So I live in a city that is rather warm at this time of year and the street where I live is rather loud. I have to keep the window in my bedroom open at night, otherwise it becomes way too hot. The thing is, this allows bugs and noise to come in as well. A wire mesh can solve the bug problem but this got me thinking - would it be theoretically possible to create a "window" in such a way that it would let air through but not noise?
The answer seems to be, somewhat surprisingly, yes.
The trick is to use a metamaterial that has subwavelength structures that interact with the sound field in the right way. The paper Ghaffarivardavagh, R., Nikolajczyk, J., Anderson, S., & Zhang, X. (2019). Ultra-open acoustic metamaterial silencer based on Fano-like interference. Physical Review B, 99(2), 024302. demonstrates this with a ring of metamaterial that lets air through but blocks sound with 94% efficiency. Indeed, they were apparently also inspired by the noisiness of city life.
The problem is that this is pretty frequency specific. Different rings could cover more of the spectrum, but it will not stop impulse noises.