IEM Technolgies

I’m behind the times. I’ve just noticed in some discussions elsewhere on the forum talk about “multiple BA IEMs”, notably in the cheap IEM threads.

If someone would like to provide a synopsis of current tech in IEMs, I’d be interested. I’ve certainly listened to standard multi-driver IEMs, also older STAX electrostatic IEMs. Never Planars in the IEM space, and I don’t know what else is out there and what I should listen for when trying them.

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As always @Torq is the go to man here. Having only recently bought the 64 Audio U18t’s I can comment a little. Firstly they’ve packed in 18 drivers on each side with 8 Low BA drivers and 8 Mid BA drivers. The other remaining 2 drivers are the much vaunted TIA (Tubless Inear Audio) type. One being for the Mids and the other for the Highs.

As well as this they also employ their APEX (Air Pressure Exchange) technology which is said to help alleviate air pressure build up in the ear canal this minimising listening fatigue. It does this via a plug in modules (apex module) which have vents of varying sizes, depending on which module is chosen. You are supplied with 2 apex modules the m15 and the m20. The m20 offering slightly less isolation -20db hence the m20, with the m15 offering -15db. The differing modules do change sound slightly but not significantly. The m20 offers a little more bass and brings a little more to the lower mids whilst the m15 gives slightly better imaging and highs.

These are just a couple of innovations in the iem arena that have crossed my path. All in all I would say they are very successful ones too.

As for planar iem’s the only ones I have tried are the iSine 20’s. You will of course read much about this polarising iem but it really is a kind of love hate with these. The sound I loved though it is my only experience with Planar’s so I cannot compare it to others. Extremely airy and dynamic to my ear the have great bass too. The only thing that stopped me keeping them was the comfort. They’re either going to be a good fit for you or they aren’t and it was very difficult for me to get any comfort, try as I might. It was a shame as they sounded great. Also I used the Cipher cable which made a huge difference to the sound over the standard cable.

Just a few of my own thoughts on a couple of iem’s ive come across.


The overwhelming majority of in-ear products use conventional dynamic drivers or balanced armatures (BAs). As @prfallon69 said, the iSine is the most widely known planar, but @antdroid has also mentioned others too. Planar drivers are so large they are not so much “in ear” as “on ear.” Similarly, the KOSS KDE-250 you own is an on ear dynamic product.

Until the rise of Chinese audio in the last few years, “In Ear Monitor” referred to Custom (CIEM) professional products. In my experience average people spoke of dynamic driver “ear buds” and never said IEM at all.

Please see below for a 36 minute presentation about the history of IEMs and the Ultimate Ears brand. This is complimented by the Wikipedia story on Jerry Harvey and UE’s page on balanced armatures. Jerry Harvey invented IEMs but later separated from UE and founded JH Audio. In brief, IEMs came from $$$$ hearing aid technology and the need for (Alex Van Halen) stage performers to hear their own performance over the amplification.


Thanks @generic that looks a great video. I will enjoy watching it. I have seen some other interviews with him but I don’t recall seeing this one, though I may have.

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I’ve gotten the opportunity to try out a ton of different IEMs (mostly under $1000) over the past couple years and here’s my thoughts on technologies:

  1. Dynamic Drivers – still the most coherent throughout frequency range and provides the biggest punch for bass impact (in general). It’s becoming harder to find dynamic driver only in-ears now especially as you move up in price.

  2. Balanced Amarture - Really good resolution. Can be limited due to physical constraints of the driver which is why #3 is a thing

  3. Multi-BA - Pack as much drivers as you can in a single shell and market it. More isn’t always better. When done right, you get a very good resolution, coherency, and extension, but when done wrong, and happens often, you get poor cross-overs and coherency/transition is bad.

  4. Hybrids (DD+BA) – in general, I think this is a good compromise. You get the quality/quantity bass of a DD plus the resolution of the BA for the upper mids and treble. Again, cross-over matters a lot, just like a speaker system with subs and bookshelf speakers.

  5. Planar - I have enjoyed the few that are out there but they have their own substantial flaws. Luckily, low distortion and and great ability to use EQ helps these out a lot and I really do enjoy iSine and the ME1 I own. The only true IEM is the RHA CL2, which has extremely good speed, attack, and resolution, but has a massive peak in the lower treble that will really mess with the tonality and create some extreme harsh sounds if you’re sensitive there. EQ does correct it though!


and piezo-electric drivers are starting to make their way into iems as well.


And Electrostats? Still only the STAX?

Shure has electrostat IEMs but I have not tried.


What is the relationship, if any, between the size of the opening in an IEM to the ear canal and its sound? Why don’t we have firehose IEMs with 4 or 5 mm wide auditory cannon aiming in? Is it just comfort issues? Do screens or gratings protecting the opening affect the sound?

And if those questions are too normal, what goofy technologies have people tried to pack into an IEM? Looking for a ‘Micro Leslie’ IEM to listen to my Hendrix on.

