Wood... but the spherical sound box is fashioned out of a whole coconut shell.

木头……不过球形的音盒是整个椰子壳做的。

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No sound comes from the shell, though there is plenty of air in the room.

虽然隔音房内有充足的空气，贝壳里却一片安静。

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The method in this paper, which can be used to calculate the interior sound field of arbitrary-shaped closed thin shell (equal or unequal thickness), suits a large scope.

本文所提出的这一方法适用面广，可以求出任意形状封闭薄壳(等厚度或不等厚度)的内部声场。

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The laser, which made a rapid-fire popping sound, cut cleanly and quickly through the outer shell of a hard-boiled egg.

WSJ: To Cut Tooth Decay: A Laser vs. a Drill

"How the sound reflects off this reflecting surface with this composite object on it - which is pretty big and has a cloaking shell on it - really reflects... just like a flat surface does, " Dr Cummer said.

BBC: Acoustic 'cloaking device' shields objects from sound