audio-sound @ hatena

An audio review & news blog. The volume should not exceed 80 dB is recommended. I usually adhere to the safe-listening style by WHO. Please note that my aural impressions and interpretations of measurements are also made from a safe-listening style.

(Chi-fi IEM Review) Yu9 U-556: Excellent Etymotic clone that overcomes the weaknesses of the ER4B and offers a more natural texture

Yu9 U-556

Yu9 U-556




  • This review is based on a sample provided by Yu9 Audio to convey a sincere quality review to our readers.
  • No remuneration or compensation, such as a manuscript fee, has been received for publishing this, and it is an honest evaluation based on measurement data from personal testing and personal opinion.
  • Please read the privacy policy of this website.


  • People who like near-field sound
  • People who want earphones for vocal songs
  • People who want earphones for practicing musical instruments
  • People who are looking for earphones for ASMR, voice drama, or narration
  • Musicians and performers who want excellent stage monitors
  • People who value textural expression
  • Etymotic Research fans


Overview of Yu9 U-556

This review will give an overview of Yu9 U-556. A complete review of this product can be found here.


audio-sound Score

  • Total Score: 9.0 / 10.0
  • Package: 8.5 / 10.0
  • Build quality: 8.5 / 10.0
  • Fitment: 9.5 / 10.0
  • High range: 8.0 / 10.0
  • Mid range: 10.0 / 10.0
  • Low range: 9.0 / 10.0
  • Less distortion: 7.5 / 10.0
  • Cost performance bonus: 11.5 / 10.0


  • Want to see the score ranking? Click here!


Basic Specifications
  • Frequency response: 20Hz to 16kHz
  • Impedance: 116Ω
  • Sensitivity: 116.5dB/Vrms
  • Cable connector: 0.78mm 2pin



Packaging meets price standard. The outer box is simple, but made of paper and easy to dispose of. The accessories are fairly complete.


Package contents
  • Yu9 U-556
  • Many ear tips
  • Carrying case
  • Cleaning cloth
  • Cleaning tool
  • Cable clip
  • Manual


Yu9 U-556
Yu9 U-556


Build quality

The build quality of the exterior is above the standard of the price range.




The fit and sound insulation are quite excellent. However, it is not at all suitable for those who do not like to put the earpiece deep into the ear.



Sound quality

REW Frequency Response

The measured values this time are shown in a normalized graph based on the measurements at HATS (blue) and a normalized graph closer to the official measurements (red)


Sound quality description

In this review, I use the standard eartips size L and drive it with the FiiO M15.


Yu9 Audio describes the U-556 as a reinterpretation of the Etymotic Research ER4B with a comfortable listening balance. In fact, the balance is so good that the midrange, which can sound somewhat loud in Etymotic target, becomes neutral and natural sounding.


Please see here for detailed reviews on sound quality.


Sound quality general comment
  • Original Sound Fidelity: S-
  • Recommendation: S-
  • Personal preference: A+


The Yu9 U-556 is proof that Yu9's passion and research for Etymotic earphones is real, bringing Etymotic's original sound closer to the natural speaker listening experience and improving the midrange texture to a more natural one. Yu9's deep knowledge of Etymotic's sound is evident in the U-556.The evolution of the U-556 from the U-554 should be enough to show that Yu9 has a deep understanding of Etymotic's sound.


The SoundPEATS Mini, on the other hand, also starts with the Etymotic sound, but has chosen to improve the low and high frequencies, sacrificing texture for better localization, definition, and, above all, most importantly, they chose to improve the range, which is the weak point of the Etymo sound. It is difficult to say which is better, but the SoundPEATS Mini's sound suggests that the U-556 still has room for improvement.


Of course, making these adjustments is ultimately a move away from the Etymotic sound, so perhaps we should be pleased that the careful and thoughtful adjustments Yu9 has demonstrated with the U-556 are within the range of what should be welcomed by fans of the original.


Sound quality features
  • High original sound fidelity
  • Near-perfect near-field sound
  • Mild highs
  • Good vocal focus
  • Excellent textural representation
  • Monitor-like low frequencies
  • Forward localization
  • Excellent sound image consistency


  • Lacks expandability
  • Lacks low-frequency depth
  • Lacks clarity, which may be insufficient for monitoring purposes


Yu9 U-556


General comment

The Yu9 U-556 is an Etymotic-like IEMs with excellent textural expression and has a sound that beats the original ER4B in that it is more accurate in the midrange. For more purist Etymotic fans, I recommend the U-554, but for those seeking a superior IEMs, I recommend the U-556 over the U-554.


Yu9 Audio U-556

Yu9 Audio U-556

Yu9 Audio U-556