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Perfect Seal Fusion 11 silicone hybrid custom in-ear monitor

World’s first silicone shelled hybrid custom in-ear monitor: The Fusion 11 by Perfect Seal

Perfect Seal has made the world’s first silicone shelled hybrid custom in-ear monitor, the Fusion 11. The silicone shell houses a 10mm dynamic bass driver and ED balanced armature with a large sound tube. Bass levels can be changed by swapping between one of 5 tuning plugs, or leaving the port open, ranging from flat to thunderous.  Phase coherence was one of the design criteria and a quick listen verifies the drivers are well integrated and coherent.


The Perfect Seal Fusion 11 uses a detachable Linum cable, which is ultra-thin and very strong, and the Fusion 11 uses the T2 connector option, which is the smallest offering.  MMCX and 2-pin designs are in the works.  Cable info:

  • Six litz conductors made up of 7 individual strands
  • Silver plated copper strands with an enamel coating
  • TPA jacket that won’t discolor
  • Pull force of 60 Newtons (equal to 13.5 lbf or 6 kgf)

Pricing is set at $499.  Pricing is not yet known, but it is slated to be less than $500.


The Perfect Seal Fusion 11 is the first silicone shelled hybrid CIEM, and that is pretty cool by itself.  But, when listening there were several things that jumped out at me and made me grab some of the top-tier CIEMs for comparison.  The first is tonal balance, which is spot on, and a close second is the coherence between drivers, which is significantly better than the other dynamic + ED hybrid I have, the Thousand Sound TS842.

The bass quantity can be adjusted by changing out plugs, and there are 5 different settings to choose from (for now).  While the solid plug has quite a neutral sound to it, the deep bass is a bit rolled-off, and the next plug up in bass quantity, the yellow filtered plug, has bass that is north of neutral.  The red filter, small hole ports, and completely open all add bass quantity, with the amount increasing in that order.  I found myself listening primarily to the yellow filter but would prefer the solid plug if the deep bass had more weight.

The midrange and treble are very neutral and reminiscent of the much more expensive Lear LCM BD4.2 in linearity, but not as detailed and with a very different presentation perspective.  While the Lear presents from a distance with a large space, the Fusion 11 presents much more forward perspective similar to a stage monitor sound.  Switching back and forth did not leave me wanting from either.  The presentation perspective is reminiscent of EarSonics products, and the EM4 is quite close.




Comparing the Fusion 11 with the Heir Audio 8.A, the tone sounds more balanced with less bass emphasis (yellow filtered plug) and more treble emphasis leading to better clarity and a more natural tonality.  Even though the Fusion 11 is a hybrid, it has better coherence and transparency, and the soundstage recreation is more linear.  Compared with the Lime Ears LE3B, the Fusion 11 offers better clarity, transparency, and coherence for a better listening experience.

Comparing the Fusion 11 with the Alclair Reference, the the Fusion 11 sounds more open, natural, clear, and precise.  The midrange presentation is slightly more laid-back, but the more 3D and coherence between other parts of the spectrum is much better on the Fusion 11.  The bass quantity with the neutral bass ports is similar to the Reference, but the Fusion 11 is much more capable in the bass region.  The upper midrange of the Reference is a bit more prominent while the treble is slightly more prominent from the Fusion 11 and smoother.  The clarity within the soundstage is superior from the Fusion 11 and details are easier to make out even though the Reference articulates notes (omre focus on individual notes) than the Fusion 11.  When A/Bing these two, the Fusion 11 sounds like a higher class of CIEM.

The Fusion 11  performs closer to the EarSonics EM4 from a technical standpoint, but the tonality is different as the Fusion 11 is brighter and not quite as smooth.   Comparing with a new flagship such as the Hidition Viento-R, the Fusion 11 doesn’t quite perform at the same level, but the fact that I can switch between the two and not be disappointed with the Fusion 11 says something.

Minerva Mi-Artist Pro: The Fusion 11 is brighter and more spacious than the forward and warmer Artist Pro.  Soundstage size of the Fusion 11 is larger with better imaging and much better focus.  Notes of the Fusion 11 are more concise with better ADSR performance and detail articulation.  Detail levels of the Fusion 11 are higher to go with better clarity and dynamics, transparency, and coherence for a much more revealing sound.  While the Fusion 11 is brighter and more resolving, neither is necessarily more forgiving of poor quality tracks.

