[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [AUDITORY] Ear Probe Mics and detecting the heartbeat?
On Jun 29 2013, Jelfs, Sam wrote:
Just a question for those of you with experience using ear probe
microphones, do you ever hear the heartbeat? I've built a couple of
in-ear microphones, and can hear my own heartbeat, but the quality is
relatively poor, and only works in very low-noise conditions. I was
looking in to using dedicated probe mics, such as Etymotic ER-7C
(http://www.etymotic.com/pro/er7c-ts.aspx) and whether that might give me
a better signal-to-noise ratio, but just wondered if anyone has any
experience of this before I buy some.
The er7 has too high a noise floor for this. I would suggest the er10c, the
dpoae system from etymotic. http://www.etymotic.com/pro/er10c.aspx
However, the main problem is that the low-frequency response of these
systems is not adequate for these measures, since the heartbeat energy is
centred below 100 Hz, and even lower (1-40 Hz). The er10c can be modified
quite easily to do this (but lists at $2000- each). Alternatively, you
could build your own microphone system, We used flat-response microphones
from the Knowles FG series electrets, with a suitable in-house
preamplifier, and could show flat response down to below 10 Hz.
Additionally/alternatively, depending on how much you occlude the meatus,
you can let the occlusion effect bring you up above the noise floor. We
observed circa 40(average) - 50 (max) dB of occlusion below 40 Hz with
realistic plugging (performed by a competent audiologist and/or ENT
surgeon). Our recorded SPLs turned out to have a total power between 80-90
dB SPL (4-30 Hz, obviously unweighted).
The work is in press to appear in a future edition of Ear & Hearing by
Stone, Paul, Axon & Moore.
Senior Research Associate
Auditory Perception Group
Dept. of Psychology
University of Cambridge