Microphone for low frequency night noises - Page 1
Forum section: electronics / projects

author: FernandoCRS
author_rank: Newbie
timestamp: December 26, 2023, 05:35:05 pm
content: Inside my room there's a noise at night that drives me crazy. It is low frequency and must be from a motor. But I can´t find the source. When I go out I ear a lot of city noise.At this stage I am trying to characterize the noise. I bought a UMIK-2 and I am testing several software in my laptop. I need low frequency, low noise and high sensitivity equipment. I think that for my case the UMIK-2 is very noisy, I only got a constant 100Hz noise but I know there are more frequencies associated with the motor. Can you advise me?I can program and solder. And learn. And buy.Thank you,Fernando

author: Benta
author_rank: Super Contributor
timestamp: December 26, 2023, 05:50:40 pm
content: For VLF, an accelerometer might be an option.Check ST Microelectronics (sensors).

author: RoGeorge
author_rank: Super Contributor
timestamp: December 26, 2023, 06:04:35 pm
content: Sometimes there are resonant places in only a specific room, or a specific corner. The noise may come from far away, sometimes from a few buildings away, or from a nearby car waiting with a running engine somewhere in the neighborhood. If so, it would be close to impossible to trace the source of the sound, because it is inaudible in other places that does not resonate.Since the microphone can not capture that sound, the next step would be to go to the nearby pharmacy and buy some earplugs. At least you'll be able to sleep while trying to find out the source. Or change the sleeping room.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 26, 2023, 06:15:56 pm
content: A resonance is possible. One would still be able to measure it, though a bit more tricky.The mentioned microphone may not have good low frequency response. A omnidirectional (pressure) response is right. For a 1st test a much simpler mircophone should be OK, even just a mobile phone could be a 1st try. How good the reponse at really low frequencies is can scatter - some audio one may intentionally cut the response as the lower frequencies are also more noisy with most microphones.A first point is to actually find the frequency of interest.100 Hz can be hum from a transformer, but also a computer issue or even EMI from mobile phone network.

author: Roehrenonkel
author_rank: Frequent Contributor
timestamp: December 26, 2023, 06:43:00 pm
content: Hi FernandoCRS,do you have windmills nearby?Good luck

author: donlisms
author_rank: Frequent Contributor
timestamp: December 26, 2023, 06:53:20 pm
content: I would be nervous buying a "reference microphone" where the data sheet never mentions "frequency response", let alone a graph to let you understand what it can and cannot do.Having said that, I would say that in your situation, it is not necessary to have a super-accurate frequency response. You need low response, to capture the sounds, but it's okay if the response at 200Hz is a little different than at 100Hz. It won't get in the way of your goals. I would want pretty good response down to 50H or below. Lots of microphones can do that.Once you're capturing the sound, the FFT will show you what the frequencies are, and their approximate relative levels, and shouldn't be bothered much by various other noise.Good luck finding the source. I don't know anything about your circumstances, but it seems like it could easily be something in contact with the building, vibrating the structure. Then the sound is more or less generated inside the room, with the surfaces acting like the speaker cone.Resonance is also quite possible, but if it were coming from outside, i would think you should be able to hear it outside. The sound energy would have to be sufficient to move the walls and then make it through.I wonder what frequency your walls resonate at when you thump them? It also should be pretty easy to do some rough calculations of the most likely resonant frequencies in the room based on the dimensions.Low frequencies are difficult to cover up with higher frequencies; for one sound to mask another, they have to share similar bandwidths, with at least one of them being a more broadband noise-like spectrum. Yours seems more like a single tone, and as you suspect, probably with harmonics, which should still be pretty easy to capture in isolation. Unless the walls are filtering them out; walls are low-pass, so even the second harmonic could be lost.

author: RoGeorge
author_rank: Super Contributor
timestamp: December 26, 2023, 06:58:42 pm
content: A studio mike might not be sensitive enough. For really low intensity and low frequency there are other ways. For example with waveguide tubeshttps://www.eevblog.com/forum/projects/infrasound-sensor-what-makes-a-narrowband-2-7-hz-signal/

author: FernandoCRS
author_rank: Newbie
timestamp: December 26, 2023, 07:02:47 pm
content: Thank you for the answers.I think that I don´t ear less than 10Hz. So from 10Hz to 1000Hz is a good range to scan.I live at the center of Lisbon, there is no windmills.The noise is continuous all the time even at night and weekend. During the day is not so easy to ear.So there is a motor somewhere that I need to locate. Some nights the noise seems a little different but it is constant.I am trying software like Sound Forge. I will test Audacity as soon as I get the ASIO driver.

