physics puzzle

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Across
  1. 5. two or more waves aligning from trough to trough and crest to crest
  2. 8. effect the change in the frequency
  3. 9. high or low sound
  4. 15. two or more waves overlapping
  5. 16. sound higher than human hearing
  6. 18. sound waves interfering
  7. 19. speed exceeding mach 5
  8. 21. sound below human hearing
Down
  1. 1. point of max amps within a wave
  2. 2. superposition principle regarding waves overlapping
  3. 3. periodic pulsating viibrations
  4. 4. phenomenon where system oscillates with high amps
  5. 6. reduction in volume
  6. 7. unit to measure sound
  7. 10. ultrasound speed
  8. 11. a constant frequency
  9. 12. frequency rate where an object oscillates or vibrates
  10. 13. wave pattern formed by intefernece
  11. 14. oscillation of an object
  12. 17. reduction of items density
  13. 20. point along standing wave where medium is at rest