What is this in theory? (Unseen Absorber)

[Ghoostknight]

Hello, we live in an quite old house and we have a industrial kind of fan next door which produces quite alot of (low frequency) noise

effectively this contraption on the window minimizes the low frequencys entered the room trough the window! not only the fan noise (tho i have tuned it to that) but also noise from the street/cars

i could even imagine it filters the same frequencys out of the room and therefore acts as some kind of panel absorber, imo quite cool (basicly free absorbtion, even if its just a few db) but you get laughed at if someone sees it lol

in theory i think this is some kind of mass-spring system, which can be found in "Seismic Dampeners" aka "Tuned Mass Damper" ( https://en.wikipedia.org/wiki/Tuned_mass_damper )

you can tune this prototype by the amount of water inside the bottle and the placement of the yellow dampener on Z axis

Any Thoughts?

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some more information....

the (double) glass window panel is 150x60cm, the bottle sits around the middle
500ml bottle (nearly full)
yellow dampener at the end of the bottle

with water amount you can do broader adjustments, with the placement of the dampener you can actually finetune things (without messing around with the exact water amount)

if i heared things right (with speaker playing the same tone/ figuring the tuning frequency out) the tuned frequency should be right around 15-25Hz

 

[2leftears]

Yes, you have likely dampened the first (lowest) resonance frequency mode of the window pane.

Lidl's finest; spritziger Geshmack, glückselige Stille...

 

[Ghoostknight]

Lidl's finest; spritziger Geshmack, glückselige Stille...

yes lol, definitely works as prototype but it looks quite ridiculous

i recently got an 3D Printer, i eventually print something better looking here
Windows honestly always bothered me with speakers, if they are not behind or opposite from the speakers you usually get quite heavy balance/reflection issues without thick curtains
So i find it quite interesting that you can actually use the window real estate for "some benefit" with this (specially absorbing low frequencys seems to be quite rare/hard to achieve)

this might not only tune the window to a certain frequency but also keeps the window quite steady on higher frequencys, atleast my subjective feeling tells me the windows behind me are more quite now (might be just the outside noise missing tho)

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i remember reading/seeing something about some active noise canceling speakers you can hook up to the windows..... this is one of them after a quick search: https://denoize.com/
tho im wondering how good this works with music playing inside the room

Yes, you have likely dampened the first (lowest) resonance frequency mode of the window pane.

are you sure about this? because to me it feels not like im dampening window resonances (well, maybe too) but the window panel actually "passively cancels the tuned frequency of the tuned mass damper"

imagine a 20Hz wave hitting the window..... the window will not resonate in its own panel frequency but in the 20Hz frequency i imagine, or maybe initially in 20Hz and then switching to self-resonance?
the thing is with closed window i can still hear the deep bass note entering the room (specially at night) so this should mean the window is actually vibrating in that frequency
now you can tune the mass dampener to 20Hz and the window will act as passive absorber in that frequency range (i imagine the added weight will also damp higher resonances)

Or did i get this wrong with my subjective testing and i should just tune the mass dampener to the glass panel resonance frequency? (i imagine this would be a bit higher?)
found this https://www.reddit.com/r/Acoustics/comments/pjjjzc/reducing_resonant_frequency_of_doubleglazed/ related to the topic

 

[gregorio]

Yes, it works quite well. It’s not that the low freqs are actually absorbed, it’s just that you don’t notice them as much. However, I’m not sure that just one bottle is enough, I find I need to drink about 5 to start having an effect. Jägermeister is more effective, just one bottle and you won’t notice any bass freqs at all, it’s like magic!

G

 

[Ghoostknight]

Yes, it works quite well. It’s not that the low freqs are actually absorbed, it’s just that you don’t notice them as much. However, I’m not sure that just one bottle is enough, I find I need to drink about 5 to start having an effect. Jägermeister is more effective, just one bottle and you won’t notice any bass freqs at all, it’s like magic!

G

i didnt suspect any other answer from you than an irony loaded one as of course all of this is inaudible dictated by science

 

[gregorio]

as of course all of this is inaudible dictated by science

Indeed, it is obviously dictated by science that humans can’t hear and therefore everything is of course inaudible. I’m not quite sure how beer is supposed to help then, does it also make low freqs drunk?

G

 

[Ghoostknight]

Indeed, it is obviously dictated by science that humans can’t hear and therefore everything is of course inaudible.

bravo

 

[2leftears]

Window panes have multiple resonance frequencies; there are the higher resonance frequencies of waves in the window pane itself, but also the lower frequencies determined by the mass of the window pane and the compliance of the air in the room. The latter is effectively a resonator, and is also affected by how air-tight the room is when all other doors windows are closed.

Resting/suspending a near 500 gram weight against the centre of an average size window is going to materially affect the window pane's ability to freely vibrate at the lowest frequency(s), and shift the other resonance modes a bit. It certainly might well affect the coupling of exterior low frequency sound waves to the window pane and the interior of the room, which is likely what @Ghoostknight is experiencing here.

