Seen many buildings where the concrete walls soundproof the rooms but plumbing ducts in bathrooms transmit sound like crazy - as in you can hear conversations f

Seen many buildings where the concrete walls soundproof the rooms but plumbing ducts in bathrooms transmit sound like crazy - as in you can hear conversations from people several floors down. The inspection hatch cover made of thin sheet metal seems to act like a microphone exciting the air in the duct causing the other covers to act like speakers