Folks speak of nasal resonance, chest resonance, bone resonance, and mask resonance. Some assume we make resonances. Others even have a person sing into a machine, with them trying to sing in such a way that certain frequencies “ring.” By the way, singing into the machine can be fun and informative. However, machines are questionable in their use as a prescriptive means for training the voice.
The truth is that any kind of “making resonance” is mechanistic, with the focus being misplaced. Rather, let us understand that resonance is a resounding of the initial vocal tone, and that resonance cannot be made or produced. Resonance is a byproduct of healthy muscle function, proper air movement, and the correct size and shape of the vowel requisite to the pitch. Once these facts are understood, we are on the path of “allowing” resonance to develop naturally.
Focus on registrational cause, and resonance will appear as a result!