Since the bass of the Fusion 11 is tunable with interchangeable ports, the quantity can be more or less than the Artist Pro, but the ability to sustain notes is far greater from the Fusion 11.  The midrange clarity is quite different as the Fusion 11 sound much more open, resolving, detailed, and places instruments within the soundstage more precisely while the Artist Pro is more personal and in-the-head.  The upper midrange and treble of the Fusion 11 are more prominent, with more natural note recreation.

The Artist Pro offers ease of purchase for those in the UK, but the Fusion 11 offers much better value with a lower price and significantly higher performance. If you want to hear more detail, a more open sound, and the ability to have bass that is thumping, neutral, or somewhere between, the Fusion 11 will do it.  If you want a more personal performance with good capability and ease of purchase in the UK market, the Artist Pro is a good choice.


Perfect Seal SportBud Silver: The Fusion 11 (with the yellow bass ports) has a more laid-back and neutral presentation in comparison with the upfront and punchy SportBud Silver (SS).  The larger presentation space of the Fusion 11 gives a more 3D feel along with a better sense of air while the SS has a bit more in-the-head feel.  Notes are very different as the SS has a quicker average attack and longer decay for a punchier yet thicker sound overall.  The Fusion 11 owns the SS in technical performance with superior dynamic range, transparency, coherence, clarity, resolution within the soundstage is higher, and detail levels, if even by a small margin.

The bass of the SS is turned up in comparison with the Fusion 11 with the yellow port and has a good amount of note sustainment capability, only showing weakness at moderate volume and with tracks that have massive amounts of bass.  However, with a different port, the Fusion 11 bass can easily decimate that of the SS in both quality and quality.  Midrange presentation is quite different, as the SS sounds smaller and more forward with an in-the-head feel compared to the laid-back and more 3D Fusion 11.  Treble is similar in quantity, but the Fusion 11’s more laid-back presentation and smoother, more refined treble gives a perception of less.

These two are quite different in sound signature as the SportBud Silver is upfront, punchy, bass heavy, and immediate compared with the more neutral, refined, and natural Fusion 11.  Also, the Fusion 11 does cost double that of the SS, so they really don’t compete with each other.  The choice between comes down to cost, usage, and sound signature preferences, but getting both will provide a nice compliment.


InEarz IE-P250: The P250 presents with a much more up-front perspective in comparison with the Fusion 11, which images better within a larger, more 3D space and brings the presentation into better focus.  The extra space results in better instrument separation for the Fusion 11 and the better proportions result in an overall cleaner sound.  While frequency response is somewhat similar, the Fusion 11 (with the yellow filters) has plenty more bass presence and capability while sounding more natural in general.  Warmth is similar, but the notes of the Fusion 11 have a faster overall response resulting in a clearer presentation.  Other than note and presentation differences, the Fusion 11 has a more natural tone in the presence area (upper midrange), which makes the P250 sound thick in comparison to the airy Fusion 11.  Treble notes of the Fusion 11 are smoother with a more natural decay and more accurate leading edge.

The P250 presents details more readily, but due to the better note capability of the Fusion 11 and the superior imaging, the Fusion 11 is more detailed overall with better resolution within the soundstage.  While the P250 stands its ground with other $500 and below CIEMs, the Fusion 11 is an outlier that readily outperforms the P250.


EarSonics Velvet: Using the DX80 as a source, here is a list of the differences between the Fusion 11 and Velvet with the bass settings similar (minimum on the Velvet, netural ports on the F11):

  • The F11 is more forward with a smaller overall average space
  • The Velvet’s more spacious soundstage has similar presentation depth but better presentation resolution and more air
  • The F11 is clearer, most likely due to the Velvet’s lower presence in the upper midrange
  • The Velvet notes are slightly smoother
  • The F11 instrument detail is more articulated
  • The F11 silicon custom fits more comfortably and provides more isolation than the Velvet
  • The Velvet is more flush fitting
  • With the bass on the lowest setting, the Velvet has more deep bass quantity than the F11 but the F11 can sustain the deepest bass notes better
  • The F11 has a bit more effortless with slightly better dynamic range

I don’t find the F11 to be fatiguing, but the Velvet is less so, and I also find the Velvet to be a bit more musical overall.


