A sphere of mono-crystalline alpha-quartz the size of a big orange makes for a very nice acoustic resonator. The acoustic Q-value is around 10 million at 1 MHz. One can measure more than one hundred thousand well resolved resonances.
A flat is cut on the sphere to make the sound wave propagation chaotic.
We also study plates. Here is a picture of a plate of silicon cut in the shape of the so-called Sinai stadium.