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

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.

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.

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

This is to target specific people, thanks though.

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?

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.

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.

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

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

You might wish to check out these contact mics: The C-ducer (Capacitive-trans-ducer) is a contact condenser microphone. (http://www.c-ducer.com/row/row_c-ducer_tape_microphone.htm)

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.

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.

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.

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.

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.
It's common place in pro recording studios to use a 'star' or other grounding scheme, allowing only one path to ground.
A balanced power transformer/configuration is also an option, though quite expensive, it cures many types of power/noise issues. Even single-coil guitar pick-ups become relativity silent.

The audio is definitely audio and needs a continuous return path.

The DC (whether phantom or "plug in power") also needs a continuous return path.

No RF is ever fed on the mic line.

So you definitely need a negative return connection between the mic and the preamp input. If you run a separate, insulated, negative return conductor, then the shield should be connected at one end only.

Noise induced into the shield, when the shield is part of the mic signal circuit, would never be a problem with a balanced mic, as there is no audio on the shield in that case. It could potentially be a problem with an unbalanced mic. In practice, it's normally not an issue, unless you're running terribly low levels and terribly high gain, or unless you're running terribly long mic wire, or unless you're in a terribly noisy environment.

Heart Sound Sensor [SEN42771M] - $59.00 : Seeed Studio Bazaar, Boost ideas, extend the reach (http://www.seeedstudio.com/depot/heart-sound-sensor-p-833.html?cPath=197)

Bingo, Thanks Richard


1 to 600hz, I wonder if that range will catch everything, hearing is from 20 to 20k

Unique Piezo Microphone for Blood Pressure Monitor-The Electronic Goldmine (http://www.goldmine-elec-products.com/prodinfo.asp?number=G18060)

1 to 600hz, I wonder if that range will catch everything, hearing is from 20 to 20k

I wouldn't use it to record bats, or even cymbals, or even voice. Based on heart recordings I've heard, I would guess 600 Hz is adequate... but then again, I don't know how some of the irregularities (murmurs, etc.) might sound.

For whom are you building this device? Does the client have any idea what frequency range is needed?

Remember it is not just for the heart, although the heart can make rather unusual noises. The lungs have many high pitch sounds as well as the stomach etc.

I am in uncharted waters and consider the range to include all of human hearing as the stethescope would provide to a listener. I think it would be unwise to create any limitations. The client is a heart patient whose mechanical heart beats do not match the holters electrical recording and wants to provide his physicain with the 5 to 8 second recording of their artythmia which induces syncopy. My how nice it would be to have some kind of timing between the holter and the audio. I figured if I made it for the heart it might as well include the lungs and others as well.

The tissue of the human body blocks high frequencies and conducts low frequencies, so any sound that travels through tissue is going to have that "underwater" sound (humans are mostly water). There's a reason they use relatively low frequency waves for sonar. So I wouldn't worry at all about trying to match the high end frequency response of the human ear IN AIR.

A friend of mine had a heart valve replaced with an artificial one. He swore he could hear it clicking at times. Whether "clicking" extends above 600 Hz is more than I can tell you.

I am in uncharted waters and consider the range to include all of human hearing as the stethescope would provide to a listener.

In that case, buy a stethoscope, cut the tubing, and insert an electret capsule. That should sound pretty similar to the way a stethoscope sounds.

If the goal is to provide a recording for the client's physician, you could always consult with the physician about what frequency range he needs. If he doesn't know, perhaps he can refer you to appropriate medical literature.

Or else invest $5.00 in an electret capsule, or $59 in the pre-made sensor, make a recording, and let the doctor evaluate it.

Seems to me that if you want to make something with wider and wider application (lung noise, digestive noises, noise of arthritic joints, etc.), you're making your job harder and harder. It might make the project more interesting to think about, but it might put you further and further from finishing this contraption for the original intent.

I think you've gotten plenty of info on the audio side of things, and any further investigation will move into the medical realm.

I'm still interested: what results?

My just done web search results suggest that in most instances equipment designed for medical or mechanical diagnoses may or is more likely to give inferior sound. One exception is the fetal stethescope or pinard horn. The example given at My Stomach (updated) How Dare You?: (http://www.negativland.com/dumb/blog/?p=16) appears to come somewhat close to using that principle for recording body sounds, though I could be gullible.

Most else degenerated into inanity; or likewise YouTube recordings done by placing mobile phone or compct camera on belly.....

and of on its own a quote from Michael Ondaatje: "Gentlemen who have placed a microphone beside a naked woman's stomach after lunch and later, after slowing down the sound considerably, have sold these noises on the open market as whale songs"