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Review: Kozee Infinity X1 custom molded IEM

post #1 of 19
Thread Starter 







I’ve already spoken at length on this forum about the proliferation of custom molded in ear monitors, but allow me to recap. In the early days we had the pioneers of the industry - Ultimate Ears and Westone. Those were the only choices, each offered a limited selection, and the prices were very high. Contrast that with today were we have dozens of companies to choose from and plenty of choices from each brand. Prices range from under $300 to well over $1000. Whether you are shopping for an entry level custom or a high end state of the art design, you will likely find several good options from which to choose.  


Kozee Sound Solutions, a new company on the scene, offers a variety of models ranging from single driver to triple driver. They handle remolds of universal IEMs, and offer you a choice of acrylic or silicone shell construction. This would be good news all by itself since more choice is always welcome in any industry. But what makes Kozee particularly appealing in my opinion is their entry level model, the Kozee Infinity X1. Pricing starts at $140 for the standard version: single balanced armature driver inside a silicone shell, with an attached cable. Also included is a do-it-yourself impressions kit, which could potentially save you the $40-50 that it would cost to get impressions done from an audiologist. Adding $50 more gets you the “executive” upgrade: different drivers, acrylic shell, detachable cable, and extra accessories including a hard storage case and cleaning tool.


All of this is noteworthy for a few reasons: First, there has not been many options offered in the sub-$200 range, and none that I’m aware of have earned a reputation for good sound. Second, silicone shells have traditionally been a more expensive option. Some companies don’t offer them at all (Ultimate Ears, JH Audio), some have used them as an extra charge option (1964 Ears until they recently discontinued that practice), and those that use silicone exclusively tend to have somewhat higher prices (Sensaphonics, ACS). For those reasons, silicone shells have typically been considered somewhat of a “luxury”. Yet here we have a custom IEM in silicone selling for a price that rivals some single driver universal models.


Despite initially wanting to try the basic model, Adam Palmquist (president of Kozee) suggested I get the upgraded Executive version. He said it offered improved frequency response on both ends in exchange for slightly less isolation. I don’t generally find that I need extreme isolation so that was not an issue for me. With that choice being made, I waited for the impression kit to be sent so I could get started.


I feel it is relevant to include a timeline for my order. This will factor in to the conclusions of my review.


January 14 – impression kit mailed from Kozee to me


January 19 – received impression kit in the mail


January 21 – impressions completed and sent back to Kozee


March 9 – completed customs received from Kozee


April 13 – sent customs back to Kozee to fix minor error on art and check performance


June 16 – completed customs received from Kozee


As you can see, there was a 6-8 week waiting period both times. This seems consistent with the experiences of other Kozee customers. I’ll discuss this later.











The X1 in the name stands for single driver. Kozee offers the X2 and X3 which are dual and triple driver models respectively. I’m not familiar with anyone posting impressions of the X2, but user Average_Joe has the X3 and has done a detailed review. Here is a link: http://www.head-fi.org/forum/thread/543326/kozee-sound-solutions-custom-iems-reshell-appreciation-thread-with-reviews-x3-reshelled-tf10


Just for the record, Joe is an excellent resource for custom IEM information and I highly recommend you check out his threads if you are interested in customs. Another great HeadFi member is ljokerl, who has also done a review of the X1. Here is a link:



That is an obscenely large thread so you’ll have to search for the X1. I made sure to stay away from his post until I had all my listening notes completed. It turns out we hear the X1 in the same way and both enjoy it.


