CH11 how are we here already

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Across
  1. 4. compression
  2. 5. frequency
  3. 7. eq_pos
  4. 9. compression_wave
  5. 11. interference
  6. 13. amplitude
  7. 15. rarefaction
  8. 17. resonance
  9. 19. pendulum
Down
  1. 1. transverse_wave
  2. 2. trough
  3. 3. node
  4. 6. crest
  5. 8. antinode
  6. 9. cycle
  7. 10. hertz
  8. 12. standing_wave
  9. 14. period
  10. 16. wave
  11. 18. shm