Final answer:
Nasal sounds like /m/, /n/, and /ŋ/ occur with an open velopharyngeal port, allowing sound to resonate in the nasal cavity. The nasal cavity's shape and its mucous membrane lining absorb and modify the sound, giving these phonemes their unique quality.
Step-by-step explanation:
The phonemes /m/, /n/, and /ŋ/ (as in 'sing') are collectively known as nasal sounds and are produced when the velopharyngeal port is open. This opening allows air to pass from the lungs into the nasal cavities, where the sound is resonated. The velopharyngeal port is closed for non-nasal sounds to prevent air from entering the nasal passages.
The reason sound waves are further absorbed and filtered as they pass through the chambers of the nasal cavity is due to the cavity acting as a resonant space with its own shape and length, which affects the sound quality. The mucous membrane lining, with its irregular shape and soft tissue, helps absorb some of the sound energy.