The document is a crossword puzzle containing terms related to sound waves. Down clues include higher frequency standing wave (harmonics), sound waves crossing a boundary (refracted wave), the ratio of pressure change to volume change (bulk modulus), and the Doppler effect increasing frequency as an ambulance approaches. Across clues include beats from two waves of slightly different frequencies, sound diminishing with distance, the lowest standing wave (fundamental), Huygens' description of wave propagation, decibels as a unit of intensity, and standing waves produced by instruments.