Sound has a comparatively big wavelength. So, it would need a reasonably large reflector to be appropriately reflected. But if the surface of the reflector has minute holes, will it really matter? Will it affect the intensity of the sound?
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1$\begingroup$ Worth checking: en.wikipedia.org/wiki/Soundproofing#Porous_absorbers, en.wikipedia.org/wiki/Acoustic_quieting, en.wikipedia.org/wiki/Radiation-absorbent_material $\endgroup$– QuilloMar 6 at 16:44
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2 Answers
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Yes it does, and here is why.
Imagine a sheet of some soft substance with holes in it spaced a fraction of an inch apart. each hole extends into the soft material to a depth of several hole diameters. These holes act as tiny organ pipe resonators which are excited by specific frequencies of sound waves that are hitting them. Since the holes are lined with soft material, they are well-damped and the resonant modes get rubbed into oblivion and are not reflected off the surface of the soft sheet of material.
In this way you can design a sheet of material that selectively absorbs a certain range of frequencies. Such sheets of material are known as acoustic tiles and are often installed as the ceiling surface in noisy rooms like cafeterias and busy offices. In recording studios, the walls themselves are often faced with acoustic tiles too.
In these cases the hole diameter, depth, and spacing are chosen to absorb most strongly in the frequency range corresponding to that of human speech, with peak absorption at about 3000Hz.
answered Mar 5 at 20:16
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Yes. Consider the following thought experiment. Take a perfect reflector, which reflects all the sound impinging on it. Then imagine the reflector is covered in tiny holes. Then imagine that the holes grow and combine. Eventually the holes grow to the point at which there is no reflecting surface left at all, when none of the incident sound is reflected. In the thought experiment, you have started with 100% reflection and ended with 0% reflection purely through the addition of holes. It seems therefore that holes matter.
