In-Ear Fidelity

Drop + JVC HA-FDX1 Review: Mod Magic


For non-audio opinions, please refer to my unboxing post.

Now I could give you a long-winded rundown of the HA-FD01 and its significance, but Drop already did my job for me so give them a little traffic.

Basically, the FD01 was an IEM that SuperBestAudioFriends user james444 discovered had some untapped potential within it, with the proper damping and tuning performed. It was subsequently picked up by other prominent members, and now it seems that it’s good enough for Drop to convince JVC to mass produce at a commercial scale. What a jump.

Now, the FD01 I heard was actually noticeably peakier than the “stock” FDX1 (which is supposed to be the same as a regular FD01) so I’m not sure if my personal experiences translate 1-to-1 with everyone else’s. I thought the FD01 was extremely bright, extremely peaky, beyond sibilant and worst of all: had a metallic timbre that made nearly everything sound unnatural. Now at that point I already knew of james444’s efforts and success in modifying the FD01, but I was listening to a store demo unit anyways so I wasn’t at liberty to do any sort of tinkering.

With the FDX1 also comes my opportunity to test out what is one of SBAF’s most critically acclaimed transducer modifications. I’m certainly excited.

Product page:

MSRP: $280 ($250 for pre-sale till 3rd October, limited to 665 units)

Driver configuration: single DD

This HA-FDX1 was kindly provided by Drop.

Frequency Response Analysis

This section is meant for those who have not learnt how to interpret the graphs that I create.

The HA-FDX1 comes with 3 sets of filters:

  • Stock, which is pretty much “naked” and apparently identical to the regular HA-FD01
  • The green filter, which has some cotton material lining its walls that acting as acoustic dampeners
  • The blue filter, which has more of the dampening material installed.
Each of the filters

The aim of the filters is to reduce as much of the upper midrange (3-4kHz) peak as possible without completely eliminating treble response. They’ve done well in this regard, for sure.

Harman Target compensated

Due to popular demand (and because Jude from Head-Fi also did so), here is an analysis with the Harman Target.

The FDX1 with stock filters come surprisingly close, with its deviations between 100Hz and 5kHz barely reaching 3dB at most. A smidgen too much emphasis at 200Hz and 1.5kHz respectively, but more-or-less within acceptable bounds. Like many, many IEMs out there, the FDX1 still cannot achieve the sub-bass boost required in Harman’s preferential average, and also lacks sufficient emphasis in the upper-midrange/treble regions of 5kHz upward.

Usual disclaimers here, this analysis only applies if you religiously follow the target. I think Harman’s bass boost and upper-midrange emphasis are too much for my own enjoyment, and the FDX1/FD01 does nothing to disprove that. Adding more upper-midrange/treble to it would probably kill my ears.

Ignore data above 8kHz as Harman’s research does not extend to that range.

Compensated with my neutral target

The “crinacle Neutral Target” is a target curve in which I perceive neutrality. It can essentially be described as a very conservative interpretation of Diffuse Field.

This compensation is more in line with what I actually hear. The stock filter, while serviceable in its own right, still has a lot of intensity in the upper midrange that is associated with shoutiness and a harshness. 

The green filter is pretty middle-of-the-road here, but the closest the FDX1 gets to my neutral target is with the blue filters. While there is a mild boost in the 4kHz region with a small dip at 6kHz, it’s more-or-less spot on and I do hear it as flat: all sounds at equal volume, with nothing being pushed into the foreground or into the background.

The FDX1 has boosted sub-bass relative to this target, with the rise beginning at 300Hz downwards. Most dynamic IEMs tend to rise late as high as 1kHz downwards, so this can be considered as a neutral lower-mid response and a sub-bass focused emphasis.

Comparisons courtesy of the Graph Comparison Tool



The FDX1 on stock filters (AKA FD01) can be considered as “Harman-neutral” as it follows the Diffuse Field upper-midrange emphasis somewhat with a boosted bass response, though not to the level of “true Harman”. 

