Mic for recording internal body sounds / help please.

[Don Parrish]

I am trying to rig a portable audio recorder for internal human sounds, stomach sounds, heart, lungs, etc that is portable like a haltor monitor and has 24 hour memory storage. My main problem in the Microphone, Do any of you folks out there know of an appropriate small microphone that can be taped to the body ?? At first I thought about using pieces of a stethoscope but then why not some kind of flat mic taped directly to the stomach / chest area. Could a lavalier be made directional ??

Any suggestions would be greatly appreciated, web searches turned up very little.

Thanks

[Greg Miller]

I can envision that the stethoscope idea is not a bad one. Get a single-tube stethoscope, snip off the rubber tube close to the "pickup head" (whatever it's called), and insert an appropriate size (omni) electret element into the tubing, and you've got a fairly closed system.

But unless the patient/subject is motionless in an anechoic chamber, you've got a tough problem. Most outside sounds (TV, conversation, traffic, etc.) will be louder than most body sounds (the exception in some cases being flatulence). And as the person moves around, movement of the mic on the skin, movement of clothing, etc., will all generate a lot of unwanted noise.

[Don Parrish]

Yes, I was thinking a lavalier stuffed into the tube close to the stethoscope pickup but did not know what role the earpieces played.

Maybe a rubberized cover would help isolate clothing sounds against the pickup.

[Buba Kastorski]

I would use sound library, saves you time and money.

[Don Parrish]

This is to target specific people, thanks though.

[Richard Crowley]

This is the kind of question I would ask in a medical/clinical research forum, not in an audio forum. As Mr. Miller suggested, the ambient artifact sound problem is probably even greater than the mic selection/placement issue. Is this original research, or you trying to duplicate other research/clinical tests?

[Don Parrish]

Original research, cardio microphones and phonocardiagrams have been in existence since 1955. They are in use for clinical settings and not portability. A zoom H2 will probably be the recorder, I do not like the battery life (6 hours) but all of the models are probably the same. Yes there are obstacles to overcome but that is just part of it.

The big surprise has been the price of lavalier mic's. Several less than $100, most from 180 to $500


Starting to see info about prenatel listeners.

[Greg Miller]

I would not buy a lavalier mic. Being a DIY design kind of guy, I'd just buy a raw electret cartridge. IIRC, the Panasonic ones are pretty good and priced very low. Try Mouser, Digi-Key, etc. as a source. With luck you can find one with an OD that will fit snugly inside the rubber tubing.

[Don Parrish]

Greg, that was terrific information, thank you thank you. Digi key 102-2190-ND will fill the bill.

[Greg Miller]

Don, glad to help! I see Digi-Key gives you a sample circuit if you need to build your own preamp. Otherwise that capsule should interface directly with the consumer "plug in power" devices.

Some of the Panasonic capsules were very highly regarded by the "tapers" community. I've used them to build microphones into eyeglasses frames, picture frames, etc.

Happy Trails,
Greg

[Gary Nattrass]

You might wish to check out these contact mics: The C-ducer (Capacitive-trans-ducer) is a contact condenser microphone.

[Don Parrish]

Thanks Gary and Greg

Greg, the only thing throwing me a curve is the power requirements vs the H2. Most lavaliers call for 48vdc. The H2 outputs 2.5vdc for microphones, the part I listed calls for 2 volts also.. I am sure there is something I am not seeing.

[Greg Miller]

There are two different ways in which a recorder or mixer can supply power to a condenser mic.

"Phantom power" is used in the professional arena. It requires a balanced mic line with two hot wires and a grounded shield, and almost always appears with XLR connectors. It involves feeding an equal positive DC voltage on both of the mic wires, with negative return on the shield. Originally phantom was usually +48 volts, but more recently some mixers feed a lower voltage. Some mics will work OK on a lower voltage, some require the full 48 volts.

"Plug in power" is used in the consumer arena. It started to appear in the days of minidisc recorders and is fairly widespread today. It requires an unbalanced mic line, with one hot wire and a grounded shield. It involves feeding positive DC voltage on the hot mic wire, with negative return on the shield. It is often found on consumer stereo mic connectors, which are 3.5mm TRS; + voltage is connected on tip (for the left channel capsule) and also on ring (for the right channel capsule) with common - return on sleeve. To the best of my knowledge there is no specified standard, but I've seen voltages anywhere from +2 volts to +9 volts, and I believe I've read of some as high as +12.

If you're using a raw capsule, then you want to connect that to a consumer-type 3.5mm connector, which plugs into the recorder's mating connector, where you will find appropriate "plug in power." If you try to connect a raw capsule (or a consumer mic, for that matter) to a professional mixer with true "phantom power" you will fry the capsule.

[John Willett]

Originally Posted by Don Parrish

I am trying to rig a portable audio recorder for internal human sounds, stomach sounds, heart, lungs, etc that is portable like a haltor monitor and has 24 hour memory storage. My main problem in the Microphone, Do any of you folks out there know of an appropriate small microphone that can be taped to the body ?? At first I thought about using pieces of a stethoscope but then why not some kind of flat mic taped directly to the stomach / chest area. Could a lavalier be made directional ??

Any suggestions would be greatly appreciated, web searches turned up very little.

Thanks

Sennheiser used to make a microphone for exactly this purpose.

It was made for their "Auscultation Trolley" which was for teaching hospitals to allow several students to listen to a single stethoscope.

The microphone was basically the bottom end of a stethoscope with a tie microphone in the tube - so the microphone would pick up the sound instead of feeding it to ear tubes.

For the trolley - the mic. was plugged into the trolley and the sound fed out via infra-red to several stethoset receivers.

This microphone was discontinued a long time ago, then the trolley was discontinued - however, buying a doctor's stethoscope and cutting off the hearing tubes and putting a tie mic. in the cut end does seem like a good idea to me.

[Don Parrish]

Great stuff greg thanks, In aviation and some military applications we use to connect the shield only at one end with a seperate ground wire, that way stray signals/voltages/noise could not conduct along the path of the shield. I wonder if this method could be useful in this industry. That is provided the audio signal is actual DC and not RF as RF needs the shield attatched to propogate the wave.


Thanks John I will look into that.