It is impossible to secure head resonance in this fashion, for it is only through free nasal resonance that the cooerdinate resonance in the air sinuses above the nasal cavity and connected with it can be established.
The fear of nasal twang and failure to distinguish between it and true nasal resonance has been the stumbling block.

They are very different,--one is to be shunned, the other to be cultivated.

The first is an obvious blemish, the second is an important essential of good singing.
Nasal tones are caused by a raised or stiffened tongue, a sagging soft palate, a stiffened jaw, or by other rigidities that prevent free tone emission and which at the same time--note this--prevent true nasal resonance.
As tone, or vocalized breath, issues from the larynx, it is divided into two streams or currents by the pendent veil of the soft palate.
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.
It is commonly supposed that tone passing in whole or in part through the nasal cavities must be nasal in quality; whereas a tone of objectionable nasal quality can be sung equally well with the nostrils either closed or open.
Browne and Behnke state the matter thus: "However tight the closure of the soft palate may be, it is never sufficient to prevent the air in the nasal cavities being thrown into co-vibrations with that in the mouth.

These co-vibrations are, in fact, necessary for a certain amount of the brilliancy of the voice, and if they are prevented by a stoppage of the posterior openings of the nasal passages, the voice will sound dull and muffled.

This is of course due, to an _absence of nasal resonance_, and must on no account be described as nasal _twang_.