I measured the noise floors of some microphones in the ear canal a couple of months ago, so I inevitably picked up some heartbeats.
To measure the heartbeat in the ear canal you pay attention to microphone and preamp specifications below, say, 100 Hz. The self-noise must be low enough and the sensitivity must be high enough. Be aware that broadband noise specifications in A-weighted dB tell very little about what the noise is at the lowest frequencies.
The microphone does not _need_ to go all the way down to 1-5 Hz. If I highpass filter my recordings at 50 Hz (I only measured myself with some mics), I can still vaguely hear the beat every ~1 s. Much energy is in the 10-30 Hz band, so your microphone needs to accommodate that at least. Above 100 Hz you start to hear breathing.
I used the ER-7C for something else some time ago. I would expect its noise floor to be way too high for quality heartbeat measurements, and its response starts rolling off at 200 Hz. You could look in the direction of the ER-10C or ER-10B+ instead; they are reasonable for this purpose.
Finally, consider whether a microphone in the ear canal is the best way to record the heartbeat.
PhD student in acoustics
Aalborg University, DK
On 06/28/2013 12:36 PM, Jelfs, Sam wrote: