Dynamic drivers are seldom used in CIEMs because they almost always require venting, and venting lowers isolation. The entire purpose of CIEMs to begin with was to provide musicians with as much isolation as possible on stage. That's why you really only see companies with less of a stage musician pedigree work on dynamic drivers for CIEMs, e.g. UM. Of course, the exception is Future Sonics, but the main reason for their going with dynamic drivers is part of legacy; they started making CIEMs before BAs were ever easily available outside of hearing aid industries. Future Sonics CIEMs are also reported to have a little less isolation than BA-based CIEMs (some musicians actually prefer less isolation, but for the most part, the goal for a CIEM is to isolate as much as possible).
With all that said, the ceiling for dynamic drivers is actually higher than that of BAs, so absolutely, more development needs to be put into dynamic drivers.
Hi Tomscy, always nice to read your posts.
I wanted to help correct a few things because I think it's interesting for the history of our hobby and also to understand better the earphones we enjoy.
First, stage monitors. The purpose of in-ear stage monitors isn't actually isolation per se, that's secondary. The primary purpose is hearing protection (I'll get to isolation in a moment), which means reducing the overall volume which the musicians' ears are exposed to. The first reason in-ear monitors were developed was to eliminate the use of stage monitor speakers (often called wedges, after their common shape)--these are speakers which point back toward the musicians during performance so they can hear themselves and the other musicians as they play. The drawback was that they added dramatically to the already loud environment created by the primary speakers pointing out to the crowd. So, in-ear monitors mean you can remove the wedges and reduce the overall volume. That was the hope, at least.
Now, why isn't isolation the primary thing, then? Wouldn't isolation be the key? Well, no. The reason is that musicians
turn up the volume in their in-ear monitors, regardless of the isolation. In fact, Sensaphonics found that, without special training, they turn it up to exactly the volume they are used to from the wedge speakers!!! It doesn't matter how much isolation there is if musicians are turning up the volume. With me so far?
So, now we get to Future Sonics and dynamic drivers. Marty Garcia, the head of Future Sonics, was the first to put in-ear monitors on stage and the first to sell in-ear stage monitors. However, it's totally, completely wrong to say that Future Sonics only uses dynamic drivers because balanced armatures weren't available! The idea that it's some sort of legacy is also garbage, sorry! In fact, Marty Garcia worked closely with Shure using balanced armature designs and was actually asked by Knowles (one of the primary manufacturers of balanced armatures in the world) to be head of their research and design. So, it's not like he doesn't know balanced armatures very, very well. Now that we've established that, let's look at why he first chose dynamic drivers and why for years now he's engineered and designed his own dynamic drivers for use in his ciems and iems.
It comes down to the purpose for in-ear stage monitors. Marty Garcia found that musicians were turning the volume up on balanced armature in-ear monitors because they weren't getting the real bass, air-moving, feeling that they were used to from stage speakers. That air-moving quality of bass
feel was the key. A vented dynamic driver allows for the real bass feel. It allows the right sort of movement in the air pressure on the ear drum--and, properly vented the dynamic driver diaphragm moves a little like the ear drum itself, each vibrating back and forth. George Cardas as a similar theory about the dynamic driver and the ear drum, incidentally, they are probably reading the same research. The vented dynamic allows for that real bass energy and you don't have to turn up the volume to get it. That's why one of their trademarks (along with the term Ear Monitor, itself) is "Bigger sound at lower volumes".
In terms of dynamics versus balanced armatures, a good quality dynamic driver can have lower distortion levels than armature designs. You can ask head-fi'er purrin about that as he has posted measurement on head-fi.
That leaves us with the question of why companies choose balanced armatures? In talking to companies, the answer that they have given me is that it actually takes more work and specialized expertise to design a high end dynamic driver design than a multi-armature design. Perhaps that's a discussion for another time, but that's the answer I've gotten.
