Moondrop Chu II IEM Review

[Bleib]

For me IEMs are played at a lower volume which kills dynamic detail and resolution. It's not possible to play at higher volumes at longer periods of time without massively increasing the chances of damaging hearing.
That they are so close to ear is also why it's easier to keep distorsion in control, they don't have to move as much air as loudspeakers and not even as much as over ear headphones.

 

[SteveL]

If you are trained then you should be able to take on my question and not side step it. Especially not by taking it personal, as it's a general question in nature.

Your question makes no sense. If you want to state a preference, go right ahead. If you want to make a claim about reality that you expect others to accept, bring evidence. That's really all there is to say.

 

[SteveL]

For me IEMs are played at a lower volume which kills dynamic detail and resolution. It's not possible to play at higher volumes at longer periods of time without massively increasing the chances of damaging hearing.
That they are so close to ear is also why it's easier to keep distorsion in control, they don't have to move as much air as loudspeakers and not even as much as over ear headphones.

Why is a given SPL coming to your eardrums from an IEM any more or less dangerous than the same SPL coming from live music or speakers?

 

[Barrelhouse Solly]

This is a review, listening tests, EQ and detailed measurements of the Moondrop Chu II In-Ear Monitor. It is on kind loan from a member and costs just $19.
View attachment 375507
Compared to some other IEMs I have tested, these are lighter weight due to lack of extra metallic parts. They are also a bit smaller which makes them more comfortable to wear. Three sets of silicone tips came with it. The nozzle is quite large so mounting the tips was a bit of a chore but not as bad as some other IEMs.

IEMs can be finnicky to mount on my GRAS 45CA and the Chu II was that. I think I got 90% there in the measurements you see below.

Moondrop Chu II Measurements
As usual, we start with our IEM frequency response measurement and comparison to target:
View attachment 375508
Wow, this is quite good! The gaps between its response and our target is very small. Since the target is not high resolution anyway, this may just as well be as good as the target with just some overshoot around 14 kHz.

Creating filters by eye/hand may be a bit tricky though due to the shape of the deviations:
View attachment 375509

What I was really impressed by was the low distortion:
View attachment 375510
View attachment 375511
Considering that we don't need to boost bass, this is extremely good results though shy of the best we have seen.

Group delay is uneventful as it typically is for IEMs:
View attachment 375512

Impedance is low:
View attachment 375513
Sensitivity is also low for an IEM but still better than just about any standard headphone:
View attachment 375514
Comfortable listening on my RME ADI-2 Pro is about -40 dB so should not be a hard load for just about any source.

Moondrop Chu II Listening Tests and Equalization
First impression was very good although I thought the bass was not quite there. It felt like a fitment issue although pushing them into my ear made no difference. I wanted to EQ it anyway so here we are:
View attachment 375515
I took the midbass down and boosted the treble. This naturally made things worse as I lost more bass response. So I put in the Band 1 filter and that added the warmth back it. I usually don't EQ above 8 kHz but here, that peak around 14 kHz was quite wide so I went after it. Can't swear it is not placebo but the effect was softening the highs and reducing their sharpness.

Playing my reference tracks with or without EQ showed very subtle difference despite the plurality of the filters. With the filters in place, the clarity improved with better ability hear fine detail like strings and vibration in voices. On the Nathaniel Rateliff track above, the result was absolutely stunning! It felt like his head was fully inside my head singing! I have listened to this track many times with my standard headphone where the experience was not this good.

The response with EQ was so good that I had to put them back on and keep listening as I type this review! Absolutely reference quality sound reproduction.

Conclusions
The last 12 months or so has definitely been the era of budget IEMs that produce level of fidelity that is jaw dropping. The Moondrop Chu II joins that crew producing very good out of box response with very low distortion. A bit of EQ adds lipstick to an already beautiful woman, producing a level of fidelity that amazes on any well recorded music. Fitment in my ears is better than some other IEMs due to lighter weight and smaller size. And the look is more conservative which is nice.

It is my pleasure to recommend Moondrop Chu II IEM. For the price of fast food for one and half people, you can have an IEM that can transform our audio experience!

------------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

Because of my hearing loss with a serious difference between ears I can't use IEMs. I'm really amazed at the performance of inexpensive ones. I'm wondering what can be done with on ear and over ear headphones.

