Question: does voicing a piano to be more mellow and less bright also effect volume and projection? Can one get a softer more mellow sound without having the piano sound more muffled? Thanks.
Yes, yes, or maybe or no. It can go any way possible depending on where you are starting from.
Let's consider the perfect hammer. It will produce a very mellow tone at the softest play and a clangorous crashing note on the most forceful play. At all levels tone in between mellow and brilliance will be gradual and even. Thus the pianist can control dynamics with tone as well as volume/.
However, a perfect hammer in a recording studio has to be much harder and have far less range in tone, (too hard to mix the piano in as a track when it is too complex a range of tone).
And, the perfect hammer for a full size piano used to accompany singers may need to be less aggressive in tone than others.
If you have a hard, inflexible hammer and it is "voiced", you may actually get more volume and projection. It might be as "loud", but often a voicer can produce a fuller, bigger tone, as well as a gradient up to brilliance. Yes, as softer sound can be had without being muffled. It requires the voicer to leave a deeply resilient hammer with some firmness close enough to the strike point to add the highs needed for definition. An overly voiced hammer doesn't produce the highest partials, (overtones) in the string, even at the most forceful play. An under voiced hammer will perhaps be clear and mellow at soft play, but quickly become harsh as soon as you add some force.