IEM Tech Talk

I thought that I would start a new thread to encompass any technical chat regarding iems. I am an iem fan and I know that there’s a large number of us on this forum.

I have been wondering after reading comments in the Campfire Andromeda thread just how many drivers it takes before requiring a crossover and such things. I don’t know if there are any hard and fast rules regarding this.

With lots of companies producing multi ba iems and the current trend to put together Hybrid iems and stck some electrostatic drivers in too, although they aren’t really full blown electrostatic drivers like the Shure KSE1500. They must be more complex to put together and tune accordingly. Just a thought.


I am certainly no IEM expert and I’m sure you will get good input, but personally I would say that any multi driver system should have some way of dividing the frequencies.


Yes I agree but I am sure that not all actually do. Don’t the Campfire use their T.A.E.C (Tuned Acoustic Expansion Chamber) technology. I don’t see a mention about use of a crossover or other technology. mind you It clearly doesn’t seem to need it though. I have a pair and they really are very good. I don’t know enough about the technology that goes into high end iems and i need to educate myself. But i always thought that the use of crossovers brought the multi driver iems together in terms of coherence and frequency. Like I said I don’t know enough. Perhaps there are others on the forum who can comment.


I am sure that many IEMs don’t have crossovers, at least crossovers in circuit form, which is certainly the case with many Chinese brands.

However, you can use an enclosure to tune a driver (which I am sure is what Campfire are doing with their T.E.A.C). By using different enclosures (or chambers in this case) you can help a driver to roll off at a specific frequency, basically giving you an acoustic frequency filter (high or low).

In the case of speakers, it is much easier to use filters (high pass, low pass, band pass) as there is plenty of space. In an IEM it is pretty incredible that such small spaces can be used for tuning.

Also, when I said “any multi driver set up” in my previous post, that is not completely true. I should have said that any multi driver set up that is not using the exact same drivers.

For example, if you have a 3 way speaker (let’s say a 10" a 5" and a 1" driver) and each driver is reproducing different frequencies, then they should be divided in some way. If, for example, you have another 3 way speaker, but in this case you are using a 10" 2x4" and a 1", the two four inch drivers are reproducing the same frequencies and do not need to be divided amongst themselves. They should, however, be identical drivers and should still be divided from the 10" and the 1".

If the drivers are not identical and are still receiving the exact same frequencies, they may turn out to sound good together but it is luck of the draw (or a lot of trial and error)


Thanks for the information. It boggles the mind that they’re able to fit all those drivers into an iem. Very clever stuff.


I don’t see how there can be that much tuning by physically might be possible. Granted the above chart is for instruments, but at 5Khz, the wavelength is 2.7 inches and a trap is 0.68 inches.

I like to willfully display sophomoric ignorance because it draws @Torq like manure draws horseflies.


I refuse to contemplate any list of instrument frequencies that doesn’t include the bass guitar :wink:


With a multi-driver IEM you can use acoustics and tuned chambers to affect resonances and attenuation to tune the levels of various frequency bands - with varying degrees of efficacy based on said frequency.

What you can’t do with that approach is prevent a driver attempting to reproduce a signal that is outside it’s sweet-spot in terms of frequency response and the consequent distortion that results.

BA drivers really only come in “woofers” (many of which show meaningful energy output up to 8 kHz or so), “full range”, which are what they say they are, and “tweeters”, which still have significant energy output down into the mids, sometimes lower). So any time you’re attempting to recreate a full-range signal, if you don’t have a crossover, you’ve got added distortions as all the drivers attempt to replay a full-range signal.

And then you get all the nice phase and timing issues on top of it for the frequencies you’d just as soon not have ALL the drivers emitting.

Every high-end multi-driver IEM I’ve owned has a crossover. 4-way with the tia Fourté, 7-way with the EE Zeus XR(A) and so on. Maybe the crossover-less designs have in-driver filters or something, but otherwise I don’t see how you get around the above.


Thank you. Great info as always. I shall have to read up on it if I can find some information that isn’t too brain bending.

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Maybe that is why I tend to like single-driver IEMs. I’m too cheap to buy good multi-drivers with crossovers and actual like…design. Never even heard any.

This is the problem. There are so many online, and no place or way to audition. At $100 and under, I can take a chance, could take a chance. Especially since I basically don’t care much for IEMs.

I have Etymolic ER-6’s somewhere
, I think they are lost. I succumbed to a bunch of reviews. They always seemed bass-shy. $200

VSonic GR06,
single driver, about 2012 vintage, sound OK, $50 bucks

1More Triple Driver -
really not bad, $125, bought specifically to use with telephone cause the mic got good reviews. Fatiguing for long periods.

Sennheiser IE-40 Pro. Single Driver. My current go-to for IEMs $99. Gorgeous clean, coherent sound, well balanced, with extended bass. Astonishing when viewing Tidal movie/videos on my phone with the DFB pushing them.

So is it just my cheapness that prevents me from liking IEMs all that much? I still need to stuff them in my hairy old ears.


I’ve had a pair of Etymotics as well. Totally agree, they’re quite bass shy. The last IEM that I had/have are the B&O H3, and they were very pleasant sounding. Similar to PortaPros, but less boomy, and more presence in the mids/highs. Unfortunately the connector bent (my fault) so they’re pretty much dead. At $140-ish I’ve contemplated replacing them with the same model, but there’s that audio itch to upgrade to something better. I’m leaning towards iSine, or possibly i4’s. I’m really fond of Audeze’s sound.

One thing I am curious about is, with multi driver IEMs, are they usually a driver for each specific frequency range or is it common to double up on drivers for certain frequencies?

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Fairly common to have two (or more), BA drivers, doubled (etc.) up for a given frequency range.

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My old (long since sold) ER-6 were not just bass-shy, they were bass-absent! I bought those from HeadRoom back when Tyll still ran it. Already had the original ER4-S, and a couple of the HeadRoom amps (Supreme, AirHead) … so pretty much stuck with the ER-4S …

Had those for over 20 years (which I think qualifies them as being the longest-retained audio product in my history) before I sold them and bought the new ER4-XR.


Yup. Bass anemic.