Hello Eric,
Many thanks for the link to Knowles' miniature mics, as that is more current
than the HA mic articles (e.g. Killion et al) I have on file. Clearly, such
mics aren't intended to compete with Neumann, Schoeps, etc. studio mics, but
their performance is quite amazing for such tiny mic elements! And their
miniscule size might make them entirely suitable for multi-element "point
source" mics, too.
Boosting the low end, as you pointed out, certainly has a deleterious effect on
noise performance. Although F0 (first formant) isn't needed for intelligible
speech--at least for normal-hearing persons--it does find an important purpose
in EAS (electric-acoustic stimulation) devices. Briefly, persons with profound
hearing loss (but with residual low-frequency hearing) have poor speech
comprehension using only their low-frequency hearing. Cochlear implant
(electric) hearing yields modest speech scores for many of these persons. But
when the low-frequency (acoustic) hearing is added to electric stimulation, the
combined results are amazingly good--much better than what researchers might
have anticipated. One of the earlier problems was preserving low-frequency
hearing while implanting an electrode array. Nowadays, shallow electrodes are
implanted in order to preserve low-frequency hearing (note: a hearing aid is
still needed to boost the low frequencies).
Questions, of course, remain, and it will be useful to study the effects of EAS
in reverberant conditions and a variety of noise types. Whether the mic used to
boost the low frequencies (conventional amplification) should be omni or
directional may not be clear, and same goes for the mic or mics used to process
the mid and high frequencies.
As you had also pointed out, there's a head-mic interaction, and this must be
considered. After all, we're looking at a system, and a holistic approach is my
objective. Although not every possible variable can be accounted for, it
doesn't hurt to try a few representative scenarios that a CI recipient would
encounter. The ability to hear and discern warning signals (and their
direction) or moving vehicles can be studied. Restaurants, Houses of Worship,
and classrooms are typical listening environments, and Ambisonic recordings
certainly provide opportunity to re-create acoustic events over and over again
in a controlled, repeatable manner. Even without loudspeakers, I believe it is
feasible to study mic directionality when using Ambisonic recordings. Combining
mic polar characteristics with HRIRs is the next step.
Thanks for reading my posts, and for taking time to share you wisdom.
Best,
Eric
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