But back to the design – The X1 uses a single full range balanced armature driver to cover the entire spectrum. The specific driver used is a Knowles Acoustics 28507. The driver is vented which facilitates better low frequency response. Looking closely, you can see a small funnel shaped attachment on the back of each driver. Adam tells me it is there to help give better air flow inside the hollow acrylic shell. The silicone used in the standard version does not allow for this tuning. Further tuning is accomplished through the use of acoustic dampers, and specific tailoring of the bore length and diameter of the sound tubes. Interestingly, I found the datasheet of this driver online, and it did not look like it would be a good candidate for this type of application. It shows the frequency response basically dropping off above 6kHz. The datasheet says this testing was with "no damping". I played some test tones and was getting clear signal playback at 12kHz, and it was still a little audible even above 15kHz. So obviously Kozee has tuned this driver to take full advantage of it. Adam also mentioned that in his experience Knowles is somewhat conservative with their driver ratings. Maybe they use a “worst case scenario” type of test, or maybe the datasheet I found was from an earlier version of the driver (it says Revision A). The datasheet does not show low frequency response down into the double digits so it was not useful in that respect. It does show the driver as having a 30 ohm impedance, but I see a resistor in the wiring prior to the driver so the total load could be somewhat different.


Externally, the X1 is a traditional looking custom IEM. Like my Westone AC2 it has a single bore that fires sound into the ear. The cables are standard detachable style, and appear to be very similar to the older Ultimate Ears cables. The only minor difference is the memory wire section which seems a few inches longer than other cables I’ve seen. I found it to be a minor annoyance at times but for the most part it didn’t matter. These cables are interchangeable with those from my other customs (except LiveWires). It’s nice to know that buying this sub-$200 budget custom gets you basically the same cable as a top of the line custom would include.
















I was somewhat surprised at how nice the X1 is overall in terms of build quality. I’m very pleased with the way my translucent blue shells turned out, and the white Kozee logos (which I imagine are optional) really pop against the blue background. Looking inside the shell, I see no evidence of any flaws; no bubbles, or haze, or cloudiness, or rought spots, or any of the other potential custom IEM issues. It might have something to do with a single driver being less complex than a multi driver, and therefore being less of a challenge in those areas. Or it might just be competent work on the part of Kozee.


While their clarity can match that of my more expensive customs, there is a notable difference in the feel of the X1. It is very lightweight, which could partially be explained by the driver count. But it also seems to have a different feel, almost as if it was less dense or a different material altogether compares to my others. This is not a good or bad thing just different. Also it seems to have less of an external polish compared to something like a Unique Melody custom which has a nice shine to it. Again, this is not necessarily a bad thing.


My particular X1 has a great fit. It found it very easy to do the impressions myself, but I have been doing my own for a while so I might not be a good example. I really do think it is at least worth trying though. Since the kit is included in the price, and there is enough impression material to allow for mistakes, it really couldn’t hurt. Obviously each person has their own comfort level when it comes to this sort of thing, but I think some people will find it surprisingly easy to do. I personally find that I can get consistently great results, which is not something that I’ve experienced by going to an audiologist. Clearly this is a “Your Mileage May Vary” situation.


One difference between these and my other customs is that the fit is not very deep. I know I made my impressions much deeper than this, but for whatever reason Kozee went with a somewhat shallow insertion. At first I was a little disappointed but I’ve grown to love them and now I’m glad they are this way. I often have difficulty using a deep fitting custom in the morning, probably due to the hot shower slightly tightening the pores of my skin, and the X1 is my most comfortable option. Even during normal use I appreciate how easy they are to slip in and out. They still get a good seal and isolate well enough, although the shallow insertion combined with the thin shell means that isolation less than other customs. This again is probably different for each user, but I’d say that the standard silicone version would probably be the better choice for someone who demands extreme isolation.


I do need to mention one issue – when I first got them, the “Kozee” lettering on one side was slightly off. I captured it in the pictures: it looks like it was somehow scratched or damaged at some point, although I don’t see how this would have occurred during shipping. I sent it back to be fixed and it looks perfect the second time around.

















For a budget product the X1 seems reasonably complete as a total package. It includes the actual IEMs and cables, a semi-hard shell storage case, the ubiquitous custom IEM cleaning tool, a user guide which is actually more like a brochure for the company, and your impressions. All of this fits in a decent looking box which slides open one each side. I like the fact that they return the impressions, and having purchased some more expensive customs in the past that came with very little, I appreciate the small touches from Kozee.









