Is there a solid material with both a low acoustic impedance (specifically, an acoustic impedance as close as possible to that of the air) as well as low attenuation? In other words, is there a material that allows a substantial portion of an incident acoustic wave traveling through air to enter into it without reflection, and also allows that acoustic wave to pass through it without substantial attenuation?
For example, porous materials like foams or aerogels generally have a low acoustic impedance, but unfortunately they tend to have a high attenuation as well. Is it possible to have "the best of both worlds"?
I am studying the formation of acoustic bandgaps in materials with periodic density variations, and it would be convenient to have a material with those properties.
Best Answer
there are materials that do this, but they are not solids: the most common is open-celled elastic rubber foam. This material is used to make windscreens for microphones, to keep the wind from creating its own noise as it flows around the external housing of a microphone. here the idea is to get as much of the sound wave to penetrate the foam which then conducts it with minimal losses to the microphone element on the other side of the sheet of foam. My Shure PE54D-CN has one of these on it and it works quite well.