The Fusion 11 is an exceptional performer for the price, with a beautiful blend of dynamic and BA drivers.  While technical performance is bested by CIEMs that cost double to quadruple, the natural tone of the F11 allows me to keep them in my ears shortly after listening to a heavyweight, which is a first for anything in the price category.  They make a great starter CIEM, but be careful because it is a long way to the next step up!

« View Fusion 11 in the List

Use the contact form on the Perfect Seal order page for more information or to place your order.





Having a life-long love of high-quality audio and gadgets, average_joe got back in touch with his audiophile side after a hiatus caused by life. His focus became headphones and related gear as the size and price fit his life better than home audio. He believes the entire audio chain is important, and likes to continue to think past the headphone and on into the head, as he believes understanding the details of how we hear will lead to a better audio experience.


30 Responses

  1. How would you compare the fusion 11 with perfect seal AR4 or AR6? I’ve been told I may not be able to get fusion 11s due to my small ears and the AR4 has been suggested as an alternative.

  2. Hi Patrick, I added a comparison in the above write-up. I hope it helps with your decision.



  3. Hi,
    just read your short review about the fusion 11 and got curious how they compare to the earsonics velvet?
    Including the earprints and customs they come down to the same price for me.
    I am looking for outsanding clarity, resolution, a realitsic detailed ( sometimes dreamy) sound with a great sound stage.
    The bass should be invloving and present, impactfull, but precise, articulate and only present when intendended.
    I tried the Fidue A83 e.g. and the sound could be piercing at times in certain high ferquencies. A non-fatiguing listening experience, which allows me to crank up the sound and engage in the music or sit back and enjoy the microdetails with great spaciousness and instrument seperation would be well received on my end.
    An analytical, but engaging sound, which I mainly use for joyfull, but still critical listening and occiáisional music production.
    I know that joker is very fond of the Velvets and says that there is nearly nothing beating them at the same price point / signature, so I am curious about your response.
    Thanks in advance.

  4. Good to know. Thanks, after I get more time to mess with them I’ll see if that’s what’s going on. I agree, if so, I’ll look into improving the seal.

  5. Good to know. Thanks, after I get more time to mess with them I’ll see if that’s what’s going on. I agree, if so, I’ll look into improving the seal.

  6. I have some decent noise cancelling headphones and have auditioned the best NC headphones out there and none sound natural to me with the NC circuit on. Some make me feel like there is constant pressure, which I can’t stand. Not that they don’t have a place, but it just depends on the goal.

  7. Just because they feel good only means the shells aren’t too big. Many manufacturers make shells a bit on the smaller side , with my speculation being people will return what hurts, but may not know what doesn’t seal properly. Since you were able to get a better seal by turning/moving your ear, that indicates to me the seal needs improvement. I believe it is ultimately worth the hassle.


  8. 90% of the reason i bought these is that i’ve been told by a few sources they should have the best isolation possible.
    I guess I’ll just see on my own when they arrive in a few days.
    I really hope I’ll be pleased.
    if u manage to make them better with equalizers that would be cool. tell me pls if u do 🙂

    btw, for airplanes, since it’s a constant bassy noise you are trying to isolate, you should consider your next headphones to have active noise cancelation in them (google it). Theoretically, at least, it should be really good.

    I’m looking more to isolate high pitched sounds like cares breaking etc

  9. For average use the seal seem fine. Although for me the real test is an airplane because I like to listen to music there and its loud. I found its actually not as good as some non-custom IEMs I’ve used, which surprised me. However, its definitely a lot more comfortable since the non-custom’s I usually have to wedge in and they cause too much pressure, so its a tradeoff. I didn’t think about average_joe’s comment that maybe my fit isn’t optimal. It does feel good, but I have no basis for comparison.

    I tried pushing them in a bit more but don’t feel like the seal or base changes much, although a little turning and moving of my ear did seem to help the seal a bit. Also, I’m playing around with equalizers and whatnot to see if that’s having an effect on bass quality.

    I don’t think they have another silicone. I’ll definitely play around to make sure I’m getting a good fit.

  10. I just ordered them (they haven’t arrived yet) and I do like a strong bass.
    Did you find any solution to your problem?

    The reason I ordered them is because I need the isolation good CIEMs offer. how good do they isolate external noises?

