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https://poal.co/s/AskPoal/712368

My recording attempts so far have yielded mixed results. Been visualizing the live spectrum with my phone and Spectroid. Seems to work some of the time but other times it won't.

When I get this https://pic8.co/sh/03mMMf.png , I think it's something to do with the electric grid because there's a clear peak at 50 Hz and the first harmonic. (Yurop uses 50 Hz)

But other days I get this https://pic8.co/sh/DyTi89.png

Today I recorded the spectrum of the appx. 70 Hz signal and I thought I had finally found the best settings in Spectroid. I thought I had won and at least found good settings to visualize. Then I tried again and... hardly any signal.

Things I have tried: Bought an USB to XLR Adapter for the one mike I own (Shure Beta 58A) This combo technically works but the noise floor is atrocious. For the level I'm looking at it might as well be "noise to signal".

I've set my mind to find better recording equipment. (And set up a web site and advertise it on a local billboard but I need good data for that)

Condenser instead of dynamic: https://www.thomann.de/de/behringer_ecm_8000.htm

Now I need a recommendation for a good digital recorder. Zoom and Tascam seem to have good products.

They all seem to be capable of 32 bit recording https://www.thomann.de/de/portable_recorder.html and 96 kHz sampling, which theoretically should not matter for this low low frequency application.

Money is not the main issue, buy once, cry once. Reason why I'm asking is disappointments with "great" products in the past. Looking for a good product with few ragrets. A live spectrum would be a feature I'd love during recording but that'd be a luxury.

Oh, almost forgot... Today, at a customer's house I worked on something IT related. Every time things got silent, "Siehe Da!" I heard the hum. I asked the (older) couple and she heard it, he wasn't sure. They live 3-4 kilometers away from me. Three weeks ago, my step son and his girlfriend were over to visit. When we had breakfast, she asked about that strange noise. Last fall I went to the forest, trying to locate the sound or at least find differences in its level. I drove, then walked about 4 kilometers from where we live and still heard it. What I'm saying is, I don't think I'm imagining this. If I do, I indent to find out.

https://poal.co/s/AskPoal/712368 My recording attempts so far have yielded mixed results. Been visualizing the live spectrum with my phone and Spectroid. Seems to work some of the time but other times it won't. When I get this https://pic8.co/sh/03mMMf.png , I think it's something to do with the electric grid because there's a clear peak at 50 Hz and the first harmonic. (Yurop uses 50 Hz) But other days I get this https://pic8.co/sh/DyTi89.png Today I recorded the spectrum of the appx. 70 Hz signal and I thought I had finally found the best settings in Spectroid. I thought I had won and at least found good settings to visualize. Then I tried again and... hardly any signal. Things I have tried: Bought an USB to XLR Adapter for the one mike I own (Shure Beta 58A) This combo technically works but the noise floor is atrocious. For the level I'm looking at it might as well be "noise to signal". I've set my mind to find better recording equipment. (And set up a web site and advertise it on a local billboard but I need good data for that) Condenser instead of dynamic: https://www.thomann.de/de/behringer_ecm_8000.htm Now I need a recommendation for a good digital recorder. Zoom and Tascam seem to have good products. They all seem to be capable of 32 bit recording https://www.thomann.de/de/portable_recorder.html and 96 kHz sampling, which theoretically should not matter for this low low frequency application. Money is not the main issue, buy once, cry once. Reason why I'm asking is disappointments with "great" products in the past. Looking for a good product with few ragrets. A live spectrum would be a feature I'd love during recording but that'd be a luxury. Oh, almost forgot... Today, at a customer's house I worked on something IT related. Every time things got silent, "Siehe Da!" I heard the hum. I asked the (older) couple and she heard it, he wasn't sure. They live 3-4 kilometers away from me. Three weeks ago, my step son and his girlfriend were over to visit. When we had breakfast, she asked about that strange noise. Last fall I went to the forest, trying to locate the sound or at least find differences in its level. I drove, then walked about 4 kilometers from where we live and still heard it. What I'm saying is, I don't think I'm imagining this. If I do, I indent to find out.
[–] • 2 pts

You should try building a barrier box on a tripod. It would need to be big and heavy and soundproof on five sides but completely open on one side. You put your listening equipment in there and then you would be able to turn it and figure out exactly which direction the sound is coming from. There may be a little bit of hit and miss due to echo but I think you would probably be able to narrow it down pretty quickly

[–] • 2 pts

Thanks for the suggestion and I'll try that if everything, and I mean everything else fails.