Here is the associated equipment I used to evaluate the Kozee Infinity X1:


Source: Squeezebox Touch, Sansa Fuze or Clip+, QLS QA350


DAC: Anedio D1, Audio GD Reference 7, Gigawork DAC


AMP: Violectric V200, Analog Design Labs Svetlana 2, TCG T-Box, Audinst AMP-HP


Cables: Beat Audio Cronus, Beat Audio Supreme Rose


I burned in the X1 for over a hundred hours before giving it any serious listening. I used about a 50/50 mix of home listening on the higher end gear and portable listening with modest equipment. Yes, I do realize the irony of using a $190 IEM with a $290 cable.















First off I have to explain my initial experience with the X1. My very first impression was that it sounded surprisingly full range. It was clearly a mid range oriented sound but with decent bass impact and fairly nice soundstage presentation. But the upper mids and treble region were rather harsh. Too harsh in fact. I listened for a while and determined that it was just not acceptable; basically anything with even mildly distorted guitar sounded like it was overloading the driver. And certain voices did the same thing – shrill, harsh, almost breaking up at any sort of moderate listening level. I could tame it a little with EQ and by playing at low volume levels, but I didn’t think I should have to. Since my art needed a touchup on one side anyway, I asked Adam to check the drivers and see if maybe something was defective. He agreed to check on them because that description didn’t match the design of the X1 or the experience of other X1 users. So I sent them back and waited.


I did not have any communication with Adam once I mailed my customs back to him. They just turned up in the mail roughly 2 months after I had sent them off. So I didn’t know what exactly he had done to them. The art looked perfect but that’s all I could tell by looking at them. Upon listening, things seemed much better to me – I was no longer getting that “glare” that had bothered me prior. And this was determined while listening to the same exact equipment and music as before.


Eventually I sent Adam an email inquiring about what the problem had been. To my surprise he answered that they had not done anything to them other than fix the art – everything else appeared to be in perfect working order. Wow.


Those of you who are familiar with me and my style know that I’m somewhat of a skeptic. I don’t believe in fancy cables, or extensive changes during hundreds of hours of burn in, or most things that qualify as “tweaks” in the audiophile community. Yet I found myself discerning a fairly large difference in sound when nothing really changed at all. I find this interesting on a number of levels. First, it shows that no matter how experienced or well intentioned a reviewer might be we are all capable of making mistakes, and are all subject to confirmation bias, placebo, and other effects that impact what we hear (or don’t hear). Second, it helps me better understand people who swear they hear changes or improvements that there is no scientific explanation for. I realize that certain readers could take that last statement as insulting or dismissive, but I don’t mean it that way at all. We are all fallible, myself included.


With that story told, I’ll continue my description of the sound. My general opinion remains similar as far as overall sound signature. It is still fairly mid-range oriented, bass is fairly fast and tight, upper mids and highs are smoother than I had perceived before but still not completely grain free. I’m enjoying them much more than I had before the “fix”.


I describe the bass performance as pretty impressive considering the single full range driver being used. It doesn’t hit extremely low, so there isn’t much rumble to it. But there is a certain amount of punch that can be fairly satisfying. Still, these are not recommended for people who love huge bass, although I’m not sure I can think of a single driver armature based IEM that would fit that description very well. Overall I find that the bass is good enough for most genres but at times it fails to satisfy with certain electronic music, hip hop, and metal. You can tease a little more impact out of it if you have a good EQ on your device, but it won’t magically change the overall performance. The sound reminds me of a pretty good bookshelf speaker of medium to larger size. Like the X1, those will usually get you solid bass at least down to 50Hz, and then start dropping off from there. By the time you get below 40Hz there usually isn’t much sound being generated. Contrast that with most higher end full size speakers that have strong output down to the low 30Hz range, or sometimes even lower. Those are better represented by high end custom IEMs.


