Noise Muffling: Locked vs Unlocked Window

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sardia
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Noise Muffling: Locked vs Unlocked Window

Postby sardia » Wed Jun 24, 2015 5:24 am UTC

I have a closed window, and I can hear a large truck outside idling. I reach out and closed the latch, which increases the pressure on the window frame. Why does the sound cutoff from the outside? Shouldn't the sound waves from the truck hit the window, and transmit to the air inside my room? Why would locking my window reduce the noise from the outside? Simply closing my window should do if it just a matter of having an air to air connection. Perhaps the increased pressure somehow reduces vibrations?

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Re: Noise Muffling: Locked vs Unlocked Window

Postby Neil_Boekend » Wed Jun 24, 2015 8:08 am UTC

AFAIK You increase the connection between the window and the house, causing the soundwaves to bleed to the house more.
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Re: Noise Muffling: Locked vs Unlocked Window

Postby Zamfir » Wed Jun 24, 2015 11:03 am UTC

An hypothesis: when the window is loose, it moves (more or less) as a rigid plane. When you close the latch, the edges become tighter fixed to the heavy walls, and only the centre of the window moves easily under pressure fluctuations.

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Re: Noise Muffling: Locked vs Unlocked Window

Postby qetzal » Wed Jun 24, 2015 1:49 pm UTC

If your window is like some of mine, latching may also close it tighter, eliminating some gaps where the sound was coming through.

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Re: Noise Muffling: Locked vs Unlocked Window

Postby sardia » Wed Jun 24, 2015 10:51 pm UTC

qetzal wrote:If your window is like some of mine, latching may also close it tighter, eliminating some gaps where the sound was coming through.

It is like you describe, and I've considered that hypothesis as well. Personally, I don't think the air flowing around the seems should matter much.


Edit: https://www.soundonsound.com/sos/mar98/ ... ofing.html
Quick googling brings me some interesting hints. Apparently increasing the pressure on a window and eliminating the air flow affects sound transmission. So a window tightly clamped to my wall but has cracks at the bottom isn't as good as a window with no cracks. That's unexpected to think such a small gap can still transmit sound.

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Re: Noise Muffling: Locked vs Unlocked Window

Postby Twistar » Thu Jun 25, 2015 7:06 am UTC

It should make sense that sound can bleed through cracks even if they're pretty small. The highest pitch we can hear has wavelength of ~1-2 cm according to Wikipedia so that can easily bleed through a crack of roughly that size. That's probably the largest effect in hearing sound through a window. If the window is shut so that there are no crack then the next biggest effect is the window being vibrated by the sound wave and then transmitting it into your room. There is going to be a lot of loss of energy when the soundwave has to transfer into the pane and a lot of energy when it has to transmit back to air. However, the difference with clamping it down is going to have to do with what happens to the energy while the sound is in the glass window pane. If it is not clamped down then only the (relatively) small mass of the pane must oscillate and it wouldn't be surprising if it is responsive at audible frequencies. Whereas if you clamp it down then now the sound wave is transferred to the whole window frame and wall and this much more massive and more dissipation system will not transmit the sound wave as well. Of course you could get all combinations of these effects depending on the relative strengths.

In this case you "tighten" the spring and that kills the oscillations. However, the opposite effect can happen as well. Consider riding your bike over bumpy terrain. If you stand up and relax your grip you can ride the bumps, but now imagine sitting on a hard seat and gripping the bar tightly while going down. Now by "tightening" the spring you've become more sensitive to the oscillations. Something similar could maybe happen based on windows sizes and the sounds involved where UNLATCHING the window may actually work better to dampen the sound.

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Re: Noise Muffling: Locked vs Unlocked Window

Postby gmalivuk » Thu Jun 25, 2015 6:51 pm UTC

Twistar wrote:It should make sense that sound can bleed through cracks even if they're pretty small. The highest pitch we can hear has wavelength of ~1-2 cm according to Wikipedia so that can easily bleed through a crack of roughly that size.
Who has cracks that big when the window is closed but not locked, though?
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Re: Noise Muffling: Locked vs Unlocked Window

Postby SDK » Thu Jun 25, 2015 7:08 pm UTC

gmalivuk wrote:
Twistar wrote:It should make sense that sound can bleed through cracks even if they're pretty small. The highest pitch we can hear has wavelength of ~1-2 cm according to Wikipedia so that can easily bleed through a crack of roughly that size.
Who has cracks that big when the window is closed but not locked, though?

And is that actually the limit to what sound can travel through anyway? My ear canal is smaller than that...
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Re: Noise Muffling: Locked vs Unlocked Window

Postby gmalivuk » Thu Jun 25, 2015 7:27 pm UTC

And earphone speakers are tiny.
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Re: Noise Muffling: Locked vs Unlocked Window

Postby Angua » Thu Jun 25, 2015 7:34 pm UTC

I've forgotten the technical word for it, but sound waves propogate along the axis of their movement, instead of perpendicular to them. Surely that means that the width of the opening isn't as important?
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Re: Noise Muffling: Locked vs Unlocked Window

Postby sevenperforce » Thu Jun 25, 2015 7:40 pm UTC

Angua wrote:I've forgotten the technical word for it, but sound waves propogate along the axis of their movement, instead of perpendicular to them. Surely that means that the width of the opening isn't as important?

Longitudinal.

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Re: Noise Muffling: Locked vs Unlocked Window

Postby Twistar » Thu Jun 25, 2015 8:09 pm UTC

gmalivuk wrote:
Twistar wrote:It should make sense that sound can bleed through cracks even if they're pretty small. The highest pitch we can hear has wavelength of ~1-2 cm according to Wikipedia so that can easily bleed through a crack of roughly that size.
Who has cracks that big when the window is closed but not locked, though?


Yeah that's what I was thinking. Well, I had cracks in my windows that big one time but that was a really old place. I guess waves can propagate through a hole smaller than their wavelength. Think about light diffraction experiments, those slits can be smaller than the wavelength. I got myself all mixed up thinking about near field and stuff but I'm pretty sure a hole, no matter how smaller will just appear as a source of sound inside the house and the transmission efficiency somehow depends on the size of it. I'm not sure if the analogies with light are as straightforward as I'm making them right now though..

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Re: Noise Muffling: Locked vs Unlocked Window

Postby Zamfir » Fri Jun 26, 2015 4:48 am UTC

Sounds does travel through small holes, then spreads as a point source if the hole is much smaller than the wavelength. Air friction in a crack seeps off energy though, so at some point very small cracks don't effectively channel sound anymore.

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Re: Noise Muffling: Locked vs Unlocked Window

Postby cphite » Fri Jun 26, 2015 6:47 pm UTC

sardia wrote:I have a closed window, and I can hear a large truck outside idling. I reach out and closed the latch, which increases the pressure on the window frame. Why does the sound cutoff from the outside? Shouldn't the sound waves from the truck hit the window, and transmit to the air inside my room? Why would locking my window reduce the noise from the outside? Simply closing my window should do if it just a matter of having an air to air connection. Perhaps the increased pressure somehow reduces vibrations?


I am guessing the window is double pane. The vibration from the truck is vibrating the whole window, which in turn vibrates the air in your room. When the window is locked, it is pressed more tightly against the frame, which means it vibrates less.


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