 

[tonybarrett]

I thought we believed in science

In case of interest, the work of Dan Sperber and Hugo Mercier (Enigma of Reason) and in Mercier’s Not Born Yesterday is really fascinating. It’s not that they completely dismiss the Kahneman hypothesis (or even his critics like Gird Gigerenzer) despite the debunking of many priming studies, for instance, it’s that they claim that they miss the point. Humans are social primates and we are geared to make arguments and cherry pick evidence that “strengthens” our case (cough). Hence the bias. The point is that being social we will have evolved to do this in groups and so it’s within the cooperative group that hearing these competing cases we will collectively coagulate around the best view. Studies have shown that many of the biases and mistakes that individuals make in psychology tests disappear when they are carried out by a group. Even groups where all individuals make such mistakes stop making them when they are allowed to discuss the problem collectively. The scientific method is an attempt to institutionalize this process. A process that also becomes internalized when you know that your ideas will be challenged at some point by competing ideas.

 

[NTK]

Why is a given SPL coming to your eardrums from an IEM any more or less dangerous than the same SPL coming from live music or speakers?

Interestingly, our perception of loudness is often different between listening to headphones and listening to loudspeakers. In tests or comparisons that are not very carefully controlled, listening to headphones can require higher SPL at the eardrums (can be as much as 6 - 10 dB) to give the same loudness impression as listening to loudspeakers. This effect is much more prominent at the lower frequencies and usually disappears at higher frequencies.

The “Missing 6 dB” Revisited: Influence of Room Acoustics and Binaural Parameters on the Loudness Mismatch Between Headphones and Loudspeakers

Generations of researchers observed a mismatch between headphone and loudspeaker presentation: the sound pressure level at the eardrum generated by a headphone has to be about 6 dB higher compared to the level created by a loudspeaker that elicits the ...

www.ncbi.nlm.nih.gov

 

[MacClintock]

Interesting. How does "resolution" differ from frequency response? If an IEM is accurate to 22,000 Hz, then it is capable of reacting quickly enough, (with sufficient resolution) to reproduce everything in a recording below that frequency, right? If the subtle echo and reverb effects are in the recording, and within the human hearing range, they would be reproduced.

How our ears determine location in real life is established science, having to do with relative loudness between ears, delay, and frequency changes. All of those things are either in the recording, or not.

I could accept that IEMs that emphasize certain frequencies may seem more "spacious" or airy than others...but that means they are either more or less accurate to the recording, right?

Exactly, supposed "speed" differences creating a distinct acoustical impression are a pure myth.

 

[MacClintock]

Human hearing is accurate to a certain frequency as well and hence capable of 'reacting quickly enough' up to that frequency. And yet it will mask softer sounds in the context of louder sounds of similar frequency. I think the key to understand this is the dissipation of resonances in a mechanical system:
If a relatively loud sound results in an excitation of mechanical resonances that need to be damped, much softer sounds of the same frequency as these resonances will get lost (will 'drown') in these resonances during the damping period. I think this effect could be responsible for the fact that some speakers seem to flesh out more details than others.
Yes, frequency response plays a role here as well, but a dynamic mechanical system like a driver is characterized by more than just distortion, directivity, and frequency response, which are all measurements on a long time scale. It also has to deal with dissipating its mechanical energy, which is an effect on a much smaller time scale.
(Like I said, this is speculation, but I do tend to hear resolution differences between drivers and they do not always seem frequency response related)

Please stop your baseless speculations, perpetuating disproven myths. You can see impulse response measurements of IEMs with different driver types and there is absolutely no relevant difference.

 

[Bleib]

Why is a given SPL coming to your eardrums from an IEM any more or less dangerous than the same SPL coming from live music or speakers?

Sound you can't escape from, headphones of any kind I tend to play lower.
I've never heard IEMs go very deep either despite specs.

 

[phoenixdogfan]

The IEM is proving to be the most affordable and accessible way for someone to get a taste of high end audio. A true gateway drug.

Thanks, again for this review, Amir.

 

[phoenixdogfan]

IEMs are a solved problem and the solution requires just one simple dynamic driver. There is no reason to pay more than $20ish for an IEM, unless you want an actually useful special feature like the crazy isolation of my ER2XR (and I can't really think of any other case). Otherwise you're paying for jewelry, and I don't know about you but I don't watch myself in the mirror while I listen to music. Cheapness also means that if you try one that you can't get to fit you well, no great loss.

Don't know about you, but I like to wear ear jewelry, and my extremely extravagant $90 Simgot EA 500 LM's are all metal black chrome and definitely make me a babe magnet. Sound really good with my EQ , though it's not Harman (which is not to my taste, personally)-- better in fact than anything else I've heard to date.

 

[markanini]

Your question makes no sense. If you want to state a preference, go right ahead. If you want to make a claim about reality that you expect others to accept, bring evidence. That's really all there is to say.