  11. Thanks for sharing and sorry to hear about the issue. To me it sounds like you may have a bad seal. Can you push and hold the CIEMs in your ears (deeper) and get better bass?

    If that doesn’t fix them, I would definitely recommend exchanging them, even if for another silicone shelled set just to try. As far as acrylic vs. silicone comfort, there really isn’t a big difference if the fit is good, and the biggest difference is on removal.

    Bottom line is you paid for them and if there is something wrong with the fit, it is worth getting fixed.

    Cheers, Joe

  12. I’ve had the headphones for a while so I thought I’d leave a comment. They do still generally fit comfortably, however, my biggest issues is that I think the bass is too light (despite using the tuning ports to keep the bass at its highest). I’m not really a basshead either. So light in fact that I think most music feels hollow when compared to other sources that I listen on. This goes even for songs that aren’t heavy in bass, like instrumental. While the quality sounded fine to me, I actually thought of exchanging these, which he did offer, but I was worried an acrylic might not be as comfortable so I stuck with these. I like the idea of custom fit, so I think at some point I’ll definitely want another pair with more bass. Otherwise, as far as my ears can tell, the quality and sound signature is what was described here. If anyone has any suggestions along these lines, I’m all ears.

  13. ok i fully read the thing and now I understand. my lack of understanding came from lack of knowledge about reflectance. ty

  14. As what I’m hearing now are 10$ sony earphones, I’m sure acoustically I’ll be pleased. I’m hoping the fit, isolation and durability would prove great.

    Oh I understand completely that high frequency sound decays much faster. my question is whether it’s possible to have a block that would selectively block higher frequencies.

  15. To my ears, for the price, they are an excellent choice and I am looking forward to your thoughts.

    This question & answer on answers the question in great detail. The short answer is higher frequencies attenuate in the atmosphere more than lower frequencies. While I don’t know your definition of “significant difference” for your two room question, the answer is yes. Play a radio in a room, open the window, and go outside and see how it sounds.



  16. Nah I just ordered them and am anxious that I made the right decision cause it costs a serious lot (for me anyway). they have the best isolation/price ration in your chart (that is why I chose them).

    I have a question in Physics though: how come some ear plugs are claimed to block more of the high frequencies than the lows? how is that possible? I understand that high-frequency sound fades much faster because of longer cycles (lower energy loss over time).

    If I have
    Room A —- block —- room B
    and I make a white sound (all frequencies) in room A, and the distance between room A and Room B isn’t very far, could there be a significant difference between the recorded sound in room B and in different frequencies?

  17. Unfortunately I don’t currently have the time to write a full review like I used to. I do have comparisons and a summarized version of my typical review. Let me know if you have specific questions.

  18. Hi kym, the TF10 has a V-shaped signature while the SM3 has somewhat of the opposite signature, with a forward midrange. While the Fusion-11 has a V-shape, but the midrange isn’t recessed nearly as much as that of the TF10, and with the adjustable bass, the response can get relatively flat.

    I attribute the listening fatigue of the TF10 to the bright presentation and sharper notes, and while the F11 is V-shaped, the notes are much smoother, closer to the SM3. From a performance standpoint, the F11 is a significant upgrade and I would agree it is a better investment vs. reshelling either the TF10 or SM3.



  19. average_joe,

    You mention that the fusion 11 has a V-shaped signature. How does it compare to the TF10s or earsonic SM3? I have both and while I like the bass of the TF10 I find the SM3s easier to listen to over a long period (the sound is less tiring rather than the fit). I’ve thought of reshelling the TF10 but I’m questioning the wisdom of doing this for IEMs that are getting old. Buying a set of CIEMs with the latest technology seems to be a better investment.

  20. Hi Rohit, thanks for sharing and glad they will become a new staple. Please feel free to share additional thoughts after you have had more time with them.



  21. Just received them, haven’t used them much but they seem great. Very comfortable, good fit, nice sound. I think they’re going to be a new staple in my daily messenger bag. Thanks for the suggestion and the helpful website!

  22. Hi Rohit,

    Everything should turn out great! Please let me know what you think once you get it and/or after you have had some time to get used to it.



