The singer must learn to habitually use all of the resonance cavities and use them simultaneously.
Lilli Lehmann, in _How to Sing_, says that, "although the nasal sound can be exaggerated,--which rarely happens,--it can be much neglected,--something that very often happens." The context makes clear that what in the English translation of the great singer's book is called "nasal sound" is exactly what we term _nasal resonance_.
After charging the monotonous quality or lack of color in the voice of a famous opera star to lack of nasal resonance, Madame Lehmann speaks of the consummate art of Marcella Sembrich who "in recent years appears to have devoted very special study to nasal resonance, whereby her voice, especially in the middle register, has gained greatly in warmth." She says further that nasal resonance "cannot be studied enough.

It ought always to be employed." "How often," she says, "have I heard young singers say, 'I no longer have the power to respond to the demands made upon me,' whereas the trouble lies only in the insufficient use of the resonance of the head cavities." From the foregoing, the conclusion follows that the head vibrations are not only an essential element, but that nasal resonance is a most important element in imparting to tone its brilliance and carrying power.

Without thought of the mechanism of _how_ nasal resonance is produced, the singer has control over it by direct influence of the will.

The tones, low as well as high, should seem to start in the nose and head, and the vibrations of the perfect tone can be plainly felt upon any part of the nose and head.

Without the head vibrations no tone can be perfect, for nothing else will compensate for the lack of these.