You can’t have a conversation across a rigid wall—all the sound impinging on it is reflected. Moreover, drilling small holes in the wall won’t do much to facilitate communication: Just as heat energy is poorly conducted through a thin wire, acoustic energy is poorly transmitted through small holes. But, reports a collaboration led by Sam Hyeon Lee of Yonsei University in South Korea and Oliver Wright of Hokkaido University in Japan, covering the holes with taut plastic film can make a world of difference. When excited at its resonance frequency, a membrane oscillates like a tiny loudspeaker and creates pressure waves that pass through the wall. The figure shows the results of a plane wave launched from the left and normally incident on a rigid, 5-mm-thick acrylic plate (white dashed line) perforated by four small holes. Red represents compression; blue, rarefaction; and yellow and green, near-zero excess pressure. Not much...

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