If your harp has an extended soundboard, projection will likely not be a problem. There are so many variables, like how loudly you play, your technique and whether you’re trying to be heard over an orchestra or as a soloist or what. Even a concert grand sometimes needs amplification in certain situations. If you can get to a store or harp conference where there are different sized harps together, get another harpist to play several of them for you so you can hear the difference and decide for yourself.