Despite being mid-range focused, there is no sweetness to be found here. The X1 handles mids in a neutral even handed manner that for some will be described as “accurate” and for others “boring”. I personally like what I hear: it might not be the last word in fun, and it certainly doesn’t help a bad recording sound better, but feed it a good track and it will reproduce it accurately. In this respect it reminds me a lot of the various Etymotic models. I still think the classic ER4S does some things better than the X1, but it is a close competition and they are clearly in the same league. Female voices sound very good on the X1, with male voices also sounding good but occasionally a little thin. I still find them enjoyable though, and in general I find that I’m not missing much here even compared to mid priced customs. Listening to Alison Krauss and Union Station, I find that Alison sounds a bit more realistic than Dan Tyminski but both are very listenable. And the Dobro as played by Jerry Douglas is very engaging.


I find myself enjoying the highs now, despite my earlier issues. It definitely has a bit of a spotlight on it, so if that isn’t something you enjoy then you might look elsewhere. There remains a bit of edginess but it isn’t anything worse than you might find in a low to mid range Grado. The highs give a nice sense of realism, and there is a good amount of air there despite a mild roll-off. But in every day use the X1 acquits itself quite well. Percussion instruments like cymbals and triangles had a good amount of sparkle without sounding overcooked, and that harshness I had heard (or thought I heard) was largely absent. I am now able to listen to bands like Thrice, Taking Back Sunday, Dead Poetic, or Jimmy Eat World without being overwhelmed by the distortion.


Soundstage is very competitive as well. It seems at least on the level of an upper-mid range universal IEM. While the stage is decently large, all out size is somewhat eschewed in favor of a more intimate and immediate presentation. Imaging has good precision and there is a mostly clear distinction between each performer. In this respect I think it is just a hair behind the Ultimate Ears UE4pro which has double the drivers and costs twice the price.


I do not think the X1 requires a dedicated amplifier. It does show a small benefit from using an amp, and of course a cleaner source will show compared to a mediocre one. But something like a Sansa Fuze should be good enough to extract most of the potential from the X1.


I have not experienced the non-executive version, so I can’t really say which option is the best value. Silicon shells do have their advantages, but so do vented drivers and detachable cables. So it remains a personal choice.








Ultimate Ears SuperFi 3

In some ways this is not a fair comparison. The venerable SF3 has been around for many years and is very long in the tooth. But it did originally cost over $100 and it does use a single balanced armature driver. So in that respect it could be considered competition. But it isn’t. The X1 runs circles around it in terms of resolution, bass clarity, coherency, and pretty much every other description you can think of. I actually still use the SF3 once in a while just for kicks, and after a while I usually get used to the sound and start enjoying it. But there really is no contest. My least favorite part is the collapsed soundstage and uncontrolled bass compared to the X1. I rarely use language this strong, but it truly is a case of “night and day” difference.


Shure SE310

The SE310 is probably my favorite single driver armature based IEM. With a huge caveat: it is nearly impossible for me to get a good fit. Even using the same tips I might only achieve the perfect fit 2 out of 5 times, and anything less than the perfect fit results in lackluster performance. I can absolutely see why these have had such mixed reviews. John Atkinson of Stereophile really enjoyed them, but they didn’t get much love around HeadFi. While I admit that some people may have genuinely disliked the sound, I suspect most never experienced the SE310s full potential.


Based purely on sound (assuming I had that elusive perfect fit) I have a hard time deciding which I like more. The Shures have the edge when it comes to linear bass response below 50Hz. Vocals come across as slightly less focused, and I generally prefer the X1 in that area. Both have similar soundstage performance, with the X1 having just a touch more air. The Shures seem smoother when it comes to micro detail presentation. They tend to occasionally blur little details, while the X1 brings them out more. Sometimes this is desirable and other times it is not. Overall I think I prefer the sound of the X1 75% of the time and the SE310 the remaining 25%. Keep in mind that these Shures sold for $299 when they were first released.



I don’t have a ton of experience with single driver BA IEMs. I have heard the Phonak PFE and the Sleek SA6 but it has been a long time. For what it’s worth I think the Kozee X1 is at least in the same league as those, again from my limited experience.


