Nasals

Nasals are formed by an oral closure accompanied by an open nasal passage. Both airflow and acoustic vibration pass through the open velar port into the nasopharynx and nasal cavities. Formants for nasals are not as dark as they are in vowels (and in approximants). The lower energy of nasals is due to the fact that the oral tract is completely blocked and the sound waves radiate from the nose.

Nasals have a prominent low-frequency F1. There are two good reasons for this. Firstly, the nasal cavity is longer than the oral. Secondly, there is a strong attenuation of higher frequencies that are absorbed by the soft mucosal tissue that lines the nasal cavities, and consequently, high-frequency energy gets ‘damped out’. One of the indicators of a nasal sound is a clear discontinuity between the formants of the nasal and those of adjacent sounds.

All three nasals have a very faint and a very low-frequency F₁ (200–450 Hz). Another visible formant is F₃, which is around 2,500 Hz. F₂ is generally not visible. Nasals reveal the abrupt loss of overall energy. The nose is less efficient than the mouth in radiating the energy to the outside.

With respect to place of articulation, formant transitions associated with nasals are very much like stops. For /m/, the bilabial nasal, the second formant has a transition pointing down. For the alveolar /n/, the second formant has a level transition. The transition for the velar points up, merging with the third formant.