author: langwadt
author_rank: Super Contributor
timestamp: December 26, 2023, 07:07:59 pm
content: try using a speaker as a microphone

author: RoGeorge
author_rank: Super Contributor
timestamp: December 26, 2023, 07:16:23 pm
content: Quote from: FernandoCRS on December 26, 2023, 07:02:47 pmOK, but don't ignore the earplugs advice. Buy some pharmaceutical earplugs.Test if you can still hear the noise while wearing the earplugs. Might be a form of tinnitus/acufenes as well. And if it isn't, and the sounds goes away with the earplugs on, at least you get good sleep at nights. It may take weeks to sort it out where from is the sound.Most probably you won't find the source at all, I couldn't. In my case, the noise source eventually went away. My guess is the rumble noise was coming from a broken ball bearing in a HVAC fan, but I still don't know for sure what it was.

author: CaptDon
author_rank: Super Contributor
timestamp: December 26, 2023, 10:44:43 pm
content: You will need a microphone with a large element such as the ones tailored for bass drums and sadly they are not cheap. The suggestion of using a speaker is a good one but it can't be just a raw speaker out in the open. The speaker should be a bass or subwoofer in a cabinet to act as a somewhat directional detector. Bass is so omnidirectional that is is often hard to pinpoint the source. I have a neighbor 3 houses over that has the car bouncing bass system in his vehicle. It is the typical overdriven 'sounds like shit' system. Sadly, I can hear the bass clearly in my livingroom even when watching T.V. but when I go outside to listen for the source it is barely audible. Good luck in your search. I am against earplugs if possible for reasons like "can't hear the smoke detector", "Can't hear vandals breaking in", "Can't hear neighbors knocking on the door telling you the apartment complex is on fire". "Can't hear Ed McMahon at the door telling you that you may have already won 10 million dollars". Cheers!!

author: coppercone2
author_rank: Super Contributor
timestamp: December 26, 2023, 11:15:07 pm
content: try ear infection and insurance that won't pay for ear antibiotics. cha chingcould also probobly the output of a dryer or forced air system etc. I heard of this happening before

author: themadhippy
author_rank: Super Contributor
timestamp: December 26, 2023, 11:25:56 pm
content: Quotewhist agreeing with a kick mic,id go with possible the smallest element kick mic,the sm91 , use its plate to find which surface the source is coming from

author: dobsonr741
author_rank: Frequent Contributor
timestamp: December 26, 2023, 11:42:37 pm
content: What happens after you found the frequency, perhaps the pattern too, that bothers you? What can you do about it?Most of the practical mitigations already mentioned - earplug, the other room. Do you have something else in mind?

author: PCB.Wiz
author_rank: Super Contributor
timestamp: December 27, 2023, 01:04:37 am
content: Quote from: FernandoCRS on December 26, 2023, 05:35:05 pmYou could try to record for > 24 hours, as it is rare for motors to run continually 24/7. The on/off times may give you clues.I see google finds thisQuote

author: coppercone2
author_rank: Super Contributor
timestamp: December 27, 2023, 02:48:54 am
content: its like slaying a dragon

author: FernandoCRS
author_rank: Newbie
timestamp: December 27, 2023, 09:56:30 am
content: I tried earplugs and a little ANC device. The noise is always there but it becomes better. And with the noise cancelling earbuds it´s ok because I can hear relaxing music. But I don't like pushing parts into my ears and after 15 minutes they become hot and uncomfortable. When I need to sleep I use sleeping pills.I'm going to give UMIK a chance and I want to try to get the minimum sound volume per frequency. It's usually easy to get the peak value but I am chasing steady noises.But I don't know how to do it, I will research. What is the best way to obtain a graph with the minimum values line in a real time spectrum?Note: It's not tinnitus, "in most cases, tinnitus pitch or frequency range is between 5 kHz and 10 kHz, and loudness between 5 and 15 dB above the hearing threshold". And I am doing ear medical exams.I know that the noise is close to my house and not in my ears because I don't hear it in other places.

author: FernandoCRS
author_rank: Newbie
timestamp: December 27, 2023, 12:05:35 pm
content: "What happens after you found the frequency, perhaps the pattern too, that bothers you? What can you do about it?"I would like to get the frequencies, filter the noise and record it, play and confirm the recorded noise is the same, get a real time filtered meter with light equipment like a laptop and a USB micro.

author: Marco
author_rank: Super Contributor
timestamp: December 27, 2023, 12:21:50 pm
content: With a moving average of the amplitude over time, system noise shouldn't really matter.Dunno what software can do a 3D spectrogram with adjustable temporal averaging, but it probably exists.

author: sharow
author_rank: Contributor
timestamp: December 27, 2023, 01:14:02 pm
content: Seems like Tunnel Boring Machines(TBM) are currently digging under Lisbon.Not only digging sound. There are ventilation pump, slurry pump etc.This may be related.-https://planodrenagem.lisboa.pt/fileadmin/pgdl/_ficheiros/Brochura_PGDL_eng.pdf-https://waterhub.pt/en/projects/plano-geral-de-drenagem-de-lisboa-2016-2030/-https://europe-cities.com/2022/10/02/construction-of-the-lisbon-drainage-plan-tunnels-starts-this-monday/

author: donlisms
author_rank: Frequent Contributor
timestamp: December 27, 2023, 04:20:14 pm
content: Quote from: coppercone2 on December 27, 2023, 02:48:54 amSo... practice, practice, practice?

