Extremely sensitive indoor microphone? - Page 1
Forum section: electronics / general

author: onesixright
author_rank: Frequent Contributor
timestamp: April 03, 2017, 09:52:12 pm
content: Would it be possible to pickup aextremelylow volume sound in a room?For example distance ~ 7 meters:Someone breathing normally?Someones heart-rate?What type of microphone would be the best?Any thoughts on amplification circuitry?Would this be doable as a 'budget' DIY (or do you very quickly get into extreme expensive stuff)?Many thanks!

author: garboui
author_rank: Regular Contributor
timestamp: April 03, 2017, 09:54:54 pm
content: how quiet is the room. Its all possible is the noise floor, ambient and circuit is low enough.

author: frozenfrogz
author_rank: Frequent Contributor
timestamp: April 03, 2017, 10:47:13 pm
content: Apart from the noise floor issue already described, you should look into small condenser microphones.If you are looking for a ready-made microphone I would suggest the Rode NTG2. This one is very sensitive and directional.Maybe an ellipsoid, or parabolic microphone dish could also help you out.The further away you are and the more ambient noise is around, the lesser your chances of recording something useful.Also, it makes a huge difference if you can use a highly directional mic (shotgun, parabolic,...), compared to using an omni-directional mic.What are your design goals? Listening in to the neighbors?The more up close you can get your mic, the better. Sound pressure level decreases 1/r (inverse proportional to the distance), meaning: Twice the distance equals half the sound level (6dB drop). If you need to record from a distance, you might want to consider a different approach like a laser microphone

author: moz
author_rank: Regular Contributor
timestamp: April 03, 2017, 11:35:53 pm
content: Quote from: onesixright on April 03, 2017, 09:52:12 pmWhat's your goal? Do you want to isolate the vital signs of one person in a crowd of 50, or are you just trying to detect the presence of a person where they shouldn't be? Can you soundproof the room or add acoustic tiles to reduce ambient noise? Can your apparatus fill the room, or should it be inconspicuous?As mentioned your first problem is noise floor. Unless the room is very quiet you're going to be operating at 20Db of more below the ambient noise, which means you'll need a lot of tricks to get your signal out.One obvious approach is an array of microphones with some DSPs so you can turn it into a 3D focussed pickup. That way you locate the target and focus on either their mouth/nose or their throat (breath and heartbeat respectively). I would start with a simple 5x5 or 6x6 array on a steel skeleton at about 20cm spacing (roughly a metre square), then foam it to reduce reflections and isolate it from the support. Feed each mic into a phase-sensitive ADC (viz, sampling way faster than 2x the frequencies of interest) and attach a timestamp to the signal. Then pump all of those into a PC for analysis.Wikipedia on beamformingis one place to start, and a search for "phased array of microphones" is also helpful, leading to stuff likethis Sparkfun discussion.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 04, 2017, 01:50:09 am
content: We have no clue (do you?) what you mean by "a room". As others have observed if you DID have a microphone of sufficient sensitivity and directionality, and noise-free gain, the ambient noise would completely swamp out the desired signal. You have an extremely NEGATIVE signal-to-noise-ratio (SNR). I would wager that it is not doable even with three or four orders of magnitude bigger budget than you have. Wildly beyond the realm of possibility, at least with current 2017 technology as we know it.And even if you had an impossibly quiet ambiance (in the best anechoic chamber on the planet) you would need a microphone of technology that doesn't exist yet to pick up those kinds of sounds at that distance. And even if you could pick up the respiratory sounds, you know from practical experience that hearing any kind of sounds of a pulse requires direct contact (i.e. a physician's stethoscope).

author: Brumby
author_rank: Unknown
timestamp: April 04, 2017, 03:43:43 am
content: Noise is a big problem here.If I were to offer an analogy, it might go something like this:....What you are trying to observe is like seeing the splash of a mosquito when it hits the surface of a body of water.- where the environment is your lounge room, that body of water is like an ocean in a hurricane.- where the environment is an anechoic chamber, that body of water is like your municipal swimming pool ... with people in it.- where the environment is close contact, that body of water is like a bucket at your feet.The mosquito will make a splash in all of the above scenarios, but you just won't be able to pick it out of the first two.... and I haven't even touched on the noise characteristics of the detection system (such as microphone and amplification.)

