Practical question re sound waves

[lyoshida]

Hi - I am a lay person with a practical question regarding sound.
I live near a busy street and am considering having noise-reducing windows installed. The noise-reducing windows would fit beside (and in addition to) the current window to block out street noise, so in effect there would be two windows covering a single opening. My question is: if I open the two windows 4 - 6 inches to get fresh air in the summer time, will all of the noise I normally get enter the apartment through that opening, or would I still have some sound reduction compared to now because a large portion of the window would be double-covered? Not sure how sound waves move and whether a "tunnel" effect would negate the value of the noise-reducing windows. Your thoughts are greatly appreciated!

 

[mfb]

Do you hear a significant difference between "current window closed" and "current window a bit open"? I would expect that - and then, the window quality does not really matter unless it is fully closed.

 

[sophiecentaur]

Welcome.
This could represent a rather expensive experiment for you if the results aren't as good as you hoped for and it may be best to ask your window supplier for a demo of a system they have already installed somewhere. Some of this is subjective but an amazing and annoying amount of noise can get through even a small gap / hole so even the best noise-reducing window system will let you down if you open it up a bit. If you want fresh air as well as no noise, you may have to consider a separate ducted ventilation system or Air Con (owch!).

 

[lyoshida]

Thank you both for your replies - this is very helpful!

 

[Khashishi]

Well, maybe I'm grossly oversimplifying things, but it seems opening the window will make the difference between windows pretty moot. Let's say a soundproof window has a noise reduction rating of 30dB and a normal window has a reduction of 20dB. So, window 1 blocks 99.9% of the noise and window 2 blocks 99% of the noise. But if the windows are 10% open, then window 1 will block 89.9% of the noise and window 2 will block 89% of the noise. Basically no difference.

I'm neglecting all the diffraction effects of the open window. Maybe it makes a small difference, but bottom line is, if the window is open, it doesn't really matter.

 

[sophiecentaur]

I'm neglecting all the diffraction effects of the open window. Maybe it makes a small difference, but bottom line is, if the window is open, it doesn't really matter.

Yes. The low frequency sounds will not get through a narrow slot. But this can make the situation even more annoying because you tend to get annoying 'tinny' sounds coming into your otherwise quiet room.
Sound-proofing is a very expensive exercise, if it's to be done well and, once you've eliminated one path, the next one rears its ugly head.

 

[mikeph]

I can say from first hand experience, if the window is actually open then the difference will be unnoticeable.

 

[sophiecentaur]

Also, if you stand outside.

 

[BenG549]

To be honest, to cut a long story short if you want fresh air and a good nights sleep buy some ear plugs.

For the longer story - The insulation provided by ANY type of window when partially open will be in the region of 10-15dB, depending on the size of the window and the spectrum of the noise. If its mainly low frequency rumble you're experiencing due to heavy goods vehicles etc then additional glazing will have no real effect. Sophiecentaur mentioned above that low frequencies will not get through the slot, this might be true although it is miss leading as they will propagate though bricks and mortar let alone glass windows.

The other problem with adding another pane or window is that, depending on the gap between the two, you may create a mass spring resonance between the glass (mass) and the air between (spring) this could actually make the problem worse if the person installing it is not an expert in noise control because you will end up with a distinctive tonal element to the noise which has been shown to be more annoying; subjectively adding around 5dB to the noise.

If it is just a high frequency problem (lots of kids in the neighbourhood ridding around on mopeds for example) extra glazing might help, if installed correctly, however its a cost/benefit thing, you might achieve an extra 5 or even 10dB reduction (if your lucky) but the cost might mean its just worth leaving the window shut or masking the annoying noise with some music or TV when it's open.

Ben.