Detail Experts: Etymotics ER4, Phonak PFE122, and Hifiman RE-0

Hifiman RE-0

The last IEM in this review comes from Hifiman. The Hifiman RE-0 is currently being offered for $79 at Head-direct’s website and for its price, it is the cheapest IEM in this comparison. For those of you who haven’t heard about the RE-0 before, this may struck you as a cheaper and perhaps an inferior product to the Phonak and ER4. However, I will tell you that in terms of pure sound quality level, it is definitely in the same class as the two above.

One of the aspects of the sound that really stands out with the RE-0 is its treble presentation. The RE-0 does treble better and differently from many IEMs I have listened to. Maybe that is an understatement; I will say that the RE-0 does treble better than anything else I have heard under the $200 price mark, save for the ER4S, and maybe even better than the’s treble. The treble extension is just exceptional, matching the ER4 easily with great clarity, and unlike many, it does so without inducing listening fatigue. Because the lack of those wince-inducing peaks, you can hear the treble detail without having to wince every time the music goes high into the treble region.

It is not the same kind of heightened clarity you get out of the ER4. With the ER4, you feel as if your music is presented through a magnifying lens, making the sound sharper than the recording itself with very vivid details. The RE-0’s presentation of clarity is akin to looking at the bottom of a clear pond, not as sharper of a focus as the ER4, but many times feel a bit more natural. Both detailed, but in a different way. Also, with the RE-0, it is just a joy that each crash and scrape of instruments has an extra layer and decay behind them that is cut short with the ER4, though the vivid forward presentation of the ER4 is also addicting. The question of “better”, then, comes down to a question: do you want the extra treble decay of the RE-0, or do you want the ultra vivid treble of the ER4 with short decay.

In terms of transparency, I would say the RE-0 does things differently from the ER4. Out of a decent source, the RE-0 is neither warm nor cold. The relatively neutral nature of this IEM really helps when the music gets though, and the whole information in the music is presented more equally than the more colored and mid-oriented ER4 and Phonak. However, the ER4 still maintains an edge on a cleaner and blacker background laid behind the music. For my listening preference, I have yet to experience much listening fatigue with the RE-0, it is transparent while being very smooth. The Phonak and the ER4 sounded a bit peaky in comparison.

The mids and bass follow the general transparent character of the RE-0. The mids is different from the the other two IEMs in this review in that it doesn’t boost the upper mids area. Many headphones and earphones in the market tend to boost this area, to create a sensation of forwardness with vocals especially female voices. The RE-0’s upper mid presentation can be an issue if you are used to the forward mid-oriented sound like that of a Grado, but in my opinion, this presentation makes the RE-0 unique and in some songs, let me focus on other aspects beside the vocals. Bass response is solid and is definitely on the tight side. Though not as textured as the ER4, it extends farther down and complements the clean nature of the RE-0 sound. If there is anything average about the RE-0, it is perhaps the soundstage. Though instrument separation is great and positioning is decent, the soundstage is not very wide, and there is a sensation of three-blobs soundstage and not much airiness. The soundstage can sometimes hinder the great instrument separation of the RE-0 to shine through.

As good as the RE-0’s sound is, I don’t know its sound presentation will be suitable for all people. For listening on the go, it is almost too neutral to a fault. Many people like certain coloration to their music, and the RE-0 doesn’t offer many. The ER4 and the Phonak can make people weep; however, the relatively laid back presentation of the RE-0 that doesn’t push anything in front of you takes more time to appreciate. I personally like its presentation, but honestly, for myself who listen to some bass-driven music, I occasionally need a dose of bassy warmth of my DT531 just for a change. But for the current cheap price of $80, I might probably keep it as a second IEM to my Eterna, since it sounds different and great enough to warrant me keeping them. The RE-0 makes my Eterna sounded muddy, but there are also lots that the Eterna offers that the RE-0 doesn’t. I’m not going to compare the Eterna and the RE-0 here, since it’s almost like asking which flavor of ice cream I want today.

Looking at the three IEMs, although the ER4 still have the best sound isolation, its design, comfort, and microphonics makes it a bit of a dinosaur when compared to the RE-0 and Phonak. This IEM needs a better shell for its drivers, not the minor design update like what Etymotic has done with the HF5.  However, based on pure sound quality only, I will pick the ER4S as my favorite of the three. For the wow effect and the kind of technicalities it projects, such as sharper transients and heightened sense of detail, clarity, speed, and instrument separation, it is hard to beat. But ultimately, the ER4S has some drawbacks like the short decay of the sound and its tendency to sound a bit clinical and tiring at times out of some sources.

