[OT]Recording the sound of my heart with a stethoscope?

Not a stethoscope, but I remember little suction cup microphones that you could attach to a phone handset for recording phone conversations. Radio Shack used to sell 'em.

Those RatShack suction cup "microphones" did not pick up sound but instead picked up the magnetic field of the speaker in the handset.

-- Marc

It won't work for anything but old telephones (not cellphones) and certainly won't work to record any sound. Although they're called microphones, these are just fixed coils intended to pick up the light magnetic field generated by the line transformer contained in old landline phones.

For the OP purpose I'd try a contact piezo mic followed by a good low pass filter and a very high sensitivity and low noise preamp. Also, a normal electret miniature mic could be stuck to the rubber pipe of an old stethoscope.

With a microphone.

Use a stethoscope end as a probe (it's intended to exclude room noise and hand-holding artifacts), and just replace the Y-junction that goes to the earpieces with a dynamic microphone. You'll want to have a low-impedance preamplifier for best noise performance. Maybe negative impedance.

Small speakers make good dynamic microphones.

Electret microphones are already preamplified, but it's uncertain how 'ideal' they are at the low frequencies in a heartbeat.

A heart beat is fine. In fact, it's what I'm looking for.

However, the quality at the start (beating heart) of the lub-dub may not indicate the true beat for a few seconds, and the true diastolic (relaxed) pressure might be a few seconds off. That is, one wants to get past the noise until the "signals" (systolic and diastolic) are at a representative point. If not done properly, one can get pretty incorrect values.

Did this a couple of weeks ago using a small external computer mic "three wire plug" and a small plastic cup (about a pint) to help couple the sound. Put the mike in the container and hold the container with the opening to your bare chest and the mike trapped inside, the mike just floats. Be very still.

Oh. Didn't know that. Learn something new every day... Thanks.

So you didn't use a stethoscope?