The green and blue filters simply sound neutral with the aforementioned sub-bass emphasis. Mid-bass presence is not very pronounced and most of the bass’ weight comes from rumble rather than punch.


The FDX1 is a lean sounding monitor. Not necessarily a bad thing; the lesser mid-bass and lower-midrange response helps with highlighting the sub-bass and is part of the reason why the bass sounds as controlled as it is. Unfortunately this means that the FDX1 is not an IEM I would describe as “rich”, “smooth” or even “musical”, whatever that’s supposed to mean. The FDX1 is not an IEM I’d reach for when I’m feeling like listening to Sinatra or some of my cello-heavy orchestral tracks for instance, not really conveying the sense of weight in the notes that these tracks require for my definition of the full experience. Imaging is also average in the grand scheme of things, with neither the soundstage size nor positional cues impressing me. Again though, something like 80% of IEMs have “average imaging” to me so this isn’t really a problem for me or most people.

A minor nitpick from a timbral standpoint: the decay could use just a little bit more linger. Just some extra reverb to put some meat on those bones, but it’s really a very minor criticism that I can happily do without. Though if that happened, it would certainly justify a rank upgrade…


With many Harman-tuned IEMs, I find myself making excuses for my enjoyment of the signature, or more specifically why I should be enjoying myself. Statements like “despite the upper-midrange emphasis” start to pop up, and the inevitable arguments about why I’m Satan for not agreeing with Harman’s research come in.

With the FDX1 there are no excuses; the pinna gain is tuned to my desired magnitude and pattern, the bass is boosted properly with zero bleed or smearing, and treble still retains sparkle and energy without being anywhere close to sibilance or harshness. From a tonal perspective, it’s as good as it gets (for my own ears).

And of course, let’s talk technicalities. Decently quick attack and lightning fast decay results in a very detail-forward and well-defined sound. And yet, despite the transients that are almost unnatural for a DD IEM, the basslines still retain its authority and impact without any diminishment common with BA woofers. Sub-bass still comes in with plenty of rumble and weight, with the weight reducing as the drivers approach the mid-bass frequencies and higher. Yet, and this is probably my anti-BA bias talking here, even the quick bass hits of the FDX1 sound more natural than the best pure-BA IEMs I’ve heard.


The FDX1 is an amazing “technical DD” chock full of all the subjective goodies that many experienced ears hold dear, yet exquistely tuned to highlight just the right parts without offending the sensibilities of the average audiophile. Its reputation even in its early days as a mod is well-justified, and it is one hell of a blessing to have this mod now available as its own standalone product.

No doubt in my mind here, the FDX1 absolutely deserves to be the cheapest IEM in its tier right now.

Grade: A-

Big thanks to all who continue to support me on Patreon! Unfortunately the FDX1 will not be going onto the giveaway roster; it will remain as a reference IEM for future reviews.

And of course, my shoutouts to my very special big-money boys:


7 thoughts on “Drop + JVC HA-FDX1 Review: Mod Magic”

  1. Great read as always Crin , you got me a little hyped for this bad boy here .

    Will you do an in depth analysis with Acoustune HS1695 or Rai Penta if you have the opportunity?

    1. I’ve done cliffnotes on the Rai Penta here but I usually won’t go too in-depth unless I have a review unit or a long-term loaner unit.

  2. Excellent review as always, comprehensive, understandable and balanced.
    You are writing that the FD01 was noticeable peakier than the stock FDX1.
    I compared FD01 and FD02 earlier this year and had the same impression, and the FDX1 and FD02 measurements in your comparison tool look extremely similar.
    So it does seem that the FDX1 is tuned different from the FD01.

    Anyway – it was fun to read and confirmed the decision of ordering this IEM!
    Thank you!

  3. Great review, I’m just wondering though, what do you mean when you describe them as “lean”? You mentioned lesser mid-bass and lower-midrange response, are they in some way withdrawn?

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