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Re: [AUDITORY] Ear Probe Mics and detecting the heartbeat?

On Jun 29 2013, Jelfs, Sam wrote:
Dear List,

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.


Michael Stone.

Michael Stone
Senior Research Associate
Auditory Perception Group
Dept. of Psychology
University of Cambridge
Downing Street
Cambridge CB23EB

Website: hearing.psychol.cam.ac.uk