Infra Sound / subsonic noice

Hello,
I have only limited knowledge so far about Arduino and electronics, but I am not afraid making Experiments :smiley:

I would like to measure the intensity of infra sound within the range from ~ 1 Hz to 20 Hz.

I haven‘t found any working application so far. Hints are welcome :slight_smile:

Has any body any idea, which kind of sensor I should use?

I am thinking about using something like a low pressure sensor e.g. BME280 or a blood pressure sensor like the MPS20N0040D.

The whole system should be able to measure the intensity of sound at a certain given frequency.

But can I measure selectively at all with such kind of sensor or this not possible?

And I want to scan the range from 1-20 Hz and see the amplitude over frequency.

My fear is, that there is probably not only a single frequency in the air, but a kind of subsonic „pink noise“.

In the first step it is not necessary to calibrate it, since I just want to find out, whether there is a Maximum, respectively what there is at all around ...

Thanks for any assistance!

Regards
Idna

The pressure variations of sound in air are extremely small. Even for extremely loud sounds (+/- 1 Pa), the variation is only about 1 part in 100,000 of standard atmospheric pressure, 101,325 Pa.

To measure sound levels at very low frequencies, special microphones and amplifiers are required.

Well, thanks for the link with the microphones

  • very interesting, great performance but they probably blow up my budget :frowning:

Is there any low cost version available for my project?

Thx

Idna

There are several possibilites, this microphone goes down to about 6 Hz: https://www.semiconductorstore.com/cart/pc/viewPrd.asp?idproduct=96843&utm_source=GoogleShopping&utm_medium=cpc&utm_content=InvenSense&utm_campaign=ICS-40300&gclid=EAIaIQobChMIz_augIeq5gIVEdRkCh1AqwhdEAQYAyABEgLQXvD_BwE
Something I did in the vacuum tube days was to use a speaker for a microphone. It worked ok but if my memory serves me right it did great on low frequencies. They also do it in intercoms. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil

@ Gil:
Thx for the microphone link; this will be a good start since it starts at 6 Hz and fits in my budget ~ 3.50$...

I just have to find a way without paying 25 bucks for shipping costs to Germany.

Regards

Idna

An alternate path might be to look at electronic barometer chips and discover how quickly they can react to and record pressure changes.

Paul

"Electronic barometer chips" are too slow, too noisy and far too insensitive for this application. See reply #1.

1 Pa is 94 dB higher than the threshold of human hearing.

Well,

I made already some progress
I have found a good digital oscilloscope software, the Digital Audio Analyzer, see here

https://www.theremino.com/wp-content/uploads/files/DAA_V4.1.zip

With this spectrum analyzer I can easily visualize the frequency range from 1 Hz to 50 Hz with my Laptop - I need just a microphone covering this range with a as linear as possible frequency response characteristics...

So now I have ordered the microphone Gil suggested for testing - unfortunately it will take some time until it arrives.

And I have also ordered some cheap low pressure sensors from my Chinese friends for further experiments.
I will keep you informed...

Regards
Idna

+1

Theremino guys have a lot of useful tips and materials, also a board PIC based, that they use for a lot of tasks.

@ Zoomx:

Yes, that is true.

I already have a Theremino Master V5 considered for this project, using a large loudspeaker as a
“microphone”...

But independent of the evaluation unit I first have to get a reasonable, sensitive infra sound source for this range.

Regards
Idna

idna001:
@ Zoomx:

Yes, that is true.

I already have a Theremino Master V5 considered for this project, using a large loudspeaker as a
“microphone”...

But independent of the evaluation unit I first have to get a reasonable, sensitive infra sound source for this range.

Regards
Idna

And get an proper anechoic chamber to test in.

Paul

Hello Paul,

What is the advantage of a proper anechoic chamber?

Since I do not want to measure absolute values but under the normal ambient conditions?
(Where also the human ear tends to be...)

And if necessary, could I just build a small box (let’s say 0.5 x 0.5 x 0.5 m) around a proper microphone, walls inside covered with sound absorbent material?

As I have learned, the subsonic sound intensity is normally not reduced by anything, but big distance.
So all higher frequencies would be reduced then but not what I want to measure, right?

Regards

Idna

Keen on learning :smiley:

the subsonic sound intensity is normally not reduced by anything

Constructive and destructive interference is always an issue when measuring sound intensity, or any wave amplitude.

The distance between nodes and antinodes increases with wavelength, though.

@jremington:
And what does this information mean for my task?

May be I should have told more about my project at the beginning:

A friend of mine, who lives ~ 500 m air distance away from my home, claims that he hears respectively feels sometimes during night subsonic noise. I do hear nothing, but may be I am not sensitive to that...

That is the reason why I want to build something to either proof attendance or absenteeism...

So once my meter works, I have a specific location with specific ambient conditions where I will set up the data logger:
My friends sleeping room :grinning:

Regards
Idna

Keen on learning :smiley:

Constructive and destructive interference creates great difficulties in measuring sound wave amplitude (for any type wave, actually). For a single tone, the intensity of the sound varies substantially with detector location.

This is an important topic and something you should understand before attempting to make measurements.

Understood

  • but is not as easy as placing the microphone right there where my friend hears that noise - if necessary at his ear?

Regards

Idna

Keen on learning :grinning:

OK, you get a number next to your friend's ear. How will you determine what that number means?

idna001:
Hello Paul,

What is the advantage of a proper anechoic chamber?

Since I do not want to measure absolute values but under the normal ambient conditions?
(Where also the human ear tends to be...)

And if necessary, could I just build a small box (let’s say 0.5 x 0.5 x 0.5 m) around a proper microphone, walls inside covered with sound absorbent material?

As I have learned, the subsonic sound intensity is normally not reduced by anything, but big distance.
So all higher frequencies would be reduced then but not what I want to measure, right?

Regards

Idna

Keen on learning :smiley:

You wrote "I would like to measure the intensity of infra sound within the range from ~ 1 Hz to 20 Hz.".

The only way to create something to measure the sound is to first calibrate your measuring instrument. And to do that you cannot have echos and stray noise not created by your test source.

Paul

@jremington & Paul:

I do not have the solution yet...

But one idea is, (once I have finally a sensor (microphone?) covering that range) analyze this spectrum via FFT with a DSO and find out whether there is a suspicious peak.

If there isn‘t any, there should be nothing at all. Done.

If yes, build a detector for this specific frequency and go and search the source - voila!

Could that work?
Ok, I do not know right now, whether it is possible to build such a detector for a single frequency, let’s say 8Hz or what ever.

Regards
Idna

Keen on learning :grinning:

An alternative path or research would be to study how scientists have recorded and analyzed the infra-sound elephants use to communicate. Chances are they mix the infra-sound with a known tone and study the sum frequencies at something us humans can hear.

Paul