Quote:
Balanced armature drivers were originally developed as small, high efficiency narrow band transducers for hearing aids. There undistorted maximum SPL is limited. you have to use sveral of them for a good wideband sound reproduction. Multiway systems have the disadvantage of time differences between the signals from the different drivers (a well known problem with loudspeakers). A single, well engineered dynamic driver can do it better
Originally yes. However, since then there are some pretty wideband balanced armatures - and to reduce distortion you can just combine more of them, assuming they're well matched. (THD is increased though.) Some crossovers and BA transducers have lots of phase shift, others not as much. May cause slight comb filtering, but usually not audible due to narrow band of effect. (unlike the following test) Phase shift is even harder to hear.
This is not like in speakers, where there can be weird interference patterns off-axis due to differing speaker polarity compounding the effect.
Usually multi-way IEMs have phase shift in the range where the ear is more sensitive, but it still doesn't matter - this is little.
Anyway, phase shift is easy to correct with an all-pass filter (anticausal if there's no other way), but fitting one into an IEM might be tricky - it's hard enough to fit crossovers, plus it will increase general impedance and might worsen THD if certain low quality capacitors are used. (but it'd be silly to do so regardless of application)
The main important part is to match any crossfeed and filter resistors very well to limit inter-channel phase shift, which does affect stereo imaging. Digital filters don't have this kind of problem.
Here's a sample phase chart (second from top on the left, pink curve) of:
- a single BA IEM (Knowles ED, pretty common for others too): http://www.innerfidelity.com/images/MEEA161P.pdf
- 2-way BA IEM: http://www.innerfidelity.com/images/JaysqJAY.pdf
- 2-way BA IEM with dual tweeters: http://www.innerfidelity.com/images/ShureSE535.pdf
- 3-way BA IEM with dual bass armatures: http://www.innerfidelity.com/images/LogitechUE900.pdf
Here's some "lots of phase shift" test. It's barely audible: https://www.youtube.com/watch?v=BYTlN6wjcvQ#t=2864s
Have a crossover phase shift blind test too. Good luck with this one: http://mark.hayenga.com/audio/phase_shift/
And analysis by prof. Linkwitz: http://www.linkwitzlab.com/x-phs-dist.htm
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A single dynamic driver is pretty hard to tune and will lag behind balanced armatures in higher frequency reproduction. (mostly either will get resonant or will be slow decay)
What they do best is moving lots of air - such as bass and subbass. They can also be more wideband, but then the driver will likely be resonant.
The problematic part is that dynamic drivers depend mostly on mechanical and acoustic dampening, which is by nature nonlinear.
So no, they cannot do it better than proper set of armatures with the above exception.
Electrostatic IEMs could perhaps do that, but the only I know of is Stax SA-003 (or the combo set with the amp, SRS-005S). It's pretty large, expensive, requires an expensive special amplifier (all electrostats do) and is open back. Also is inverse phase, which you might want to correct by a trivial filter. The amps are not portable either. (good luck trying to run 580V bias from anything portable)
Similarly orthodynamic IEMs, the only one I know of is Yamaha YH-5M, quite unavailable anywhere? Also huge.