One stream flows directly into the mouth, where it produces oral resonance; the other stream passes through the nasopharynx into the hollow chambers of the face and head, inducing nasal and head resonance.
"Resonance in Singing and Speaking"
Thomas Fillebrown
A nasal tone is always a cramped tone, due to impediment, tension, or muscular contraction, particularly in the nasopharynx.
"Resonance in Singing and Speaking"
Thomas Fillebrown