How can a question not make sense if it doesn't contain any presupposition? I agree bring the evidence. The rest you, lost me.
If it helps assume that I'm 100% on your side and seeking a foundation that's not circular. Not that it should change the question or the answer....

 

[SteveL]

Don't know about you, but I like to wear ear jewelry, and my extremely extravagant $90 Simgot EA 500 LM's are all metal black chrome and definitely make me a babe magnet. Sound really good with my EQ , though it's not Harman (which is not to my taste, personally)-- better in fact than anything else I've heard to date.

This is more than fine! You paid a little extra for something you appreciate and you're enjoying it.

 

[SteveL]

How can a question not make sense if it doesn't contain any presupposition? I agree bring the evidence. The rest you, lost me.
If it helps assume that I'm 100% on your side and seeking a foundation that's not circular. Not that it should change the question or the answer....

You're over-complicating something quite simple. Preferences only need to be stated. Truth claims, meant to be accepted by others as valid, need to be supported. This is not a deep thought at all, it's very shallow. People tend to struggle with it when they have a strong belief which they can't support. (If your "circle" is the circle of confusion, I already suggested that comparing live vs recorded acoustic music is a good start at breaking out of it.) I won't respond further because this isn't getting anywhere.

 

[markanini]

You're over-complicating something quite qsimple. Preferences only need to be stated. Truth claims, meant to be accepted by others as valid, need to be supported. This is not a deep thought at all, it's very shallow. People tend to struggle with it when they have a strong belief which they can't support. And I won't respond further because this isn't getting anywhere.

I'm wanting something simpler than you. I wish to have a standard for evidence without engaging in circular reasoning. Everything you assumed about me so far has been wrong, but I won't hold it against you. That's what you get used to on the internet, it quickly becomes about taking sides and it causes it's own biases. I'm letting this one go. But I'll continue differentiating the veracity of a claim from someone's perception, because I'm interested in objectivity and perception is known to be unreliable. For that reason I'd rather deal with likelihoods given known data, before referencing psychology.

 

[GGroch]

.....I wish to have a standard for evidence without engaging in circular reasoning.

The discussion of perception vs. evidence here has circularized and frustrates.

The 1st post in this thread that mentions perception also provides the accepted scientific evidence standard. A blind test.

A statistically valid ABX blind test can prove that a perceived characteristic exists in the sound itself and is not imagined.
If the characteristic mentioned is a recognized property of sound, as in "The Chu has more deep bass.", the perception can also be validated through measurement.

When the characteristic describes the feeling or emotion an IEM elicits in the listener, as in "The Chu was more spacious and easy" a valid blind test can prove that characteristic is not imagined. But, only multiple blind tests with multiple listeners can confirm that the characteristic will be perceived by many subjects as spacious and easy.

Even then, confirming this combination of characteristics is an accurate perception is only valid if the multiple subjects cognitive maps are also valid. That is, if the subjects all think "This sounds like a fox", it is only valid if the subjects had previously heard a fox.

If your audiophile goal is just to find components that make you happy, none of this matters a whit.
An ASR post that "I really like the Chu" or "I really hate the Chu" is not likely to be challenged.

But, if you assert that an IEM exhibits x or y characteristics "that could easily be distinguished in a blind test." That is not valid evidence unless you do the blind test.

 

[Toroid]

This or the Tanchjim one?

 

[markanini]

The discussion of perception vs. evidence here has circularized and frustrates.

The 1st post in this thread that mentions perception also provides the accepted scientific evidence standard. A blind test.

A statistically valid ABX blind test can prove that a perceived characteristic exists in the sound itself and is not imagined.
If the characteristic mentioned is a recognized property of sound, as in "The Chu has more deep bass.", the perception can also be validated through measurement.

When the characteristic describes the feeling or emotion an IEM elicits in the listener, as in "The Chu was more spacious and easy" a valid blind test can prove that characteristic is not imagined. But, only multiple blind tests with multiple listeners can confirm that the characteristic will be perceived by many subjects as spacious and easy.

Even then, confirming this combination of characteristics is an accurate perception is only valid if the multiple subjects cognitive maps are also valid. That is, if the subjects all think "This sounds like a fox", it is only valid if the subjects had previously heard a fox.

If your audiophile goal is just to find components that make you happy, none of this matters a whit.
An ASR post that "I really like the Chu" or "I really hate the Chu" is not likely to be challenged.

But, if you assert that an IEM exhibits x or y characteristics "that could easily be distinguished in a blind test." That is not valid evidence unless you do the blind test.

