his productions are perfectly reproduced.

Keep us in the loop!

 

[ian91]

U-556 x Plussound Verse (silverplated copper) (left), U-554 x Penon Flow (silver) (right)


Switching to balanced cables / output has helped a great deal with power delivery but also appears to have helped with stage size and imaging. Very happy!

 

[ian91]

Parameter	U-554 (Sonion 2354)	Yu9 4B (Knowles 29689)
Bass	More midbass warmth More 'felt' subbass Possibly slightly less bass texture	Flat-neutral Equivalent low-end extension Possibly more bass texture
Midrange	Better note weight*, cleaner, more natural fundamental harmonic detail	More uppermid/lower treble bite (?harshness)*
Treble	Similar extension and air	Possibly more fine detail in lower treble
Technicalities	Better layering & depth* Soundstage more spherical & taller* Better positional accuracy*	Slight wider stage (?) Shallower front-back dimension More resolving
Timbre	Slower attack and decay* More natural harmonic detail	Dry, more incisive notes, less natural harmonic detail
Tonality	See graph below	See graph below

*Asterix represents more noticable differences.

Tested on Shanling M8, high gain, SE out, same tips, attempted to volume match as best I could.
Test Artists(tracks) include: Lorn (Oxbow B), Hans Olav Gorset, Philidor: Suites for Flute and B.C. (Dixieme Suitte: ii. Rondeau).

Relative differences between models (difference is more subtle than the graph suggests). The graph must be read on all axes.

Primary characteristics (green arrows) of the U-554 are a bright and flat signature. Strong secondary characteristics (blue balloons) include forward highs and weak secondary characteristics (smaller blue balloons) include forward mids and a distant but reassuring warmth. The Yu9 4B in comparison to the U-554 sounds more critical to my ear at the expense of some organic character, the U-554 leans more toward detailed.

The U-556 (Sonion 2356; placed on the graph but without characteristics for the sake of clarity) presents itself more naturally with with similar primary and secondary characteristics of bright and flat but being less extreme, leaning more towards smooth and with a stronger secondary characteristic of forward mids and weak secondary characteristic of warmth. I would maintain that the U-556 represents the most natural tonal balance (with well treated room-like acoustic qualities) but loses some of the air, soundstage, excitement and sparkle I have been enjoying from the U-554.

Overall, the U-554 proves to have the more engaging presentation for my tastes with more spherical staging and deeper dimensions and a more natural embodied tonality compared to the Yu9 4B. The Yu9 4B is no slouch. I would say it possibly retreives more detail from tracks and manages electronic music well but sounds too dry and incisive for instruments for my taste. Stage is possibly wider but instrument separation and layering is weaker with most information pushed further out to the extremes of L-R. The Yu9 4B is more 'supernatural' while the U-554 offers a taste of the supernatural but doesn't lose as much of the emotional engagement in the process.

I hope this post helped anyone interested. I know we have a few members with sets on the way and I look forward to more discussion soon

 

[Guipnox]

Parameter	U-554 (Sonion 2354)	Yu9 4B (Knowles 29689)
Bass	More midbass warmth More 'felt' subbass Possibly slightly less bass texture	Flat-neutral Equivalent low-end extension Possibly more bass texture
Midrange	Better note weight*, cleaner, more natural fundamental harmonic detail	More uppermid/lower treble bite (?harshness)*
Treble	Similar extension and air	Possibly more fine detail in lower treble
Technicalities	Better layering & depth* Soundstage more spherical & taller* Better positional accuracy*	Slight wider stage (?) Shallower front-back dimension More resolving
Timbre	Slower attack and decay* More natural harmonic detail	Dry, more incisive notes, less natural harmonic detail
Tonality	See graph below	See graph below

*Asterix represents more noticable differences.

Tested on Shanling M8, high gain, SE out, same tips, attempted to volume match as best I could.
Test Artists(tracks) include: Lorn (Oxbow B), Hans Olav Gorset, Philidor: Suites for Flute and B.C. (Dixieme Suitte: ii. Rondeau).

Relative differences between models (difference is more subtle than the graph suggests). The graph must be read on all axes.



Primary characteristics (green arrows) of the U-554 are a bright and flat signature. Strong secondary characteristics (blue balloons) include forward highs and weak secondary characteristics (smaller blue balloons) include forward mids and a distant but reassuring warmth. The Yu9 4B in comparison to the U-554 sounds more critical to my ear at the expense of some organic character, the U-554 leans more toward detailed.

The U-556 (placed on the graph but without characteristics for the sake of clarity) presents itself more naturally with with similar primary and secondary characteristics of bright and flat but being less extreme, leaning more towards smooth and with a stronger secondary characteristic of forward mids and weak secondary characteristic of warmth. I would maintain that the U-556 represents the most natural tonal balance (with well treated room-like acoustic qualities) but loses some of the air, excitement and sparkle I have been enjoying from the U-554.

Overall, the U-554 proves to have the more engaging presentation for my tastes with more spherical staging and deeper dimensions and a more natural embodied tonality compared to the Yu9 4B. The Yu9 4B is no slouch. I would say it possibly retreives more detail from tracks and manages electronic music well but sounds too dry and incisive for instruments for my taste. Stage is possibly wider but instrument separation and layering is weaker with most information pushed further out to the extremes of L-R. The Yu9 4B is more 'supernatural' while the U-554 offers a taste of the supernatural but doesn't lose as much of the emotional engagement in the process.

I hope this post helped anyone interested. I know we have a few members with sets on the way and I look forward to more discussion soon

Nice job, man.
I just came across this thread and I'm very intrigued by these IEMs.
As I mainly listen to electronic music (Drum & Bass, Dubstep, etc), I bought a 7hz Timeless (it's very good), but I'm thinking about trying something different.
Which of the two would you recommend?
Also, I don't have a problem with deep insertion fit as I tried almost all IEMs of the ER 2, 3 & 4 series.