The paranasal (sinus) cavities are spaces in the skull that have various purposes such as airflow, drainage, etc. These cavities are found within the bone structure of the face, where they act as acoustic resonating chambers. They are not the same as the nasal cavities, but both are part of the nasal vestibule.
There are four pairs of sinus cavities and they are named after the bones that contain them. The maxillary sinuses are near the cheekbones, located on each side of your nose. The frontal sinuses are located near the lower center of your forehead, above the eyes. The ethmoid sinuses are located between the eyes, on each side of the bridge of your nose. And the sphenoid sinuses located behind your nose. Who knew we had so many sinuses!
One thing is certain, the sinuses do not play a significant role in singing. Yes, they resonate (along with the rest of the skull), but their audible contribution to vocal resonance is small. Though they resonate they do not significantly change the sound coming from the mouth. The bone-conducting sound you hear and the vibration you feel when you are singing can be affected.
JOKE FOR THE DAY:
My husband has a sinus condition that suppresses his ability to detect odors.
But he gets offended when I tell people he doesn’t smell good!