Hum / vibration over winter... at wits end

[thrope]

This weekend I found time to record with a condenser mic. With the mic in the stand I didn't see much, but with the mic lightly touching the wall I am able to see a difference between when the hum was there in the morning, and later in the day when it's gone.

 

Orange line is power recorded for different frequencies when I could hear the hum, yellow line is same setup but later in the day when the hum was off. The blue line is a control with the mic off to see the line noise in the laptop and audio interface.

 

Looks like there are two things there, a tight frequency around 20.5 + harmonics up to 102.5 (5 x 20.5) and also some peaks at 47 and 49 Hz.

 

I suspect the thing around 30Hz is fridges and freezers as it appears in both conditions. I could try this with the electricity in the house off as recording on a laptop with a USB interface.

 

I think 20.5 is certainly in the ball park for resonant frequency of a pitched roof and I think mechanical resonance induces harmonics so that's still the best guess.

 

Will try a longer recording (this was based on 1 minute) to try to pin down the frequency as accurately as possible. Best I get from this (using a longer analysis window is 20.52Hz).

 

I found this:

Just a moment...

WWW.RESEARCHGATE.NET

 

So crudely interpolating to say a height of 4.5m would give a 1st mode of 20.3Hz and second mode of 48.5Hz. So I'm thinking the stuff around 47/49 could be the 2nd mode of the roof.

 

 

Edited November 6, 2022 by thrope

[difflock]

I spent months imagining I was imagining hearing something weird while lying in bed, an odd intermittent humming. I finally figured out it is almost certainly the Leibherr freezer just on the other side of our downstairs bedroom wall. Resonating through the poured concrete floor that was cast hard up against the outside wall of the house( with no polystyrene expansion strip placed pre pour)

Doh!

[AHPP]

2 hours ago, thrope said:

This weekend I found time to record with a condenser mic. With the mic in the stand I didn't see much, but with the mic lightly touching the wall I am able to see a difference between when the hum was there in the morning, and later in the day when it's gone.

 

Orange line is power recorded for different frequencies when I could hear the hum, yellow line is same setup but later in the day when the hum was off. The blue line is a control with the mic off to see the line noise in the laptop and audio interface.

 

Looks like there are two things there, a tight frequency around 20.5 + harmonics up to 102.5 (5 x 20.5) and also some peaks at 47 and 49 Hz.

 

I suspect the thing around 30Hz is fridges and freezers as it appears in both conditions. I could try this with the electricity in the house off as recording on a laptop with a USB interface.

 

I think 20.5 is certainly in the ball park for resonant frequency of a pitched roof and I think mechanical resonance induces harmonics so that's still the best guess.

 

Will try a longer recording (this was based on 1 minute) to try to pin down the frequency as accurately as possible. Best I get from this (using a longer analysis window is 20.52Hz).

 

I found this:

Just a moment...

WWW.RESEARCHGATE.NET

 

So crudely interpolating to say a height of 4.5m would give a 1st mode of 20.3Hz and second mode of 48.5Hz. So I'm thinking the stuff around 47/49 could be the 2nd mode of the roof.

 

 

Is the thinking to identify the frequencies and fire back the same frequency out of phase to neutralise it?

[thrope]

1 minute ago, AHPP said:

Is the thinking to identify the frequencies and fire back the same frequency out of phase to neutralise it?

 

Not thinking of any active correction, but first to identify what it is, and if it is the roof resonating I thought if I could shift the resonant frequency of the roof by adding weight maybe to some of the beams, then it might move away from whatever vibration is coming from the farm and reduce the effect.

 

Or construct a tuned mass damper like I linked in earlier post to target the 20.52Hz resonance. That's a mass and spring system tuned I think to have the same resonant frequency, but with a damper attached. Mostly they seem to be on a much larger scale though (bridges, skycrapers etc.)

[Stubby]

26 minutes ago, difflock said:

I spent months imagining I was imagining hearing something weird while lying in bed, an odd intermittent humming. I finally figured out it is almost certainly the Leibherr freezer just on the other side of our downstairs bedroom wall. Resonating through the poured concrete floor that was cast hard up against the outside wall of the house( with no polystyrene expansion strip placed pre pour)

Doh!

Some nights , lying in bed , I would be listening to what sounded like to me a big diesel engine ticking over . I would get up and open the window to listen , nothing . This happened quite frequently . It took me several months to realize that it was my pulse ! The blood pumping in my head near my ears . Bonkers innit ? 

[GWYNFIL]

not read all pages but. had a new arieal fitted in an previous property used to vibrate and projuced a hum! made worse by on the chimney.

 

[Lowestoft Firewood]

Holmfield Hum: Yorkshire villagers say they're 'tortured' by noise

WWW.BBC.CO.UK

---

A constant hum is driving some Holmfield residents to despair, but the source remains a mystery.

 

[Rachy]

Did you find out where the vibration was coming from? I have similar issue only over winter