Whether what Ghoosty has built himself is the tuned mass damper he suspects it is, or whether he has simply added to the effective vibrating mass of the window pane is more difficult to determine by just looking at it. Much depends on e.g. the exact location and damping/compliance properties of that yellow bit of material, as well as exactly where on the window that suction cup has been attached.

I don't see anything controversial here from a science perspective. For once, I would say that this is a tweak that actually has the ability to work in theory, and costs virtually nothing (if you consider empty beer bottles a cost-free byproduct of drinking Lidl's finest anyway ). Of course, what the neighbours think of this tweak is a different matter entirely; they just see a house full of beer bottles suspended from windows...

@Ghoostknight; just make sure what you are experiencing actually has an external cause and is not related to some physiologically self-induced phenomenon such as tinnitus or spontaneous otoacoustic emissions. You may find this phenomenon interesting in context: The Hum . I also suffer from it but based on my own observations in my case I am 95% certain it is a form of either tinnitus or SOAE.

 

[Ghoostknight]

@Ghoostknight; just make sure what you are experiencing actually has an external cause and is not related to some physiologically self-induced phenomenon such as tinnitus or spontaneous otoacoustic emissions. You may find this phenomenon interesting in context: The Hum . I also suffer from it but based on my own observations in my case I am 95% certain it is a form of either tinnitus or SOAE.

yesterday i actually completely solved the mystery after talking with my neighbor
we took a look at the AC room where the fan is located and he said "we can reduce the fan speed" well that was the whole issue, the thing had an dimmer switch making the fan run unsmooth! we put it on 100% and while the audible hissing sound of the air obviously increased slightly (it was 70-90% before that) the actual hum (really a periodic 2 second bass wave/impulse) deminished by quite alot

yesterday with open window it was by far the quietest night (as i was hearing the bass note probably twice as loud at night time, same fact you find on pretty much all "the hum" reports)

imo its fair to assume it was a real thing, specially the dimmer thing makes sense from what i read

tho, keep in mind even my neighbor was looking funny at me as he wasnt noticing it, its what its with these sort of things... mainly happy now that the "spook" is over

Window panes have multiple resonance frequencies; there are the higher resonance frequencies of waves in the window pane itself, but also the lower frequencies determined by the mass of the window pane and the compliance of the air in the room. The latter is effectively a resonator, and is also affected by how air-tight the room is when all other doors windows are closed.

Resting/suspending a near 500 gram weight against the centre of an average size window is going to materially affect the window pane's ability to freely vibrate at the lowest frequency(s), and shift the other resonance modes a bit. It certainly might well affect the coupling of exterior low frequency sound waves to the window pane and the interior of the room, which is likely what @Ghoostknight is experiencing here.

Whether what Ghoosty has built himself is the tuned mass damper he suspects it is, or whether he has simply added to the effective vibrating mass of the window pane is more difficult to determine by just looking at it. Much depends on e.g. the exact location and damping/compliance properties of that yellow bit of material, as well as exactly where on the window that suction cup has been attached.

yea there are alot of variables going on specially if you consider double/triple glass windows with different glas plane thicknesses, which seems to be one countermeasure against resonances adding up

in terms of helmholtzresonators or tuned absorbers for that matter i find it much simpler to play a sinewave with speakers and audible tune the absorber, it works quite well (just listen for an obvious dip) and depending on additional variables this is probably also in the end much more accurate then just doing some calculations, putting it in a room and calling it a day

i might try todo this with the window at 40Hz (as my speakers only ouput low volume under 30Hz) and take some measurements, we might be wiser afterwards and can discuss further wether this is a tuned absorber or only dampens the window movement


----------------------------------------- DOUBLE POST

first audible/subjective test was indeed sucessful

- tuned the window to 40Hz, i have the biggest roommode at 42Hz (40-44Hz really) and was able to reduce the roommode EQ by 3-4db afterwards (from -8db to -4, quite substantial imo try to do that with pouros absorbers and your room is full lol)
- needed to remove around half the water, so the previous frequency was indeed somewhere around 20Hz
- playing a 40Hz sinewave, i can literally feel the window shaking to that frequency without tuned mass, with tuned mass it still vibrates but its not in sync with the played sine wave anymore (cancelation, i guess)
- @2leftears the dampener are these yellow ones for 2-6kg cut in half https://frankenschaum.de/PolySound-...Fuesse-Schwingungsdaempfer-8er-Set-gelb-2-6kg
actually switching the orientation of the dampener (flat cut side against the window, bottle on curved outer edge) improved things by 1-2db compared to the orientation you see on the picture..... im pretty sure it was todo with the bottle hanging and not being in the optimal weight-class for this dampener and orientating in such way has better dampening properties

im actually not sure if you could use any better dampener here, as these speaker ones are already optimized for low frequency dampening down to a few Hz (which means, it also actively dampens the (low) mass vibrations, which seems crucial from what i read)

- with the previous 20Hz it felt like it reduced it by around 6-10db, really not sure here, i dont wanna either exclude the possibility that overall window dampening did something or that this was just a subjective audible thing with nearly inaudible low frequencys, more tests would be needed i guess

EDIT: i just found out that the roommode peak region of the first half-wavelength roommode (40Hz) is directly in front of the windows, that might make this tweak particular effective in my case