How does the soft palate affect nasal sounds such as m, n, and ng?

The soft palate, also known as the velum, is a flexible muscular flap at the back of the mouth that acts as a gatekeeper for the nasal cavity during speech production.12

To produce nasal sounds such as m, n, and ng, the soft palate is lowered. This position allows the airstream to pass through the nasal tract rather than being blocked off. For these specific nasal consonants, the mouth is simultaneously occluded at a point by the lips or tongue, forcing the entire airstream to exit through the nose.31

Conversely, when the soft palate is raised and pressed against the back wall of the pharynx, it creates a velic closure that shuts off the nasal tract. This prevents air from escaping through the nose, which is necessary for the production of oral stops and other non-nasal sounds. If the soft palate is only partially lowered, the airstream is expelled through both the nose and the mouth, resulting in nasalized sounds, such as nasalized vowels found in languages like French.213