  23. Thanks again. That was all very helpful. I’m going with the fusion 11 considering all the factors. Wish me luck.

  24. Hi Rohit,

    A no return policy is standard for most CIEM manufacturers since they can’t resell the CIEM they make for you, and it is time consuming to make your set. They work with customers to resolve issues with fit and/or sound.

    If you don’t like the sound signature there is little they can do except adjust the tuning or exchange for a different model. Many manufacturers won’t adjust the tuning, and an exchange for a different model will be at the manufacture’s discretion and could incur additional costs.

    There are very few lower cost alternatives, and actually one one that uses a silicone shell (by Custom Art), but the sound signature and capability is quite different. If you want to start with a lower cost alternative and get closer in sound signature, take a look at the AAW lineup, but the cost savings aren’t great.



  25. Thanks for the great reply. As for working out, I’m not sure how much I sweat and how much that would affect that but I’m willing to just try and see if they work.

    I have one other concern: They say they won’t allow returns. I don’t know what’s standard for this kind of purchase. Considering I’m not an audiophile and I already know i like this sound signature I think $500 CIEMs will probably sound fine to me. I’m just not sure if I’ll have any other concerns (fit? comfort? other?).

    One thought I have is to buy cheap(er) CIEMs that might be representative of this type of fit/material/etc. Then if I like them I’ll just buy these if i want the improved audio quality.

    Would you have any suggestions along those lines?

    Thanks again.

  26. Hi Rohit,

    Thanks for the question and providing the context. The Fusion 11 is a stellar performer at the price range and has a V-shaped sound signature.
    – It works well for all the genres you mentioned.
    – There are bass ports so you can adjust the amount of bass to your liking, so chances are it won’t have too much or too little.
    – The silicone shell will provide a good level of isolation. It is ported due to the dynamic driver, but the sound leakage isn’t too much in my experience, but a non-ported acrylic shelled CIEM can provide better isolation.
    – What are the most important options? Also, if the Fusion 11 sound is truly what you are looking for, you have to double the price to get a worthwhile improvement in my experience.
    – The Fusion 11 isn’t the most beautiful thing out there and I am not sure if Perfect Seal has improved their artwork capability. They may be able to make a carbon fiber face plate, or some other exotic, nice looking material.

    If you want a bit more isolation (not too much more though), the InEarz IE-P250 would work. There is also the Thousand Sound TS842, if you can get it shipped from China. While it is good and competitive in the stock form (not quite as smooth as the Fusion 11, and no bass adjustment ability), doubling the price by adding the Whiplash TWau Reference Gold cable pushes the performance to a $1K+ CIEM level.

    My biggest concern would be using any CIEM while running. How much do you sweat? Will there be occlusion while you run (hearing your footsteps), which is anatomy dependent? Using a CIEM for working out, especially when you sweat a lot, requires extra care.

    Let me know if you have any other questions.



  27. Hello,

    I need some advice on custom IEMs. I’m not sure the best place to ask but I think this might be good. I never owned CIEMs. I had a low-mid range ultimate ears IEM and loved the clear intimate sound. I think the biggest issues I had were reliable fit (my two ears appear to be different) and comfortable fit, which impaired the passive noise cancellation which I didn’t like. So I think I’d like a CIEM. I’ve read all kinds of articles on this site and see there are a lot of factors, so I figure I might list things that I think are relevant in case anyone has some ideas for me:
    – I tried three items from this guide ( Philips SHE3590BK/28, Original Gold Xiaomi 2nd Piston Earphone, Etymotic Research ETY-Kids5. I clearly liked the philips the best and definitely didn’t like the xiamoni. The Phillips was described as V-shaped, so after going to the CIEM buyer’s guide and looking in the 300-500 range I came across this headset.

    – I listen to a variety of music including acoustic, hip/hop, alternative, etc. I do not listen to EDM, hard rock if that helps any?
    – I don’t think I’m a basshead but I wouldn’t like if its weak.
    – I tend to listen when I can lie down, generally in quiet areas. The only exceptions: I like to listen on a plane. One of the biggest reasons I like IEM is to remove as much of that terrible droning plane sound as possible. It would also be a nice perk to listen while running (my last IEM would always fall out).
    -300-500 is a good price range but I could go up or down depending on options
    -aesthetics is the last factor but all else being equal I’d pay more to get better looking headphones.

    If anyone has useful ideas/suggests/considerations I’d appreciate it. Thanks!

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