The Phonak PFE is a very well designed IEM with the best comfort and form-factor here. Though it lacks bells and whistles of RE-0’s and ER4’s technicalities, it has a coherent and clear but very slightly creamy mid-oriented vocal sound, definitely worth a try for vocal lovers or Etymotic ER4 lovers looking for a smoother sound. I can’t wait for the new Perfect Bass version.

Last but not least, the RE-0 gives fine detail and admirable accuracy and neutrality not very common among most IEMs. At a mere price of $79, it competes with the ER4 and the Phonak, and it offers the best bang-for-the buck treble performance out of any headphones, earphones, and IEMs I have tried.

Gear used for the review:
Headphones: Etymotics ER4, Phonak PFE122, and Hifiman RE-0
Source: Nuforce uDAC, Ipod Nano 1st Gen
Amplifer: Nuforce uDAC

4/5 - (7 votes)



  • Reply June 30, 2010


    Great review Hadi! Like it a lot 🙂

    From the three, which one has better bass?


    • Reply July 1, 2010


      Thanks, Earfonia :). I'm partial toward the ER4's bass for its surprising punch and vivid texture (easier to imagine the actual drum being hit) though extension is not the greatest. Some people may prefer the RE0's bass presentation.

  • Reply June 30, 2010


    Thank you for the nice review Hadi,

    I've read quite a few rave reviews for the RE0 but remained skeptical at best.

    Recently i tried out the RE0, the unit very new but it immediately caught my attention with its clarity. Its like you mentioned, the details are all there but it is smooth, refined and in no way fatiguing after prolonged usage.

    The next thing was the bass, there was much less quantity compared to my Eterna but it is much tighter and detailed. Not to say the Eterna's bass is bad but the RE0 presented it in a whole new way all together and they are definitely not bass lite. It provides just the right amount of warmth and does not flood into other regions of the sound. It is tight yet very gentle to the listener.

    Besides that, i've been trying hard but i could not find anything that really stands out from the sound. Its like they don't have a signature of their own. I think they may have a hint of warmth making their treble sound smooth and relaxing while still retaining all the details.

    Also, i noticed that they are not very efficient but can be played directly from a portable player such as an Ipod and still sound good. I wouldn't say an amp is an absolute necessity but it certainly sounds better with one. I've been pairing them with the Asus Xonar U1. I know its only a budget dac/amp with a usb connection. However they pair up pretty nicely with each other. The Xonar U1 complements the RE0 by not adding anything else but actually refining the way it sounds. Thus giving better bass control, impact and cleans up the overall sound produced.

    I bought them almost immediately after auditioning due to the fact that details are presented so effortlessly yet managing to sound relaxing. You can really just sit back and let them do the rest of the job of presenting the music to you without having to strain your ears to hear the details.

    At this point, some may think that the RE0 will sound boring on Pop and RnB or other types of bassier songs. I was worried about the same at first but after giving them a chance i loved the end result, it was very refreshing.

    In conclusion, the RE0 sounds neutral maybe with a hint of warmth. There is no real emphasis to any spectrum of the sound. Vocals and instruments produced sound are complemented with just the right amount of bass making them sound real and natural. In simple words, everything sounds just as it is, nothing less nothing more.

    Everytime, i try my best to listen with a clean state of mind and not biased towards any type of sound signature. What i've mentioned above is based purely on my honest and humble opinion and is subjective to each individual. I'm open to criticism and please forgive me if i applied any audio terms wrongly as i'm still new and inexperienced.

    Thank you.

  • Reply July 1, 2010


    Sorry about hogging the comment section, i just wanted to share my opinion and clearly got carried away.

    • Reply June 30, 2010


      That’s cool, HC. It’s always good to hear other people’s thoughts on the subject.

      We don’t put limits on the comments section, especially when they are honest and thoughtful such as yours.


    • Reply July 1, 2010


      Thank you for the comments, HC. I think you made some very well-thought points about the RE-0 ;), thanks for posting it up. Enjoy your RE-0, you have quite a nice combo there with the RE-0 and the Eterna.

    • Reply July 2, 2010


      Thank you very much Mike and Hadi,

      The Eterna and RE0 seems to compliment each other.

      They are both enjoyable in their own way and i often find myself swapping between them whichever suits my mood best.

      Now eagerly awaiting the long anticipated comparison between the HD800 & T1. =D

      • Reply July 2, 2010


        I've finished the HD800 & T1 comparison, and it'll be published tomorrow (Friday) :D.

  • Reply July 2, 2010


    Nice review. I have both the RE0s, and now the ER4P. Really enjoy the ER4s over the RE0, they just do everything better while being a little smoother sounding – but that could also be because I get a far better fit with ER4s which go deeper inside.