Moving up the line of customs, the next cheapest models I own all cost twice as much as the X1. The Westone AC2, Ultimate Ears UE4pro, 1964 Ears 1964-T and LiveWires Trips all have significantly higher resolution, with deeper bass extension, more treble detail, and an overall fuller sound. All of them are a significant upgrade from the X1. I don’t want to give the wrong impression – the X1 is very good for the price, but it isn’t a giant killer. The dual driver Kozee Infinity X2 might well compete with those models for $100 less, but I can’t say for sure.


The other possibility is of course the used market. There are plenty of choices in the sub- $200 category – UE TripleFi 10, Monster Turbine Pro Copper, various HiFiMan IEMs, etc. Some of these might be preferable to the X1 depending on what sort of sound the listener prefers. But of course none of them will offer the comfort of a custom molded IEM.


There is also the option of remolding an existing BA IEM into a custom, which can be done through Kozee or other companies. But by the time you pay for the IEM and the remold, you quickly match or exceed the price of the X1. You may or not get better sound, and of course you no longer would have any warranty.




This may read like a somewhat negative review. That is absolutely not the case. Frankly I’m rather impressed by the sound produced by the X1. If this was a universal IEM I’d say it was fairly average for the price; competitive but not quite a standout product, an option to consider for fans of this type of sound. The fact that it is a custom molded IEM changes everything though.


Rarely will you even find a cable of this caliber at the sub-$200 price range. Rarer still will it be easily replaceable. It’s nice that Kozee didn’t skimp on any of these details. From the build quality to the included accessories, the X1 gives up very little compared to its higher priced custom molded competitors. Combined with sound quality that could be described as top class for a single BA driver design, the X1 makes a compelling case for itself.


There is one significant thing that I have to mention: Kozee has been less than perfect with regards to customer service. I personally have always gotten a pleasant and informative reply to every email I’ve sent, usually within a day or two. But multiple people have posted that they are not getting any replies at all. Adam from Kozee has himself posted on HeadFi, admitting that they are overwhelmed with orders and not able to fill them anywhere near as quickly as they would like. He apologized for the inconvenience, stated they had a new system in place for streamlining the process, and expressed dedication to improving the buying experience. That was welcome information, but it was posted over a month ago. As of today, people are still complaining of 8+ weeks worth of wait time and emails going repeatedly unanswered. My dealings with Adam have convinced me that he is genuine and absolutely does want to get things on the right track with this new business. But unfortunately we have to judge results rather than intentions and so far the results are not improving. I would love to see Kozee thrive and become a larger, well respected player in the custom IEM world. I think they have the knowledge and the skill to do so, if they can just manage the process well enough.


So there you have it: the X1 is a very nice product with a potentially difficult purchasing experience. If someone is fully prepared to wait a few months for their order, and then possibly wait a few months more if a refit is needed, then I can wholeheartedly recommend the Kozee Infinity X1. Perhaps they would be pleasantly surprised with a much shorter wait time.




Edited by project86 - 7/12/11 at 3:34pm
post #2 of 19



EDIT: Just finished the read. Excellent write-up! I read it with the sole intent of getting an idea of where Kozee stands with regards to build and SQ, since my JH16's have been in their trusted hands for over 3 weeks now. I admire the fact that you did not fail to mention any "drawbacks" you encountered with Kozee or the X1. Thank you for all your efforts my friend, much appreciated! smile.gif

Edited by i2ehan - 7/12/11 at 4:52pm
post #3 of 19
Thread Starter 

Of course! I have to mention the good and the bad so people know what to expect. I honestly do think that Adam/Kozee has the best intentions, and I really hope they can get to a point where they are surprising people with shorter wait times. 

post #4 of 19

Nice detailed review. Great picutures! Thanks

As for the frequency charts provided by Knolwes. It all comes down to measuring equipment. Depending on coupler results will vary. And what's more important your ear will perceive different than any testing equipment. Simply put measuring gear is imperfect and thus you can't rely only on graphs.

post #5 of 19

look interesting and very tempted to get it. By any chance you try it out with any classical music?

post #6 of 19
Thread Starter 
Originally Posted by Ronald Lee View Post

look interesting and very tempted to get it. By any chance you try it out with any classical music?