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It’ll vary with size and profile of the bore and the amount of air being moved by the driver(s) inside. With some designs using a single bore and mixing in an acoustic chamber, and others using acoustic guides (tubes) to bring several separate frequencies to the exit point at the same time (since the drivers are all positioned at different distances to the port).

Oh, those exist.

Exit bore on the tia Fourté is 4.5mm, for example. That’s a single-bore design. The CA Andromeda (original) has a 5.5mm nozzle size, but it’s actually three separate bores*.

No, but in some cases it can be just to accommodate the necessary bores for the acoustic tubes/guides involved, with enough extra diameter to allow for material to make the thing solid.

They certainly can, but you can design around that. Some of the big-flat-not-very-well-machined-discs-with-random-small-holes-pocked-in-them likely block/reflect/filter more than the very open mesh/tiny-wires-spaced-fairly-wide affairs.

*Note due to the “TARDIS” effect, the original Andromeda measures 5.5mm until you put them in your ears at which point they instantly expand to 2 AUs).


Thank you. I appreciate the TARDIS effect, although I would have expected Andromeda to expand to about 110,000 light years instead of a mere 2 AU.


This is very interesting. I’m sure I’m getting into areas of design that proper IEM manufacturers take into account. First, since I see so many different exterior shapes - from barrels to the shape of say the Andromeda or Tia Forte, to Apple’s earbud shape, that I wonder if many manufacturers just make something with no design theory considered.

Second, I looked up some things on waveguides. Clearly, as we get into the mid and higher frequencies, the length of the guide will go from longer than a quarter wavelength to possibly shorter, and even the cross-section of the guide may get to be longer than a quarter wavelength.

Third - as the IEM dumps into the ear canal, what is the acoustic impedance? The ear canal itself is a waveguide. So does this create pressure, reflections, and sign changes of sound relative to what was sent? If so, is it, as I imagine quite different depending on frequency? We’re not trying to create an organ pipe here, it must be all over the place.

It’s a wonder we can hear at all…

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The exterior shape of an IEM obviously sets limits on what can be done within the shell, and how things can be arranged. And as the number of drivers increased, and/or hybrids with dynamic bass drivers became more common, the shells grew just to fit them in.

Obviously you have much more physical placement flexibility putting 4 drivers in a shell than you do if you’re squeezing in 14 or 18.

Interestingly, most recent flagship models, from the brands most notable for high-driver counts in prior iterations, have typically reduced their driver count - sometimes significantly.

I’m sure there are some manufacturers that just wedge things in where they’ll fit. And for single-driver designs it only really matters in terms of avoiding internal reflections. One reason the ER4-XR/SR are so coherent is that they only have a single driver firing down a simple tube.

BUT … there’s more than one instance where the high-end manufacturers (Empire Ears and 64Audio to name but two) are clearly paying attention to where things are placed, even in their open-acoustic designs, as both have models they can currently ONLY builds as universal units, because the variation in shells and tubes for a custom build doesn’t allow them to place the drivers properly.

They could probably combat that by using much larger shells, but that’s not the path they’ve gone down (so far).

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Early Chinese IEMs…sigh…

You might like the first KZ ZS10 if you ears resemble cat ears on the inside, or you are a fan of the Star Trek Uhura look. It also helps if you like a 3x blast of treble and slow rubber-bass hit. I sincerely believe they just slapped some parts together as an engineering prototype and then sold it as “good enough”.

And this is why good tips or custom moldings are important for IEM performance. The ear did not evolve to have sound directly injected into a sealed chamber from 0 millimeters away.


Ordered myself a set of the Universal Melody MEST IEMs …

Sooooo tired of IEMS getting +++++ ratings when they’re clearly massively-treble-boosted, Anime-OST tuned nonsense, that has about zero relevance to real instruments, in live settings, as a wet-fart, in a paper bag, on a dark night, in the fog …

If that’s your thing, more power to you … bet lets not claim it’s accurate when it comes to natural, acoustic, instruments.

Step away from the computer. Close the YouTube tab. Go listen to a live acoustic concert (no PA). Maybe even learn an instrument. Then come back and tell me these peaky, treble-centric, nightmares are “natural”, let alone “neutral”.


It wasn’t clear from your post, but I’m assuming that you’re not categorizing the MEST as a peaky treble heavy mess?

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Actually, is the MEST even a thing?

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Has, it is, and it’s a hybrid with bone conduction. Interesting!


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I’m assuming that the MESS has the more natural/realistic treble I hear in actual, live, acoustic, music … vs. the constant iteration of “massively treble boosted/bass-shy” IEMs that seems to be the fashion in IEM-centric markets.

The AAW Canary is a good example of natural/neutral tuning in objective terms. It’s treble-shy, maybe even dark, for the Anime-OST/treble=detail/focused on electronic music crowd … but not with real instruments …

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