    Any chance of doing a review of earsonic SM3s?

    • Reply July 4, 2010


      Thanks for the comments, rayk.

      I heard good things about the SM3. No definite plan for now, but we might consider it.

  • Reply July 9, 2010


    good review Hadi, I have all three IEMs that you compared here, I prefer er4p over the other two, it has better bass presentation and good seal for my ears. I am intrigue by your impedance adapter, may want to try that and experience how it can improve the sound qualities for the IEMs that I have

    • Reply July 13, 2010


      Hi; i'm not an expert but this is what I have,

      "impedance adapter" for audio signal works as a "low-pass filter" (, but it's different in my own experience; with low impedance, ER4 has more bass quantity… and so for another phones; if you combine with impedance adapter, your phone's bass quantity would be reduced.

      btw Hadi, would you like to add e-Q7 as comparison for ER4?

      I'm interested on it 😀

      • Reply July 14, 2010


        Yes, that is also what I'm hearing. The 75 ohm impedance adapter takes off some bass quantity (mainly midbass) from the ER4P and the Phonak. Surprisingly, it's harder to notice the difference when I pair the adapter with the Eterna and the DT531.

        Maybe we should let Mike chime in on that :D. I haven't had the chance to listen to the e-Q7.

      • Reply July 14, 2010


        Yes, adding a resistor between a headphone and amp will make the sound more bassy. I tried it before with the HD650, but I was using something in the range of 470 Ohms. A 75 Ohms resistor is barely felt.

        The ER4 is quite the opposite in this sense. I really don't know why specifically. Different driver I guess. I also tried the 75 Ohms adapter on the JH customs, and I didn't like the effect. It was more congested with the added impedance.

        Ortofon eQ-7 is totally different sounding than the ER4. The ER4 is superb on clarity, technicalities, separation. The e-Q7 is more midrange oriented, mellow, great vocals, though instrument separation is not so great.


        • Reply July 14, 2010


          I've test using a 75ohm adapter to my CK10… results: the high become less edgy; harsh & piercing sound of cymbals and female vocals never bother my hearing anymore…

          Just as Mike says, It's totally opposite of ER4.

          In my own conclusion; if resistor works alone without capacitor, it won't act as filter, neither low-pass or high-pass(mistake on my early statement). I want to catch up more clue about it.

          cheers 😀

  • Reply July 10, 2010


    Thanks, jendol. Impedance adapter may or may not be useful depending on your IEM and/or synergy with your setup. But it's fun and always worth a try since it's relatively easy to get :D.

  • Reply July 22, 2011


    Very well said. Really comprehensive, “direct-to-the-point”  review. I own both the REO and ER4 and have the same observations. Hope to see more reviews from HADI

    • Reply July 22, 2011


      Yes, Hadi does have that kind of clinical precision when he writes. 🙂

  • Reply August 17, 2011


    Using the ER4S without proper external amplification is no good.
    Furthermore, I found the review too lengthy at times (to much text to explain simple things), and not that coherent.  For example, criticizing the Etys for fucusing on a narrow frequency bandwidth: mids and highs (hmmm, that’s seems at least 2/3 of the bandwidth !?) 
    I found the ER4S much better than the other two when amplified. It makes a real difference. Not so much width the ER4P. Also, proper ear canal seal is of great importance to get that wonderful bass. It takes some experimentation and it may well be impossible for some to get that seal. That is the real problem with the Etys: if you don’t seal the ear canal as it should you loose bass extension, power and definition and a lot of soundstage. When properly used (correct seal and decent amplification) the ER4S are as good as any top earphone/headphone, except of course, those exotic and very expensive  offerings from Grado, Stax, Ultrasone, Westone and the like…


    PS: My comment is, of course, biased, but I have seen to many people/critics to jump to conclusions without proper use of the marvelous ER4S.

    • Reply August 17, 2011


      Thanks, Bruno.

      I think your points are valid, and the ER4S is indeed truly remarkable, and still one of the best IEMs around. I didn’t write this review though, Hadi did, and he is not so much of an amplifier guy.

  • Reply January 2, 2014


    I hate to say this but really, the ER4S really performs in every way better when amped or at least with a decent source like the fiio x3. I admit the bass quantity is lesser but I find the ER4P bass almost muddy. I agree totally with BDias about the fact that a proper seal is very important. I used it the first time with a bad seal and said it was bassless but remember this is coming from a guy who used the kilpsch s4 which have quite a lot of sub bass thus my basshead needs :d But after a while, I fell in love with the er4s and my friends when he tried it just went ‘yucks, this sucks man, how do you even endure them’ So I guess sometimes it’s just personal preference.

    PS: I insert the er4s seriously deep.

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