Great response. This also relates to how an effort such as a the Harman target is valid despite relying on perception. Only by putting it to the test, by pooling perception and defeating biasing stimuli.

 

[Maiky76]

This is a review, listening tests, EQ and detailed measurements of the Moondrop Chu II In-Ear Monitor. It is on kind loan from a member and costs just $19.
View attachment 375507
Compared to some other IEMs I have tested, these are lighter weight due to lack of extra metallic parts. They are also a bit smaller which makes them more comfortable to wear. Three sets of silicone tips came with it. The nozzle is quite large so mounting the tips was a bit of a chore but not as bad as some other IEMs.

IEMs can be finnicky to mount on my GRAS 45CA and the Chu II was that. I think I got 90% there in the measurements you see below.

Moondrop Chu II Measurements
As usual, we start with our IEM frequency response measurement and comparison to target:
View attachment 375508
Wow, this is quite good! The gaps between its response and our target is very small. Since the target is not high resolution anyway, this may just as well be as good as the target with just some overshoot around 14 kHz.

Creating filters by eye/hand may be a bit tricky though due to the shape of the deviations:
View attachment 375509

What I was really impressed by was the low distortion:
View attachment 375510
View attachment 375511
Considering that we don't need to boost bass, this is extremely good results though shy of the best we have seen.

Group delay is uneventful as it typically is for IEMs:
View attachment 375512

Impedance is low:
View attachment 375513
Sensitivity is also low for an IEM but still better than just about any standard headphone:
View attachment 375514
Comfortable listening on my RME ADI-2 Pro is about -40 dB so should not be a hard load for just about any source.

Moondrop Chu II Listening Tests and Equalization
First impression was very good although I thought the bass was not quite there. It felt like a fitment issue although pushing them into my ear made no difference. I wanted to EQ it anyway so here we are:
View attachment 375515
I took the midbass down and boosted the treble. This naturally made things worse as I lost more bass response. So I put in the Band 1 filter and that added the warmth back it. I usually don't EQ above 8 kHz but here, that peak around 14 kHz was quite wide so I went after it. Can't swear it is not placebo but the effect was softening the highs and reducing their sharpness.

Playing my reference tracks with or without EQ showed very subtle difference despite the plurality of the filters. With the filters in place, the clarity improved with better ability hear fine detail like strings and vibration in voices. On the Nathaniel Rateliff track above, the result was absolutely stunning! It felt like his head was fully inside my head singing! I have listened to this track many times with my standard headphone where the experience was not this good.

The response with EQ was so good that I had to put them back on and keep listening as I type this review! Absolutely reference quality sound reproduction.

Conclusions
The last 12 months or so has definitely been the era of budget IEMs that produce level of fidelity that is jaw dropping. The Moondrop Chu II joins that crew producing very good out of box response with very low distortion. A bit of EQ adds lipstick to an already beautiful woman, producing a level of fidelity that amazes on any well recorded music. Fitment in my ears is better than some other IEMs due to lighter weight and smaller size. And the look is more conservative which is nice.

It is my pleasure to recommend Moondrop Chu II IEM. For the price of fast food for one and half people, you can have an IEM that can transform our audio experience!

------------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

Here are some thoughts about the EQ.
Please report your findings, positive or negative!

Notes about the EQ design:

• The average L/R is used to calculate the score.
• The resolution is 12 points per octave interpolated from the raw data (provided by @amirm)
• A Genetic Algorithm is used to optimize the EQ.
• The EQ Score is designed to MAXIMIZE the Score WHILE fitting the Harman target curve (and other constrains) with a fixed complexity.
  This will avoid weird results if one only optimizes for the Score, start your journey here or there.
  There is a presentation by S. Olive here.
  It will probably flatten the Error regression doing so, the tonal balance should be therefore more neutral.
• The EQs are starting point and may require tuning (certainly at LF and maybe at HF).
• The range around and above 10kHz is usually not EQed unless smooth enough to do so.
• I am using PEQ (PK) as from my experience the definition is more consistent across different DSP/platform implementations than shelves.
• With some HP/amp combo, the boosts and preamp gain (loss of Dynamic range) need to be carefully considered to avoid issues with, amongst other things, too low a Max SPL or damaging your device. You have beed warned.
• Not all units of the same product are made equal. The EQ is based on the measurements of a single unit. YMMV with regard to the very unit you are trying this EQ on.
• I sometimes use variations of the Harman curve for some reasons. See rational here and here
• NOTE: the score then calculated is not comparable to the scores derived from the default Harman target curve if not otherwise noted.
• Occluding IE devices generally must have very good fitting/seal in the user's ear canal for best performance.
  please spend a few minutes to pick up the best ear tip... Be sure to perform this step otherwise the FR/Score/EQ presented here are just worthless.
• 1. more bass = better seal
  2. More isolation from the outside world = better fit
  3. Comfort

Good L/R match.

