Help singing a low D?

Hello. My choir is singing "There Will Be Rest," a beautiful composition by Frank Ticheli, and Lauridsen's "O Magnum Mysterium." I'm singing b, and have to go down to a low D, the one almost two octaves below middle C. I can get it sometimes, but usually its not very musical, or loud enough to be heard. Any one got general tips/advice on how to produce a clearer, more open sound, and produce it with consistency? Thanks!!