I have gone through a lot of topics regarding resonance, although I have an understanding of the term, I am not clear on the best way to achieving resonance.
I listened to a friend having her vocal exercise and the word resonance flashed accross my mind because I thought something was lacking. I wanted to say something to her but didn't know what exactly to say so I let it pass.
Does anyone have a link on preferably youtube that best defines of explain what the term means and how it can be achieved?
Thank you..

I normally ask pupils to produce a rounder sound, and this increases their access to their natural resonance.

Resonance is normally achieved through relaxation and not forcing the sound, by finding the correct placing, using the correct vowels and working with the breath. As soon as tension is introduced it disappears.

By concentrating on a roundness of sound, pupils normally open their mouths better, and relax the tongue, this is the first way of accessing resonance. Next they need to free up their necks and relax the shoulders - think yawn, and more resonance is accessed.

The correct tilt of the thyroid and crychoid cartilidges occurs with this relaxation. The only way to produce a bigger sound after that is by strengthening all the support muscles. However nothing should be forced.

Thank you for comment jod. This is quite helpful until it got to the third paragraph, quite technical.. . Do you know any youtube link that can best demonstrate this?
Thanks again..

"Resonance" as such is a very ominous word, because if you ask 10 teachers, you usually get 10 different opinions.

The question would have to be, in that particular case, WHAT was lacking? Was it projection? Was the colour too bright or too dark? Was the sound unfocused?

Some people believe resonance in classical singing to be the ideal balance (chiaroscuro), or indeed a slightly darker tone than we have in contemporary singing. If that's what's missing, lowering the larynx slightly (!), and widening the pharynx might be the way forward, because it "enlarges the tube" and therefore gives a darker, fuller tone close-up. That alone doesn't make the voice project though, and can even make it muffled, although it will sound immensely big in your own head.

If it's projection and focus that are lacking, you are looking for the singer's formant, and that's actually not achieved by just widening - classical and opera singing are so tricky because you use antagonistic muscle groups, and projection actually involves an element of tightening/narrowing the aryepiglottic region (the "Twanger") whilst still keeping the rest of the pharynx wide and the larynx comparably low.

So we probably would have to know what was missing, and what wasn't right with the sound in the first place.

Sometimes you hear a hint of a "warmer, richer" tone in the voice which are words that can often be helpful to a singer re balancing the tone. On occassions my singing teacher - and others I've heard in masterclasses often will say "just try to warm up the tone a little" and sometimes the mental picture can often produce the desired effect as you may raise the palate to give more space inside the mouth keeping the tongue low and allowing more access to the natural resonators.

I would agree with Dugazon that you really need to hear a voice to try to work out what element may be the undernourished one to know what requires tweaking. Generally a "free" sound or feeling can be the best words to suggest change as the more technical you become about the anatomy the more tension is created - precisly the element you need to avoid - tension is never good!

Difficult to give an answer but perhaps different views will help!