Greatest Electronic Invention

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Across
  1. 3. / powers the device, energy source
  2. 4. / Hearing aids using a vacuum tube
  3. 6. / makes the sound louder
  4. 7. / sends the sound into the ear
Down
  1. 1. / hearing aids digital brain
  2. 2. / the part that picks up the sound
  3. 5. / tiny conductors connecting the device to the speaker
  4. 8. / custom-made plastic piece that sits in the ear