[–] • 1 pt

How about a couple of Ear Trumpets?

This one made me laugh. But hey!! You never know what might work.

https://makerworld.com/en/models/669319?from=search#profileId-596970

[–] • 1 pt

Might help me to hear but I want to record and analyze. I hear the phenomenon fine.

[–] • 1 pt

I've had issues with this but I determined that it was some kind of tinnitus that occurs only when it's very quiet. It was right at 60 Hz too.

[–] • 1 pt

Definitely not ruling that out yet. I've had two people claiming they can hear it after I prompted but that might be power of suggestion.

Would explain many things, like hearing it far away from home and having a hard time to nail a consistent recording.

One young woman, who spent the night here some weeks ago, prompted me the next morning at breakfast. That made my day, because I was almost convinced of an auditory hallucination at that point.

[–] • 1 pt

Years ago I chased some low-frequency noise, which might have been the house just resonating with some frequencies from traffic and other things. I spent hours trying to eliminate it (a fence outside, supports inside). I ended up just having a bathroom ventilation fan with a weight bolted to one blade to make it badly off-balance, screwed to the baseboard so it would resonate the wall some to create its own low-frequency sound to mask the other at night. These days I just have an old small subwoofer connected to an mp3 player playing brown noise with strong low-frequency content, at a low volume. It knocks out all the cars idling and driving by, especially in the morning.

I was actually relieved to find that what I was experiencing was likely internal (tinnitus), since it meant I didn't need to go on another chase trying to find a case/solution. Well, as long as it only occurred in dead silence, since even a quiet fan made it go away. If it was all the time I think I'd go out of my mind. It's actually not acted up in weeks, even in dead silence (which also confirms that it's not external, because I couldn't have many days in a row of dead silence all day in the house even though they were busy days out in the world).

[–] • 1 pt

There's a hum at my old man's house on moist days. High tension lines are just behind the backyard. Had a friend who's wall was humming, turned out to be a yellow jacket hive in the wall. Back when I was a high school jerk we had a substitute that was clearly new and nervous. I started humming, 4 or 5 other guys around the room joined in. She couldn't figure out who was doing it or how to stop it. She ended up getting a more experienced teacher to lay down the law.

[–] • 0 pt

The bird is the word.

[–] • 0 pt

Definitely condenser over dynamic microphones for this application. I can vouch for that Behringer ECM 8000 metrics microphone. I use those with my Behringer DSP 8024 active EQ/spectrum analyzer room correction units. They are good for a wide range of frequencies and should do well at the ~70 Hz you have with the hum. I'm more a fan of Tascam over Zoom, but I think Zoom has really stepped up their game over the last few years.

As for the hum itself...70/77 Hz is noteworthy, no pun intended. It's not AC power frequency, it's not any standard harmonic of AC power frequency and it's not at all common in the world. That rules out a huge number of manmade sources. Not sure if you've measured any higher order harmonics at 140, 280, etc. but there presence or absence would help rule out some natural phenomenon as well. If there is only the fundamental harmonic, well that makes this a lot spookier since that would indicate a manmade source of very deliberate purpose.

If you're so inclined, look for some surface conduction transducers to use as microphones. These transducers are often used as speaker drivers that attach to a wall or a hard surface to turn the whole thing into a speaker. You can use them as microphones just the same. These could be attached to a sheet of plywood or even insulation panel and placed on bare ground to see if the hum is emanating from the earth or the atmosphere. You could even just use a large woofer driver as a mic and get good results too. I used to listen to my whole house as a teenager with such a setup. Never could make conversations out clearly but it was fun nonetheless.

BTW, I checked Spectroid on my phone to be sure the app doesn't have a natural "whistle" at 70/77 Hz. Some FFT apps tend to have false indications at specific frequencies, but my phone doesn't indicate that. But...phone hardware varies and the phone itself could have various "whistles" in it but it's rare to see one at such a low frequency. Hmm, I do see a whistle at 50 Hz. I'm not in Europe and have 60 Hz AC. Weird.

[–] • 1 pt (edited )

Ordered the Behringer plus a wind screen fur thingie and a good short XLR cable.

For the recorder, I'm currently looking at the Tascam Portacapture X6, might be overkill but it has the 32 bit resolution, which I would like to have.

Thank you so much for your input, it helps and is very much appreciated.

I'll keep you in the loop.

ETA: Also looking into surface transducers. Any recommendations? Only found this in a cursory search: https://www.sparkfun.com/surface-transducer-large.html