I have generated three EQ, the APO config files are attached.
The feature around 100Hz is most probably a measurement artefact: mass spring resonance with the eartip spring and the mass of the earbud, the GRAS pinna lacks damping compared to a real human ear.
An additional biquad can be added like the 21Hz from amirm to compensate for a less than optimal fit.

Score no EQ: 84.1%
Score Amirm: 89.2%
Score with EQ: 93.2%

Moondrop Chu II Harman EQ
June172024-111412

Preamp: -2.10 dB

Filter 1: ON PK Fc 197.6 Hz Gain -3.17 dB Q 1.10
Filter 2: ON PK Fc 3329.0 Hz Gain -2.38 dB Q 0.67
Filter 3: ON PK Fc 6438.7 Hz Gain 3.55 dB Q 2.99
Filter 4: ON PK Fc 13470.8 Hz Gain -8.42 dB Q 4.77

OTT version for comparison:

Score no EQ: 84.1%
Score Amirm: 89.2%
Score with EQ: 95.7%

Moondrop Chu II Harman OTT EQ
June172024-111303

Preamp: -2.50 dB

Filter 1: ON PK Fc 203.7 Hz Gain -3.20 dB Q 0.95
Filter 2: ON PK Fc 562.1 Hz Gain 0.88 dB Q 1.28
Filter 3: ON PK Fc 1460.1 Hz Gain -1.63 dB Q 1.85
Filter 4: ON PK Fc 3734.1 Hz Gain -2.67 dB Q 1.16
Filter 5: ON PK Fc 6293.7 Hz Gain 3.55 dB Q 3.54
Filter 6: ON PK Fc 10221.9 Hz Gain 3.72 dB Q 4.02
Filter 7: ON PK Fc 13449.8 Hz Gain -8.57 dB Q 3.10

The following score are NOT comparable as they use teh Knowles target, base on the OTT Harman.

Score no EQ: 79.0%
Score with EQ: 95.7%

Moondrop Chu II Knowles OTT EQ
June172024-111021

Preamp: -6.00 dB

Filter 1: ON PK Fc 205.4 Hz Gain -3.20 dB Q 0.97
Filter 2: ON PK Fc 579.6 Hz Gain 0.88 dB Q 1.18
Filter 3: ON PK Fc 1451.1 Hz Gain -1.63 dB Q 1.85
Filter 4: ON PK Fc 3748.4 Hz Gain -2.67 dB Q 1.16
Filter 5: ON PK Fc 6315.2 Hz Gain 3.71 dB Q 2.98
Filter 6: ON PK Fc 10256.5 Hz Gain 5.54 dB Q 3.16
Filter 7: ON PK Fc 15981.8 Hz Gain 5.51 dB Q 2.99

 

[JaMaSt]

When the characteristic describes the feeling or emotion an IEM elicits in the listener, as in "The Chu was more spacious and easy" a valid blind test can prove that characteristic is not imagined. But, only multiple blind tests with multiple listeners can confirm that the characteristic will be perceived by many subjects as spacious and easy.

Even then, confirming this combination of characteristics is an accurate perception is only valid if the multiple subjects cognitive maps are also valid. That is, if the subjects all think "This sounds like a fox

There is a difference between using words to describe a tacit experience (Chu sounds spacious and easy compared to IEM 'X') and saying that something "sounds like a fox." Your two examples are a false equivalence and/or a categorical error.

No one sense modality has its own unique dictionary of words. We use analogies from one sense modality to describe a tacit experience in another sense modality. The term "spacious" draws upon vision. The term "easy" may draw upon fluidity of movement in a medium.

Analogy.

Analogy plays a significant role in problem solving, as well as decision making, argumentation, perception, generalization, memory, creativity, invention, prediction, emotion, explanation, conceptualization and communication. It lies behind basic tasks such as the identification of places, objects and people, for example, in face perception and facial recognition systems. Hofstadter has argued that analogy is "the core of cognition".

An analogy is not a figure of speech but a kind of thought. Specific analogical language uses exemplification, comparisons, metaphors, similes, allegories, and parables, but not metonymy. Phrases like and so on, and the like, as if, and the very word like also rely on an analogical understanding by the receiver of a message including them. Analogy is important not only in ordinary language and common sense (where proverbs and idioms give many examples of its application) but also in science, philosophy, law and the humanities.