Here's a project for studying compression waves in different soil types. It uses a homemade wave tank for solids, with a frequency generator, amplifier, and loudspeaker as the vibration source. There are lots of interesting possibilities...

Extensive information about how waves behave in an elastic medium. Covers different types of waves, their characteristics and behavior, the anatomy of the ear, the speed of sound in different media, the parts of a wave, and wave phenomena.

Students explore the characteristics of both transverse and longitudinal waves.