author: berke
author_rank: Frequent Contributor
timestamp: December 27, 2023, 04:48:23 pm
content: I had a similar issue a while ago, it was the ceiling fan of the downstairs neighbour.If recording the sound is difficult, you could try to cancel it. Use a tone generator on your computer (or from a signal generator) and adjust its frequency, phase and amplitude until you are able to locally cancel the hum.Start by roughly adjusting the amplitude and the frequency until it sounds similar to the hum, then slowly adjust phase, frequency and amplitude. You probably won't be able to track the signal exactly (esp. if it is a mechanical device) but when you get beat frequencies you know you're not crazy and that gives you an approximate frequency.The vibration sensor idea is not bad, they work very well at low frequencies esp. if you can mechanically couple them to the walls or the ceiling. Example piezeo film sensor:https://www.te.com/usa-en/product-CAT-PFS0006.html

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: December 27, 2023, 05:03:01 pm
content: MXL has various condenser mics with large diaphragms that are just under a hundred bucks. They have pretty good LF response and low noise with the right input circuits. I'd start with something like that. If you can find the offending device, and if it's a motor, balancing it will probably eliminate the noise. If it's an underground boring machine, you're probably screwed.

author: Dundarave
author_rank: Regular Contributor
timestamp: December 27, 2023, 05:24:36 pm
content: Can’t help you with a mic option, but if you have hydronic (hot water) heating in your living space, it could be the recirculating pump noise/vibration being transmitted through the pipes or the structure.Some domestic hot water systems (i.e. hot tap water) also have recirculators on them to provide instant hot water.When all else is silent during the night, one can often hear these running.

author: CaptDon
author_rank: Super Contributor
timestamp: December 27, 2023, 05:29:47 pm
content: I have noted that in some HVAC ducting there can be a tendency for the air movement to set up an annoying resonance in the duct work which becomes basically a very low frequency whistle! The resonance can be 15Hz and often much lower like 3 to 7 hertz. It can at times be felt more so than heard.

author: Martinn
author_rank: Frequent Contributor
timestamp: December 29, 2023, 03:40:10 pm
content: For a similar problem, I purchased a Rode NT-USB and used the free spectrum lab software:https://www.qsl.net/dl4yhf/spectra1.htmlSpectrum lab works great, particularly the possibility to run long time waterfall displays helps a lot in finding intermittent sources and seeing patterns.The microphone is great, having a built-in USB interface means you don't have problems with audio interfaces or cable induced hum.

author: soldar
author_rank: Super Contributor
timestamp: December 29, 2023, 06:16:36 pm
content: If you cannot locate the source, if it feels like it is coming from everywhere, then it is being transmitted through the walls and floors, through the structure, and I would try looking for the vibrations directly in the solid mass of the building and not through the air.

author: nali
author_rank: Frequent Contributor
timestamp: December 29, 2023, 06:23:05 pm
content: If you're looking at noise through walls floors etc, it might be better to get a "structure borne driver" type speaker and use it in reverse as a mic. These are designed to attach to a mass (window, table, whatever) to make it the sounder, but should work fine the other way around.https://www.visaton.de/en/products/drivers-accessories/structure-borne-drivers

author: Terry Bites
author_rank: Super Contributor
timestamp: December 31, 2023, 04:42:00 pm
content: Try probing with a stethoscope to track down the source.Your neighbours will think you're insane if they catch you in the act though.1. Put a pink noise source by your bed. They mask low frequencies quite well. There are plenty of pink noise generator apps.2. Tune it out with "Active noise control". Again, there are noise-cancelling apps you might apply.3. Move to the country.

author: FernandoCRS
author_rank: Newbie
timestamp: January 10, 2024, 06:16:10 pm
content: Thank you.We have underground and drainage works in Lisbon: http//planodrenagem.lisboa.pt/fileadmin/pgdl/_ficheiros/Brochura_PGDL_eng.pdfBut I think my problem is from the neighborhood. Maybe I'll find outNow I´m looking for sounds in the air. Later I will try vibrations. It´s too much information for me.I saw there are 2 mics from RODE: NT-USB (Amazon-110€) and NT-USB+ (Amazon 182€). I need a low noise high sensitivity mic. Reading the datasheet I don't know which is better. I just bought an UMIK-2 and I am not rich to buy a very expensive mic when I don't know if I can locate the noise source with it.Ideas?

author: themadhippy
author_rank: Super Contributor
timestamp: January 11, 2024, 06:21:44 pm
content: QuoteHire one for a week,round here less than £20 will get you something suitable.