author: DavidDLC
author_rank: Frequent Contributor
timestamp: April 04, 2017, 05:26:37 am
content: Looks like a project to check a baby or an old person while sleeping.David DLC

author: Brumby
author_rank: Unknown
timestamp: April 04, 2017, 06:57:18 am
content: If it is for monitoring someone asleep, there have been micro-movement monitors around for decades. There are ones for babies that have a sensor mat that is placed under the cot mattress and it detects the breathing movement of the infant. When no movement is detected for a number of seconds, an alarm sounds.

author: moz
author_rank: Regular Contributor
timestamp: April 04, 2017, 10:52:14 am
content: Quote from: evb149 on April 04, 2017, 04:59:27 amI was thinking more of theMurchison Widefield Arraywhich works more or less as I suggested above - by manipulating analogue delays in the different signal paths they "aim" the field of view of each tile (of 16 antennas), which gives them a signal that's less down in the noise. By combining a shedload of the tiles they end up with something that they can analyse. But their stuff is so far down in the noise that they can't have digital stuff anywhere near the antennas hence the analogue trickery.In this case you're working with low frequency sound so digital electronics isn't a problem, and it's easier to deal with most of this stuff in digital. Although you could, I suppose, look at theacoustic telescopestuff that was around before radar was invented, used for spotting aeroplanes. Sadly you'd have a big heavy telescope to move every time you wanted to shift the focus. But it would be cool

author: onesixright
author_rank: Frequent Contributor
timestamp: April 04, 2017, 12:22:16 pm
content: Thank you all for the replies! Sorry, should have been more clearLet me elaborate: Residential area, a normal room as in: living, bedroom. Time is probably at night, and no, I have no interest what the neighbours are saying! ;-)I got to this question, because a mosquito kept me awakeHow does this relate to a MIC? Well, when turning on the light, obviously, the s.o.b. was nowhere to be found. Looking for 30 minutes, nothing, nada. So i went bed to bed, within 2 minutes it was on top of me, grrr....I needed something to figure out where he (she?) was hiding. Althoughprobablyvery impractical, I was thinking if you could catch the sound (and direction) once its airborne. Now mosquitos are quite noisy when they are within a meter or so. But no so much when they are on the other side of the room.Which lead to me the question: picking upverylow SPL. Like: hear-rate, breathing, mouse walking on the ground, spider walking on the wall, etc. I do understand that a walking spider isextreme, but was more questioning it in terms ofdoableDIY. How low can you practically go (so just one mic, no (big) parabolic dish?Many thanks, once again!PS: how did it end with the mosquito? well found the bastard, 2 days later. I'm happy to report its days of terror are over!

author: frozenfrogz
author_rank: Frequent Contributor
timestamp: April 04, 2017, 02:03:07 pm
content: All you need is a mosquito laser!What happened to the mosquito zapping laser?When the study came out in 2010 (?) I was super excited!Is it overkill? Maybe.Sounds like fun? Definitely!Wikipedia states build cost of 50€ per unit would be possible. Sadly it did not yet happen.Mosquito laser @wikipediaEdit:Mosquito hunting laser tanks!

author: Brumby
author_rank: Unknown
timestamp: April 04, 2017, 02:09:49 pm
content: Yes- the mosquito laser!!That was my immediate thought as well.Show no mercy!

author: onesixright
author_rank: Frequent Contributor
timestamp: April 04, 2017, 02:21:18 pm
content: Quote from: frozenfrogz on April 04, 2017, 02:03:07 pmCool! Yeah, that crossed my mind as-well. But The risk of looking into a laser was to much of a risk. So, if i can localise it, then I can wack it by hand :-)

author: moz
author_rank: Regular Contributor
timestamp: April 04, 2017, 09:35:55 pm
content: Quote from: onesixright on April 04, 2017, 12:22:16 pmOn a more practical note, we have one of the somewhat priceylight+fan bug traps that uses TiO to generate CO2and that works really well. Sadly the cheaper version with just light+fan does not appear to work at all (I too had that one mosquito in my bedroom... I eventually found it on the curtain less than a metre from the cheap "bug killer"). The pricey one, on the other hand, fills up with mosquitoes and moths quite readily.