You've probably noticed that the ACOUSTICS of a room can change the way your voice sounds. Don't we all sound lovely in the shower? Reverberations of sound against different materials and across varying spaces affect the way our voices resonate.  If we practice in a small carpeted room every day and then go audition on a large wooden stage, we might end up confused and thrown off. We often sing differently when we perceive that our voice sounds differently. The best way to combat this problem is to practice in a wide variety of settings. Monitor the vocal adjustments you make in each environment. Then, when you do find yourself in a space with poor acoustics, you will trust your training and you won't overcompensate! Don't just sing in one place. Sing EVERYWHERE!