I have. It is not overwhelmingly amazing, but still very competent. They are fairly fast and have a good balance. Albeniz: Suite Espanola (Rafael Fruhbeck de Burgos, XRCD release) is a good test for brightness. The X1 comes across well, with only a bit of harshness on the occasional very loud horn sections. Soundstage is reasonably wide too which obviously suites the genre. Listen to something like The Planets (Holst) to hear the main drawback  - a lack of dynamics and weight compared to better headphones. I see it as a trade off though, since under $200 you likely won't get everything you want, even in a universal IEM. 

post #7 of 19



Im currently using my Phonak PFE and HJE900 and thinking of selling both and getting a budget custom (probably single driver) was wondering if you had either of these to compare with?  Also dont know if it was the ZO thread of Fiio X3 thread i saw you on but how do the X1's sound if you have the ZO.


Thanks mate its an excellent write up you made there, gives me food for thought.

post #8 of 19
Thread Starter 
Originally Posted by stozzer123 View Post



Im currently using my Phonak PFE and HJE900 and thinking of selling both and getting a budget custom (probably single driver) was wondering if you had either of these to compare with?  Also dont know if it was the ZO thread of Fiio X3 thread i saw you on but how do the X1's sound if you have the ZO.


Thanks mate its an excellent write up you made there, gives me food for thought.

I don't think I can recommend Kozee at this point. Until we start seeing some big increases in customer satisfaction, I just can't send anyone to them knowing it will probably become a hassle.


If maybe 4 or 5 people came forward in the next month documenting a clean experience from start to finish, with solid communication the whole time, and less than 4 weeks total wait time, I would probably be able to recommend them again. The product itself is good, it's just the other stuff that needs lots of work. 


post #9 of 19

How is it you do your own ear impressions at home? tongue_smile.gif

post #10 of 19

theres some youtube videos, i also think there might be one from kozee as well.


Im emailing back and forth with them right now.  Seems snappy enough and helpful response, they did mention that they do have some troubles as the are a new company etc.


Does anyone know which would be likely higher bass, the acrylic or silicone.


Im actually just wanting a custom with a warm bassy sound (not balanced), its mainly for the comfort and isolation while traveling listening to EBM and industrial tracks.  Iv got my pfe when I want analytical and my hje900 with the ZO for boom but would like an extremely isolated iem with similar charactaristics as my third option.

post #11 of 19

forgot to mention i might be willing to go guinee pig on this one for you folk.

post #12 of 19

they dont so silicone anymore

post #13 of 19
Thread Starter 

Guinea pig? Go for it, as long as it is a spare $200 that you are willing to risk. Maybe risk is the wrong word..... you won't get scammed or anything, it just may take forever to get the product, or you may end up with unresolved issues. If that sounds like it might be worth it then by all means let us know how it turns out. I'd go for silicone if you are most concerned about isolation, and acrylic if you want the most bass. It still isn't what I'd specifically call a "bassy" sound though, overall. 


Adam is a super nice guy and I believe his heart is in the right place, but now is the time for actions rather than words.


By the way, I think it is just the silicone with detachable cable that Kozee isn't doing any longer. They should still have a normal silicone version. 1964 Ears stopped offering silicone, maybe that's what you are thinking of? 

post #14 of 19

Yeh its more of a case of willing to wait pretty sure they will get there eventually, since im used to waiting months for parts for custom watches i make im sure id be ok with it, 


Since they are not going to be primarily for the sq more for isolation and comfort id probably go for the silicone (costs less also) and pair it with the zo for the added base.


Will have a few more back and forths with adam before i make a decision though.

post #15 of 19

Can anyone tell me how this compares to another popular portable headphone like the HD25-1 II? I understand they are different in a lot of ways but can someone suggest one for vocal based indie music? Also, what about similarly priced universals, i.e. the Westone 2s or the Triple Fi 10s?

Edited by Herky151 - 10/11/11 at 7:09pm
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